Matching ventilation and perfusion Flashcards
How much blood does the lung receive per minute?
5l/min (cardiac output)
How much air does the lung receive per minute?
5l/min
Why does the intra-pleural pressure cary along the lung?
Due to gravity on the base
Is the intra-pleural pressure positive or negative?
Negative
Does the base or the apex of lung have the least negative pressure and why?
The base because it is more compressed due to gravity
Why does the base expand better on inspiration than the apex?
Because it has a less negative intra-pleural pressure and is more compressed due to gravity (under its own weight)
Why do the lungs and chest cavity pull away from each other?
Intra-pleural pressure is more negative than the atmospheric pressure
Does posture effect the efficiency of ventilation?
Yes
What happens to the apex of the lung due to the higher pressure at the base?
The apex becomes distended (swollen)
When the diaphragm contracts it expands the bottom part of the thoracic cavity. Why is this more efficient that expanding the apex?
Because the base is easier to expand than the apex due to it being more compressed (less negative pressure)
How much does the pulmonary circulation accept?
The entire cardiac output always
Why is vascular resistance less than systemic resistance?
Vascular circulation is at a lower pressure
Why does perfusion occur easier in pulmonary circulation?
It has a lower resistance than systemic
At the base is ventilation and perfusion efficient or not?
Efficient
At the apex is ventilation and perfusion efficient or not?
Not
When is the apex well perfused?
When blood pressure increases
This increases the number of capillaries and alveoli that are used and causes the apex to be well perfused
The proportion of which molecules are monitored to change levels of perfusion/ventilation?
Oxygen and CO2
How is ventilation/perfusion changed?
affecting smooth muscles of bronchioles and capillaries
What happens in the lungs when there is a high ventilation perfusion ratio and what does high V/Q mean?
Means there is a high alveolar oxygen concentration and a low alveolar CO2 concentration.
Causes vasodilation and broncho constriction
What is the effect of vasodilation on blood concentration?
Increases blood flow so more CO2 and be moved into the lungs and more O2 can be moved out
What is the effect of broncho-constriction on gas composition?
More O2 can leave the alveoli. Constriction will increase resistance, decreasing the amount of air coming into a space that is not well perfused. More oxygen leaves the well perfused alveoli
What happens in the lungs when there is a low ventilation effusions ratio and what does low V/Q mean?
Means there is a low alveolar oxygen concentration and high alveolar CO2 concentration
Causes vasoconstriction dn broncho-dilation
What is the effect of vasoconstriction on blood concentration?
Decrease in blood flow so more CO2 can leave the alveoli and more O2 can enter
What happen in systemic circulation when there is a low V/Q?
Leads to arterial vasodilation
When does hypoxic vasoconstriction occur?
When V/Q is low
What is hypoxic vasoconstriction?
Drop in oxygen saturation causes constriction of the pulmonary capillaries causing blood supply to be reduced in the hypoxic region and diverted to the well ventilated areas of the lung where V/Q will be matched
Why can hypoxic vasoconstriction be harmful to someone with pulmonary disease?
In the hypoxic area hypoxic vasoconstriction will occur and this will increase resistance in that area. This will increase pulmonary BP and so induce right ventricle heart failure.
As BP rises more blood is pressed into capillaries and causes pulmonary oedema
Why is partial pressure of oxygen lower in the arteries than alveoli?
Anatomical shunt. Bronchiole arteries to pulmonary vein - bypass gas exchange, so oxygenated blood goes straight back to the lung.
What is anatomical shunt?
Bronchiole arteries drain straight into pulmonary veins
Miss gas exchange
What is pulmonary shunt?
Ventilation/perfusion ratio is 0
alveoli are perfused but no ventilation to that area
How doe left ventricle heart failure impact V/Q?
Lv heart failure leads to an increase in pulmonary pressure.
This disturbs the hydrostatic/oncotic pressure balance
Causes H2O to be trapped in the lung causing pulmonary oedema
Why is giving a hypoxic patient oxygen dangerous?
Increased oxygen reduces ventilation and causes less CO2 to be released so CO2 concentrations increase and H2CO3 forms this decreases pH.
This will mean less CO2 will enter the alveoli so when the O2 leaves the alveoli will collapse
