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Question 1Cardiopulmonary Anatomy, Physiology, and Pathophysiology

Which lung volume remains in the lungs after a maximal forced expiration and therefore cannot be measured by standard spirometry?

  1. Tidal volume
  2. Expiratory reserve volume
  3. Inspiratory reserve volume
  4. Residual volume Correct answer.

Explanation

Residual volume is the air that remains in the lungs after the most complete expiration, so a spirometer cannot capture it because that gas is never exhaled. It is measured indirectly by helium dilution, nitrogen washout, or body plethysmography. Expiratory reserve, inspiratory reserve, and tidal volumes are all exchanged volumes that spirometry can record.

Question 2Cardiopulmonary Anatomy, Physiology, and Pathophysiology

What is the principal effect of pulmonary surfactant on alveolar mechanics?

  1. It reduces surface tension at the air-liquid interface Correct answer.
  2. It increases surface tension at the air-liquid interface
  3. It increases elastic recoil of lung tissue
  4. It decreases compliance of the chest wall

Explanation

Surfactant is secreted by type II alveolar cells and lowers surface tension along the alveolar air-liquid interface. This reduces the collapsing pressure predicted by Laplace's law and helps stabilize alveoli of different sizes during expiration. It does not act on the chest wall or increase elastic recoil.

Question 3Cardiopulmonary Anatomy, Physiology, and Pathophysiology

Which condition shifts the oxyhemoglobin dissociation curve to the right and reduces hemoglobin's affinity for oxygen?

  1. Decreased temperature
  2. Decreased PaCO2
  3. Increased pH
  4. Increased 2,3-BPG Correct answer.

Explanation

A rightward shift means hemoglobin releases oxygen more readily to tissues. Increased 2,3-bisphosphoglycerate, increased temperature, increased PaCO2, and decreased pH all produce this shift. Decreased temperature, increased pH, and decreased PaCO2 shift the curve left.

Question 4Cardiopulmonary Anatomy, Physiology, and Pathophysiology

A pulmonary embolism abruptly stops blood flow through one lobar artery while the affected alveoli remain ventilated. How is the regional ventilation-perfusion (V/Q) ratio best described?

  1. It approaches infinity, creating alveolar dead space Correct answer.
  2. It falls below normal but remains greater than zero
  3. It approaches zero, creating a true shunt
  4. It remains at the normal value of approximately 0.8

Explanation

V/Q is ventilation divided by perfusion. If perfusion falls to zero while ventilation continues, the ratio rises toward infinity and the ventilated but unperfused alveoli become alveolar dead space. A ratio approaching zero occurs in shunt, where perfusion persists without ventilation.

Question 5Cardiopulmonary Anatomy, Physiology, and Pathophysiology

Which statement best describes the effect of decreased lung compliance on the pressure required to inflate the lungs?

  1. A smaller transpulmonary pressure change produces the same volume change
  2. Transpulmonary pressure is unrelated to lung volume
  3. The lungs become easier to inflate at any given pressure
  4. A larger transpulmonary pressure change is required for the same volume change Correct answer.

Explanation

Compliance is the change in lung volume per unit change in transpulmonary pressure. When compliance falls, the lung is stiffer, so a greater pressure change is needed to produce a given volume change. The pressure-volume relationship therefore shifts downward and to the right.

Question 6Cardiopulmonary Anatomy, Physiology, and Pathophysiology

A patient with COPD has an arterial blood gas showing pH 7.34, PaCO2 58 mm Hg, and HCO3- 30 mEq/L. Which acid-base disturbance is most likely?

  1. Metabolic alkalosis with respiratory compensation
  2. Mixed metabolic acidosis and respiratory alkalosis
  3. Chronic respiratory acidosis with metabolic compensation Correct answer.
  4. Acute respiratory acidosis without metabolic compensation

Explanation

The elevated PaCO2 indicates respiratory acidosis, and the elevated bicarbonate indicates renal retention of base. The only mildly reduced pH in the presence of marked hypercapnia is consistent with chronic respiratory acidosis and metabolic compensation. An acute respiratory acidosis would usually show a much lower pH with little bicarbonate elevation.

