L16 Respiratory Physiology Flashcards
What factors affect the diffusion of gas?
Movement of gas is directly proportional to:
1) pressure gradient of the gas
2) solubility of the gas in liquid
3) temperature
What does Dalton’s law state about total pressure (P) ?
The total pressure is exerted by a mixture of gases is equal to the sum of the pressures exerted by the individual gases
How is the pressure exerted by an individual gas determined?
By its relative abundance in the mixture and is independent of the molecular size or mass of the gas
What is the equation for the partial pressure of a gas?
atmospheric pressure X % of gas
What does the partial pressure of gas in air depend on?
Depends on the water vapour present
What is Henry’s law?
About the solubility of gas
- 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
Explain the diffusion of gases at alveolar surface
Movement of gas is directly proportional to:
Pressure gradient of gas
- Po2 alveolar air > Po2 blood
- Pco2 alveolar air < Pco2 blood
Solubility of the gas in liquid
- both co2 and o2 are soluble
- co2 solubility > o2 solubility
Temperature
- alveolar air is at core, body temperature
What are the characteristics of pulmonary circulation?
- low pressure system
- high flow
- parallel to the lower respiratory tract
- close association of capillaries and alveoli
What is the route for pulmonary circulation?
Right ventricle -> pulmonary trunk -> pulmonary arteries -> lungs -> pulmonary veins -> left atrium
What cells does the alveolar consist of?
1) Type I alveolar cell - 90% of alveolar cells, very thin, gas exchange
2) Type II alveolar cell - smaller, thicker, produce surfactant
3) Macrophages - protect alveolar structures from non-filtered, small particles
How is the diffusion distance reduced in alveoli?
The basal laminae of Type I alveolar cells and endothelial cells of capillary are fused
What is the equation for Fick’s law of diffusion?
For gas diffusion across the respiratory membrane
Flux = (P x change in C) / X
P = permeability of barrier x surface area
C = concentration gradient across the membrane barrier
X = distance to diffuse (minimised by fused basement membranes)
What is gas exchange in the alveoli driven by and give examples
By concentration gradients
Po2 alveoli > blood - o2 movement into capillaries
Pco2 blood > alveoli - co2 movement into alveoli
What effect does the change in ventilation ave on Po2 and Pco2?
They are inversely related during changes in ventilation
- as alveolar ventilation increases, alveolar Po2 increases and alveolar Pco2 decreases
What does hyperventilation result in?
Increased alveolar Po2 and decreased alveolar Pco2
What does hypoventilation result in?
Decreases alveolar Po2 and increased alveolar Pco2 and hypoxemia
Define hyperbaric
Higher than normal partial pressure of oxygen
What is hyperbaric oxygen therapy?
A person is placed in a chamber and exposed to higher than normal Po2 which leads to increased alveolar Po2 levels and o2 exchange
-> dissolved in plasma and delivered in tissues
What is hyperbaric oxygen therapy used to treat?
Conditions that benefit from increased oxygen delivery such as:
- severe blood loss
- crush injuries
- anaemia
- chronic wounds
Used for decompression sickness
How does hyperbaric oxygen therapy work to treat decompression sickness?
- this sickness is caused by dissolved gases in the blood coming out of the solution and forming bubbles in the bloodstream
- the therapy forces gases back into the solution which eliminates bubbles
What pathological changes that adversely affect gas exchange cause hypoxia?
SURFACE AREA
- decrease in amount of aleveoar surface area e.g. emphysema
DIFFUSION BARRIER PERMEABILITY
- increase in thickness of alveolar membrane e.g. fibrotic lung disease
DIFFUSION DISTANCE - increase in diffusion distance between alveoli and blood e.g. pulmonary edema
What causes emphysema?
The alveoli are destructed which means less surface area for gas exchange
- alveoli Po2 is normal/low
- po2 in the blood is low
What causes fibrotic lung disease?
Gas exchange is slowed due to thickened alveolar membrane
Loss of lung compliance may decrease alveolar ventilation
- Po2 in alveolar is normal/low
- Po2 in blood is low
What causes pulmonary edema?
Fluid in the interstitial space increases diffusion distance
The arterial Pco2 may be normal due to higher co2 solubility in water
- Po2 in alveoli is normal
- Po2 in blood is low
