ventilation and perfusion Flashcards
what is ventilation?
process by which air moves in and out of lung
what is perfusion?
process by which deoxygenated blood passes thru the lung and becomes oxygenated
what is the relationship between ventilation and perfusion called?
V/Q ratio
what is the V/Q ratio a major determinant of?
normal gas exchange so level of PO2 and PCO2 in blood
why is ventilation not uniformly distributed in lung?
gravity
where is pleural pressure more negative?
apex - not base
what other pressure is higher at apex?
transpulmonary
where is there increased alveolar volume?
apex
what is compliance?
how much effort is required to stretch the lung and chest wall
what pulmonary conditions of decreased compliance a common feature of?
scarring in lung tissue, lung filled with fluid, deficiency in surfactant prod., destruction of elastic fibres (emphysema)
what is resistance?
narrowing or obstruction of the airway that may reduce airflow
what pulmonary conditions is increased resistance a feature of?
asthma, COPD
what is anatomical dead space?
volume of gas during each breath that fills the conducting airways?
what is physiological dead space?
total volume of gas in each breath that does not participate in gas exchange- ventilated not perfused
which circulation is influenced by gravity?
pulmonary- greater flow to base than apex
what is the V/Q ratio for a single alveolus?
alveolar ventilation divided by capillary flow
what is the V/Q ratio for a whole lung?
total alveolar ventilation divided by cardiac output
what is alveolar ventilation in healthy individuals?
~4-6 L/min
what is pulmonary blood flor in a healthy individual?
~5 L/min
what is average V/Q value?
0.8-1.2
what is V/Q when ventilation exceeds perfusion?
> 1
what is V/Q when perfusion exceeds ventilation?
<1
what is arterial hypoxemia?
arterial PO2 < 80mmHg
what is hypoxia?
when insufficient O2 to carry out metabolic functions- arterial PO2 < 60mmHg
what is hypercapnia?
increase in arterial CO2>40mmHG
what is hypocapnia?
decrease in arterial PCO2 < 35 mmHg
what is V/Q mismatching?
most frequent cause of arterial hypoxia in patients with respiratory disorders
what is an anatomical shunt?
mixed venous blood directly into arterial blood- alveolar ventilation same, distribution of blood flow changed, PO2 varied depending on size
where do most anatomical shunts occur and what does this result in?
in heart- RA/V to LA/V
results in varying degrees of hypoxia
what is a physiological shunt?
ventilation to lung units in presence of continuing perfusion- venous mixture-alveolar ventilation different, distribution of blood flow same
what blood mixes in a physiological shunt?
blood perfusing non-ventilated alveolus is mixed venous- mixes with arterial
what occurs if V/Q = 0?
ventilation to a region is 0 eg blocked airway- ventilation redistributed to other alveoli
what is the cause of low V/Q
asthma, chronic bronchitis
what is the cause of high V/Q?
emphysema- distupted gas exchange
pulmonary fibrosis- decreased gas exchange
what is COPD?
condition in which airflow is obstructed- emphysema and chronic bronchitis- cause long term smoking
what is emphysema?
structures in alveoli over inflated- inhale but exhale difficult due to decreased elastic recoil
what is chronic bronchitis?
inflammation of bronchi causing mucous production and excessive swelling, shortness of breath, chest infections more prevalent
what is pulmonary fibrosis?
interstitial lung disease, scarring and thickening of tissue, decreased elasticity, decreased gas exchange
