Respiratory System Practice Questions

Q: Transpulmonary pressure is the difference between:

Pressure in alveoli and intrapleural pressure. ***Pressure in alveoli and intrapleural pressure*** - Transpulmonary pressure is the **pressure gradient** across the lung wall, which is essential for maintaining alveolar inflation. - It is calculated as the **alveolar pressure minus the intrapleural pressure**. *The pressure in the bronchus and atmospheric pressure* - This difference would represent the pressure driving airflow through the **bronchial tree**, not the pressure across the lung wall itself. - It's a measure relevant to **airway resistance**, not lung distension. *The difference between atmospheric pressure and intrapleural pressure* - This difference is related to the **intrathoracic pressure**, which influences venous return and cardiac function, but not directly the distension of the lungs. - It does not account for the **alveolar pressure**, which is the primary internal pressure expanding the lung. *The difference between atmospheric pressure and intraalveolar pressure* - This difference is the **driving pressure for airflow** into or out of the lungs. - It represents the pressure gradient that causes air to move between the **atmosphere and the alveoli** during inspiration and expiration.

Q: Gas exchange in tissues takes place at?

Capillary. ***Capillary*** - **Capillaries** are the smallest and most numerous blood vessels, with very thin walls (only one cell thick), which facilitates the efficient exchange of gases, nutrients, and waste products between blood and tissues. - Their extensive network ensures close proximity to nearly every cell in the body, maximizing the surface area and minimizing the diffusion distance for **gas exchange**. *Artery* - Arteries carry **oxygenated blood** away from the heart to the tissues but have thick, muscular walls designed for high pressure and transport, not for direct exchange with tissues. - They branch into smaller arterioles, which then lead to capillaries, making them a conduit rather than an exchange site. *Vein* - Veins carry **deoxygenated blood** back to the heart from the tissues and have relatively thin walls compared to arteries but are still too thick for efficient gas exchange. - They primarily serve as blood return vessels and reservoirs. *Venules* - Venules are small blood vessels that merge from capillaries and eventually combine to form veins; they primarily function in collecting blood from capillary beds. - While slightly more permeable than larger veins, their main role is still collection and transport, not the extensive gas exchange facilitated by capillaries.

Q: What is the difference between the amount of Oxygen consumed and Carbon Dioxide produced per minute at rest?

50 ml/min. ***50 ml/min*** - The body typically consumes about **250 ml/min of oxygen** at rest and produces approximately **200 ml/min of carbon dioxide**. - The difference between oxygen consumed and carbon dioxide produced is therefore **50 ml/min** (250 - 200 = 50). - This difference exists because the **respiratory quotient (RQ)** is approximately **0.8** (200/250), meaning less CO2 is produced than O2 consumed on a molar basis. *20 ml/min* - This value is **too low** and underestimates the physiological difference between oxygen consumption and carbon dioxide production. - With typical O2 consumption of 250 ml/min and RQ of 0.8, the difference cannot be this small. *75 ml/min* - This value represents an **overestimation** of the difference between oxygen consumption and carbon dioxide production under normal resting conditions. - This would imply an RQ of approximately 0.7, which is lower than the typical mixed diet RQ of 0.8. *100 ml/min* - This value is a significant **overestimation** of the physiological difference. - This would suggest an RQ of 0.6, which is not physiologically normal for resting conditions on a mixed diet.

Q: What is the estimated PaO2 after giving FiO2 at 0.5 in a normal person?

> 200 mmHg. ***> 200 mmHg*** - In a **normal healthy person** breathing FiO2 of 0.5 (50% oxygen), the expected **PaO2** is typically **250-300 mmHg**. - Using the **alveolar gas equation**: PAO2 = FiO2(PB - PH2O) - PaCO2/RQ = 0.5(760 - 47) - 40/0.8 ≈ **306 mmHg** - The normal **A-a gradient** is 5-15 mmHg, so PaO2 = 306 - 10 ≈ **296 mmHg** - **Clinical rule of thumb**: PaO2 ≈ 5 × FiO2% = 5 × 50 = **250 mmHg** (approximation accounting for physiological shunt) - Therefore, the expected range is clearly **> 200 mmHg** in a normal individual *150–200 mmHg* - This range would indicate **mild oxygenation impairment** or increased shunt fraction - While adequate for tissue oxygenation, this is **lower than expected** for a normal person on 50% oxygen - May suggest underlying **mild V/Q mismatch** or early pulmonary dysfunction *100–150 mmHg* - This represents **moderate impairment** in oxygen transfer - Indicates significant **pulmonary pathology** such as pneumonia, ARDS, or substantial shunt - Not consistent with normal lung function on FiO2 0.5 *< 100 mmHg* - This represents **severe hypoxemia** despite supplemental oxygen - Indicates **critical pulmonary dysfunction** with large shunt or severe V/Q mismatch - Requires immediate intervention and is never expected in a healthy individual on 50% oxygen

