Gas Exchange Flashcards
What is the difference between pulmonary ventilation and alveolar ventilation
Pulmonary ventilation is the volume of air breathed in and out per minute
Alveolar ventilation is the volume of air exchanged between the atmosphere and alveoli per minute. Represents new air available for gas exchange with blood
What’s the significance of anatomical dead space
Inspired air that is left in the airways which is not available for gas exchange
Explain ventilation perfusion
The transfer of gases between the body and atmosphere depends on:
Ventilation - rate gas passes through the lungs
Perfusion - rate blood passes through the lungs
Both blood flow and ventilation vary from bottom to top of lung
Describe the significance of alveolar dead space
Ventilated alveoli which are not adequately perfused with blood are considered as alveolar dead space
This is very small and of little importance in normal people but can increase significantly in disease
Explain the basic principles of ventilation perfusion matching
Local controls act on the smooth muscles of airways and arterioles to match airflow to blood flow
Accumulation of CO2 in alveoli as a result of increased perfusion decreases airway resistance leading to increased airflow
Increase in alveolar O2 concentration as a result of the increase ventilation causes pulmonary vasodilation which increases bloodflow to match larger airflow
What is the physiological dead space
Anatomical dead space and alveolar dead space
What are the four factors that influence the rate of gas exchange across the alveolar membrane
- Partial pressure gradient of O2 and CO2
- Diffusion coefficient O2 and CO2
- Surface area of alveolar membrane
- Thickness of alveolar membrane
Explain Daltons law of partial pressures
The total pressure exerted by a gaseous mixture = the sum of the partial pressures of each individual component in the gas mixture
Explain the partial pressure of gas
The pressure that one gas in a mixture of gases would exert if it were the only gas present in the whole volume occupied by the mixture at a given temperature
How to gases move
Gases move across the cell membranes etc by pressure gradient. The partial pressure of a gas determines the pressure gradient for that gas
What is the alveolar gas equation
Partial pressure of oxygen in the alveolar air (PAO2)
PAO2 = PiO2 - (PaCO2/0.8)
PAO2 = 150 - (40/0.8) = 150 - 50 = 100mmHg at sea level
Explain the diffusion coefficient
The solubility of gas in membranes is this known as diffusion coefficient for the gas.
CO2 is more soluble in membranes than O2 the diffusion coefficient of CO2 is 20 times that of O2
Explain the gradient between alveolar and arterial PO2
A small gradient between Alveolar PO2 (PAO2) and arterial PO2 (PaO2) is normal due to ventilation perfusion match not being perfect
A big gradient indicates problems with the gas exchange in the lungs or a right to left shunt in the heart
Explain Flick’s law of diffusion
The amount of gas that moves across a sheet of tissue in unit time is proportional to the area of the sheet but inversely proportional to its thickness
Identify the non respiratory functions of respiratory system
- route for water loss
- enhances venous return
- helps maintain normal acid base balance
- enables speech, singing, and other other vocalisations
- defends against inhaled foreign matter
- removes, modifies, activities or inactivates various materials passing pulmonary circulation
- nose serves as the organ of smell
