Respiratory System Practice Questions

Q: Which time points on the Cheyne-Stokes breathing graph are associated with the highest pCO2 of lung blood and highest pCO2 of the neurons in the respiratory centre?

Z. ***Z*** - Point Z represents the **late apnea phase** when CO2 has accumulated maximally in the blood due to cessation of ventilation, leading to the **highest pCO2 in lung blood**. - The **circulation delay** (lung-to-brain transit time) means that peak CO2 from the lungs reaches the **respiratory centre neurons** at this same time point, causing both compartments to have maximum pCO2 simultaneously. *X* - Point X represents the **early apnea phase** when CO2 levels are still relatively low as ventilation has just ceased. - The **respiratory centre neurons** have not yet received the accumulated CO2 from the lungs due to **circulation delay**. *Y* - Point Y occurs during the **hyperpnea phase** when active ventilation is **blowing off CO2**, resulting in decreasing pCO2 levels. - Both lung blood and respiratory centre show **declining CO2** concentrations as ventilation eliminates excess carbon dioxide. *W* - Point W represents the **end of hyperpnea phase** when CO2 levels have been reduced below the **apnea threshold**. - This is when ventilation ceases again due to **low CO2 drive**, marking the beginning of the next cycle with relatively low pCO2 levels.

Q: Caisson's disease is due to which of the following?

Gas embolism. **Explanation:** **Caisson’s disease**, also known as Decompression Sickness (DCS) or "the bends," is a clinical condition caused by the formation of nitrogen bubbles in the blood and tissues. **Why Gas Embolism is correct:** When a person (like a deep-sea diver) is under high atmospheric pressure, nitrogen gas dissolves into the blood and tissues according to **Henry’s Law**. If the person ascends to the surface too rapidly, the sudden drop in pressure causes the dissolved nitrogen to come out of solution, forming **gas bubbles**. These bubbles act as **gas emboli**, obstructing small blood vessels and triggering inflammatory responses. This leads to joint pain (the bends), respiratory distress (the chokes), and neurological deficits. **Why the other options are incorrect:** * **Fat Embolism:** Typically occurs after fractures of long bones (e.g., femur) or severe soft tissue trauma, where marrow fat enters the circulation. * **Amniotic Fluid Embolism:** A rare obstetric emergency where amniotic fluid enters the maternal circulation during labor or delivery. * **Tumor Embolism:** Occurs when clusters of cancer cells break off from a primary tumor and enter the bloodstream, potentially leading to metastasis. **High-Yield Clinical Pearls for NEET-PG:** * **Henry’s Law:** The amount of dissolved gas in a liquid is proportional to its partial pressure. * **The Chokes:** Shortness of breath and cough caused by gas bubbles in the pulmonary vasculature. * **Treatment:** The definitive treatment is **Hyperbaric Oxygen Therapy**, which forces the nitrogen bubbles back into solution. * **Chronic Form:** Chronic decompression sickness can lead to **Dysbaric Osteonecrosis** (avascular necrosis), most commonly affecting the head of the femur or humerus.

Q: Carbon monoxide affinity to hemoglobin is how many times compared to oxygen?

200-300 times. **Explanation:** The correct answer is **D (200-300 times)**. **Underlying Medical Concept:** Hemoglobin (Hb) has a significantly higher affinity for Carbon Monoxide (CO) than for Oxygen ($O_2$). When CO binds to the heme iron, it forms **Carboxyhemoglobin**. This binding is competitive; however, because the affinity of CO is approximately **200 to 250 times** (often cited in the range of 200–300) greater than that of $O_2$, even minute concentrations of CO in the inspired air can displace oxygen from Hb, leading to tissue hypoxia. **Analysis of Options:** * **Option A (250 times):** While 250 is a precise figure often used in textbooks (like Guyton), the range provided in Option D is more comprehensive and is the standard format for NEET-PG questions. * **Option B & C (500 and 100 times):** These values are physiologically inaccurate. 100 is too low to explain the severity of CO poisoning, and 500 is an overestimation of the binding kinetics. **High-Yield Clinical Pearls for NEET-PG:** 1. **Haldane Effect vs. CO:** CO not only displaces $O_2$ but also causes a **Leftward shift** of the Oxygen-Dissociation Curve (ODC). This increases the affinity of the remaining heme sites for $O_2$, preventing its release into tissues. 2. **Color Change:** Patients with CO poisoning classically present with **"Cherry Red"** skin/mucosa (due to the color of carboxyhemoglobin), not cyanosis. 3. **Treatment:** The management of choice is **100% Hyperbaric Oxygen**, which reduces the half-life of carboxyhemoglobin by physically displacing the CO. 4. **P50 Value:** CO poisoning decreases the P50 value (reflecting increased affinity/left shift).

