## Lesson 15 Video 10 Slide 4

ArielM
Posts: 31
Joined: Mon Oct 02, 2017 9:15 pm

### Lesson 15 Video 10 Slide 4

Question 23 states:

A man suspected of DUI is brought in for a Breathalyzer analysis. At the exact moment between peak exhalation and onset of inhalation, which of the following is true?

A. The pressure of air within the alveoli is greater than the pressure of air in the atmosphere.
B. The pressure of air within the alveoli is less than the pressure of air in the atmosphere.
C. The pressure of air within the alveoli is equal to the pressure of air in the atmosphere.
D. The partial pressure of oxygen in the alveoli is less than the partial pressure of oxygen in the capillaries.

The correct answer is C, the pressure of air within the alveoli is equal to the pressure of air in the atmosphere.

There is a graph that is given to aid in answering the question, I have posted it below.

In the lesson, it is stated that intra-alveolar pressure varies between -1 and +1 during normal breathing. During inhalation, the intra-alveolar pressure falls to -1. At Peak inhalation, intra-alveolar pressure = 0. During exhalation, intra-alveolar pressure rises to +1.

I do not understand this graph. 0 is supposed to mean peak inhalation... so the graph begins with peak inhalation. Then we inhale more to the point of reaching a negative intra-alveolar pressure value of -1, is this correct? Then during inhalation, does the intra-alveolar pressure decrease because the intra-alveolar volume increases? Then when we reach peak inhalation again- after we have inhaled...? I am lost after this. Then we exhale and until we reach the intra-alveolar pressure of +1. And is this intra-alveolar pressure value of +1 a positive value because we have decreased the intra-alveolar volume (essentially, is alveolar pressure inversely related to volume in this graph)?