ventilation & perfusion Flashcards
what is ventilation?
the exchange of air between the lungs and the atmosphere so that oxygen can be exchanged for CO2 in the alveoli
what are 2 important factors that affect ventilation?
-compliance
-airway resistance
define compliance
the measure of the ability of the lungs to stretch and expand
how is surface tension related to compliance?
a decreased surface tension allows compliance to be more easily achieved
what is airway resistance?
airway diameter
ie the smaller the airway the greater the resistance
what effect can a small change in the diameter (radius) of the airway have on resistance?
-small changes in radius leads to a big change in resistance - poiselluels law
-leads to decreased airflow and causes airflow limitation
what is perfusion Q?
the delivery of blood to a capillary bed in the alveoli
what are examples of factors that affect perfusion?
-destruction of the alveolar capillaries (ie emphysema)
-pulmonary embolus PE
-tumour
why is V/Q matching important?
-we need ventilation and perfusion to match for gas exchange to occur
-inadequacy of either will have a significant effect of the oxygenation of blood and removal of CO2.. this is termed a V/Q mismatch
what is the V/Q ratio?
-ratio of alveolar ventilation (4L/min) to cardio output (5L/min) giving 0.8
what is V/Q matching primarily influenced by in health?
body position
gravity
define dead space gas
air that does not participate in gas exchange
is ventilation distributed evenly in lungs?
no - alveoli in the apex of the lungs are more inflated, then air travels to the lower regions
which body position is ventilation greatest?
in the upright position - ie sitting up in bed or sitting out in chair
where is blood flow greatest in the lungs?
the bottom of the lungs - there is a steep gradient from the bottom to the top of the lungs
