Respiratory System Practice Questions

Q: Cyanosis is caused by which of the following conditions?

All of the above. **Explanation:** Cyanosis is the bluish discoloration of the skin and mucous membranes resulting from an excessive amount of deoxygenated (reduced) hemoglobin or abnormal hemoglobin derivatives in the capillary blood. **1. Reduced Hemoglobin (Option A):** The classic clinical threshold for detecting central cyanosis is when the absolute concentration of **reduced hemoglobin exceeds 5 g/dL** in the capillary blood. Since 7.5 g/dL is well above this threshold, it will definitely manifest as cyanosis. **2. Abnormal Hemoglobin Derivatives (Options B & C):** Cyanosis can also occur due to dyshemoglobins, which have a lower affinity for oxygen or an altered color. * **Methemoglobin:** Cyanosis becomes clinically apparent when the concentration exceeds **1.5 g/dL** (or >10-15% of total Hb). * **Sulfhemoglobin:** This is a very potent cause of discoloration; cyanosis appears even at low levels, typically above **0.5 g/dL**. **Why "All of the above" is correct:** All three conditions represent the physiological or biochemical thresholds required to produce the blue pigment necessary for a clinical diagnosis of cyanosis. **High-Yield Clinical Pearls for NEET-PG:** * **Anemia vs. Polycythemia:** A severely anemic patient (Hb < 5 g/dL) cannot develop cyanosis because they cannot reach the 5 g/dL threshold of reduced Hb, even if completely hypoxic. Conversely, polycythemic patients develop cyanosis more easily. * **Peripheral vs. Central:** Central cyanosis (tongue/lips) implies systemic arterial desaturation, while peripheral cyanosis (fingertips) often implies increased oxygen extraction due to sluggish blood flow (e.g., heart failure or cold exposure). * **Differential Cyanosis:** Seen in PDA with reversal of shunt (Eisenmenger syndrome), where the lower limbs are cyanotic but the upper limbs are not.

Q: What is the normal intrapleural pressure?

-3 to -4 mm Hg. **Explanation:** The **intrapleural pressure (IPP)** is the pressure within the pleural cavity (the space between the visceral and parietal pleura). Under normal physiological conditions, this pressure is **sub-atmospheric (negative)**. **1. Why Option D is Correct:** At the end of a quiet expiration (Functional Residual Capacity), the intrapleural pressure is approximately **-3 to -4 mm Hg** (relative to atmospheric pressure). This negativity is created by two opposing elastic forces: * The **lungs** have a natural tendency to recoil inward. * The **chest wall** has a natural tendency to expand outward. These opposing forces "pull" the pleural layers away from each other, creating a vacuum-like effect that maintains the negative pressure, keeping the lungs inflated. **2. Analysis of Incorrect Options:** * **Options A & B (1-2 and 2-4 mm Hg):** These represent positive values. Positive intrapleural pressure is pathological (e.g., tension pneumothorax), as it would cause the lung to collapse. * **Option C (9.5-10 mm Hg):** While IPP becomes *more* negative during deep inspiration (reaching -6 to -8 mm Hg), a value of -10 mm Hg is not the "normal" resting baseline. Positive 10 mm Hg would indicate severe respiratory distress or injury. **3. Clinical Pearls for NEET-PG:** * **Inspiration:** IPP becomes more negative (approx. **-6 mm Hg**) as the chest wall expands, further pulling on the lungs. * **Müller's Maneuver:** Forced inspiration against a closed glottis can drop IPP to **-40 mm Hg**. * **Valsalva Maneuver:** Forced expiration against a closed glottis can make IPP positive (up to **+50 to +100 mm Hg**). * **Pneumothorax:** If the pleural cavity is breached, IPP equilibrates with atmospheric pressure (becomes 0), leading to immediate lung collapse.

Q: Given a respiratory rate of 12 breaths/min, calculate the minute ventilation.

