Questions -

Q1. Consider two different sized alveoli, as in figure 6.1.6. The alveolus on the left has a radius of 0.6mm and the alveolus on the right has a radius of 0.25mm. Suppose that the surface tension was constant at 70 dyne/cm.

a. What is the pressure, in dynes/cm² in each of the alveoli?

b. What is the pressure in Pa, atm, and mmHg?

FIGURE 6.1.6 Schematic diagram of the predicted instability of alveoli. According to the Law of Laplace, the pressure within alveoli at mechanical equilibrium would be given by P=2y/r. If the surface tension is the same in both alveoli, but r is smaller on the right, then the pressure on the right will be larger and air will move from the smaller alveolus to the are not independent, individual spheres. The alveoli are connected to other alveoli because they share walls and as one collapses it is supported or kept open by its neighbors.

Q2. Explain the following:

a. At what lung volumes do the lungs tend to collapse, as depicted in figure 6.1.8 the Relaxation volume-pressure curves?

b. Why do the lungs have a tendency to collapse at these volumes?

lungs, and combined respiratory system, so named because the muscles are relaxed when pressures are measured. At a single volume, the contribution to the total pressure is the sum of the pressures contributed by the chest wall and by the lungs (see Eqn (6.1.8). Thus the pressures add as vectors along the dashed horizontal lines to form the combined chest and wall curve (solid line). Throughout most of the volume range: the chest wall tends to recoil toward a larger volume. At large volumes, the chest wall tends to recoil inward. Such large volumes can be accomplished by the action of respiratory muscles. The lungs always tend to collapse, and the tendency becomes larger with increasing volume. Except at high volumes, then, the lungs and the chest wall act in opposite directions: the lung tends to shrink whereas the chest wall tends to expand.

P_A - P_B = P_lung + P_{chest wall} = P_rs        [6.1.8]

where P_rs is the pressure of the entire respiratory system consisting of lung and chest wall.

Q3. Identify at least 4 different physiological impacts of Surfactant on respiration and explain how the presence of Surfactant contributes to these benefits.

Q4. Draw a spirometer trace and label TV, IRV, ERV, RV, IC, FRC, VC, and TLC. Indicate which cannot be measured by spirometry alone.

Q5. The lung capabilities in an older individual were measured by spirometry and the following data were obtained: TV = 041 L; IRV = 2.3 L; ERV = 1.19 L; FEV1 = 2.1 L

a. Calculate the VC and FRC

b. Are the values for VC and FRC normal?

c. Calculate the airway resistance. Is this normal?