Respiratory

Loss of elastic recoil, stiffer chest wall, rising closing capacity and falling oxygen tension

A memory aid for the normal respiratory changes of ageing.

Gas is fully saturated at body temperature by the time it reaches the isothermic boundary

A memory aid for how inspired gas is conditioned.

Medium-sized bronchi contribute most resistance, not the smallest airways

A memory aid for where airway resistance is greatest and what alters it.

Inspired oxygen minus carbon dioxide divided by the respiratory quotient

A memory aid for calculating alveolar oxygen tension.

Alveolar carbon dioxide is inversely proportional to alveolar ventilation

A memory aid for the relationship between ventilation and carbon dioxide.

A normal gradient points to hypoventilation or low inspired oxygen; a wide gradient points to lung disease

A memory aid for interpreting the A-a gradient.

Bronchial and thebesian veins drain deoxygenated blood into the systemic circulation

A memory aid for the normal physiological shunt.

The kidney adjusts bicarbonate over days to offset a change in carbon dioxide

A memory aid for renal compensation of respiratory acid-base disorders.

Immature respiratory control with a paradoxical response to hypoxia

A memory aid for why premature infants stop breathing.

Diffuse alveolar damage causes non-cardiogenic oedema, shunt and stiff lungs

A memory aid for the physiology of acute respiratory distress syndrome.

Bronchoconstriction, gas trapping and hyperinflation with V/Q mismatch

A memory aid for the physiological changes in acute asthma.

Bohr is carbon dioxide affecting oxygen carriage; Haldane is oxygen affecting carbon dioxide carriage

A mnemonic for distinguishing the Bohr and Haldane effects.

Rising carbon dioxide is the main stimulus, with falling oxygen contributing later

A memory aid for what terminates a breath hold.

Histamine and leukotrienes early, cellular infiltration late

A memory aid for the mediators of the early and late asthmatic response.

Bicarbonate about 70 per cent, carbamino about 23 per cent, dissolved about 7 per cent

A memory aid for the three forms in which carbon dioxide is carried.

It binds haemoglobin 240 times more avidly than oxygen and shifts the curve left

A memory aid for why carbon monoxide is so dangerous.

Low inspired oxygen, hypoventilation, diffusion impairment, V/Q mismatch, shunt

A mnemonic for the five mechanisms of arterial hypoxaemia.

Bicarbonate leaves the red cell in exchange for chloride entering

A memory aid for the Hamburger phenomenon in red cells.

The volume at which dependent small airways begin to close

A memory aid for closing capacity and its relationship to functional residual capacity.

The lung follows a different path on inflation than on deflation

A memory aid for why the inflation and deflation curves differ.

Chronic obstructive pulmonary disease

A chronic respiratory condition characterised by persistent airflow limitation.

Loss of elastic recoil, airway collapse, gas trapping and impaired gas exchange

A memory aid for the physiological changes in chronic obstructive pulmonary disease.

Inspiration, glottic closure, compression, then explosive expiration

A memory aid for the stages and pathway of the cough reflex.

Physiological dead space equals anatomical plus alveolar dead space

A memory aid for anatomical, alveolar and physiological dead space.

Measured with carbon monoxide, reflecting surface area, membrane thickness and haemoglobin

A memory aid for the transfer factor and what alters it.

Beyond a certain effort, higher pleural pressure compresses airways and flow cannot increase

A memory aid for why forced expiration is effort independent.

Falling barometric pressure lowers inspired oxygen, driving hyperventilation and acclimatisation

A memory aid for the respiratory adaptations to altitude.

Reduced functional residual capacity, blunted drive, and atelectasis

A memory aid for the respiratory changes under general anaesthesia.

Pressure rises by one atmosphere for every 10 metres of seawater

A memory aid for the respiratory effects of increased ambient pressure.

Chloride-driven secretion in utero switches to sodium-driven absorption at birth

A memory aid for the clearance of lung fluid at birth.

Scooped expiratory limb in obstruction; flattening indicates large airway obstruction

A memory aid for interpreting the shape of the flow-volume loop.

The balance point where inward lung recoil equals outward chest wall recoil

A memory aid for what raises and lowers functional residual capacity.

Inflation inhibits further inspiration; deflation stimulates it

A memory aid for the pulmonary stretch reflexes.

Uneven hypoxic pulmonary vasoconstriction overperfuses some capillaries

A memory aid for the mechanism of high altitude pulmonary oedema.

Respiratory alkalosis causes paraesthesiae, tetany and cerebral vasoconstriction

A memory aid for the physiological consequences of acute hyperventilation.

Pulmonary arterioles constrict in hypoxia, diverting blood to better ventilated alveoli

A memory aid for the pulmonary vascular response to alveolar hypoxia.

Peripheral chemoreceptors respond only below about 8 kPa

A memory aid for the ventilatory response to hypoxia.

A capacity is two or more volumes added together

A memory aid for the four lung capacities and the volumes that make them up.

Change in volume per unit change in pressure, determined by elastic tissue and surface tension

A memory aid for the determinants of lung compliance.

Volume, Air, Tidal, Inspiratory, Residual, Expiratory

A mnemonic for the key lung volumes and capacities measured in spirometry.

Minute ventilation includes dead space; alveolar ventilation does not

A memory aid for the difference between total and effective ventilation.

Cilia beat in a watery sol layer, moving an overlying gel layer of mucus upwards

A memory aid for the airway's mucociliary escalator.

