Which of the following is FALSE concerning airway resistance (R)?

Correct Answer: A

Rationale: Airway resistance (R) follows Poiseuille's law (R ∝ 1/r^4), but total resistance depends on cross-sectional area. Later generations (bronchioles) have smaller radii, yet their vast number increases total area (e.g., ~300 cm² vs. trachea's 3-4 cm²), reducing overall R most resistance is in larger airways (trachea, bronchi), where flow is turbulent, making this false. Normally, ~80% of R is in large airways, dropping in smaller ones due to laminar flow and area. Increased R (e.g., asthma) lowers FEV1/FVC (<70%), as FEV1 falls more, a true obstructive sign. Loss of elasticity (emphysema) and bronchoconstriction (asthma) raise R by collapsing or narrowing airways, also true. The false idea of increasing R in later generations misinterprets branching dynamics, where resistance peaks proximally, not distally, aligning with physiological airflow distribution.

Correct Answer: A

Rationale: Air enters the lungs during inspiration per Boyle's law: thoracic expansion lowers intrapulmonary pressure below atmospheric (e.g., 760 to 758 mmHg), creating a pressure gradient driving airflow. Increasing this gradient via stronger diaphragm and intercostal contraction directly boosts inspired volume (e.g., from 500 ml to 600 ml), the primary factor. Increase in action potential' likely means neural impulses to respiratory muscles; more impulses enhance contraction, but this is secondary to the gradient they produce. Combining both overcomplicates pressure is the direct mechanism. Decreasing the gradient reduces flow, opposing the goal. The pressure gradient is the key driver, quantifiable (e.g., 1-2 mmHg for tidal breathing), linking muscle action to volume via physics, distinguishing it as the most impactful factor in ventilation mechanics.

Correct Answer: D

Rationale: Minute ventilation (VE) = tidal volume (VT) × respiratory rate (RR), fixed at 6 L/min (6000 ml/min). Alveolar ventilation (VA) = (VT - VD) × RR, with anatomic dead space (VD) = 150 ml. For 200 ml at 30/min: VE = 200 × 30 = 6000 ml/min, VA = (200 - 150) × 30 = 50 × 30 = 1500 ml/min. For 300 ml at 20/min: VA = (300 - 150) × 20 = 150 × 20 = 3000 ml/min. For 400 ml at 15/min: VA = (400 - 150) × 15 = 250 × 15 = 3750 ml/min. For 600 ml at 10/min: VA = (600 - 150) × 10 = 450 × 10 = 4500 ml/min. The 600 ml at 10/min maximizes VA (4.5 L/min), as larger VT exceeds VD more, despite lower RR. High RR with low VT wastes ventilation in dead space, reducing VA efficiency. This deeper, slower pattern optimizes gas exchange, making it the best choice.

Correct Answer: D

Rationale: Pneumothorax introduces air into the pleural space, negating intrapleural pressure (~-4 mmHg), collapsing the lung via elastic recoil and expanding the chest wall outward via its recoil increasing thoracic diameter, true. Venous return drops as positive pleural pressure (e.g., tension pneumothorax) compresses vena cava, reducing preload true. Vital capacity (VC) falls as collapsed lung limits exhalable volume (e.g., from 4-5 L) true. Lung compliance (C = ΔV / ΔP) doesn't increase collapsed lung tissue isn't more stretchable; compliance is a lung property unaffected by deflation, effectively zero in collapse, not raised. The false notion of increased compliance misrepresents pneumothorax, where pressure loss, not elasticity, drives effects, making it the untrue statement amid accurate mechanical outcomes.

Correct Answer: A

Rationale: Functional residual capacity (FRC) = expiratory reserve volume (ERV) + residual volume (RV). RV = 1.0 L via helium dilution. The spirogram shows vital capacity (VC = IRV + VT + ERV) from max inhalation to max exhalation. Without the figure, assume typical female values: VC ~4 L, TLC ~5 L. FRC is post-normal expiration; if ERV (exhalable beyond tidal) is ~1 L (common for young women), FRC = ERV + RV = 1 + 1 = 2.0 L. Higher FRC (2.5-3.5 L) fits larger frames or males (~3 L). The 2.0 L aligns with RV and minimal ERV, plausible for a 22-year-old female, reflecting resting volume per standard physiology.