RS: ventilation, perfusion & VQ relationship Flashcards
what is ventilation?
process by which air moves in and out of lungs
what is perfusion?
process by with deoxygenated blood passes through the lung and becomes oxygenated
what is the relationship between ventilation and perfusion called?
V/Q ratio
what 3 things affect the distribution of ventilation?
gravity
compliance
resistance
how does gravity effect the distribution of ventilation?
gravity pulls lung down and away from chest wall.
what is the difference in pleural pressure, alveolar pressure and transpulmonary pressure at the apex and base of the lung?
pleural pressure more negative at apex
trans pulmonary pressure greater at apex
alveolar volume increased
how does compliance affect the distribution of ventilation in the lung?
high compliance means that the lungs and chest wall expand easily
what is compliance?
how much effort is required to stretch the lungs and chest wall
decreased compliance is common in pulmonary conditions such as:
- scarring of lung tissue (tuberculosis)
- lungs filled with fluid (edema)
- deficiency in surfactant production
- destruction of elastic fibres (emphysema)
what is resistance?
any narrowing or obstruction of the airway that might reduce airflow
how does resistance affect the distribution of ventilation?
large diameter airways have decreased resistance
increased resistance is common in pulmonary conditions such as:
- asthma
- COPD (emphysema, chronic bronchitis) due to obstruction or colapse of airways
what is anatomical dead space?
volume of gas in each breath that does not participate in gas exchange eg. alveoli that are perfused but not ventilated
what is physiological dead space?
total volume of gas in each breath that does not participate in gas exchange eg. alveoli that are perfused but not ventilated
what is the pulmonary circulation of the lungs?
brings deoxygenated blood from heart to lung and oxygenated blood from lung to heart
- low resistance
what is the bronchial circulation of lung
brings oxygenated blood to lung parenchyma
what circulation is more affected by gravity?
pulmonary - low pressure, low resistance
in pulmonary blood flow does the base or the apex get better blood flow?
base
what is the V/Q ratio in the lung?
total alveolar ventilation
divided by
capillary flow
what is the V/Q ratio in a single alveolus?
alveolar ventilation
divided by
capillary flow
what is the alveolar ventilation, pulmonary blood flow and V/Q for lung?
alveolar ventilation = 4-6 L/min
pulmonary blood flow = 5 L/min
V/Q for lung = 0.8-1.2
what is the V/Q when ventilation exceed perfusion?
> 1
what is the V/Q when perfusion exceeds ventilation?
< 1
in a ‘perfect’ model, inspired gas and cardiac output shared equally between alveoli V/Q =?
1
what is arterial hypoxemia?
arterial PO2 < 80mmHg (normally 100)
what is hypoxia?
when insufficient O2 to carry out metabolic functions - when arterial PO2 < 60 mmHg
what is hypercapnia?
increase in arterial PPCO2>40mmHg
what is hypocania?
decrease in arterial PCO3<35mmHg
what is an anatomical shunt?
usually in the lung
- blood from right atrium or ventricle crosses over septum to left atrium or ventricle (right to left shunt)
in a right to left shunt, is the blood oxygenated or deoxygenated?
deoxygenated
how does an anatomical shunt affect PO2?
varies depending on the size of shunt
how does an anatomical shunt effect the alveolar ventilation and the distribution of blood flow?
alveolar ventilation = same
distribution of blood flow = changed
what does a physiological shunt?
ventilation to lung units is absent in presence of continuing perfusion (venous admixture)
what happens to alveolar ventilation and the distribution of blood flow in a physiological shunt?
alveolar ventilation = different
distribution of blood flow = same
what is atelectasis?
obstruction of ventilation due to mucous plugs, airway oedema, foreign bodies, tumour in airways
what is the most common cause of arterial hypoxemia in patients with respiratory disorders?
V-Q mismatching
what does V- Q mismatching result in?
alveolar and capillary gas contents varying
what is chronic obstuctive pulmonary disease? COPD
- condition where airflow is obstructed
- encompasses emphysema and chronic bronchitis
what causes chronic obstuctive pulmonary disease and what are the symptoms? COPD
cause = long term smoking
symptoms = chronic cough, chest tightness, shortness of breath, increases mucous production
what is emphysema?
- structures in alveoli over inflated
- longs loose elasticity and can’t fully expand or 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 swelling
- shortness of breath with mild exertion
- chest infection more prevalent
what is pulmonary fibrosis?
- type of lung disease
- scarring and thickness of tissue
- decreased elasticity
- decreased gas exchange
