Values in [square brackets] are American
Most values are approximate.

N = normal.
Δ = change, e.g. ΔV/ΔP = change in volume in response to change in pressure, i.e. compliance.
μ = micro-, prefix indicating 10-6, i.e. 0.000001.
μm = micrometer or micron, i.e. one millionth of a metre, or 1×10−6 of a metre.
µmol = micromole, i.e. one millionth of a mole
> = more than
< = less than
± = ‘and/or’ or ‘with/without’
~ = about
Dot over symbol: value per unit time, e.g. V̇O2: oxygen consumption.
Line over symbol: mean value, e.g. v̅: mixed venous.
Conversion of mmHg to kPa – multiply the value by 0.1333 (see also: App.F).

1RM - one repetition maximum, i.e. the maximum load that can be moved once over full range of motion without compensatory movements

5 year survival - term used to indicate cancer prognosis because if a cancer is going to come back, it is most likely to do so within this time.

6-minute distance average - 571 ± 90 m

A - alveolar, e.g. PAO2.

a - arterial, e.g. PaO2.

AAA - abdominal aortic aneurysm.

ABGs - arterial blood gases.

ABPA - allergic bronchopulmonary aspergillosis.

Absolute humidity - water in a given volume of gas, which increases or decreases with temperature (mgH2O/l).

ACBT - active cycle of breathing techniques.

ACBT/AD - active cycle of breathing techniques ± autogenic drainage.

ACE inhibitors - angiotensin-converting enzyme inhibitor drugs.

Acidaemia - acidosis of blood.

Acidosis - pH <7.35.
- respiratory acidosis is caused by malfunctioning respiration, metabolic acidosis by malfunctioning metabolism.

Acinus - portion of lung participating in gas exchange, supplied by a primary respiratory bronchiole.

ACPRC - Association of Chartered Physiotherapists in Respiratory Care (UK).

ACS - acute coronary syndrome.

AD - autogenic drainage.

ADL - activities of daily living.

Adult epiglottitis - supraglottic inflammation of the oropharynx caused by infective, thermal, or caustic insult, leading to swelling of the epiglottis and airway obstruction.

Adult respiratory distress syndrome - old terminology for acute respiratory distress syndrome.

Adventitious sounds - added sounds on auscultation.

Aerosol - suspension of solid or liquid particles, e.g. pollen, dust, mist, viruses or therapeutic aerosol for humidification or drug delivery.

Aetiology - study of the causes of a disease.

Aerophagia - gas in stomach.

AF - atrial fibrillation

Aggressive treatment - intensive treatment

AIDS - acquired immune deficiency syndrome.

Air bronchogram - visibility of airways on x-ray due to opacification of surrounding alveoli.

Airway - (1) natural passageway for air to travel from atmosphere to alveoli, or (2) artificial device to hold open upper airway for relief of obstruction or to allow mechanical ventilation.

Airway closure - closure of small airways, common in dependent lung regions at end-expiration.

Airway resistance - see Resistance

Albumin - N: 40-60 g/l, [4.0-6.0 g/100ml].

Albuterol - US terminology for salbutamol

ALI - acute lung injury

Alkalaemia - alkalosis of blood.

Alkalosis - pH >7.45.

Alveolar-arterial oxygen gradient - see PAO2−PaO2.

Ambulate - walk.

Ambulatory surgery - day surgery (not surgery while walking about!).

Anabolism - constructive phase of metabolism when simple substances become complex living matter.

Anastomosis - surgical union of tubular structures.

Anaerobic threshold - highest O2 consumption during exercise, above which sustained lactic acidosis occurs.

Angina - crushing chest pain due to impaired blood supply to the myocardium, worsened with exertion or stress.

Angioplasty - invasive but non-surgical dilation of coronary artery stenosis, using catheter via femoral puncture, or laser.

Anoxia - complete lack of oxygen.

Antibody - substance produced by interaction of antigen with body's defenses, also known as immunoglobulin.

Antigen - allergen, i.e. irritant that elicits an immune response.

Antioxidant - substance which counteract the effects of free radicals such as tobacco smoke.

AP - anteroposterior.

APACHE - Acute Physiology And Chronic Health Evaluation: scoring system to measure severity of illness, using predictor variables such as diagnosis, age and physiological measures.

Apgar score - scoring system to measure birth asphyxia, using a combination of heart rate, respiratory effort, muscle tone, reflex irritability and colour.

Apneustic breathing - prolonged inspiration, usually due to brain damage.

Apnoea - absence of breathing for >10 secs.

APTT - see clotting studies.

ARDS - acute respiratory distress syndrome.

ARF - (1) acute respiratory failure, or (2) acute renal failure

Arnold’s nerve - auricular branch of vagus nerve, responsible for the cough reflex in a small proportion of the population, whereby a cough can be facilitated by ear stimulation; also responsible for ear pain being an occasional early presentation of laryngeal cancer.

Arteriovenous oxygen difference - difference between O2 delivered to and returning from the tissues.
- calculated from arterial and mixed venous blood samples.
- related to metabolic rate.

Ascites - fluid in the abdominal cavity.

Aspiration - (1) inhalation of unwanted substances (e.g. gastric acid or sea water) beyond the vocal cords, or (2) therapeutic removal of fluid or gas from a cavity such as the pleural space.

Asthenia - mental fatigue (impaired mental concentration and memory), physical fatigue and weakness.

Asystole - no heartbeat.

Atelectasis - collapse of alveoli.

Atelectrauma - damage to alveoli due to repetitive opening and collapse.

Atopy - allergic hypersensitivity.

ATP - adenosine triphosphate, a nucleotide which governs Cl− secretion and Na+ absorption, thereby regulating airway surface liquid.

Auscultation - use of stethoscope to hear sounds from a body cavity.

Auto PEEP - intrinsic PEEP

Automatic tube compensation - facility on some ventilators to eliminate the excess work of breathing through the tubing

Autoregulation - ability of an organ to maintain constant blood flow despite changes in perfusion pressure.

BAL - bronchoalveolar lavage: bronchoscopic washing out of bronchioles and alveoli with sterile saline for diagnosis.

Barotrauma - air in the wrong place, e.g. pneumothorax or subcutaneous emphysema.

b.d. - twice a day

Biofilm - cluster of bacteria enclosed in a matrix, e.g. in the fluid film lining the endotracheal tube.

Biot's respiration - irregular cycles of deep gasps and apnoea.

BiPAP - bilevel positive airway pressure.

BIPAP - biphasic positive airway pressure.

Bleb - collection of air under visceral pleura (see also bulla).

Blood culture - blood taken from a pyrexial patient to identify micro-organisms.

Blood pressure - pressure exerted by the blood on the arteries.
see also: mean arterial pressure.

Blood sugar - 3.5–5.5 mmol/l before meals, rising after meals by a few mmol/l.
↑ in stress, ↑↑ in diabetes mellitus,  in liver failure or starvation.

Bohr effect - reduced availability of O2 from oxyhaemoglobin in regions of low PCO2.

Bohr equation - difference between end-tidal and arterial PCO2.
Calculates physiological dead space.

BOOP - bronchiolitis obliterans organising pneumonia.
- occurs secondary to lung or bone marrow transplant, drug reaction, aspiration or collagen vascular disease.

bpm - breaths per minute or (heart) beats per minute.

