ventilation & perfusion Flashcards
what is the importance in ventilation?
what is alveolar ventilation?
what is dead space air?
what volume is in dead space air?
what is alveolar ventilation a major factor for?
1- the importance of alveolar ventilation is the renew air in gas exchange areas
2- alveolar ventilation is defined as the volume of air entering and leaving the alveoli per minute.
3- dead space air is air the is breathed, but never reaches gas exchange areas, instead filling the respiratory pathway.
4_ normally about 150ml.
5- alveolar ventilation is one of the major factors determining O2 and CO2 concentrations in alveoli.
what is the equation for alveolar ventilation rate?
What is a consequence of gas exchange?
As a consequence of gas exchange, the fraction of O2 decreases and the fraction of CO2 increases in the alveolus
What equation is the relationship between O2 and CO2 given?
what is the alveolar air equation?
What does the alveolar air equation describe?
Relationship between the 2 gases is given by alveolar air equation
Alveolar air equation describes ideal case of what PAO2 should be
When will PAO2 = PaO2?
Why will this not happen?
What can PaO2 be affected by?
What is the Alveolar – arterial (A-a) gradient?
What is a typical value for this?
What can a high value indicate?
If there is perfect transport and no venous admixture, PAO2 = PaO2
This will not happen, as deoxygenated blood from bronchiole vessels can be shunted into the pulmonary vein where there is oxygenated blood (this is a normal process)
PaO2 can affected by disease e.g COPD
The Alveolar – arterial (A-a) gradient is the difference between PAO2 and PaO2
It is normally less than 15 mmHg, with higher values indicating problems with exchange
define the term “ventilation -perfusion ratio”
this is a ratio that is used to assess the efficiency and adequacy of the matching of two variables: ventilation and the air that actually reaches the alveoli.
what is the difference in ventilation across the lung
perfusion increases more than ventilation at the base of the lungs.
what are the reasons for the difference in ventilation across the lungs?
because the pleural pressure at the apex is higher than the pleural pressure at the base.
therefore the alveoli will have different expansions.
why do we have the alveolar gas equation?
- as a consequence of gas exchange, fraction of O2 decreases and CO2 increases in alveolus.
So the relationship between the 2 gases will be given by alveolar air equation.
why is ventilation not uniformly distributed in lung?
what is tis due too?
due to the effects of gravity.
- the alveoli at the apex of the lungs are much more expanded than the alveoli at the base of the lung.
- this is due to there being a greater pressure at the apex of the lung in comparison to the base. (pleural pressure decreases as we move from the apex to the base)
so what alveoli gets most of the ventilation are?
- why is this?
the alveoli at the base will receive most of the ventilation air (the alveoli at the apex will receive the least)
- this is because they alveoli at the base are able to expand more because they start of more crushed than the alveoli at the apex.- under inflated alveoli at the base of the lung receive more tidal volume
- overinflated alveoli at the top have a lower compliance and receive less tidal volume.
Describe the 6 steps in the pulmonary circulation.
Why might blood not reach the apex of the lung?
How can this be overcome in exercise?
6 steps in the pulmonary circulation:
1) Pulmonary circulation begins with RA
2) Deoxygenated blood pumped via RV into pulmonary artery
3) Pulmonary artery divides into right and left main artery then enters lung tissue
4) Ends in mesh like network of capillaries where rbc flow single file through alveolus
5) Capillaries drain into pulmonary venules
6) Finally, 2 large pulmonary veins emerge from each lung to empty into LA
Blood may not be able to reach the apex of the lung if the pressure generated by the right ventricle can’t overcome the pressure in the apex of the lung.
This can be overcome during exercise, as the heart pressure increases, meaning blood can be pushed into the apex of the lung
what are the 2 blood supplies of the lungs?
what do pulmonary arteries carry?
what do pulmonary veins carry?