Q: Decreased oxygen carrying capacity with normal partial pressure of oxygen (PO2) is a feature of which type of hypoxia?

Anemic hypoxia. ### Explanation **1. Why Anemic Hypoxia is Correct:** The partial pressure of oxygen ($PO_2$) in arterial blood is determined solely by the amount of oxygen dissolved in the plasma, which depends on alveolar ventilation and gas exchange—not on hemoglobin levels. In **Anemic Hypoxia**, the lungs function normally, so $PO_2$ remains normal. However, the total **oxygen-carrying capacity** is reduced because there is either a decrease in total hemoglobin (e.g., anemia, hemorrhage) or the hemoglobin is unable to bind oxygen (e.g., Carbon Monoxide poisoning, Methemoglobinemia). **2. Why Other Options are Incorrect:** * **Hypoxic Hypoxia:** Characterized by **low arterial $PO_2$**. This occurs due to low environmental oxygen (high altitude), hypoventilation, or V/Q mismatch. * **Stagnant (Ischemic) Hypoxia:** $PO_2$ and oxygen capacity are typically normal, but **blood flow (delivery)** to the tissues is reduced (e.g., heart failure, shock, or local embolism). * **Histotoxic Hypoxia:** $PO_2$ and oxygen capacity are normal, but the **tissues cannot utilize** the oxygen delivered to them due to cellular enzyme inhibition (e.g., Cyanide poisoning inhibiting Cytochrome oxidase). **3. High-Yield Clinical Pearls for NEET-PG:** * **CO Poisoning:** A classic cause of anemic hypoxia where $PO_2$ is normal, but the oxygen-hemoglobin dissociation curve shifts to the **left**, preventing oxygen release to tissues. * **Arteriovenous (A-V) Oxygen Difference:** * Increased in **Stagnant Hypoxia** (tissues extract more $O_2$ due to slow flow). * Decreased in **Histotoxic Hypoxia** (tissues cannot use $O_2$, so venous blood remains highly oxygenated). * **Cyanosis:** Usually absent in anemic hypoxia because there isn't enough total hemoglobin to produce the required 5g/dL of deoxygenated hemoglobin.

Q: All of the following can be measured by a simple spirometer except?

Residual volume. ### Explanation The core concept tested here is the limitation of **static spirometry**. A simple spirometer measures the volume of air that can be moved into or out of the lungs. However, it cannot measure any volume of air that remains trapped in the lungs and cannot be exhaled. **1. Why Residual Volume (RV) is the Correct Answer:** **Residual Volume** is the volume of air remaining in the lungs after a maximal forced expiration. Since this air never leaves the respiratory system, a spirometer cannot "see" or measure it. Consequently, any lung capacity that includes RV—specifically **Functional Residual Capacity (FRC)** and **Total Lung Capacity (TLC)**—also cannot be measured by simple spirometry. These require indirect methods like **Helium Dilution**, **Nitrogen Washout**, or **Body Plethysmography**. **2. Why the other options are incorrect:** * **Tidal Volume (TV):** This is the volume of air inspired or expired during normal quiet breathing, which is easily recorded by a spirometer. * **FEV1 (Forced Expiratory Volume in 1 sec):** This is a dynamic volume measured during a forced expiratory maneuver. Spirometers are specifically designed to track this over time. * **Vital Capacity (VC):** This is the maximum volume of air a person can expel from the lungs after a maximum inhalation. Since it involves active air movement, it is measurable. **Clinical Pearls for NEET-PG:** * **Mnemonic:** Spirometry cannot measure **FRC**, **RV**, and **TLC** (Remember: **"FRT"** or **"Gold Standard"** volumes). * **RV/TLC Ratio:** This ratio increases in obstructive lung diseases (like Emphysema) due to air trapping. * **Vital Capacity (VC) = TV + IRV + ERV.** * **Total Lung Capacity (TLC) = VC + RV.**

Q: Apneusis occurs when transection is at which level?

