20 - Ventilation and Perfusion Relationships – Vocabulary Flashcards

Vocabulary-style flashcards covering key ventilation, perfusion, V/Q concepts, regional differences, and mechanisms the lecture notes discuss.

Ventilation (V̇)

Airflow into and out of the alveoli; one half of the V/Q relationship that determines gas exchange.

Perfusion (Q̇)

Blood flow through the pulmonary capillaries around the alveoli; the other half of the V/Q relationship.

V/Q ratio

The ratio of alveolar ventilation to pulmonary capillary perfusion in a region; determines local alveolar gas composition and gas exchange efficiency.

Physiologic Shunt (V/Q = 0)

Alveoli with ventilation essentially zero relative to perfusion; blood bypasses gas exchange (includes thebesian and bronchial contributions).

Dead Space (V/Q = ∞)

Ventilated alveoli with little or no perfusion; gas exchange does not occur in these regions.

Ideal V/Q (V/Q = 1)

Perfect match between ventilation and perfusion; alveolar gas exchange operates with balanced gas addition and removal.

Thebesian veins

Small cardiac venous drainage that contributes to venous admixture; part of physiologic shunt (<5% of CO normally).

Bronchial circulation

Systemic blood supply to the airways that can return blood to the left heart, contributing to venous admixture.

Hypoxic Pulmonary Vasoconstriction (HPV)

Local vasoconstriction of pulmonary vessels in poorly ventilated regions to redirect blood flow to better-ventilated areas and reduce V/Q mismatch.

Recruitment

Opening of collapsed pulmonary capillaries to increase regional perfusion.

Distension

Expansion of vessels with pressure, increasing local perfusion and influencing the regional V/Q by altering Q̇.

Vasoactive factors

Substances that modulate vascular tone and thus regional perfusion and V/Q distribution.

Regional V/Q distribution

Variation of ventilation and perfusion across different lung regions due to gravity and local mechanics.

Gravity and ventilation

Gravity causes nonuniform ventilation across the lung because of differences in distending pressures and compliance.

Zone model of pulmonary blood flow

Classification of lung regions by blood flow relative to alveolar pressure (often described as Zone 1–4 with varying flow patterns).

Apex vs Base V/Q distribution

Regional variation in V/Q along the vertical axis; typically higher V/Q at the apex and lower V/Q at the base due to gravity and perfusion differences.

Gas exchange and regional gas contents

Gas exchange depends on regional alveolar gas contents; overall arterial gas content is the weighted average of regional contributions.

Minimising V/Q mismatch

Physiological strategies to reduce mismatch by regional control of ventilation and perfusion (e.g., HPV, bronchoconstriction/dilation, vasodilation).