Bradyarrythmia - slow and abnormal heart beat.

Bradycardia - resting HR <60/min in adults.

Bradypnoea - slow breathing.

Bronchiole - airway unsupported by cartilage.

Bronchitis - acute or chronic inflammation of mucous membranes of tracheobronchial tree.

Bronchomalacia - disorder characterized by degeneration of elastic and connective tissue of trachea and bronchi.

Bronchopleural fistula - communication between lung and pleura, caused by thoracic surgery, trauma or pulmonary disease.

Bronchorrhoea - excess production of watery sputum, i.e. >100 ml/day.

Bronchospasm - abnormal contraction of smooth bronchial muscle, causing narrowing of airway.

BTS - British Thoracic Society.

Buffer - substance that binds or releases hydrogen ions in order to keep pH constant.

Bulla - collection of air in lung tissue which is more than 1 cm in diameter, caused by alveolar destruction.

BUN - blood urea nitrogen: US term for urea.

CABG - coronary artery bypass graft.

Calcium - N: 2.2-2.6 mmol/L.

CaO2 - see oxygen content.

Capnography measurement of inspired and expired CO2 concentration and its graphical display

Cardiac enzymes - enzymes released from damaged heart muscle after myocardial infarction.

Cardiac index - cardiac output / body surface area.
- N: 2.5-3.5 l/min/m2.
- highest at age 10, then decreasing with age.

Cardiac output (CO or Q) - blood ejected by left ventricle per minute, i.e. HR x stroke volume.
- N: 4-8 l/min at rest, up to 25 l/min on exercise.

Cardioplegia - cooling of heart to reduce metabolic rate during surgery.

Care bundle - a group of evidence-based interventions which, when performed together, bring a better outcome than if performed individually.

Catabolism - series of degradative chemical reactions that break down complex molecules into small molecules, releasing energy and CO2.

Catecholamine - compound having sympathomimetic action, e.g. adrenaline.

Caudad - towards the feet.

CCF - congestive cardiac failure.

Centrilobular emphysema - emphysema affecting mainly the respiratory bronchioles

Central line - catheter inserted into a large vein such as the internal jugular, subclavian or femoral for monitoring or the administration of thick fluids.

Central venous oxygen saturation (ScvO2) oxygen saturation of Hb in large central veins, reflecting gas exchange in lungs, cardiac output, metabolic rate, Hb levels and tissue oxygen uptake
- N: 73–82%.

Cephalad - towards the head.

CF - cystic fibrosis.

CFA - cryptogenic fibrosing alveolitis.

CHD - coronary heart disease.

Chest wall - structures outside lung that are involved in breathing movements, i.e. rib cage, diaphragm, abdominal wall and pelvic wall

Cheyne-Stokes breathing - episodes of rapid breathing, slow breathing and apnoea.

Chloride (Cl-) - chief anion in extracellular fluid,
-  levels in plasma: acidosis, some kidney problems, prolonged vomiting,
-  levels in sweat can be diagnostic of cystic fibrosis.

Churg-Strauss Syndrome - multi-organ necrotising arteritis that occurs occasionally in people with severe asthma.

Chylothorax - effusion of chyle from thoracic duct into pleural space.

CI - see cardiac index.

Circadian - over 24 hours.

Closing capacity - lung volume at which airway closure begins due to narrowing of dependent airways as lung deflates, i.e. sum of closing volume and residual volume
- reduced by obesity or the supine position.

Closing volume - closing capacity minus residual volume.
- increases (becomes a greater proportion of FRC) with small airways disease, smoking, obesity and young or old age.
- young person: 10% of VC.
- age 65: 40% of VC.

Clotting studies (Broomhead & Mallett 2013)
• ACT (activated clotting time): monitors high-dose heparin therapy, e.g. during cardiopulmonary bypass. N: 100-140 secs.
• APTT (activated partial thromboplastin time): monitors low-dose heparin therapy. N: 30-40 secs.
• Bleeding time. N: 3-9 mins.
• FDPs (fibrinogen degradation products). N: <10 mg/ml.
• Fibrinogen level. N: >150 mg/dl.
• INR (international normalized ratio): Ratio of time blood normally takes to clot compared to increased time it takes to clot, e.g. for monitoring warfarin or detecting bleeding disorders. N: 1-3. Higher means increased clotting time and risk of bleeding, e.g. 2-4 for a patient on warfarin, 10 in a patient at severe risk of bleeding.
• KPTT (kaolin partial thromboplastin time). N: <7 sec above control.
• Platelet count. N: 140,000-450,000 mm-3. Risk of bleeding with suction: <50,000 mm-3. Spontaneous bleeding: <20,000 mm-3.
• PT (prothrombin time). N: 11-15 secs.
• PTT (partial thromboplastin time). N: 12-30 secs.

CMV - (1) controlled mandatory ventilation or conventional mechanical ventilation, or (2) cytomegalovirus.

CO - (1) cardiac output, or (2) carbon monoxide.

CO2 - carbon dioxide.

Coagulation v see clotting studies.

Coefficient of reliability - scale indicating reliability of an outcome measure, with 0 meaning no reliability and 1.0 meaning perfect reliability.

Cognition - mental activities involved in acquiring and processing information.

Collateral channels - airways between adjacent lung units which allow inspired gas to bypass normal airways if these are obstructed.

Collateral ventilation - ventilation through collateral channels when normal airways are obstructed

Compliance of lung - change in volume in response to change in transpulmonary pressure, i.e. ΔV/ΔP
- static compliance: compliance with zero gas flow, N: 200 ml/cmH2O, measurement on MV: VT / Pplat - PEEP
- dynamic compliance: compliance during gas flow (less than or equal to static lung compliance), N: 180 ml/cmH2O, measurement on MV: VT / PIP – PEEP.

Consolidation - replacement of alveolar air by substance of greater density, e.g. the inflammatory exudate of pneumonia.

Consciousness - multifaceted concept combining awareness and wakefulness, involving sensory input, activation of cortical neurons, sensory-motor interaction and neurotransmitter modulation.

Contralateral - opposite side.

COPD - chronic obstructive pulmonary disease.

Coryza - symptoms of the common cold.

Cough peak flow see: peak cough flow

Cough syncope - loss of consciousness for a few seconds following cough (benign unless while driving).

CPAP - continuous positive airway pressure.

CPR - cardiopulmonary resuscitation.

Creatinine - electrolyte in plasma or urine, formed from muscle breakdown (end-product of normal muscle metabolism) and excreted by kidneys.
- N in plasma: 50-100 μmol/l [0.6-1.2 mg/100ml].
- ↑ in hypovolaemia or kidney failure, ↑↑ in septic shock.

Cryptogenic - of unknown cause.

CSF - cerebrospinal fluid.

CT - computed tomography.

CvO2 - see mixed venous oxygen content.

CVP - central venous pressure.
N: 1-7 mmHg or 5-12 cmH2O.

CXR - chest x-ray.

Cytokine - inflammatory product.

Cytomegalovirus - virus to which immunocompromised people are susceptible.

Day surgery - admission, operation, recovery and discharge within one working day.

DB - deep breathing.

Decubitus - side-lying.
- right decubitus: lying on R side.
- left decubitus: lying on L side.

Deglutition - swallowing.

Delirium - potentially reversible disorder of cognition and attention, including disorientation, fear, misperception and hallucination.

