Respiratory System Practice Questions

Q: What is the normal ratio of forced expiratory volume in the first second (FEV1) to the forced vital capacity (FVC) in an adult male?

80%. **Explanation:** The **FEV1/FVC ratio** (also known as the Tiffeneau-Pinelli index) is a critical parameter in spirometry used to differentiate between obstructive and restrictive lung diseases. In a healthy adult, approximately **80%** of the total air that can be forcibly exhaled (FVC) is expelled within the very first second (FEV1). **Why 80% is correct:** In healthy lungs with normal airway resistance and elastic recoil, the majority of the vital capacity is cleared rapidly. A ratio of 0.75 to 0.85 (averaging 80%) is considered the physiological norm. **Analysis of Incorrect Options:** * **95% (Option A):** This is abnormally high. While seen in some cases of severe restrictive lung disease (where FVC drops more than FEV1), it is not the standard physiological average. * **65% (Option C):** This indicates mild **obstructive** lung disease (e.g., Asthma or COPD). A ratio below 70% is the diagnostic threshold for airflow limitation. * **50% (Option D):** This represents significant airway obstruction. Such low values are typical of moderate-to-severe COPD. **High-Yield Clinical Pearls for NEET-PG:** 1. **Obstructive Disease (Asthma/COPD):** Both FEV1 and FVC decrease, but **FEV1 decreases significantly more**, leading to a **decreased ratio (<70%)**. 2. **Restrictive Disease (Fibrosis):** Both FEV1 and FVC decrease proportionately, or FVC decreases more. Consequently, the **ratio remains normal or is increased**. 3. **Flow-Volume Loops:** In obstructive disease, the loop shows a "scooped-out" appearance; in restrictive disease, the loop is tall, narrow, and shifted to the right.

Q: Which gas is used to measure the diffusing capacity of the lungs?

Carbon monoxide. **Explanation:** The diffusing capacity of the lung (DLCO) measures the ability of the lungs to transfer gas from the inhaled air to the red blood cells in the pulmonary capillaries. **Why Carbon Monoxide (CO) is the Correct Answer:** Carbon monoxide is the gas of choice because it is **diffusion-limited**. CO has an extremely high affinity for hemoglobin (approximately 210–240 times that of oxygen). When a small, non-toxic amount is inhaled, it binds almost instantaneously to hemoglobin, keeping the partial pressure of CO in the plasma near zero. This creates a stable and maximal partial pressure gradient between the alveoli and the capillary, ensuring that the rate of transfer depends solely on the properties of the alveolar-capillary membrane (thickness and surface area). **Analysis of Incorrect Options:** * **B. Carbon Dioxide (CO₂):** CO₂ diffuses 20 times faster than oxygen; its transfer is limited by perfusion (blood flow), not diffusion, making it unsuitable for measuring diffusing capacity. * **C. Nitrogen (N₂):** Nitrogen is an inert gas that does not bind to hemoglobin and reaches equilibrium rapidly, making it ineffective for measuring membrane diffusion. * **D. Helium (He):** Helium is used in pulmonary function tests to measure **Functional Residual Capacity (FRC)** and residual volume via the helium dilution method, but it does not cross the alveolar-capillary membrane. **High-Yield Clinical Pearls for NEET-PG:** * **DLCO is increased in:** Polycythemia, Alveolar hemorrhage (e.g., Goodpasture syndrome), and early stages of Congestive Heart Failure (due to increased pulmonary capillary blood volume). * **DLCO is decreased in:** Emphysema (loss of surface area), Interstitial Lung Disease/Fibrosis (increased membrane thickness), and Anemia. * **Formula:** $DLCO = \text{Rate of CO uptake} / (\text{Alveolar } P_{CO} - \text{Capillary } P_{CO})$. Since capillary $P_{CO}$ is negligible, it simplifies the calculation.

Q: What is the effect of cutting the spinal cord above the medulla on respiration?

