Applied Respiratory Physiology — MCQs
Which of the following is a common cause of hypoxia due to ventilation-perfusion mismatch?
Which of the following factors does not directly influence oxygen delivery to tissues?
What does zero pressure indicate in the pressure-volume curve?
In acute respiratory distress syndrome (ARDS), which type of cell is primarily damaged?
Patient of pneumonia on ventilator with wt. 50 kg. RR 14/min, bicarbonate - 18, pH 7.3, pCO2 48 mmHg, pO2 110 mmHg, PEEP 12 cm H2O, tidal volume 420 mL, SpO2 - 100% with FiO2 90%. What is next step in management?
Which of the following laboratory findings most directly indicates tissue hypoxia in a patient with chronic obstructive pulmonary disease (COPD)?
Blood gas measurements of a patient show the following values: pH 7.2, pCO2 80 mm Hg, and pO2 46 mm Hg. Which of the following could be the most probable diagnosis?
In an emphysematous patient with bullous lesions, which is the best investigation to measure lung volumes?
Which of the following conditions are contraindications for noninvasive positive-pressure ventilation in patients with respiratory failure? I. Craniofacial abnormalities II. Significant burns III. Respiratory failure with PaCO_2 of 60 mm Hg IV. Cardiovascular instability Select the correct answer using the code given below :
Which of the following parameters is most critical for maintaining optimal oxygenation?
Applied Respiratory Physiology Indian Medical PG Practice Questions and MCQs
Question 1: Which of the following is a common cause of hypoxia due to ventilation-perfusion mismatch?
- A. Methemoglobinemia
- B. Pulmonary embolism (Correct Answer)
- C. Anemia
- D. Asthma
Explanation: ***Pulmonary embolism*** - A **pulmonary embolism** blocks blood flow to a portion of the lung, but ventilation to that area may remain intact, creating a high V/Q ratio as **perfusion is reduced** relative to ventilation [1]. - This **V/Q mismatch** means that ventilated alveoli are not adequately perfused, preventing efficient gas exchange and leading to hypoxemia [1]. *Methemoglobinemia* - This condition involves an altered form of hemoglobin that cannot bind oxygen or releases it abnormally, leading to **functional anemia** and tissue hypoxia [2]. - While it causes hypoxia, it primarily affects the **oxygen-carrying capacity of blood** rather than causing a ventilation-perfusion mismatch within the lungs [2]. *Anemia* - **Anemia** is a reduction in the number of red blood cells or the amount of hemoglobin, leading to a decreased **oxygen-carrying capacity** of the blood [2]. - It results in **hypoxic hypoxia** due to insufficient oxygen delivery to tissues, but it does not primarily cause a V/Q mismatch in the lungs [2]. *Asthma* - **Asthma** causes **airway obstruction** (bronchoconstriction, mucus plugging, inflammation), leading to areas of reduced ventilation. - While asthma can cause V/Q mismatch (low V/Q areas), it's typically due to **impaired ventilation**, whereas pulmonary embolism primarily causes mismatch by impairing perfusion [1].
Question 2: Which of the following factors does not directly influence oxygen delivery to tissues?
- A. Type of fluid administered (Correct Answer)
- B. Cardiac output
- C. Oxygen saturation
- D. Hemoglobin concentration
Explanation: ***Type of fluid administered*** - While fluid administration can indirectly affect oxygen delivery by altering blood volume and cardiac output, the **type of fluid itself (e.g., crystalloid vs. colloid)** does not directly influence the oxygen-carrying capacity of the blood or its release to tissues. - The direct effect of fluid resuscitation is on **hemodynamic parameters**, which then influence delivery. *Oxygen saturation* - **Oxygen saturation** directly reflects the percentage of hemoglobin binding sites occupied by oxygen, thus determining the amount of oxygen carried by each unit of blood. - A decrease in oxygen saturation significantly reduces the **total oxygen content** available for tissue delivery. *Cardiac output* - **Cardiac output** (heart rate × stroke volume) is a primary determinant of blood flow to tissues, and therefore directly influences the rate at which oxygenated blood is delivered throughout the body. - A lower cardiac output leads to **reduced oxygen delivery** despite adequate oxygen content in the blood. *Hemoglobin concentration* - **Hemoglobin concentration** directly dictates the blood's capacity to carry oxygen, as hemoglobin is the main oxygen-carrying molecule in red blood cells. - A low hemoglobin concentration (anemia) results in **decreased oxygen-carrying capacity** and thus impaired oxygen delivery to tissues.
