Respiratory System Practice Questions

Q: Early in an attack of asthma, which of the following sets of arterial blood values is most likely?

Low PO2 and low PCO2. **Explanation:** The correct answer is **Low PO2 and low PCO2**. **1. Why it is correct:** During an acute asthma attack, bronchospasm and airway inflammation lead to **Ventilation-Perfusion (V/Q) mismatch**. Some areas of the lung are poorly ventilated but well-perfused, leading to a drop in arterial oxygen levels (**Hypoxemia/Low PO2**). In the **early stage**, the body compensates for this hypoxia through a reflex increase in the respiratory rate (tachypnea). Because Carbon Dioxide ($CO_2$) is highly diffusible (20 times more than $O_2$), this hyperventilation effectively "washes out" $CO_2$ from the blood, resulting in **Hypocapnia (Low PCO2)** and respiratory alkalosis. **2. Why the other options are incorrect:** * **Option A & B:** These are incorrect because even a mild asthma attack typically causes enough V/Q mismatch to lower the $PO_2$ below normal levels. * **Option C:** An elevated $PCO_2$ (Hypercapnia) is a **late and ominous sign** in asthma. It indicates that the patient’s respiratory muscles are fatiguing, and they can no longer maintain the high minute ventilation required to blow off $CO_2$. **3. NEET-PG High-Yield Pearls:** * **The "Normal" PCO2 Trap:** In a severe asthma attack, a "normal" $PCO_2$ value is a **danger sign**. It suggests the patient is transitioning from hyperventilation to respiratory failure. * **Acid-Base Status:** Early asthma presents with **Respiratory Alkalosis**; late/status asthmaticus presents with **Respiratory Acidosis**. * **A-a Gradient:** The Alveolar-arterial (A-a) oxygen gradient is typically **increased** in asthma due to V/Q mismatch.

Q: What happens in decreased lung compliance?

Increased respiratory rate and decreased tidal volume. **Explanation:** The core concept behind this question is the **Work of Breathing (WOB)**. In conditions with **decreased lung compliance** (e.g., Pulmonary Fibrosis, ARDS, or Pulmonary Edema), the lungs become "stiff." To expand these stiff lungs, the body must overcome significant **elastic resistance**. 1. **Why Option A is correct:** To minimize the energy expenditure (WOB), the body adopts a **Rapid Shallow Breathing Pattern**. * **Decreased Tidal Volume ($V_T$):** Taking a deep breath requires significant pressure to stretch stiff elastic fibers. By decreasing $V_T$, the elastic work is minimized. * **Increased Respiratory Rate (RR):** To maintain adequate **Minute Ventilation** ($\text{RR} \times V_T$) and prevent hypercapnia, the body compensates for the low $V_T$ by increasing the frequency of breaths. 2. **Why other options are incorrect:** * **Options B & C:** Increasing Tidal Volume in a non-compliant lung would exponentially increase the elastic work of breathing, leading to rapid respiratory muscle fatigue. * **Options C & D:** Decreasing the respiratory rate alongside a low or high $V_T$ would result in inadequate alveolar ventilation, leading to respiratory failure. **NEET-PG High-Yield Pearls:** * **Elastic Work:** Increased in restrictive diseases (decreased compliance). Minimized by rapid, shallow breathing. * **Non-Elastic (Airway) Work:** Increased in obstructive diseases (e.g., Asthma, COPD). Minimized by **slow, deep breathing** (Decreased RR, Increased $V_T$). * **Compliance Formula:** $C = \Delta V / \Delta P$. In fibrosis, the slope of the Pressure-Volume curve shifts to the **right and downwards**. * **Total Work of Breathing:** Normally represents only ~5% of total oxygen consumption but can increase significantly in disease states.

