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PROBLEM SESSION

1. A patient has a VC of 4.8 L, an ERV of 1.2 L, and an FRC of 2.5 L. What are his RV, TLC, and IC? Are these volumes within the normal range (assume the patient is a young adult male of average size)?

2. After recovery from surgery involving cardiopulmonary bypass, patients often require positive pressure ventilation to assist their breathing. In a certain patient, a pressure of 30 cm H2O is needed for a tidal volume of 0.9 L. Calculate respiratory system compliance, and decide whether the result of your calculation indicates the respiratory system is stiffer than normal, more compliant than normal, or within the normal range.

3. Below are shown alveolar pressure, intrapleural (intrathoracic) pressure, and lung volume for a typical respiratory cycle of a normal person at rest.

A. Explain the shape of the intrapleural and alveolar pressure curves.

B. How would these curves be expected to change during heavy exercise?

C. How would these curves be expected to change in a person with severe restrictive disease (e.g. fibrosis)?

D. How would these curves be expected to change in a person with severe emphysema?

4. A bright lad decides to lengthen his short snorkel with a 3 meter (10 foot) hose so he can dive deeper. Should you notify the lifeguard?

5. The composition of air remains constant at altitudes near the earth's surface, but barometric pressure decreases progressively with height. At 4250 meters (14,000 feet), total barometric pressure averages 450 mmHg. If ventilation remained normal (neither hyper- nor hypoventilation), what would be the expected value of PA-O2? Do you think you could survive at that altitude. (Hint 1: Assume PA-CO2 = 40 mmHg. Why? Hint 2: Do not forget to include the effect of PH2O. Hint 3: To estimate your survival chances, estimate the blood O2 saturation at the PA-O2 you have calculated.

6. Suppose you attempted to compensate for the reduced oxygen in the preceding problem by doubling alveolar ventilation rate, while metabolic rate (including O2 consumption and CO2 production) remained constant. How much would this hyperventilation increase PAO2? By how much would blood O2 saturation increase?

7. At the cruising altitude of modern jet planes (10,000 meters, 33,000 feet), the total barometric pressure is about 200 mmHg. Suppose you are flying in an airplane and a window blows out, causing the cabin pressure to fall to the ambient barometric pressure. Do you think you could survive breathing air? Do you think you could survive breathing pure oxygen?

8. The following measurements were taken on a 23 year old female with a recent history of dyspnea and cyanosis on exertion.

Respiratory Ventilation	Predicted	Measured	Measure after bronchodilator
Vital Capacity	3.3 L	2.3 L	2.4 L
Residual Volume	0.8 L	0.6 L	0.6 L
Total Lung Capacity	4.1 L	2.9 L	3.0 L
FEV-1	2.6 L	1.9 L	2.0 L
FEV-1 / FVC	> 80%	83%	83%

Blood Gases	Rest (on air)	Exercise (on air)	Rest (on 100% O2)
Pa-O2	75 mmHg	61 mmHg	580 mmHg
Pa-CO2	38	37	40
Ca-O2	200ml O2/L blood	80 ml/L blood	240mlO2/L blood
Cv-O2	150	80	190

Diffusion	Predicted	Measured
D-CO	22 ml/min/mmHg	11.5

A. Does this patient have restrictive pulmonary disease?
B. Does she have obstructive pulmonary disease?
C. Is she hypoventilating?
D. Does she have an unusually high AaDO2 at rest breathing air?
E. Is her AaDO2 primarily due to diffusion limitation, shunt, or ventilation to perfusion nonuniformity/mismatch?
F. Is she anemic?
G. Does she have stagnant hypoxia?
H. What is the major cause of her cyanosis on exercise?