Respiratory System Practice Questions

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: 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: Which of the following is markedly decreased in restrictive lung disease?

FVC. ***FVC*** - In **restrictive lung disease**, there is a reduction in lung volume due to various causes, leading to a markedly decreased **Forced Vital Capacity (FVC)**. - **FVC** directly measures the total amount of air a person can exhale after a maximal inhalation, which is inherently limited in restrictive conditions. - This is the **hallmark finding** in restrictive lung disease and the most clinically significant decrease. *FEV1* - While **FEV1** (Forced Expiratory Volume in 1 second) is also decreased in restrictive lung disease, its decrease is proportional to the FVC decrease. - A decrease in FEV1 alone is less specific, as it could also indicate obstructive lung disease. - The key is that both FEV1 and FVC decrease together, maintaining a normal or increased ratio. *FEV1/FVC* - The **FEV1/FVC ratio** is typically **normal or even increased** in restrictive lung disease, as both FEV1 and FVC decrease proportionally or FEV1 decreases slightly less. - A decreased FEV1/FVC ratio is characteristic of **obstructive lung disease**, not restrictive. *RV* - **Residual Volume (RV)** is also **decreased** in restrictive lung disease, along with all other lung volumes (TLC, VC, FRC). - However, RV is not measured by standard spirometry and requires body plethysmography or gas dilution techniques. - While RV does decrease, **FVC** is the more clinically significant and readily measurable parameter that is "markedly decreased" and defines restrictive disease on routine pulmonary function testing.

Q: What does Boyle's Law state?

PV = constant. ***PV = constant*** - **Boyle's Law** states that at constant temperature, the pressure and volume of a gas are inversely proportional. - Mathematically expressed as **PV = constant** or **P₁V₁ = P₂V₂** - This means that if the volume of a gas decreases, its pressure increases proportionally, and vice versa. - **Clinically relevant** in understanding lung mechanics during respiration - as thoracic volume increases during inspiration, intrapulmonary pressure decreases, allowing air to flow in. *Pressure divided by temperature is constant.* - This describes **Gay-Lussac's Law** (P/T = constant), which relates pressure and temperature at constant volume. - Shows the direct relationship between pressure and temperature. *Volume divided by temperature is constant.* - This statement describes **Charles's Law** (V/T = constant), which relates the volume and temperature of a gas at constant pressure. - Indicates a direct relationship between volume and temperature. *Pressure multiplied by volume equals the number of moles times the gas constant times temperature.* - This represents the **Ideal Gas Law**: PV = nRT - Combines Boyle's, Charles's, and Avogadro's laws to relate pressure, volume, temperature, and the number of moles of a gas.

Q: Which of the following best describes hypoxic pulmonary vasoconstriction?

Reversible pulmonary vasoconstriction due to hypoxia. ***Reversible pulmonary vasoconstriction due to hypoxia*** - Hypoxic pulmonary vasoconstriction (HPV) is a physiological response in which **pulmonary arterioles constrict** in areas of the lung with low oxygen levels. - This mechanism is **reversible**, meaning that when oxygen levels improve, the constricted vessels will dilate again. - The underlying mechanism involves hypoxia-induced inhibition of voltage-gated K⁺ channels in pulmonary arterial smooth muscle, leading to membrane depolarization, Ca²⁺ influx, and smooth muscle contraction. *Irreversible pulmonary vasoconstriction due to hypoxia* - This statement is incorrect because HPV is fundamentally a **reversible process**, designed to adapt to transient changes in alveolar oxygen. - Irreversible vasoconstriction typically occurs in chronic hypoxia, leading to **pulmonary hypertension** and structural remodeling (vascular remodeling with medial hypertrophy), which is a pathological state rather than the acute physiological response of HPV. *Redirects blood to well-ventilated areas* - While this is the **physiological purpose** and overall effect of hypoxic pulmonary vasoconstriction, it describes the functional outcome rather than what HPV fundamentally is. - The redirection of blood flow is the **consequence** of vasoconstriction in hypoxic areas, which optimizes ventilation-perfusion matching. *Occurs immediately in response to hypoxia* - While HPV does begin rapidly in response to hypoxia (within seconds to minutes), this describes the **timing characteristic** rather than what HPV is. - This statement is also somewhat imprecise, as the response involves intracellular signaling pathways that take time to manifest fully, though the onset is relatively quick compared to other vascular responses.

Q: What is the air remaining in the lung after normal expiration?

Functional Residual Capacity (FRC). ***Functional Residual Capacity (FRC)*** - **FRC** represents the volume of air remaining in the lungs after a **normal expiration**. - It is the sum of the **expiratory reserve volume (ERV)** and the **residual volume (RV)**. *Tidal Volume (TV)* - **TV** is the volume of air inspired or expired with a **normal breath**. - It does not represent the total air remaining in the lungs after expiration. *Residual Volume (RV)* - **RV** is the volume of air remaining in the lungs after a **maximal expiration**. - It is a component of FRC but does not fully describe the air remaining after a *normal* expiration. *Vital Capacity (VC)* - **VC** is the maximum volume of air that can be exhaled after a **maximal inspiration**. - It represents the maximum amount of air that can be exchanged with a single breath, not the air remaining after normal expiration.

Q: Central chemoreceptors are most sensitive to which of the following changes in blood?