Question 3: What does zero pressure indicate in the pressure-volume curve?
- A. Functional residual capacity (Correct Answer)
- B. Inspiratory reserve volume
- C. Tidal volume
- D. Residual volume
Explanation: ***Functional residual capacity*** - This is the lung volume at which the **elastic recoil of the lungs** exactly balances the **elastic recoil of the chest wall**, resulting in zero net pressure across the respiratory system. - At **functional residual capacity (FRC)**, there is no airflow, and the **alveolar pressure equals atmospheric pressure (zero)**, indicating the equilibrium point. - Note: The **transpulmonary pressure remains positive** at FRC (approximately +5 cm H₂O), which keeps the lungs inflated against their elastic recoil. *Inspiratory reserve volume* - This is the **extra volume of air** that can be forcibly inhaled after a normal inspiration. - It involves active inspiration and therefore is associated with a **negative intrathoracic pressure**, not zero pressure. *Tidal volume* - This is the **volume of air inhaled and exhaled** during a normal quiet breathing cycle. - While breathing, pressures fluctuate, and the respiratory system is not at an equilibrium point of **zero pressure** throughout the tidal breath. *Residual volume* - This is the **volume of air remaining in the lungs** after a maximal exhalation. - The chest wall's outward recoil is greater than the lung's inward recoil at this point, resulting in a **negative intrapleural pressure** to keep the lungs from collapsing.
Question 4: In acute respiratory distress syndrome (ARDS), which type of cell is primarily damaged?
- A. Type 2 pneumocytes
- B. Type 1 pneumocytes (Correct Answer)
- C. Alveolar macrophages
- D. Bronchial epithelial cells
Explanation: ***Type 1 pneumocytes*** - These cells form an **extensive network of thin cells** that cover approximately 95% of the alveolar surface and are primarily responsible for **gas exchange** [4]. - Their thinness and large surface area make them particularly vulnerable to injury during the **initial inflammatory phase of ARDS**, leading to increased permeability and alveolar edema [1]. *Type 2 pneumocytes* - While important for producing **surfactant** and differentiating into Type 1 pneumocytes during repair, Type 2 cells are generally **more resistant to acute injury** than Type 1 cells [2]. - They play a role in the **repair phase** of ARDS, regenerating damaged alveolar epithelium [2]. *Alveolar macrophages* - These are **immune cells** that reside in the alveoli, primarily responsible for **phagocytosis** of foreign particles and initiating immune responses [3]. - While they are activated and contribute to the inflammation in ARDS, they are not the primary cells damaged in the early stages as the epithelial barrier cells are [1]. *Bronchial epithelial cells* - These cells line the airways (bronchi and bronchioles) and are involved in **mucociliary clearance** [3]. - While severe lung injury can extend to these areas, the hallmark of ARDS is damage primarily to the **alveolar-capillary membrane**, not the larger airways.
Question 5: Patient of pneumonia on ventilator with wt. 50 kg. RR 14/min, bicarbonate - 18, pH 7.3, pCO2 48 mmHg, pO2 110 mmHg, PEEP 12 cm H2O, tidal volume 420 mL, SpO2 - 100% with FiO2 90%. What is next step in management?
- A. Increase PEEP
- B. Increase tidal volume
- C. Decrease fio2 (Correct Answer)
- D. Decrease RR
Explanation: **Decrease FiO2** - The patient has an **SpO2 of 100% with a FiO2 of 90%**, indicating **hyperoxia** induced by excessive oxygen delivery. - Decreasing FiO2 is the appropriate next step to prevent **oxygen toxicity** (e.g., absorption atelectasis, free radical damage) while maintaining adequate oxygenation. *Increase PEEP* - The patient's **PaO2 of 110 mmHg** is already well within the normal to high range, suggesting that oxygenation is adequate. - Increasing PEEP would be considered if the patient had **refractory hypoxemia**, not hyperoxia. *Increase tidal volume* - The current tidal volume of **420 mL for a 50 kg patient (8.4 mL/kg)** is already at the higher end of lung-protective ventilation (typically 6-8 mL/kg). - Increasing tidal volume further could lead to **ventilator-induced lung injury** (VILI) due to volutrauma, especially in a patient with pneumonia. *Decrease RR* - The patient has a **pCO2 of 48 mmHg** and a **pH of 7.3**, indicating **respiratory acidosis** (hypoventilation). - Decreasing the respiratory rate would further exacerbate the acidosis by reducing minute ventilation and increasing pCO2, which is inappropriate.
