Respiratory System Practice Questions

Q: The kind of hypoxia seen in the collapse of lungs and depression of the respiratory centre is:

Hypoxic hypoxia. **Explanation:** **1. Why Hypoxic Hypoxia is Correct:** Hypoxic hypoxia (also known as arterial hypoxia) is characterized by a **low partial pressure of oxygen ($PaO_2$)** in the arterial blood. In cases of **lung collapse (atelectasis)**, there is a reduction in the surface area available for gas exchange. In **depression of the respiratory center** (e.g., opioid overdose), hypoventilation occurs. Both conditions lead to inadequate oxygenation of the blood in the lungs, resulting in a decreased $PaO_2$ and low oxygen saturation ($SaO_2$), which is the hallmark of hypoxic hypoxia. **2. Why the Other Options are Incorrect:** * **Anemic Hypoxia:** Here, $PaO_2$ is normal, but the **oxygen-carrying capacity** of the blood is reduced due to low hemoglobin levels or dysfunctional hemoglobin (e.g., CO poisoning). * **Stagnant (Ischemic) Hypoxia:** $PaO_2$ and hemoglobin are normal, but **blood flow to the tissues is inadequate** (e.g., heart failure, shock, or local embolism). * **Histotoxic Hypoxia:** The blood delivers oxygen perfectly, but the **tissues cannot utilize it** because cellular enzymes (like cytochrome oxidase) are poisoned (e.g., Cyanide poisoning). **3. Clinical Pearls for NEET-PG:** * **Cyanosis:** Most commonly seen in Hypoxic and Stagnant hypoxia. It is **not** seen in Anemic hypoxia (Hb is too low to show blue color) or Histotoxic hypoxia (blood remains bright red). * **P50 Value:** A right shift in the oxygen-dissociation curve (increased P50) is a compensatory mechanism in most hypoxias except Histotoxic. * **High Altitude:** The most common physiological cause of Hypoxic hypoxia.

Q: The approximate amount of air left in the lungs after maximal forced expiration in a normal woman is:

1.1 L. ### Explanation The volume of air remaining in the lungs after a maximal forced expiration is defined as the **Residual Volume (RV)**. This volume cannot be exhaled because the small airways collapse at low lung volumes, trapping air, and the chest wall reaches its inward limit of compression. **Why 1.1 L is correct:** In a healthy adult, the average Residual Volume is approximately **1.2 L in males** and **1.1 L in females**. Since the question specifically asks for the value in a **normal woman**, 1.1 L is the most accurate physiological estimate. **Analysis of Incorrect Options:** * **0.5 L (Option A):** This value corresponds to the **Tidal Volume (TV)**, which is the volume of air inspired or expired during a single normal breath. * **2.0 L (Option B) & 1.8 L (Option D):** These values are too high for RV. However, a value around 2.2–2.4 L would represent the **Functional Residual Capacity (FRC)**—the air remaining after a *normal* (passive) expiration (FRC = RV + ERV). **High-Yield NEET-PG Pearls:** 1. **Measurement:** Residual Volume **cannot** be measured by simple spirometry because the air never leaves the lungs. It must be measured using indirect methods: **Helium Dilution**, **Nitrogen Washout**, or **Body Plethysmography**. 2. **Clinical Correlation:** RV is significantly **increased** in obstructive lung diseases (e.g., Emphysema, Asthma) due to air trapping, leading to hyperinflation. 3. **Formula:** $FRC - ERV = RV$ (where ERV is Expiratory Reserve Volume). 4. **Aging:** RV typically increases with age as the elastic recoil of the lungs decreases.

Q: What is the normal vital capacity of the lungs?

