Respiratory Physiology and Function Tests

Timing and character of the added sound localise the pathology

A memory aid for interpreting crackles, wheeze and rubs.

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.

Oxygenation first, then pH, then carbon dioxide, then bicarbonate

A memory aid for the order in which to read an arterial blood gas.

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

A mnemonic for distinguishing the Bohr and Haldane effects.

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.

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

A mnemonic for the five mechanisms of arterial hypoxaemia.

Peripheral chemoreceptors sense oxygen; central chemoreceptors sense carbon dioxide

A memory aid for the peripheral and central chemoreceptors.

Percussion note, breath sounds and vocal resonance identify the pathology

A memory aid for the combination of chest signs in each condition.

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.

Physiological dead space equals anatomical plus alveolar dead space

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

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.

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.

Four volumes combining into four capacities

A memory aid for the lung volumes and which cannot be measured by spirometry.

Minute ventilation includes dead space; alveolar ventilation does not

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

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

A memory aid for why high inspired oxygen causes collapse.

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.

Delivery equals cardiac output multiplied by arterial oxygen content

A memory aid for calculating oxygen delivery to the tissues.

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.

Resonant, dull, stony dull and hyperresonant

A memory aid for what each chest percussion note means.

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.

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.

Hands, face, neck, then chest front and back with the same four steps

A memory aid for the order of a respiratory examination.

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

A memory aid for the respiratory quotient of different fuels.

Obstructive lowers the ratio; restrictive lowers both values proportionately

A memory aid for distinguishing obstructive from restrictive spirometry.

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.

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.

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.