Dependent - underneath.

Derecruitment - collapse of alveoli.

Desaturation -  oxygen saturation of haemoglobin in arterial blood.

Dextrocardia - a condition in which the heart is on the right side of the body, usually undiagnosed until routine chest x-ray or ECG.

Diastole - ventricular relaxation

DIC - disseminated intravascular coagulation.

Dissociation curve - see oxygen dissociation curve

Diuresis - increased formation and secretion of urine, e.g. with diabetes mellitus or water intake.

DNAR - do not attempt resuscitation.

DO2 - see oxygen delivery.

Doppler - use of changes in frequency of light and sound waves to monitor relative motion.

Driving pressure of ventilator - inspiratory plateau pressure minus PEEP

Duty cycle - see tension time index.

DVT - deep vein thrombosis.

Dysarthria - difficulty speaking due to weak muscles.

Dysphagia - difficulty swallowing.

Dyspnoea - distressing breathlessness.

ECCO2R extracorporeal CO2 removal.

ECG - electrocardiogram.

ECMO - extracorporeal membrane oxygenation.

-ectomy - removal.

EEG - electroencephalogram: recording of electric potential of brain cells as brain waves.

Eisenmenger syndrome - pulmonary vascular disease with cyanosis due to extrapulmonary shunt in which congenital heart disease causes systemic-to-pulmonary circulation connection.

EKC - US terminology for ECG

Elastance - opposite of compliance.

EMD - electromechanical dissociation: dissociation of electrical and mechanical activity of the heart, represented by clinical signs of cardiac arrest with normal ECG.
- causes include tension pneumothorax, cardiac trauma or severe electrolyte or acid-base imbalance.
- leads to full cardiac arrest.

EMLA - eutectic mixture of local anaesthetics: cream for numbing skin before venipuncture.

Empyema - pus in pleural cavity.

Encephalopathy - damage to structure or function of brain tissue.

Endotoxaemia - endotoxins in blood.

Endotoxin - toxin inside bacterial cell, released after destruction of bacterial cell wall.

Endurance - capacity of muscle to sustain contraction.

Enteral - via the gut.

Entonox - analgesic gas mixture comprising 50% nitrous oxide and 50% oxygen, otherwise known as laughing gas.

Eosinophilia - excess eosinophils, indicating allergic state.

Eosinophils - inflammatory cells associated with hypersensitivity reaction.
- ↑ in allergy e.g. extrinsic asthma.

Epinephrine - US terminology for adrenaline.

Epiglottis - cartilage which diverts food to oesophagus by closing over trachea.

Epistaxis - nose bleed.

ERCP - endoscopic retrograde cholangiopancreatography: procedure for detection and treatment of gallstones.

Erythrocytosis - polycythaemia.

Entrainment - dilution of gas stream or aerosol with external gas such as room air.

ESR - erythrocyte sedimentation rate

ETCO2 - end-tidal CO2.
- N: 4-6%.

ETT - endotracheal tube.

Eucapnia - normal PaCO2.

Evidence based medicine - the conscientious, explicit, and judicious use of current best evidence in making decisions about the care of individual patients.

Extracorporeal - outside the body.

- central: reduced force generation due to events proximal to neuromuscular junction
- peripheral: failure at or beyond neuromuscular junction.

FBC - full blood count.

FDP - see clotting studies.

FET - forced expiration technique.

FEV1 - forced expiratory volume in one second.

FFP - fresh frozen plasma, contains all clotting factors at normal concentration.

FG - size of catheter or tube defined as the outside diameter in units of ⅓ mm, e.g. 12 French Gauge catheter has outer diameter of 4 mm.

FiO2 - fraction of inspired oxygen, expressed as decimal, e.g. FiO2 of 0.6 = 60% inspired oxygen, FiO2 of 0.21 = room air.

First-pass metabolism - metabolism of a drug other than systemically, due to insufficient absorption or metabolism by gut or liver before drug enters systemic circulation.

Fluid bolus between 100 ml and >1000 ml intravenous fluids delivered from immediately to 60 minutes (Eastwood et al 2016).

Fluid overload - 10% or greater increase in weight due to excess fluid.

FRC - functional residual capacity.

Free radical - reactive oxygen species which are physiological byproducts of aerobic metabolism,
- high concentrations formed when oxygen reacts with certain molecules to start a chain reaction implicated in ageing, cancer and inflammation,
- counteracted by a defense system of antioxidants.

Fremitus - vibratory tremors detectable through the chest wall

FVC - forced vital capacity.

GCS - Glasgow Coma Scale.

Generation - branches of tracheobronchial tree, numbering between 10 and 23.

Glottis - vocal folds and space between them.

Glucose - see blood sugar.

Goal-directed therapy - manipulation of cardiopulmonary parameters to balance oxygen delivery and consumption.

GOR - gastroesophageal reflux.

Gram-negative bacteria - virulent organisms which thrive in moist environments, e.g. Haemophilus, Klebsiella, Pseudomonas, Salmonella.

H+ - hydrogen ion.

H2CO3 - carbonic acid.

HAD-A - Hospital Anxiety and Depression Scale: anxiety component.

HAD-D - Hospital Anxiety and Depression Scale: depression component.

Haematocrit - concentration of red blood cells in blood.
- N: 36-46% in women, 40-50% in men,
- anaemia: < 36%. polycythaemia: > 55%.

Haemoglobin - respiratory pigment in red blood cells which combines reversibly with oxygen.
- N: 11.5-15 g/100 ml in women, 14-17 g/100 ml in men.
-  in anaemia,  in polycythaemia.

Haemopneumothorax - blood and air in pleural space.

Haemoptysis coughing up blood (‘frank haemoptysis’ is coughing up pure blood).

Haemostasis - physiological cascade with multiple checks and balances that results in cessation of bleeding following injury (Broomhead & Mallett 2013).

Haldane effect - property of haemoglobin allowing it to carry more oxygen when blood is deoxygenated and less oxygen when blood is oxygenated.

Hamman's sign - crunching sound synchronous with heart beat, indicating pneumomediastinum.

Harrison's sulcus - permanent indentation of the chest wall along the costal margins where the diaphragm inserts, caused by pull of diaphragm on ribs which are either not yet calcified or weakened by rickets.

Hb - see haemoglobin.

HCO3- - bicarbonate ion concentration.

HDL - high-density lipoprotein

Hepatomegaly - enlarged liver.

HF - heart failure.

Hiccup - involuntary clonic spasm of intercostals and diaphragm followed by abrupt glottic closure, of unknown aetiology.

Hickman line - central venous access line, e.g. for chemotherapy.

Histotoxic - tissue poisoning.

HIV - human immunodeficiency virus

H:L ratio - ratio of power in high and low frequency bands of electromyogram of respiratory muscle, decreased with respiratory muscle fatigue.

HME - heat-moisture exchanger.

Homeostasis - regulation of internal environment, e.g. temperature, pH and glucose, despite environmental variations.

HR - heart rate, N: 60-100 bpm.

HRCT - high resolution computed tomography.

HRQoL - health-related quality of life: effects of illness and its treatment as perceived by the patient.

Humoral - non-cellular.

HVS - hyperventilation syndrome.

Hyaline membrane disease - respiratory distress syndrome in neonates

Hypercapnia -  PaCO2.