4700 ml. **Explanation:** **Vital Capacity (VC)** is the maximum volume of air a person can exhale from the lungs after a maximum inhalation. It is a key indicator of pulmonary function and reflects the total "usable" gas exchange surface. **Why Option D is Correct:** The normal Vital Capacity in a healthy adult male is approximately **4600–4700 ml**. It is calculated by the sum of three primary lung volumes: * **Tidal Volume (TV):** 500 ml * **Inspiratory Reserve Volume (IRV):** 3000 ml * **Expiratory Reserve Volume (ERV):** 1100–1200 ml * **Calculation:** $500 + 3000 + 1200 = 4700 \text{ ml}$. **Analysis of Incorrect Options:** * **Option A (500 ml):** This represents the **Tidal Volume (TV)**, which is the volume of air inspired or expired during a normal, quiet breath. * **Option B (1200 ml):** This represents the **Residual Volume (RV)**—the air remaining in the lungs after forceful expiration—or the **Expiratory Reserve Volume (ERV)**. * **Option C (3000 ml):** This represents the **Inspiratory Reserve Volume (IRV)**, the additional volume that can be inspired above the normal tidal volume. **High-Yield NEET-PG Pearls:** 1. **VC vs. TLC:** Vital Capacity does *not* include Residual Volume. Total Lung Capacity (TLC) = VC + RV (approx. 5800–6000 ml). 2. **Clinical Significance:** VC is decreased in **Restrictive Lung Diseases** (e.g., Pulmonary Fibrosis, Kyphoscoliosis) but remains relatively normal or is only slightly reduced in obstructive diseases. 3. **Timed VC:** The most clinically significant measurement is **FEV1** (Forced Expiratory Volume in 1 second), which is normally 80% of the FVC (Forced Vital Capacity). 4. **Factors:** VC is higher in males, taller individuals, and athletes; it decreases with age and in the supine position.

Q: Carbon dioxide retention is seen in all, except?

Carbon monoxide poisoning. **Explanation:** The core concept here is the difference between **Type I** and **Type II respiratory failure**. Carbon dioxide retention (Hypercapnia) occurs when there is an issue with **ventilation** (the movement of air in and out of the lungs), whereas oxygenation issues can occur even when ventilation is preserved. **Why Carbon Monoxide (CO) Poisoning is the correct answer:** In CO poisoning, the primary pathology is **impaired oxygen transport**, not a failure of ventilation. CO binds to hemoglobin with 210 times the affinity of oxygen, causing a leftward shift of the oxygen-dissociation curve. However, the lungs' ability to exhale $CO_2$ remains intact. In fact, patients often hyperventilate due to tissue hypoxia, which leads to **decreased** $PaCO_2$ (hypocapnia) rather than retention. **Analysis of Incorrect Options:** * **Respiratory Failure:** Specifically Type II respiratory failure (Ventilatory failure) is defined by the inability to eliminate $CO_2$, leading to hypercapnia. * **Ventilator Failure:** Any mechanical failure or setting mismatch that reduces alveolar ventilation will directly result in $CO_2$ accumulation. * **Pulmonary Edema:** While initially causing Type I failure (hypoxia with low $CO_2$), severe or end-stage pulmonary edema leads to respiratory muscle fatigue and increased dead space, eventually resulting in $CO_2$ retention. **High-Yield Clinical Pearls for NEET-PG:** * **CO Poisoning Triad:** Cherry-red skin (rarely seen clinically), headache, and normal $SpO_2$ (pulse oximeters cannot distinguish between carboxyhemoglobin and oxyhemoglobin). * **Type I Respiratory Failure:** Hypoxia with normal/low $PaCO_2$ (e.g., Pneumonia, early Pulmonary Edema). * **Type II Respiratory Failure:** Hypoxia with high $PaCO_2$ (e.g., COPD, Neuromuscular weakness, Opioid overdose).

Q: Carbon monoxide poisoning causes which of the following types of hypoxia?

Anemic hypoxia. **Explanation:** **Why Anemic Hypoxia is Correct:** Anemic hypoxia occurs when the oxygen-carrying capacity of the blood is reduced, even though the partial pressure of arterial oxygen ($PaO_2$) remains normal. In Carbon Monoxide (CO) poisoning, CO binds to hemoglobin with an affinity **200–250 times greater** than oxygen, forming **carboxyhemoglobin**. This effectively reduces the amount of hemoglobin available to transport oxygen. Furthermore, CO causes a **leftward shift** of the oxygen-hemoglobin dissociation curve, meaning the remaining oxygen binds more tightly to hemoglobin and is not easily released to the tissues. **Why Other Options are Incorrect:** * **Histotoxic Hypoxia:** Occurs when tissues cannot utilize oxygen despite adequate delivery (e.g., **Cyanide poisoning** inhibiting cytochrome oxidase). * **Anoxic (Hypoxic) Hypoxia:** Characterized by low arterial $PaO_2$ due to external factors like high altitude, airway obstruction, or alveolar hypoventilation. * **Stagnant (Ischemic) Hypoxia:** Occurs when blood flow to tissues is reduced despite normal oxygen content (e.g., heart failure, shock, or local embolism). **High-Yield Clinical Pearls for NEET-PG:** * **Pulse Oximetry:** Standard pulse oximeters cannot distinguish between oxyhemoglobin and carboxyhemoglobin, often giving **falsely normal** $SpO_2$ readings. * **Clinical Sign:** Patients may present with "cherry-red" skin discoloration (a classic but late sign). * **Treatment:** 100% Hyperbaric oxygen is the treatment of choice to displace CO from hemoglobin. * **Curve Shift:** CO poisoning is a classic cause of a **Left Shift** (along with Alkalosis, decreased 2,3-DPG, and Hypothermia).