6 L/min. ### Explanation **1. Why the Correct Answer is Right:** Minute Ventilation ($\dot{V}_E$) is the total volume of gas entering (or leaving) the lungs per minute. It is calculated using the formula: $$\text{Minute Ventilation} = \text{Tidal Volume (TV)} \times \text{Respiratory Rate (RR)}$$ In a healthy adult, the standard **Tidal Volume (TV)** is approximately **500 mL** (0.5 L). Given the **Respiratory Rate (RR)** is **12 breaths/min**: $$\dot{V}_E = 500 \text{ mL} \times 12 = 6,000 \text{ mL/min} = \mathbf{6 \text{ L/min}}$$ Therefore, Option D is the correct physiological calculation. **2. Why the Incorrect Options are Wrong:** * **Options A & B (1 L/min & 2 L/min):** These values are physiologically insufficient to sustain life in an adult. Such low volumes would lead to rapid hypercapnia (CO2 retention) and hypoxia. * **Option C (4 L/min):** This value is closer to the **Alveolar Ventilation** ($\dot{V}_A$). Alveolar ventilation subtracts the dead space volume ($V_D \approx 150 \text{ mL}$) from the tidal volume: $(500 - 150) \times 12 = 4.2 \text{ L/min}$. While 4 L/min is a significant respiratory parameter, it does not represent the total *minute* ventilation. **3. Clinical Pearls & High-Yield Facts for NEET-PG:** * **Anatomical Dead Space:** Usually estimated as **2 mL/kg** of ideal body weight (approx. 150 mL in a 70 kg adult). * **Alveolar Ventilation:** This is the most important factor for gas exchange. If a patient breathes shallowly (low TV), even with a high RR, alveolar ventilation may drop to zero if TV $\leq$ Dead Space. * **Hyperventilation vs. Tachypnea:** Hyperventilation specifically refers to an increase in alveolar ventilation that lowers arterial $PCO_2$, whereas tachypnea simply refers to an increased respiratory rate.

Q: Which of the following is not reduced in an elderly patient?

Functional residual capacity. In the elderly, the respiratory system undergoes structural changes often referred to as "senile emphysema." The primary driver is the **loss of elastic recoil** of the lung parenchyma and increased stiffness of the chest wall. **Explanation of the Correct Answer:** * **Functional Residual Capacity (FRC):** As lung elasticity decreases, the lungs' inward pull weakens, while the chest wall's tendency to expand remains relatively unopposed. This shifts the equilibrium point outward, leading to an **increase** (or maintenance) of FRC and Residual Volume (RV). Therefore, FRC is **not reduced**; it typically increases with age. **Explanation of Incorrect Options:** * **Arterial Oxygen Tension ($PaO_2$):** This **decreases** with age due to an increase in the alveolar-arterial (A-a) gradient. This is caused by early airway closure (increased closing volume) leading to ventilation-perfusion ($V/Q$) mismatch. * **Alveolar Oxygen Tension ($PAO_2$):** While $PAO_2$ itself stays relatively stable if ventilation is adequate, the question asks what is *not reduced*. In many clinical contexts of aging (like decreased chest wall compliance), $PAO_2$ may slightly decline, but $PaO_2$ is the more significant clinical drop. * **Forced Expiratory Volume ($FEV_1$):** This **decreases** significantly (approx. 20-30 ml/year) due to the loss of elastic recoil, which reduces the driving pressure for expiratory airflow and leads to premature small airway collapse. **High-Yield Clinical Pearls for NEET-PG:** * **Increases with age:** FRC, Residual Volume (RV), Closing Volume (CV), and A-a gradient. * **Decreases with age:** Vital Capacity (VC), $FEV_1$, $PaO_2$, and Chest wall compliance. * **Unchanged:** Total Lung Capacity (TLC) generally remains constant as the increase in RV offsets the decrease in VC. * **Formula for $PaO_2$ decline:** $PaO_2 = 100 - (0.3 \times \text{Age in years})$.

Q: Which of the following types of hypoxia presents with normal arterial oxygen concentration?

