Respiratory System Practice Questions

Q: During an asthma attack, a patient experiences difficulty exhaling air. What is the impact of this condition on airway resistance and lung volumes?

Increases airway resistance and increases residual volume. ***Increases airway resistance and increases residual volume*** - During an asthma attack, **bronchoconstriction** and **mucus plugging** lead to narrowing of the airways, significantly **increasing airway resistance**. - Difficulty in exhaling air (air trapping) causes a greater volume of air to remain in the lungs after complete exhalation, thus **increasing residual volume**. *Increases airway resistance and decreases total lung capacity* - While airway resistance does increase, **total lung capacity (TLC)** typically remains normal or can even increase due to hyperinflation in chronic asthma, rather than decrease. - A decrease in TLC is more characteristic of **restrictive lung diseases**, not obstructive conditions like asthma. *Decreases airway resistance and decreases total lung capacity* - Airway resistance actively **increases** in asthma due to inflammation and bronchoconstriction, it does not decrease. - **Decreased total lung capacity** is inconsistent with the air-trapping pathophysiology of asthma. *Decreases airway resistance and increases total lung capacity* - Airway resistance in asthma is **increased**, not decreased, due to obstructed airflow. - While **total lung capacity** can be increased in chronic asthma due to hyperinflation, the correct answer focuses on the immediate effect of **increased residual volume**, which is the key pathophysiologic change during an acute attack.

Q: Identify the muscle that assists in both breathing and changes in the volume of the thoracic cavity.

Diaphragm. ***Diaphragm*** - The **diaphragm** is the primary muscle of inspiration, and its contraction causes it to flatten, increasing the **vertical diameter** of the thoracic cavity [1]. - This increase in thoracic volume leads to a decrease in intrapleural pressure, drawing air into the lungs [1]. *External oblique* - The **external oblique** is an abdominal muscle involved in forced expiration by compressing the abdominal contents and pushing the diaphragm upwards. - It does not directly affect the initial increase in thoracic volume during quiet breathing. *Rectus abdominis* - The **rectus abdominis** is an abdominal muscle that aids in forced expiration by pulling the sternum and rib cage downwards, thereby decreasing thoracic volume. - It is not a primary muscle involved in increasing thoracic volume for inspiration. *Internal intercostal* - The **internal intercostals** are primarily involved in forced expiration, pulling the ribs downwards and inwards to decrease the thoracic volume. - During quiet inspiration, the **external intercostals** elevate the ribs to increase thoracic volume, not the internal intercostals [1].

Q: A patient presents with shortness of breath and cyanosis. An ABG shows a PaO2 of 55 mmHg. Which compensatory mechanism is likely to be activated?

Increased alveolar ventilation. ***Increased alveolar ventilation*** - **Hypoxemia** (PaO2 of 55 mmHg) is a powerful stimulus for the peripheral chemoreceptors, particularly the carotid bodies. - Activation of these chemoreceptors leads to an increase in the **rate and depth of breathing**, thereby increasing **alveolar ventilation** to improve oxygen uptake. *Decreased cardiac output* - In response to **hypoxemia**, the body typically tries to increase oxygen delivery to tissues by increasing **cardiac output**, not decreasing it. - A decreased cardiac output would further exacerbate tissue hypoxia. *Decreased erythropoietin production* - **Hypoxemia** stimulates the kidneys to increase the production of **erythropoietin**, not decrease it. - Increased erythropoietin production leads to an increase in **red blood cell mass**, which enhances the oxygen-carrying capacity of the blood as a long-term compensatory mechanism. *Decreased alveolar ventilation* - A **decreased alveolar ventilation** would worsen the hypoxemia by reducing the amount of oxygen reaching the alveoli and consequently the blood. - The body's immediate compensatory response to hypoxemia is to increase ventilation to counteract the low PaO2.

Q: What is the definition of Functional Residual Capacity (FRC)?

After normal expiration. ***After normal expiration*** - **Functional Residual Capacity (FRC)** is the volume of air remaining in the lungs after a **normal, quiet exhalation** - It represents the sum of **Expiratory Reserve Volume (ERV)** and **Residual Volume (RV)** - This is the equilibrium point where the inward recoil of the lungs equals the outward recoil of the chest wall *After normal inspiration* - This would represent FRC plus the **tidal volume**, which is not a standard lung capacity measurement - The lungs are at their highest volume during a quiet breathing cycle at this point *After forceful expiration* - This describes the point at which only the **Residual Volume (RV)** remains in the lungs - All of the expiratory reserve volume has been expelled, leaving only RV - FRC exists *before* a forceful expiration, not after *After forceful inspiration* - This represents the **Total Lung Capacity (TLC)**, which is the maximum volume of air the lungs can hold - TLC = FRC + Inspiratory Capacity (IC), or RV + ERV + TV + IRV

Q: What happens to gas exchange when the Va/Q ratio approaches infinity?