Question 6: Which of the following laboratory findings most directly indicates tissue hypoxia in a patient with chronic obstructive pulmonary disease (COPD)?
- A. Elevated hematocrit
- B. Elevated lactic acid levels (Correct Answer)
- C. Increased erythropoietin levels
- D. Hypercapnia
Explanation: ***Elevated lactic acid levels*** - **Lactic acid** is a direct byproduct of **anaerobic metabolism**, which occurs when tissues are deprived of sufficient oxygen (hypoxia) [2]. - An increase in lactic acid indicates that cells are unable to meet their energy demands through aerobic pathways [2]. *Elevated hematocrit* - An elevated hematocrit signifies **polycythemia**, a compensatory mechanism to increase the oxygen-carrying capacity of the blood in response to chronic hypoxia. - While it indicates a chronic state of low oxygen, it's an *adaptive response* rather than a direct measure of immediate tissue hypoxia. *Increased erythropoietin levels* - **Erythropoietin (EPO)** is a hormone released by the kidneys in response to hypoxia, stimulating red blood cell production. - Like elevated hematocrit, increased EPO levels reflect the body's long-term *compensatory response* to hypoxia rather than a direct indicator of immediate tissue oxygen deprivation. *Hypercapnia* - **Hypercapnia** is an elevated level of carbon dioxide in the blood, often due to hypoventilation in COPD [1]. - While it frequently co-occurs with hypoxia in respiratory failure, it is a measure of CO2 retention, not a direct indicator of tissue oxygenation status [1].
Question 7: Blood gas measurements of a patient show the following values: pH 7.2, pCO2 80 mm Hg, and pO2 46 mm Hg. Which of the following could be the most probable diagnosis?
- A. Acute exacerbation of COPD (Correct Answer)
- B. Acute bronchospasm
- C. Pulmonary embolism
- D. Chronic pneumonia
Explanation: ***Acute exacerbation of COPD*** - The patient presents with **respiratory acidosis** (pH 7.2, normal 7.35-7.45) and **hypercapnia** (pCO2 80 mm Hg, normal 35-45 mm Hg), combined with severe **hypoxemia** (pO2 46 mm Hg, normal 80-100 mm Hg) [2]. - This pattern is highly indicative of an acute exacerbation of **Chronic Obstructive Pulmonary Disease**, where worsening airflow obstruction leads to inadequate alveolar ventilation and impaired gas exchange; clinical evidence suggests long-term oxygen therapy can decrease mortality in these chronic patients [1]. *Acute bronchospasm* - While acute bronchospasm can cause hypoxemia and hypercapnia, the degree of hypercapnia (pCO2 80 mm Hg) seen here is typically more severe and prolonged than commonly observed in isolated bronchospasm. Indications for assisted ventilation in severe asthma include a rising PaCO2 above 45 mmHg [3]. - Acute bronchospasm would likely result in less pronounced acidosis and more rapid response to bronchodilator therapy, which isn't described. *Pulmonary embolism* - Pulmonary embolism typically causes **hypoxemia** and **hypocapnia** (low pCO2) due to reflex hyperventilation in response to V/Q mismatch, which contradicts the presented blood gas values [2]. - The primary defect in pulmonary embolism is an obstruction of blood flow, not a global ventilation impairment leading to severe hypercapnia. *Chronic pneumonia* - Chronic pneumonia can cause **hypoxemia** due to V/Q mismatch or shunting, but it generally leads to **hypocapnia** or normal pCO2 if the patient is able to compensate by increasing ventilation [2]. - Severe hypercapnia (pCO2 80 mm Hg) with acute acidosis is less typical for uncomplicated chronic pneumonia, unless it's a very advanced or acute severe presentation with respiratory muscle fatigue.
Question 8: In an emphysematous patient with bullous lesions, which is the best investigation to measure lung volumes?
