Respiratory System — MCQs

Respiratory System Indian Medical PG Practice Questions and MCQs

Question 781: During an asthma attack, a patient experiences difficulty exhaling air. What is the impact of this condition on airway resistance and lung volumes?

A. Increases airway resistance and decreases total lung capacity
B. Increases airway resistance and increases residual volume (Correct Answer)
C. Decreases airway resistance and decreases total lung capacity
D. Decreases airway resistance and increases total lung capacity

Explanation: ***Increases airway resistance and increases residual volume*** - During an asthma attack, **bronchoconstriction** and **mucus plugging** lead to narrowing of the airways, significantly **increasing airway resistance**. - Difficulty in exhaling air (air trapping) causes a greater volume of air to remain in the lungs after complete exhalation, thus **increasing residual volume**. *Increases airway resistance and decreases total lung capacity* - While airway resistance does increase, **total lung capacity (TLC)** typically remains normal or can even increase due to hyperinflation in chronic asthma, rather than decrease. - A decrease in TLC is more characteristic of **restrictive lung diseases**, not obstructive conditions like asthma. *Decreases airway resistance and decreases total lung capacity* - Airway resistance actively **increases** in asthma due to inflammation and bronchoconstriction, it does not decrease. - **Decreased total lung capacity** is inconsistent with the air-trapping pathophysiology of asthma. *Decreases airway resistance and increases total lung capacity* - Airway resistance in asthma is **increased**, not decreased, due to obstructed airflow. - While **total lung capacity** can be increased in chronic asthma due to hyperinflation, the correct answer focuses on the immediate effect of **increased residual volume**, which is the key pathophysiologic change during an acute attack.

Question 782: A patient presents with shortness of breath and cyanosis. An ABG shows a PaO2 of 55 mmHg. Which compensatory mechanism is likely to be activated?

A. Decreased cardiac output
B. Decreased erythropoietin production
C. Increased alveolar ventilation (Correct Answer)
D. Decreased alveolar ventilation

Explanation: ***Increased alveolar ventilation*** - **Hypoxemia** (PaO2 of 55 mmHg) is a powerful stimulus for the peripheral chemoreceptors, particularly the carotid bodies. - Activation of these chemoreceptors leads to an increase in the **rate and depth of breathing**, thereby increasing **alveolar ventilation** to improve oxygen uptake. *Decreased cardiac output* - In response to **hypoxemia**, the body typically tries to increase oxygen delivery to tissues by increasing **cardiac output**, not decreasing it. - A decreased cardiac output would further exacerbate tissue hypoxia. *Decreased erythropoietin production* - **Hypoxemia** stimulates the kidneys to increase the production of **erythropoietin**, not decrease it. - Increased erythropoietin production leads to an increase in **red blood cell mass**, which enhances the oxygen-carrying capacity of the blood as a long-term compensatory mechanism. *Decreased alveolar ventilation* - A **decreased alveolar ventilation** would worsen the hypoxemia by reducing the amount of oxygen reaching the alveoli and consequently the blood. - The body's immediate compensatory response to hypoxemia is to increase ventilation to counteract the low PaO2.

Question 783: Which of the following statements about Wright's spirometer is true?

A. Flow rates can be calculated
B. Gives false high values at low flow rates
C. Gives false low values at high flow rates
D. All of the options (Correct Answer)

Explanation: ***All of the options*** Wright's spirometer is a **vane-type spirometer** that measures respiratory volumes. All three statements about this device are correct: **Flow rates can be calculated:** - Wright's spirometer measures the **total volume** of air that passes through it - Flow rates can be calculated by dividing the measured volume by time **(flow = volume/time)** - This allows for determination of various flow parameters from the volume measurements **Gives false high values at low flow rates:** - At low flow rates, the mechanical **inertia of the vanes** causes them to continue rotating even after the flow has decreased - This leads to **overestimation** of the actual volume at slow flows - The device lacks sensitivity to detect when flow slows down rapidly **Gives false low values at high flow rates:** - At high flow rates, the **vanes cannot rotate fast enough** to keep up with the rapid airflow - This results in **underestimation** of the true volume at fast flows - The mechanical limitations prevent accurate capture of peak flows These characteristics make Wright's spirometer **less accurate at extreme flow rates** but still useful for measuring tidal volumes and minute ventilation in clinical settings.

Question 784: What happens to gas exchange when the Va/Q ratio approaches infinity?

A. Oxygen exchange is completely absent.
B. Gas exchange is impaired due to lack of blood flow. (Correct Answer)
C. Carbon dioxide exchange is completely absent.
D. Gas exchange remains normal.

