Respiratory System — MCQs

Respiratory System Indian Medical PG Practice Questions and MCQs

Question 851: The rhythm for inspiration starts in:

A. Pneumotaxic centre
B. Apneustic centre
C. DRG
D. Pre-Botzinger complex (Correct Answer)

Explanation: ***Pre-Botzinger complex*** - The **Pre-Botzinger complex** is a cluster of neurons in the medulla oblongata recognized as the primary site for generating the **respiratory rhythm**. - It establishes the basic pattern for **inspiratory efforts**, acting as the central pattern generator for breathing. *Pneumotaxic centre* - The **pneumotaxic center** (located in the pons) fine-tunes the respiratory rhythm by **inhibiting inspiration**, thus regulating the rate and depth of breathing. - While it modulates respiration, it does not originate the basic inspiratory rhythm. *Apneustic centre* - The **apneustic center** (located in the pons) prolongs inspiration by stimulating the inspiratory neurons in the medulla. - Its main role is to promote deep, prolonged inspiratory gasps, but not to initiate the rhythm. *DRG* - The **Dorsal Respiratory Group (DRG)** in the medulla contains inspiratory neurons that primarily control the **diaphragm** and **external intercostals**. - While essential for inspiration, the DRG receives its rhythmicity from the Pre-Botzinger complex and acts as an integration center for various inputs.

Question 852: What is the primary function of the diaphragm in the human body?

A. Helps in digestion
B. Regulates abdominal pressure
C. Assists in breathing and separates thoracic and abdominal cavities (Correct Answer)
D. Plays a role in vocalization

Explanation: ***Assists in breathing and separates thoracic and abdominal cavities*** - The diaphragm is the **principal muscle of inspiration**, contracting to increase thoracic volume and draw air into the lungs. - It forms a **musculofibrous septum** that physically separates the **thoracic cavity** (containing heart and lungs) from the **abdominal cavity** (containing digestive organs). *Helps in digestion* - While the diaphragm's movement can indirectly affect abdominal organs, its primary role is **not in the chemical or mechanical breakdown of food**. - **Peristalsis** and digestive enzyme secretion are the main mechanisms of digestion. *Regulates abdominal pressure* - Although the diaphragm contributes to changes in **intra-abdominal pressure** (e.g., during defecation or coughing), this is a secondary function. - Its main role is linked to changes in **intrathoracic pressure** for respiration. *Plays a role in vocalization* - **Vocalization** primarily involves the **larynx**, vocal cords, and respiratory airflow controlled by smaller muscles. - While breathing is necessary for vocalization, the diaphragm itself does not directly produce sound or modulate pitch.

Question 853: In a patient with clinical signs of asthma, which of the following tests will confirm the diagnosis?

A. > 200 ml increase in FEV1 after Methacholine
B. Increase in FEV1/FVC
C. Diurnal variation in PEF > 20 percent (Correct Answer)
D. Reduction of FEV1 > 20% after bronchodilators

Explanation: ***Diurnal variation in PEF > 20 percent*** - A significant **diurnal variation in peak expiratory flow (PEF)**, typically greater than 20%, indicates **variable airflow obstruction** characteristic of asthma. - This variability reflects **bronchial hyperresponsiveness**, where airways constrict in response to triggers throughout the day. *Increase in FEV1/FVC* - An increase in the **FEV1/FVC ratio** would suggest an improvement in lung function, not the presence of obstructive lung disease like asthma, where this ratio is typically reduced. - A normal or increased FEV1/FVC ratio would rule out an obstructive pattern. *> 200 ml increase in FEV1 after Methacholine* - An increase in FEV1 after **methacholine** challenge is an indicator of responsiveness to bronchodilators, which is consistent with asthma, but it is typically measured *after* a bronchodilator, not after a bronchoconstrictor like methacholine. - The methacholine challenge test is used to induce bronchoconstriction in suspected asthma, where a *decrease* in FEV1 (typically 20%) at low dose methacholine confirms hyperresponsiveness. *Reduction of FEV1 > 20% after bronchodilators* - A reduction in **FEV1 after bronchodilators** would indicate a worsening of airway obstruction, which is contrary to the expected response in asthma where bronchodilators improve FEV1. - In asthma, a significant *increase* in FEV1 after bronchodilator administration is expected, demonstrating **reversibility** of airflow obstruction.

Question 854: Regarding the peak expiratory flow rate, which of the following statements is false?