- A. Body plethysmography (Correct Answer)
- B. Helium dilution
- C. Trans diaphragmatic pressure
- D. DLCO
Explanation: ***Body plethysmography*** - This method measures **total lung capacity (TLC)** by applying **Boyle's Law** and is not significantly affected by **trapped air** in bullae. - It directly measures changes in volume and pressure within a sealed chamber, providing accurate lung volumes even in the presence of **non-communicating air spaces**. *Helium dilution* - The **helium dilution technique** underestimates lung volumes in conditions with **trapped air** or poorly communicating air spaces, such as **bullae**, because helium cannot diffuse into these areas. - This method relies on the equilibration of a known amount of helium throughout the lungs, which is unreliable when significant parts of the lung are not ventilated. *Trans diaphragmatic pressure* - **Transdiaphragmatic pressure (Pdi)** is primarily used to assess **diaphragmatic strength and function**, not for measuring static lung volumes. - It involves measuring the pressure difference between the gastric and esophageal balloons and is unrelated to **total lung capacity** or **residual volume**. *DLCO* - **Diffusing capacity of the lung for carbon monoxide (DLCO)** measures the efficiency of gas transfer from the alveoli to the red blood cells, not lung volumes. - While it is a valuable test in emphysema (typically reduced), it does not provide information about the **absolute volumes of the lung**.
Question 9: Which of the following conditions are contraindications for noninvasive positive-pressure ventilation in patients with respiratory failure? I. Craniofacial abnormalities II. Significant burns III. Respiratory failure with PaCO_2 of 60 mm Hg IV. Cardiovascular instability Select the correct answer using the code given below :
- A. I, III and IV
- B. II, III and IV
- C. I, II and IV (Correct Answer)
- D. I, II and III
Explanation: ***I, II and IV*** - **Craniofacial abnormalities** (I) can prevent a proper mask seal, leading to air leaks and ineffective ventilation. - **Significant burns** (II), especially on the face, can make mask application impossible due to pain, skin integrity issues, and infection risk. - **Cardiovascular instability** (IV), such as severe hypotension or active myocardial ischemia, can be worsened by the positive intrathoracic pressure applied by NPPV, which can decrease venous return and cardiac output. *I, III and IV* - While **craniofacial abnormalities** (I) and **cardiovascular instability** (IV) are contraindications, NPPV can be beneficial for **respiratory failure with a PaCO2 of 60 mm Hg** (III) as it helps reduce CO2 levels and avoids intubation. - Therefore, including III as a contraindication makes this option incorrect. *II, III and IV* - **Significant burns** (II) and **cardiovascular instability** (IV) are clear contraindications. However, **respiratory failure with a PaCO2 of 60 mm Hg** (III) is often an indication for NPPV, not a contraindication. - This option incorrectly identifies a key indication as a contraindication. *I, II and III* - **Craniofacial abnormalities** (I) and **significant burns** (II) are valid contraindications for NPPV. - However, **respiratory failure with a PaCO2 of 60 mm Hg** (III) is a common indication for NPPV, especially in conditions like COPD exacerbations, as it helps improve ventilation and reduce hypercapnia.
Question 10: Which of the following parameters is most critical for maintaining optimal oxygenation?
- A. FiO2
- B. Respiratory rate
- C. PEEP (Correct Answer)
- D. Tidal volume
Explanation: ***PEEP*** - **Positive End-Expiratory Pressure (PEEP)** is crucial for maintaining optimal oxygenation because it prevents **alveolar collapse** at the end of expiration, thereby increasing the **functional residual capacity** and improving gas exchange. - By keeping alveoli open, PEEP increases the number of available alveoli for ventilation, preventing **atelectasis** and optimizing the **venous admixture** from non-ventilated lung units. *FiO2* - While **Fraction of Inspired Oxygen (FiO2)** is essential for providing sufficient oxygen, simply increasing FiO2 without proper alveolar recruitment and patency (often achieved with PEEP) can be less effective and potentially harmful due to **oxygen toxicity**. - High FiO2 can improve oxygenation in cases of **hypoxemia**, but it doesn't address underlying problems like **alveolar collapse** or **ventilation-perfusion mismatch** as directly as PEEP does. *Respiratory rate* - **Respiratory rate** primarily affects **carbon dioxide elimination** (PaCO2) and, to some extent, alveolar ventilation. - While an adequate respiratory rate is necessary for overall gas exchange, it is not the most direct or critical parameter for optimizing **oxygenation** compared to PEEP's role in maintaining alveolar patency. *Tidal volume* - **Tidal volume** also primarily affects **carbon dioxide elimination** and plays a role in overall minute ventilation. - Excessive tidal volume can lead to **ventilator-induced lung injury (VILI)**, while insufficient tidal volume can reduce minute ventilation, but it does not directly optimize oxygenation by preventing **alveolar collapse** in the same way PEEP does.
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