Question

Figure 12.2 indicates some events during two respiratory cycles, where I = inspiration and E = expiration. In the second cycle, tidal volume was three times that in the first cycle. Expiration was not forced. It can be concluded that:

a. Record A shows the changes in intrapleural pressure.

b. Record B shows the changes in intrapulmonary pressure.

c. Record C shows the rate of gas flow into and out of the lungs.

d. The compliance of the lungs and chest wall is increased markedly in the second cycle.

e. Maximum airflow occurs at the end of inspiration.

Answer 1

a. True Intrapleural pressure is negative throughout the cycle and is minimum at the end of inspiration; it becomes more negative with a deeper inspiration.

b. True Intrapulmonary pressure (that is intra-alveolar pressure) reaches its minimum around mid-inspiration and its maximum around mid-expiration.

c. False The flow record closely follows the intrapulmonary pressure record B since flow is directly related to pressure gradient between alveoli and atmosphere; record C shows changes in lung volume.

d. False Compliance, the volume change for a given pressure change, is similar in both; though the pressure gradient is increased about three times in the second cycle, so is the tidal volume.

e. False Airflow is zero at end inspiration; it is maximum in mid-inspiration and midexpiration.