Respiratory System Practice Questions

Q: Which condition is primarily responsible for the decrease in arterial PO2 in patients with chronic obstructive pulmonary disease (COPD)?

Ventilation-perfusion mismatch. ***Ventilation-perfusion mismatch*** - In **COPD**, structural changes in the lungs (emphysema, chronic bronchitis) lead to areas where **ventilation (V)** is poor but **perfusion (Q)** is still present, and vice versa. - This mismatch means that blood flowing through poorly ventilated areas does not pick up enough oxygen, leading to a decreased **arterial PO2**. *Cyanide poisoning* - **Cyanide** inhibits cytochrome c oxidase, blocking **cellular oxygen utilization**, but does not directly cause a decrease in arterial PO2. - Arterial PO2 levels in **cyanide poisoning** are often normal because oxygen is delivered to the tissues but cannot be used. *CO poisoning* - **Carbon monoxide (CO)** binds to **hemoglobin** with a much higher affinity than oxygen, forming **carboxyhemoglobin (COHb)** and reducing the oxygen-carrying capacity of the blood. - While it reduces the oxygen available to tissues, it generally does not significantly decrease the **arterial PO2** itself, as the amount of dissolved oxygen in plasma (which determines PO2) may remain relatively normal initially. *Shock* - **Shock** is a state of inadequate tissue perfusion, which can lead to **hypoxia** at the cellular level. - While systemic issues in shock can impact overall oxygen delivery and utilization, shock itself does not primarily cause a decrease in **arterial PO2** through a direct lung mechanism like ventilation-perfusion mismatch.

Q: What is the definition of Muller's maneuver?

Forceful inspiration against closed glottis. ***Forceful inspiration against closed glottis*** - **Muller's maneuver** involves attempting to inhale deeply while keeping the mouth and nose closed, creating a significant **negative intrathoracic pressure**. - This maneuver is used to assess conditions like **tracheomalacia** or **obstructive sleep apnea**, where the decreased pressure can cause airway collapse. *Forceful expiration against closed glottis* - This describes the **Valsalva maneuver**, which increases **intrathoracic pressure**, often used to test autonomic function. - Unlike **Muller's maneuver**, it involves pushing air out rather than drawing it in. *Forceful expiration against open glottis* - This action is a normal **forced exhalation**, often used in spirometry measurements to assess lung function. - It does not involve a closed glottis and therefore does not create the same pressure changes as the Muller or Valsalva maneuvers. *Normal inspiration against closed glottis* - While it involves inspiration against a closed glottis, the key distinction is "normal" inspiration, which would not generate the significant negative intrathoracic pressures characteristic of a **Muller's maneuver**. - **Muller's maneuver** specifically implies a **forceful** attempt to inhale.

Q: Surfactant acts to maintain lung compliance by decreasing which factor?

Surface tension. ***Surface tension*** - **Surfactant** directly reduces the **surface tension** at the air-liquid interface within the alveoli. - By lowering surface tension, surfactant prevents alveolar collapse, particularly at low lung volumes, and increases **lung compliance**. *Intrathoracic pressure* - **Intrathoracic pressure** (also known as pleural pressure) is the pressure within the chest cavity, which fluctuates with breathing. - While surfactant affects lung mechanics, it doesn't directly influence the overall intrathoracic pressure. *Pleural fluid secretion* - **Pleural fluid** lubricates the pleural surfaces and is secreted by the pleural membranes. - Surfactant's primary role is in the alveoli to reduce surface tension, not to regulate **pleural fluid secretion**. *Pleural pressure* - **Pleural pressure** is the pressure in the space between the parietal and visceral pleura. - Surfactant improves lung compliance, which indirectly affects how pressure changes during breathing, but it doesn't directly control the **pleural pressure** itself.

