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BRAVO
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physio-Afterload by definition :
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01.17.06 (2 years ago)
#1
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 Afterload by definition :
1)Is systolic myocardial wall tension
2)Is not the same as peripheral resistance
3)preload can determine after load
4)all of the above..
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vimoj
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01.17.06 (2 years ago)
#2
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is not the same as peripheral resistance??????
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trinity
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01.17.06 (2 years ago)
#3
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But then dont we talk abt reduced peripheral resistance when we use anti hypertensives, and that it reduces afterload????
why not 1?
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trinity
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01.17.06 (2 years ago)
#4
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even i'm confused!!! 
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vineetgsvm
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01.17.06 (2 years ago)
#5
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well astonishingly i wud go for option 4..
1 is abs correct
2. is also correct as tpr is one of the factor determining afterload
3.preload may determine the dilatation of the heart hence contribute to 1 by virtue of frank starling law... hence this option too is true
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draditithegreat
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Re: physio-Afterload by definition :
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01.17.06 (2 years ago)
#6
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| BRAVO wrote: |
Afterload by definition :
1)Is systolic myocardial wall tension
2)Is not the same as peripheral resistance
3)preload can determine after load
4)all of the above.. |
i think there is some problem wid option 2 it says Afterload by definition :)Is not the same as peripheral resistance
so how can this be true?
Afterload can be viewed as the "load" that the heart must eject blood against. In simple terms, the afterload is closely related to the aortic pressure. More precisely, afterload is related to ventricular wall stress (s ),
The pressure that the ventricle generates during systolic ejection is very close to aortic pressure, unless aortic stenosis is present. At a given pressure, wall stress and therefore afterload is increased by an increase in radius (ventricular dilation). A hypertrophied ventricle (thickened wall) reduces wall stress and afterload.
Afterload per se does not alter preload; however, preload changes secondarily to changes in afterload.
increasing afterload not only reduces stroke volume, but it also increases left ventricular end-diastolic pressure (LVEDP) (i.e., increases preload). This occurs because the increase in end-systolic volume is added to the venous return into the ventricle and this increases end-diastolic volume. This increase in preload activates the Frank-Starling mechanism to partially compensate for the reduction in stroke volume caused by the increase in afterload.
The interaction between afterload and preload is utilized in the treatment of heart failure, in which vasodilator drugs are used to augment stroke volume by decreasing afterload, and at the same time, reduce ventricular preload.
Afterload is increased when aortic pressure and systemic vascular resistance are increased, by aortic valve stenosis, and by ventricular dilation. When afterload increases, there is an increase in end-systolic volume and a decrease in stroke volume.
an increase in afterload shifts the Frank-Starling curve down and to the right. The basis for this is found in the force-velocity relationship for cardiac myocytes. Briefly, an increase in afterload decreases the velocity of fiber shortening. Because the period of time available for ejection is finite (~150-200 msec), a decrease in fiber shortening velocity reduces the rate of volume ejection so that more blood is left within the ventricle at the end of systole (increase end-systolic volume).
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trinity
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01.17.06 (2 years ago)
#7
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so what answer u suggest aditi?
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draditithegreat
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01.17.06 (2 years ago)
#8
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see this what i got:
as the question in particular the definition..
read following:
Significant differences exist among textbook definitions for the terms preload and afterload, leading to confusion and frustration among students and faculty alike. Many faculty also chose to use in their teaching simple terms such as "end-diastolic volume" or "aortic pressure" as common-usage approximations of preload and afterload, respectively, but these are only partial representations of these important concepts.
Straightforward definitions both of preload and afterload that are concise yet still comprehensive can be developed using the Law of LaPlace to describe the relationships among chamber pressure, chamber radius, and wall thickness.
Within this context, the term "preload" can be defined as all of the factors that contribute to passive ventricular wall stress (or tension) at the end of diastole, and the term "afterload" can be defined as all of the factors that contribute to total myocardial wall stress (or tension) during systolic ejection.
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trinity
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01.18.06 (2 years ago)
#9
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Well, so maybe vineet is right that way..if we say that afterload can be defined as ALL those factors which contribute to total myocardial tension during systolic ejection, right?
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dr4jc
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01.18.06 (2 years ago)
#10
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I think the answer should be 1.systolic myocardial tension...Afterload is the force required to contract under tension...It does refer to diastolic pressure...which is at the arteriolar level...preload is the passive tension prior to contraction and is very different frm afterload which is under tension.
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