BSCI450: CV Forces

what controls the heart

electrical activity

P wave

atrial depolarization

PR segment

AV node delay and conduction through bundle of His

QRS complex

ventricular depolarization

T wave

ventricular repolarization

what occurs during the flat phase between P and Q wave

atria can begin contraction

QT interval

heart contracts and blood leaves

where do all signals from atria converge

AV node

what is the only path from atria to ventricles

bundle of His

Ohm’s Law

V = IR

voltage = current(resistance)

fluid analog for Ohm’s law

P = FR

pressure = flow(resistance)

systemic organs

everything but lungs

right ventricle sends blood to

lungs

left ventricle sends blood to

systemic organs

stroke volume equation

Vstroke = EDV - ESV

end diastolic volume

blood in during filling

end systolic volume

blood left after ejection

diastole

relax

refill

systole

contract

squeeze blood out

stroke volume definition

how much blood flows from ventricle during cardiac cycle

cardiac cycle =

one heart beat

cardiac output is a ____ value

flow

volume per time

cardiac output =

stroke volume(heart rate)

mean arterial pressure/total peripheral resistance

what drives blood flow

pressure differences

rank blood vessel pressure high to low

aorta

arteries

arterioles

capillaries

venules

veins

venae cavae

what explains the large pressure drop when blood reaches arterioles

narrow = more resistance

what is the role of capillaries

site of nutrient, O2, CO2 exchange between blood and tissue

what does higher resistance entail for the heart

must contract harder to generate more pressure

blood wants more blood flow to certain tissues — how can this happen

constrict vessels to increase resistance

Poiseuilles law:

R = 8Ln/(pir^4)

R = resistance

L = length

n = viscosity

r = radius

what factors in poiseulle’s law are constant in the heart

length, viscosity

how can blood viscosity change

dehydration

coronary artery disease

cholesterol forms plaque in arteries → arterial lining damaged → plaque ruptures → platelets try to repair artery → clotting blocks artery causing heart attack

units of flow rate

L/sec

units of velocity of flow

m/sec

relate velocity, flow rate, cross-sectional area

Q = Av

compare velocity of flow for narrow vs wide vessel

narrow has higher velocity in single tube

benefit of low blood velocity

more time for diffusion between blood and tissues

why don’t capillaries (smallest vessel) have high velocity of flow

high total cross sectional area