Control of Breathing — MCQs
Peripheral and central chemoreceptors may both contribute to the increased ventilation that occurs as a result of which of the following?
What physiological mechanism is responsible for the increase in the duration of expiration?
All of the following statements about acid-base disorders are true, EXCEPT:
Which of the following statements about the Hering-Breuer inflation reflex is false?
Which of the following structures in the central nervous system contains major autonomic reflex centers?
Which of the following is the most important clinical principle regarding acute high-altitude pulmonary edema (HAPE)?
Which physiological adaptation does not happen at high altitudes?
Damage to pneumotaxic center along with vagus nerve causes which type of respiration?
Which of the following statements about breathing is incorrect?
Curare notch seen in capnograph is due to
Control of Breathing Indian Medical PG Practice Questions and MCQs
Question 1: Peripheral and central chemoreceptors may both contribute to the increased ventilation that occurs as a result of which of the following?
- A. A decrease in arterial oxygen content
- B. A decrease in arterial blood pressure
- C. An increase in arterial carbon dioxide tension (Correct Answer)
- D. A decrease in arterial oxygen tension
Explanation: ***An increase in arterial carbon dioxide tension*** - An increase in **arterial PCO2** (hypercapnia) leads to a rapid decrease in the **pH of the cerebrospinal fluid (CSF)**, which strongly stimulates **central chemoreceptors** in the medulla. - While overwhelmingly driven by central chemoreceptors, a significant increase in **arterial PCO2** also causes a slight decrease in **arterial pH**, which can additionally stimulate **peripheral chemoreceptors** in the carotid and aortic bodies, leading to increased ventilation. *A decrease in arterial oxygen content* - A decrease in **arterial oxygen content** (e.g., due to anemia or carbon monoxide poisoning) without a significant drop in **arterial PO2** primarily affects oxygen delivery to tissues. - It does not directly stimulate peripheral chemoreceptors, which are sensitive to **PO2**, not content, nor does it affect central chemoreceptors directly to increase ventilation in this manner. *A decrease in arterial blood pressure* - A decrease in **arterial blood pressure** is sensed by **baroreceptors** and primarily triggers cardiovascular reflexes (e.g., increased heart rate and vasoconstriction) to restore blood pressure. - It does not directly stimulate peripheral or central chemoreceptors to significantly increase ventilation unless severe hypoperfusion leads to significant changes in arterial blood gases. *A decrease in arterial oxygen tension* - A decrease in **arterial oxygen tension (PO2)**, especially when it falls below approximately 60 mmHg, acts as a potent stimulus for **peripheral chemoreceptors**. - However, **central chemoreceptors** are primarily sensitive to **PCO2** and CSF pH, and a decrease in **arterial PO2** alone has little direct effect on their activity.
Question 2: What physiological mechanism is responsible for the increase in the duration of expiration?
- A. J-reflex
- B. Head's paradoxical reflex
- C. Proprioceptors
- D. Hering-Breuer reflex (Correct Answer)
Explanation: ***Hering-Breuer reflex*** - The **Hering-Breuer reflex** is initiated by **stretch receptors in the bronchi and bronchioles** which are activated during lung inflation. - This reflex **inhibits inspiration** and **prolongs expiration**, preventing overinflation of the lungs. *J-reflex* - The **J-reflex** is stimulated by **juxtacapillary (J) receptors** in the alveolar walls, usually in response to pulmonary edema or congestion. - It typically causes **rapid, shallow breathing** and **bronchoconstriction**, not prolonged expiration. *Head's paradoxical reflex* - **Head's paradoxical reflex** (also known as the **inflation reflex** in newborns) involves an inspiratory effort triggered by lung inflation, often overcoming the Hering-Breuer reflex in specific conditions. - It tends to **increase respiratory rate** and depth, not prolong expiration. *Proprioceptors* - **Proprioceptors** are sensory receptors in muscles, tendons, and joints that provide information about body position and movement. - While they can influence respiration during exercise, they are not primarily responsible for directly **increasing the duration of expiration** as a reflex mechanism against overinflation.
