Flashcards in Lecture 2 Deck (52):
What are the 3 types of cardiac muscle within the heart?
Atrial, ventricular, and specialized excitatory and conductive
What are some characteristics of cardiac muscle?
-found only in heart
-acts as a syncytium
-under nervous, endocrine, and other chemical control
What are characteristics of skeletal muscle?
-most skeletal fibers extend entire length of the muscle and striated
-not self stimulating
-have motor units
-under nervous system control
What are characteristics of smooth muscle?
-contraction is prolonged tonic contraction (may last hours or day)
-has slow cycling of the myosin cross bridges that cause prolonged contraction
-located in nurtures, blood vessels, intestines
-low energy requirement to sustain contraction
-maximum force of contraction is often great than in skeletal muscle
What are components of cardiac output?
heart rate x stroke volume
What is normal resting cardiac output?
What are the normal parameters for HR and SV to determine normal CO?
HR: 70 b/m
SV: 71 mL/b
What is normal HR at rest?
What does normal HR indicate?
-healthy myocardial cells
-healthy SA node
What is the significance of chronotropic effects?
they are mechanisms that alter cardiac rate
What are examples of positive chronotropic effect and effect on HR?
What are examples of negative chronotropic effect and effect on HR?
What are the effects of the sympathetic NS on cardiovascular system?
-vasodialtes coronary aa to increase blood flow to the heart
-increases myocardial contraction
What are the effects of the parasympathetic NS on cardiovascular system?
-vasoconstricts coronary aa
-depresses myocardial contraction
What effect does aerobic exercise have on HR?
-increase in HR with increase intensity due to a decrease in the vagus nerve inhibition and increase sympathetic nervous system stimulation
What happens to HR in a well trained athlete?
low resting HR may be due to enhanced parasympathetic input to the heart
What effect does β-blockers have on HR and why?
-have a blunted HR response during exercise
-β receptors on the myocardial wall are unable to respond to sympathetic stimulation which causes HR to increase
how should you monitor someone during exercise if they are on β-blockers?
Borg RPE scale
how is stroke volume regulated?
-preload (sometimes referred to as end diastolic volume)
What is EDV?
the max blood in the ventricles immediately prior to contraction
What equals what in a normal healthy heart?
what does EDV=SV mean?
That the volume of blood that enters the ventricles completely leaves with the contraction of the heart.
what is preload in a normal healthy heart?
the amount of stretch on the myocardial wall prior to contraction
What is the Frank-Starling Mechanism?
an intrinsic property of heart muscle to increase SV based on the pre contractile myocardial cell length
what happens in a non healthy heart in terms of preload/EDV?
the heart does not react to the stretch and the pt might have to take digitalis in order to increase the contraction of the heart
normally the force of the contraction _____ as the blood volume ______ in a healthy heart?
what happens in a diseased heart with force of contraction and what is the result?
-don't get increase force of contraction with diseased heart
- you get backup of blood either in lungs of RV
what is related to EDV in terms of contractibility?
the intrinsic control of contraction strength
what does extrinsic control of contraction depend on?
on the activity of the sypathooadrenal system
what produces a positive ionotropic effect?
Epinephrine from the adrenal and norepi from the sympathetic nerve ending which causes an increase in myocardial contractility which causes an increase in HR
what happens when there is a reduction of sympathetic stimulation?
reduces HR and reduces myocardial contractility
what is MVo2?
-myocardial oxygen consumption
-the amount of oxygen the myocardium is using
how is MVo2 calculated?
-by rate pressure product (RPP)
how is rate pressure produce (RPP) calculated?
HRx systolic BP=RPP
what will increase MVo2?
any increase in HR or BP will increase MVo2
Normal there is a linear relationship between MVo2 and what?
Coronary blood flow (CBF)
-not the case in diseased heart states
what does myocardial oxygen supply depend on?
-delivery of oxygenated blood through coronary aa
-the oxygen carrying capacity of arterial blood
-the ability of the myocardial cells to extract oxygen from the atrial blood
What are factors that influence a positive inotropic effect?
-increase sympathetic tone
-increase in endogenous catecholamine
What are factors that influence a negative inotropic effect?
-decrease function ventricular muscle mass
-decrease myocardial o2 supply demand
-circulating myocardial depressant factors
What is after load?
pressure against which the ventricle must work in order to eject blood=pressure resisting the ejection of blood during systole
If you have an increase in after load what is stroke volume?
what causes an increase in after load?
systemic HTN or aortic valve stenosis
If you have a decrease in after load what is stroke volume?
what causes a decrease in after load?
during aerobic exercise or vasodilators (beta-blocks)
What is ejection fraction? (EF)
% of ventricular filling that is ejected with each heart beat (EF=SV/EDV)
what is normal EF?
what is EF widely used as?
an index of contractility
what is end systolic volume (ESV)?
-the amount of blood that remains in the heart following contraction
- there must be a volume of blood that remains in the heart to maintain a certain degree of stretch within the muscle fibers of the myocardial cells
what can then EF be as low as in pt's with heart failure?
40% which is really low
What is ventricular compliance?
ease to which the ventricle descends when filled with blood?
what happens if you have decreased compliance?
-caused by ventricles stiffer (LV hypertrophy)
-a given volume of filling will result in higher end diastolic pressure