COMSAE PHASE 1 RESPIRATORY
PHYSIOLOGY PRACTICE EXAM WITH
ACTUAL QUESTIONS AND VERIFIED
ANSWERS, PLUS EXPLAINED
RATIONALES/EXPERT VERIFIED FOR
GUARANTEED 100% PASS 2026/LATEST
UPDATE/INSTANT DOWNLOAD PDF
1. A healthy 24-year-old medical student has a tidal volume of 500
mL, respiratory rate of 12/min, and an anatomic dead space of 150
mL. What is his alveolar ventilation per minute?
A. 1,800 mL/min
B. 3,600 mL/min
C. 4,200 mL/min
D. 6,000 mL/min
Answer: B. 4,200 mL/min
Rationale: Alveolar ventilation is calculated as (tidal volume − dead
space) × respiratory rate. Therefore, (500 − 150) × 12 = 4,200 mL/min.
This represents the volume of fresh inspired air reaching gas-
exchanging regions of the lung each minute. Total minute ventilation
would be 500 × 12 = 6,000 mL/min, but not all of that volume
participates in gas exchange.
2. A patient with severe pulmonary embolism has areas of ventilated
lung that receive little or no pulmonary blood flow. Which
alteration in ventilation-perfusion relationships best describes these
regions?
A. Low V/Q approaching zero
B. Normal V/Q of approximately 0.8
1
,C. High V/Q approaching infinity
D. Complete absence of ventilation with preserved perfusion
Answer: C. High V/Q approaching infinity
Rationale: A region that is ventilated but essentially not perfused has a
very high V/Q ratio, theoretically approaching infinity. This is
physiologic dead-space behavior. In contrast, a perfused but
completely unventilated alveolus has a V/Q ratio approaching zero and
behaves like a shunt.
3. A 67-year-old man with emphysema has destruction of alveolar
walls and loss of pulmonary capillary beds. Which change in
pulmonary function is most directly expected?
A. Decreased physiologic dead space
B. Increased diffusion capacity
C. Increased pulmonary vascular resistance in affected regions
D. Decreased residual volume
Answer: C. Increased pulmonary vascular resistance in affected
regions
Rationale: Emphysematous destruction removes alveolar septa and
associated pulmonary capillary beds, reducing the cross-sectional area
available for pulmonary blood flow. This increases pulmonary
vascular resistance. Emphysema also increases dead space, decreases
diffusion capacity because of loss of alveolar-capillary surface area,
and commonly increases residual volume because of air trapping.
4. A patient ascends rapidly from sea level to a high-altitude location.
Which change occurs in the inspired partial pressure of oxygen?
A. It increases because oxygen diffuses more rapidly at altitude
B. It remains constant because atmospheric oxygen remains
approximately 21%
2
,C. It decreases because total barometric pressure decreases
D. It increases because alveolar ventilation immediately increases
Answer: C. It decreases because total barometric pressure decreases
Rationale: The fraction of oxygen in dry atmospheric air remains
approximately 21%, but inspired PO₂ equals the fractional
concentration of oxygen multiplied by the pressure available to that
gas. As barometric pressure falls at altitude, inspired PO₂ falls.
Increased ventilation can partially compensate by lowering alveolar
PCO₂, but it does not restore the original inspired PO₂.
5. Which mechanism is primarily responsible for hypoxic pulmonary
vasoconstriction?
A. Relaxation of pulmonary arteriolar smooth muscle in response to low
alveolar PO₂
B. Constriction of pulmonary arterioles supplying poorly ventilated
alveoli
C. Systemic arterial vasoconstriction caused by elevated PaCO₂
D. Increased pulmonary blood flow to hypoxic alveoli
Answer: B. Constriction of pulmonary arterioles supplying poorly
ventilated alveoli
Rationale: Hypoxic pulmonary vasoconstriction redirects blood away
from poorly ventilated alveoli toward better-ventilated regions. This
improves overall V/Q matching. It differs from systemic circulation,
where hypoxia generally causes vasodilation. Diffuse hypoxia, such as
at high altitude or in chronic lung disease, can produce pulmonary
hypertension.
6. A 45-year-old woman develops alveolar hypoventilation following
administration of an opioid. Her PaCO₂ rises substantially. Which
immediate change is most likely?
3
, A. Increased alveolar PO₂
B. Decreased alveolar PCO₂
C. Increased alveolar PO₂ and decreased PCO₂
D. Decreased alveolar PO₂ and increased PCO₂
Answer: D. Decreased alveolar PO₂ and increased PCO₂
Rationale: Hypoventilation reduces the delivery of fresh air to alveoli.
Consequently, alveolar PCO₂ rises while alveolar PO₂ falls. This
relationship is reflected by the alveolar gas equation. Opioids can
cause hypoventilation by depressing medullary respiratory drive.
7. Which portion of the respiratory system contributes most directly
to anatomic dead space?
A. Alveoli with normal perfusion
B. Conducting airways
C. Pulmonary capillaries
D. Alveolar macrophages
Answer: B. Conducting airways
Rationale: Anatomic dead space consists primarily of the conducting
airways, including the nose, pharynx, larynx, trachea, bronchi, and
bronchioles. These structures conduct air but do not normally
participate directly in gas exchange. Physiologic dead space includes
anatomic dead space plus ventilated alveoli that are inadequately
perfused.
8. A premature infant develops respiratory distress because of
insufficient pulmonary surfactant. Which alteration in alveolar
mechanics is expected?
