Respiratory System Practice Questions

Q: What is the shape of the myoglobin dissociation curve?

Rectangular hyperbola. **Explanation:** The shape of the dissociation curve is determined by the oxygen-binding affinity and the number of binding sites on the protein. **Why Rectangular Hyperbola is Correct:** Myoglobin is a monomeric protein containing only **one heme group** (one iron atom). Because it has only one binding site, it does not exhibit "cooperative binding." It follows simple Michaelis-Menten kinetics, where oxygen binding occurs independently. This results in a **rectangular hyperbola** shape. Myoglobin has a very high affinity for oxygen (P50 ≈ 2–3 mmHg), allowing it to remain saturated at low partial pressures and only release oxygen when levels in the muscle drop significantly during intense exercise. **Why Other Options are Incorrect:** * **Sigmoid:** This is the shape of the **Hemoglobin** dissociation curve. Hemoglobin is a tetramer (four subunits). The binding of the first oxygen molecule increases the affinity for subsequent ones (positive cooperativity), creating the S-shaped curve. * **Almost Linear:** No physiological respiratory pigment follows a linear curve, as binding sites are finite and must reach saturation. * **Parabola:** While a hyperbola and parabola are both conic sections, the mathematical relationship of gas-binding kinetics specifically describes a hyperbolic function. **High-Yield Facts for NEET-PG:** 1. **P50 Values:** Hemoglobin P50 is ~26.7 mmHg; Myoglobin P50 is ~2–3 mmHg. A lower P50 signifies a higher affinity. 2. **Function:** Myoglobin acts as an **oxygen storage** unit in skeletal and cardiac muscle, whereas Hemoglobin acts as an **oxygen transporter**. 3. **Left Shift:** The myoglobin curve is located far to the left of the hemoglobin curve, meaning myoglobin will take up oxygen from hemoglobin at the tissue level. 4. **Bohr Effect:** Unlike hemoglobin, myoglobin is **not** affected by pH, $CO_2$, or 2,3-BPG.

Q: Which reflex is considered the first respiratory reflex that aids in the initial breath of a newborn?

Head's Paradox reflex. **Explanation:** **Head’s Paradoxical Reflex** is the correct answer because it describes a phenomenon where lung inflation triggers a further *increase* in inspiratory effort, rather than inhibiting it. While most stretch receptors in the lungs trigger a negative feedback loop to stop inspiration, the receptors involved in Head’s reflex provide **positive feedback**. This is physiologically crucial during the **first breath of a newborn**, as it helps in the initial expansion of the collapsed alveoli (atelectatic lungs) and promotes the distribution of surfactant. **Analysis of Incorrect Options:** * **Hering-Breuer Inflation Reflex:** This is a protective mechanism where lung inflation triggers the termination of inspiration to prevent over-distension. It is a negative feedback mechanism and is generally inactive during quiet breathing in adults, becoming active only at high tidal volumes. * **J-reflex (Juxtacapillary reflex):** Triggered by the stimulation of J-receptors in the alveolar wall (usually due to pulmonary edema or congestion), this reflex leads to rapid shallow breathing (tachypnea), apnea, bradycardia, and hypotension. It is not involved in the initiation of the first breath. **Clinical Pearls for NEET-PG:** * **Receptors:** Head’s reflex is mediated by **rapidly adapting stretch receptors** (RARs) in the airways. * **Afferent Pathway:** The sensory signals for these respiratory reflexes travel via the **Vagus nerve (CN X)**. * **High-Yield Fact:** Head’s reflex is also responsible for the **"gasp"** or deep inspiration seen during periodic sighing in adults, which helps reopen collapsed small airways.

Q: Hypercarbia is characterized by:

Hypertension. ### Explanation **Hypercarbia (Hypercapnia)** refers to an elevation in the partial pressure of carbon dioxide ($PaCO_2$) in the blood. The physiological response to hypercarbia is primarily driven by the stimulation of the **sympathoadrenal system**. **1. Why Hypertension is Correct:** Hypercarbia causes a dual effect: a direct local vasodilator effect and a central sympathetic stimulant effect. In a conscious or lightly anesthetized patient, the **sympathetic stimulation** predominates, leading to the release of catecholamines. This results in **hypertension** and **tachycardia**. Additionally, $CO_2$ acts as a potent cerebral vasodilator, increasing cerebral blood flow. **2. Why Other Options are Incorrect:** * **Miosis:** Hypercarbia typically causes **mydriasis** (pupillary dilation) due to the massive sympathetic surge and increased adrenaline levels. Miosis (pinpoint pupils) is more characteristic of opioid overdose. * **Cool Extremities:** Because hypercarbia causes peripheral vasodilation (direct effect of $CO_2$ on vascular smooth muscle), the skin usually appears **flushed, warm, and sweaty** (diaphoretic), rather than cool. * **Bradycardia:** The initial and most common response to hypercarbia is **tachycardia** due to sympathetic activation. Bradycardia only occurs as a terminal event or in cases of severe, acute acidosis that depresses the myocardium. **Clinical Pearls for NEET-PG:** * **The "CO2 Narcosis" Zone:** $PaCO_2$ levels above 90–100 mmHg can lead to CNS depression, coma, and respiratory arrest. * **Arrhythmias:** Hypercarbia sensitizes the myocardium to catecholamines, increasing the risk of ventricular arrhythmias (especially when using halothane). * **Signs of Hypercarbia under Anesthesia:** Rising blood pressure, tachycardia, and increased oozing at the surgical site (due to vasodilation).