Irregular and gasping. ### Explanation **Correct Answer: D. Irregular and gasping** **Underlying Concept:** The fundamental rhythm of respiration is generated by the **Pre-Bötzinger complex** and the **Medullary Respiratory Centers** (Dorsal and Ventral Respiratory Groups). While the medulla can generate a basic rhythm, it requires input from higher centers (Pons and Cortex) and peripheral feedback to maintain a smooth, regular pattern. When the spinal cord is cut **above the medulla** (specifically at the midbrain-medullary junction or high medullary level), the connection between the **Pons** (Pneumotaxic and Apneustic centers) and the **Medulla** is severed. The isolated medulla, deprived of the "fine-tuning" influence of the pontine centers, produces a primitive, disorganized rhythm characterized by **irregular and gasping** breaths (ataxic breathing). **Why other options are incorrect:** * **A. Breathing becomes slower and deeper:** This occurs when the **Vagus nerve** is bilaterally transected (loss of Hering-Breuer reflex) or when the **Pneumotaxic center** is inhibited. * **B. Apneustic breathing:** This is characterized by prolonged inspiratory gasps. It occurs when there is a lesion in the **upper pons** (Pneumotaxic center) combined with a bilateral **Vagotomy**. * **C. Breathing ceases:** Respiration stops (Apnea) only if the lesion is **below the medulla** (at or above C3-C5), which severs the connection between the respiratory centers and the phrenic nerve (which innervates the diaphragm). **High-Yield Facts for NEET-PG:** * **Pneumotaxic Center (Upper Pons):** Acts as the "off-switch" for inspiration; limits tidal volume. * **Apneustic Center (Lower Pons):** Delays the "off-switch," prolonging inspiration. * **C3, 4, 5 keep the diaphragm alive:** A spinal cord injury at C3 or above leads to immediate respiratory arrest. * **Cheyne-Stokes Breathing:** Often seen in heart failure or cortical brain damage (uphill/downhill pattern).

Q: Laminar flow is dependent on which of the following factors?

Critical velocity. **Explanation:** The type of airflow in the respiratory tract (laminar vs. turbulent) is determined by the **Reynolds Number (Re)**. According to the formula $Re = \frac{\rho vd}{\eta}$ (where $\rho$ is density, $v$ is velocity, $d$ is diameter, and $\eta$ is viscosity), flow remains **laminar** as long as the velocity of the gas stays below a specific threshold known as the **Critical Velocity**. 1. **Why A is correct:** Critical velocity is the maximum velocity at which airflow remains laminar. Once the gas velocity exceeds this point, the Reynolds number surpasses 2000, and the flow transitions from smooth, streamlined (laminar) layers to disorganized, eddy-forming **turbulent flow**. Therefore, the maintenance of laminar flow is directly dependent on staying below this critical velocity. 2. **Why B is incorrect:** While viscosity ($\eta$) influences the Reynolds number, laminar flow itself is primarily driven by the pressure gradient and is inversely proportional to viscosity (Poiseuille’s Law). However, the *transition* and *dependency* of flow type are defined by the velocity threshold. 3. **Why C is incorrect:** Constant velocity simply means the speed does not change; it does not dictate whether the flow is laminar or turbulent. 4. **Why D is incorrect:** Critical closing pressure refers to the pressure at which small airways or blood vessels collapse (Laplace’s Law), which is unrelated to the pattern of fluid flow. **High-Yield NEET-PG Pearls:** * **Laminar Flow:** Occurs in small peripheral airways (bronchioles) where velocity is low. * **Turbulent Flow:** Occurs in large airways (trachea) where velocity is high. * **Heliox Therapy:** In airway obstruction, replacing Nitrogen with Helium (lower density) reduces the Reynolds number, converting turbulent flow back to laminar flow, thereby decreasing the work of breathing.

Q: Binding of O2 to hemoglobin reduces its affinity for CO2 by which effect?