Hyperdynamic - status signalling onset of septic shock: galloping pulse, pyrexia, shaking chill, flushing of skin, high cardiac output, unstable BP.

Hyperkalaemia - ↑ serum potassium.

Hypermetabolism - ↑ energy expenditure by >10%.

Hypernatraemia - ↑ serum sodium.

Hyperosmolar -  concentration of osmotically active ingredients.

Hyperoxia - abnormally high oxygen tension in blood.

Hyperreactivity -  sensitivity to variety of stimuli
- present in airways with asthma, sometimes present with COPD, bronchiectasis, CF, sarcoidosis, LVF.

Hyperthermia - core temperature >40.5oC.

Hyperventilation - CO2 removal in excess of CO2 production, causing PaCO2 <4.7 kPa (35 mmHg).

Hypervolaemia - fluid overload.

Hypoalbuminaemia -  albumin.

Hypocalcaemia - calcium in blood.

Hypocapnia - CO2 in arterial blood.

Hypocarbia - as above.

Hypogammaglobulinaemia -reduced gamma globulin in blood, associated with reduced resistance to infection.

Hypokalaemia - potassium in blood.

Hyponatraemia - sodium in blood.

Hypopnoea - shallow slow breathing.

Hypoventilation - CO2 production in excess of CO2 removal, leading to PaCO2 >6.0 kPa (45 mmHg).

Hypovolaemia -  blood volume due to e.g. haemorrhage or dehydration.

Hypoxaemia -  oxygen in arterial blood.

Hypoxia -  oxygen in tissues.

Hysteresis - difference in compliance between inspiration and expiration, due to extra energy required during inspiration to recruit additional alveoli.

IABP - intra-aortic balloon pump.

Iatrogenic - causing or exacerbating harm by medical intervention.

ICF framework - International Classification of Functioning, Disability and Health.

ICP - intracranial pressure.

ICU - intensive care unit.

Idiopathic - of unknown cause.

I:E ratio - see inspiratory:expiratory ratio.

Ileus - gut obstruction, e.g. due to paralytic ileus, as indicated by lack of bowel sounds.

Immotile cilia syndrome - primary ciliary dyskinesia.

Immunoglobulin - antibody,
- examples in respiratory secretions: IgA, IgE, IgG, IgM.

Infarction - death of tissue due to lack of blood supply.

Infection - presence of microorganisms or their products in normally sterile tissue.

Infiltrate - fluid, cells or other substance in tissue space, e.g. pulmonary interstitial infiltrate = fluid between capillary and alveolus, showing on x-ray as diffuse shadowing.

Inotropes - drugs which ↑ force of cardiac contraction.

INR - see clotting studies.

Inspiratory capacity - volume inspired during maximum inspiration from resting end-expiratory position.

Inspiratory:expiratory ratio - duration of inspiration relative to expiration.

Inspiratory force - see MIP.

Inspissated - thick.

Insufflation - blowing air into the lungs.

Intracranial hypertension - ↑ intracranial pressure.

Intrapleural pressure - pressure in pleural space.

Intrapulmonary pressure - alveolar pressure.

Intrathoracic pressure - pleural pressure.

Intrinsic PEEP - trapped gas left in lungs at end-exhalation due to obstructed airways ± breathing through artificial airways.

IPPB - intermittent positive pressure breathing.

IPPV - intermittent positive pressure ventilation, i.e. mechanical ventilation.

Ipsilateral - same side.

IRT - immune reactive trypsin: antibody identified in cystic fibrosis screening.

IRV - inspiratory reserve volume.

IS - incentive spirometry.

Ischaemia - inadequate blood supply.

Isotonic - same osmotic pressure as body fluids, e.g. isotonic saline contains salt equal to that in body.

Isotonic exercise - active exercise with movement, force of contraction remaining constant.

IV - intravenous.

JVP - jugular venous pressure.

K - potassium.

Kerley B lines - thin radiological 2 cm horizontal lines, perpendicular to visceral pleural surface, representing engorged lymphatics and thickened interlobular septa,
- become visible when the pulmonary artery wedge pressure exceeds 25 mmHg, indicating pulmonary oedema.

kPa - kilopascal (unit of pressure).

KTPP - see clotting studies.

Kussmaul breathing - deep sighing breathing often seen in patients with metabolic acidosis.

Kyphoscoliosis - anteroposterior and lateral curvature of spine.

L - left

l - litre.

Lactate (in blood, i.e. serum lactate) biomarker of tissue hypoxia and anaerobic metabolism, due to cellular decompensation, reflecting disease severity
- N: <1 mmol/l, anaerobic metabolism: >2 mmol/l, poor prognosis: >3 mmol/l.

Lactic acidosis - increased serum lactate due to insufficient oxygen in tissues, causing metabolic acidosis (see also anaerobic threshold).

Laminar - streamline.

Laparoscopy - minimal access incision through abdominal wall.

Laparotomy - full surgical incision through abdominal wall.

Larynx - airway connecting pharynx and trachea, formed by cartilages and containing vocal cords.

Leukocyte - white blood cell.

Leukocytosis - increased white blood cells.

LFT - (1) lung function test, or (2) liver function test.

Lobectomy - surgical removal of lobe of a lung.

LOC - length of stay, or loss of consciousness.

Locked-in syndrome - total paralysis below third cranial nerve, with patient partially or fully aware.

Loculated pleural effusion - pleural effusion in which fluid is trapped in pockets.

LTOT - long term oxygen therapy.

Lung clearance index - index of ventilation homogeneity derived from the multiple breath washout of an inert gas,
- correlates with symptoms in patients with cystic fibrosis (Vermeulen et al 2014).

LVEDP - left ventricular end-diastolic pressure.

LVEDV - left ventricular end-diastolic volume,
- determinant of preload
- depends on venous return to L ventricle, circulating blood volume and efficiency of L atrial contraction
- measured, by assumption, from PAWP, which relates to LVEDP.

LVF - left ventricular failure.

Lymphadenopathy - enlarged lymph nodes.

Lymphangioleiomyomatosis - overgrowth of smooth muscles around airways, blood vessels and lymph vessels, leading to cysts in the lung.

Lymphocyte - small leucocytes comprising 25% total white blood cell count.

-lysis - breakdown.

MAP - see mean arterial pressure.

Mast cells - connective tissue cells involved in hypersensitivity reactions, releasing histamine in response to specific stimuli,
- increased in asthma.

Maximal HR - 220–age.

Maximum expiratory flow rate - US terminology for peak expiratory flow rate (peak flow).

Maximum oxygen consumption - maximal rate at which oxygen can be used by the body during maximal work, i.e. aerobic capacity, reflecting neural, cardiopulmonary and metabolic components of aerobic fitness and requiring V̇O2 to attain a plateau
-  with fitness,  with advancing age but rate of decline slower in physically active people
- N: 2 l/min or >25 ml/kg/min or 25 times resting level
- COPD: typically 1 l/min
- see also anaerobic threshold.

MDI - metered dose inhaler.

Mean arterial pressure - average pressure pushing blood through systemic circulation, i.e. cardiac output x peripheral vascular resistance
- N: 80-100 mmHg
- compromised circulation to vital organs: <60 mmHg
- compromised circulation to injured brain: <80 mmHg.

Mean corpuscular haemoglobin - amount of haemoglobin in red blood cells.

Mediastinum - part of thoracic cavity between lungs, containing all other thoracic viscera.

