MCQs to try:
1. Regarding Compliance of the lung, which is truE?
(a) It is increased by surfactant
(B) It is maximal at the beginning of inspiration
(C) It is decreased in pulmonary emphysema
(D) It is lowest at birth
(answer below)
(a) It is increased by surfactant
(B) It is maximal at the beginning of inspiration
(C) It is decreased in pulmonary emphysema
(D) It is lowest at birth
(answer below)
answer
A is correct - surfactant decreases the surface tension of the fluid at the alveolar surface. The surface tension of this fluid tends to cause alveoli to want to collapse and decreases compliance of the lung. Thus, surfactant increases compliance of the lung
B is incorrect - the lung compliance curve is nonlinear, with lowest compliance occurring at low and high volumes. It is maximal in midinspiration at normal volumes
C is incorrect - compliance is actually increased in pulmonary emphysema, probably due to the decrease in elastic tissue in the lungs
D is incorrect - compliance of the lung is very high at birth, and the first few breaths of life require significant pressure to overcome alveolar surface tension.
2 Regarding pulmonary pressure-volume loops:
(A) At a pressure of zero, the volume of air in the lungs is zero
(B) At any given pressure, during expiration the lung volume is higher than during inspiration
(C) Increasing PEEP typically decreases compliance
(D) The loop shows less hysteresis during positive pressure ventilation than during normal breathing
(ANSWER BELOW)
(A) At a pressure of zero, the volume of air in the lungs is zero
(B) At any given pressure, during expiration the lung volume is higher than during inspiration
(C) Increasing PEEP typically decreases compliance
(D) The loop shows less hysteresis during positive pressure ventilation than during normal breathing
(ANSWER BELOW)
answer
A is incorrect – even at pressure, there is a residual volume of air in the lungs
B is correct – the dynamic P-V loop shows hysteresis – ie the expiratory limb follows a higher volume than the inspiratory limb
C is incorrect – increasing PEEP (within sensible values) moves the P-V loop to the right to the most compliant part of the curve (“ideal pressure” range) to increase compliance
D is incorrect – the loops are the same regardless of the positive pressure ventilation or normal breathing