Ventilation, Perfusion and V/Q Relationship Flashcards
what is ventilation?
the process by which air moves in and out of lung
what is perfusion?
the process by which deoxygenated blood passes through the lung and becomes deoxygenated
what is the relationship between ventilation and perfusion called?
V/Q ratio
where in the alveoli is the pleural pressure more negative?
at the apex than at the base
where in the alveoli is the transpulmonary pressure the greatest?
at the apex
where in the alveoli is the alveolar volume greater?
at the apex
what affects distribution of ventilation?
gravity, compliance (C) and resistance (R)
what is compliance?
how much effort is required to stretch the lungs and the chest wall
what does high compliance mean?
the lungs and the chest wall expand easily
what is decreased compliance common in?
pulmonary conditions
what is scarring in lung tissue more commonly known as?
tuberculosis
what is lung filled with fluid known as?
edema
what is the destruction of elastic fibres called?
emphysema
what are the four pulmonary conditions that decreased compliance is common in?
scarring in lung tissue, lung filled with fluid, deficiency in surfactant production and destruction of elastic fibres
what does resistance mean?
any narrowing or obstruction of the airway that may reduce airflow
what part of the respiratory system has decreased resistance?
large diameter airways
what pulmonary conditions is increased resistance common in?
asthma, COPD due to obstruction or collapse of airways
what are the two types of dead space?
anatomical and physiological
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 e.g. alveoli that are ventilated but not perfused
what is the function of the pulmonary circulation?
brings deoxygenated blood from heart to lung and oxygenated blood from lung to heart
what is the function of bronchial circulation?
brings oxygenated blood to lung parenchyma
comment on the systemic circulation in terms of pressure and resistance
high pressure - 120/80mmHg and high resistance
comment on the pulmonary circulation in terms of pressure and resistance
low pressure - 24/9 mmHg and low resistance
what is the difference between the vessels of the systemic and pulmonary circulation
smooth muscle in systemic vessels whereas wider vessels with less smooth muscle in pulmonary vessels
what type of circulation does gravity influence more?
pulmonary
what factors influence flow and ventilation-perfusion relationships?
the greater blood flow to base than apex and the wide variations in arterial and venous pressure from apex to base
what is the V/Q ratio?
the ratio of ventilation to blood flow
what is the V/Q ratio for a single alveolus defined as?
alveolar ventilation divided by capillary flow
what is the V/Q ratio for the entire lung defined as?
total alveolar ventilation divided by cardiac output
what is the alveolar ventilation in healthy individuals?
4-6 L/min
what is the pulmonary blood flow in healthy individuals?
5L/min
what is the V/Q for lungs in healthy individuals?
0.8-1.2
what happens to the V/Q ratio when ventilation exceeds perfusion
V/Q > 1
what happens to the V/Q ratio when perfusion exceeds ventilation?
V/Q < 1
what does the mismatching of pulmonary blood flow and ventilation result in?
impaired O2 and CO2 transfer
what is arterial hypoexmia?
arterial PO2 < 80mmHg
what is arterial hypoxia?
when insufficient O2 to carry out metabolic functions - when arterial PO2 < 60 mmHg
what is hypercapnia?
increase in arterial PCO2 > 40 mmHg
what is hypocapnia?
decrease in arterial PCO2 < 35 mmHg
what is V-Q mismatching?
some alveoli V/Q > 1 and some < 1
where does V/Q mismatching result in?
varying alveolar and capillary gas contents
what is an anatomical shunt
mixed venous blood shunted directly into arterial blood (in the case of lung - mixed pulmonary artery blood shunted into the pulmonary veins)
what happens to the alveolar ventilation and the distribution of blood flow in an anatomical shunt?
alveolar ventilation is the same but distribution of blood flow changed
where do most anatomical shunts occur?
within heart - blood from right atrium or ventricle crosses septum to left atrium or ventricle: right to left shunt
what does an anatomical shunt result in?
varying degrees of hypoxemia
what is the effect on the PCO2 in an anatomical shunt?
PCO2 not increased because central chemoreceptors are very sensitive to CO2 changes - leads to increased ventilation and therefore reduction in PCO2
what happens to the lung unit ventilation in a physiological shunt?
ventilation to lung units is absent in presence of continuing perfusion
what happens in a physiological shunt?
blood perfusing non-ventilated alveolus is mixed venous blood, blood leaving continues to be mixed venous then mixes with arterial
what is atelectasis?
obstruction of ventilation due to mucous plugs, airway oedema, foreign bodies or tumours in airways
what happens when the V/Q = 0
ventilation to a region is 0, blocks airway, ventilation redistributed to other alveoli - elevated V/Q in other regions, e.g. child inhaling a peanut
what happens with low V?Q?
asthma and chronic bronchitis
what happens when the V/Q is infinite
no blood flow; perfusion to a region is 0, physiological deadspace, blood diverted to ther capillaries - low V/Q in other regions, e.g. pulmonary embolism
what happens when there is a high V/Q?
emphysema - disrupted gas exchange and pulmonary fibrosis - decreased gas exchange
what is COPD
condition in which the airflow is obstructed
what does COPD usually appear as?
emphysema and chronic bronchitis
what is COPD caused by?
long terms smoking
what are the symptoms of COPD?
chronic cough, chest tightness, shortness of breath, increased mucous production
what is emphysema?
structures in alveoli over inflated, lungs loose elasticity and cannot fully expand and contract, patients can inhale but exhalation is difficult due to decreased elastic recoil
what is chronic bronchitis?
inflammation of bronchi causing mucous production and excessive, shortness of breath with mild exertion, chest infections more prevalent
what is pulmonary fibrosis?
a type of interstitial lung disease, scarring and thickening of tissue, decreased elasticity, decreased gas exchange
what are the regional differences in ventilation and perfusion due to
gravity
what is the V/Q ratio in a healthy lung?
0.8