Question 7Cardiopulmonary Anatomy, Physiology, and Pathophysiology

A patient has a tidal volume of 500 mL and a physiologic dead space of 150 mL. At a respiratory rate of 12 breaths/min, what is the approximate alveolar ventilation?

  1. 7,200 mL/min
  2. 6,000 mL/min
  3. 1,800 mL/min
  4. 4,200 mL/min Correct answer.

Explanation

Alveolar ventilation equals respiratory rate multiplied by the difference between tidal volume and physiologic dead space. Here, (500 mL - 150 mL) × 12 breaths/min = 350 mL × 12 = 4,200 mL/min. Using tidal volume alone would overestimate fresh gas reaching the alveoli.

Question 8Cardiopulmonary Anatomy, Physiology, and Pathophysiology

In a healthy upright adult, which lung region has the highest ventilation-perfusion (V/Q) ratio?

  1. Lung base
  2. Midlung zone
  3. Lung apex Correct answer.
  4. Most dependent region

Explanation

Gravity reduces pulmonary blood flow more than ventilation at the apex, so ventilation is relatively preserved while perfusion is low. This makes the apical V/Q ratio the highest in the upright lung. At the base, perfusion is high and the V/Q ratio is lower.

Question 9Cardiopulmonary Anatomy, Physiology, and Pathophysiology

Which change most strongly stimulates the central chemoreceptors to increase ventilation?

  1. A fall in arterial PCO2
  2. A rise in arterial PCO2 with a fall in cerebrospinal fluid pH Correct answer.
  3. A rise in arterial pH caused by hyperventilation
  4. A fall in arterial PaO2 below 60 mm Hg

Explanation

Central chemoreceptors respond primarily to hydrogen ion concentration in cerebrospinal fluid. Carbon dioxide crosses the blood-brain barrier and generates hydrogen ions there, so a rise in PaCO2 strongly stimulates central drive. Hypoxia below 60 mm Hg acts mainly through peripheral chemoreceptors.

Question 10Cardiopulmonary Anatomy, Physiology, and Pathophysiology

Which spirometry pattern is most characteristic of a severe obstructive defect?

  1. Reduced total lung capacity with a normal FEV1/FVC ratio
  2. Reduced FEV1/FVC ratio with increased or normal total lung capacity Correct answer.
  3. Normal FEV1/FVC ratio with an isolated reduction in diffusing capacity
  4. Increased FEV1/FVC ratio with reduced total lung capacity

Explanation

Obstructive disease slows expiratory airflow, so FEV1 falls more than FVC and the FEV1/FVC ratio is reduced. Hyperinflation may raise total lung capacity or leave it normal. Restrictive disease instead reduces total lung capacity with a preserved or increased FEV1/FVC ratio.

Question 11Cardiopulmonary Anatomy, Physiology, and Pathophysiology

A supine patient vomits and aspirates. Which anatomic feature of the right main bronchus best explains why aspirated material most often enters the right lung?

  1. It is wider, shorter, and more vertically oriented than the left main bronchus. Correct answer.
  2. It is narrower and more sharply angled than the left main bronchus.
  3. It is encircled by complete cartilage rings that block particulate matter.
  4. It arises directly from the larynx above the vocal cords.

Explanation

The right main bronchus is wider, shorter, and more vertical than the left, so aspirated material follows the straighter path into the right lung. The left main bronchus branches at a sharper angle, which makes it less likely to receive aspirated contents. This anatomy is why right lower lobe aspiration is common in supine patients.

Question 12Cardiopulmonary Anatomy, Physiology, and Pathophysiology

Which receptors primarily mediate the increase in ventilation caused by arterial hypoxemia in a patient breathing room air?

  1. Pulmonary stretch receptors in the airways
  2. Central chemoreceptors in the medulla
  3. Carotid body peripheral chemoreceptors Correct answer.
  4. Juxtapulmonary capillary (J) receptors

Explanation

Peripheral chemoreceptors in the carotid bodies are the main sensors that increase ventilation when PaO2 falls, especially below about 60 mm Hg. Central chemoreceptors respond primarily to changes in cerebrospinal fluid pH driven by CO2, not to hypoxemia. J receptors and stretch receptors influence breathing pattern but are not the primary hypoxemic drive.

