Gas exchange Flashcards
what factors affect alveolar gas exchange?
-pressure gradient
-solubility
-membrane thickness
-membrane area
-ventilation-perfusion matching
List the diffusion pathway
-alveolar gas
-liquid lining alveoli with surfactant
-alveolar epithelium
-epithelial basement membrane
-interstitial space
-capillary basement membrane
-cappilary endothelial cells
-plasma
-RBC membrane
What diseases cause the alveolar cappilary membrane to thicken?
-pulmonary fibrosis
-emphysema
-pulmonary oedema
What is ficks law?
volume of gas diffusing through the membrane per minuete (ml/min)
What is ficks equation?
A X D X (P1-P2) /T
A-surface area of membrane
D-diffusion coefficent
P1-P2- partial pressure difference of gas
T- membrane thickness
what is the equation of ventilation perfusion rate?
V/Q ration = alveolar ventilation / cardiac output
define V/Q mismatch
well ventilated but poorly perfused or poorly ventilated and well perfused
what happens when ventilation is reduced or perfusion is increased?
-reduced alveolar and arterial PO2 and increased PCO2
-Reducing ventilation
-build up of CO2 and a reduction in O2 in alveoli
What happens if perfusion increases without a change in ventilation?
more CO2 brought to the lungs that can be removed-decrease in PaO2 and increase in PaCO2
What happens when ventilation is increased and perfusion reduced?
-increased alveolar and arterial PO2 and decreased PCO2
-increasing ventilation causes more CO2 to be exhaled increasing PO2 in the alveoli and blood
-increased PaO2 and decreased PaCO2
What is a physiological shunt?
an area which isnt ventilated will result in reduced V/Q
example- alveoli blocked by secretions or a physical block such as an inhaled peanut
What is an anatomical shunt?
when blood doesnt enter the lungs
example-blood passing from the right to left ventricle without passing through the lungs
What happens to V/Q in COPD/ emphysema?
-alveoli and damaged causing large air spaces to develop and the loss of cappilaries
-V/Q mismatch
-hypoxia
-hypercapnia
What causes an increased V/Q?
an area which isnt perfused
(example-pulmonary embolism)
What are the two responses to change in V/Q?
-hypoxic vasoconstriction
-bronchoconstriction
