Passage IV

The respiratory cycle for resting humans who are breathing normally has been studied by physiologists. The figure shows 4 average measures of the cycle: lung volume, air flow (the rate at which air flows into or out of the lungs), pleural pressure (the pressure in the area between the lungs and the chest wall), and alveolar pressure (the pressure in the alveoli, small sacs in the lungs where air exchange takes place). Pleural pressure and alveolar pressure are represented as values above or below atmospheric pressure (1,033 cm H2O). The next inspiration begins at the end of the pause.

21. When the diaphragm contracts during the first 0. 5 sec of inspiration, the chest wall expands away from the lungs, which causes the lungs to expand. Based on the figure, what is the effect of the contraction of the diaphragm on pleural pressure and alveolar pressure ?

Answer and Explanation

Your Answer is

Correct Answer is D

Explanation

Refer to the third and fourth lines in the figure, when the abscissa is less than or equal to 0.5 s, both lines are in a downward trend, so they are both decreasing