Q: Hyaline membrane disease of the lungs is characterized by –

FRC is reduced compared to closing volume. ***FRC is reduced compared to closing volume*** - In **Hyaline Membrane Disease (HMD)**, severe **surfactant deficiency** leads to widespread **atelectasis** and a significant reduction in **functional residual capacity (FRC)**. - Due to the collapse of alveoli and small airways, the **closing volume (CV)**, which is the lung volume at which small airways begin to close, becomes relatively larger than the already reduced FRC. *FRC is increased compared to closing volume* - This statement is incorrect because HMD is characterized by diffuse **atelectasis**, which drastically reduces **FRC**. - An increased FRC relative to closing volume would imply better lung compliance and less small airway closure, contrary to the pathology of HMD. *FRC is equal to closing volume* - This scenario would represent a critical point where extensive airway closure occurs, but in HMD, the **FRC is significantly lower** than the critical closing volume due to severe **surfactant deficiency** and widespread collapse. - While there is considerable airway closure, the FRC is typically *below* the closing volume, leading to shunt and severe hypoxemia. *FRC is not related to closing volume* - This is incorrect because FRC and closing volume are intimately related in lung mechanics, especially in conditions like HMD. - **Closing volume** reflects the point at which airways begin to collapse, and in disease states like HMD, the interplay between a reduced FRC and an elevated closing volume explains the severe gas exchange abnormalities.

Q: The effort during normal respiration is primarily due to?

Creating negative pleural pressure. ***Creating negative pleural pressure*** - **Inspiration** (the active phase of normal respiration) occurs when the diaphragm contracts and the external intercostal muscles lift the rib cage, increasing the volume of the thoracic cavity. - This increase in volume creates a **negative pressure in the pleural space**, which pulls the lungs outward and causes air to rush in. *Lung elasticity* - Lung elasticity is crucial for **expiration**, as the elastic recoil of the lungs helps to push air out passively. - It does not actively contribute to the effort of **inspiration**; rather, it creates the opposing force that needs to be overcome. *Respiratory air passages* - The respiratory air passages (trachea, bronchi, bronchioles) serve as conduits for air flow but do not directly create the "effort" of breathing. - Their primary role is to **conduct, warm, humidify, and filter** the air. *Alveolar air spaces* - Alveolar air spaces are where **gas exchange** takes place between the air and the blood. - They are the destination of the inspired air and do not generate the mechanical effort required for breathing.

Q: Which lung volume cannot be measured by spirometry?

RV. ***RV (Residual Volume)*** - **Residual volume (RV)** is the volume of air remaining in the lungs after a maximal exhalation and cannot be expelled. - Since it cannot be exhaled, it cannot be directly measured by a spirometer, which relies on the movement of air in and out of the lungs. *TV (Tidal Volume)* - **Tidal volume (TV)** is the volume of air inspired or expired with a normal breath. - It is easily measured by a spirometer during normal breathing. *IRV (Inspiratory Reserve Volume)* - **Inspiratory reserve volume (IRV)** is the additional volume of air that can be forcibly inhaled after a normal inspiration. - This volume can be measured by spirometry as it represents a change in lung air volume achievable by the patient. *ERV (Expiratory Reserve Volume)* - **Expiratory reserve volume (ERV)** is the additional volume of air that can be forcibly exhaled after a normal expiration. - This volume can be directly measured by a spirometer during a forced exhalation.

Q: Which of the following is measured by the Bellows spirometer?

ERV. ***ERV*** - The **Bellow's spirometer**, like other spirometers, measures **expiratory reserve volume (ERV)** directly. - Spirometry measures volumes that can be exhaled or inhaled, but not those that remain in the lungs after complete exhalation. *TLC* - **Total lung capacity (TLC)** cannot be measured directly by a spirometer because it includes the **residual volume (RV)**. - TLC is typically calculated using techniques like **helium dilution** or **body plethysmography**. *RV* - **Residual volume (RV)** is the volume of air remaining in the lungs after a maximal exhalation and cannot be expelled. - Since RV cannot be exhaled, it cannot be measured directly by a spirometer; it requires indirect methods. *Closing volume* - **Closing volume** is the lung volume at which small airways begin to close during exhalation. - It is measured using **specialized techniques** involving tracer gases, not standard spirometry.

Q: Which of the following statements about peripheral chemoreceptors is true?