Question 13Cardiopulmonary Anatomy, Physiology, and Pathophysiology

During quiet inspiration, what happens to intrapleural pressure?

  1. It becomes positive and compresses the great vessels.
  2. It becomes more negative as the thorax expands. Correct answer.
  3. It remains equal to atmospheric pressure throughout the breath.
  4. It becomes less negative and approaches zero.

Explanation

As the diaphragm contracts and the thoracic cavity enlarges, intrapleural pressure falls from roughly -5 cm H2O to -8 cm H2O. This more negative pressure inflates the lungs and assists venous return. Positive intrapleural pressure occurs during forced expiration or Valsalva, not quiet inspiration.

Question 14Cardiopulmonary Anatomy, Physiology, and Pathophysiology

Which statement best describes the Haldane effect?

  1. Increased temperature reduces hemoglobin oxygen saturation.
  2. Deoxygenated hemoglobin carries more carbon dioxide than oxygenated hemoglobin. Correct answer.
  3. Increased CO2 shifts the oxyhemoglobin dissociation curve to the right.
  4. Increased 2,3-BPG decreases hemoglobin's affinity for oxygen.

Explanation

The Haldane effect describes how deoxygenation of hemoglobin in tissues increases its capacity to carry carbon dioxide, mainly as carbamino compounds. In the lungs, oxygenation promotes CO2 unloading. The other choices describe the Bohr effect or related right-shift factors, not the Haldane effect.

Question 15Cardiopulmonary Anatomy, Physiology, and Pathophysiology

Which mechanism most directly leads to cor pulmonale in a patient with chronic hypoxemic COPD?

  1. Systemic hypertension increases left ventricular afterload and causes backup failure.
  2. Hypoxic pulmonary vasoconstriction raises pulmonary vascular resistance. Correct answer.
  3. Increased alveolar surface tension collapses alveoli and reduces left atrial pressure.
  4. Chronic hypercapnia directly dilates the pulmonary arteries and lowers right ventricular workload.

Explanation

Chronic alveolar hypoxia causes hypoxic pulmonary vasoconstriction and vascular remodeling, increasing pulmonary vascular resistance. The right ventricle must generate higher pressure, leading to right ventricular hypertrophy and eventually failure, which defines cor pulmonale. Left-sided disease and hypercapnic vasodilation do not explain this sequence.

Question 16Cardiopulmonary Anatomy, Physiology, and Pathophysiology

Which circulation supplies oxygenated blood to the conducting airways and contributes to the normal anatomic right-to-left shunt?

  1. Lymphatic vessel
  2. Bronchial artery Correct answer.
  3. Pulmonary vein
  4. Pulmonary artery

Explanation

Bronchial arteries arise from the systemic circulation and deliver oxygenated blood to the tracheobronchial tree. Part of the bronchial venous drainage empties into the pulmonary veins, returning less-oxygenated blood to the left atrium and creating a small normal right-to-left shunt. The pulmonary artery carries deoxygenated blood to the alveoli for gas exchange.

Question 17Cardiopulmonary Anatomy, Physiology, and Pathophysiology

In cardiogenic pulmonary edema, which Starling force is primarily increased to cause fluid to move into the alveolar spaces?

  1. Pulmonary capillary hydrostatic pressure Correct answer.
  2. Plasma oncotic pressure
  3. Alveolar surface tension
  4. Interstitial colloid osmotic pressure

Explanation

Left ventricular failure raises left atrial and pulmonary capillary hydrostatic pressure. When this force exceeds the opposing oncotic pressure, fluid filters into the interstitium and then the alveoli. Plasma oncotic pressure and interstitial osmotic pressure do not primarily drive cardiogenic edema.

Question 18Cardiopulmonary Anatomy, Physiology, and Pathophysiology

A patient with a partially obstructed lobar bronchus breathes a high fraction of inspired oxygen. Which mechanism promotes absorption atelectasis in the affected lobe?

  1. Oxygen is less soluble than nitrogen, so it accumulates and expands the alveoli.
  2. High oxygen directly relaxes bronchial smooth muscle and worsens obstruction.
  3. Oxygen replaces nitrogen and is absorbed faster than it is replenished. Correct answer.
  4. Oxygen enhances surfactant production, which increases alveolar collapse.

