Respiratory Physiology — MCQs
Damage to pneumotaxic center along with vagus nerve causes which type of respiration?
The transport of CO2 in the blood is primarily influenced by which of the following factors?
Functional residual capacity (FRC) is defined as the volume of air remaining in the lungs at which specific moment in the respiratory cycle?
Which equation is used to calculate physiological dead space?
Which of the following is markedly decreased in restrictive lung disease?
Which of the following statements about lung compliance is false?
When VA/Q is infinity, it means
In a patient with multiple fractures, what is the most important initial management step?
What is the potential respiratory complication associated with the use of Trilene in combination with Sodalime?
A 10-month-old child weighing 5 kg and measuring 65 cm in length presents with cough and cold. He has a respiratory rate of 48 per minute, with no retractions, grunting, or cyanosis. There is no history of convulsions. Which statement is true?
Respiratory Physiology Indian Medical PG Practice Questions and MCQs
Question 1: 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 2: The transport of CO2 in the blood is primarily influenced by which of the following factors?
- A. Binding to hemoglobin as carbaminohemoglobin
- B. Conversion to bicarbonate ions by carbonic anhydrase (Correct Answer)
- C. Transport as carbonic acid in red blood cells
- D. Direct dissolution in blood plasma
Explanation: ***Conversion to bicarbonate ions by carbonic anhydrase*** - This is the **primary mechanism** for CO2 transport, accounting for approximately **70%** of total CO2 transport in blood. - Inside red blood cells, CO2 combines with water to form carbonic acid (H2CO3), catalyzed by the enzyme **carbonic anhydrase**. - Carbonic acid **immediately dissociates** into hydrogen ions (H+) and **bicarbonate ions (HCO3-)**. - Bicarbonate ions then diffuse into plasma in exchange for chloride ions (chloride shift), making this the most quantitatively significant transport mechanism. - **Carbonic anhydrase** is the key enzyme that influences this process by accelerating the reaction by approximately **5000-fold**. *Binding to hemoglobin as carbaminohemoglobin* - Approximately **20-23%** of CO2 is transported by directly binding to amino groups on hemoglobin to form **carbaminohemoglobin**. - This is significant but less than bicarbonate transport. - Deoxygenated hemoglobin binds CO2 more readily than oxygenated hemoglobin (Haldane effect). *Transport as carbonic acid in red blood cells* - This is **not correct** because carbonic acid (H2CO3) is only a **transient intermediate** that exists momentarily. - It immediately dissociates into H+ and HCO3-, so CO2 is not actually transported "as carbonic acid" but rather as **bicarbonate ions**. - The carbonic acid step is part of the mechanism, but bicarbonate is the actual transport form. *Direct dissolution in blood plasma* - Only about **7-10%** of CO2 is transported dissolved directly in plasma. - CO2 has limited solubility in plasma, making this the least significant mechanism. - This dissolved CO2 contributes to the partial pressure of CO2 (PCO2) in blood.
Question 3: Functional residual capacity (FRC) is defined as the volume of air remaining in the lungs at which specific moment in the respiratory cycle?
- A. During active expiration
- B. After normal expiration (Correct Answer)
- C. At peak inspiration
- D. During active inspiration
Explanation: ***After normal expiration*** - **Functional residual capacity (FRC)** is the volume of air remaining in the lungs at the end of a **normal, passive expiration**. - It represents the sum of the **expiratory reserve volume (ERV)** and the **residual volume (RV)**. *During active expiration* - **Active expiration** involves the use of accessory muscles to force more air out of the lungs than during normal expiration. - This process would result in a lung volume less than FRC, closer to the **residual volume**. *At peak inspiration* - **Peak inspiration** represents the total lung capacity (TLC), which is the maximum volume of air the lungs can hold after a maximal inspiratory effort. - This is the largest lung volume, significantly greater than FRC. *During active inspiration* - **Active inspiration** is the process of inhaling air, which increases lung volume. - FRC is a static volume measured at the end of expiration, not during the dynamic process of inhaling.
Question 4: Which equation is used to calculate physiological dead space?
