Respiratory System Practice Questions

Q: Functional residual capacity (FRC) is defined as the volume of air remaining in the lungs at which specific moment in the respiratory cycle?

After normal expiration. ***After normal expiration*** - **Functional residual capacity (FRC)** is the volume of air remaining in the lungs at the end of a **normal, passive expiration**. - It represents the sum of the **expiratory reserve volume (ERV)** and the **residual volume (RV)**. *During active expiration* - **Active expiration** involves the use of accessory muscles to force more air out of the lungs than during normal expiration. - This process would result in a lung volume less than FRC, closer to the **residual volume**. *At peak inspiration* - **Peak inspiration** represents the total lung capacity (TLC), which is the maximum volume of air the lungs can hold after a maximal inspiratory effort. - This is the largest lung volume, significantly greater than FRC. *During active inspiration* - **Active inspiration** is the process of inhaling air, which increases lung volume. - FRC is a static volume measured at the end of expiration, not during the dynamic process of inhaling.

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

No exchange of O2 and CO2 occurs.. ***No exchange of O2 and CO2 occurs.*** - When the **Va/Q ratio approaches infinity**, it signifies a scenario of **ventilation without perfusion** (Q approaches zero). - This represents **alveolar dead space** - despite adequate ventilation, there is **no blood flow** to participate in gas exchange. - Therefore, **no O2 enters the blood** and **no CO2 leaves the blood**, making this the most accurate description of what happens to gas exchange. *Partial pressure of O2 becomes negligible.* - This statement is incorrect because with **no blood flow** (Q = 0), the alveolar air retains high O2 partial pressure. - O2 is being delivered via ventilation but not removed by blood, so **alveolar PO2** would approach that of **inspired air (~150 mmHg)**, not become negligible. *Partial pressure of CO2 becomes negligible.* - While this statement is technically true (alveolar PCO2 would approach zero/inspired air levels), it doesn't directly answer what happens to **gas exchange**. - With no blood flowing through the alveolus, no **CO2 from venous blood** can reach the alveolus to be excreted. - However, the question asks about **gas exchange** itself, not just partial pressures, making the first option more comprehensive. *Partial pressures of both CO2 and O2 remain normal.* - This statement is incorrect as the **Va/Q mismatch** significantly alters the partial pressures of both gases. - In infinite Va/Q scenario (dead space ventilation), **alveolar PO2 would be high** (approaching inspired air ~150 mmHg) and **alveolar PCO2 would be low** (approaching zero).

Q: With increase in age, which of the following statements about lung function is true?

Pulmonary compliance increases. ***Pulmonary compliance increases*** - With **increasing age**, there is a loss of **elastic recoil** in the lungs due to changes in elastin and collagen fibers, leading to an increase in **pulmonary compliance**. - This increased compliance means the lungs become less stiff and easier to inflate, but also less able to recoil and expel air effectively. - The **net effect** of aging is increased compliance, as the loss of elastic fibers is the predominant change in normal aging. *Residual volume decreases* - **Residual volume (RV)** actually **increases** with age. This is because the loss of elastic recoil makes it harder to fully exhale, causing more air to remain in the lungs after a maximal exhalation. - An increased residual volume contributes to an overall rise in **functional residual capacity** and total lung capacity in older adults. *Mucociliary clearance increases* - **Mucociliary clearance** generally **decreases** with age. This is due to a reduction in the number and function of cilia, as well as changes in mucus quality. - Impaired mucociliary clearance makes older individuals more susceptible to respiratory infections and difficulties in clearing secretions. *Fibrosis of the interstitium decreases* - The **fibrosis of the interstitium** can **increase** with age in some individuals. However, in normal aging (without pathological conditions), the predominant change is loss of elastic recoil rather than significant fibrotic changes. - When present, increased interstitial fibrosis would make the lungs stiffer, but this is not the primary age-related change in healthy individuals.

