Pulmonary Ventilation: Volumes, Flows, Dead Space and Preoxygenation

Question 1

Regarding the measurement of lung volumes:

FRC can be measured using a water sealed spirometer.

Answer 1

False. FRC is made up of residual volume and expiratory reserve volume. As it is impossible to exhale below RV, this cannot be measured by any spirometer. Instead, helium dilution or body plethysmography must be used.

Question 2

Regarding the measurement of lung volumes:

Body plethysmography is based upon Boyle’s Law, where the pressure and temperature of a gas are directly proportional to each other at a constant volume.

Answer 2

False. Body Plethysmography is based upon Boyle’s Law, but Boyle’s Law states that at a constant temperature, the pressure and volume of a gas are inversely proportional to one another.

Question 3

Regarding the measurement of lung volumes:

Body plethysmography allows the measurement of all lung units, including those that are collapsed or have poor air entry.

Answer 3

True. Body plethysmography is able to measure all available lung units.

Question 4

Regarding the measurement of lung volumes:

Helium is used in dilution techniques as it has a lower density than air and therefore distributes better throughout the lung.

Answer 4

False. Although helium is less dense than air, this is not the reason why it is used in dilution techniques. It is the low solubility of helium that makes is a useful gas, as minimal amounts are absorbed during measurement.

Question 5

Regarding FRC:

FRC falls with increasing age.

Answer 5

False. FRC is unaffected by age, but closing capacity increases with age, making airway collapse more likely in elderly patients.

Question 6

Regarding FRC:

FRC is the lung volume of maximal lung compliance and maximal pulmonary vascular resistance (PVR).

Answer 6

False. Lung compliance is maximal at FRC, but PVR is minimal.

Question 7

Regarding FRC:

FRC is decreased by supine positioning, obesity and anaesthesia.

Answer 7

True. These factors are of great clinical importance to anaesthetists.

Question 8

Regarding FRC:

Preoxygenation involves denitrogen of the FRC.

Answer 8

True. The FRC is very useful oxygen reservoir, and is the major store of oxygen within the body.

Question 9

Regarding dead space:

Fowler’s method involves the inspiration of helium.

Answer 9

False. Fowler’s method uses a maximal breath of 100% oxygen and then expired nitrogen is measured. Helium is used in helium dilution techniques to measure FRC.

Question 10

Regarding dead space:

Anatomical dead space = physiological dead space + alveolar dead space.

Answer 10

False. Physiological dead space = Anatomical dead space + alveolar dead space.

Question 11

Regarding dead space:

Fowler’s method can measure anatomical dead space and closing capacity.

Answer 11

True. Anatomical dead space is the midpoint of the slope in phase 2, whilst closing capacity correlates with the start of phase 4.