Midpontine. **Explanation:** The respiratory centers are located in the medulla and pons. Understanding the effect of transections at different levels is a high-yield concept for NEET-PG. **1. Why Midpontine is Correct:** Apneusis is characterized by deep, gasping inspiration with a pause at full inspiration. This occurs due to the removal of the inhibitory influence of the **Pneumotaxic center** (located in the upper pons/nucleus parabrachialis) over the **Apneustic center** (located in the lower pons). * A **midpontine transection** effectively separates the pneumotaxic center from the lower respiratory centers. * **Crucial Note:** For apneusis to manifest fully, the **Vagus nerve** must also be severed. If the Vagus is intact, it provides inhibitory feedback (Hering-Breuer reflex) that prevents apneusis even if the pneumotaxic center is disconnected. **2. Analysis of Incorrect Options:** * **Above the pons:** A transection at the midbrain level leaves all pontine and medullary centers intact. Respiration remains normal. * **Pontomedullary junction:** This removes the influence of both the pneumotaxic and apneustic centers. The result is **ataxic breathing** (irregular) because the rhythm generator in the medulla (Pre-Bötzinger complex) is no longer modulated by the pons. * **Below the medulla:** This separates the respiratory centers from the spinal motor neurons (phrenic nerve). This results in **complete respiratory arrest** (apnea) and death. **High-Yield Clinical Pearls:** * **Pneumotaxic Center:** Acts as an "off-switch" for inspiration; limits tidal volume. * **Pre-Bötzinger Complex:** The "Pacemaker" of respiration, located in the medulla. * **Vagus Nerve:** The most important peripheral modifier of the pontine centers. If the Vagus is cut at the midpontine level, breathing becomes slow, deep, and apneustic.

Question 1

Which time points on the Cheyne-Stokes breathing graph are associated with the highest pCO2 of lung blood and highest pCO2 of the neurons in the respiratory centre?

Accepted Answer

Z

Answer

X

Answer

Y

Answer

W

Question 2

Caisson's disease is due to which of the following?

Accepted Answer

Gas embolism

Answer

Fat embolism

Answer

Amniotic fluid embolism

Answer

Tumor embolism

Question 3

Oxygen therapy is least useful in which of the following conditions?

Accepted Answer

Anemia

Answer

ARDS

Answer

Alveolar damage

Answer

COPD

Question 4

Most of the airway resistance is from which part of the respiratory system?

Accepted Answer

Trachea

Answer

Terminal bronchioles

Answer

Respiratory bronchioles

Answer

Medium sized bronchi

Question 5

Carbon monoxide affinity to hemoglobin is how many times compared to oxygen?

Accepted Answer

200-300 times

Answer

250 times

Answer

500 times

Answer

100 times

Question 6

What is the Haldane effect?

Accepted Answer

The effect of oxygen on the carbon dioxide carriage in the blood.

Answer

The effect of carbon dioxide on the oxygen carriage in the blood.

Answer

The effect of partial pressure of carbon dioxide on carbon dioxide carriage in the blood.

Answer

The effect of pH on oxygen carriage in the blood.

Question 7

Decreased oxygen carrying capacity with normal partial pressure of oxygen (PO2) is a feature of which type of hypoxia?

Accepted Answer

Anemic hypoxia

Answer

Histotoxic hypoxia

Answer

Stagnant hypoxia

Answer

Hypoxic hypoxia

Question 8

What is the key factor in the transport of carbon dioxide as bicarbonate?

Accepted Answer

The presence of carbonic anhydrase in the erythrocytes

Answer

The high solubility of CO2 in H2O

Answer

The presence of Hb in blood

Answer

The acid nature of carbon dioxide and the alkaline nature of bicarbonate

Question 9

All of the following can be measured by a simple spirometer except?

Accepted Answer

Residual volume

Answer

Tidal volume

Answer

FEV1

Answer

Vital capacity

Question 10

Apneusis occurs when transection is at which level?

Accepted Answer

Midpontine

Answer

Above the pons

Answer

Pontomedullary junction

Answer

Below the medulla

Respiratory System — MCQs

Respiratory System — MCQs

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