Respiratory Physiology: Gas Laws, V/Q Ratio, Shunts & Hypoxia

32 vocabulary flashcards summarizing key respiratory physiology concepts: gas laws, diffusion, oxygen transport, V/Q relationships, shunts, and forms of hypoxia.

Dalton’s Law of Partial Pressures

The total pressure of a gas mixture equals the sum of the partial pressures each gas would exert if it occupied the same space alone.

Pressure Gradient

The difference in pressure that drives gas movement from high to low concentration areas during ventilation.

Gas Diffusion

Movement of individual gas molecules from an area of higher partial pressure to an area of lower partial pressure.

Fick’s Law of Diffusion

States that diffusion rate is proportional to surface area, diffusion constant, and pressure gradient, and inversely proportional to membrane thickness.

Dissolved Oxygen

About 1.5 % of total blood O2 carried directly in plasma.

Hemoglobin-Bound Oxygen

Roughly 98.5 % of blood O2 is reversibly bound to hemoglobin inside red blood cells.

Total Oxygen Content (CaO2)

The sum of dissolved O2 and hemoglobin-bound O2 present in 100 mL of blood.

Oxygen Dissociation Curve

Graph showing the relationship between hemoglobin saturation (SaO2) and arterial oxygen pressure (PaO2).

Left Shift of O2 Curve

Indicates increased hemoglobin affinity for O2, making O2 unloading to tissues harder.

Right Shift of O2 Curve

Indicates decreased hemoglobin affinity for O2 (P50 > 27 mm Hg), enhancing O2 release to tissues.

P50

The PaO2 at which hemoglobin is 50 % saturated; normally about 27 mm Hg.

Ventilation-Perfusion Ratio (V/Q)

The ratio of alveolar ventilation (≈4 L min⁻¹) to pulmonary blood flow (≈5 L min⁻¹); normal overall value is 0.8.

High V/Q Ratio

Regions with more ventilation than perfusion (e.g., lung apices); PAO2 rises and PACO2 falls.

Low V/Q Ratio

Regions with more perfusion than ventilation; PAO2 falls and PACO2 rises.

Alveolar Oxygen Pressure (PAO2)

Determined by oxygen entering alveoli minus its removal by blood flow.

Alveolar Carbon Dioxide Pressure (PACO2)

Determined by CO2 entering alveoli from blood minus its elimination via ventilation.

Physiological Shunt

Normal mixing of deoxygenated venous blood with arterial blood via thebesian and bronchial veins or underventilated alveoli (<10 % of CO).

Thebesian Veins

Small cardiac veins that drain directly into the left atrium, contributing to physiological shunt.

Bronchial Venous Drainage

Bronchial veins empty into pulmonary veins, adding deoxygenated blood to systemic circulation.

Anatomic Shunt

Blood that bypasses alveoli completely (normal ≈3 % of cardiac output).

Capillary Shunt

Perfusion of non-ventilated alveoli caused by collapse, fluid accumulation, or consolidation.

Absolute Shunt

Total of anatomic and capillary shunts; blood passes through lungs without gas exchange.

Pulmonary Shunting (Qs/Qt)

Portion of cardiac output that reaches the left heart without oxygenation; <10 % normal, 10–20 % mild, 20–30 % significant.

Hypoxemia

Abnormally low oxygen tension in arterial blood (low PaO2).

Hypoxia

Insufficient oxygen at tissue level, regardless of cause.

Hypoxic Hypoxia

Tissue hypoxia resulting from low arterial PaO2.

Anemic Hypoxia

Tissue hypoxia due to decreased hemoglobin concentration or altered Hb function.

Circulatory (Stagnant) Hypoxia

Tissue hypoxia caused by inadequate blood flow or perfusion.

Histotoxic Hypoxia

Tissue cells cannot use delivered O2, as in cyanide poisoning.

Early Sign of Hypoxia – Tachycardia

Increased heart rate is typically the first clinical sign of tissue hypoxia.

Additional Hypoxia Signs

Hypertension, peripheral vasoconstriction, dizziness, and confusion.