- A. Dalton's law
- B. Bohr equation (Correct Answer)
- C. Charles's law
- D. Boyle's law
Explanation: ***Bohr equation*** - The Bohr equation is used to calculate **physiological dead space**, which is the sum of anatomical dead space and alveolar dead space. - It relates the partial pressure of carbon dioxide in arterial blood to the partial pressure of carbon dioxide in expired air, along with **tidal volume** and expired volume. *Dalton's law* - Dalton's law states that the **total pressure** exerted by a mixture of non-reactive gases is equal to the **sum of the partial pressures** of individual gases. - It is used to calculate partial pressures of gases in a mixture, not dead space. *Charles's law* - Charles's law describes the relationship between the **volume and temperature** of a gas at constant pressure. - It states that the volume of a given mass of gas is directly proportional to its absolute temperature. *Boyle's law* - Boyle's law describes the inverse relationship between the **pressure and volume** of a gas at constant temperature. - It is fundamental to understanding mechanics of breathing, but not dead space calculation.
Question 5: Which of the following is markedly decreased in restrictive lung disease?
- A. FVC (Correct Answer)
- B. RV
- C. FEV1/FVC
- D. FEV1
Explanation: ***FVC*** - In **restrictive lung disease**, there is a reduction in lung volume due to various causes, leading to a markedly decreased **Forced Vital Capacity (FVC)**. - **FVC** directly measures the total amount of air a person can exhale after a maximal inhalation, which is inherently limited in restrictive conditions. - This is the **hallmark finding** in restrictive lung disease and the most clinically significant decrease. *FEV1* - While **FEV1** (Forced Expiratory Volume in 1 second) is also decreased in restrictive lung disease, its decrease is proportional to the FVC decrease. - A decrease in FEV1 alone is less specific, as it could also indicate obstructive lung disease. - The key is that both FEV1 and FVC decrease together, maintaining a normal or increased ratio. *FEV1/FVC* - The **FEV1/FVC ratio** is typically **normal or even increased** in restrictive lung disease, as both FEV1 and FVC decrease proportionally or FEV1 decreases slightly less. - A decreased FEV1/FVC ratio is characteristic of **obstructive lung disease**, not restrictive. *RV* - **Residual Volume (RV)** is also **decreased** in restrictive lung disease, along with all other lung volumes (TLC, VC, FRC). - However, RV is not measured by standard spirometry and requires body plethysmography or gas dilution techniques. - While RV does decrease, **FVC** is the more clinically significant and readily measurable parameter that is "markedly decreased" and defines restrictive disease on routine pulmonary function testing.
Question 6: Which of the following statements about lung compliance is false?
- A. Decreased in emphysema (Correct Answer)
- B. Total compliance is 0.2 L/cm H2O
- C. A measure of lung distensibility
- D. Change in volume per unit change in pressure
Explanation: ***Decreased in emphysema*** - This statement is **false** because **emphysema** is characterized by the destruction of elastic fibers in the lung parenchyma, which paradoxically leads to an **increase** in lung compliance. - The loss of elastic recoil makes the lungs more distensible and easier to inflate, but also impairs their ability to passively exhale. *Total compliance is 0.2 L/cm H2O* - This value represents the **normal total lung compliance** in a healthy adult (0.17 to 0.25 L/cm H2O), including both lung and chest wall compliance. - Lung compliance alone is typically around 0.2 L/cm H2O for healthy lungs. *A measure of lung distensibility* - **Compliance** is intrinsically defined as a measure of how easily the lungs or chest wall can be stretched or distended. - High compliance means the lungs are easy to inflate, while low compliance means they are stiff and difficult to inflate. *Change in volume per unit change in pressure* - This is the explicit **formula and definition of compliance** (C = ΔV/ΔP). - It quantifies the change in lung volume in response to a given change in transpulmonary pressure.
Question 7: When VA/Q is infinity, it means
- A. Dead space (Correct Answer)
- B. Unrelated to VA/Q ratio
- C. The PO2 of alveolar air is 159 mmHg and PCO2 is 0 mmHg
- D. Atelectasis
Explanation: ***Dead space*** - An infinite V/Q ratio implies that **ventilation (V)** is occurring, but **perfusion (Q)** is zero. - This scenario defines **dead space**, where air enters the alveoli but no blood flow is available for gas exchange. - This is the **most accurate and complete answer** to describe the physiological meaning of VA/Q = ∞. *Unrelated to VA/Q ratio* - This statement is incorrect because VA/Q being infinity is a specific and highly significant state within the **ventilation-perfusion relationship**. - An infinite ratio directly indicates a complete decoupling of ventilation and perfusion, with profound physiological consequences. *The PO2 of alveolar air is 159 mmHg and PCO2 is 0 mmHg* - While this describes the **gas composition** in dead space (VA/Q = ∞), it is not the **physiological term** for the condition. - With no perfusion, alveolar air remains essentially **unchanged from inspired air**: PO2 ≈ 150-159 mmHg (atmospheric level) and PCO2 ≈ 0 mmHg. - No oxygen is extracted and no CO2 is added because there is **no blood flow**. - However, "dead space" is the more precise physiological answer. *Atelectasis* - **Atelectasis** refers to the collapse of lung tissue, which typically leads to an absence of **ventilation (V)** in that region. - This condition would result in a **VA/Q ratio of zero** (V=0, Q present), the opposite of infinity.