Medical model - view of disease or disability which sees it as intrinsic to the individual and requiring medical care provided by professionals.

MEF50 - maximum expiratory flow in mid-expiration.

Mendelson's syndrome - aspiration of gastric contents into lungs.

MEP - maximum expiratory pressure
- N: 100 cmH2O, inadequate cough: <40 cmH2O.

mEq - milliequivalent, i.e. one thousandth of molecular weight of substance.

mEq/l - milliequivalents per litre of solution, e.g. of electrolyte concentration
- also expressed as mmol/l.

MET - metabolic energy expenditure: metabolic unit representing oxygen consumed at rest
- normal: 3.5 ml oxygen/kg body weight/min,
- basal metabolism consumes one MET, eating consumes 2 METs, dressing consumes 3 METs, vacuuming consumes 5 METs, brisk walking consumes 9-10 METs.

Metabolism - chemical processes of body, comprising anabolism and catabolism,
- varies with healing, activity level and temperature.

Miliary TB - homogenous tuberculosis of lung manifest by mottling on x-ray.

MH - manual hyperinflation.

MI - see myocardial infarction.

Micro - one millionth.

Microatelectasis - collapse of lung units smaller than a segment, not detectable clinically or radiologically.

Micrometer or micron (μm) - one millionth of a metre.

Minute ventilation - see below.

Minute volume or minute ventilation (V̇E) - amount of gas expelled from lungs per minute, i.e. tidal volume x RR
- N: 5-9 litres.

MIP - maximum inspiratory pressure: assessment of respiratory muscle strength
- N: minus 100-130 cmH2O (men), minus 70-100 (women)
- typical value for hypercapnic COPD: minus 55 (men), minus 40 (women)

Mixed venous blood - blood in pulmonary artery.

Mixed venous oxygen content - (Hb x Sv̅O2 x 1.39) + (PvO2 x 0.023).

Mixed venous oxygen saturation (Sv̅O2) - oxygen saturation of Hb in pulmonary artery, reflecting gas exchange in lungs, cardiac output, metabolic rate, Hb levels and tissue oxygen uptake
- N: 75%.

MMEF - maximum mid-expiratory flow.

mmHg - millimeters of mercury (unit of pressure)

mmHg - millimetres of mercury.

MMV - mandatory minute ventilation: a mode of mechanical ventilation.

mmol - millimol: one one-thousandth of molecular weight of substance.

Mole - number of atoms, ions, or other elementary entities in a given sample of any substance.

MRI - magnetic resonance imaging.

MRSA - methicillin-resistant staphylococcus aureus.

Mucoactive - affecting quality or quantity of mucus.

Mucokinetic - accelerating mucus transport.

Mucolytic - destroys mucin in mucus gel.

Mucoviscidosis - cystic fibrosis.

Multi-organ failure - multisystem failure.

MV - mechanical ventilation.

MVA - motor vehicle accident (US).

Mycoplasma pneumonia - atypical pneumonia which affects otherwise healthy people.

Myocardial infarction - death of portion of heart muscle due to myocardial ischaemia.

Na - see sodium.

NBM - nil by mouth (NPO in US).

Neuromuscular blockade - chemical paralysis by neuromuscular blocking agents.

Neutropaenia -  neutrophils, i.e. <1.5 x 109, leaving patient vulnerable to infection.

Neutrophil - white blood cell used for phagocytosis of bacteria but which in excess releases tissue-damaging enzymes as part of uncontrolled inflammation.

Neutrophilia - increased neutrophils.

NFR - not for resuscitation.

NICE - National Institute for Care Excellence: UK body established to reduce the postcode lottery in provision of health services.

NICU - neonatal intensive care unit.

NIPPV - nasal (or noninvasive) intermittent positive pressure ventilation, i.e. noninvasive ventilation.

NIV - noninvasive ventilation.

NO - nitric oxide.

Nociceptive - painful.

Normocapnia - normal PaCO2.

Normoxaemia - normal blood oxygenation.

Normovolaemia - normal blood volume.

NPO - nil per os, i.e. nil by mouth (US).

Number needed to treat - method of using research information to identify benefits or risks of a treatment.

O2 - oxygen

Obesity-hypoventilation syndrome - a severe form of obstructive sleep apnoea seen in markedly obese people which may require noninvasive ventilation at night to unload the respiratory muscles

Occult PEEP - intrinsic PEEP.

Occupational lung disease - disease due to inhalation of dust, particles, fumes or gases while working.

Oesophageal varices - dilated veins in lower third of the oesophagus, at junction of portal and systemic venous systems, due to raised portal pressure

Oliguria -  urine output, i.e. <20 ml/hr (normal 50-60 ml/hr).

Oncotic pressure - osmotic pressure exerted by colloids.

Operation - surgery plus anaesthesia.

Orthopnoea - dyspnoea on lying flat.

Orthostatic hypotension/intolerance - drop of >20 mmHg in systolic ± drop of >10 mmHg in diastolic BP on standing up.

Orthotopic transplantation - replacement of recipient’s organ with that of donor.

-oscopy - visual examination of interior of organ.

Osmolar load - osmolality of solution x volume infused.

Osmolality - number of osmotically active particles per kg of solvent, and the most significant factor in the distribution of water between intracellular and extracellular fluid.

Osmolarity - number of osmotically active particles per litre of solution.

-ostomy - formation of artificial opening to skin surface.

-otomy - incision.

OT - occupational therapy/therapist

Oxidants - substances which occur naturally in the body but can damage the immune system if not neutralised by anti-oxidants.

Oxidative stress imbalance between generation and breakdown of oxygen free radicals (reactive oxygen species), accelerated by smoking, air pollution, hyperoxia and hypoxia, which results in net gain of oxygen free radicals and potential for harm, including respiratory disease

Oxygen consumption - amount of oxygen consumed by tissues each minute, i.e. CI x (CaO2-CvO2) x 10 ml/min/m2,
- N at rest: 150-300 ml/min/m2 (if contributing values normal, i.e. CO 5 l/min, Hb 15 g/100ml, SaO2 97%, Sv̅O2 75%),
- critical illness: >600 ml/min/m2.

Oxygen content (CaO2) - total amount of oxygen in blood, i.e. (Hb x SaO2 x 1.39) + (PaO2 x 0.023),
- N in arterial blood: 16-20 ml/100ml or ml/dl.

Oxygen cost of breathing - energy requirements of respiratory muscles and indirect measure of work of breathing,
- N: one ml/l of ventilation.

Oxygen delivery (DO2) - volume of oxygen presented to tissues, i.e. CI x CaO2,
- N: 600-1000 ml/min, i.e. ~25% of oxygen the tissues receive
- may  in hyperdynamic states.

Oxygen demand - oxygen needed by cells for aerobic metabolism, estimated by V̇O2.

Oxygen extraction - oxygen transferred from blood to tissues, i.e. CaO2 difference between arterial and mixed venous blood, equivalent to V̇O2/DO2
- N: 20-30%
- 32% indicates ↑ oxygen demand or occasionally  DO2
- <22% indicates damaged tissues unable to extract O2, or hyperdynamic circulation e.g. early sepsis.

