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47 Cards in this Set

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4 important types of differences between pulmonary and systemic vessels:
1. Wall thickness
2. Compliance
3. Pressures
4. Blood volume
How does wall thickness compare between pulmonary and systemic vessels?
Pulmonary vessels are thinner
How does compliance compare between pulmonary and systemic vessels?
Pulmonary vessels are more compliant than systemic.
How do pressures compare between pulmonary and systemic vessels?
Pulmonary blood pressures are lower than systemic
How does blood volume compare between pulmonary and systemic vessels?
Only 10% of blood volume is in the pulmonary vasculature at any given time
Average pulsatile pressure of the pulmonary arteries:
What are the varying levels?
Avg = 15 mm Hg
Varies between 8-25 mm Hg
Where does the variability of pulmonary pressure end?
At pulmonary capillaries
What is the avg pressure in pulmonary veins?
7 mm Hg
How much can the volume devoted to pulmonary circulation increase during exercise?
From the normal 10% to as much as 15% of total blood volume.
How much can left atrial pressure fluctuate and pulmonary arterial pressure remain at about 15 mm Hg?
LAP can range from 1-10 mm Hg and pulmonary pressure will remain the same.
Why are the pulmonary vessels more compliant than systemic?
To accommodate the stroke volume output of the right ventricle.
How much blood enters the bronchial arteries to supply the lung structures?
1-2% of Cardiac output
Where does bronchial blood flow afeter giving nourishment to the lungs?
Into the pulmonary veins to empty back into the left atrium.
How does bronchial circulation affect flow in the heart?
Left ventricular output is 1-2% greater than right ventricular output.
What causes bp in the foot of a standing person to exceed the bp at the level of the heart by as much as 90 mm Hg?
Hydrostatic pressure - the weight of the blood itself in the systemic blood vessels.
How many centimeters are between the highest and lowest points of the lungs?
30
What is the pressure difference due to hydrostatic pressure in the top of lung vs bottom?
23 mm Hg difference
What is the pulmonary pressure of the lungs above the level of the heart, relative to the pressure at the level of heart?
15 mm Hg less
What is the pulmonary pressure of the lungs below the level of the heart, relative to the pressure at the level of heart?
8 mm Hg more
What is the result of there being a pulmonary artery pressure gradient within the lungs?
More blood flows to the lower lungs than the upper lungs.
What is the cause of the pressure gradient in the lungs?
Hydrostatic pressure
What are the "zones" of lung bloodflow?
Areas that have different degrees of blood pressure and flow
What 2 pressures act upon pulmonary capillaries?
1. Alveolar air pressure (compresses caps from outside)
2. Capillary blood pressure (distends caps from inside)
So what causes bloodflow to stop in pulmonary caps?
If alveolar pressure exceeds pulmonary capillary pressure.
What are the 3 zones of pulmonary bloodflow?
Zone 1 = no flow
Zone 2 = intermittent flow
Zone 3 = continuous flow
Why is there no flow in zone 1?
Because alveolar pressure always exceeds arterial pressure (highest parts of the lungs), so the caps are always shut.
Why is there intermittent flow in zone 2?
Because systolic pressure exceeds alveolar pressure and allows capillary flow; diastolic dips below alveolar pressure tho, so flow stops as caps shut.
Why is flow continuous in zone 3?
Because arterial pressure is always higher than alveolar.
How much of the lung is normally in zone 1?
Not much
2 components of pulmonary vascular resistance (PVR):
1. Alveolar resistance
2. Extraalveolar resistance
How does alveolar vessel resistance change as the lungs fill with volume?
It increases
How does extraalveolar vessel resistance change as the lungs fill with volume?
It decreases
What are alveolar vessels?
Capillaries
What are extraalveolar vessels?
Arterioles and Venules
So where is the lowest PVR?
At FRC
Where is highest PVR?
At RV due to extraalveolar vessel resistance
AND
At TLC due to alveolar vessel resistance
What happens to pulmonary bloodflow during exercise?
All of the lung becomes zone 3, but the top of the lung still has a relatively lower perfusion pressure and thus lower flow than the bottom of the lung.
Why is there a slight DECREASE in bloodflow at the bottom of the lung, despite the fact that pressure and flow are highest there?
Possibly due to a slight pos pleural pressure compressing the vasculature.
Is gravity the sole determinant of regional differences in lung perfusion?
No
What is the effect of alveolar hypoxia on pulmonary regional bloodflow?
As inspired PO2 decreases, PVR increases; this effect is exaggerated and occurs sooner at lower pH (increased acidity).
What occurs to maintain a long pulmonary transit time during conditions of increased flow?
The capillariew expand to increase lung volume, so each unit of blood wil remain in the lung for a longer period of time.
What factor accounts for differences in the rate at which various gases reach equilibrium between alveoli and capillaries?
The degree of binding of each gas to blood molecules.
What gas reaches equilibrum fastest/slowest?
-N2O
-O2
-CO
N2O - fastest b/c completely unbound in blood.
O2 - 2nd fastest b/c bound to hemoglobin
CO - slowest because binds Hb sooo very tightly
3 Factors that keep the lungs dry:
Balances of
1. Hydrostatic pressure
2. Oncotic pressure
3. Lymphatic pump
When does pulmonary edema occur?
When left atrial pressure reaches ~25 mm Hg
Why doesn't pulm edema occur until LAP reaches 25 mm Hg?
Because the pulm vasculature is highly compliant and allows that much increase in LAP before pulmonary pressure increases.
What other than hydrostatic pressure maintainance prevents pulmonary edema from occurring before LAP of 25 mm Hg?
Lymphatic pump is highly efficient to remove excess water - until LAP reaches 25 mm Hg.