Question 8: In a patient with multiple fractures, what is the most important initial management step?
- A. Intravenous fluids
- B. Open reduction of fractures
- C. Blood transfusion
- D. Airway maintenance (Correct Answer)
Explanation: ***Airway maintenance*** - In any trauma patient, ensuring a **patent airway** is the absolute priority to prevent hypoxia and brain damage. - This is part of the primary survey (**ABCDE**) in trauma management, where life-threatening issues are addressed first. *Intravenous fluids* - While essential for managing **hypovolemia** due to blood loss in polytrauma, fluid resuscitation comes after securing the airway and ensuring adequate breathing. - Administering fluids to a patient who cannot breathe effectively will not resolve the primary issue. *Blood transfusion* - **Blood transfusion** is necessary for significant hemorrhage and can be life-saving, but it is not the *initial* management step. - Airway, breathing, and circulation (which includes addressing significant hemorrhage) collectively precede the decision and initiation of blood transfusions. *Open reduction of fractures* - **Open reduction of fractures** is a definitive treatment for musculoskeletal injuries that is performed much later, after the patient has been stabilized. - It is an elective procedure in the context of initial trauma management and is not a life-saving measure in the acute phase.
Question 9: What is the potential respiratory complication associated with the use of Trilene in combination with Sodalime?
- A. Renal toxicity
- B. Hepatotoxicity
- C. Myocardial depression
- D. Airway irritation and inflammation (Correct Answer)
Explanation: ***Airway irritation and inflammation*** - The interaction between **Trilene (trichloroethylene)** and **soda lime** in a closed anesthetic circuit can produce **dichloroacetylene**. - **Dichloroacetylene** is a highly toxic compound that can cause severe airway irritation, inflammation, and even **necrosis** of the respiratory tract. *Renal toxicity* - While some halogenated anesthetics (e.g., methoxyflurane) are associated with **renal toxicity** due to fluoride ion release, this is not the primary or most severe respiratory complication of Trilene with soda lime. - The main concern with Trilene and soda lime is the formation of a **toxic airway irritant**. *Hepatotoxicity* - **Halothane** is more classically associated with **hepatotoxicity** (halothane hepatitis) due to metabolism into toxic intermediates. - **Trilene** itself is not primarily known for causing severe hepatotoxicity, and the interaction with soda lime does not specifically target the liver for toxicity. *Myocardial depression* - Many inhaled anesthetics, including Trilene, can cause some degree of **myocardial depression**. - However, this is a general effect of the anesthetic on cardiac function and is not a unique or specific complication arising from the **interaction with soda lime** that produces dichloroacetylene.
Question 10: A 10-month-old child weighing 5 kg and measuring 65 cm in length presents with cough and cold. He has a respiratory rate of 48 per minute, with no retractions, grunting, or cyanosis. There is no history of convulsions. Which statement is true?
- A. No pneumonia, only cough and cold (Correct Answer)
- B. The child may have pneumonia
- C. The child has severe pneumonia
- D. The child has very severe disease
Explanation: **_No pneumonia, only cough and cold_** - The child's respiratory rate of 48 breaths per minute is within the normal range for a 10-month-old child, where a respiratory rate **less than 50 breaths per minute** is considered normal. - The absence of **retractions, grunting, or cyanosis** further indicates no signs of respiratory distress or severe illness. *The child may have pneumonia* - The child does not meet the criteria for pneumonia, as there is **no fast breathing** (respiratory rate below 50/min) and **no signs of chest indrawing**. - Pneumonia would typically involve a significantly **elevated respiratory rate** for the child's age or signs of severe respiratory distress. *The child has severe pneumonia* - Severe pneumonia is characterized by signs such as **chest indrawing**, deep or labored breathing, or symptoms like inability to drink, convulsions, or lethargy none of which are present. - A respiratory rate of 48/min is not considered fast breathing for this age group, ruling out even non-severe pneumonia based on respiratory rate criterion. *The child has very severe disease* - Very severe disease would manifest with critical signs like **cyanosis**, inability to breastfeed or drink, repeated vomiting, or convulsions, none of which are exhibited by the child. - The child's symptoms are limited to a cough and cold without any alarming signs, suggesting a mild, uncomplicated illness.
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