Respiratory System Practice Questions

Q: Calculate the minute ventilation from the spirogram assuming the respiratory rate as 12/min?

6 L/min. ***6 L/min*** - **Minute ventilation** = **Tidal Volume** × **Respiratory Rate** = 500 mL × 12/min = 6000 mL/min = **6 L/min**. - From the spirogram, the **tidal volume** is typically **500 mL** during quiet breathing at rest. *1 L/min* - This would require a **tidal volume** of only 83 mL (1000 mL ÷ 12), which is far below normal physiological values. - Normal **tidal volume** ranges from **400-600 mL**, making this calculation incorrect. *2 L/min* - This would correspond to a **tidal volume** of 167 mL (2000 mL ÷ 12), still significantly below normal. - Such low minute ventilation would result in **hypoventilation** and inadequate gas exchange. *4 L/min* - This implies a **tidal volume** of 333 mL (4000 mL ÷ 12), which is below the normal range. - While closer to normal values, it underestimates the actual **tidal volume** observed on spirograms.

Q: The ratio of carbon dioxide produced to oxygen consumed is known as what?

Respiratory quotient. **Explanation:** The correct answer is **Respiratory Quotient (RQ)**. **1. Why Respiratory Quotient is Correct:** The Respiratory Quotient is the ratio of the volume of carbon dioxide ($CO_2$) produced to the volume of oxygen ($O_2$) consumed per unit of time at the cellular level. It is calculated as: $$RQ = \frac{\text{Volume of } CO_2 \text{ produced}}{\text{Volume of } O_2 \text{ consumed}}$$ The value of RQ depends entirely on the type of substrate being oxidized for energy. For example, the RQ for carbohydrates is **1.0**, for lipids it is **0.7**, and for proteins it is approximately **0.8**. **2. Why the Other Options are Incorrect:** * **Basal Metabolic Rate (BMR):** This refers to the minimum amount of energy required by the body to maintain vital functions (like breathing and circulation) at complete rest. It is measured in calories, not as a gas ratio. * **Specific Dynamic Action (SDA):** Also known as the thermic effect of food, this is the extra heat production by the body over the basal metabolic rate during the digestion and processing of food. * **Partial Pressure of Carbon Dioxide ($PCO_2$):** This is the individual pressure exerted by $CO_2$ in a mixture of gases or dissolved in blood. It is measured in mmHg or kPa, not as a ratio. **3. High-Yield Clinical Pearls for NEET-PG:** * **Respiratory Exchange Ratio (RER):** While RQ is measured at the cellular level, RER is measured at the mouth (expired air). In steady-state conditions, RQ = RER. * **Mixed Diet:** The average RQ for an individual on a standard mixed diet is **0.82**. * **Overfeeding/Lipogenesis:** If the RQ exceeds **1.0**, it indicates lipogenesis (conversion of carbohydrates to fats), often seen in overfed patients on TPN (Total Parenteral Nutrition). * **Starvation:** During prolonged starvation or uncontrolled Diabetes Mellitus, the RQ drops toward **0.7** as the body shifts to fat utilization.

Q: What is the percentage of normal physiological dead space?

30-40%. ### Explanation **1. Understanding the Correct Answer (C: 30-40%)** Physiological dead space refers to the total volume of inhaled air that does not participate in gas exchange. It is the sum of **Anatomical Dead Space** (conducting airways like the trachea and bronchi) and **Alveolar Dead Space** (alveoli that are ventilated but not perfused). In a healthy individual, the anatomical dead space is approximately **150 mL**. Given a normal tidal volume ($V_T$) of **500 mL**, the ratio of dead space ($V_D$) to tidal volume ($V_D/V_T$) is roughly: $$\frac{150}{500} = 0.3 \text{ or } 30\%$$ In clinical practice and standard physiological texts (like Guyton), the normal range is accepted as **20-40%** (averaging **30-40%**). **2. Why Other Options are Incorrect** * **Option A (50-70%) & D (80-90%):** These values are pathologically high. Such high dead space fractions occur in severe respiratory failure or massive pulmonary embolism, where ventilation occurs but perfusion is absent. * **Option B (20-30%):** While 20-30% is close to the lower limit of normal, standard medical examinations for NEET-PG typically favor the **30-40%** range as the most representative average for a healthy adult. **3. High-Yield Clinical Pearls for NEET-PG** * **Bohr’s Equation:** Used to calculate physiological dead space: $V_D/V_T = (PaCO_2 - PeCO_2) / PaCO_2$. (Remember: "Alveolar minus Expired over Alveolar"). * **Anatomical vs. Physiological:** In healthy individuals, physiological dead space nearly equals anatomical dead space. It increases significantly in lung diseases like **COPD** or **Pulmonary Embolism**. * **Positioning:** Dead space is higher in the **upright position** (due to gravity-dependent perfusion mismatch at the apex) compared to the supine position. * **Equipment:** Artificial ventilation (tubing) increases "mechanical" dead space.

