Cardio physiology

[Convalaria]

Hi everyone,

I'm reviewing heart physio and I got some questions, hope that someone will help me out:

1. Decreased compliance -> increased systolic pressure and decreased diastolic pressure.
I can't get why DP is gonna be decreased, as I remember DP depends on vascular resistance (TPR). Decreased compliance means vessels are less distensible and that will make them more resistant. If so, that means DP should have been increased.
Where did I go wrong?

2. Velocity and cross-sectional area relationship:
First, comparing aorta and network of numerous small capillaries we can make conclusions:
- cross-sectional area of aorta < cross-sectional area of whole bunch of capillaries, thus:
- velocity in aorta > velocity in capillary network.

Second, comparing aorta and one little-tiny blood vessel:
- cross-sectional area of aorta > cross-sectional area of one small blood vessel, thus:
- velocity in aorta < velocity in small blood vessel.
Am I right?

Thanks in advance!

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[HelpPleaseMD]

Hi everyone,

I'm reviewing heart physio and I got some questions, hope that someone will help me out:

1. Decreased compliance -> increased systolic pressure and decreased diastolic pressure.
I can't get why DP is gonna be decreased, as I remember DP depends on vascular resistance (TPR). Decreased compliance means vessels are less distensible and that will make them more resistant. If so, that means DP should have been increased.
Where did I go wrong?

2. Velocity and cross-sectional area relationship:
First, comparing aorta and network of numerous small capillaries we can make conclusions:
- cross-sectional area of aorta < cross-sectional area of whole bunch of capillaries, thus:
- velocity in aorta > velocity in capillary network.

Second, comparing aorta and one little-tiny blood vessel:
- cross-sectional area of aorta > cross-sectional area of one small blood vessel, thus:
- velocity in aorta < velocity in small blood vessel.
Am I right?

Thanks in advance!

i thought u took your test already ? 1. map = 1/3 systolic + 2/3 diastoilic. Basically when you exercise your blood vessels at the muscles vasodilate and that is enough to decrease the bp slightly.

as for question 2, I am pretty sure 99% that your second conclusion is false. The aorta would burst if the blood in the individual small vessels were faster than that in the aorta when the sum of the volume of the small blood vessels is greater than that of the aorta.

hope that helps

 

[Convalaria]

i thought u took your test already ? 1. map = 1/3 systolic + 2/3 diastoilic. Basically when you exercise your blood vessels at the muscles vasodilate and that is enough to decrease the bp slightly.

as for question 2, I am pretty sure 99% that your second conclusion is false. The aorta would burst if the blood in the individual small vessels were faster than that in the aorta when the sum of the volume of the small blood vessels is greater than that of the aorta.

hope that helps

not yet, next saturday, although I wish it was tomorrow 🙂

1. I agree with exercising muscles. But I meant blood pressure in aorta depending not on physical activity. Let's say: patient is 60smth yo and as we know aorta becomes less compliant with age due to atherosclerosis and all that stuff. So his pulse pressure increases because decreased compliance causes increased systolic BP and decreased diastolic BP. And I can't understand why does decreased compliance decrease diastolic BP.

2. I made that conclusion from what I found in kaplan book:
V ~ 1/cross sectional area
V ~ 1/r squared

 

[usmlesuccess]

during diastole, the compliance of the vessels functions to "squeeze" the low pressure diastolic blood forward, kind of like a wave. When there is hardening of the arteries, there is no elasticity to promote this forward flow "squeezing" during diastole. Thus, diastolic pressure decrease.

 

[Charles_Carmichael]

1. Decreased compliance -> increased systolic pressure and decreased diastolic pressure.
I can't get why DP is gonna be decreased, as I remember DP depends on vascular resistance (TPR). Decreased compliance means vessels are less distensible and that will make them more resistant. If so, that means DP should have been increased.
Where did I go wrong?

During systole, when blood is pumped from the heart, the arteries expand (increase in diameter) due to their compliance and essentially "store" blood. Because arteries have low compliance (and thus, high elastance), during diastole, the recoil of the arteries (back to their original diameter) pushes that stored blood through the circulatory tree to give the diastolic pressure. When you decrease compliance of arteries, their capacity to "store" blood also decreases and thus, you see a drop in diastolic pressure.

2. Velocity and cross-sectional area relationship:
First, comparing aorta and network of numerous small capillaries we can make conclusions:
- cross-sectional area of aorta < cross-sectional area of whole bunch of capillaries, thus:
- velocity in aorta > velocity in capillary network.

Second, comparing aorta and one little-tiny blood vessel:
- cross-sectional area of aorta > cross-sectional area of one small blood vessel, thus:
- velocity in aorta < velocity in small blood vessel.
Am I right?

Think about it intuitively. Where does nutrient/gas exchange take place? In the capillaries. Do you want blood to be rushing through capillaries at a high velocity with barely enough time for exchange to occur? Or do you want the capillary blood to be running slow and thus, optimizing the time for gas/nutrient exchange?

The velocity in a single small blood vessel (such as a capillary) should be lower than the velocity of blood in the aorta. You have to take into account the
total cross-sectional area and not just cross-sectional area of an individual vessel.

Hope this helps.

 

[Convalaria]

thank you, guys!