PRACTICE QUESTIONS______

1. Calculate the alveolar oxygen tension (PAo₂) of an anes­thetized cow when the barometric pressure is 750 mm Hg, PH₂O at body temperature = 50 mm Hg, and Paco₂ = 80 mm Hg.

a. 270 mm Hg

b. 620 mm Hg

c. 275 mm Hg

d. 195 mm Hg

e. 670 mm Hg

2. Which of the following will decrease the rate of oxygen transfer between the alveolar air and the pulmonary capillary blood?

a. Increasing PAo₂ from 100 to 500 mm Hg.

b. Perfusing previously unperfused pulmonary capil­laries.

c. Decreasing the mixed venous oxygen tension from 40 to 10 mm Hg.

d. Destruction of alveolar septa and pulmonary capil­laries by a disease known as alveolar emphysema.

e. None of the above.

3. During exercise, recruitment of muscle capillaries that are unperfused in the resting animal results in all the following except:

a. An increase in the velocity of capillary blood flow

b. An increase in the surface area for gas diffusion between tissues and blood

c. A decrease in distance between tissue capillaries

d. Maintenance of tissue Po₂ in the presence of increased demand for oxygen

e. A shorter distance for gas diffusion

4. Which of the following could potentially result in more low V/Q regions within the lung?

a. Atelectasis of one lobe of a dog lung

b. Obstruction of both pulmonary arteries

c. Doubling the ventilation to the right cranial lobe while its blood flow remains constant

d. Vasoconstriction of the pulmonary arteries of the left lung in a cow

e. None of the above

5. Which of the following statements is correct⁷

a. Right-to-left shunts represent an extremely high V/Q ratio.

b. Right-to-left shunts are not a cause of elevated alveolar-arterial oxygen difference.

c. An increase in the alveolar dead-space can result from an increase in the number of high V/Q units in the lung.

d. The shape of the oxyhemoglobin dissociation curve means that low V/Q units in the lung are not a cause ofhypoxemia (low Pao₂).

e. Totally occluding the right pulmonary artery increases the right-to-left shunt fraction by 50%.

6. A horse has difficulty inhaling, especially during exercise. Arterial blood gas tensions at rest are Pao₂ = 55 mm Hg and Paco₂ = 70 mm Hg. After you give the horse oxygen to breathe, Pao₂ increases to 550 mm Hg, and Paco₂ remains unchanged. The cause of these gas ten­sions is:

a. Right-to-left shunt through a complex cardiac defect

b. Alveolar hyperventilation

c. A large number of alveoli with high V/Q ratios

d. Alveolar hypoventilation

e. None of the above