Anemic hypoxia. ### Explanation The correct answer is **Anemic Hypoxia**. **1. Why Anemic Hypoxia is Correct:** In anemic hypoxia, the **partial pressure of oxygen ($PaO_2$) is normal**, but the total oxygen-carrying capacity of the blood is reduced due to a decrease in functional hemoglobin (Hb) levels or altered Hb binding (e.g., Carbon Monoxide poisoning). Since $PaO_2$ (dissolved oxygen) remains normal, the **arterial oxygen concentration ($CaO_2$)**—which is primarily determined by Hb concentration and saturation—is reduced. However, in the context of NEET-PG questions, "normal arterial oxygen" often refers specifically to the **Partial Pressure ($PaO_2$)**, which remains unaffected because the lungs and gas exchange mechanisms are intact. **2. Analysis of Incorrect Options:** * **Stagnant Hypoxia:** Occurs due to reduced blood flow (e.g., heart failure or shock). $PaO_2$ and $CaO_2$ are initially normal, but the tissue oxygen delivery is compromised. * **Histotoxic Hypoxia:** Occurs when tissues cannot utilize oxygen (e.g., Cyanide poisoning). Arterial $PaO_2$ and $CaO_2$ are normal, but the **venous oxygen concentration is elevated** because oxygen is not unloaded. * **Hypoxic Hypoxia:** Characterized by **low arterial $PaO_2$**. This is caused by low environmental $O_2$ (high altitude), hypoventilation, or V/Q mismatch. **3. High-Yield Clinical Pearls for NEET-PG:** * **CO Poisoning:** A classic cause of anemic hypoxia where $PaO_2$ is normal, but $SaO_2$ is falsely normal on pulse oximetry (as it can't distinguish carboxyhemoglobin). * **Cyanosis:** Is typically **absent** in anemic hypoxia because there isn't enough total hemoglobin to produce the required 5g/dL of deoxygenated Hb. * **Arterio-venous (A-V) $O_2$ difference:** Is increased in stagnant hypoxia but decreased in histotoxic hypoxia.

Q: Which of the following is NOT a metabolic function of the lung?

Inactivation of vasopressin. **Explanation:** The lungs are not merely organs of gas exchange; they possess significant metabolic and endocrine functions, primarily involving the processing of substances circulating in the blood. **Why Option D is Correct:** **Vasopressin (Antidiuretic Hormone/ADH)** is synthesized in the hypothalamus and released by the posterior pituitary. Its primary metabolism and inactivation occur in the **liver and kidneys**, not the lungs. Therefore, the lung does not play a role in the clearance of vasopressin. **Why the other options are incorrect:** * **A. Synthesis of Surfactant:** Type II pneumocytes in the lung alveoli synthesize and secrete surfactant (mainly dipalmitoylphosphatidylcholine), which reduces surface tension and prevents alveolar collapse. * **B. Inactivation of Bradykinin:** The pulmonary endothelium contains **Angiotensin-Converting Enzyme (ACE)**, which is responsible for the hydrolysis and inactivation of up to 80% of circulating bradykinin. * **C. Formation of Angiotensin II:** The lungs are the primary site for the conversion of Angiotensin I to the potent vasoconstrictor **Angiotensin II**, catalyzed by ACE located on the luminal surface of pulmonary capillary endothelial cells. **High-Yield Clinical Pearls for NEET-PG:** * **Substances inactivated by the lungs:** Bradykinin, Serotonin (5-HT), Prostaglandins (E and F series), and Noradrenaline (partial). * **Substances NOT affected by the lungs:** Epinephrine, Dopamine, Oxytocin, and Vasopressin. * **ACE Inhibitors:** Drugs like Enalapril work in the pulmonary vasculature, leading to an accumulation of bradykinin, which is the physiological basis for the common side effect of a **dry cough**.

Q: The oxyhaemoglobin dissociation curve is shifted to the right in which of the following conditions?