Q: Which of the following oxygen-hemoglobin dissociation curves corresponds to blood during resting (dark purple line) and during exercise (light purple line)?

Curve B. ***Curve B*** - During exercise, the oxygen-hemoglobin dissociation curve shifts to the **right** due to the **Bohr effect** - increased CO₂, temperature, decreased pH, and increased **2,3-DPG** facilitate oxygen release to tissues. - Curve B correctly shows the **resting curve** (dark purple) on the left and the **exercise curve** (light purple) shifted rightward, promoting oxygen unloading at the tissue level. *Curve D* - Shows an **incorrect leftward shift** during exercise, which would actually **increase** hemoglobin's oxygen affinity and impair oxygen delivery to active tissues. - This pattern contradicts the physiological need for **enhanced oxygen release** during increased metabolic demand. *Curve A* - Demonstrates **no shift** between resting and exercise states, failing to account for the metabolic changes that occur during physical activity. - Ignores the **Bohr effect** and other factors like increased temperature and **2,3-DPG** that naturally shift the curve rightward during exercise. *Curve C* - Shows an **excessive rightward shift** that would indicate pathological conditions rather than normal physiological adaptation to exercise. - The dramatic shift suggests severe **acidosis** or **hyperthermia** beyond what occurs in normal exercise physiology.

Q: What is the normal tidal volume in a resting man?

0.5 L. **Explanation:** **Tidal Volume (TV)** is defined as the volume of air inspired or expired during a single breath under resting (quiet) conditions. In a healthy adult male, the average tidal volume is approximately **500 mL (0.5 L)**. This volume is essential for maintaining adequate alveolar ventilation and gas exchange. * **Why 0.5 L is correct:** In a standard 70 kg adult, the TV is calculated at roughly 6–8 mL/kg of ideal body weight. This equates to ~500 mL. Out of this 0.5 L, approximately 350 mL reaches the alveoli for gas exchange, while the remaining 150 mL occupies the anatomical dead space. * **Why 1 L, 1.5 L, and 2 L are incorrect:** These values significantly exceed resting requirements. A TV of 1 L or more is typically seen during physical exertion or in states of respiratory distress (hyperpnea). These volumes are closer to the **Inspiratory Capacity** (TV + Inspiratory Reserve Volume) rather than the resting tidal volume. **High-Yield Facts for NEET-PG:** * **Anatomical Dead Space:** Roughly 2 mL/kg or 150 mL; it is the volume of air in the conducting airways that does not participate in gas exchange. * **Minute Ventilation:** Calculated as $TV \times \text{Respiratory Rate}$. At rest: $500\text{ mL} \times 12\text{ bpm} = 6\text{ L/min}$. * **Alveolar Ventilation:** $(TV - \text{Dead Space}) \times \text{Respiratory Rate}$. At rest: $(500 - 150) \times 12 = 4.2\text{ L/min}$. * **Measurement:** Lung volumes and capacities (except Residual Volume, FRC, and TLC) are measured using a **Spirometer**.

Q: When a normal subject develops a spontaneous pneumothorax of their right lung, which of the following would you expect to occur?