Q: An increase in which of the following parameters will shift the oxygen dissociation curve to the left?

Oxygen affinity of hemoglobin. **Explanation:** The Oxygen Dissociation Curve (ODC) represents the relationship between the partial pressure of oxygen ($PO_2$) and the percentage saturation of hemoglobin ($SaO_2$). **Why the Correct Answer is Right:** A **Left Shift** indicates that hemoglobin has an **increased affinity for oxygen**. This means hemoglobin binds oxygen more tightly and is less willing to release it to the tissues. By definition, any factor that increases the oxygen affinity of hemoglobin will shift the curve to the left. At any given $PO_2$, the hemoglobin saturation will be higher than normal. **Why the Other Options are Wrong:** Options A, B, and C all cause a **Right Shift** (decreased affinity), which facilitates oxygen unloading to tissues (the Bohr Effect). * **A. Temperature:** Increased temperature (e.g., during fever or exercise) decreases affinity, shifting the curve to the right. * **B. Partial pressure of $CO_2$ ($PCO_2$):** Increased $CO_2$ leads to increased $H^+$ concentration (decreased pH). This stabilizes the "Tense" (T) state of hemoglobin, shifting the curve to the right. * **C. 2,3 DPG concentration:** This byproduct of glycolysis binds to the beta chains of hemoglobin, decreasing its affinity for $O_2$ and shifting the curve to the right. **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic for Right Shift:** "**CADET**, face Right!" (**C**-$CO_2$, **A**-Acid/H+, **D**-2,3 DPG, **E**-Exercise, **T**-Temperature). * **Left Shift Causes:** Fetal Hemoglobin (HbF), Carbon Monoxide poisoning (COHb), Methemoglobinemia, and Alkalosis. * **$P_{50}$ Value:** The $PO_2$ at which hemoglobin is 50% saturated. A **Left Shift decreases $P_{50}$**, while a **Right Shift increases $P_{50}$**. Normal $P_{50}$ is approximately 26-27 mmHg.

Q: What is Critical Closing Volume?

Close to Residual Volume. ### Explanation **1. Why the correct answer is right:** **Closing Volume (CV)** is the volume of air remaining in the lungs during expiration at the point when the small airways (bronchioles) in the dependent (lower) parts of the lung begin to close. Physiologically, this occurs because the intrapleural pressure becomes less negative (or even positive) at the base of the lung, causing airway collapse. In healthy young individuals, this closure occurs at a very low lung volume, specifically **close to the Residual Volume (RV)**. The Closing Capacity (CC) is the sum of Closing Volume and Residual Volume (CC = CV + RV). **2. Why the incorrect options are wrong:** * **Option A:** The volume at the end of forceful expiration is the **Residual Volume (RV)** itself, not the closing volume. * **Option B:** The volume at the end of forceful inspiration is the **Total Lung Capacity (TLC)**. * **Option C:** The volume remaining after FRC is measured is not a standard physiological definition. FRC is the volume remaining after a *normal* tidal expiration. **3. Clinical Pearls & High-Yield Facts for NEET-PG:** * **Age Factor:** Closing volume increases with age. In children and the elderly, the closing volume may exceed the FRC, leading to airway closure during normal tidal breathing and impaired gas exchange. * **Position:** Closing volume is reached sooner in the **supine position** compared to standing. * **Measurement:** It is measured using the **Nitrogen Washout Method** (Spirogram Phase IV). * **Pathology:** Conditions like COPD, pulmonary edema, and chronic smoking increase the closing volume, leading to early airway collapse and ventilation-perfusion (V/Q) mismatch.