A. Decreases with age
B. In normal adults is often more than 500L/min (Correct Answer)
C. Can be measured by the wright’s peak flow meter
D. Can be measured by a pneumotachograph

Explanation: ***In normal adults is often more than 500L/min*** - This statement is **false** because the peak expiratory flow rate (PEFR) in healthy adult males is typically around **450-480 L/min**, while in females, it's about **350-380 L/min**. - A value greater than **500 L/min** would be unusually high for the average adult and not considered "often" the case. *Can be measured by a pneumotachograph* - A **pneumotachograph** is a device used to measure gas flow rate, including the **peak expiratory flow rate**, by sensing pressure differences. - It is often utilized in **laboratory settings** for precise physiological measurements. *Decreases with age* - Peak expiratory flow rate (PEFR) generally **decreases with age** due to the natural decline in lung elasticity and respiratory muscle strength. - This decline starts in **early adulthood** and continues throughout life. *Can be measured by the wright’s peak flow meter* - The **Wright's peak flow meter** is a common and portable device specifically designed to measure **peak expiratory flow rate (PEFR)**. - It provides a quick and reliable assessment of **airflow obstruction** in patients at home or in clinical settings.

Question 855: Central chemoreceptors are most sensitive to changes in which of the following blood components?

A. Partial pressure of carbon dioxide (PCO2) (Correct Answer)
B. Partial pressure of oxygen (PO2)
C. Blood pH
D. Bicarbonate ion concentration (HCO3-)

Explanation: ***Partial pressure of carbon dioxide (PCO2)*** - Central chemoreceptors, located in the medulla oblongata, are **most sensitive to changes in blood PCO2**. - **CO2 readily crosses the blood-brain barrier** and rapidly forms carbonic acid in the CSF, which dissociates into hydrogen ions (H+) and bicarbonate. - The resulting **decrease in CSF pH** (increase in H+ concentration) directly stimulates central chemoreceptors. - This makes blood PCO2 the **most potent stimulus** for central chemoreceptors, even though the actual receptor mechanism involves H+ detection. *Partial pressure of oxygen (PO2)* - Peripheral chemoreceptors (carotid and aortic bodies) are the **primary detectors of hypoxemia**. - Central chemoreceptors are relatively insensitive to changes in PO2 under normal conditions. *Blood pH* - While central chemoreceptors ultimately respond to H+ concentration, **metabolic changes in blood pH do not readily cross the blood-brain barrier**. - H+ ions from metabolic acidosis/alkalosis cannot easily enter the CSF to stimulate central chemoreceptors. - In contrast, respiratory changes in pH (via CO2) rapidly affect CSF pH because CO2 crosses the BBB freely. *Bicarbonate ion concentration (HCO3-)* - **HCO3- does not readily cross the blood-brain barrier** to directly influence central chemoreceptors. - While bicarbonate is part of the buffering system, changes in blood bicarbonate have minimal direct effect on central chemoreceptor activity compared to PCO2.

Question 856: Which of the following is increased in elderly patients compared with their younger counterparts?

A. Vital capacity
B. Ventilatory response to hypoxia or hypercarbia
C. Air trapping (Correct Answer)
D. Resting arterial oxygen tension (PaO2 )

Explanation: ***Air trapping*** - As a result of age-related changes such as decreased lung elasticity and stiffening of the chest wall, elderly patients often experience increased **air trapping**, leading to higher residual volume and functional residual capacity. - This occurs because the small airways are more prone to collapse during exhalation, preventing complete emptying of the lungs. *Vital capacity* - **Vital capacity** typically **decreases** with age due to reduced lung elasticity and weakening of respiratory muscles. - This decrease reflects a reduction in the maximum amount of air that can be exhaled after a maximal inspiration. *Ventilatory response to hypoxia or hypercarbia* - The **ventilatory response to hypoxia or hypercarbia** generally **decreases** in elderly individuals. - This blunted response makes them more vulnerable to respiratory decompensation during periods of stress or illness. *Resting arterial oxygen tension (PaO2)* - Resting **arterial oxygen tension (PaO2)** typically **decreases** with advancing age due to changes in ventilation-perfusion matching and alveolar-capillary gas exchange. - This physiological change is often accompanied by an increase in the alveolar-arterial oxygen gradient.

Question 857: During inspiration, where does the main current of airflow occur in a normal nasal cavity?

A. Superior meatus of the nasal cavity
B. Inferior meatus of the nasal cavity
C. Middle meatus of the nasal cavity (Correct Answer)
D. Olfactory area of the nasal cavity

Explanation: ***Middle meatus of the nasal cavity*** - The main current of inspiratory airflow is directed through the **middle meatus** in an arc-like pattern from the anterior nares. - During normal quiet breathing, air enters through the vestibule and flows upward and backward through the middle portion of the nasal cavity, following the contour of the middle turbinate. - This pathway allows optimal contact with the highly vascular nasal mucosa for **humidification, warming, and filtration** of inspired air. *Inferior meatus of the nasal cavity* - The inferior meatus is located below the inferior turbinate and receives **minimal airflow** during normal inspiration. - Its primary function is as a drainage pathway for the **nasolacrimal duct** (tear duct), not as a major airflow channel. - Airflow along the floor of the nasal cavity is relatively minimal during quiet breathing. *Superior meatus of the nasal cavity* - The superior meatus is a small passage located high in the nasal cavity, primarily associated with drainage of the **posterior ethmoidal sinuses**. - It receives very little of the main inspiratory airflow due to its location and size. *Olfactory area of the nasal cavity* - The olfactory region is located in the uppermost part of the nasal cavity near the cribriform plate. - During normal breathing, most air bypasses this area; **sniffing** is required to direct air turbulently upward to stimulate olfactory receptors. - Its primary function is **olfaction** (smell detection), not bulk airflow.