Right lung contracts. ### Explanation **1. Why the Correct Answer is Right:** The lungs and the chest wall are held together by the **negative intrapleural pressure** (typically -5 cm H₂O). This pressure acts as a "vacuum" that counteracts the natural elastic recoil of the lungs (which want to collapse inward) and the elastic recoil of the chest wall (which wants to expand outward). In a **spontaneous pneumothorax**, air enters the pleural space, equalizing the intrapleural pressure with atmospheric pressure. Once this negative pressure is lost, the lung’s inherent **elastic recoil** is unopposed, causing the **right lung to contract** or collapse toward the hilum. **2. Why the Other Options are Wrong:** * **B. Chest wall on the right contracts:** Incorrect. Because the chest wall’s natural tendency is to expand outward, the loss of negative intrapleural pressure allows the chest wall on the affected side to **expand** or move outward, not contract. * **C. Diaphragm on the right moves up:** Incorrect. The accumulation of air in the pleural space increases pressure, which typically pushes the diaphragm **downward** (flattening it) on the affected side. * **D. Mediastinum moves to the right:** Incorrect. In a pneumothorax, the increased pressure on the affected side (right) pushes the mobile mediastinum toward the **opposite side (left)**. This is most pronounced in a tension pneumothorax. **3. High-Yield Clinical Pearls for NEET-PG:** * **Resting Position:** At Functional Residual Capacity (FRC), the inward recoil of the lung exactly balances the outward recoil of the chest wall. * **Tension Pneumothorax:** Characterized by a "one-way valve" mechanism leading to rapid mediastinal shift, decreased venous return, and hypotension. This is a medical emergency requiring immediate needle decompression. * **Radiology:** Look for a "visceral pleural line" and the absence of peripheral lung markings on a chest X-ray.

Question 1

A transaction at the mid-pons level with intact vagi leads to which type of breathing pattern?

Accepted Answer

Deep breathing

Answer

Apneusis

Answer

Rapid, shallow breathing

Answer

Hyperventilation

Question 2

Calculate the minute ventilation from the spirogram assuming the respiratory rate as 12/min?

Accepted Answer

6 L/min

Answer

1 L/min

Answer

2 L/min

Answer

4 L/min

Question 3

The ratio of carbon dioxide produced to oxygen consumed is known as what?

Accepted Answer

Respiratory quotient

Answer

Basal metabolic rate

Answer

Specific dynamic action

Answer

Partial pressure of carbon dioxide

Question 4

Which of the following variants of hypoxia does not stimulate peripheral chemoreceptors?

Accepted Answer

Anemic hypoxia

Answer

Hypoxic hypoxia

Answer

Stagnant hypoxia

Answer

Histotoxic hypoxia

Question 5

What is the percentage of normal physiological dead space?

Accepted Answer

30-40%

Answer

50-70%

Answer

20-30%

Answer

80-90%

Question 6

Which of the following statements concerning airflow in the lung is TRUE?

Accepted Answer

Airway resistance increases during scuba diving.

Answer

Flow is more likely to be turbulent in small airways than in the trachea.

Answer

The lower the viscosity, the less likely is turbulence to occur.

Answer

In pure laminar flow, halving the radius of the airway increases its resistance eightfold.

Question 7

Which of the following oxygen-hemoglobin dissociation curves corresponds to blood during resting (dark purple line) and during exercise (light purple line)?

Accepted Answer

Curve B

Answer

Curve D

Answer

Curve A

Answer

Curve C

Question 8

What is the normal tidal volume in a resting man?

Accepted Answer

0.5 L

Answer

1 L

Answer

1.5 L

Answer

2 L

Question 9

When a normal subject develops a spontaneous pneumothorax of their right lung, which of the following would you expect to occur?

Accepted Answer

Right lung contracts

Answer

Chest wall on the right contracts

Answer

Diaphragm on the right moves up

Answer

Mediastinum moves to the right

Question 10

Hypoxemia in emphysema is due to all of the following except:

Accepted Answer

Anatomical dead space

Answer

Destruction of alveoli

Answer

Physiological dead space

Answer

Reduced elastic recoil

Respiratory System — MCQs

Respiratory System — MCQs

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