Respiratory System Practice Questions

Q: Damage to pneumotaxic center along with vagus nerve causes which type of respiration?

Apneustic breathing. ***Apneustic breathing*** - Damage to the **pneumotaxic center** prevents the normal inhibition of inspiration, leading to **prolonged inspiratory gasps**. - **Vagal nerve damage** further removes the inhibitory feedback from the lungs, exacerbating the inspiratory "holds" characteristic of apneustic breathing. *Cheyne-Stokes breathing* - This pattern is characterized by a **crescendo-decrescendo pattern** of breathing, interspersed with periods of **apnea**. - It is often associated with conditions like **heart failure**, stroke, or severe neurological damage, not specifically the pneumotaxic center and vagus nerve. *Deep and slow breathing* - This pattern can be seen in conditions like **Kussmaul breathing** (due to metabolic acidosis) or as a compensatory mechanism. - It does not directly result from the combined damage of the **pneumotaxic center** and the **vagus nerve**. *Shallow and rapid breathing* - This pattern is commonly seen in restrictive lung diseases, anxiety, or pain, where tidal volume is decreased and respiratory rate increased. - It does not reflect the **prolonged inspiration** that would result from a compromised pneumotaxic center and vagal input.

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: 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.

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: 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: What is the respiratory quotient?

CO2 released to O2 consumed. **CO2 released to O2 consumed** - The **respiratory quotient (RQ)** is a ratio used in metabolism to describe the proportion of **carbon dioxide (CO2) produced** by the body relative to the **oxygen (O2) consumed**. - It is calculated as the **volume of CO2 released** divided by the **volume of O2 consumed** over a specific period. - RQ = VCO2/VO2, where VCO2 is CO2 production and VO2 is O2 consumption. *CO2 consumed to O2 released* - This option is incorrect as it reverses the correct order and refers to **CO2 consumption and O2 release**, which are not the standard components of the RQ calculation. - The body primarily **releases CO2** and **consumes O2** during cellular respiration. *O2 released to CO2 consumed* - This option is also incorrect because it inverts both the gases and the direction of their metabolic flow (release vs. consumption). - Metabolic processes involve **O2 consumption** and **CO2 release**, not the other way around. *O2 consumed to CO2 released* - This option incorrectly reverses the numerator and denominator in the RQ formula. - The standard definition places **CO2 production** in the numerator and **O2 consumption** in the denominator.

Q: In zero gravity, the V/Q ratio is?

1. ***Correct: 1*** - In **zero gravity**, the normal physiological effects of gravity on both ventilation and perfusion are eliminated, leading to a more uniform distribution. - Without gravity, blood flow and gas distribution become more even throughout the lungs, resulting in a V/Q ratio that approaches **unity (1)** across all lung regions. - This represents the ideal physiological state where ventilation perfectly matches perfusion. *Incorrect: 0.8* - A V/Q ratio of **0.8** represents the **average normal V/Q ratio** in an upright individual on Earth, where gravity creates disparities in ventilation and perfusion. - This value is an average, with regional variations (apex ~3.3, base ~0.6) in the lungs; it does not reflect the uniform conditions of zero gravity. *Incorrect: 2* - A V/Q ratio of **2** would indicate a significant **ventilation-perfusion mismatch** where ventilation greatly exceeds perfusion. - This scenario suggests substantial **dead space ventilation**, which is not the expected outcome in a zero-gravity environment where distribution is balanced. *Incorrect: 3* - A V/Q ratio of **3** represents an even more extreme case of **ventilation exceeding perfusion**, indicating severe physiologic dead space. - Such a high V/Q ratio would signify a major functional impairment, which is contrary to the more ideal and uniform distribution expected in zero gravity.

Q: What is the partial pressure for oxygen in the inspired air?

158 mm Hg. ***158 mm Hg*** - The partial pressure of oxygen in inspired air (PIO2) is calculated by multiplying the **fraction of inspired oxygen (FiO2)** by the total atmospheric pressure. - At sea level, atmospheric pressure is approximately **760 mm Hg** and FiO2 is 21% (0.21), so 0.21 × 760 mm Hg = **159.6 mm Hg**, which rounds to 158 mm Hg. - This represents **dry atmospheric air** before it enters the respiratory tract. *116 mm Hg* - This value does not correspond to a standard physiological measurement in respiratory physiology. - It is lower than inspired air PO2 but higher than alveolar PO2, making it an intermediate value used as a distractor. - **Humidified tracheal air** has PO2 of approximately 150 mm Hg: (760-47) × 0.21 = 149.7 mm Hg, where 47 mm Hg is water vapor pressure. *0.3 mm Hg* - This value is extremely low and represents the approximate **partial pressure of oxygen in mixed venous blood**, not inspired air. - Such a low value in inspired air would indicate **severe hypoxia** incompatible with life. - This is used as an unrealistic distractor. *100 mm Hg* - This value represents the approximate **partial pressure of oxygen in alveolar air (PAO2) and arterial blood (PaO2)**. - It is lower than inspired air due to humidification, mixing with residual air, and continuous oxygen uptake by blood. - It does not represent the partial pressure of oxygen in the inspired atmospheric air.

Question 1

Damage to pneumotaxic center along with vagus nerve causes which type of respiration?

Accepted Answer

Apneustic breathing

Answer

Cheyne-Stokes breathing

Answer

Deep and slow breathing

Answer

Shallow and rapid breathing

Question 2

What is the normal O2 extraction ratio of tissues?

Accepted Answer

25 percent

Answer

5 percent

Answer

15 percent

Answer

40 percent

Question 3

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 4

Which of the following statements is TRUE regarding the Bohr effect?

Accepted Answer

Decreased affinity of Hb to O2 is associated with decreased pH & increased CO2

Answer

Decreased affinity of Hb to O2 is associated with increased pH & decreased CO2

Answer

Decreased affinity of Hb to O2 is associated with increased pH & CO2

Answer

Decreased affinity of Hb to O2 is associated with decreased pH & decreased CO2

Question 5

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

Question 6

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 7

Vital capacity is measured by:

Accepted Answer

Spirometer

Answer

Plethysmography

Answer

Nitrogen washout technique

Answer

Gas-dilution method

Question 8

What is the respiratory quotient?

Accepted Answer

CO2 released to O2 consumed

Answer

CO2 consumed to O2 released

Answer

O2 released to CO2 consumed

Answer

O2 consumed to CO2 released

Question 9

In zero gravity, the V/Q ratio is?

Accepted Answer

1

Answer

0.8

Answer

2

Answer

3

Question 10

What is the partial pressure for oxygen in the inspired air?

Accepted Answer

158 mm Hg

Answer

116 mm Hg

Answer

0.3 mm Hg

Answer

100 mm Hg

Respiratory System — MCQs

Respiratory System — MCQs

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