L16- Factors affecting gas exchange in the alveoli

what is Dalton’s Law

the total pressure (P) exerted by a mixture of gases is equal to the sum of the pressures exerted by the individual gases

• the pressure of an individual gas in a mixture is the partial pressure of the gas (P_gas)

what is the equation to find a gas’s partial pressure

P_atmos X % of gas

what is Henry’s Law

at constant temperature, the amount of gas that dissolves in a liquid depends on the solubility of the gas in the liquid and the partial pressure of the gas

what is the movement of gas directly proportional to

• pressure gradient of the gas

• solubility of the gas in liquid

• temperature

what are the characteristics of pulmonary circulation

• low pressure system

• high flow

• close association of capillaries and alveoli

• parallel to lower respiratory tract

describe Fick’s Law of diffusion

Flux= (P x delta C) / X

• P= permeability of barrier x surface area (~1000 square feet)

• delta C= concentration gradient across membrane barrier

• X= distance to diffuse (minimised by fused basement membrane)

define hyperbaric

higher than normal pressure

what is hyperbaric oxygen therapy used to treat

conditions benefiting from increased oxygen delivery:

• severe blood loss

• crush injuries

• anemia

• chronic wounds

• certain infections

• burns

• decompression sickness (bends in divers that ascend too rapidly)

what pathological change occurs in the surface area that affects gas exchange, causing hypoxia

surface area

• decrease in the amount of alveolar surface area

• e.g. Emphysema

what pathological change occurs in the diffusion barrier permeability that affects gas exchange, causing hypoxia

increase in thickness of alveolar membrane

• e.g. fibrotic lung diseases

what pathological change occurs in the diffusion distance that affects gas exchange, causing hypoxia

increase in diffusion distance between alveoli and blood

• e.g. pulmonary edema, infections

what does alveolar ventilation (V_A) depend on

• posture

• rate of inspiration

• amount of air inspired

how is lung perfusion (Q) determined by gravity

• hydrostatic pressure in pulmonary arteries

• pressure in pulmonary veins

• alveolar air pressure

what is V/Q mismatch

when V does not match Q, blood is shunted from the right to the left side of the heart without adequate oxygenation

what is hypoxic pulmonary vasoconstriction

• redirects blood flow to ventilated alveoli

• improves gas exchange

• contrast with systemic circulation

what is the V/Q for ideal gas exchange

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