The diaphragm alone at rest, with accessory muscles for forced inspiration and abdominals for forced expiration

A memory aid for which muscles are used in quiet and forced breathing.

Nitrogen splints alveoli open; replacing it with rapidly absorbed oxygen allows collapse

A memory aid for why high inspired oxygen causes collapse.

Filtration, metabolism, immune defence, acid-base balance and a blood reservoir

A memory aid for the metabolic and defensive roles of the lung.

Repeated pharyngeal collapse causes intermittent hypoxia and arousals

A memory aid for the mechanism and consequences of obstructive sleep apnoea.

Obstruction traps gas and raises volumes; restriction reduces all volumes

A memory aid for the physiological differences between obstruction and restriction.

Automatic breathing is brainstem driven; voluntary breathing bypasses it through corticospinal tracts

A memory aid for the distinction between automatic and voluntary breathing.

Oxygen tension falls stepwise from atmospheric to about 1 kPa in the mitochondrion

A memory aid for the fall in oxygen tension from air to mitochondria.

Tension drives diffusion, saturation describes haemoglobin, content determines delivery

A memory aid for distinguishing oxygen tension, saturation and content.

A sigmoid curve with P50 of about 3.5 kPa or 27 mmHg

A memory aid for the shape and key points of the oxyhaemoglobin curve.

Acid, carbon dioxide, temperature and 2,3-DPG all shift it right

A mnemonic for what shifts the oxygen dissociation curve right.

Variable devices depend on the patient's breathing pattern; fixed devices do not

A memory aid for fixed and variable performance oxygen devices.

Pulmonary damage from free radicals, plus central nervous system toxicity at high pressure

A memory aid for the harmful effects of prolonged high inspired oxygen.

Nitrous oxide is perfusion limited, carbon monoxide is diffusion limited, oxygen is normally perfusion limited

A memory aid for distinguishing perfusion-limited from diffusion-limited gas transfer.

Cheyne-Stokes waxes and wanes; Kussmaul is deep and rapid; Biot's is irregular

A memory aid for the abnormal breathing patterns and their causes.

Transudates from altered Starling forces; exudates from increased permeability

A memory aid for the formation and classification of pleural effusions.

Pleural pressure is more negative at the apex than at the base

A memory aid for the vertical gradient in pleural pressure.

Loss of negative pleural pressure allows the lung to collapse and the chest wall to spring out

A memory aid for the physiological consequences of air in the pleural space.

It reverses the normal negative intrathoracic pressure, reducing venous return

A memory aid for the physiological consequences of positive pressure ventilation.

It makes ventilation more uniform while perfusion remains relatively unchanged

A memory aid for why proning improves oxygenation.

Increased dead space, hypoxaemia from mismatch, and right ventricular strain

A memory aid for the physiological consequences of pulmonary embolism.

Raised hydrostatic pressure or increased permeability floods the interstitium then alveoli

A memory aid for the mechanisms of pulmonary oedema.

Two wavelengths distinguish oxyhaemoglobin from deoxyhaemoglobin in pulsatile blood

A memory aid for how pulse oximetry works and when it misleads.

Medullary dorsal and ventral groups, with pontine pneumotaxic and apneustic centres

A memory aid for the brainstem centres controlling breathing.

Tidal volume and minute ventilation rise, functional residual capacity falls

A memory aid for the respiratory adaptations of pregnancy.

Type 1 is hypoxaemia alone; type 2 adds hypercapnia

A memory aid for distinguishing type 1 from type 2 respiratory failure.

Carbohydrate 1.0, protein 0.8, fat 0.7, mixed diet about 0.8

A memory aid for the respiratory quotient of different fuels.

Respiratory rate

The number of breaths per minute.

Ventilation falls, carbon dioxide rises slightly and upper airway tone is reduced

A memory aid for the respiratory changes during sleep.

Impaired clearance, carboxyhaemoglobin, protease imbalance and accelerated decline in FEV1

A memory aid for the physiological effects of cigarette smoking.

Obstructive lowers the ratio; restrictive lowers both values proportionately

A memory aid for distinguishing obstructive from restrictive spirometry.

Peripheral oxygen saturation

An estimate of haemoglobin oxygen saturation measured by pulse oximetry.

Surfactant deficiency causes high surface tension, alveolar collapse and stiff lungs

A memory aid for the physiology of neonatal respiratory distress syndrome.

Reduces surface tension, increases compliance, stabilises alveoli and keeps them dry

A memory aid for the roles of pulmonary surfactant.

Time constant equals resistance multiplied by compliance

A memory aid for how compliance and resistance determine filling and emptying.

Alveolar pressure minus pleural pressure

A memory aid for the pressure that actually inflates the lung.

Hypoxic, anaemic, stagnant and histotoxic

A mnemonic for the four classes of tissue hypoxia.

Dependent regions receive more ventilation and more perfusion in the spontaneously breathing patient

A memory aid for how posture changes the distribution of ventilation and perfusion.

Ventilation rises linearly with work until the anaerobic threshold, then disproportionately

A memory aid for the ventilatory response to exercise.

A ratio of zero is shunt; a ratio of infinity is dead space

A memory aid for the V/Q ratio and its extremes.

Carbon dioxide is the dominant drive, sensed centrally through cerebrospinal fluid pH

A memory aid for the main stimulus to breathing.

Alveolar pressure dominates at the apex, arterial pressure at the base

A memory aid for the three zones of pulmonary blood flow.

Elastic work plus resistive work, minimised at an optimal respiratory rate

A memory aid for the components of the work of breathing.