A. Decreased surface tension
B. Increased lung compliance
C. Increased surface tension and decreased compliance
D. Increased functional residual capacity due to alveolar stabilization
4
PHYSIOLOGY PRACTICE EXAM WITH
ACTUAL QUESTIONS AND VERIFIED
ANSWERS, PLUS EXPLAINED
RATIONALES/EXPERT VERIFIED FOR
GUARANTEED 100% PASS 2026/LATEST
UPDATE/INSTANT DOWNLOAD PDF
1. A healthy 24-year-old medical student has a tidal volume of 500
mL, respiratory rate of 12/min, and an anatomic dead space of 150
mL. What is his alveolar ventilation per minute?
A. 1,800 mL/min
B. 3,600 mL/min
C. 4,200 mL/min
D. 6,000 mL/min
Answer: B. 4,200 mL/min
Rationale: Alveolar ventilation is calculated as (tidal volume − dead
space) × respiratory rate. Therefore, (500 − 150) × 12 = 4,200 mL/min.
This represents the volume of fresh inspired air reaching gas-
exchanging regions of the lung each minute. Total minute ventilation
would be 500 × 12 = 6,000 mL/min, but not all of that volume
participates in gas exchange.
2. A patient with severe pulmonary embolism has areas of ventilated
lung that receive little or no pulmonary blood flow. Which
alteration in ventilation-perfusion relationships best describes these
regions?
A. Low V/Q approaching zero
B. Normal V/Q of approximately 0.8
1
,C. High V/Q approaching infinity
D. Complete absence of ventilation with preserved perfusion
Answer: C. High V/Q approaching infinity
Rationale: A region that is ventilated but essentially not perfused has a
very high V/Q ratio, theoretically approaching infinity. This is
physiologic dead-space behavior. In contrast, a perfused but
completely unventilated alveolus has a V/Q ratio approaching zero and
behaves like a shunt.
3. A 67-year-old man with emphysema has destruction of alveolar
walls and loss of pulmonary capillary beds. Which change in
pulmonary function is most directly expected?
A. Decreased physiologic dead space
B. Increased diffusion capacity
C. Increased pulmonary vascular resistance in affected regions
D. Decreased residual volume
Answer: C. Increased pulmonary vascular resistance in affected
regions
Rationale: Emphysematous destruction removes alveolar septa and
associated pulmonary capillary beds, reducing the cross-sectional area
available for pulmonary blood flow. This increases pulmonary
vascular resistance. Emphysema also increases dead space, decreases
diffusion capacity because of loss of alveolar-capillary surface area,
and commonly increases residual volume because of air trapping.
4. A patient ascends rapidly from sea level to a high-altitude location.
Which change occurs in the inspired partial pressure of oxygen?
A. It increases because oxygen diffuses more rapidly at altitude
B. It remains constant because atmospheric oxygen remains
approximately 21%
2
,C. It decreases because total barometric pressure decreases
D. It increases because alveolar ventilation immediately increases
Answer: C. It decreases because total barometric pressure decreases
Rationale: The fraction of oxygen in dry atmospheric air remains
approximately 21%, but inspired PO₂ equals the fractional
concentration of oxygen multiplied by the pressure available to that
gas. As barometric pressure falls at altitude, inspired PO₂ falls.
Increased ventilation can partially compensate by lowering alveolar
PCO₂, but it does not restore the original inspired PO₂.
5. Which mechanism is primarily responsible for hypoxic pulmonary
vasoconstriction?
A. Relaxation of pulmonary arteriolar smooth muscle in response to low
alveolar PO₂
B. Constriction of pulmonary arterioles supplying poorly ventilated
alveoli
C. Systemic arterial vasoconstriction caused by elevated PaCO₂
D. Increased pulmonary blood flow to hypoxic alveoli
Answer: B. Constriction of pulmonary arterioles supplying poorly
ventilated alveoli
Rationale: Hypoxic pulmonary vasoconstriction redirects blood away
from poorly ventilated alveoli toward better-ventilated regions. This
improves overall V/Q matching. It differs from systemic circulation,
where hypoxia generally causes vasodilation. Diffuse hypoxia, such as
at high altitude or in chronic lung disease, can produce pulmonary
hypertension.
6. A 45-year-old woman develops alveolar hypoventilation following
administration of an opioid. Her PaCO₂ rises substantially. Which
immediate change is most likely?
3
, A. Increased alveolar PO₂
B. Decreased alveolar PCO₂
C. Increased alveolar PO₂ and decreased PCO₂
D. Decreased alveolar PO₂ and increased PCO₂
Answer: D. Decreased alveolar PO₂ and increased PCO₂
Rationale: Hypoventilation reduces the delivery of fresh air to alveoli.
Consequently, alveolar PCO₂ rises while alveolar PO₂ falls. This
relationship is reflected by the alveolar gas equation. Opioids can
cause hypoventilation by depressing medullary respiratory drive.
7. Which portion of the respiratory system contributes most directly
to anatomic dead space?
A. Alveoli with normal perfusion
B. Conducting airways
C. Pulmonary capillaries
D. Alveolar macrophages
Answer: B. Conducting airways
Rationale: Anatomic dead space consists primarily of the conducting
airways, including the nose, pharynx, larynx, trachea, bronchi, and
bronchioles. These structures conduct air but do not normally
participate directly in gas exchange. Physiologic dead space includes
anatomic dead space plus ventilated alveoli that are inadequately
perfused.
8. A premature infant develops respiratory distress because of
insufficient pulmonary surfactant. Which alteration in alveolar
mechanics is expected?
A. Decreased surface tension
B. Increased lung compliance
C. Increased surface tension and decreased compliance
D. Increased functional residual capacity due to alveolar stabilization
4
