Physiology - Gas Exchange Flashcards
What is anatomical dead space?
Where some inspired air remains in airways where it cannot be involved in gas exchange. Slide 6
Why is alveolar ventilation less than pulmonary ventilation?
Alveolar ventilation is less because of the anatomical dead space, therefore have to subtract 0.15 from tidal volume. Slide 6
What is pulmonary and alveolar ventilation and which is more important?
PV = volume of air breathed in and out per min.
AV = volume of air exchanged between the atmosphere and alveoli per min.
AV is more important as it shows the new air available for gas exchange. Slide 7
How do you increase pulmonary ventilation and why?**** double check
Increase both depth and rate of breathing due to dead space being taken into account.
If it was shallow, then the tidal volume would be minimal so once dead space is taken into account there would be basically no net volume of air. Slide 9
What is ventilation and perfusion?
Ventilation is the rate at which GAS passes through lungs.
Perfusion is the rate at which BLOOD passes through lungs. Slide 10
Blood flow and ventilation is …. at the bottom of the lung compared to the top.
Higher. Slide 11
What is ALVEOLAR dead space?
The ventilated alveoli which is not adequately perfused with blood and is very small in healthy people. Slide 12
What happens when perfusion is greater than ventilation?
There is high CO2, so the airways dilate to increase airflow. There is less O2 as it is being taken away so blood vessels constrict which decreases blood flow. Slide 14
What happens when ventilation is greater than perfusion?
There is low CO2 which causes constriction of airways, decreasing the airflow. The O2 increases so blood vessels dilate to increase blood flow. Slide 15
What are the different effects of low O2 on pulmonary and systemic arterioles?
When there is low O2 it causes:
Constriction in pulmonary
Dilation in systemic
Slide 16
What are the 4 factors that influence the rate of gas exchange?
Partial pressure gradient of O2 and CO2
Diffusion coefficient of O2 and CO2
Surface area of alveolar membrane
Thickness of alveolar membrane. Slide 17
What is partial pressure and Dalton’s Law of Partial Pressure?
Partial pressure is the pressure one gas in a mixture would exert if it were the only gas present.
Dalton’s Law is that if you add all the partial pressures up, it gives you the total pressure exerted. Slide 18
What is the alveolar gas equation?
PAO2 = PiO2 - [PaCO2/0.8]
When calculating the partial pressure of O2 in the alveolar air what do you have to take into account?
The air is saturated with water which contributes a water vapour pressure of 47 mmHg, so pressure of inspired air is 760-47 = 713mmHg. Slide 22
What does the partial pressure gradient allow gases to do in gas exchange?
Flow from a high to low pressure gradient.
E.g. for O2, pressure gradient from alveoli to blood is 60 mmHg and from blood to tissue cell is >60 allowing O2 to flow in. Slide 24