Question 3: All of the following statements about acid-base disorders are true, EXCEPT:
- A. Metabolic acidosis is compensated by increasing Pco2 (Correct Answer)
- B. Buffering may be intra & extra cellular
- C. pH determined by Pco2 and HCO3
- D. Respiratory acidosis is compensated by HCO3
Explanation: ***Metabolic acidosis is compensated by increasing Pco2*** - In **metabolic acidosis**, the primary problem is a decrease in **bicarbonate (HCO3-)**. - The compensatory response is **respiratory**, involving an increase in **respiratory rate** and depth to **decrease Pco2**, thereby *raising* the pH back towards normal. Increasing Pco2 would worsen the acidosis. *Buffering may be intra & extra cellular* - **Buffering systems** operate both **intracellularly** (e.g., proteins, phosphates) and **extracellularly** (e.g., bicarbonate-carbonic acid system, hemoglobin). - This dual buffering ensures a rapid and widespread response to changes in acid-base balance throughout the body. *pH determined by Pco2 and HCO3* - According to the **Henderson-Hasselbalch equation**, pH is directly proportional to the ratio of **bicarbonate (HCO3-)** to **Pco2**. - This means that changes in either Pco2 (respiratory component) or HCO3- (metabolic component) will directly influence the overall pH of the blood. *Respiratory acidosis is compensated by HCO3* - In **respiratory acidosis**, the primary problem is an increase in **Pco2** due to hypoventilation. - The compensatory response is **renal**, involving increased reabsorption of **bicarbonate (HCO3-)** and increased excretion of H+ ions to buffer the excess acid.
Question 4: Which of the following statements about the Hering-Breuer inflation reflex is false?
- A. Is mediated by vagal afferents from pulmonary stretch receptors.
- B. Involves stimulation of the inspiratory center.
- C. Protects against underinflation of the lungs. (Correct Answer)
- D. Inhibits further inspiration when lung inflation is excessive.
Explanation: ***Protects against underinflation of the lungs.*** - The **Hering-Breuer inflation reflex** is activated by **stretch receptors** in the lungs during excessive inspiration, preventing overinflation. - Its primary role is to protect against **overinflation**, not underinflation, by terminating inspiration prematurely when lungs are excessively inflated. *Is mediated by vagal afferents from pulmonary stretch receptors.* - This statement is **true** and correctly describes the neural pathway of the reflex. - **Pulmonary stretch receptors** detect lung inflation and send signals via **vagal afferents** (vagus nerve) to the respiratory centers in the medulla oblongata. *Involves stimulation of the inspiratory center.* - The Hering-Breuer reflex is a **protective reflex** that is *inhibitory* to the inspiratory center, not stimulatory. - It works by sending signals via the **vagus nerve** to *inhibit* inspiratory neurons in the **medulla oblongata** when stretch receptors in the lungs are activated during excessive inflation. *Inhibits further inspiration when lung inflation is excessive.* - This statement is **true** and describes the key function of the reflex, which is to prevent overexpansion of the lungs. - When lung volume increases significantly, **stretch receptors** are activated, sending signals that *inhibit* the inspiratory effort and promote expiration.
Question 5: Which of the following structures in the central nervous system contains major autonomic reflex centers?
- A. Medulla oblongata (Correct Answer)
- B. Thalamus
- C. Cerebellum
- D. Hypothalamus
Explanation: ***Medulla oblongata*** - The **medulla oblongata** contains the most critical **vital autonomic reflex centers** including the cardiovascular center (regulating heart rate and blood pressure), respiratory center (controlling breathing rhythm), and vasomotor center - It also houses reflex centers for coughing, sneezing, swallowing, and vomiting - These are **immediate, life-sustaining reflexes** that operate without higher center input *Hypothalamus* - The **hypothalamus** is indeed a major autonomic control center and the **highest level integrator** of autonomic function - However, it functions more as a **regulatory and integrative center** rather than a direct reflex center - It modulates autonomic responses through connections with brainstem centers like the medulla *Cerebellum* - The **cerebellum** is primarily responsible for motor coordination, balance, and posture control - While it may influence some autonomic functions indirectly, it does not contain autonomic reflex centers *Thalamus* - The **thalamus** serves as a relay station for sensory information and plays a role in consciousness and alertness - It is not involved in autonomic reflex pathways
Question 6: Which of the following is the most important clinical principle regarding acute high-altitude pulmonary edema (HAPE)?