Haldane effect. **Explanation:** The correct answer is **B. Haldane effect**. The **Haldane Effect** describes how the oxygenation of hemoglobin in the lungs promotes the dissociation of carbon dioxide ($CO_2$). When $O_2$ binds to hemoglobin, the molecule becomes more acidic. This conformational change reduces its affinity for $CO_2$ and causes the release of $H^+$ ions. These $H^+$ ions then react with bicarbonate ($HCO_3^-$) to form carbonic acid, which dissociates into $H_2O$ and $CO_2$, allowing $CO_2$ to be exhaled. Essentially, **$O_2$ displacement of $CO_2$** occurs in the lungs. **Analysis of Incorrect Options:** * **A. Bohr’s Effect:** This is the opposite physiological process occurring at the **tissue level**. It describes how increased $CO_2$ and $H^+$ (acidity) decrease hemoglobin’s affinity for $O_2$, facilitating oxygen unloading to metabolically active tissues. * **C. Chloride Shift (Hamburger Phenomenon):** This refers to the exchange of bicarbonate ($HCO_3^-$) for chloride ($Cl^-$) ions across the RBC membrane to maintain electrical neutrality during $CO_2$ transport. * **D. Ohm’s Effect:** This is a distractor related to physics (Ohm’s Law: $V=IR$). In cardiovascular physiology, a similar principle applies to hemodynamics ($Q = \Delta P/R$), but it has no relation to gas binding. **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic:** **H**aldane effect happens in the **H**eart/Lungs (Oxygenation helps $CO_2$ release); **B**ohr effect happens in the **B**ody tissues (Acidity helps $O_2$ release). * The Haldane effect is quantitatively more important in promoting $CO_2$ transport than the Bohr effect is in promoting $O_2$ transport. * In patients with chronic COPD, administering high-flow oxygen can worsen hypercapnia partly due to the Haldane effect (displacing $CO_2$ from hemoglobin into the blood).

Q: During inspiration, what is the main pathway of airflow in a normal nasal cavity?

Middle part of the cavity in a parabolic curve. **Explanation:** The nasal cavity is designed to optimize the conditioning (warming, humidifying, and filtering) of inspired air. During normal, quiet inspiration, the primary stream of air does not travel along the floor of the nose; instead, it rises and passes through the **middle part of the cavity** (between the turbinates and the septum), following a **parabolic curve**. **Why Option A is correct:** The anatomy of the nasal conchae (turbinates) creates resistance and directs the bulk of the airflow through the widest part of the nasal passage—the middle meatus area. The air rises from the nostrils, reaches its highest point in the middle of the cavity, and then curves downward toward the posterior choanae. This parabolic path increases the surface area contact with the respiratory mucosa, ensuring maximum humidification and temperature regulation. **Why other options are incorrect:** * **Option B:** The lower part (inferior meatus) is primarily a drainage pathway for the nasolacrimal duct and does not accommodate the main inspiratory stream. * **Option C & D:** The superior part of the cavity contains the **olfactory area**. Under normal breathing conditions, only a small fraction of air reaches this high. To direct air to the olfactory epithelium, one must "sniff" (forced inspiration), which creates higher velocity and turbulence. **High-Yield NEET-PG Pearls:** * **Airflow Type:** Airflow in the nasal cavity is normally **laminar** at low flow rates but becomes **turbulent** near the turbinates to facilitate heat and moisture exchange. * **Nasal Resistance:** The nose contributes approximately **50% of the total respiratory resistance**. * **Conditioning:** By the time air reaches the nasopharynx, it is already warmed to 31–37°C and saturated with 75–95% humidity.

Q: The oxyhemoglobin dissociation curve is shifted to the left in which of the following conditions?