Q: Anatomic dead space in a non-smoker under normal conditions is:

2.2 cc/kg. ### Explanation **1. Understanding the Correct Answer (Option A: 2.2 cc/kg)** Anatomic dead space refers to the volume of the conducting airways (from the nose/mouth down to the terminal bronchioles) where no gas exchange occurs because there are no alveoli. In a healthy, non-smoking adult, the anatomic dead space is roughly proportional to body size. The standard physiological estimate is **2.2 mL per kg (or 1 mL per pound)** of ideal body weight. For an average 70 kg adult, this equates to approximately **150 mL**. This volume is essential for warming and humidifying inspired air but does not contribute to the respiratory zone. **2. Analysis of Incorrect Options** * **Option B (5.1 cc/kg):** This value is significantly higher than physiological norms. Such a high dead space would imply severe pathological conditions or massive over-inflation of conducting zones, leading to inefficient ventilation. * **Option C (3.1 cc/kg):** While closer, this exceeds the standard 2.2 cc/kg ratio. It might be seen in specific clinical scenarios involving high PEEP (Positive End-Expiratory Pressure) or large instrumental dead space (e.g., long ventilator tubings), but it is not the "normal" value. * **Option D (1.5 cc/kg):** This value is too low for an adult. While children have a slightly different ratio, 2.2 cc/kg remains the standard benchmark for medical examinations. **3. NEET-PG High-Yield Pearls** * **Fowler’s Method:** Used to measure **Anatomic Dead Space** using single-breath nitrogen washout. * **Bohr’s Equation:** Used to measure **Physiological Dead Space** using arterial and expired $CO_2$ levels. * **Physiological vs. Anatomic:** In healthy individuals, Anatomic Dead Space $\approx$ Physiological Dead Space. In lung diseases (like COPD), Physiological Dead Space increases because of "Alveolar Dead Space" (ventilated but non-perfused alveoli). * **Positioning:** Dead space is higher when standing than when supine.

Q: Which of the following physiological conditions will lead to pulmonary vasodilation?

Baroreceptor stimulation. **Explanation:** The pulmonary circulation is unique because its primary function is gas exchange, and its vascular resistance is regulated differently compared to the systemic circulation. **1. Why Baroreceptor Stimulation is Correct:** The pulmonary vasculature is innervated by the autonomic nervous system. Stimulation of the **arterial baroreceptors** (located in the carotid sinus and aortic arch) in response to high systemic blood pressure triggers a reflex that increases parasympathetic activity and decreases sympathetic tone. This leads to **pulmonary vasodilation**, helping to accommodate volume and prevent pulmonary hypertension. **2. Why the Other Options are Incorrect:** * **Hypercapnia (A) and Chemoreceptor Stimulation (D):** In the lungs, hypercapnia (high $CO_2$) and acidosis (often sensed by chemoreceptors) act as potent **vasoconstrictors**. This is part of the body’s mechanism to divert blood flow away from poorly ventilated areas (where $CO_2$ is high) toward better-ventilated areas to optimize gas exchange. * **Decreased $PaCO_2$ (B):** While hypocapnia (low $CO_2$) generally causes vasodilation in the systemic and cerebral circulation, its effect on the pulmonary vasculature is relatively weak compared to the profound **Hypoxic Pulmonary Vasoconstriction (HPV)** triggered by low $O_2$. **Clinical Pearls for NEET-PG:** * **Hypoxic Pulmonary Vasoconstriction (HPV):** This is the most important local control mechanism. Unlike systemic vessels (which dilate during hypoxia), pulmonary vessels **constrict** in response to low alveolar $PO_2$. * **Nitric Oxide (NO):** The most potent endogenous pulmonary vasodilator; often used therapeutically in persistent pulmonary hypertension of the newborn (PPHN). * **Zone of West:** Remember that pulmonary vascular resistance is lowest at **Functional Residual Capacity (FRC)**.

Q: Which of the following is a neuroendocrine function of the lungs?