Q: Spirometry measures all of the following, except:

None of the above. **Explanation:** The correct answer is **None of the above** because all the parameters listed (Tidal Volume, Vital Capacity, and FEV1) can be directly measured using a standard spirometer. **Understanding the Concept:** Spirometry is a pulmonary function test that measures the **volume** of air an individual can inhale or exhale as a function of **time**. * **Tidal Volume (TV):** The volume of air inspired or expired during a normal breath. * **Vital Capacity (VC):** The maximum volume of air that can be exhaled after a maximum inspiration. * **FEV1 (Forced Expiratory Volume in 1 second):** The volume of air exhaled during the first second of a forced expiratory maneuver. **Why the other options are incorrect:** Options A, B, and C are all measurable by spirometry. Therefore, they cannot be the answer to an "except" question. **High-Yield Clinical Pearls for NEET-PG:** * **The "Rule of Residual":** Spirometry **cannot** measure any lung volume that includes the **Residual Volume (RV)**. This is because RV is the air that remains in the lungs even after maximal expiration and cannot be exhaled into the machine. * **What Spirometry CANNOT measure:** 1. Residual Volume (RV) 2. Functional Residual Capacity (FRC) 3. Total Lung Capacity (TLC) * **How to measure RV/FRC/TLC:** These require specialized techniques such as **Helium Dilution**, **Nitrogen Washout**, or **Body Plethysmography** (the gold standard). * **FEV1/FVC Ratio:** This is the most important parameter for differentiating between Obstructive (ratio decreased) and Restrictive (ratio normal or increased) lung diseases.

Q: What is the effect on spirometry following lobectomy for bronchogenic carcinoma?

Increased dead space ventilation. **Explanation:** The correct answer is **C. Increased dead space ventilation.** **Mechanism:** Following a lobectomy, a portion of the functional lung tissue (alveoli) is removed. However, the large conducting airways (trachea and main bronchi) remain intact. Because the total lung volume decreases while the volume of the conducting zones remains relatively constant, the ratio of **dead space to tidal volume ($V_D/V_T$) increases**. Furthermore, the remaining lung tissue often undergoes compensatory hyperinflation to fill the thoracic cavity; this expansion increases the diameter of the remaining airways, further increasing the anatomical dead space. **Analysis of Incorrect Options:** * **A. Increased residual volume:** After surgical resection of lung tissue, the total lung capacity and all its sub-components, including Residual Volume (RV), typically **decrease** due to the loss of lung parenchyma. * **B. Increased vital capacity:** Vital Capacity (VC) is the maximum volume of air exhaled after a maximum inspiration. Removing a lobe directly reduces the number of functioning alveoli, leading to a **decreased** VC (a restrictive pattern). * **D. Increased closing volume:** Closing volume is the volume at which small airways in the dependent parts of the lung begin to close. While it can be affected by age and smoking, it does not characteristically increase as a direct physiological result of lobectomy itself. **High-Yield Clinical Pearls for NEET-PG:** * **Dead Space Calculation:** Remember Bohr’s equation: $V_D = V_T \times [(PaCO_2 - PeCO_2) / PaCO_2]$. * **Post-Op Spirometry:** Lobectomy results in a **Restrictive pattern** (decreased FVC, decreased FEV1, but a normal or increased FEV1/FVC ratio). * **Compensatory Changes:** The remaining lobes undergo "compensatory emphysema" (hyperinflation), which is a physiological adaptation, not a pathological one.

Q: Which lung volume or capacity can be measured by Hutchison's spirometer?

Expiratory reserve volume. **Explanation:** The core principle of spirometry (including the classic **Hutchison’s spirometer**) is that it can only measure volumes of air that can be **actively moved into or out of the lungs**. 1. **Why Expiratory Reserve Volume (ERV) is correct:** ERV is the maximum volume of air that can be exhaled after a normal tidal expiration. Since this air is physically displaced from the lungs into the spirometer, it can be directly measured. Other volumes measurable by spirometry include Tidal Volume (TV), Inspiratory Reserve Volume (IRV), and Vital Capacity (VC). 2. **Why the other options are incorrect:** * **Residual Volume (RV):** This is the air remaining in the lungs after a maximal forced expiration. Because it never leaves the lungs, a spirometer cannot "see" or measure it. * **Functional Residual Capacity (FRC) & Total Lung Capacity (TLC):** Both of these capacities include the Residual Volume (FRC = ERV + RV; TLC = VC + RV). Since RV cannot be measured by spirometry, any capacity containing it also cannot be measured. **High-Yield Clinical Pearls for NEET-PG:** * **Measurement of RV, FRC, and TLC:** These require indirect methods such as **Helium Dilution**, **Nitrogen Washout**, or **Body Plethysmography** (the gold standard). * **Hutchison’s Spirometer:** Invented by John Hutchison, it is a "water-seal" spirometer. It cannot measure flow rates (like FEV1) accurately; for those, a computerized pneumotachometer is used. * **Formula to remember:** Vital Capacity (VC) = TV + IRV + ERV. This is the largest volume measurable by a spirometer.

