Respiratory System Practice Questions

Q: Vital capacity is measured by:

Spirometer. ***Spirometer*** - A **spirometer** is a device used to measure lung volumes and capacities, including **vital capacity**. - It measures the volume of air inspired and expired by evaluating mechanical changes in the volume of air in the lungs. *Plethysmography* - **Plethysmography** is primarily used to measure **residual volume** and **total lung capacity**, not vital capacity directly. - This method measures changes in body volume to infer changes in lung volume. *Gas-dilution method* - The **gas-dilution method**, typically using helium, is used to measure the **functional residual capacity (FRC)** and subsequently calculate residual volume and total lung capacity. - It involves rebreathing a known concentration of gas to determine the volume of gas already in the lungs. *Nitrogen washout technique* - The **nitrogen washout technique** is also used to measure **functional residual capacity (FRC)** and detect uneven ventilation. - It involves breathing 100% oxygen to wash out all nitrogen from the lungs, allowing for calculation of lung volumes.

Q: In the relaxation pressure curve, at zero relaxation pressure in chronic smokers:

Lung volume remains elevated. ***Lung volume remains elevated*** - In chronic smokers, conditions like **emphysema** lead to loss of elastic recoil and **air trapping**. - At zero relaxation pressure (the point where the respiratory system is at its resting equilibrium), the **functional residual capacity (FRC)** is higher due to less elastic recoil, which maintains the lungs at a more inflated state. - The balance between inward lung recoil and outward chest wall recoil shifts, resulting in a new equilibrium at a higher lung volume. *Lung volume decreases significantly* - This would imply increased elastic recoil or significant **airway obstruction** preventing air from entering, which is contrary to the typical pathophysiological changes in chronic smokers (e.g., emphysema). - In emphysema, the **loss of elastic recoil** actually prevents the lungs from deflating efficiently, leading to increased rather than decreased lung volume at rest. *No significant change in lung volume* - Chronic smoking often results in **structural changes** to the lungs, particularly **emphysema**, which significantly alters lung mechanics. - These changes directly impact the **resting lung volume (FRC)** as the balance between elastic recoil and chest wall compliance is disturbed, leading to a noticeable increase. *Lung compliance decreases* - This is incorrect; in emphysema, lung **compliance actually increases** due to destruction of alveolar walls and loss of elastic tissue. - Increased compliance means the lungs are more easily distensible but have reduced elastic recoil, contributing to air trapping and elevated FRC.

Q: What physiological mechanism is responsible for the increase in the duration of expiration?

Hering-Breuer reflex. ***Hering-Breuer reflex*** - The **Hering-Breuer reflex** is initiated by **stretch receptors in the bronchi and bronchioles** which are activated during lung inflation. - This reflex **inhibits inspiration** and **prolongs expiration**, preventing overinflation of the lungs. *J-reflex* - The **J-reflex** is stimulated by **juxtacapillary (J) receptors** in the alveolar walls, usually in response to pulmonary edema or congestion. - It typically causes **rapid, shallow breathing** and **bronchoconstriction**, not prolonged expiration. *Head's paradoxical reflex* - **Head's paradoxical reflex** (also known as the **inflation reflex** in newborns) involves an inspiratory effort triggered by lung inflation, often overcoming the Hering-Breuer reflex in specific conditions. - It tends to **increase respiratory rate** and depth, not prolong expiration. *Proprioceptors* - **Proprioceptors** are sensory receptors in muscles, tendons, and joints that provide information about body position and movement. - While they can influence respiration during exercise, they are not primarily responsible for directly **increasing the duration of expiration** as a reflex mechanism against overinflation.

Q: Which of the following statements about lung compliance is false?

Decreased in emphysema. ***Decreased in emphysema*** - This statement is **false** because **emphysema** is characterized by the destruction of elastic fibers in the lung parenchyma, which paradoxically leads to an **increase** in lung compliance. - The loss of elastic recoil makes the lungs more distensible and easier to inflate, but also impairs their ability to passively exhale. *Total compliance is 0.2 L/cm H2O* - This value represents the **normal total lung compliance** in a healthy adult (0.17 to 0.25 L/cm H2O), including both lung and chest wall compliance. - Lung compliance alone is typically around 0.2 L/cm H2O for healthy lungs. *A measure of lung distensibility* - **Compliance** is intrinsically defined as a measure of how easily the lungs or chest wall can be stretched or distended. - High compliance means the lungs are easy to inflate, while low compliance means they are stiff and difficult to inflate. *Change in volume per unit change in pressure* - This is the explicit **formula and definition of compliance** (C = ΔV/ΔP). - It quantifies the change in lung volume in response to a given change in transpulmonary pressure.