Explanation

Nitrogen normally remains in the alveoli and helps splint them open because it is poorly soluble in blood. When high FiO2 washes out nitrogen, the remaining oxygen is absorbed rapidly into pulmonary capillary blood. If the airway is partially obstructed and gas cannot be replenished, the alveoli collapse, producing absorption atelectasis.

Question 19Cardiopulmonary Anatomy, Physiology, and Pathophysiology

In early ARDS, hypoxemia often persists despite increasing FiO2. Which pathophysiologic mechanism best explains this?

  1. Ventilation is uniformly reduced, producing a pure hypoventilation acidosis.
  2. Diffusion distance decreases due to alveolar wall thinning, limiting oxygen uptake.
  3. Blood perfuses unventilated alveoli, creating a true intrapulmonary shunt. Correct answer.
  4. Alveolar dead space increases because pulmonary capillaries are destroyed while ventilation continues.

Explanation

ARDS causes alveolar flooding and collapse, so some alveoli are perfused but not ventilated. This intrapulmonary shunt means oxygen-rich gas cannot reach the affected alveoli, and supplemental oxygen cannot correct the hypoxemia fully. Dead space and diffusion limitation can coexist, but shunt is the dominant explanation for refractory hypoxemia in early ARDS.

Question 20Cardiopulmonary Anatomy, Physiology, and Pathophysiology

In an older adult, why does airway closure occur in dependent lung regions even during tidal breathing?

  1. Surfactant production increases with age and stabilizes small airways.
  2. Closing capacity can exceed functional residual capacity in dependent regions. Correct answer.
  3. Elastic recoil of the lung increases, keeping small airways open.
  4. Functional residual capacity increases faster than closing capacity with age.

Explanation

Aging reduces elastic recoil and small-airway support, so closing capacity rises. In dependent regions, pleural pressure is higher and airways close at higher lung volumes. When closing capacity exceeds functional residual capacity, airway closure occurs during tidal breathing, promoting ventilation-perfusion mismatch and hypoxemia.

Question 21Cardiopulmonary Anatomy, Physiology, and Pathophysiology

During quiet inspiration in a healthy adult, which muscle is the principal generator of tidal volume?

  1. External intercostal muscles
  2. Diaphragm Correct answer.
  3. Rectus abdominis muscle
  4. Sternocleidomastoid muscle

Explanation

The diaphragm is the principal muscle of inspiration and generates most of the tidal volume during quiet breathing. Its contraction lowers intrapleural pressure and draws air into the lungs.

Question 22Cardiopulmonary Anatomy, Physiology, and Pathophysiology

Which vessel carries deoxygenated blood from the right ventricle to the lungs?

  1. Pulmonary vein
  2. Superior vena cava
  3. Aorta
  4. Pulmonary artery Correct answer.

Explanation

The pulmonary artery carries deoxygenated blood from the right ventricle to the pulmonary capillaries, where gas exchange occurs. It is the only artery in the body that normally carries deoxygenated blood.

Question 23Cardiopulmonary Anatomy, Physiology, and Pathophysiology

What is a typical resting tidal volume for a healthy adult?

  1. About 1,200 mL Correct answer.
  2. About 500 mL
  3. About 2,500 mL
  4. About 150 mL

Explanation

A typical resting tidal volume in a healthy adult is approximately 500 mL per breath. This volume moves into and out of the lungs during quiet breathing and is much smaller than vital capacity.

Question 24Cardiopulmonary Anatomy, Physiology, and Pathophysiology

A patient's functional residual capacity measured by body plethysmography is significantly larger than the value obtained by helium dilution. What does this discrepancy most likely indicate?

  1. Gas trapped behind closed airways Correct answer.
  2. A leak around the plethysmograph mouthpiece
  3. Normal variability between the two techniques
  4. An increase in chest wall compliance

Explanation

Body plethysmography measures all thoracic gas, including gas behind closed airways, whereas helium dilution measures only gas that communicates with the airway. A plethysmographic FRC larger than the helium-dilution FRC therefore suggests air trapping.