Explanation: ***Gas exchange is impaired due to lack of blood flow.*** - When the **V̇A/Q̇ ratio approaches infinity**, it means **ventilation** (V̇A) is present but **perfusion** (Q̇) approaches zero. - This represents **alveolar dead space** - alveoli are ventilated but have no blood flow to participate in gas exchange. - **Both oxygen and carbon dioxide exchange are completely impaired** because there is no blood available to pick up O₂ or deliver CO₂ for elimination. - Clinical examples include **pulmonary embolism** and destroyed pulmonary vasculature. - This option correctly identifies the mechanism (lack of blood flow) and the outcome (impaired gas exchange for all gases). *Oxygen exchange is completely absent.* - While this statement is true, it is **incomplete** as it only addresses oxygen. - When perfusion is absent, **both O₂ and CO₂ exchange are equally affected**. - This option is too narrow and misses the complete physiological picture. *Carbon dioxide exchange is completely absent.* - Similar to the oxygen option, this is **incomplete** as it only mentions one gas. - Both gases require blood flow for exchange, so both are equally impaired. *Gas exchange remains normal.* - This is clearly **incorrect**. - V̇A/Q̇ → ∞ represents an extreme **ventilation-perfusion mismatch** with complete absence of perfusion. - This scenario results in severe impairment of all gas exchange.

Question 785: What is the definition of Functional Residual Capacity (FRC)?

A. After normal inspiration
B. After normal expiration (Correct Answer)
C. After forceful expiration
D. After forceful inspiration

Explanation: ***After normal expiration*** - **Functional Residual Capacity (FRC)** is the volume of air remaining in the lungs after a **normal, quiet exhalation** - It represents the sum of **Expiratory Reserve Volume (ERV)** and **Residual Volume (RV)** - This is the equilibrium point where the inward recoil of the lungs equals the outward recoil of the chest wall *After normal inspiration* - This would represent FRC plus the **tidal volume**, which is not a standard lung capacity measurement - The lungs are at their highest volume during a quiet breathing cycle at this point *After forceful expiration* - This describes the point at which only the **Residual Volume (RV)** remains in the lungs - All of the expiratory reserve volume has been expelled, leaving only RV - FRC exists *before* a forceful expiration, not after *After forceful inspiration* - This represents the **Total Lung Capacity (TLC)**, which is the maximum volume of air the lungs can hold - TLC = FRC + Inspiratory Capacity (IC), or RV + ERV + TV + IRV

Question 786: Respiratory acidosis is recognized primarily by an increase in which of the following?

A. PaCO2 (Correct Answer)
B. pH
C. HCO3-
D. PaO2

Explanation: ***PaCO2*** - **Respiratory acidosis** is directly caused by **hypoventilation**, leading to impaired **carbon dioxide (CO2)** elimination from the lungs. - The accumulation of **CO2** in the blood increases its partial pressure (**PaCO2**), which then reacts with water to form **carbonic acid**, lowering the blood **pH**. *PaO2* - **PaO2** (partial pressure of oxygen) usually decreases in conditions causing hypoventilation, but its increase is not the primary indicator of **respiratory acidosis**. - While both can be affected in respiratory compromise, **PaCO2** is the defining determinant of the respiratory component of acid-base balance. *HCO3-* - **HCO3-** (bicarbonate) is primarily involved in **metabolic acid-base balance** and acts as a buffer against acidity. - In **respiratory acidosis**, bicarbonate levels might increase as a compensatory mechanism (renal compensation) over time to buffer the excess acid, but an initial increase is not the primary hallmark of respiratory acidosis itself. *pH* - **pH** measures the overall acidity or alkalinity of the blood. In acidosis, the **pH** decreases. - While a low pH is present in acidosis, it is a *result* of the increased **PaCO2**, not the primary driver for recognizing respiratory acidosis.

Question 787: Which of the following factors can cause an increase in pulmonary arterial pressure?

A. Histamine
B. Hypoxia (Correct Answer)
C. ANP
D. PGI2

Explanation: ***Hypoxia*** - Hypoxia causes **pulmonary vasoconstriction**, which is a unique response of the pulmonary circulation compared to systemic circulation. - This vasoconstriction increases **pulmonary vascular resistance**, directly leading to an elevation in pulmonary arterial pressure. - This phenomenon is known as **hypoxic pulmonary vasoconstriction (HPV)**, an important physiological mechanism. *Histamine* - In the pulmonary vasculature, histamine primarily causes **vasodilation**, which would *decrease* pulmonary arterial pressure. - While it can cause bronchoconstriction, its direct effect on pulmonary arterial pressure is not an increase. *ANP* - **Atrial natriuretic peptide (ANP)** primarily causes **vasodilation** and diuresis. - This effect would lead to a *reduction* in blood volume and systemic vascular resistance, thereby *decreasing* pulmonary arterial pressure. *PGI2* - **Prostacyclin (PGI2)** is a potent **vasodilator** and **platelet aggregation inhibitor**. - Its vasodilatory action would lead to a *decrease* in pulmonary vascular resistance and thus *lower* pulmonary arterial pressure.