Gas exchange is impaired due to lack of blood flow.. ***Gas exchange is impaired due to lack of blood flow.*** - When the **V̇A/Q̇ ratio approaches infinity**, it means **ventilation** (V̇A) is present but **perfusion** (Q̇) approaches zero. - This represents **alveolar dead space** - alveoli are ventilated but have no blood flow to participate in gas exchange. - **Both oxygen and carbon dioxide exchange are completely impaired** because there is no blood available to pick up O₂ or deliver CO₂ for elimination. - Clinical examples include **pulmonary embolism** and destroyed pulmonary vasculature. - This option correctly identifies the mechanism (lack of blood flow) and the outcome (impaired gas exchange for all gases). *Oxygen exchange is completely absent.* - While this statement is true, it is **incomplete** as it only addresses oxygen. - When perfusion is absent, **both O₂ and CO₂ exchange are equally affected**. - This option is too narrow and misses the complete physiological picture. *Carbon dioxide exchange is completely absent.* - Similar to the oxygen option, this is **incomplete** as it only mentions one gas. - Both gases require blood flow for exchange, so both are equally impaired. *Gas exchange remains normal.* - This is clearly **incorrect**. - V̇A/Q̇ → ∞ represents an extreme **ventilation-perfusion mismatch** with complete absence of perfusion. - This scenario results in severe impairment of all gas exchange.

Q: FEV1/FVC is decreased in:

Obstructive lung disease such as asthma. ***Obstructive lung disease such as asthma*** - In **obstructive lung diseases**, there is difficulty with **airflow out of the lungs**, leading to a disproportionate decrease in **FEV1** compared to FVC [1]. - This results in a **reduced FEV1/FVC ratio**, which is a hallmark of conditions like asthma and COPD [1]. *Kyphosis and scoliosis* - These are **restrictive lung conditions** due to chest wall deformities, which typically show a reduced FVC but a **normal or increased FEV1/FVC ratio**. - The primary problem is reduced lung volume, not airflow obstruction. *Restrictive lung disease* - In general, **restrictive lung diseases** are characterized by **reduced lung volumes** (decreased FVC) but **preserved or even increased airflow rates**. - Therefore, the **FEV1/FVC ratio** is usually **normal or elevated**, not decreased. *Pulmonary fibrosis* - **Pulmonary fibrosis** is a type of **restrictive lung disease** where lung tissue becomes stiff and scarred, leading to decreased lung volumes. - While FVC is decreased, the **FEV1/FVC ratio typically remains normal or even increases** because both FEV1 and FVC decrease proportionally, or FEV1 decreases less.

Q: Closing volume is related to which of the following?

Residual volume. ***Residual volume*** - **Closing volume (CV)** is the lung volume at which the smallest airways in dependent lung regions begin to close during expiration. - CV is measured as the volume of gas expired from the beginning of airway closure (phase IV of the single-breath nitrogen test) down to **residual volume (RV)**. - **Closing Capacity (CC) = Closing Volume (CV) + Residual Volume (RV)**, demonstrating their direct mathematical relationship. - When CC exceeds FRC (functional residual capacity), airways close during normal tidal breathing, leading to gas trapping and V/Q mismatch. - CV increases with age, smoking, and obstructive lung diseases, encroaching on the expiratory reserve volume and eventually affecting tidal breathing. *Tidal volume* - **Tidal volume (TV)** is the volume of air inhaled or exhaled during normal, quiet breathing (approximately 500 mL in adults). - TV is not used in the measurement or definition of closing volume. - While increased CV can cause airway closure *during* tidal breathing (when CC > FRC), TV itself is not mathematically or definitionally related to CV. *Vital capacity* - **Vital capacity (VC)** is the maximum volume of air that can be exhaled after maximal inspiration (VC = IRV + TV + ERV). - VC is a measure of overall ventilatory capacity but does not specifically relate to the point at which airways begin to close. - CV represents a small fraction of the total lung volumes and is specifically about airway mechanics, not maximal breathing capacity. *None of the options* - This is incorrect because **residual volume** has a direct mathematical relationship with closing volume through the equation CC = CV + RV.

Q: Distending capacity of lung (maximum change in volume during inspiration) is maximum at?

Base of the lung. ***Base of the lung*** - Due to **gravitational forces**, the negative intrapleural pressure is less negative at the base compared to the apex, meaning the alveoli at the base are less stretched at rest. - This **lesser distension at rest** allows the alveoli at the base to have a greater capacity to expand and distend during inspiration, leading to better ventilation. *Apex of the lung* - The **more negative intrapleural pressure** at the apex causes alveoli to be more distended (larger) at functional residual capacity (FRC). - These already stretched alveoli have **less capacity to further distend** during inspiration, leading to less ventilation compared to the base. *Mid region of the lung* - The distending capacity in the mid-region is **intermediate** between the apex and the base. - It is **not the maximum** because the gravitational gradient of intrapleural pressure still allows the base to have a greater change in volume. *Lower lobe of the lung* - While the base of the lung is part of the lower lobe, referring specifically to the "lower lobe" is still **less precise** than the "base." - The specific term "base" refers to the region with the **largest distending capacity** due to the physiological pressure gradient.