Question 25Cardiopulmonary Anatomy, Physiology, and Pathophysiology

A patient has hypoxemia caused by opioid-induced hypoventilation. Which arterial blood gas finding is most characteristic?

  1. An increased physiologic dead space fraction
  2. Refractory hypoxemia despite 100% oxygen
  3. A normal alveolar-arterial oxygen gradient Correct answer.
  4. A widened alveolar-arterial oxygen gradient

Explanation

Hypoventilation lowers PaO2 and raises PaCO2 but does not impair alveolar-capillary diffusion or cause shunt, so the alveolar-arterial oxygen gradient remains normal. Other causes of hypoxemia with a normal A-a gradient include low inspired oxygen tension.

Question 26Cardiopulmonary Anatomy, Physiology, and Pathophysiology

What happens to pulmonary vascular resistance when lung volume is increased well above functional residual capacity?

  1. It remains unchanged because blood flow is constant
  2. It decreases because hypoxic vasoconstriction is abolished
  3. It increases because alveolar vessels are compressed Correct answer.
  4. It decreases because extra-alveolar vessels dilate

Explanation

At high lung volumes, the alveolar vessels are stretched and compressed by expanded alveoli, which increases pulmonary vascular resistance. Resistance is lowest near functional residual capacity, where the balance between alveolar and extra-alveolar vessel effects is most favorable.

Question 27Cardiopulmonary Anatomy, Physiology, and Pathophysiology

A patient with a large tension pneumothorax becomes hypotensive. Which mechanism best explains the fall in blood pressure?

  1. Decreased venous return from increased intrathoracic pressure Correct answer.
  2. Increased left ventricular afterload from systemic vasoconstriction
  3. Reflex bradycardia from vagal stimulation
  4. Direct compression of the abdominal aorta

Explanation

Tension pneumothorax raises intrathoracic pressure, which compresses the vena cavae and reduces venous return to the right heart. The resulting fall in cardiac output causes hypotension.

Question 28Cardiopulmonary Anatomy, Physiology, and Pathophysiology

A patient with chronic anemia has a normal arterial oxygen tension and normal hemoglobin saturation. Which arterial oxygen parameter is most likely reduced?

  1. Arterial oxygen tension
  2. Hemoglobin saturation
  3. Arterial oxygen content Correct answer.
  4. Dissolved oxygen in plasma

Explanation

Arterial oxygen content is determined mainly by hemoglobin concentration, hemoglobin saturation, and PaO2. In anemia, reduced hemoglobin lowers CaO2 even when PaO2 and SaO2 are normal.

Question 29Cardiopulmonary Anatomy, Physiology, and Pathophysiology

In a patient receiving positive-pressure ventilation, which condition defines West zone 1 of the lung?

  1. Pulmonary arterial pressure exceeds alveolar pressure throughout the cardiac cycle
  2. Pulmonary venous pressure exceeds alveolar pressure and drives flow
  3. Alveolar pressure exceeds pulmonary arterial pressure, so blood flow is minimal or absent Correct answer.
  4. Alveolar pressure exceeds pulmonary venous pressure but remains below arterial pressure

Explanation

West zone 1 occurs when alveolar pressure exceeds pulmonary arterial pressure, which collapses the capillary and minimizes or abolishes flow. It is uncommon in healthy upright lungs but can occur with positive-pressure ventilation or reduced pulmonary blood flow.

Question 30Cardiopulmonary Anatomy, Physiology, and Pathophysiology

A patient with severe COPD has a flattened diaphragm on chest imaging. Which change best explains the reduced inspiratory effectiveness?

  1. The diaphragm becomes solely responsible for expiratory airflow
  2. The lungs lose elastic recoil and collapse
  3. The diaphragm operates at a shorter length with less force-generating capacity Correct answer.
  4. The accessory muscles lose their innervation

Explanation

A flattened diaphragm is shorter than normal and operates on a less favorable portion of its length-tension curve. It therefore generates less force for the same neural drive, reducing inspiratory effectiveness.

Question 31Cardiopulmonary Anatomy, Physiology, and Pathophysiology

Which change in alveolar mechanics is produced by pulmonary surfactant?