Oxygen extraction ratio (V̇O2/DO2) - ratio of oxygen consumption to oxygen delivery, indicating efficiency of tissues in extracting oxygen.
- calculation: CaO2 - Cv̅O2/CaO2,
- N: 25%
- high oxygen extraction to meet excess metabolic needs: >35%
- maximum for most tissues: 60-70%.

Oxygen flux - % oxygen that reaches tissues.

Oxygen transport - transport of oxygen from lungs to mitochondria.

Oxygen uptake - oxygen consumption.

Ozone - gas that provides protective layer to earth's atmosphere, but at ground level causes inflammation in hyperreactive airways.

P50 - PO2 at which 50% of haemoglobin is saturated with oxygen.
- N: 27-28 mmHg.

PA - postero-anterior.

Pack years - average number of packs smoked daily x years smoked, e.g. smoking one pack/day for 30 yrs = 30 pack-year history.

Packed cell volume - equivalent to haematocrit
- N: 0.36-0.46 (women), 0.40-0.50 (men)
- ↑ in polycythaemia,  in anaemia.

PaCO2 - partial pressure of CO2 in arterial blood
- N: 4.7-6.0 kPa (35-45 mmHg).

Palliation - alleviation of symptoms.

Panic attack - rapid onset of fear accompanied by somatic symptoms.

Panacinar or panlobular emphysema - emphysema affecting mainly alveoli.

PAO2 - partial pressure of oxygen in alveoli.

PaO2 - partial pressure of oxygen in arterial blood
- N: 11-14 kPa (80-100 mmHg), declining by 0.55 kPa (4 mmHg) per 10 years.

PaO2/FiO2 - ratio of PaO2 to inspired oxygen, more relevant than PaO2 alone, estimates shunt
- N: 40 kPa (300 mmHg),
- e.g. PaO2:FiO2 of 27 could mean PaO2 of 10.7 kPa at FiO2 of .40 or PaO2 of 16 kPa at FiO2 of .60.

PAO2-PaO2 - alveolar-arterial oxygen gradient or A-a gradient: difference in oxygen tension across alveolar membrane, i.e. PAO2 minus PaO2
- indicates efficiency of gas transfer, varies with FIO2
- N on room air: 0.7-2.7 kPa (5-20 mmHg), reflecting normal anatomical shunt
- ↑ on exercise, ↑ in the elderly, ↑ on supplemental oxygen, ↑ with diffusion impairment e.g. pulmonary oedema, fibrosis or ARDS.

PAOP - pulmonary artery occlusion pressure (= PAWP).

PAP - (1) peak airways pressure (peak inspiratory pressure) or (2) pulmonary artery pressure.

Paralytic ileus - decrease or absence of peristalsis.

Parenchyma - foamlike substance comprising gas exchanging part of lung, made up of alveoli, small airways, capillaries and supporting tissue.

Parenchymal lung disease - disease affecting parenchyma, e.g. interstitial lung disease, pneumonia, TB, ARDS.

Parenteral - other than through the gut, usually relates to intravenous feeding.

Pathogen - bacteria, viruses, etc, which can cause disease

Patient group direction - legal framework that allows non-medical health professionals, after training, to administer drugs such as oxygen in specific situations.

PAWP - pulmonary artery wedge pressure
- N: 5-15 mmHg
- pulmonary congestion: 20 mmHg
- pulmonary oedema: 25 mmHg.

Paw - mean airway pressure.

PC - pressure contol ventilation.

PCA - patient controlled analgesia.

PCV - see packed cell volume.

PCWP - pulmonary capillary wedge pressure (= PAWP).

PD - postural drainage.

Pdi - transdiaphragmatic pressure.

PE - pulmonary embolus.

Peak cough flow - N: 720 l/min.

Peak V̇O2 - oxygen consumption averaged over a 20- to 30-sec period of maximal effort, may or may not equal V̇O2max

PEEP - positive end-expiratory pressure.

PEEPi - intrinsic positive end-expiratory pressure.

PEFR - peak expiratory flow rate.

PEG - percutaneous endoscopic gastrostomy: surgical opening into stomach for enteral feeding.

PEmax - maximum expiratory pressure at mouth. See MEP.

PEP - positive expiratory pressure.

Percussion - (1) (therapeutic) clapping the chest wall to loosen airway secretions, or (2) (diagnostic) tapping chest wall to identify density of underlying tissue.

Percutaneous - through the skin.

Petechiae - small skin haemorrhages.

PF - peak flow, i.e. peak expiratory flow rate

pH - measure of hydrogen ions in solution, i.e. inverse of log of hydrogen ion concentration
- N: 7.35-7.45.

Pharmacodynamics - what a drug does to the body.

Pharmacokinetics - what the body does to a drug.

Phlebotomy - therapeutic withdrawal of blood.

Phrenic - relating to the diaphragm.

Physiologic dead space - anatomic + alveolar dead space.

PiCCO - pulse index continuous cardiac output.

PICU - paediatric intensive care unit.

Pickwickian syndrome - obesity hypoventilation syndrome.

PIF - peak inspiratory flow
- N: 40-50 l/min
- when breathless or with exercise: up to 200 l/min.

PIFR - peak inspiratory flow rate (peak inspiratory flow).

PImax - maximum inspiratory pressure at the mouth. See MIP.

PIP -peak inspiratory pressure.

Plasma colloid osmotic pressure - N: 3.4 kPa (26 mmHg)
- risk of pulmonary oedema: 1.45 kPa (11 mmHg).

-plasty- reconstruction.

Plate atelectasis - subsegmental atelectasis.

Platelets - cell fragments in blood which assist in clotting.

Platelet count -see clotting studies.

Platypnoea - difficulty breathing when sitting up.

Plethoric - florid complexion due to excess red blood cells.

Pleural pressure - pressure in pleural space.

PM - passive movements (ROM or range of motion in the USA).

PN - percussion note.

PND - paroxysmal nocturnal dyspnoea.

Pneumectomy - lung volume reduction surgery (cf. pneumonectomy: removal of a lung).

Pneumomediastinum - air in mediastinum.

Pneumonitis - inflammation of lung tissue

Pneumopericardium - air in pericardium.

PO2 - partial pressure or tension of oxygen.

Polycythaemia - excess red blood cells due to late-stage lung disease, cyanotic congenital heart disease, high-altitude living or sleep apnoea.

Polypharmacy - multiple medications ± more medications than clinically indicated.

Polysomnography - recording of physiological parameters during sleep.

Polyuria - ↑ urine output, i.e. >100 ml/hr.

Postural hypotension -  BP of >5 mmHg on moving to upright position.

Potassium (K) - electrolyte in plasma or urine
- N in plasma: 3.5-5.0 mmol/l.

Poudrage - pleurodesis.

Pplat - plateau pressure on MV.

PR - pulmonary rehabilitation.

Prader-Willi syndrome - congenital disorder of obesity, hypotonia, sleep apnoea and impaired cognition

Preload - volume of blood in ventricle just before it contracts.

Pressure-time product - pressure generated by respiratory muscles during inspiration.
- average: 90 cmH2O/sec/min.

p.r.n. - ‘as required’, i.e. when the patient requests; usually relates to drug administration.

PS - pressure support ventilation.

Psittacosis - infectious disease of birds transmitted to humans, causing atypical pneumonia.

PSV - pressure support ventilation.

PT - see clotting studies.

PTCA - percutaneous transluminal coronary angioplasty.

PtcCO2 - transcutaneous CO2 tension.