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

Plethysmography. ***Plethysmography*** - This method accurately measures **total lung capacity (TLC)**, functional residual capacity (FRC), and residual volume (RV) by determining the **volume of gas in the thorax**. - It is particularly useful in conditions like **emphysema** with air trapping and bullae, as it accounts for **non-communicating air spaces** that other methods miss. *Spirometry* - Spirometry measures volumes of air that can be **exhaled or inhaled forcibly**, such as FVC and FEV1. - It cannot measure residual volume (RV) or total lung capacity (TLC) directly, especially in cases of **air trapping** where trapped air cannot be exhaled. *Helium dilution method* - The helium dilution method measures **communicating lung volumes**, like functional residual capacity (FRC), by assessing the dilution of a known concentration of helium after rebreathing. - In conditions with **emphysematous bullae** and air trapping, it **underestimates total lung volume** because it cannot measure air in non-communicating or poorly communicating spaces. *Any of the above* - Only plethysmography can accurately measure total lung volume in the presence of **emphysematous bullae** due to its ability to measure both communicating and non-communicating air spaces. - Spirometry and helium dilution methods would provide **inaccurate or incomplete measurements** in this clinical scenario.

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: Which of the following parameters indicates the elimination of CO2 from the lungs?

PaCO2. ***PaCO2*** - **Partial pressure of carbon dioxide in arterial blood (PaCO2)** directly reflects the efficiency of **alveolar ventilation**, which is the process of eliminating CO2 from the lungs. - When CO2 elimination is adequate, PaCO2 remains within the normal range (35-45 mmHg); higher or lower values indicate ventilatory impairment or hyperventilation, respectively. *PaO2* - **PaO2** measures the partial pressure of **oxygen in arterial blood** and indicates oxygenation, not the efficiency of carbon dioxide elimination. - While CO2 elimination and oxygenation are interdependent, **PaO2** primarily reflects how well oxygen is being transported from the lungs to the blood. *pH* - **pH** indicates the **acidity or alkalinity of the blood**, which is influenced by both respiratory (CO2) and metabolic (bicarbonate) components. - Although CO2 elimination affects pH through the carbonic acid-bicarbonate buffer system, pH itself is an overall measure of acid-base balance, not a direct indicator of CO2 elimination. *HCO3 level* - **Bicarbonate (HCO3-)** is a **metabolic component** of the acid-base balance, primarily regulated by the kidneys. - While it helps buffer CO2-induced acid changes, HCO3 level alone does not directly reflect the efficiency of CO2 elimination from the lungs.

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: 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 Haldane Effect?

CO2 delivery by increased O2. ***CO2 delivery by increased O2*** - The **Haldane effect** describes how **oxygenation of hemoglobin** decreases its affinity for **carbon dioxide (CO2)**, leading to the release of CO2 from the blood. - This is crucial in the lungs, where high oxygen levels promote CO2 unloading for exhalation. *O2 delivery by increased CO2* - This describes the **Bohr effect**, where an increase in **carbon dioxide (CO2)** or acidity in the tissues causes hemoglobin to release **oxygen (O2)**. - The Haldane effect is the converse, relating oxygen binding to CO2 release, not the other way around. *CO2 delivery by increased CO2* - This statement is inherently circular and does not describe a physiological effect. - It confuses the mechanism with the substance being transported. *O2 delivery by increased CO* - **Carbon monoxide (CO)** has a much higher affinity for hemoglobin than oxygen, forming **carboxyhemoglobin** and impairing oxygen delivery. - This is related to **carbon monoxide poisoning**, not a physiological regulatory effect like the Haldane or Bohr effects.

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**.

Question 1

Functional residual capacity (FRC) is defined as the volume of air remaining in the lungs at which specific moment in the respiratory cycle?

Accepted Answer

After normal expiration

Answer

During active expiration

Answer

At peak inspiration

Answer

During active inspiration

Question 2

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

Accepted Answer

No exchange of O2 and CO2 occurs.

Answer

Partial pressure of O2 becomes negligible.

Answer

Partial pressure of CO2 becomes negligible.

Answer

Partial pressures of both CO2 and O2 remain normal.

Question 3

With increase in age, which of the following statements about lung function is true?

Accepted Answer

Pulmonary compliance increases

Answer

Fibrosis of the interstitium decreases

Answer

Residual volume decreases

Answer

Mucociliary clearance increases

Question 4

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 5

What is the typical oxygen saturation level of venous blood?

Accepted Answer

70%

Answer

30%

Answer

50%

Answer

90%

Question 6

Which of the following parameters indicates the elimination of CO2 from the lungs?

Accepted Answer

PaCO2

Answer

pH

Answer

PaO2

Answer

HCO3 level

Question 7

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 8

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 9

What is the Haldane Effect?

Accepted Answer

CO2 delivery by increased O2

Answer

O2 delivery by increased CO2

Answer

CO2 delivery by increased CO2

Answer

O2 delivery by increased CO

Question 10

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

Respiratory System — MCQs

Respiratory System — MCQs

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