Systolic and Diastolic heart pressure HELP!!

[jiny2]

Ok, I've been thinking about this question for awhile and no one was able to exlain in a way that I could understand. So the question is why does the diastole pressure go down when the elasticity of aorta decreses? Also, why does the diasotole pressure of left ventricle go down when the radius of aortic valve decreases? I understand that systolic pressure would go up because the decrease in radius of aorta means increase in R thus P goes up. I don't understand why would diastole pressure would go down. PLEASE HELP !!

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[TieuBachHo]

Edited: I think I misread the questions.

 

[Airplay355]

I think the answer to the first question could be that since there is a systemic pressure decrease during diastole (hence BP is given as systolic/diastolic) with an inelastic aorta that is unable to shrink when pressure is less and is instead held open, pressure might be even less in the aorta as a result of a larger radius.

Also pulled out of my ass. I'm going to ask my CV phys teacher on tuesday just because I want to know now.

 

[Airplay355]

Apparently I can't edit my post so here's what I think about the 2nd question.

Decreased aortic valve radius is a condition called aortic stenosis. This usually causes ventricular hypertrophy because the ventricle must now work harder during systole to pump blood out. This causes stiffening of the ventricular wall as hypertrophied myocardium is less compliant. This can lead to an INCREASE in pressure causing congestion from reduced ventricular volume. However, eventually the ventricle would increase in size (eccentric hypertrophy) as a result chronic dilation. Maybe the eccentric hypertrophy would cause the decrease in diastolic pressure since the ventricular volume increased?

 

[Jubal Early]

From Wikipedia http://en.wikipedia.org/wiki/Aorta

The aorta is an elastic artery, and as such is quite distensible. When the left ventricle contracts to force blood into the aorta, the aorta expands. This stretching gives the potential energy that will help maintain blood pressure during diastole, as during this time the aorta contracts passively.

 

[Airplay355]

I talked to my teacher today and after being a little confused at first he seemed to come up with a good explanation of why CHF will cause decreased pressure in the left ventricle.

I think this question has to do with the frank starling mechanism of the heart. Aortic stenosis is progressive so you're not going to just wake up one morning with stenosis. As the diameter of the aortic valve becomes smaller, pressure will increase behind the valve in the ventricle because the ventricle must now pump against an increased afterload. The ventricle will hypertrophy in order to compensate for the increase in afterload. Concentric hypertrophy will decrease the ventricular volume and lead to increased preload. This increase in preload will move this patient farther to the right on the frank starling curve causing stroke volume to decrease. When stroke volume begins to decrease, compensatory mechanisms like the RAA axis will begin attempting to raise the blood volume to compensate the decrease in stroke volume. This decreases the stroke volume even more so now we get the typical dz positive feedback mechanism.

The decreased stroke volume as a result of the length tension relationship of the ventricles ends up causing decreased ventricular pressure because the ventricles aren't able to contract as forcefully.

 

[sepia]

how does constriction of arterioles affect systolic and diastolic blood pressure

a. systole increase dias decrease
b. systole dec dias dec
c. systole dec diastole increases
d systole increases and diastole increases

 

[TRN1983]

how does constriction of arterioles affect systolic and diastolic blood pressure

a. systole increase dias decrease
b. systole dec dias dec
c. systole dec diastole increases
d systole increases and diastole increases

I can see how this can be confusing. You see in bernoulli's equation that if volume increases, pressure increase, etc, right? While that's true, that's for a different type of situation. That would explain where a SINGLE PIPE goes from large diameter to small diameter. That doesn't describe where the entire diameter of the whole pipe system decreases!

Constriction of all of the arterioles is like reducing the diameter of the entire pipe system. in addition, its effectively increasing the "restoring force" that the elastic arterioles have (F=-Kx; this increases the K value.) Consider P = F/A and think about the area decreasing and the K value increasing.

The pressure should increase uniformly for diastole and systole because during both events the area of the entire system is smaller and the restoring force of the arterioles has increased.

 

[sepia]

thanks for ur explanation

I can see how this can be confusing. You see in bernoulli's equation that if volume increases, pressure increase, etc, right? While that's true, that's for a different type of situation. That would explain where a SINGLE PIPE goes from large diameter to small diameter. That doesn't describe where the entire diameter of the whole pipe system decreases!

Constriction of all of the arterioles is like reducing the diameter of the entire pipe system. in addition, its effectively increasing the "restoring force" that the elastic arterioles have (F=-Kx; this increases the K value.) Consider P = F/A and think about the area decreasing and the K value increasing.

The pressure should increase uniformly for diastole and systole because during both events the area of the entire system is smaller and the restoring force of the arterioles has increased.