Q: What is the resting rate of O2 delivery to tissues?

250 ml/min. **Explanation:** The resting rate of oxygen delivery to tissues, also known as **Oxygen Consumption ($\dot{V}O_2$)**, refers to the amount of oxygen the body extracts and utilizes from the blood per minute under basal conditions. **Why Option B is Correct:** In a healthy adult at rest, the average oxygen consumption is approximately **250 ml/min**. This is calculated using the Fick Principle: *$\dot{V}O_2 = \text{Cardiac Output} \times (\text{Arterial } O_2 \text{ content} - \text{Venous } O_2 \text{ content})$.* With a cardiac output of 5 L/min, arterial $O_2$ at 200 ml/L, and venous $O_2$ at 150 ml/L, the consumption is: $5 \times (200 - 150) = 250 \text{ ml/min}$. **Analysis of Incorrect Options:** * **Option A (150 ml/min):** This is too low for a standard adult; it might be seen in states of extreme hypometabolism or in much smaller pediatric patients. * **Option C (300 ml/min) & D (350 ml/min):** These values represent elevated metabolic states. Oxygen consumption increases significantly during exercise, fever, or hyperthyroidism, but does not represent the "resting" rate. **High-Yield Clinical Pearls for NEET-PG:** * **Total Oxygen Delivery ($DO_2$):** Do not confuse $VO_2$ (consumption) with $DO_2$ (delivery). Total $DO_2$ is ~1000 ml/min (Cardiac Output $\times$ Arterial $O_2$ content). * **Utilization Coefficient:** At rest, tissues extract about 25% of delivered oxygen ($250/1000$). During strenuous exercise, this can increase to 75-85%. * **Respiratory Quotient (RQ):** While $O_2$ consumption is 250 ml/min, $CO_2$ production is ~200 ml/min, giving a resting RQ of 0.8 ($200/250$).

Question 1

What is the shape of the myoglobin dissociation curve?

Accepted Answer

Rectangular hyperbola

Answer

Almost linear

Answer

Parabola

Answer

Sigmoid

Question 2

Which reflex is considered the first respiratory reflex that aids in the initial breath of a newborn?

Accepted Answer

Head's Paradox reflex

Answer

Hering-Breuer's reflex

Answer

J-reflex

Answer

None of the above

Question 3

Hypercarbia is characterized by:

Accepted Answer

Hypertension

Answer

Miosis

Answer

Cool extremities

Answer

Bradycardia

Question 4

A 38-year-old man's snoring becomes louder soon after falling asleep, interrupted by a long silent period of no breathing (apnea). He was diagnosed with Obstructive Sleep Apnea (OSA). Individuals with OSA awaken when aerial hypoxemia and hypercapnia stimulate both peripheral and central chemoreceptors. The activity of the central chemoreceptors is stimulated by which of the following?

Accepted Answer

An increase in the partial pressure of carbon dioxide (PCO2) of blood flowing through the brain

Answer

A decrease in the partial pressure of oxygen (PO2) of blood flowing through the brain

Answer

An increase in the pH of the cerebrospinal fluid (CSF)

Answer

Hypoxemia, Hypercapnia, and Metabolic acidosis

Question 5

Spirometry measures all of the following, except:

Accepted Answer

None of the above

Answer

Tidal volume

Answer

Vital capacity

Answer

FEV1

Question 6

What is the effect on spirometry following lobectomy for bronchogenic carcinoma?

Accepted Answer

Increased dead space ventilation

Answer

Increased residual volume

Answer

Increased vital capacity

Answer

Increased closing volume

Question 7

Oxygen content of the arterial blood is reduced in all except:

Accepted Answer

Methemoglobinemia

Answer

Fallot's tetralogy

Answer

Carbon monoxide poisoning

Answer

Fibrosing alveolitis

Question 8

Which lung volume or capacity can be measured by Hutchison's spirometer?

Accepted Answer

Expiratory reserve volume

Answer

Residual volume

Answer

Functional residual capacity

Answer

Total lung capacity

Question 9

Administration of pure oxygen to hypoxic patients is dangerous because?

Accepted Answer

Apnea occurs due to hypostimulation of peripheral chemoreceptors.

Answer

Pulmonary edema.

Answer

Increased 2,3-Diphosphoglycerate (DPG) levels.

Answer

Convulsions.

Question 10

What is the resting rate of O2 delivery to tissues?

Accepted Answer

250 ml/min

Answer

150 ml/min

Answer

300 ml/min

Answer

350 ml/min

Respiratory System — MCQs

Respiratory System — MCQs

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