- A. HAPE is more common at altitudes above 2500 meters but can occur at lower altitudes.
- B. Elevated ESR is the most specific diagnostic marker for HAPE
- C. The primary treatment for HAPE is immediate descent to a lower altitude. (Correct Answer)
- D. HAPE only occurs at altitudes above 4000 meters
Explanation: The primary treatment for HAPE is immediate descent to a lower altitude [1]. - **Immediate descent** is crucial as it reverses the hypoxic vasoconstriction and reduces pulmonary artery pressure, which are central to HAPE pathophysiology [1], [2]. - This intervention directly addresses the underlying cause and significantly improves outcomes, making it the most important clinical principle. *Elevated ESR is the most specific diagnostic marker for HAPE* - **Elevated ESR** (Erythrocyte Sedimentation Rate) is a non-specific inflammatory marker and is not used as a diagnostic marker for HAPE. - Diagnosis of HAPE relies primarily on clinical symptoms, signs, and imaging findings. *HAPE is more common at altitudes above 2500 meters but can occur at lower altitudes.* - While it is true that HAPE most commonly occurs at altitudes above 2500 meters [2], this statement describes an epidemiological fact rather than the most important **clinical principle** for management. - The most crucial clinical principle focuses on the immediate action required for patient safety, which is descent [1]. *HAPE only occurs at altitudes above 4000 meters* - HAPE can occur at **altitudes much lower than 4000 meters**, typically starting around 2500 meters, especially in susceptible individuals or with rapid ascent [2]. - This statement is factually incorrect and misrepresents the altitude range for HAPE development.
Question 7: Which physiological adaptation does not happen at high altitudes?
- A. Pulmonary vasoconstriction
- B. Respiratory acidosis (Correct Answer)
- C. Hypoxia
- D. Polycythemia
Explanation: ***Respiratory acidosis*** - At high altitudes, the primary physiological response to **hypoxia** is to increase ventilation, leading to a decrease in **arterial PCO2**. - This reduction in **PCO2** causes **respiratory alkalosis**, not acidosis, as the body tries to compensate for the lower oxygen levels. *Pulmonary vasoconstriction* - This is a significant physiological response to **hypoxia** at high altitudes, leading to an increase in **pulmonary artery pressure**. - Its purpose is to divert blood flow to better-ventilated areas of the lung, but it can also contribute to **pulmonary hypertension**. *Hypoxia* - Reduced **atmospheric pressure** at high altitudes directly results in a lower partial pressure of oxygen (**PO2**), leading to **hypoxia**. - This low **PO2** is the primary trigger for most other physiological adaptations seen at high altitudes. *Polycythemia* - Prolonged exposure to **hypoxia** stimulates the kidneys to release **erythropoietin (EPO)**, which in turn increases **red blood cell production**. - This adaptive increase in **red blood cell count** and **hemoglobin concentration** aims to enhance the oxygen-carrying capacity of the blood.
Question 8: Damage to pneumotaxic center along with vagus nerve causes which type of respiration?