Sensitive to hypoxia. ***Sensitive to hypoxia*** - **Peripheral chemoreceptors**, located in the **carotid bodies** and **aortic arch**, are highly sensitive to decreases in arterial **PO2 (hypoxia)**. - This response is crucial for initiating increased ventilation to correct low oxygen levels. *Primarily sensitive to PCO2* - While peripheral chemoreceptors do respond to high **PCO2**, the **central chemoreceptors** in the brainstem are the primary and most powerful regulators of ventilation in response to changes in **arterial PCO2**. - The response of peripheral chemoreceptors to PCO2 is secondary to their hypoxia-sensing role. *Insensitive to oxygen levels* - This statement is incorrect as peripheral chemoreceptors are the main physiological sensors for **arterial PO2** and are acutely responsive to hypoxia. - Their sensitivity to falling PO2 becomes significant when arterial PO2 drops below 60 mmHg. *Sensitive to pH changes, but not primarily responsive to hypoxia* - Peripheral chemoreceptors are indeed sensitive to changes in **pH**, particularly metabolic acidosis, largely due to their sensitivity to the resulting changes in PCO2 and direct pH effects. - However, they are also **primarily responsive to hypoxia**, making the latter part of the statement incorrect.

Question 1

Which condition is primarily responsible for the decrease in arterial PO2 in patients with chronic obstructive pulmonary disease (COPD)?

Accepted Answer

Ventilation-perfusion mismatch

Answer

CO poisoning

Answer

Shock

Answer

Cyanide poisoning

Question 2

What is the definition of Muller's maneuver?

Accepted Answer

Forceful inspiration against closed glottis

Answer

Forceful expiration against closed glottis

Answer

Forceful expiration against open glottis

Answer

Normal inspiration against closed glottis

Question 3

Surfactant acts to maintain lung compliance by decreasing which factor?

Accepted Answer

Surface tension

Answer

Pleural fluid secretion

Answer

Intrathoracic pressure

Answer

Pleural pressure

Question 4

Hyaline membrane disease of the lungs is characterized by –

Accepted Answer

FRC is reduced compared to closing volume

Answer

FRC is increased compared to closing volume

Answer

FRC is equal to closing volume

Answer

FRC is not related to closing volume

Question 5

The effort during normal respiration is primarily due to?

Accepted Answer

Creating negative pleural pressure

Answer

Respiratory air passages

Answer

Alveolar air spaces

Answer

Lung elasticity

Question 6

Which lung volume cannot be measured by spirometry?

Accepted Answer

RV

Answer

TV

Answer

IRV

Answer

ERV

Question 7

Which of the following is measured by the Bellows spirometer?

Accepted Answer

ERV

Answer

TLC

Answer

RV

Answer

Closing volume

Question 8

What physiological mechanism is primarily responsible for apnea in patients undergoing mechanical ventilation?

Accepted Answer

Decreased carbon dioxide tension (PCO2) leads to reduced respiratory drive.

Answer

Increased sensitivity of central chemoreceptors to elevated PCO2 causes hyperventilation.

Answer

Elevated arterial oxygen tension (PaO2) reduces central chemoreceptor activity.

Answer

Elevated arterial oxygen tension (PaO2) reduces peripheral chemoreceptor activity.

Question 9

The oxygen-hemoglobin dissociation curve is sigmoid because

Accepted Answer

Binding of one oxygen molecule increases the affinity of binding other O2 molecules

Answer

Binding of one oxygen molecule decreases the affinity of binding other O2 molecules

Answer

Oxygen affinity of Hemoglobin decreases when the pH of blood falls

Answer

Binding of oxygen to Hemoglobin reduces the affinity of Hb for CO2

Question 10

Which of the following statements about peripheral chemoreceptors is true?

Accepted Answer

Sensitive to hypoxia

Answer

Insensitive to oxygen levels

Answer

Primarily sensitive to PCO2

Answer

Sensitive to pH changes, but not primarily responsive to hypoxia

Respiratory System — MCQs

Respiratory System — MCQs

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