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Dr. X
05-12-2007, 01:17 AM
since many of us use BRS phys and FA.. im running across some confusion which i would like to clear up. i consider phys my weakest.. :(

1) brs states (pg. 70):
cardiac output = (MAP - Right Atrial pressure)/TPR

FA states (formula section): MAP = CO/TPR

(i wonder who's gonna say.. most likely it won't show up on the exam)

2) pg. 71 of 4th edition brs phys:

Laminar flow vs. turbulent flow:

Increase in ******** number means turbulence (audible bruits) and it is seen in:

Decreased blood viscosity (decreased hematocrit, anemia)
Increased blood velocity (eg. narrowing of a vessel)

I agree with the above except for the "narrowing of a vessel" part.
let me jus post the formulas so its easy to work through it.

a) Q = MAP-RAP/TPR
b) R = 8nl/pie r^4
c) V = Q/A

with formula b, Narrowing of a vessel means decrease in radius would cause an increase the resistance. (inverse relationship) (side note: decreased resistance means decreased viscosity as in "decreased hematocrit and anemia")

with formula a, Increase in resistance would mean Decrease in Cardiac output (Q) (inverse relationship)

with formula c, decrease in cardiac output means decrease in velocity (direct proportional relationship)...

which conflicts with the bottom bold statement. so should it be "dilation of the vessel" or am i jus missing something in btw..

Dr. X
05-12-2007, 01:21 AM
i wrote r e y n o l d s number and it gave me the **********.

dskuri2001
06-27-2007, 08:10 PM
Could someone explain the concept of contractility?
By definition it states that it is the intrinsic ability of a heart muscle fiber to contract at a given fiber length. And that anything that can't be explained by the notion of preload is defined as contractility. I understand the concept of preload but what are the specific parameters that can't be explained by preload.

FedeUBA
01-13-2008, 10:32 AM
MAP=CO/TPR is wrong!!!!
the correct formula is: MAP=COXTPR

madeeha khan
01-16-2008, 11:07 PM
MAP=COXTPR
given in FA 2006 page 218

tehmina
04-29-2009, 10:00 PM
Map=coxtpr given in kaplan physio too!!!!!!!!!

Protoman2050
09-29-2009, 11:21 PM
Could someone explain the concept of contractility?
By definition it states that it is the intrinsic ability of a heart muscle fiber to contract at a given fiber length. And that anything that can't be explained by the notion of preload is defined as contractility. I understand the concept of preload but what are the specific parameters that can't be explained by preload.

There's only two things that a needed to understand cardiovascular physiology: preload and afterload. Preload is how far the myocyte is stretched by the incoming blood during diastole; the higher the preload, the higher the stroke volume, to a point. Afterload is the pressure produced by a myocyte in order to contract, the higher the afterload, the lower the stroke volume.

The five parameters affecting myocardial performance:

1. Preload
2. Afterload
3. Contractility
4. Conduction velocity
5. Heart rate

Cardiomyopathies generally cause problems with contractility. Pulmonary vasculopathies or right heart failure cause decreases in preload. Hypertension and aortic stenosis cause increases in afterload. AV and SA node disease cause decreases in conduction velocity. Lots of things can cause drops in heart rate. All of these will lead to a decreased cardiac output, if not compensated for.

Read this website: CV Physiology: Home Page (http://www.cvphysiology.com/)

And learn the Frank-Starling curve!

atropine
10-01-2009, 05:16 PM
1) brs states (pg. 70):
cardiac output = (MAP - Right Atrial pressure)/TPR

FA states (formula section): MAP = CO/TPR

This is the basic physics formula for flow (or in the case of the body, your cardiac output), which is delta P / TPR. Delta P in this case is the difference between the start and end of the circuit, or the aortic pressure and the right atrial presure (MAP-RAP).

Since RAP is normally close to 0, you can estimate by just saying cardiac output is MAP / TPR, instead of MAP-RAP / TPR.

atropine
10-01-2009, 05:21 PM
Could someone explain the concept of contractility?
By definition it states that it is the intrinsic ability of a heart muscle fiber to contract at a given fiber length. And that anything that can't be explained by the notion of preload is defined as contractility. I understand the concept of preload but what are the specific parameters that can't be explained by preload.
Make sure you know the Frank Starling curve. As you increase preload of the heart, stroke volume will also increase up to a certain point. That is the heart's intrinsic ability to pump higher volumes as it gets more blood returning to it. A higher contractility then refers to the heart being able to pump more blood at any one given preload. This is mainly due to higher amounts of intracellular calcium. Contractility will increase from activation of beta-1 adrenergic receptors on the heart. Preload will increase simply from higher blood volumes. The combination of the two with afterload is what finally determines stroke volume of the heart. I think someone above mentioned conduction velocity and heart rate as well, which are important under more extreme conditions.

Put another way, the preload:stroke volume association is due to better alignment of actin-myosin fibres as the heart stretches out. Contractility then refers to how forcefully the heart contracts for a given overlap of actin and myosin. This will be better as more calcium enters and allows more cross-bridge formations to occur.

statiastudent347
05-24-2010, 11:34 AM
flow = pressure gradiant / resistance
and then u can play around with that for the rest of the hemodynaics chapter but its all the same if u use simple allgebra







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