Physiology - An Illustrated Review

Questions & Answers

Review Questions

1. During expiration,

A.   airway compression may occur if pressure within the airways is less than the pressure in the pleural space.

B.   airway compression will most likely occur at high lung volumes.

C.   pressures due to recoil properties of the lungs are greatest at low lung volumes.

D.   airway resistance is highest at high lung volumes.

E.   muscular effort is required for airflow.

2. In a premature infant without pulmonary surfactant,

A.   surface tension of alveoli is less than normal.

B.   a greater than normal pressure difference between the inside and outside of the lungs is required for lung inflation.

C.   large alveoli collapse more easily than small alveoli.

D.   pressures due to surface tension in large and small alveoli are equal.

E.   the lungs can be inflated with normal muscular effort.

3. What is the cause of a decrease in arterial Po2 with chronic bronchitis?

A.   Increased V/Q for all regions of the lungs

B.   Abnormally uneven V/Q

C.   Decreased shunting of blood from the right to the left side of circulation

D.   A higher Po2 in arterial blood than in alveolar gas

E.   Decreased functional residual capacity

4. A patient with a normal vital capacity expires only 40% of his forced expiratory volume/forced vital capacity in 1 second (FEV1/FVC). Which problem does this suggest?

A.   Abnormally low lung compliance

B.   Obstructive disease

C.   Restrictive disease

D.   Weak inspiratory muscles

E.   Airflow limitation due to airway compression is less than normal.

5. Physiological dead space volume is unchanged by

A.   increases in volume of the alveolar dead space.

B.   widening of the airways above the respiratory zone.

C.   increases in breathing frequency.

D.   increases in volume of the anatomical dead space.

E.   breathing through a tube (e.g., a snorkel).

For Question 6 and 7, the following data were obtained from a man during a pulmonary screening test: tidal volume = 447 mL, respiratory rate = 10 breaths/min, dead space volume =147 mL, Paco2 = 44 mm Hg.

6. What is his minute ventilation?

A.   40 mL/min

B.   44.7 mL/min

C.   4000 mL/min

D.   4200 mL/min

E.   4470 mL/min

7. What is his alveolar ventilation?

A.   1470 mL/min

B.   2940 mL/min

C.   3000 mL/min

D.   4323 mL/min

E.   5940 mL/min

8. When the ambient pressure in an aircraft is suddenly reduced to 190 mm Hg (¼ atmosphere, altitude 34,000 ft [10,363 m]), the pilot discovers that his O2 equipment fails to deliver any O2. What is the O2 tension in the cabin of the aircraft?

A.   20 mm Hg

B.   40 mm Hg

C.   60 mm Hg

D.   80 mm Hg

E.   100 mm Hg

9. Which of the following is true in pulmonary embolism?

A.   The surface area available for gas exchange decreases.

B.   The dead space is decreased.

C.   Loose emboli travel to the brain.

D.   Loose emboli cause strokes.

E.   Pulmonary embolism is never fatal.

10. An elderly person is found unconscious after her gas house heater malfunctions. One-half the hemoglobin in her blood is bound to carbon monoxide. Which of the following is true?

A.   P50 for O2 will be decreased from normal.

B.   O2 content of blood at a Po2 of 100 mm Hg will be normal.

C.   Arterial Pco2 will be increased by 50%.

D.   Arterial Pco2 will be decreased by 50%.

E.   O2 carried in physically dissolved form at a Po2 of 100 mm Hg will be less than normal.

11. An alveolar-to-arterial difference (a-a gradient) in the partial pressure of oxygen (Po2) will increase when

A.   alveolar ventilation is reduced by a drug overdose.

B.   shunting of blood from the right to the left side of the circulation is increased when a lobe of the lung fills with fluid (pneumonia).

C.   diffusing capacity decreases because one lobe of a lung is removed.

D.   breathing through a tracheostomy tube.

E.   ventilation and perfusion in all parts of the lung are doubled.

12. Which of the following stimulates activity in central chemoreceptors?

A.   Decreased partial pressure of oxygen (Po2)

B.   Increased Pao2

C.   Normal A-a Po2

D.   Increased partial pressure of carbon dioxide (Pco2)

E.   Increased pH

13. During light to moderate exercise, i.e., before anaerobic metabolism becomes significant (and lactic acid production is increased), then you would expect that

A.   Paco2 increases linearly with the severity of exercise.

B.   Pao2 decreases linearly with the severity of exercise.

C.   alveolar ventilation increases in proportion to the increased CO2 production.

D.   minute ventilation increases in proportion to the increased Paco2.

E.   the ratio of the dead space volume to tidal volume (VD/VT) increases.

Answers and Explanations

1. A. If pressure in the pleural space is greater than that within the airways, the pressure difference can compress the airways (p. 126).