Question 788: Which of the following is a feature of pulmonary oxygen toxicity?

A. Decreased mucociliary transport in airways
B. Increased capillary endothelial permeability
C. Inhibition of phagocytosis function of alveolar macrophages
D. All of the options (Correct Answer)

Explanation: ***All of the options*** - All three listed features are well-established manifestations of **pulmonary oxygen toxicity** - **Oxygen free radicals** generated during prolonged exposure to high O₂ concentrations cause synergistic damage affecting multiple cellular and physiological processes - The combination of these effects leads to significant **lung injury** and respiratory dysfunction **Why each option is correct:** **Increased capillary endothelial permeability:** - Oxygen free radicals directly damage endothelial cells, disrupting tight junctions - Results in **pulmonary edema** and impaired gas exchange - One of the earliest manifestations of O₂ toxicity **Decreased mucociliary transport in airways:** - High O₂ concentrations impair ciliated epithelial cell function - Alters mucus viscosity and composition - Reduces clearance of inhaled particles and pathogens, increasing risk of **respiratory infections** **Inhibition of phagocytosis function of alveolar macrophages:** - Alveolar macrophages are highly susceptible to oxidative stress - Impaired ability to phagocytose pathogens and cellular debris - Compromises the **lung's immune defense** and promotes inflammation

Question 789: Which of the following statements about the O2-Hb dissociation curve is correct?

A. It demonstrates cooperative binding. (Correct Answer)
B. The curve is a straight line.
C. It is 100% saturated at a PO2 of 100 mmHg.
D. A hemoglobin molecule can carry 4 molecules of O2.

Explanation: ***It demonstrates cooperative binding.*** - **Cooperative binding** describes how the binding of one oxygen molecule to hemoglobin increases the affinity of the remaining binding sites for oxygen. - This property gives the O2-Hb dissociation curve its characteristic **sigmoid (S-shaped)** appearance, allowing for efficient oxygen loading in the lungs and unloading in the tissues. *The curve is a straight line.* - The O2-Hb dissociation curve is **sigmoid or S-shaped**, not a straight line, due to the phenomenon of cooperative binding. - A straight line would imply a constant affinity of hemoglobin for oxygen, which is not the case. *It is 100% saturated at a PO2 of 100 mmHg.* - Hemoglobin is typically around **97-98% saturated** at a PO2 of 100 mmHg (arterial blood). - Complete 100% saturation is rarely achieved under physiological conditions. *A hemoglobin molecule can carry 4 molecules of O2.* - While this statement is factually true (one hemoglobin molecule has **four heme groups** and can bind up to **four molecules of oxygen**), it describes the structure and oxygen-carrying capacity of hemoglobin rather than a characteristic of the dissociation **curve itself**. - The question asks about features of the O2-Hb dissociation curve, and cooperative binding is the key property that defines the curve's behavior and sigmoid shape.

Question 790: Closing volume is related to which of the following?

A. Tidal volume
B. Residual volume (Correct Answer)
C. Vital capacity
D. None of the options

Explanation: ***Residual volume*** - **Closing volume (CV)** is the lung volume at which the smallest airways in dependent lung regions begin to close during expiration. - CV is measured as the volume of gas expired from the beginning of airway closure (phase IV of the single-breath nitrogen test) down to **residual volume (RV)**. - **Closing Capacity (CC) = Closing Volume (CV) + Residual Volume (RV)**, demonstrating their direct mathematical relationship. - When CC exceeds FRC (functional residual capacity), airways close during normal tidal breathing, leading to gas trapping and V/Q mismatch. - CV increases with age, smoking, and obstructive lung diseases, encroaching on the expiratory reserve volume and eventually affecting tidal breathing. *Tidal volume* - **Tidal volume (TV)** is the volume of air inhaled or exhaled during normal, quiet breathing (approximately 500 mL in adults). - TV is not used in the measurement or definition of closing volume. - While increased CV can cause airway closure *during* tidal breathing (when CC > FRC), TV itself is not mathematically or definitionally related to CV. *Vital capacity* - **Vital capacity (VC)** is the maximum volume of air that can be exhaled after maximal inspiration (VC = IRV + TV + ERV). - VC is a measure of overall ventilatory capacity but does not specifically relate to the point at which airways begin to close. - CV represents a small fraction of the total lung volumes and is specifically about airway mechanics, not maximal breathing capacity. *None of the options* - This is incorrect because **residual volume** has a direct mathematical relationship with closing volume through the equation CC = CV + RV.

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