PtcO2 - transcutaneous oxygen tension.

PTSD - post traumatic stress disorder.

PTT - see clotting studies.

Pulmonary artery pressure
- N: 10-20 mmHg (systolic 22, diastolic 10, mean 15)
- pulmonary hypertension: 25 mmHg.

Pulmonary infarction -death of area of lung, usually due to pulmonary embolus.

Pulmonary osteoarthropathy - pain and swelling of joints associated with lung, liver or congenital heart disease.

Pulmonary vascular resistance
- N: 25-125

Pulse pressure - difference between systolic and diastolic pressures: indicates blood flow
- N: 40 mmHg
-  with hypertension,  with poor stroke volume
- dangerously low tissue perfusion: 20 mmHg.

Pulsus paradoxus - weaker pulse on inspiration than expiration caused by expansion of pulmonary vascular bed on inspiration. i.e. excess negative pressure in chest
- occurs with severe acute asthma, hypovolaemic patient on MV, cardiac tamponade
- N: 10 mmHg, higher value indicating laboured breathing.

Purulent - containing pus.

Pv̅CO2 - mixed venous CO2 tension
- N: 6.1 kPa (46 mmHg).

Pv̅O2 - mixed venous oxygen tension
- N: 4.7-5.3 kPa
- minimum acceptable: 3.7 kPa (28 mmHg).

Pyothorax - large empyema.

Pyrexia - fever.

Q - blood flow.

QALY - quality-adjusted life year: number of years of life that would be added by a treatment, modified by a numerical evaluation of that life (1: perfect health, 0: death).

QoL - quality of life.

Qs - shunted blood.

QT - alternative abbreviation for cardiac output.

Qs/QT - shunt fraction.

R - right

Radiolabelling - monitoring radiolabelled aerosol, which, for estimating mucous clearance, is inhaled and its clearance followed by gamma camera.

RAP - right atrial pressure.

Rapid shallow breathing index - ratio of RR to VT, e.g. patient with RR of 25/min and VT of 250 ml/breath has rapid shallow breathing index of (25/0.25) = 100 breaths/min/l.
- used to judge if patients have the strength to wean from mechanical ventilation.

Raynaud's phenomenon of the lung - vasospasm in the lungs associated with Raynaud's syndrome.

RCP - Royal College of Physicians (UK).

Rebreathing - inspired breath containing the CO2 and the reduced oxygen content from the previous exhaled breath.

Recruitment - opening up of alveoli.

Relative humidity - water in gas expressed as a percentage of that which would fully saturate the volume of gas at a given temperature (%). See also absolute humidity
- N in ambient air: 25-50%.
- N in upper trachea: 95%.

REM - rapid-eye-movement phase of sleep cycle.

Resection - surgical cutting out.

Resistance to gas flow through airways
- spontaneous ventilation: 0.5-5.0 cmH2O/l/sec
- mechanical ventilation: (peak inspiratory pressure – plateau pressure) / mean flow
- COPD: 13-18 cmH2O/l/sec.

Respiratory inductive plethysmography - spirometry for ventilated patients, including measurement of lung volume to detect intrinsic PEEP.

Respiratory pump - components that deliver oxygen to alveolar-capillary membrane and remove CO2, i.e. respiratory centres, nerves, muscles, chest wall (thoracic cage + thoraco-abdominal interface).

Respiratory quotient (RQ) - ratio of CO2 produced to O2 consumed, providing a measure of energy consumption
- N: <1.0, expired V̇E being less than inspired V̇E, because CO2 is used for other purposes and less is excreted than O2 absorbed
- RQ of carbohydrate oxidation: 1.0
- RQ of fat oxidation: 0.7.

Respiratory syncytial virus - virus responsible for respiratory infections such as bronchiolitis, bronchopneumonia, and the common cold.

Respiratory therapist (US) - Respiratory physiotherapist (UK) combined with respiratory technician.

- cardiopulmonary (CPR) – manual attempt to restart circulation and breathing
- fluid – replacement of intravascular fluids after dehydration, diarrhoea, vomiting, surgery, trauma or shock.

Reverse Trendelenberg - positioning of the whole bed head up.

RFT - respiratory function test.

Rhinitis - inflammation of mucus membrane of nose, either seasonal (hayfever) or perennial.

Rhonchi - low-pitched snoring-like wheeze on auscultation, often related to airway secretions.

Right middle lobe syndrome - recurrent atelectasis, pneumonitis ± bronchiectasis of middle lobe in children due to poor collateral ventilation (Sehitogullari et al 2012).

ROM - range of motion.

RPE - rate of perceived exertion.

RQ - see respiratory quotient.

RR - respiratory rate,
- normal: 12-16/min.

RTA - road traffic accident.

RV - residual volume.

SaO2 - saturation of haemoglobin with oxygen in arterial blood
- N: 95-98%.

Sarcopenia - loss of muscle cells

SARS - severe acute respiratory syndrome: viral disease that may be contracted by exposure to coronavirus, causing fever and dry cough.

Saturation - oxygen saturation of haemoglobin in arterial blood.

Scopolamine - US terminology for hyoscine.

Sepsis syndrome - SIRS caused by infection.

SGAW - specific airways conductance.

SGRQ - St Georges Hospital Respiratory Questionnaire.

SH - social history.

Shock - failure of oxygen supply to meet oxygen demand.

Shunt - proportion of blood passing through pulmonary vasculature without extracting oxygen
- N: 2% of CO.

Silent lung zone - small airways where airflow resistance is difficult to measure so that damage may not be detectable in early obstructive airways disease.

SIMV - synchronous intermittent mandatory ventilation.

Sinusitis - inflammation of sinus cavities of face
- if chronic, may cause or exacerbate some pulmonary diseases.

SIRS systemic inflammatory response syndrome: generalized inflammatory response, manifest by two or more of the above and caused by infection or other insult such as trauma or pancreatitis.

Situs inversus - transposition of organs in chest and abdomen to the opposite side, e.g. heart on right side.

Sjögren’s syndrome - chronic autoimmune systemic disease in which white blood cells attack moisture-producing glands, causing dry eyes, dry mouth, bronchial hyperresponsiveness and fatigue.

Small airways - terminal and respiratory bronchioles, i.e. those of <1 mm diameter, unsupported by cartilage therefore influenced by transmitted pleural pressures.

SOB - shortness of breath.

SOBOE - shortness of breath on exertion.

SOOB - sit out of bed.

Sodium (Na) - electrolyte in plasma or urine
- N in plasma: 134-148 mmol/l [135-147 mEq/l].

Sol layer - watery layer lining airways in which the cilia beat.

Somatization - distress expressed as a physical symptom.

Speech pathologist - US term for speech language therapist.

Splanchnic - related to viscera.

SpO2 - oxygen saturation by pulse oximetry, usually equivalent to SaO2.

Sputum expectorated secretions

SSRI - antidepressant selective serotonin reuptake inhibitors.

Stent - device for maintaining patency of obstructed structure.

Sternotomy - surgical cutting through the sternum.

Stokes Adams attack - transient but pulseless loss of consciousness, often associated with complete heart block.

Strength - ability of muscle to create force.

Stridor - high-pitched sound produced by turbulent airflow through partially obstructed upper airway, heard on inspiration, expiration or both.