  1. It converts type II pneumocytes into type I cells, thinning the alveolar wall.
  2. It lowers surface tension, reducing the pressure needed to keep small alveoli open. Correct answer.
  3. It increases elastic recoil of the chest wall, raising functional residual capacity.
  4. It increases alveolar surface tension so that alveoli recoil more evenly during expiration.

Explanation

Surfactant is secreted by type II pneumocytes and lowers alveolar surface tension. By the Laplace relationship, pressure is proportional to tension divided by radius, so surfactant reduces the collapsing pressure of small alveoli and improves compliance. It does not stiffen the chest wall or transform alveolar cells.

Question 32Cardiopulmonary Anatomy, Physiology, and Pathophysiology

Central chemoreceptors in the medulla primarily increase ventilation in response to which change?

  1. A rise in arterial oxygen tension detected by aortic bodies.
  2. A fall in lung stretch detected by pulmonary irritant receptors.
  3. A rise in hydrogen ion concentration in cerebrospinal fluid. Correct answer.
  4. A fall in arterial oxygen tension detected by the carotid bodies.

Explanation

Central chemoreceptors respond to hydrogen ions in cerebrospinal fluid, which rise when arterial PCO2 increases and CO2 crosses the blood-brain barrier. They are not directly stimulated by arterial hypoxemia, which is sensed mainly by peripheral chemoreceptors.

Question 33Cardiopulmonary Anatomy, Physiology, and Pathophysiology

Transpulmonary pressure is defined as the difference between which two pressures?

  1. Alveolar pressure and pleural pressure. Correct answer.
  2. Mouth pressure and alveolar pressure.
  3. Alveolar pressure and atmospheric pressure.
  4. Pleural pressure and atmospheric pressure.

Explanation

Transpulmonary pressure is alveolar pressure minus pleural pressure. It is the distending pressure across the lung and determines lung volume for a given compliance.

Question 34Cardiopulmonary Anatomy, Physiology, and Pathophysiology

A rightward shift of the oxyhemoglobin dissociation curve has which effect?

  1. Increased hemoglobin affinity for oxygen and reduced oxygen unloading at tissues.
  2. Decreased hemoglobin affinity for oxygen and enhanced oxygen unloading at tissues. Correct answer.
  3. Decreased P50 and increased arterial oxygen saturation at a given PaO2.
  4. No change in oxygen content but increased dissolved oxygen.

Explanation

A rightward shift means hemoglobin releases oxygen more readily, so P50 increases and affinity decreases. This enhances tissue oxygen unloading and is favored by increased CO2, hydrogen ions, temperature, and 2,3-DPG.

Question 35Cardiopulmonary Anatomy, Physiology, and Pathophysiology

A patient with a pulmonary embolus occluding a lobar pulmonary artery is most likely to show which change?

  1. Increased shunt fraction because perfused alveoli are not ventilated.
  2. Increased alveolar dead space because ventilated alveoli are no longer perfused. Correct answer.
  3. Decreased physiologic dead space because blood flow is redistributed.
  4. A reduced V/Q ratio in the affected lobe because blood flow exceeds ventilation.

Explanation

Obstruction of a pulmonary artery stops perfusion to ventilated alveoli, creating alveolar dead space and a high V/Q ratio. This reduces effective gas exchange even though the affected alveoli are still ventilated.

Question 36Cardiopulmonary Anatomy, Physiology, and Pathophysiology

According to the Poiseuille law, which change in an airway produces the greatest increase in resistance to laminar airflow?

  1. Doubling the driving pressure.
  2. Halving the gas viscosity.
  3. Halving the airway radius. Correct answer.
  4. Doubling the airway length.

Explanation

Poiseuille law states that resistance is inversely proportional to the fourth power of radius. Halving the radius therefore raises resistance sixteen-fold, far more than doubling length or changing other variables.

Question 37Cardiopulmonary Anatomy, Physiology, and Pathophysiology

Which condition most typically reduces the diffusing capacity of the lung for carbon monoxide (DLCO)?

  1. Asthma with acute bronchospasm.
  2. Acute bronchitis with increased mucus production.
  3. Obesity with reduced chest wall compliance.
  4. Emphysema with loss of alveolar surface area. Correct answer.

