Respiratory Function Tests — MCQs
What is the air remaining in the lung after normal expiration?
A 50-year-old man who has worked in a coal mining factory for 16 years develops symptoms of progressively worsening breathlessness and cough with expectoration. Spirometry reveals values of FEV1 - 1.4 L and FVC 2.8 L. What could be the cause?
Which of the following statements about lung compliance is false?
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?
Which of the following statements is true regarding the diagnostic criteria for Chronic Obstructive Pulmonary Disease (COPD)?
Consider the following statements regarding respiratory function in old age: I. There is increasing ventilation-perfusion mismatch II. There is increased ventilatory response to hypoxia and hypercapnia III. There is a decline in maximum oxygen uptake leading to reduction in cardiorespiratory reserve IV. There is decline in the Forced Expiratory Volume to Forced Vital Capacity ratio (FEV1/FVC) by around 0.2% per year after the forties Which of the statements given above are correct?
What is the estimated PaO2 after giving FiO2 at 0.5 in a normal person?
A patient of Scleroderma presents with acute respiratory distress. Chest X-ray shows B/L reticular basilar shadows. What is the next line of investigation in this patient?
In forceful expiration, which of the following neurons gets fired?
Why does hyperventilation cause paresthesia?
Respiratory Function Tests Indian Medical PG Practice Questions and MCQs
Question 1: What is the air remaining in the lung after normal expiration?
- A. Tidal Volume (TV)
- B. Residual Volume (RV)
- C. Functional Residual Capacity (FRC) (Correct Answer)
- D. Vital Capacity (VC)
Explanation: ***Functional Residual Capacity (FRC)*** - **FRC** represents the volume of air remaining in the lungs after a **normal expiration**. - It is the sum of the **expiratory reserve volume (ERV)** and the **residual volume (RV)**. *Tidal Volume (TV)* - **TV** is the volume of air inspired or expired with a **normal breath**. - It does not represent the total air remaining in the lungs after expiration. *Residual Volume (RV)* - **RV** is the volume of air remaining in the lungs after a **maximal expiration**. - It is a component of FRC but does not fully describe the air remaining after a *normal* expiration. *Vital Capacity (VC)* - **VC** is the maximum volume of air that can be exhaled after a **maximal inspiration**. - It represents the maximum amount of air that can be exchanged with a single breath, not the air remaining after normal expiration.
Question 2: A 50-year-old man who has worked in a coal mining factory for 16 years develops symptoms of progressively worsening breathlessness and cough with expectoration. Spirometry reveals values of FEV1 - 1.4 L and FVC 2.8 L. What could be the cause?
- A. Silicosis
- B. Hypersensitivity pneumonitis
- C. COPD (Correct Answer)
- D. Idiopathic pulmonary fibrosis
Explanation: ***COPD*** - Working in a **coal mining factory** for 16 years is a significant occupational exposure for developing **Chronic Obstructive Pulmonary Disease (COPD)**, particularly **coal workers' pneumoconiosis** which can manifest as COPD [1], [3]. - The spirometry values show a **reduced FEV1/FVC ratio** (1.4/2.8 = 0.5), which is characteristic of an **obstructive lung disease** like COPD [3]. *Silicosis* - While silicosis is an occupational lung disease associated with exposure to **silica dust**, it typically presents as a **restrictive lung disease**, meaning both FEV1 and FVC would be reduced proportionally, or FVC would be reduced more significantly than FEV1 [1]. - The spirometry pattern in this case is clearly **obstructive**, with a disproportionate reduction in FEV1 relative to FVC. *Hypersensitivity pneumonitis* - This is an **immunological reaction** to inhaled organic or chemical antigens, often presenting with symptoms like cough, dyspnea, and fever, but it usually causes a **restrictive or mixed ventilatory defect**. - There is no information provided about specific organic or chemical exposures typically associated with hypersensitivity pneumonitis in a coal mining setting, and the spirometry pattern is obstructive. *Idiopathic pulmonary fibrosis* - This is a **restrictive lung disease** characterized by progressive scarring of the lung tissue, leading to reduced lung volumes (both FEV1 and FVC are reduced, often with a normal or increased FEV1/FVC ratio) [2]. - The spirometry results showing an **obstructive pattern** (reduced FEV1/FVC ratio) rule out idiopathic pulmonary fibrosis as the primary cause [2].
Question 3: 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 4: 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 5: Which of the following statements is true regarding the diagnostic criteria for Chronic Obstructive Pulmonary Disease (COPD)?
- A. A post-bronchodilator FEV1/FVC ratio above the threshold indicates normal lung function.
- B. A post-bronchodilator FEV1/FVC ratio below the threshold indicates airflow limitation. (Correct Answer)
- C. Residual Volume (RV) is normal.
