Which physical law explains the mechanism of pulmonary ventilation (the relationship between pressure and vol… - DSSSB 6 September 2024

DSSSB 6 September 2024

Applied Physiology

Easy

Appeared in: DSSSB 6 September 2024

Explanation

Boyle's Law states that for a fixed mass of gas at a constant temperature, the pressure and volume are inversely proportional (P₁V₁ = P₂V₂).
This law directly explains the mechanics of breathing (pulmonary ventilation).
During inspiration, the chest cavity volume increases, causing lung pressure to drop below atmospheric pressure, and air flows in.
During expiration, the chest cavity volume decreases, causing lung pressure to rise above atmospheric pressure, and air flows out.

Option A: Dalton's Law describes the concept of partial pressures within a mixture of gases. It is crucial for understanding how oxygen and carbon dioxide move across the alveolar-capillary membrane but does not explain the mechanical act of breathing.
Option C: Henry's Law explains the solubility of gases in a liquid. It is important for understanding how much oxygen and carbon dioxide can be dissolved and transported in the blood, but it does not govern the movement of air into and out of the lungs.
Option D: Starling's Law is not related to respiratory mechanics. It typically refers to the Frank-Starling law of the heart (relating stroke volume to end-diastolic volume) or Starling's forces (governing fluid movement across capillaries).

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Physical laws of gas exchange and pulmonary ventilation as background academic context rather than a clinical decision trigger.
Understanding Boyle's Law is fundamental for nurses to comprehend how mechanical ventilators work. Positive pressure ventilators force air into the lungs by increasing airway pressure, essentially overriding the natural pressure gradients.
Conditions like a pneumothorax (collapsed lung) are a direct clinical example of Boyle's Law. When air enters the pleural space, it disrupts the negative pressure, causing the lung to collapse due to its natural elastic recoil.
What if? - If a patient has a flail chest (multiple rib fractures causing a segment of the chest wall to move paradoxically), during inspiration, the injured segment moves inward instead of outward. This negates the volume increase described by Boyle's Law, leading to impaired ventilation and severe respiratory distress.

How to Approach the Question

First, identify the key concepts in the question: 'pulmonary ventilation', 'pressure', and 'volume'.
The question asks for the physical law that connects pressure and volume in the context of breathing.
Recall the basic gas laws learned in physiology.
Analyze each option: Dalton's Law (partial pressures), Boyle's Law (pressure-volume relationship), Henry's Law (gas solubility), and Starling's Law (cardiac/capillary dynamics).
Recognize that the inverse relationship between pressure and volume is the definition of Boyle's Law and directly matches the mechanism of air movement during ventilation.
Select Boyle's Law as the correct answer.

Concept Tested & Keywords

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E6 Physiology Guyton 4SAE Part 2A pp. 39-41, 42-44, 84-86