PCO2. ***PCO2*** - Central chemoreceptors, located in the **medulla oblongata**, are exquisitely sensitive to changes in the **partial pressure of carbon dioxide (PCO2)** in the arterial blood. - An increase in blood PCO2 readily crosses the **blood-brain barrier** to the cerebrospinal fluid (CSF), where it is converted to carbonic acid and then to H+ and HCO3-. The resulting **drop in CSF pH** directly stimulates these chemoreceptors, leading to increased ventilation. *PO2* - While **peripheral chemoreceptors** (carotid and aortic bodies) are sensitive to changes in **PO2**, particularly when it drops significantly (below 60 mmHg), central chemoreceptors are not. - The primary role of central chemoreceptors is to monitor and respond to changes in CO2 and pH, rather than oxygen levels. *pH* - Central chemoreceptors are indirectly sensitive to **pH changes** in the cerebrospinal fluid (CSF), which result from blood PCO2 changes. - However, they are not directly or primarily sensitive to changes in **blood pH** because hydrogen ions do not readily cross the blood-brain barrier. *HCO3-* - Bicarbonate ions (**HCO3-**) are important in buffering pH, but central chemoreceptors do not directly sense bicarbonate levels. - Changes in HCO3- indirectly affect pH, and it is the resultant **H+ concentration** in the CSF, derived from CO2, that primarily stimulates central chemoreceptors.

Q: Maximum voluntary ventilation is:

150 L/min. ***150 L/min*** - The **Maximum Voluntary Ventilation (MVV)** represents the largest volume of air that can be breathed in and out using maximal effort over a 10-15 second period. - While it varies among individuals, a typical average value for a healthy adult is approximately **150-170 L/min**. *25 L/min* - This value is significantly lower than the typical MVV; 25 L/min is closer to a normal **resting minute ventilation** (tidal volume multiplied by respiratory rate). - Resting minute ventilation reflects the volume of air exchanged at rest, not the maximum capacity. *50 L/min* - This value is still considerably lower than the average MVV and does not represent the maximum capacity of the respiratory system. - It might be seen in individuals with **severe pulmonary impairment** or at a very high resting metabolic rate. *100 L/min* - While higher than resting values, 100 L/min is generally below the average maximum voluntary ventilation for a healthy adult. - It could represent a MVV in individuals with **mild to moderate respiratory compromise** or less effort during the test.

Q: Which equation is used to calculate physiological dead space?

Bohr equation. ***Bohr equation*** - The Bohr equation is used to calculate **physiological dead space**, which is the sum of anatomical dead space and alveolar dead space. - It relates the partial pressure of carbon dioxide in arterial blood to the partial pressure of carbon dioxide in expired air, along with **tidal volume** and expired volume. *Dalton's law* - Dalton's law states that the **total pressure** exerted by a mixture of non-reactive gases is equal to the **sum of the partial pressures** of individual gases. - It is used to calculate partial pressures of gases in a mixture, not dead space. *Charles's law* - Charles's law describes the relationship between the **volume and temperature** of a gas at constant pressure. - It states that the volume of a given mass of gas is directly proportional to its absolute temperature. *Boyle's law* - Boyle's law describes the inverse relationship between the **pressure and volume** of a gas at constant temperature. - It is fundamental to understanding mechanics of breathing, but not dead space calculation.

Question 1

What is the normal O2 extraction ratio of tissues?

Accepted Answer

25 percent

Answer

5 percent

Answer

15 percent

Answer

40 percent

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

Which of the following is markedly decreased in restrictive lung disease?

Accepted Answer

FVC

Answer

RV

Answer

FEV1/FVC

Answer

FEV1

Question 4

What does Boyle's Law state?

Accepted Answer

PV = constant

Answer

Pressure divided by temperature is constant.

Answer

Volume divided by temperature is constant.

Answer

Pressure multiplied by volume equals the number of moles times the gas constant times temperature.

Question 5

Which of the following best describes hypoxic pulmonary vasoconstriction?

Accepted Answer

Reversible pulmonary vasoconstriction due to hypoxia

Answer

Irreversible pulmonary vasoconstriction due to hypoxia

Answer

Redirects blood to well-ventilated areas

Answer

Occurs immediately in response to hypoxia

Question 6

What is the air remaining in the lung after normal expiration?

Accepted Answer

Functional Residual Capacity (FRC)

Answer

Tidal Volume (TV)

Answer

Residual Volume (RV)

Answer

Vital Capacity (VC)

Question 7

Central chemoreceptors are most sensitive to which of the following changes in blood?

Accepted Answer

PCO2

Answer

PO2

Answer

HCO3-

Answer

pH

Question 8

Which of the following statements about breathing is incorrect?

Accepted Answer

Normal breathing occurs when transpulmonary pressure is 5-8 cm H2O

Answer

Inspiration is an active process

Answer

Expiration during quiet breathing is passive

Answer

Compliance is influenced by multiple factors including surfactant.

Question 9

Maximum voluntary ventilation is:

Accepted Answer

150 L/min

Answer

25 L/min

Answer

50 L/min

Answer

100 L/min

Question 10

Which equation is used to calculate physiological dead space?

Accepted Answer

Bohr equation

Answer

Dalton's law

Answer

Charles's law

Answer

Boyle's law

Respiratory System — MCQs

Respiratory System — MCQs

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