Explanation

Emphysema destroys alveolar walls and the pulmonary capillary bed, reducing surface area for diffusion and lowering DLCO. Asthma, obesity, and acute bronchitis usually do not reduce DLCO because alveolar-capillary diffusion is preserved.

Question 38Cardiopulmonary Anatomy, Physiology, and Pathophysiology

During carbon dioxide transport, what is the chloride shift in systemic capillaries?

  1. Chloride enters the red cell as bicarbonate leaves during systemic capillary transit. Correct answer.
  2. Chloride binds hemoglobin and directly displaces oxygen in peripheral tissues.
  3. Chloride moves into plasma while bicarbonate enters the red cell.
  4. Chloride leaves plasma and enters alveolar fluid to buffer carbonic acid.

Explanation

In systemic capillaries, bicarbonate produced in the red cell leaves via band 3 in exchange for chloride entering the cell, preserving electroneutrality. This chloride shift reverses in the lungs as bicarbonate re-enters the red cell and chloride leaves.

Question 39Cardiopulmonary Anatomy, Physiology, and Pathophysiology

A patient has an oxygen consumption of 250 mL/min, arterial oxygen content of 20 mL/dL, and mixed venous oxygen content of 15 mL/dL. Using the Fick principle, what is the cardiac output?

  1. 20 L/min
  2. 5 L/min Correct answer.
  3. 2.5 L/min
  4. 10 L/min

Explanation

The Fick principle states that oxygen consumption equals cardiac output times the arteriovenous oxygen content difference. The difference is 5 mL/dL, or 50 mL/L; 250 mL/min divided by 50 mL/L gives 5 L/min.

Question 40Cardiopulmonary Anatomy, Physiology, and Pathophysiology

In an upright healthy adult at rest, which region of the lung receives the greatest pulmonary blood flow per unit lung volume?

  1. The nondependent apical regions.
  2. The dependent basal regions. Correct answer.
  3. The hilar regions only.
  4. All regions equally.

Explanation

Gravity increases pulmonary arterial pressure in dependent lung regions, so the base receives more blood flow per unit volume than the apex in an upright resting person. This corresponds to West zone 3 at the base.

Question 41Respiratory Care Equipment, Medical Gas Therapy, and Airway Management

A patient is receiving oxygen through a low-flow nasal cannula at 2 L/min. Which FiO2 range is most consistent with this setting?

  1. 44% to 50%
  2. 60% to 70%
  3. 24% to 28% Correct answer.
  4. 35% to 40%

Explanation

A nasal cannula is a low-flow device; at 1 L/min it provides roughly 24% FiO2, and each additional liter adds about 4%. At 2 L/min the expected FiO2 is therefore about 28%, so the 24% to 28% range is correct. Higher ranges require higher flows or a different oxygen interface.

Question 42Respiratory Care Equipment, Medical Gas Therapy, and Airway Management

A bag-valve-mask with an attached oxygen reservoir is being used for manual ventilation. What oxygen flow rate should be connected to deliver nearly 100% oxygen?

  1. 2 to 4 L/min
  2. 15 L/min Correct answer.
  3. 10 to 12 L/min
  4. 6 to 8 L/min

Explanation

A bag-valve-mask with an attached reservoir must receive at least 15 L/min to fill the bag and reservoir and deliver close to 100% oxygen. Lower flows allow room air entrainment and reduce delivered FiO2. The reservoir should remain inflated during ventilation.

Question 43Respiratory Care Equipment, Medical Gas Therapy, and Airway Management

What is the minimum oxygen flow rate needed for a simple face mask to reduce the risk of carbon dioxide rebreathing?

  1. 3 to 4 L/min
  2. 1 to 2 L/min
  3. 5 to 6 L/min Correct answer.
  4. 10 to 12 L/min

Explanation

A simple face mask has no reservoir and depends on adequate flow to wash out exhaled carbon dioxide. A minimum of 5 to 6 L/min is recommended; lower flows allow CO2 rebreathing. The mask typically delivers about 35% to 55% oxygen at those flows.

Question 44Respiratory Care Equipment, Medical Gas Therapy, and Airway Management

What endotracheal tube cuff pressure range is recommended for an adult patient to minimize both aspiration risk and tracheal mucosal injury?