Q: Which of the following has the highest affinity for hemoglobin?

CO. **Explanation:** The correct answer is **CO (Carbon Monoxide)**. The affinity of hemoglobin (Hb) for a gas refers to the strength of the bond formed between the gas molecule and the heme iron. Carbon monoxide (CO) has an extremely high affinity for the ferrous ($Fe^{2+}$) iron of hemoglobin—approximately **210 to 250 times greater** than that of oxygen ($O_2$). When CO binds to Hb, it forms **Carboxyhemoglobin**, which is highly stable. This binding not only prevents $O_2$ from loading but also causes a **leftward shift** of the Oxygen-Hemoglobin Dissociation Curve (OHDC), making it harder for existing $O_2$ to be released into tissues, leading to cellular hypoxia. **Analysis of Incorrect Options:** * **B. $O_2$ (Oxygen):** While Hb is designed to transport oxygen, its affinity is significantly lower than that of CO. $O_2$ binds reversibly to form oxyhemoglobin. * **C. $CO_2$ (Carbon Dioxide):** $CO_2$ binds to the globin chain (forming carbaminohemoglobin), not the heme iron. Its affinity is much lower than both CO and $O_2$. * **D. $NO_2$ (Nitrogen Dioxide):** While Nitric Oxide (NO) has a very high affinity for Hb, $NO_2$ is primarily a respiratory irritant and does not compete for the heme binding site in the same physiological context as CO. **NEET-PG High-Yield Pearls:** 1. **Haldane Effect:** Binding of $O_2$ to Hb promotes the displacement of $CO_2$. 2. **Bohr Effect:** Increased $CO_2$ and $H^+$ ions decrease Hb affinity for $O_2$ (Right shift). 3. **Treatment of CO Poisoning:** 100% Hyperbaric Oxygen is used to "force" the dissociation of CO from Hb by increasing the partial pressure of $O_2$. 4. **Pulse Oximetry Pitfall:** Standard pulse oximeters cannot distinguish between oxyhemoglobin and carboxyhemoglobin, often giving falsely normal $SpO_2$ readings in CO poisoning.

Question 1

The kind of hypoxia seen in the collapse of lungs and depression of the respiratory centre is:

Accepted Answer

Hypoxic hypoxia

Answer

Anemic hypoxia

Answer

Stagnant hypoxia

Answer

Histotoxic hypoxia

Question 2

The approximate amount of air left in the lungs after maximal forced expiration in a normal woman is:

Accepted Answer

1.1 L

Answer

0.5 L

Answer

2.0 L

Answer

1.8 L

Question 3

What is the normal vital capacity of the lungs?

Accepted Answer

4700 ml

Answer

500 ml

Answer

1200 ml

Answer

3000 ml

Question 4

Respiration stops in the last stage of expiration, during forced expiration, because of:

Accepted Answer

Dynamic compression of airways

Answer

Respiratory muscle fatigue

Answer

Collapse of alveoli

Answer

Breaking effect of inspiratory muscles

Question 5

Carbon dioxide retention is seen in all, except?

Accepted Answer

Carbon monoxide poisoning

Answer

Respiratory failure

Answer

Ventilator failure

Answer

Pulmonary edema

Question 6

Carbon monoxide poisoning causes which of the following types of hypoxia?

Accepted Answer

Anemic hypoxia

Answer

Histotoxic hypoxia

Answer

Anoxic hypoxia

Answer

Stagnant hypoxia

Question 7

What is the effect on respiration when the pons is transected at its superior level?

Accepted Answer

Breathing becomes slower and deeper

Answer

Apneustic breathing

Answer

Breathing ceases

Answer

Irregular and gasping respirations

Question 8

An increase in which of the following parameters will shift the oxygen dissociation curve to the left?

Accepted Answer

Oxygen affinity of hemoglobin

Answer

Temperature

Answer

Partial pressure of CO2

Answer

2,3 DPG concentration

Question 9

What is Critical Closing Volume?

Accepted Answer

Close to Residual Volume

Answer

Volume at the end of forceful expiration

Answer

Volume at the end of forceful inspiration

Answer

Volume remaining after Functional Residual Capacity is measured

Question 10

Which of the following has the highest affinity for hemoglobin?

Accepted Answer

CO

Answer

O2

Answer

CO2

Answer

NO2

Respiratory System — MCQs

Respiratory System — MCQs

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