- A. Cheyne-Stokes breathing
- B. Deep and slow breathing
- C. Shallow and rapid breathing
- D. Apneustic breathing (Correct Answer)
Explanation: ***Apneustic breathing*** - Damage to the **pneumotaxic center** prevents the normal inhibition of inspiration, leading to **prolonged inspiratory gasps**. - **Vagal nerve damage** further removes the inhibitory feedback from the lungs, exacerbating the inspiratory "holds" characteristic of apneustic breathing. *Cheyne-Stokes breathing* - This pattern is characterized by a **crescendo-decrescendo pattern** of breathing, interspersed with periods of **apnea**. - It is often associated with conditions like **heart failure**, stroke, or severe neurological damage, not specifically the pneumotaxic center and vagus nerve. *Deep and slow breathing* - This pattern can be seen in conditions like **Kussmaul breathing** (due to metabolic acidosis) or as a compensatory mechanism. - It does not directly result from the combined damage of the **pneumotaxic center** and the **vagus nerve**. *Shallow and rapid breathing* - This pattern is commonly seen in restrictive lung diseases, anxiety, or pain, where tidal volume is decreased and respiratory rate increased. - It does not reflect the **prolonged inspiration** that would result from a compromised pneumotaxic center and vagal input.
Question 9: Which of the following statements about breathing is incorrect?
- A. Inspiration is an active process
- B. Normal breathing occurs when transpulmonary pressure is 5-8 cm H2O (Correct Answer)
- C. Expiration during quiet breathing is passive
- D. Compliance is influenced by multiple factors including surfactant.
Explanation: ***Normal breathing occurs when transpulmonary pressure is 5-8 cm H2O*** - This statement is **incorrect** because it misrepresents transpulmonary pressure during normal breathing. - Normal **transpulmonary pressure** during quiet breathing typically ranges from approximately **3-6 cm H2O** during inspiration, with an average of about **5 cm H2O** at functional residual capacity. - The range "5-8 cm H2O" is too high for normal quiet breathing. While transpulmonary pressure can reach 8 cm H2O during deeper inspiration, stating this as the range for "normal breathing" is inaccurate. - Transpulmonary pressure is the difference between alveolar pressure and pleural pressure (P_L = P_alv - P_pl), which drives lung inflation. *Expiration during quiet breathing is passive* - During quiet breathing, **expiration is a passive process** driven by the **elastic recoil of the lungs** and chest wall. - No active muscular contraction is required for air to leave the lungs during unforced expiration. *Inspiration is an active process* - **Inspiration is an active process** requiring muscular contraction, primarily of the **diaphragm and external intercostal muscles**. - These muscles contract to increase the thoracic volume, which decreases intrapleural and alveolar pressures, drawing air into the lungs. *Compliance is influenced by multiple factors including surfactant* - **Lung compliance**, a measure of the lung's distensibility, is significantly influenced by **surfactant**. - Surfactant reduces **surface tension** in the alveoli, preventing their collapse and increasing compliance.
Question 10: Curare notch seen in capnograph is due to
- A. Spontaneous breathing (Correct Answer)
- B. Carbon dioxide rebreathing
- C. Valve malfunction
- D. Bronchospasm
Explanation: ***Spontaneous breathing*** - The "Curare notch" a dip in the expiratory plateau of the **capnograph waveform**, occurs when a patient begins to initiate **spontaneous breaths** against the ventilator. - This signifies that the **neuromuscular blockade** from paralytic agents (like curare derivatives) is wearing off. *Carbon dioxide rebreathing* - **CO2 rebreathing** would typically elevate the baseline of the capnogram and potentially prolong the expiratory plateau, but it would not create a characteristic notch. - This is usually caused by insufficient fresh gas flow or a faulty absorbent, leading to the patient inhaling previously exhaled CO2. *Valve malfunction* - A **valve malfunction**, such as a stuck expiratory valve, would typically cause a persistent elevation of the expiratory CO2 plateau or an inability to exhale, rather than a transient notch. - This would indicate a problem with the mechanical ventilation circuit. *Bronchospasm* - **Bronchospasm** typically results in a **sloping or shark fin-shaped expiratory plateau** on the capnogram due to prolonged expiration and uneven gas emptying from the lungs. - It does not produce a distinct "notch" as seen with the return of spontaneous breathing.
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