Angiotensin conversion. The lungs are not just organs for gas exchange; they also function as a vital metabolic and endocrine site. ### **Explanation of the Correct Answer** **Option B (Angiotensin conversion)** is the correct answer because the pulmonary capillary endothelium contains high concentrations of **Angiotensin-Converting Enzyme (ACE)**. This enzyme is responsible for converting **Angiotensin I** (decapeptide) into **Angiotensin II** (octapeptide), a potent vasoconstrictor. This conversion is a key step in the Renin-Angiotensin-Aldosterone System (RAAS), which regulates systemic blood pressure and fluid balance. ### **Analysis of Incorrect Options** * **Option A (Erythropoietin secretion):** Erythropoietin is primarily secreted by the **peritubular interstitial cells of the kidney** (85%) and the liver (15%) in response to hypoxia. The lungs do not produce this hormone. * **Option C (Surfactant manufacture):** While this is a vital lung function performed by **Type II Alveolar cells (Pneumocytes)**, it is considered a **secretory/exocrine** function rather than a neuroendocrine one. Surfactant reduces surface tension to prevent alveolar collapse. * **Option D (Fibrinolytic substance secretion):** The lungs do produce substances like plasminogen activator to dissolve small clots, but this is categorized under the **hematologic/protective** function of the pulmonary endothelium, not neuroendocrine signaling. ### **High-Yield NEET-PG Pearls** * **Metabolic Inactivation:** The lungs are responsible for the inactivation of **Bradykinin** (via ACE), **Serotonin**, and **Prostaglandins (E1, E2, F2α)**. * **Substances NOT cleared by lungs:** Epinephrine, Dopamine, and Angiotensin II pass through the pulmonary circulation unchanged. * **Kulchitsky Cells:** These are the actual neuroendocrine cells of the lung (Small Granular Cells). They are the cells of origin for **Small Cell Carcinoma** and **Carcinoid tumors**.

Q: In COPD, which of the following statements is true?

FEV1/FVC < 0.7. **Explanation:** Chronic Obstructive Pulmonary Disease (COPD) is characterized by persistent airflow limitation. The physiological hallmark of obstructive lung diseases is an increased resistance to airflow, particularly during expiration. **1. Why Option A is Correct:** In COPD, the **Forced Expiratory Volume in 1 second (FEV1)** decreases significantly more than the **Forced Vital Capacity (FVC)** due to airway narrowing and loss of elastic recoil. According to GOLD guidelines, a post-bronchodilator **FEV1/FVC ratio of 0.7 is seen in normal individuals or patients with **Restrictive Lung Diseases** (where both FEV1 and FVC decrease proportionately, or FVC decreases more). * **Option C & D:** In COPD, air becomes trapped in the distal airspaces (air-trapping). This leads to **Hyperinflation**, which causes an **increase** in **Residual Volume (RV)**, Functional Residual Capacity (FRC), and **Total Lung Capacity (TLC)**. Decreased RV and TLC are characteristic features of restrictive diseases like Interstitial Lung Disease (ILD). **High-Yield Clinical Pearls for NEET-PG:** * **Flow-Volume Loop:** In COPD, the expiratory limb shows a characteristic **"scooped-out" appearance**. * **Diffusion Capacity (DLCO):** Decreased in Emphysema (due to alveolar destruction) but typically normal in Chronic Bronchitis. * **Compliance:** Lung compliance is **increased** in emphysema due to the loss of elastic fibers.

Q: Spirometry cannot measure which of the following?

Residual Volume (RV). **Explanation:** Spirometry is a gold-standard pulmonary function test that measures the volume of air an individual can inhale or exhale as a function of time. However, it has a fundamental limitation: **it can only measure air that moves in and out of the lungs.** **Why Residual Volume (RV) is the correct answer:** Residual Volume is defined as the volume of air remaining in the lungs after a maximal forced expiration. Since this air never leaves the respiratory tract during normal or forced breathing maneuvers, a spirometer cannot "see" or measure it. Consequently, any lung capacity that includes RV—such as **Functional Residual Capacity (FRC)** and **Total Lung Capacity (TLC)**—also cannot be measured by simple spirometry. These require specialized techniques like Helium Dilution, Nitrogen Washout, or Body Plethysmography. **Why the other options are incorrect:** * **Tidal Volume (TV):** This is the volume of air inspired or expired during a normal resting breath. Since it involves active air movement, it is easily recorded. * **Inspiratory Reserve Volume (IRV):** This is the extra volume of air that can be inspired over and above the normal tidal volume. * **Expiratory Reserve Volume (ERV):** This is the extra volume of air that can be expired by forceful exertion after the end of a normal tidal expiration. **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic:** Spirometry cannot measure **"FRV"** (FRC, RV, and TLC). * **Vital Capacity (VC):** The maximum volume of air a person can expel from the lungs after maximum inhalation (VC = TV + IRV + ERV). It is the largest volume measurable by spirometry. * **Body Plethysmography:** This is the most accurate method to measure RV as it follows Boyle’s Law ($P_1V_1 = P_2V_2$) and accounts for trapped air in the thorax.

