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: 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 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 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: 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 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: 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 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.

Question 1

Vital capacity is measured by:

Accepted Answer

Spirometer

Answer

Plethysmography

Answer

Nitrogen washout technique

Answer

Gas-dilution method

Question 2

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 3

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 4

What is the typical oxygen saturation level of venous blood?

Accepted Answer

70%

Answer

30%

Answer

50%

Answer

90%

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

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 7

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 8

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 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

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

Respiratory System — MCQs

Respiratory System — MCQs

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