Question 858: What is the primary mechanism of action of pulmonary surfactant?

A. Lubricates the flow of CO2 diffusion
B. Binds oxygen
C. Makes the capillary surface hydrophilic
D. Reduces surface tension in the alveoli (Correct Answer)

Explanation: ***Reduces surface tension in the alveoli*** - Pulmonary surfactant is a complex of **lipids and proteins** produced by **type II alveolar cells** that lines the alveolar surface. - Its primary role is to **lower the surface tension** at the air-liquid interface within the alveoli, preventing their collapse during exhalation. - This is particularly important in **small alveoli** where surface tension forces are proportionally greater (Laplace's law). *Lubricates the flow of CO2 diffusion* - This is an incorrect statement; surfactant does not lubricate CO2 diffusion. - **The diffusion of gases** across the alveolar-capillary membrane is driven by **partial pressure gradients** and facilitated by the thinness of the membrane. - Lubrication is not a factor in gas exchange. *Binds oxygen* - Surfactant does not bind oxygen. - **Hemoglobin** within red blood cells is primarily responsible for binding and transporting oxygen in the blood. - Surfactant's function is structural, related to alveolar mechanics, not oxygen transport. *Makes the capillary surface hydrophilic* - This is an incorrect statement; the pulmonary surfactant is located on the **alveolar surface**, not the capillary surface. - The capillary endothelial cells themselves regulate their permeability and interaction with blood components, independent of surfactant.

Question 859: Transection at mid-pons level with intact vagus results in:

A. Apneusis
B. Hyperventilation
C. Irregular shallow breathing
D. Deep and slow breathing (Correct Answer)

Explanation: ***Deep and slow breathing*** - A transection at the **mid-pons level** disconnects the **pneumotaxic center** from the medullary respiratory centers, while the **vagus nerves remain intact**. - Without the inhibitory input from the pneumotaxic center, inspirations become deep and prolonged due to the unopposed effect of the **apneustic center**, but the intact vagus still provides some inspiratory off-switch, preventing full apneusis. This leads to **deep and slow breathing**. *Apneusis* - **Apneusis**, characterized by prolonged inspiratory gasps, occurs when both the **pneumotaxic center and vagal afferents** (from lung stretch receptors) are non-functional or cut. - In this scenario, the vagus nerves are intact, providing an inspiratory off-switch that prevents the full development of apneusis. *Hyperventilation* - **Hyperventilation** typically results from metabolic acidosis, hypoxemia, or anxiety, leading to an increased rate and depth of breathing. - A mid-pons transection primarily affects the rhythm and duration of inspiration, not necessarily increasing the overall minute ventilation in a compensatory manner. *Irregular shallow breathing* - **Irregular shallow breathing** can be seen with damage to the **medullary respiratory centers** or severe respiratory muscle weakness. - The transection described primarily impacts the integration of pontine and medullary control, particularly the interaction between the apneustic and pneumotaxic centers, leading to deep and slow breaths, not shallow ones.

Question 860: Transection at the mid-pons level results in:

A. Complete cessation of airflow
B. Increased respiratory rate and depth
C. Sustained inspiratory phase followed by quick expiration
D. Prolonged inspiratory phase (Correct Answer)

Explanation: ***Prolonged inspiratory phase*** - Transection at the mid-pons isolates the **apneustic center** from the **pneumotaxic center**, leading to an unopposed inspiratory drive. - This results in **apneusis**, characterized by prolonged, gasping inspirations with brief expirations. - The pneumotaxic center normally limits inspiration; without it, the apneustic center's excitatory effect on the dorsal respiratory group is unopposed. *Complete cessation of airflow* - This typically occurs with transections that damage the **medullary respiratory centers** (ventral and dorsal respiratory groups) or their efferent connections. - A mid-pons transection primarily disrupts regulatory inputs to the medullary centers, rather than abolishing their fundamental activity. *Increased respiratory rate and depth* - This pattern is often associated with conditions like **metabolic acidosis** (Kussmaul breathing) or direct stimulation of the respiratory centers. - A mid-pons transection disrupts rhythmic breathing rather than enhancing it in a coordinated manner. *Sustained inspiratory phase followed by quick expiration* - While apneusis involves a sustained inspiratory phase, the expiration following it is typically brief but not necessarily "quick" in the sense of being forceful. - This option doesn't fully capture the characteristic pattern of apneusis, where the primary abnormality is the prolonged inspiration itself.

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