All the above. The **Oxyhaemoglobin Dissociation Curve (ODC)** represents the relationship between the partial pressure of oxygen ($PO_2$) and the percentage saturation of haemoglobin. A **"Shift to the Right"** indicates a decreased affinity of haemoglobin for oxygen, meaning oxygen is released more easily to the tissues. ### **Explanation of the Correct Answer** The correct answer is **D (All the above)** because all three conditions decrease haemoglobin's affinity for oxygen: 1. **Acidosis (Option A):** An increase in $H^+$ concentration (decreased pH) stabilizes the "Tense" (T) state of haemoglobin, promoting oxygen unloading. This is known as the **Bohr Effect**. 2. **Increased 2,3-DPG (Option B):** 2,3-Diphosphoglycerate is a byproduct of glycolysis in RBCs. It binds to the beta chains of deoxyhaemoglobin, stabilizing the T-state and pushing the curve to the right. 3. **Hyperthermia (Option C):** Increased temperature weakens the bond between oxygen and haemoglobin, facilitating the release of oxygen to metabolically active (warm) tissues. ### **Clinical Pearls & High-Yield Facts** To remember the factors shifting the curve to the **Right**, use the mnemonic **"CADET, face Right!"**: * **C** – $CO_2$ (Hypercapnia) * **A** – Acidosis ($H^+$) * **D** – 2,3-DPG increase * **E** – Exercise * **T** – Temperature (Fever) **Key NEET-PG Points:** * **$P_{50}$ Value:** This is the $PO_2$ at which haemoglobin is 50% saturated (Normal $\approx$ 26-27 mmHg). A **Right shift increases the $P_{50}$**, while a Left shift decreases it. * **Left Shift Factors:** Hypothermia, Alkalosis, decreased 2,3-DPG, and **Fetal Haemoglobin (HbF)**. HbF has a higher affinity for $O_2$ to facilitate oxygen transfer from mother to fetus. * **Carbon Monoxide (CO):** Causes a **Left shift** and changes the curve to a **hyperbolic** shape, preventing oxygen release to tissues.

Question 1

Which of the following is NOT TRUE regarding carbon monoxide (CO) poisoning?

Accepted Answer

Tissue toxicity plays an important role in clinical CO poisoning.

Answer

The oxyhemoglobin dissociation curve shifts to the left.

Answer

A partial pressure as low as 0.6 mmHg can be lethal.

Answer

Hyperbaric oxygen is used for treatment.

Question 2

Cyanosis is caused by which of the following conditions?

Accepted Answer

All of the above

Answer

Reduced hemoglobin concentration above 7.5 g/dl

Answer

Methemoglobin concentration above 1.5 g/dl

Answer

Sulfhemoglobin concentration above 0.5 g/dl

Question 3

What is the mechanism of overdrive observed during hyperventilation?

Accepted Answer

Decreased PaCO2

Answer

Increased pulmonary vascular resistance

Answer

Decreased cerebral blood flow

Answer

Increased central venous pressure

Question 4

What is the normal intrapleural pressure?

Accepted Answer

-3 to -4 mm Hg

Answer

1-2 mm Hg

Answer

2-4 mm Hg

Answer

9.5-10 mm Hg

Question 5

Given a respiratory rate of 12 breaths/min, calculate the minute ventilation.

Accepted Answer

6 L/min

Answer

1 L/min

Answer

2 L/min

Answer

4 L/min

Question 6

Which of the following occurs after hyperventilation with 6% CO2 in inspired air?

Accepted Answer

Continued hyperventilation

Answer

Apnoea

Answer

Cheyne-stokes breathing

Answer

Kussumaul's breathing

Question 7

Which of the following is not reduced in an elderly patient?

Accepted Answer

Functional residual capacity

Answer

Arterial oxygen tension

Answer

Alveolar oxygen tension

Answer

Forced expiratory volume

Question 8

Which of the following types of hypoxia presents with normal arterial oxygen concentration?

Accepted Answer

Anemic hypoxia

Answer

Stagnant hypoxia

Answer

Histotoxic hypoxia

Answer

Hypoxic hypoxia

Question 9

Which of the following is NOT a metabolic function of the lung?

Accepted Answer

Inactivation of vasopressin

Answer

Synthesis of surfactant

Answer

Inactivation of bradykinin

Answer

Formation of angiotensin II

Question 10

The oxyhaemoglobin dissociation curve is shifted to the right in which of the following conditions?

Accepted Answer

All the above

Answer

Acidosis

Answer

Increased 2,3-DPG level

Answer

Hyperthermia

Respiratory System — MCQs

Respiratory System — MCQs

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