Respiratory Physiology Flashcards
- Which of the following lung volumes or capacities can be measured by spirometry?
(a) Functional residual capacity (FRC)
(b) Physiologic dead space
(c) Residual volume (RV)
(d) Total lung capacity (TLC)
(e) Vital capacity (Vc)
The answer is E [I A 4, 5, B 2, 3, 5].
Residual volume (RV) cannot be measured by spirometry. Therefore, any lung volume or capacity that includes the RV cannot be measured by spirometry. Measurements that include RV are functional residual capacity (FRC) and total lung capacity (TLC). Vital capacity (Vc) does not include RV and is, therefore, measurable by spirometry. Physiologic dead space is not measurable by spirometry and requires sampling of arterial Pco2 and expired CO2.
An infant born prematurely in gestational week 25 has neonatal respiratory distress syndrome. Which of the following would be expected in this infant?
(a) Arterial Po2 of 100 mm Hg
(b) Collapse of the small alveoli
(c) Increased lung compliance
(d) Normal breathing rate
(e) Lecithin:sphingomyelin ratio of greater than 2:1 in amniotic fluid
The answer is B [II D 2].
Neonatal respiratory distress syndrome is caused by lack of adequate surfactant in the immature lung. Surfactant appears between the 24th and the 35th gestational week. In the absence of surfactant, the surface tension of the small alveoli is too high. When the pressure on the small alveoli is too high (P = 2T/r), the small alveoli collapse into larger alveoli. There is decreased gas exchange with the larger, collapsed alveoli, and ventilation/perfusion (V/Q) mismatch, hypoxemia, and cyanosis occur. The lack of surfactant also decreases lung compliance, making it harder to inflate the lungs, increasing the work of breathing, and producing dyspnea (shortness of breath). Generally, lecithin:sphingomyelin ratios greater than 2:1 signify mature levels of surfactant.
In which vascular bed does hypoxia cause vasoconstriction?
(a) Coronary
(b) Pulmonary
(c) Cerebral
(d) Muscle
(e) Skin
The answer is B [VI C].
Pulmonary blood flow is controlled locally by the Po2 of alveolar air. Hypoxia causes pulmonary vasoconstriction and thereby shunts blood away from unventilated areas of the lung, where it would be wasted. In the coronary circulation, hypoxemia causes vasodilation. The cerebral, muscle, and skin circulations are not controlled directly by Po2.
A 12-year-old boy has a severe asthmatic attack with wheezing. He experiences rapid breathing and becomes cyanotic. His arterial Po2 is 60 mm Hg and his Pco2 is 30 mm Hg.
Which of the following statements about this patient is most likely to be true?
(a) Forced expiratory volume1/forced vital capacity (FEV1/FVC) is increased
(b) Ventilation/perfusion (V/Q) ratio is increased in the affected areas of his lungs
(c) His arterial Pco2 is higher than normal because of inadequate gas exchange
(d) His arterial Pco2 is lower than normal because hypoxemia is causing him to hyperventilate
(e) His residual volume (RV) is decreased
The answer is D [VIII B 2 a].
The patient’s arterial Pco2 is lower than the normal value of 40 mm Hg because hypoxemia has stimulated peripheral chemoreceptors to increase his breathing rate; hyperventilation causes the patient to blow off extra CO2 and results in respiratory alkalosis. In an obstructive disease, such as asthma, both forced expiratory volume (FEV1) and forced vital capacity (FVC) are decreased, with the larger decrease occurring in FEV1. Therefore, the FEV1/FVC ratio is decreased. Poor ventilation of the affected areas decreases the ventilation/perfusion (V/Q) ratio and causes hypoxemia. The patient’s residual volume (RV) is increased because he is breathing at a higher lung volume to offset the increased resistance of his airways.
A 12-year-old boy has a severe asthmatic attack with wheezing. He experiences rapid breathing and becomes cyanotic. His arterial Po2 is 60 mm Hg and his Pco2 is 30 mm Hg.
To treat this patient, the physician should administer
(a) an α1-adrenergic antagonist
(b) a β1-adrenergic antagonist
(c) a β2-adrenergic agonist
(d) a muscarinic agonist
(e) a nicotinic agonist
The answer is C [II E 3 a (2)].
A cause of airway obstruction in asthma is bronchiolar constriction. β2-adrenergic stimulation (β2-adrenergic agonists) produces relaxation of the bronchioles.
Which of the following is true during inspiration?
(a) Intrapleural pressure is positive
(b) The volume in the lungs is less than the functional residual capacity (FRC)
(c) Alveolar pressure equals atmospheric pressure (d) Alveolar pressure is higher than atmospheric pressure
(e) Intrapleural pressure is more negative than it is during expiration
The answer is E [II F 2].
During inspiration, intrapleural pressure becomes more negative than it is at rest or during expiration (when it returns to its less negative resting value). During inspiration, air flows into the lungs when alveolar pressure becomes lower (due to contraction of the diaphragm) than atmospheric pressure; if alveolar pressure were not lower than atmospheric pressure, air would not flow inward. The volume in the lungs during inspiration is the functional residual capacity (FRC) plus one tidal volume (Vt).
Which volume remains in the lungs after a tidal volume (Vt) is expired?
(a) Tidal volume (Vt)
(b) Vital capacity (Vc)
(c) Expiratory reserve volume (ERV)
(d) Residual volume (RV)
(e) Functional residual capacity (FRC)
(f) Inspiratory capacity
(g) Total lung capacity
The answer is E [I B 2].