Q: The chloride shift occurs rapidly and is essentially complete within:

1 second. ***1 second*** - The **chloride shift**, an exchange of bicarbonate and chloride ions across the red blood cell membrane, is a very rapid process. - This rapid kinetics ensures efficient **CO2 transport** from tissues to the lungs. *2 seconds* - While seemingly a short duration, **2 seconds** is generally considered longer than the actual time frame for the completion of the chloride shift. - The physiological need for immediate CO2 buffering necessitates a faster mechanism. *5 seconds* - A duration of **5 seconds** would imply a slower rate of gas exchange than physiologically required for efficient CO2 transport. - Such a delay could lead to transient but significant alterations in **blood pH**. *60 seconds* - **60 seconds** (1 minute) is far too long for a process critical to immediate blood gas regulation. - If the chloride shift took this long, it would severely impair the body's ability to excrete **CO2** and maintain acid-base balance.

Q: What is the physiological effect of very high positive end-expiratory pressure in a patient with respiratory distress?

Decreased blood pressure. ***Decreased blood pressure*** - Very high **positive end-expiratory pressure (PEEP)** increases intrathoracic pressure, which in turn reduces **venous return** to the heart. - This decreased preload leads to a **reduction in cardiac output**, ultimately causing **hypotension** (decreased blood pressure). - This is a well-recognized hemodynamic complication of excessive PEEP in mechanical ventilation. *Increased blood pressure* - High PEEP typically lowers, rather than increases, blood pressure due to its effects on **venous return** and **cardiac output**. - The elevated intrathoracic pressure acts as a barrier to venous return, reducing preload and thus blood pressure. *Decreased body temperature* - **PEEP** primarily affects cardiovascular and respiratory physiology, not **thermoregulation**. - Body temperature changes are usually related to systemic inflammation, infection, or environmental factors, not directly to PEEP settings. *Increased body temperature* - Similar to decreased body temperature, **PEEP** does not directly regulate body temperature. - An elevated body temperature (fever) would suggest an underlying **infection** or **inflammatory process**, which might be present in a patient with respiratory distress but is not a direct physiological effect of high PEEP.

Q: Which test is primarily used to assess gas diffusion capacity in the lungs?

DLCO. ***DLCO*** - **DLCO (Diffusing Capacity of the Lungs for Carbon Monoxide)** specifically measures the transfer of gas from the alveoli to the red blood cells, directly assessing the **gas diffusion capacity** of the lungs. - It is crucial for identifying interstitial lung diseases, emphysema, or other conditions affecting the **alveolar-capillary membrane**. *Spirometry* - **Spirometry** primarily assesses **lung volumes and airflow rates**, such as FEV1 and FVC, to diagnose obstructive or restrictive ventilatory defects. - It does not directly measure the efficiency of **gas exchange** across the alveolar-capillary membrane. *Both DLCO and Spirometry* - While both are important in pulmonary function testing, they measure different aspects of **lung function**. DLCO specifically measures **diffusion capacity**, while spirometry measures **airflow and lung volumes**. - Therefore, they are not primarily used for the *same* assessment. *None of the options* - DLCO is indeed the primary test for assessing **gas diffusion capacity** in the lungs. - This option is incorrect because a correct answer is provided.

Q: All of the following factors influence the hemoglobin dissociation curve, except.