Stroke volume - volume ejected from ventricle with each beat
- dependent on preload, afterload and contractility, normally the same for each ventricle
N: 60-130 ml.

Subcutaneous emphysema - collection of air under the skin

Surfactant - phospholipid protein complex that lines alveoli.

Surgical emphysema - subcutaneous emphysema.

SVR - see systemic vascular resistance.

Sv̅O2 - see mixed venous oxygen saturation.

Syncope - transient loss of consciousness, e.g. faint.

Systemic lupus erythematosus (SLE or lupus) - chronic systemic autoimmune disease leading to fluctuating inflammation of the lungs, joints and other organs.

Systemic vascular resistance - (MAP-CVP / cardiac output) x 79.9
- N: 800-1400
- septic shock: <300.

Systole - ventricular contraction.

Tachycardia - heart rate >100/min in adults.

Tamponade - fluid in pericardium.

TBI - traumatic brain injury

t.d.s. - three times a day.

TENS - transcutaneous electrical nerve stimulation.

Tension time index (TT) or diaphragmatic tension time index (TTdi) or duty cycle (TI/TTOT)
- ratio of inspiratory time to total respiratory cycle time
- indicates proportion of muscle's maximum capacity that can be sustained indefinitely
- quantifies relationship between load and capacity.

Thoracentesis or thoracocentesis or pleural tap - withdrawal of fluid from pleural cavity.

Thoracoscopy - minimal access incision through chest wall.

Thoracotomy - full incision through chest wall.

Thrombocytopaenia - reduced platelet count.

Thrombolysis - dissolution of thrombus.

TIA - transient ischaemic attack.

Tidal breathing - breathing at tidal volume.

Tidal volume - volume of air inhaled and exhaled at each normal sized breath
- N: 7 ml/kg with spontaneous breathing, 7-10 ml/kg with MV, up to 12 ml/kg in acute respiratory failure.

Time constant - function of a lung’s resistance and compliance, expressing how quickly an alveolar group can react to an alteration of pressure and giving an indication of the filling or emptying velocity,
- variability in time constants is often exaggerated in lung disease and the more inhomogeneous the lung ventilation, the wider the spectrum of regional time constants, causing variation in the filling and emptying periods as well as the filling volumes for individual compartments.

TI/TTOT - see tension time index.

TLC - total lung capacity.

TLCO - total lung transfer capacity for carbon monoxide.

Tonicity - osmotic equivalence of fluids: isotonic fluids have same osmolality as plasma, hypotonic fluids have less, hypertonic fluids have more.

Torr - measurement of pressure (US) equivalent to mmHg.

Toxic shock syndrome - shock caused by a storm of inflammatory mediators, leading to respiratory failure and vascular leakage (Low 2013).

TPN - total parenteral nutrition, i.e. food administered intravenously.

Tracheal sounds - sounds heard on auscultation at suprasternal notch.

Tracheal tube - endotracheal or tracheostomy tube.

Transdiaphragmatic pressure - diaphragmatic strength, measured by comparing oesophageal and gastric pressures using swallowed balloons. See also twitch diaphragmatic pressure.

Transmural (transpulmonary) pressure - pressure difference inside and outside lung, i.e. difference between alveolar and pleural pressures, representing driving pressure responsible for inflating lungs.

Transpulmonary pressure - as above.

Trendelenburg position - head down tilt.

TTdi - diaphragmatic tension-time index.

TTOT - total respiratory cycle.

Turbulent flow - flow that is not smooth or laminar, resulting in eddy currents which reduce the volume of gas moved per unit of time per pressure gradient.
Tussive related to cough.

Twitch diaphragmatic pressure - measurement of diaphragmatic strength by bilateral phrenic nerve stimulation
- N: 35 cmH2O
- weakness: typically 20 cmH2O in patients with respiratory muscle weakness secondary to COPD
- weak enough to require MV: 15 cmH2O or less (Tobin et al 2010).

U & Es - urea and electrolytes.

Upper respiratory tract - nose (or mouth), pharynx and larynx.

Urea - electrolyte in plasma or urine, formed from protein breakdown and excreted by kidneys
- N in plasma: 2.5-10 mmol/l
- dehydration: >8, hypovolaemia: >18, kidney injury: 55.

Urea to creatinine ratio - ratio of urea to serum creatinine,
- normal: 1,
- pre-kidney injury: >1 because urea increases disproportionately to creatinine due to enhanced proximal tubular reabsorption.

Uraemia - toxic accumulation of waste products in the blood caused by deficiency in secretion of urine.

Urine output
- normal: 1 ml/hr/kg, average 50-60 ml/hr
- renal failure:
V - volume of gas.

v - venous.

V50 - flow rate half-way through expiration.

Valsalva manoeuvre - forced expiration against closed glottis.

VAP - ventilator-associated pneumonia.

VAS - visual analogue scale.

Vascath - vascular catheter, i.e. specialized central venous catheter used in dialysis.

Vasoactive drugs - vasodilators and vasopressors.

Vasodilator - drug which relaxes smooth muscle in blood vessels.

Vasopressor - drug that constricts blood vessels.

VATS - video-assisted thoracoscopic surgery.

VC - (1) vital capacity, or (2) volume controlled ventilation.

VCO2 - CO2 production
- N: 200 ml/min at rest, increasing by 7% for each 1oC rise in body temperature.

VCIRV - volume control inverse-ratio ventilation.

VD - volume of dead space gas
- N: for anatomical VD: 2 ml/kg body weight.

VD/VT - dead space in relation to tidal volume
- N: 0.3, i.e. 30%, depending on body position
- critical increase: 0.6.

Venous return - blood returning to heart.

Venous admixture - mixing of shunted venous blood with oxygenated blood, i.e. mixture of 'true' shunt which bypasses pulmonary capillary bed, and 'effective' shunt due to V̇A/Q̇ mismatch
- N: 5% of cardiac output.

Ventilatory pump - see: respiratory pump.

Venturi effect - reduction in pressure of air or liquid when a it flows through narrow tubing.

VF - ventricular fibrillation.

VILI - ventilator-induced lung injury

Vital capacity - maximum volume of gas that can be exhaled after a full inspiration.

Volutrauma - damage to alveoli due to overstretch.

VT - see tidal volume.

v̅ - mixed venous.

v̇ - volume of gas per unit time, i.e. flow.

V̇A/Q̇ - ratio of alveolar ventilation to perfusion,
- N: 0.8 (4 l/min for alveolar ventilation, 5 l/min for perfusion).

V̇E - see minute volume.

V̇O2 - see oxygen consumption.

V̇O2/DO2 - see oxygen extraction ratio.

V̇O2max - see maximum oxygen consumption.

WCC - see white blood cell count.

Well year of life - outcome measure incorporating morbidity and mortality, e.g. if a disease halves the quality of life for 2 years, the patient has lost one full well year of life.

White blood cell count - 4-10 109 cells/litre [4,000-10,000/mm-3]
- bacterial infection: >10,000/mm3
- vulnerability to infection: <4,000/mm3.

WHO - World Health Organisation

WOB - work of breathing (below).

Work of breathing - N: 0.3-0.5 kg m/min or joules/l.

Xenotransplant - cross-species transplant.

Eastwood GM, Parke R, Peck L et al (2016) Intravenous fluid bolus therapy: a bi-national survey of critical care nurses' self-reported practice. Anaesth Intensive Care; 44(1):44-51