Q: Total lung capacity is dependent on which of the following?

Lung compliance. **Explanation:** **Total Lung Capacity (TLC)** is the maximum volume of air the lungs can hold after a maximal inspiratory effort. It is determined by the balance between the strength of the inspiratory muscles and the inward elastic recoil of the lungs. **Why Lung Compliance is Correct:** Compliance refers to the "distensibility" or the ease with which the lungs expand. TLC is directly dependent on lung compliance. In restrictive lung diseases (e.g., Pulmonary Fibrosis), compliance decreases, making the lungs "stiff" and reducing TLC. Conversely, in obstructive diseases like Emphysema, compliance increases due to the loss of elastic tissue, leading to hyperinflation and an increased TLC. **Analysis of Incorrect Options:** * **Size of Airway:** This primarily affects airway resistance and flow rates (like FEV1), not the total volume the lung can hold. * **Closing Tidal Volume:** This relates to the point during expiration when small airways in the dependent parts of the lung begin to close; it does not determine the maximum capacity of the lungs. * **Residual Volume (RV):** While RV is a component of TLC (TLC = VC + RV), it is a volume, not a physiological determinant. TLC is the independent variable that dictates the limits of other volumes based on the lung's physical properties. **High-Yield Clinical Pearls for NEET-PG:** * **TLC Formula:** TLC = Vital Capacity (VC) + Residual Volume (RV). * **Measurement:** TLC cannot be measured by simple spirometry (because it includes RV); it requires **Body Plethysmography** or Helium Dilution. * **Compliance Equation:** Compliance (C) = ΔV / ΔP. * **Surfactant:** Increases compliance by reducing surface tension, thereby preventing the collapse of alveoli and supporting TLC.

Question 1

Early in an attack of asthma, which of the following sets of arterial blood values is most likely?

Accepted Answer

Low PO2 and low PCO2

Answer

Normal PO2 and normal PCO2

Answer

Normal PO2 and low PCO2

Answer

Normal PO2 and elevated PCO2

Question 2

What will be the effect on respiration if a transaction is made between the pons and medulla?

Accepted Answer

Irregular and gasping

Answer

Apnea

Answer

No effect

Answer

Slow and deep

Question 3

What happens in decreased lung compliance?

Accepted Answer

Increased respiratory rate and decreased tidal volume

Answer

Increased respiratory rate and increased tidal volume

Answer

Decreased respiratory rate and increased tidal volume

Answer

Decreased respiratory rate and decreased tidal volume

Question 4

Anatomic dead space in a non-smoker under normal conditions is:

Accepted Answer

2.2 cc/kg

Answer

5.1 cc/kg

Answer

3.1 cc/kg

Answer

1.5 cc/kg

Question 5

Which of the following physiological conditions will lead to pulmonary vasodilation?

Accepted Answer

Baroreceptor stimulation

Answer

Hypercapnia

Answer

Decreased PaCO2

Answer

Chemoreceptor stimulation

Question 6

At which point is the concentration of CO2 the least?

Accepted Answer

Anatomical dead space at the end of inspiration

Answer

Anatomical dead space at the end of expiration

Answer

Alveoli at the end of inspiration

Answer

Alveoli at the end of expiration

Question 7

Which of the following is a neuroendocrine function of the lungs?

Accepted Answer

Angiotensin conversion

Answer

Erythropoietin secretion

Answer

Surfactant manufacture

Answer

Fibrinolytic substance secretion

Question 8

In COPD, which of the following statements is true?

Accepted Answer

FEV1/FVC < 0.7

Answer

FEV1/FVC > 0.7

Answer

RV is decreased

Answer

TLC is decreased

Question 9

Spirometry cannot measure which of the following?

Accepted Answer

Residual Volume (RV)

Answer

Tidal Volume (TV)

Answer

Inspiratory Reserve Volume (IRV)

Answer

Expiratory Reserve Volume (ERV)

Question 10

Total lung capacity is dependent on which of the following?

Accepted Answer

Lung compliance

Answer

Size of airway

Answer

Closing tidal volume

Answer

Residual volume

Respiratory System — MCQs

Respiratory System — MCQs

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