Plasma sodium concentration. ***Plasma sodium concentration*** - While essential for **osmolality** and **electrolyte balance**, plasma sodium concentration does not directly influence the binding affinity of hemoglobin for oxygen. - Changes in sodium concentration primarily affect fluid shifts and neural function, not the **hemoglobin dissociation curve**. *CO2 tension* - An increase in **PCO2** (hypercapnia) leads to a **rightward shift** of the hemoglobin dissociation curve, indicating decreased oxygen affinity. - This effect, known as the **Bohr effect**, facilitates oxygen release in tissues with high metabolic activity. *Temperature* - An increase in **body temperature** causes a **rightward shift** in the hemoglobin dissociation curve, leading to reduced oxygen affinity. - This is beneficial during exercise or fever, as it promotes oxygen unloading to active tissues. *2–3 DPG levels* - **2,3-bisphosphoglycerate (2,3-BPG)** binds to deoxygenated hemoglobin, stabilizing its T-state and reducing its affinity for oxygen, thus shifting the curve to the **right**. - During chronic hypoxia or anemia, 2,3-BPG levels increase to enhance oxygen delivery to tissues.

Q: Which of the following is not a normal stimulus for resting ventilation?

J receptors. ***J receptors*** - **J receptors** (juxtacapillary receptors) are located in the alveolar walls and are primarily stimulated by **pulmonary edema**, inflammation, or vascular congestion. - Their stimulation typically causes rapid, shallow breathing, but they are **completely inactive during normal, resting ventilation**. - These receptors only become active under pathological conditions, making them **not a normal stimulus for resting breathing**. *Stretch receptors* - **Pulmonary stretch receptors** in the airways respond to lung distension, mediating the **Hering-Breuer reflex** which helps regulate breathing depth and rate. - These receptors are **active during normal tidal breathing** and contribute to the rhythmic pattern of respiration at rest. *PO2* - **Peripheral chemoreceptors** (carotid and aortic bodies) monitor **arterial PO2** and do have **tonic baseline activity** at normal PO2 levels (~95-100 mmHg). - While their contribution is **minimal at normal oxygen levels**, they are present and functioning, making them technically a (weak) normal stimulus. - They become a **major stimulus only when PO2 drops below 60 mmHg** (hypoxemia). *PCO2* - **PCO2** (specifically, the H+ concentration in the cerebrospinal fluid derived from PCO2) is the **most potent and immediate normal stimulus** for resting ventilation. - **Central chemoreceptors** in the medulla are extremely sensitive to changes in CSF pH, directly regulating breathing to maintain arterial PCO2 within a narrow range (~40 mmHg).

Question 1

Transpulmonary pressure is the difference between:

Accepted Answer

Pressure in alveoli and intrapleural pressure

Answer

The pressure in the bronchus and atmospheric pressure

Answer

The difference between atmospheric pressure and intrapleural pressure

Answer

The difference between atmospheric pressure and intraalveolar pressure

Question 2

Gas exchange in tissues takes place at?

Accepted Answer

Capillary

Answer

Artery

Answer

Vein

Answer

Venules

Question 3

What is the difference between the amount of Oxygen consumed and Carbon Dioxide produced per minute at rest?

Accepted Answer

50 ml/min

Answer

20 ml/min

Answer

75 ml/min

Answer

100 ml/min

Question 4

True about normal expiration is:

Accepted Answer

Chest wall has a tendency to move outward which is balanced by inward recoil of alveoli

Answer

In expiration pleural pressure is equal to alveolar pressure

Answer

Muscles that elevate the chest cage are classified as muscles of expiration

Answer

At the end of normal expiration, the air in the lung is FRC

Question 5

What is the estimated PaO2 after giving FiO2 at 0.5 in a normal person?

Accepted Answer

> 200 mmHg

Answer

< 100 mmHg

Answer

150–200 mmHg

Answer

100–150 mmHg

Question 6

The chloride shift occurs rapidly and is essentially complete within:

Accepted Answer

1 second

Answer

2 seconds

Answer

5 seconds

Answer

60 seconds

Question 7

What is the physiological effect of very high positive end-expiratory pressure in a patient with respiratory distress?

Accepted Answer

Decreased blood pressure

Answer

Increased blood pressure

Answer

Decreased body temperature

Answer

Increased body temperature

Question 8

Which test is primarily used to assess gas diffusion capacity in the lungs?

Accepted Answer

DLCO

Answer

Spirometry

Answer

Both DLCO and Spirometry

Answer

None of the options

Question 9

All of the following factors influence the hemoglobin dissociation curve, except.

Accepted Answer

Plasma sodium concentration

Answer

Temperature

Answer

2–3 DPG levels

Answer

CO2 tension

Question 10

Which of the following is not a normal stimulus for resting ventilation?

Accepted Answer

J receptors

Answer

Stretch receptors

Answer

PCO2

Answer

PO2

Respiratory System — MCQs

Respiratory System — MCQs

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