Q: What is the total surface area of the respiratory membrane in a healthy adult human?

75 m2. ***75 m²*** - The **total surface area** of the respiratory membrane in a healthy adult human is approximately **70-80 m²**, with 75 m² being the most accurate estimate among the given options. - This large surface area is primarily attributed to the presence of approximately **300-500 million alveoli**, which are crucial for efficient gas exchange. - Modern measurements using **stereological techniques** have refined earlier estimates and established this range as the current standard. *100 m²* - This value represents an **older estimate** that has been revised downward with more accurate measurement techniques. - While historically cited in older textbooks, current physiological data supports a **smaller surface area** of approximately 70-80 m². *30 m²* - This value is significantly **underestimated** for the total respiratory membrane surface area. - Such a small surface area would result in highly **inefficient gas exchange**, leading to severe respiratory compromise and inability to meet metabolic demands. *50 m²* - While larger than 30 m², this is still an **underestimation** of the full respiratory membrane surface area. - It does not adequately account for the extensive and intricate branching of the **respiratory bronchioles** and the vast number of alveolar sacs.

Q: What is the normal O2 extraction ratio of tissues?

25 percent. ***25 percent*** - The normal **O2 extraction ratio** (or **oxygen utilization coefficient**) is approximately 25%, meaning tissues extract about one-fourth of the oxygen delivered by arterial blood. - This ratio is crucial for understanding **tissue oxygenation** and can increase significantly during times of high metabolic demand, such as exercise. *5 percent* - An O2 extraction ratio of 5% is **too low** for normal physiological function, indicating that tissues are receiving much more oxygen than they are utilizing. - Such a low ratio would be seen only in situations of **excessive oxygen delivery** or **severely reduced metabolic demand**. *15 percent* - While 15% represents some oxygen extraction, it is **below the normal physiological range** for resting tissues. - An extraction ratio of 15% would mean the tissues are not extracting sufficient oxygen to meet their typical metabolic needs efficiently. *40 percent* - An O2 extraction ratio of 40% is **higher than the normal resting value** and suggests increased oxygen demand by the tissues. - This level of extraction is typically seen during **strenuous exercise** or in conditions of **reduced oxygen delivery** where tissues compensate by extracting more oxygen from available blood.

Q: What is the typical oxygen saturation level of venous blood?

70%. ***70%*** - Venous blood has a lower oxygen saturation compared to arterial blood because tissues have extracted a significant amount of oxygen for **cellular respiration**. - A typical mixed venous oxygen saturation (SvO2) is around **70-75%**, indicating the amount of oxygen remaining after tissues have taken what they need. *30%* - This level of oxygen saturation is **too low** for typical venous blood and would indicate severe tissue hypoperfusion or extreme oxygen extraction. - Such low levels are usually not compatible with normal physiological function for prolonged periods. *50%* - While lower than normal, a 50% venous oxygen saturation is still indicative of **increased oxygen extraction** by tissues, often seen in conditions of increased metabolic demand or decreased oxygen delivery. - It's not the typical resting value for healthy individuals. *90%* - An oxygen saturation of 90% is more characteristic of **arterial blood** (normal arterial saturation is 95-100%). - Venous blood, having already delivered oxygen to tissues, would normally have a lower saturation.

Q: What is the normal value of respiratory compliance in ml/cm H2O?

200 ml/cm H2O. ***200 ml/cm H2O*** - Normal respiratory system compliance is approximately **200 ml/cm H2O**, indicating a relatively compliant lung and chest wall system. - This value reflects the **change in lung volume per unit change in pressure**, with higher values indicating greater elasticity and ease of inflation (distensibility). *50 ml/cm H2O* - A compliance of **50 ml/cm H2O** is significantly lower than normal, suggesting a **stiff respiratory system**. - This could be indicative of conditions like **pulmonary fibrosis**, **acute respiratory distress syndrome (ARDS)**, or severe asthma, where the lungs are harder to inflate. *100 ml/cm H2O* - A compliance of **100 ml/cm H2O** is typically considered **reduced compliance**, although not as severely as 50 ml/cm H2O. - This value might be seen in moderate lung diseases or conditions causing **reduced chest wall expansion**. *150 ml/cm H2O* - While closer to the normal range, **150 ml/cm H2O** is generally still considered to be on the **lower side of normal or mildly reduced compliance**. - This could indicate early or mild conditions affecting **lung or chest wall mechanics**.

Q: In patients with emphysematous bullae, total lung volume is best determined by?