- D. Total Lung Capacity (TLC) is decreased.
Explanation: ***A post-bronchodilator FEV1/FVC ratio below the threshold indicates airflow limitation.*** [1] - This is the **hallmark diagnostic criterion** for COPD, confirming persistent **airflow obstruction** that is not fully reversible. [1] - The threshold typically used is **< 0.70** or below the **fifth percentile** of the lower limit of normal (LLN). *A post-bronchodilator FEV1/FVC ratio above the threshold indicates normal lung function.* - An FEV1/FVC ratio **above the threshold** indicates the absence of significant **airflow obstruction**, but does not automatically guarantee normal lung function as other parameters like **FEV1** could be affected. - This measurement would suggest a **restrictive lung disease** or **normal lung function**, depending on other spirometry values. *Residual Volume (RV) is normal.* - In COPD, **air trapping** due to airflow obstruction leads to an **increased Residual Volume (RV)**, not a normal RV. - An elevated RV reflects **hyperinflation** of the lungs, a characteristic feature of emphysema and chronic bronchitis. *Total Lung Capacity (TLC) is decreased.* - COPD is characterized by **hyperinflation**, which typically results in an **increased Total Lung Capacity (TLC)** as the lungs become more distended. - A **decreased TLC** would be indicative of a **restrictive lung disease**, which is different from obstructive patterns seen in COPD.
Question 6: Consider the following statements regarding respiratory function in old age: I. There is increasing ventilation-perfusion mismatch II. There is increased ventilatory response to hypoxia and hypercapnia III. There is a decline in maximum oxygen uptake leading to reduction in cardiorespiratory reserve IV. There is decline in the Forced Expiratory Volume to Forced Vital Capacity ratio (FEV1/FVC) by around 0.2% per year after the forties Which of the statements given above are correct?
- A. I, III and IV (Correct Answer)
- B. I, II and IV
- C. II, III and IV
- D. I, II and III
Explanation: ***I, III and IV*** - With aging, there is a **loss of elastic recoil** in the lungs and a structural decrease in **alveolar surface area**, leading to increased **ventilation-perfusion (V/Q) mismatch** as gravity-dependent areas collapse. - The **maximum oxygen uptake (VO2 max)** declines with age due to reduced cardiac output and skeletal muscle mass, thus decreasing **cardiorespiratory reserve**. The **FEV1/FVC ratio** also decreases by approximately **0.2% per year** after age 40 because of reduced elastic recoil and increased airway collapsibility. *I, II and IV* - While statement I and IV are correct, statement II is incorrect because the **ventilatory response to hypoxia and hypercapnia** actually **decreases** with age. - Older adults have a blunted response to changes in oxygen and carbon dioxide levels, making them more susceptible to respiratory compromise. *II, III and IV* - Statement II is incorrect as the **ventilatory response to hypoxia and hypercapnia decreases** with age, not increases. - Statements III and IV accurately describe the decline in **maximum oxygen uptake** and the **FEV1/FVC ratio** with aging. *I, II and III* - Statement II is incorrect; the **ventilatory response to hypoxia and hypercapnia is diminished** in older adults. - Statements I and III correctly identify increased **ventilation-perfusion mismatch** and decreased **maximum oxygen uptake** as age-related changes in respiratory function.
Question 7: What is the estimated PaO2 after giving FiO2 at 0.5 in a normal person?
- A. > 200 mmHg (Correct Answer)
- B. < 100 mmHg
- C. 150–200 mmHg
- D. 100–150 mmHg
Explanation: ***> 200 mmHg*** - In a **normal healthy person** breathing FiO2 of 0.5 (50% oxygen), the expected **PaO2** is typically **250-300 mmHg**. - Using the **alveolar gas equation**: PAO2 = FiO2(PB - PH2O) - PaCO2/RQ = 0.5(760 - 47) - 40/0.8 ≈ **306 mmHg** - The normal **A-a gradient** is 5-15 mmHg, so PaO2 = 306 - 10 ≈ **296 mmHg** - **Clinical rule of thumb**: PaO2 ≈ 5 × FiO2% = 5 × 50 = **250 mmHg** (approximation accounting for physiological shunt) - Therefore, the expected range is clearly **> 200 mmHg** in a normal individual *150–200 mmHg* - This range would indicate **mild oxygenation impairment** or increased shunt fraction - While adequate for tissue oxygenation, this is **lower than expected** for a normal person on 50% oxygen - May suggest underlying **mild V/Q mismatch** or early pulmonary dysfunction *100–150 mmHg* - This represents **moderate impairment** in oxygen transfer - Indicates significant **pulmonary pathology** such as pneumonia, ARDS, or substantial shunt - Not consistent with normal lung function on FiO2 0.5 *< 100 mmHg* - This represents **severe hypoxemia** despite supplemental oxygen - Indicates **critical pulmonary dysfunction** with large shunt or severe V/Q mismatch - Requires immediate intervention and is never expected in a healthy individual on 50% oxygen
Question 8: A patient of Scleroderma presents with acute respiratory distress. Chest X-ray shows B/L reticular basilar shadows. What is the next line of investigation in this patient?