2 blood supplies of the lungs:
1) Pulmonary arteries
2) Bronchial arteries
Pulmonary arteries carry deoxygenated mixed venous blood from right ventricle to alveoli of lungs
Pulmonary veins return oxygenated blood to left atrium
where do bronchial arteries originate from?
what do bronchial arteries supply?
Bronchial arteries branch from aorta and supply oxygenated blood to conducting airways
where is the majority of venous blood drained from the lungs?
what does this lead to?
Bronchial veins exist, but majority of blood drains into pulmonary veins via a shunt
This leads to Venous admixture, where venous blood is going into oxygenated blood
what are 2 ways that pulmonary arterioles differ from systemic arterioles?
1) Less smooth muscle in pulmonary arterioles
- This is because they deal with lower pressures
- This gives arterioles less control over the blood flow going through capillaries
2) There is less autonomic regulation in lung arterioles
- Lung arterioles expand and contract predominantly as a result of production of metabolic substances
- So in this case, it is about PO2 and PCO2 present in different areas
what happens if perfusion is greater than ventilation?
in disease
CO2 increases -> vasodilation of local airway -> airflow increases
O2 decreases -> vasoconstriction of local blood vessels -> blood Flow decreases
what happens if ventilation is greater than perfusion?
co2 decreases -> vasoconstriction of local airways -> airflow decreases
O2 increases -> vasodilation of local blood vessels -> blood flow increases
What are the hydrostatic and colloid osmotic pressure inside pulmonary capillaries and interstitial fluid?
What do these values result in the net pressure being?
Hydrostatic pressure inside pulmonary capillaries is +7mmHg
Hydrostatic pressure inside pulmonary interstitial fluid is -8mmHg
The colloid osmotic (aka oncotic) pressure inside pulmonary capillaries is +28mmHg
The colloid osmotic pressure inside pulmonary interstitial fluid is +14mmHg
These values result in the net pressure being +1 in favour of hydrostatic pressure, meaning some fluid is lost along the length of the pulmonary capillary and drained by the lymphatic system
How can pulmonary oedema be caused?
Pulmonary oedema can be caused by the presence of too much fluid in the interstitial spaces around alveoli
This can lead to fluid collecting in the alveolar walls and alveolar spaces of the lungs, which can affect alveolar capacity, and lead to shortness of breath and coughing
zone 1
1) Zone 1
* Apex of lung under specific conditions
- PA>PPA>PPV
- No blood flow during all portions of the cardiac cycle
- Blood flow doesn’t occur normally, only under conditions such as shock, haemorrhage or positive pressure being put through airways in medical treatments
(there is no blood flow to these alveoli, so does not happen in human under normal circumstances)
zone 2
2) Zone 2
- Apex to mid lung
- PPA>PA>PPV
- Intermittent blood flow only during the pulmonary artery pressure peaks
- Systolic Ppc > Palv (pressure in pulmonary capillary > pressure in alveoli)
- Diastolic Ppc < Palv
- this is because alveolar pressure is less than the pressure on the pulmonary artery. but it will always have a greater pressure than the pressure in the pulmonary vein.
zone 3
continuous blood flow through capillaries because the pressure in the capillaries will always be lower than the pressure in the pulmonary artery and vein.
3) Zone 3
- Mid to lower lung
- PPA>PPV>PA
- Continuous blood flow during entire cardiac output
- Ppc » Palv
- Get distension of pulmonary capillaries
zone 4
peak flow decreases because of the increase in expansion of alveoli at the base.
4) Zone 4
- Extreme base of lung
- PPA>PPV>PA
- Constriction of extra-alveolar vessels
- Peak flow decreases
what is the:
- fraction of total lung volume
- Va/Q
- pO2
-pCO2
pH
- Q (L/min)
for the APEX
what is the:
- fraction of total lung volume
- Va/Q
- pO2
-pCO2
pH
- Q (L/min)
for the BASE
what is the:
- fraction of total lung volume
- Va/Q
- pO2
-pCO2
pH
- Q (L/min)
OVERALL
effects of V/Q mismatch in different regions?
what are the 4 different types of V/Q mismatch?