During normal breathing, the volume inspired and then expired is a tidal volume (Vt). The volume remaining in the lungs after expiration of a Vt is the functional residual capacity (FRC).
A 35-year-old man has a vital capacity (Vc) of 5 L, a tidal volume (Vt) of 0.5 L, an inspiratory capacity of 3.5 L, and a functional residual capacity (FRC) of 2.5 L. What is his expiratory reserve volume (ERV)?
(a) 4.5 L
(b) 3.9 L
(c) 3.6 L
(d) 3.0 L
(e) 2.5 L
(f) 2.0 L
(g) 1.5 L
The answer is G [I A 3; Figure 4.1].
Expiratory reserve volume (ERV) equals vital capacity (Vc) minus inspiratory capacity [Inspiratory capacity includes tidal volume (Vt) and inspiratory reserve volume (IRV)].
When a person is standing, blood flow in the lungs is
(a) equal at the apex and the base
(b) highest at the apex owing to the effects of gravity on arterial pressure
(c) highest at the base because that is where the difference between arterial and venous pressure is greatest
(d) lowest at the base because that is where alveolar pressure is greater than arterial pressure
The answer is C [VI B].
The distribution of blood flow in the lungs is affected by gravitational effects on arterial hydrostatic pressure. Thus, blood flow is highest at the base, where arterial hydrostatic pressure is greatest and the difference between arterial and venous pressure is also greatest. This pressure difference drives the blood flow.
Which of the following is the site of highest airway resistance?
(a) Trachea
(b) Largest bronchi
(c) Medium-sized bronchi
(d) Smallest bronchi
(e) Alveoli
The answer is C [II E 4].
The medium-sized bronchi actually constitute the site of highest resistance along the bronchial tree. Although the small radii of the alveoli might predict that they would have the highest resistance, they do not because of their parallel arrangement. In fact, early changes in resistance in the small airways may be “silent” and go undetected because of their small overall contribution to resistance.
A 49-year-old man has a pulmonary embolism that completely blocks blood flow to his left lung. As a result, which of the following will occur?
(a) Ventilation/perfusion (V/Q) ratio in the left lung will be zero
(b) Systemic arterial Po2 will be elevated
(c) V/Q ratio in the left lung will be lower than in the right lung
(d) Alveolar Po2 in the left lung will be approximately equal to the Po2 in inspired air
(e) Alveolar Po2 in the right lung will be approximately equal to the Po2 in venous blood
The answer is D [VII B 2].
Alveolar Po2 in the left lung will equal the Po2 in inspired air. Because there is no blood flow to the left lung, there can be no gas exchange between the alveolar air and the pulmonary capillary blood. Consequently, O2 is not added to the capillary blood. The ventilation/perfusion (V/Q) ratio in the left lung will be infinite (not zero or lower than that in the normal right lung) because Q (the denominator) is zero. Systemic arterial Po2 will, of course, be decreased because the left lung has no gas exchange. Alveolar Po2 in the right lung is unaffected.
Which volume remains in the lungs after a maximal expiration?
(a) Tidal volume (Vt)
(b) Vital capacity (Vc)
(c) Expiratory reserve volume (ERV)
(d) Residual volume (RV)
(e) Functional residual capacity (FRC)
(F) Inspiratory capacity
(g) Total lung capacity
The answer is D [I A 3].
During a forced maximal expiration, the volume expired is a tidal volume (Vt) plus the expiratory reserve volume (ERV). The volume remaining in the lungs is the residual volume (RV).
Compared with the systemic circulation, the pulmonary circulation has a
(a) higher blood flow
(b) lower resistance
(c) higher arterial pressure
(d) higher capillary pressure
(e) higher cardiac output
The answer is B [VI A].
Blood flow (or cardiac output) in the systemic and pulmonary circulations is nearly equal; pulmonary flow is slightly less than systemic flow because about 2% of the systemic cardiac output bypasses the lungs. The pulmonary circulation is characterized by both lower pressure and lower resistance than the systemic circulation, so flows through the two circulations are approximately equal (flow = pressure/resistance).
A healthy 65-year-old man with a tidal volume (Vt) of 0.45 L has a breathing frequency of 16 breaths/min. His arterial Pco2 is 41 mm Hg, and the Pco2 of his expired air is 35 mm Hg. What is his alveolar ventilation?
(a) 0.066 L/min
(b) 0.38 L/min
(c) 5.0 L/min
(d) 6.14 L/min
(e) 8.25 L/min
The answer is D [I A 5 b, 6 b].
Alveolar ventilation is the difference between tidal volume (Vt) and dead space multiplied by breathing frequency. Vt and breathing frequency are given, but dead space must be calculated. Dead space is Vt multiplied by the difference between arterial Pco2 and expired Pco2 divided by arterial Pco2. Thus: dead space = 0.45 × (41 - 35/41) = 0.066 L. Alveolar ventilation is then calculated as: (0.45 L - 0.066 L) × 16 breaths/min = 6.14 L/min.
Compared with the apex of the lung, the base of the lung has
(a) a higher pulmonary capillary Po2
(b) a higher pulmonary capillary Pco2
(c) a higher ventilation/perfusion (V/Q) ratio
(d) the same V/Q ratio
The answer is B [VII C; Figure 4.10; Table 4.5].
Ventilation and perfusion of the lung are not distributed uniformly. Both are lowest at the apex and highest at the base. However, the differences for ventilation are not as great as for perfusion, making the ventilation/ perfusion (V/Q) ratios higher at the apex and lower at the base. As a result, gas exchange is more efficient at the apex and less efficient at the base. Therefore, blood leaving the apex will have a higher Po2 and a lower Pco2.