- A. High resolution CT to characterize the lung parenchyma. (Correct Answer)
- B. Pulmonary function tests to assess lung function.
- C. Contrast-enhanced CT scan for vascular assessment.
- D. Echocardiography to evaluate cardiac complications.
Explanation: ***High resolution CT*** - A **high-resolution CT (HRCT) scan** is the gold standard for evaluating **interstitial lung disease (ILD)**, which is commonly seen in **scleroderma** and presents with basilar reticular shadows on chest X-ray. - HRCT provides detailed images of the lung parenchyma, allowing for accurate characterization of the **fibrotic changes** and extent of ILD. *Pulmonary function tests to assess lung function.* - **Pulmonary function tests (PFTs)** provide functional information about lung capacity and gas exchange but do not offer detailed anatomical imaging of the lung parenchyma. - While essential for monitoring disease progression and severity, PFTs are not the primary diagnostic tool to further characterize the **reticular basilar shadows** seen on X-ray in an acute setting. *Contrast-enhanced CT scan for vascular assessment.* - A **contrast-enhanced CT scan** is primarily used to assess **vascular structures** or rule out conditions like **pulmonary embolism**, which is not directly indicated by the description of bilateral reticular basilar shadows. - The primary concern here is **interstitial lung disease**, which is best evaluated by **HRCT** without contrast. *Echocardiography to evaluate cardiac complications.* - **Echocardiography** is used to assess cardiac function and look for complications like **pulmonary hypertension** or **myocardial fibrosis**, which can occur in scleroderma. - However, it does not directly evaluate the **lung parenchyma** or the cause of the reticular basilar shadows.
Question 9: In forceful expiration, which of the following neurons gets fired?
- A. DRG
- B. Chemoreceptors
- C. VRG (Correct Answer)
- D. Pneumotaxic centre
Explanation: ***VRG (Correct Answer)*** - The **ventral respiratory group (VRG)** contains neurons that are active during both **inspiration** and **expiration**, particularly during forceful or active breathing. - During **forceful expiration**, the **expiratory neurons** within the VRG are stimulated, sending signals to the **abdominal muscles and internal intercostals** to contract and increase the rate of airflow out of the lungs. - These neurons fire actively to produce the motor output needed for active expiration. *DRG* - The **dorsal respiratory group (DRG)** primarily controls **inspiration** and is active during both quiet and forceful inspiration. - It contains mainly inspiratory neurons that control the diaphragm and external intercostals. - While it can influence the rhythm of breathing, its direct role is not in generating the active muscle contractions required for forceful expiration. *Chemoreceptors* - **Chemoreceptors** (central and peripheral) monitor blood levels of **oxygen, carbon dioxide, and pH** and send input to the respiratory centers in the brainstem. - They are sensory receptors providing afferent input, not motor neurons that directly fire to cause muscle contraction for forceful expiration. - They modify the activity of the respiratory groups but do not directly control expiratory muscles. *Pneumotaxic centre* - The **pneumotaxic center** (located in the upper pons) fine-tunes the breathing rhythm and limits the duration of inspiration. - It plays a role in making breathing smooth and preventing overinflation of the lungs by inhibiting the apneustic center. - It is not directly involved in generating the motor commands for forceful expiration.
Question 10: Why does hyperventilation cause paresthesia?
- A. Increased O2
- B. Decreased CO2 (Correct Answer)
- C. Decreased pH
- D. Increased CO2
Explanation: ***Decreased CO2*** - Hyperventilation leads to an excessive loss of **carbon dioxide (CO2)** from the body, causing **respiratory alkalosis**. - The resulting alkalosis decreases the concentration of **ionized calcium** in the blood, leading to neuronal excitability and thus paresthesia. *Increased O2* - While hyperventilation increases the amount of **oxygen (O2)** breathed in, it is not the direct cause of paresthesia. - The key physiological change leading to paresthesia is related to changes in **blood gas chemistry**, specifically CO2 and pH. *Decreased pH* - Hyperventilation causes a **decrease in CO2**, which subsequently leads to an **increase in pH** (respiratory alkalosis), not a decrease in pH. - A decrease in pH (acidosis) generally leads to different symptoms, and is not the cause of paresthesia in this context. *Increased CO2* - Hyperventilation by definition involves **expelling more CO2** than normal, leading to a decrease in CO2 levels, not an increase. - An underlying increase in CO2 would lead to **respiratory acidosis**, which has a different clinical presentation.
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