Plethysmography. ***Plethysmography*** - Uses **Boyle's Law** to measure total thoracic gas volume by detecting pressure changes during breathing, accurately capturing both **communicating and non-communicating air spaces**. - Essential in **emphysematous bullae** where trapped air in bullae cannot equilibrate with other methods, making plethysmography the gold standard for measuring **true total lung capacity (TLC)**. *Spirometry* - Only measures **dynamic lung volumes** (FVC, FEV1) that can be actively exhaled or inhaled through forced maneuvers. - Cannot determine **residual volume (RV)** or **total lung capacity (TLC)**, particularly problematic in emphysema where significant air trapping occurs. *Helium dilution method* - Measures lung volume by **helium equilibration** in communicating airspaces, determining functional residual capacity through gas mixing. - **Significantly underestimates** total lung volume in emphysematous bullae because helium cannot reach **non-communicating bullous spaces**, leading to falsely low TLC measurements. *Any of the above* - Only **plethysmography** provides accurate total lung volume measurement in emphysematous conditions due to its unique mechanism. - Other methods have **specific limitations** that make them unsuitable for this clinical scenario with air trapping and bullae formation.

Q: What is the normal transpulmonary pressure during quiet breathing?

+5 to +8 cm H2O. ***+5 to +8 cm H2O*** - Transpulmonary pressure (P_tp) is the **difference between alveolar pressure and pleural pressure** (P_alv - P_pl). - During quiet breathing at **functional residual capacity (FRC)**, alveolar pressure is **0 cm H2O** (atmospheric) while pleural pressure is approximately **-5 cm H2O**, giving P_tp = **+5 cm H2O**. - At end-inspiration during quiet breathing, pleural pressure becomes more negative (**-8 cm H2O**) while alveolar pressure remains near atmospheric, resulting in P_tp ≈ **+8 cm H2O**. - This positive transpulmonary pressure gradient is essential to **keep the lungs inflated** against elastic recoil and prevent **atelectasis**. *0 to +1 cm H2O* - This pressure is far too low to maintain lung inflation against elastic recoil forces. - Normal transpulmonary pressure must be several cm H2O positive to counterbalance the lung's tendency to collapse. - This value would result in **near-complete lung collapse**. *0 to -1 cm H2O* - A negative or zero transpulmonary pressure would mean pleural pressure equals or exceeds alveolar pressure. - This condition would cause **immediate lung collapse (pneumothorax)** as there would be no pressure gradient to keep the lungs expanded. *-8 to -5 cm H2O* - This range represents **pleural pressure**, not transpulmonary pressure. - Pleural pressure is indeed -5 to -8 cm H2O during quiet breathing, but transpulmonary pressure is calculated as the difference between alveolar and pleural pressures. - Confusing pleural pressure with transpulmonary pressure is a common error.

Question 1

Vital capacity is measured by:

Accepted Answer

Spirometer

Answer

Plethysmography

Answer

Nitrogen washout technique

Answer

Gas-dilution method

Question 2

In the relaxation pressure curve, at zero relaxation pressure in chronic smokers:

Accepted Answer

Lung volume remains elevated

Answer

Lung volume decreases significantly

Answer

No significant change in lung volume

Answer

Lung compliance decreases

Question 3

What physiological mechanism is responsible for the increase in the duration of expiration?

Accepted Answer

Hering-Breuer reflex

Answer

J-reflex

Answer

Head's paradoxical reflex

Answer

Proprioceptors

Question 4

Which of the following statements about lung compliance is false?

Accepted Answer

Decreased in emphysema

Answer

Total compliance is 0.2 L/cm H2O

Answer

A measure of lung distensibility

Answer

Change in volume per unit change in pressure

Question 5

What is the total surface area of the respiratory membrane in a healthy adult human?

Accepted Answer

75 m2

Answer

30 m2

Answer

50 m2

Answer

100 m2

Question 6

What is the normal O2 extraction ratio of tissues?

Accepted Answer

25 percent

Answer

5 percent

Answer

15 percent

Answer

40 percent

Question 7

What is the typical oxygen saturation level of venous blood?

Accepted Answer

70%

Answer

30%

Answer

50%

Answer

90%

Question 8

What is the normal value of respiratory compliance in ml/cm H2O?

Accepted Answer

200 ml/cm H2O

Answer

100 ml/cm H2O

Answer

150 ml/cm H2O

Answer

50 ml/cm H2O

Question 9

In patients with emphysematous bullae, total lung volume is best determined by?

Accepted Answer

Plethysmography

Answer

Spirometry

Answer

Any of the above

Answer

Helium dilution method

Question 10

What is the normal transpulmonary pressure during quiet breathing?

Accepted Answer

+5 to +8 cm H2O

Answer

0 to + 1 cm H2O

Answer

0 to -1 cm H2O

Answer

- 8 to - 5 cm H2O

Respiratory System — MCQs

Respiratory System — MCQs

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