  1. 35 to 45 cm H2O
  2. 20 to 30 cm H2O Correct answer.
  3. 10 to 15 cm H2O
  4. 50 to 60 cm H2O

Explanation

Endotracheal tube cuff pressure should be maintained at 20 to 30 cm H2O. Pressures below 20 cm H2O increase the risk of aspiration and air leak, while pressures above 30 cm H2O impair tracheal mucosal capillary perfusion and can cause ischemic injury. Cuff pressure should be measured with a calibrated manometer.

Question 45Respiratory Care Equipment, Medical Gas Therapy, and Airway Management

An adult patient requires oropharyngeal suctioning. Which vacuum pressure is appropriate?

  1. 40 to 60 mmHg
  2. 140 to 160 mmHg
  3. 200 to 250 mmHg
  4. 80 to 120 mmHg Correct answer.

Explanation

For adult oropharyngeal suctioning, a vacuum of 80 to 120 mmHg is recommended. Higher negative pressures increase the risk of mucosal trauma, hypoxemia, and atelectasis. Suction should be applied only during withdrawal and limited to less than 15 seconds.

Question 46Respiratory Care Equipment, Medical Gas Therapy, and Airway Management

A COPD patient with chronic CO2 retention requires controlled oxygen therapy. Which device provides the most predictable FiO2?

  1. Venturi mask Correct answer.
  2. Simple face mask
  3. Nasal cannula
  4. Nonrebreather mask

Explanation

A Venturi mask uses air entrainment through a fixed orifice to deliver a predictable FiO2, commonly 24% to 50%. This predictability makes it the preferred device when controlled oxygen therapy is needed, such as in a COPD patient with chronic CO2 retention. Nasal cannula and simple masks deliver variable FiO2.

Question 47Respiratory Care Equipment, Medical Gas Therapy, and Airway Management

Which condition is most likely to cause pulse oximetry to read falsely low despite adequate arterial oxygenation?

  1. Polycythemia
  2. Elevated serum bilirubin
  3. Severe peripheral vasoconstriction Correct answer.
  4. Carbon monoxide poisoning

Explanation

Pulse oximetry depends on adequate peripheral perfusion to detect the pulsatile signal. Severe vasoconstriction, hypotension, or cold extremities can reduce signal quality and produce falsely low readings. Carbon monoxide poisoning falsely elevates SpO2, while anemia and bilirubin do not directly lower the reading.

Question 48Respiratory Care Equipment, Medical Gas Therapy, and Airway Management

What gas flow is typically used to drive a small-volume jet nebulizer?

  1. 4 L/min
  2. 2 L/min
  3. 12 to 15 L/min
  4. 6 to 8 L/min Correct answer.

Explanation

A small-volume jet nebulizer is typically driven at 6 to 8 L/min. This flow produces particles in the 1 to 5 micrometer range, which can reach the lower respiratory tract. Higher flows may increase output but are not the standard starting setting.

Question 49Respiratory Care Equipment, Medical Gas Therapy, and Airway Management

An E-cylinder contains about 660 L of oxygen at 2200 psi. The gauge currently reads 1100 psi, and the patient is receiving 5 L/min. Approximately how long will the cylinder last?

  1. 99 minutes
  2. 33 minutes
  3. 132 minutes
  4. 66 minutes Correct answer.

Explanation

An E-cylinder holds about 660 L of oxygen at 2200 psi. At 1100 psi, half the contents remain, or about 330 L. Dividing 330 L by 5 L/min gives 66 minutes.

Question 50Respiratory Care Equipment, Medical Gas Therapy, and Airway Management

A patient with severe upper airway obstruction from a tumor has increased work of breathing. Why does heliox reduce work of breathing in this situation?

  1. It lowers gas density, reducing turbulent flow and work of breathing. Correct answer.
  2. It increases hemoglobin oxygen saturation directly.
  3. It humidifies inspired gas and loosens secretions.
  4. It dilates bronchial smooth muscle like a beta agonist.

Explanation

Heliox is a low-density gas mixture, usually 80% helium and 20% oxygen. Reduced density decreases Reynolds number and promotes laminar flow, lowering resistance and work of breathing in upper airway obstruction. It does not treat the underlying obstruction or increase oxygen-carrying capacity.