medicine beginner 10 sample questions

Respiratory Function MCQ Practice Test

Breathing mechanics and gas exchange

Q1. During a Valsalva maneuver (forced expiration against a closed glottis), the rise in intrathoracic pressure produces which immediate cardiovascular effect?

A. Reduced venous return to the heart ✓
B. Increased cardiac output
C. Pulmonary surfactant secretion
D. Collapse of the diaphragm

Explanation: Elevated intrathoracic pressure compresses the vena cava, transiently reducing venous return and thus stroke volume — the basis of the Valsalva maneuver’s four-phase cardiovascular response.

Q2. During a forced expiration against a closed glottis, which of the following structures is most responsible for the rapid decrease in lung volume?

A. The diaphragm
B. The external intercostal muscles
C. The internal intercostal muscles ✓
D. The abdominal muscles

Explanation: During a forced expiration against a closed glottis, the internal intercostal muscles contract to help increase the intrapleural pressure, which in turn causes the rib cage to move downward and outward, and the lung volume to decrease rapidly.

Q3. Which of the following pulmonary capillary wedge pressure (PCWP) values best correlates with the increased lung compliance and decreased lung volume associated with atelectasis in the dependent lung regions of a patient in the supine position?

A. The PCWP value is typically higher than 12 mmHg in the dependent lung regions.
B. Atelectasis in the dependent lung regions is associated with a lower PCWP value. ✓
C. The PCWP value is not affected by lung compliance and volume changes.
D. The PCWP value is typically lower than 6 mmHg in the dependent lung regions.

Explanation: Atelectasis in the dependent lung regions of a patient in the supine position is associated with increased lung compliance and decreased lung volume. This condition is characterized by a lower pulmonary capillary wedge pressure (PCWP) value due to the reduced lung volume and increased compliance. The PCWP value is a measure of the pressure in the left atrium, which is reflected in the pressure in the pulmonary capillaries. In the dependent lung regions, the PCWP value is typically lower than in the non-dependent regions due to the increased compliance and decreased volume.

Q4. During forced expiration against a closed glottis, which of the following muscles is responsible for the rapid decrease in lung volume and the associated increase in pleural pressure?

A. The internal intercostal muscles ✓
B. The abdominal muscles
C. The diaphragm
D. The crural fibers of the diaphragm

Explanation: During forced expiration against a closed glottis, the internal intercostal muscles contract to pull the ribs downward and inward, thereby increasing the volume of the thoracic cavity and decreasing the lung volume. This action also increases the pleural pressure, which helps to force air out of the lungs.

Q5. During inspiration, what is the primary mechanism that creates the pressure difference between the alveoli and the pleural space?

A. The diaphragm contraction and downward movement ✓
B. The elastic recoil of the lungs
C. The alveolar surface tension
D. The intercostal muscle contraction and rib cage elevation

Explanation: The contraction of the diaphragm and the intercostal muscles expands the thoracic cavity. This expansion decreases the intrapleural pressure, creating a pressure gradient between the alveoli (which are at atmospheric pressure initially) and the pleural space. This pressure difference drives air into the lungs. The elastic recoil of the lungs, including alveolar surface tension, opposes lung expansion, but it doesn't create the initial pressure difference.

Q6. Which of the following nerves is primarily responsible for innervating the diaphragm, thereby causing its contraction and influencing the rate and depth of breathing during inspiration?

A. The vagus nerve
B. The phrenic nerve ✓
C. The accessory nerve
D. The recurrent laryngeal nerve

Explanation: The phrenic nerve is the primary motor nerve that innervates the diaphragm. It carries motor fibers that cause the diaphragm to contract, which is essential for inspiration. The vagus nerve has some influence on breathing but is not the primary nerve for diaphragm control.

Q7. During forced expiration against a closed glottis (Valsalva maneuver), what is the primary change in the activity of the diaphragm and external intercostal muscles?

A. They contract to increase intrathoracic pressure.
B. They relax, contributing to increased intrathoracic pressure. ✓
C. Their activity is unaffected by the maneuver.
D. They switch from inspiration to expiration phase but do not change in intensity.

Explanation: During the Valsalva maneuver (forced expiration against a closed glottis), the diaphragm and external intercostal muscles relax. This relaxation, combined with contraction of abdominal muscles, increases intrathoracic pressure.

Q8. During forced expiration against a closed glottis, the pressure in the bronchi is approximately equal to the pressure in the?

A. alveoli ✓
B. terminal bronchioles
C. residual air in the lungs
D. pulmonary capillaries

Explanation: During forced expiration against a closed glottis, the pressure in the bronchi is approximately equal to the pressure in the alveoli due to the equalization of pressure throughout the respiratory system. This is because the bronchi are in continuity with the alveoli, and the pressure in the alveoli is transmitted to the bronchi. This phenomenon is known as alveolar pressure.

Q9. Which of the following structures is primarily responsible for the terminal bronchioles' transition to the respiratory bronchioles in the human lung?

A. The bronchiolar smooth muscle layer thickens
B. The mucous glands become less prominent
C. The cartilaginous support disappears
D. The Clara cells become more abundant ✓

Explanation: The Clara cells, also known as club cells, play a crucial role in the transition from terminal bronchioles to respiratory bronchioles. They are involved in the detoxification of the airway surface liquid and produce surfactant proteins, which help to reduce surface tension in the airways. As the airways transition to the respiratory zone, the Clara cells become more abundant, and their role becomes more significant in maintaining airway function.

Q10. During inhalation, the diaphragm contracts and descends, increasing the volume of the thoracic cavity. However, in individuals with a flail chest, the movement of the rib cage is altered. Which of the following best describes the effect of a flail chest on the respiratory system?

A. The flail segment of the chest wall moves inward during inhalation, increasing intrathoracic pressure and decreasing lung volume. ✓
B. The flail segment of the chest wall moves outward during inhalation, increasing lung volume and improving respiratory function.
C. The flail segment of the chest wall remains immobile during inhalation, but the unaffected parts of the chest wall continue to move normally.
D. The flail segment of the chest wall moves outward during exhalation, increasing intrathoracic pressure and decreasing lung volume.

Explanation: A flail chest occurs when a segment of the rib cage is broken, causing the affected portion of the chest wall to move paradoxically, or in the opposite direction, of the rest of the chest wall during breathing. During inhalation, the flail segment of the chest wall moves inward, increasing intrathoracic pressure and decreasing lung volume, making it more difficult for the individual to breathe.

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