Hypothermia. **Explanation:** The **Oxyhemoglobin Dissociation Curve (ODC)** represents the relationship between the partial pressure of oxygen ($PO_2$) and the percentage saturation of hemoglobin. A **shift to the left** indicates an increased affinity of hemoglobin for oxygen, meaning hemoglobin binds oxygen more tightly and is less willing to release it to the tissues. **Why Hypothermia is Correct:** Temperature is a key regulator of hemoglobin affinity. **Hypothermia (decreased temperature)** stabilizes the bond between oxygen and hemoglobin, shifting the curve to the left. Conversely, hyperthermia (fever) shifts the curve to the right to facilitate oxygen unloading during increased metabolic demand. **Analysis of Incorrect Options:** * **Metabolic Acidosis (A):** A decrease in pH (acidosis) shifts the curve to the **right**. This is known as the **Bohr Effect**, where hydrogen ions bind to hemoglobin, reducing its affinity for oxygen. * **Hypercapnia (B):** Increased $PCO_2$ levels lead to increased $H^+$ production. This shifts the curve to the **right**, aiding oxygen delivery to tissues with high metabolic activity. * **Increased 2,3-DPG (D):** 2,3-Diphosphoglycerate is a byproduct of glycolysis in RBCs. It binds to the beta chains of deoxyhemoglobin and stabilizes the "T" (tense) state, shifting the curve to the **right**. **NEET-PG High-Yield Pearls:** * **Mnemonic for Left Shift:** **"HALT"** (**H**ypothermia, **A**lkalosis, **L**ow 2,3-DPG, **T**oxic levels of CO/MetHb). * **P50 Value:** The $PO_2$ at which hemoglobin is 50% saturated. A **left shift decreases the P50**, while a right shift increases it. * **Fetal Hemoglobin (HbF):** Naturally has a higher affinity for $O_2$ than adult hemoglobin (HbA) to facilitate $O_2$ transfer across the placenta, thus the HbF curve is always to the **left** of the HbA curve.

Question 1

What is the normal ratio of forced expiratory volume in the first second (FEV1) to the forced vital capacity (FVC) in an adult male?

Accepted Answer

80%

Answer

95%

Answer

65%

Answer

50%

Question 2

Which gas is used to measure the diffusing capacity of the lungs?

Accepted Answer

Carbon monoxide

Answer

Carbon dioxide

Answer

Nitrogen

Answer

Helium

Question 3

The provided graph illustrates the relationship between lung volume and intrapleural pressure during inspiration and expiration. What is the most likely explanation for the observed pattern?

Accepted Answer

The difference in surfactant activity during inspiration and expiration.

Answer

The difference between active and passive work performed during respiration.

Answer

The variation in airway resistance between inspiration and expiration.

Answer

The fluctuations in intrapleural pressure.

Question 4

What is the effect of cutting the spinal cord above the medulla on respiration?

Accepted Answer

Irregular and gasping

Answer

Breathing becomes slower and deeper

Answer

Apneustic breathing

Answer

Breathing ceases

Question 5

Laminar flow is dependent on which of the following factors?

Accepted Answer

Critical velocity

Answer

Viscosity

Answer

Constant velocity

Answer

Critical closing pressure

Question 6

Binding of O2 to hemoglobin reduces its affinity for CO2 by which effect?

Accepted Answer

Haldane effect

Answer

Bohr's effect

Answer

Chloride shift

Answer

Ohm's effect

Question 7

Which of the following is seen in pneumothorax?

Accepted Answer

Reduced concentration of surfactant

Answer

Over expanded chest wall

Answer

More negative intrapleural pressure

Answer

Increased lung compliance

Question 8

During inspiration, what is the main pathway of airflow in a normal nasal cavity?

Accepted Answer

Middle part of the cavity in a parabolic curve

Answer

Lower part of the cavity in a parabolic curve

Answer

Superior part of the cavity in a parabolic curve

Answer

Through the olfactory area

Question 9

The oxyhemoglobin dissociation curve is shifted to the left in which of the following conditions?

Accepted Answer

Hypothermia

Answer

Metabolic acidosis

Answer

Hypercapnia

Answer

Increased 2,3-DPG levels

Question 10

Holding one's breath after hyperventilating for some time is dangerous because:

Accepted Answer

Due to lack of stimulation by CO2, anoxia can reach dangerous levels.

Answer

A decrease in CO2 shifts the O2 dissociation curve to the left.

Answer

Alkalosis can lead to tetany.

Answer

It can lead to CO2 Narcosis.

Respiratory System — MCQs

Respiratory System — MCQs

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