Chap 21 Flashcards
How many ml/min do coronary arteries supply to the myocardium?
200-250 ml/min
% of blood supply the left coronary artery delivers to the myocardium?
85%
Connections between arterioles that provide backup circulation on the myocardium
Anastomoses
% of volume needed in the right ventricle to make the right atrium contract?
70%
% of blood pumped under stress
300-400%
Phases of the cardiac cycle
Phase 1: ventricular filling (middle of late diastole)
Phase 2: ventricular systole (atria relaxes & the ventricles begin contracting)
Phase 3: isovolumetric relaxation (early diastole)
Isovolumetric contraction phase
0.02-0.03 seconds, the moment the ventricles are completely closed chambers & blood volume in the chambers remain constant
Stroke volume
Amount of blood ejected from the heawith each ventricular contraction
Preload
Volume of the blood returning to the heart
After load
Resistance against which the heart muscle must pump
The pressure within the aorta before ventricular contraction
Myocardial contractibility
The performance of the cardiac muscle
End diastolic volume
Volume of blood returning to each ventricle (normally 120-130ml)
End systolic volume
50-60 ml as the ventricles empty during systole
Average adult stroke volume (amount of blood ejected during each cardiac cycle)
About 70ml
Ml’s the end systolic volume is reduced to during the strong contraction of a healthy heart via exercise
10-30 ml
Healthy heart, volume of end diastolic volume if large amount of blood flow into the ventricles during diastole?
As much as 200-250 ml
Starling law
Myocardial fibers contract more forcefully when they are stretched
Cardiac output
Amount of blood pumped by the ventricles in 1 minute
Stroke volume x heart rate
Ways vagus nerve may be stimulated
Valsalva maneuver
Carotid sinus massage
Pain
Distention of the urinary bladder
Beats/min heart rate is decreased with strong parasympathetic stimulation
20 or 30 beats/min
(Has little effect on stroke volume)
How is stroke volume affected by a decreased heart rate?
Increased,
because the longer interval between heartbeats allows the heart to fill with a larger amount of blood and thus contract more forcefully (startling law)
Epi’s effect on cardiac muscle & body
Increases the rate and force of contraction.
Causes blood vessels to constrict in the skin, kidneys, GI tract, & other visceral organs.
Causes dilation of skeletal & coronary blood vessels.
Takes longer to act on heart than does direct sympathetic innervation, but effects last longer
Norepinephrine’s effect on the body
Causes constriction of peripheral blood vessels in most areas of the body & stimulates cardiac muscle
Specialized cells of the electrical conduction system
Responsible for the formation & conduction of electrical current
Working myocardial cells
Have the property of contractility & perform the actual pumping of blood
What do separated particles with opposing charges have that is similar to the force of attraction similar to that of an electrical magnet?
Potential energy
How is the electrical charge (potential difference) expressed?
Millivolts (1mV equals 0.001 volt)
When is electrical charge’s potential energy released?
When the cell membrane appearing the ions becomes permeable
Resting membrane potential
The electrical charge difference when the cell is in its resting state
Synonym of POTENTIAL used in the electrical sense?
Voltage
How is the membrane potential recorded?
From the inside of the cell
(-70 to -90 mV)
What is the resting membrane potential a result from?
The balance between 2 opposing forces
Reentry & what causes it?
The reactivation of myocardial tissue for the second or subsequent time by the same impulse
The progression of an electrical impulse is delayed or blocked (or both) in one or more segments of the electrical conduction system of the heart
P wave
Represents Atrial depolarization
Duration: 0.10 seconds or less
Amplitude: 0.5 to 2.5 mm
PR interval
The time required for an electrical impulse to be conducted through the atria & the AV node up to the instant of ventricular depolarization
Duration: 0.12-0.20 seconds (3 to 5 small squares(
A normal PR interval indicates that the electrical impulse has been conducted from the atria through the AV node normally
QRS complex
Represents ventricular depolarization
Rapidly transmitted through the bundle of his
Duration: 0.08-0.10 seconds (2-2.5 small squares)
Amplitude: less than 5 mm - no more than 15 mm
What does it mean when a QRS complex is 0.11 seconds?
Indicates a partial or incomplete bundle branch block (IBBB) where there is an intraventricular conduction delay.
Although abnormal, it’s not always pathologic.
Can be seen in healthy people or as a normal variation between beats.
Can also be seen in:
- Congenital heart disease (especially atrial septal defects)
- myocarditis
- pulmonary emboli
- right ventricular hypertrophy
- induced syndrome following cardiac surgery