Q: Which of the following statements about the O2-Hb dissociation curve is correct?

It demonstrates cooperative binding.. ***It demonstrates cooperative binding.*** - **Cooperative binding** describes how the binding of one oxygen molecule to hemoglobin increases the affinity of the remaining binding sites for oxygen. - This property gives the O2-Hb dissociation curve its characteristic **sigmoid (S-shaped)** appearance, allowing for efficient oxygen loading in the lungs and unloading in the tissues. *The curve is a straight line.* - The O2-Hb dissociation curve is **sigmoid or S-shaped**, not a straight line, due to the phenomenon of cooperative binding. - A straight line would imply a constant affinity of hemoglobin for oxygen, which is not the case. *It is 100% saturated at a PO2 of 100 mmHg.* - Hemoglobin is typically around **97-98% saturated** at a PO2 of 100 mmHg (arterial blood). - Complete 100% saturation is rarely achieved under physiological conditions. *A hemoglobin molecule can carry 4 molecules of O2.* - While this statement is factually true (one hemoglobin molecule has **four heme groups** and can bind up to **four molecules of oxygen**), it describes the structure and oxygen-carrying capacity of hemoglobin rather than a characteristic of the dissociation **curve itself**. - The question asks about features of the O2-Hb dissociation curve, and cooperative binding is the key property that defines the curve's behavior and sigmoid shape.

Q: Diffusion related to O2 transport across respiratory membrane is an example of?

Simple diffusion. ***Simple diffusion*** - Oxygen crosses the **respiratory membrane** (alveolar and capillary walls) directly through the lipid bilayer, driven by its **partial pressure gradient**. - This process does not require protein carriers or metabolic energy, fitting the definition of **simple diffusion**. *Facilitated diffusion* - This type of diffusion requires a **specific protein carrier** to transport molecules across the membrane. - While it does not require metabolic energy, oxygen transport across the respiratory membrane is efficient enough via simple diffusion due to its small size and lipid solubility. *Active diffusion* - This term is a **misnomer**; diffusion is by definition a passive process. - **Active transport** involves moving molecules against their concentration gradient, which requires metabolic energy (ATP). *Osmotic diffusion* - **Osmosis** specifically refers to the diffusion of **water** across a selectively permeable membrane. - It does not describe the movement of gases like oxygen.

Question 1

During an asthma attack, a patient experiences difficulty exhaling air. What is the impact of this condition on airway resistance and lung volumes?

Accepted Answer

Increases airway resistance and increases residual volume

Answer

Increases airway resistance and decreases total lung capacity

Answer

Decreases airway resistance and decreases total lung capacity

Answer

Decreases airway resistance and increases total lung capacity

Question 2

Identify the muscle that assists in both breathing and changes in the volume of the thoracic cavity.

Accepted Answer

Diaphragm

Answer

External oblique

Answer

Rectus abdominis

Answer

Internal intercostal

Question 3

A patient presents with shortness of breath and cyanosis. An ABG shows a PaO2 of 55 mmHg. Which compensatory mechanism is likely to be activated?

Accepted Answer

Increased alveolar ventilation

Answer

Decreased cardiac output

Answer

Decreased erythropoietin production

Answer

Decreased alveolar ventilation

Question 4

What is the definition of Functional Residual Capacity (FRC)?

Accepted Answer

After normal expiration

Answer

After normal inspiration

Answer

After forceful expiration

Answer

After forceful inspiration

Question 5

What happens to gas exchange when the Va/Q ratio approaches infinity?

Accepted Answer

Gas exchange is impaired due to lack of blood flow.

Answer

Oxygen exchange is completely absent.

Answer

Carbon dioxide exchange is completely absent.

Answer

Gas exchange remains normal.

Question 6

FEV1/FVC is decreased in:

Accepted Answer

Obstructive lung disease such as asthma

Answer

Kyphosis and scoliosis

Answer

Restrictive lung disease

Answer

Pulmonary fibrosis

Question 7

Closing volume is related to which of the following?

Accepted Answer

Residual volume

Answer

Tidal volume

Answer

Vital capacity

Answer

None of the options

Question 8

Distending capacity of lung (maximum change in volume during inspiration) is maximum at?

Accepted Answer

Base of the lung

Answer

Apex of the lung

Answer

Mid region of the lung

Answer

Lower lobe of the lung

Question 9

Which of the following statements about the O2-Hb dissociation curve is correct?

Accepted Answer

It demonstrates cooperative binding.

Answer

The curve is a straight line.

Answer

It is 100% saturated at a PO2 of 100 mmHg.

Answer

A hemoglobin molecule can carry 4 molecules of O2.

Question 10

Diffusion related to O2 transport across respiratory membrane is an example of?

Accepted Answer

Simple diffusion

Answer

Facilitated diffusion

Answer

Active diffusion

Answer

Osmotic diffusion

Respiratory System — MCQs

Respiratory System — MCQs

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