VQ relationships and disorders Flashcards
what is the VQ ratio
the relationship between ventilation and perfusion (ventilation to blood flow)
what is ventilation
process by which air moves in and out of the lung
what is perfusion
process by which deoxygenated blood passes through the lung and becomes oxygenated
what does the VQ ratio determine
the level of partial pressure of oxygen and carbon dioxide in the blood
describe the pleural pressure distribution in the lungs
more negative at the apex than at the base
what is compliance
how much effort is required to stretch the lungs and the chest wall
what are some pulmonary conditions that lead to reduced compliance
scarring in the lung tissue
fluid in the lungs
deficient surfactant production
destruction of elastic fibres
what is resistance
narrowing or obstruction in the airway that may reduce airflow
what are some conditions that lead to an increase in resistance
asthma
obstruction or collapse of airways due to COPD
what is COPD
chronic obstructive pulmonary disease including ephysema or chronic bronchitis
what are the two types of dead space
anatomical dead space or physiological dead space
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 eg alveoli that are perfused but not ventilated
describe pulmonary blood flow distribution
pulmonary circulation is a low pressure and low resistance system, influenced by gravity more than systemic circulation
describe pulmonary circulation when sat upright
greater blood flow to the base than to the apex
what can influence flow and the VQ ratio
the variations in arterial and venous pressure
summarise pressure and resistance of pulmonary circulation
low pressure
low resistance
what is the VQ ratio defined as for a single alveolus
alveolar ventilation divided by capillary flow
what is the VQ ratio defined as for the lungs as a whole
total alveolar ventilation divided by cardiac output
what is the VQ for lungs in healthy people
0.8-1.2
what does the perfect model for VQ ratio actually mean
where the alveolar partial pressure of oxygen and arterial partial pressure of oxygen are the same
what is the arterial blood gas for someone with arterial hypoxemia
arterial partial pressure of oxygen is less than 80mmHG
what is the partial pressure for hypoxia
less than 60mmHg
what is hypoxia
this is when there is insufficient oxygen to carry out metabolic functions
what is the partial pressure for hypercapnia
over 40 mmHg
what is the partial pressure for hypocapnia
less than 35 mmHg
what is anatomical shunting
this is when mixed venous blood is shunted directly into arterial blood
when this happens, the alveolar ventilation is the same, but the distribution of blood flow is changed
what is a right to left shunt
blood being shunted is deoxygenated
where do most anatomical shunts occur
in the heart, where the blood from the right ventricle or atrium crosses the septum to the left atrium or ventricle
what does anatomical shunting lead to
hypoxemia
does anatomical shunting affect the partial pressure of carbon dioxide
no, because central chemoreceptors are very sensitive to carbon dioxide changes to increase ventilation. this leads to a reduction in partial pressures of carbon dioxide
describe physiological shuntings impact on VQ
the alveolar ventilation is different, but the distribution of the blood flow is the same
what is the VQ ratio in physiological shunting
0
what is physiological shunting
blood perfusing non ventilated alveolus is mixed venous blood, and the blood leaving continues to be mixed venous then mixes with arterial blood
what is atelectasis
obstruction of ventilation due to mucous plugs, airway oedema, foreign bodies and tumours in airways
what is the most frequent cause of artieral hypoxemia in patients with respiratory disorders
VQ mismatching
what does VQ mismatching lead to
varying alveolar and capillary gas contents
what is encompassed in COPD
emphysema and chronic bronchitis
what are the symptoms of COPD
chronic cough
chest tightness
shortness of breath
increased mucous production
what is the most frequent cause of COPD
long term smoking
what is emphysema
structures in the alveoli are inflated, and the lungs lose their elasticity and cannot fully expand and contract
patients can inhale but exhalation is difficult due to decreased elastic recoil
describe chronic bronchitis
inflammation of the bronchi causes mucous production and excessive swelling
shortness of breath with mild exertion
what is pulmonary fibrosis
this is a type of interstital lung disease, and leads to scarring and thickening of tissue.
there is decreased elasticity and decreased gas exchange
what is used to measure lung volume
vitalograph or spirogram
what are the four major results obtained from vitalograph
forced vital capacity
forced expiratory volume in one second
ratio of forced expiratory volume to forced vital capacity
average mixmaximal expiratory flow
what is the main cause for the regional differences between ventilation and perfusion
gravity
what is the VQ when ventilation exceeds perfusion
over one
what is the VQ ration when perfusion exceeds ventilation
less than one