B,D Airway compression is least likely to occur at high lung volumes because elastic recoil of the lungs is maximal, and airway resistance is minimal.

C Pressures due to recoil properties of the lungs are greatest at high lung volumes.

E Expiratory airflow is normally produced by elastic recoil, the potential energy stored in the lungs from the previous inspiration, and not by muscular effort.

2. B. According to the law of Laplace, the transpulmonary pressure (measured in dynes/cm2) required to prevent collapse of an alveolus (P) is directly proportional to surface tension (T) and inversely proportional to alveolar radius (r), as expressed by P = 2T/r. Therefore, a greater pressure difference is required to inflate alveoli to overcome surface forces (p. 130).

A Lack of surfactant will increase surface tension.

C Small alveoli collapse more easily than large alveoli.

D Lack of surfactant makes pressures different in large and small alveoli.

E More effort is needed to inspire.

3. B. Chronic bronchitis is associated with uneven ventilation to perfusion ratio (p. 139).

A V/Q does not increase.

C Blood flow does not change.

D Po2 in blood can never be higher than alveolar O2.

E The functional residual capacity is increased in chronic obstructive pulmonary disease (COPD).

4. B. Constricted bronchioles and bronchi in obstructive lung disease slow the rate of expiration (and inspiration) (p. 133).

A,D Abnormally low lung compliance and weak inspiratory muscles are typical of restrictive lung disease.

C In restrictive lung disease, the ratio FEV1/FVC is not reduced.

E Airway compression produces decreased vital capacity.

5. C. Increasing the frequency of breathing increases the ventilation of the dead space per minute, although it does not significantly affect the volume of the dead space for each breath (p. 134).

A,B,D Increases in alveolar or anatomical dead space, or widening the airways above the respiratory zone change physiological dead space.

E A snorkel also increases dead space, changes airway volume, and increases anatomical dead space.

6. E. His minute ventilation is tidal volume multiplied by the respiratory rate, or 447 mL × 10 breaths/min = 4470 mL/min (p. 134).

7. C. His alveolar ventilation is alveolar volume multiplied by the respiratory rate. Alveolar volume is tidal volume minus dead space, or 447 mL − 147 mL = 300 mL. 300 mL × 10 breaths/min = 3000 mL/min (p. 134).

8. B. The partial pressure of O2 is still 21% of the total pressure, so 0.21 × 190 mm Hg = 40 mm Hg (p. 136).

9. A. Emboli block the pulmonary arterial system, decreasing the area for gas exchange (p. 139)

B Pulmonary embolism increases dead space.

C,D The pulmonary capillary circulation filters emboli, so they do not travel to the brain and cause stroke.

E Severe emboli cause death due to hypoxia.

10. A. Poisoning of hemoglobin with CO causes the O2 dissociation curve to shift to the left, so the partial pressure where the available hemoglobin is 50% saturated with O2 is reduced (p. 141).

B Because CO competes with O2 for sites on the hemoglobin molecule, less O2 will be carried at a given Po2 level.

C, D Pco2 is determined by alveolar ventilation and virtually unaffected by the presence of CO.

E The presence of CO has no effect on O2 solubility in blood.

11. B. The A-a gradient increases when arterial Po2 is decreased, such as when blood is shunted from right-to-left. In this latter situation, the arterial Po2 is lowered when nonoxygenated blood mixes with oxygenated blood (p. 142).

A,D Hypoventilation by itself or a change in dead space is not associated with an increased alveolar-to-arterial Po2 difference.

C While removal of one lobe of a lung reduces diffusing capacity, an increase in the A-a gradient will only occur under extreme conditions (e.g., strenuous exercise).

E Uniformly doubling the ventilation (V) and perfusion (Q) in all parts of the lungs will not change the ratio, V/Q.

12. D. Central chemoreceptors are highly sensitive to increased Pco2 or [H+] (p. 145).

A A low arterial Po2 stimulates peripheral chemoreceptors.

B, C An increased alveolar Po2 or normal A-a Po2 difference has no effect on chemoreceptors.

E Increasing pH means decreasing [H+], which decreases chemoreceptor activity.

13. C. Ventilation matches CO2 production during light to moderate exercise (p. 147).

A,B Paco2 and Pao2 change little during light to moderate exercise.

D Increased minute ventilation keeps Paco2 from increasing.

E The ratio VD/VT decreases because light to moderate exercise causes the dead space volume (VD) to decrease, and the tidal volume (VT) to increase.