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Flashcards in test 2 Deck (114):

what is slow conduction in the heart mainly caused by

diminished numbers of gap junctions along pathway resulting in an increase in the resistance to conduction


what is the threshold for the SA node

-40 mV


what is the parasympathetic system mostly distributed to in the heart

SA and AV nodes


what is the sympathetic system mostly innervation in the heart

distributed to all parts of the heart, but mainly the ventricles


what is depolarization represented by in an ECG

P and QRS waves:
P=atrial depolarization
QRS= ventricular depolarization


what is depolarization represented by in ECG

T wave (ventricular repolarization)


what does an ECG measure

extracellular potential


what are the normal time durations for the P-Q (P-R) interval and the Q-T interval

P-Q = 0.16 sec
Q-T: 0.35 sec


what does the limb lead 1 connect

neg terminal end connected to right arm
positive term end is connected to left arm
*looks at the heart from left to right


what does the limb lead 2 connect

neg term is connected to right arm
pos term connected to left leg
*looks at heart from upper right to lower left


what does the limb lead 2 connect

neg term connected to left arm
positive term connected to left leg
*looks at heart from upper left to lower left


what is eithoven's law

if the electrical potentials of any 2 of the 3 bipolar limb ECG leads are known at any given instant, the 3rd can be determined by summing the first 2


how does current typically flow in the ventricles (ECG)

negative to positive primarily in the direction from the base of the heart toward the apex for most of the heart cycle until the very end


define vector

arrow that points in the direction of the electrical potential generated by the current flow, with the arrowhead in the positive direction


what is the direct of the lead for lead 1-3

1: 0
2: 60


what is the degree for the QRS vector in relation to the zero reference point

+59 degrees


where does atrial depolarization begin

Sinus node


what is the first part to become depolarized in the atrial T-wave

sinus node area


what are the main leads used for ECG

3 conventional bipolar limb leads
six standard leads (V1-V6)
Three augmented leads (aVR, aVL, aVF)


what are some abnormal ventricular conditions that cause axis deviation

change in position of heart in the chest
hypertrophy of one ventricle
bundle branch block
fluid in pericardium
pulmonary emphysema


what is the most common cause of increased voltage in the standard bipolar leads

hypertrophy of the ventricle


what is decreased voltage of the QRS complex typically caused by

cardiac myopathies
conditions around the heart


what are abnormalities that cause current of injury

mechanical trauma
infectious processes
ischemia (most common cause)


what is the effect of current of injury on QRS complex

abnormal negative current flows from infarcted area and spreads toward the rest of the ventricles


what is the J point

reference point for analyzing current of injury


define tachycardia

fast heart rate (>100 beats/min)


what are the causes of tachycardia

increased body temperature
stimulation of the heart by sympathetic nerves
toxic conditions of the heart


what occurs during endogenously mediated tachycardia (i.e. exercise)

heart rate increases, cardiac output increases, filling time is reduced by SV does not fall


what occurs during pathologically mediated tachycardia

heart rate increases
cardiac output decreases
occurs because atrial pressure decreases and activates the sympathetic nervous system, which occurs after the fact and is unable to compensate


define bradycardia

slow heart rate (


what are the causes of bradycardia

athletic heart
vagal stimulate
extremely sensitive carotid baroreceptors in carotid sinus syndrome


what does spillover signals do (respiratory type of sinus arrhythmia)

alternately increase and decrease number of impulses transmitted through sympathetic and vagus nerves to the heart


what are characteristics of sinoatrial block

sudden cessation of P waves
resultant standstill of atria
ventricles pick up a new rhythm, usually originating in the AV node
Rate of QRS is slowed but not otherwise altered


what conditions cause atrioventricular block

ischemia of AV node or AV bundle fibers through coronary insufficiency
compression of AV bundle by scar tissue or calcified portions of the heart
inflammation of the AV node or bundle
Extreme stimulation of the heart by the vagus nerves


when does a first degree incomplete atrioventricular block occur

when the P-R interval increases to greater than 0.20 sec, the P-R interval is prolonged


when does a 2nd degree incomplete atrioventricular block occur

P-R time interval increases to 0.25 to 0.45 sec
atria P wave is present by QRS-T wave may be missing, resulting in dropped beats of the ventricle,
2:1 rhythm or other variations may develop


what usually occurs as a result from a complete atrioventricular block

person will faint due to lack of blood to the brain until the ventricles escape
typically these fainting spells are referred to as Stokes-Adams syndrome


define partial intraventricular block

referred to as electrical alternans
refers to an alternation in the amplitude of P waves, QRS complexes, or T waves


what do most premature contraction result from

ectopic foci: local ischemic areas, calcified plaques, irritation of the conduction system or nodes


what occurs during paroxysmal tachycardia

heart becomes rapid in paroxysms:
paroxysm begins suddenly and lasts for a few seconds, minutes or longer
paroxysm ends suddenly
pacemaker of the heart instantly shifts back to the sinus node


define fibrillation

twitching (usually slow) of individual muscle fibers in the atria or ventricles and also in recently denervated skeletal muscle fibers
occurs as a result of circus movements


what are 3 different conditions that cause circus movement

pathway around the circle is too long'
length of the pathway remains constant but the velocity of the conduction slows down
refractory period of the muscle might become greatly shortened


what causes the length of the pathway to remain normal. but the conduction velocity of the impulse to slow down (circus movement)

because of blockage of the purkinje system, ischemia or high potassium levels


what causes the refractory period of the muscle to shorten (circus movement)

may occur in response to drugs such as epinephrine
may occur after repetitive electrical stimulation


how are the atrial muscle fibers separated from the ventricular muscle fibers

cardiac fibrous skeleton


what are causes of atrial fibrillation

enlargement of atria
inadequate emptying of the ventricles causing blood to back up into the atria


what are the values for arterial pressure

120 mm Hg (systolic)
80 mm Hg (diastolic)


what is the arterial pressure at the vena cava

0 mm Hg


what is the systolic pulmonary artery pressure value

25 mm Hg


what is the pulmonary diastolic pressure value

8 mm Hg


what are the functional parts of circulation

arteries (transport under high pressure)
arterioles (control conduits)
capillaries (exchange between blood and extra cell fluid)
venules (collect blood from the capillaries and gradually coalesce into progressively larger veins)
veins (function as conduits for transport of blood from the venules back to the heart & serve as a major reservoir of extra blood )


what is the distribution of blood (percentages)

84% in systemic circulation (64% in veins, 13% in arteries, 7% in systemic arterioles and capillaries)
16% in heart and lungs


what is the equation for velocity of blood flow

V=F/A (F=volume of blood flow)


what are the 3 functional principles of the circulatory system

*rate of blood flow to each tissue of the body is almost always precisely controlled in relation to the tissue need
*cardiac output is controlled mainly by the sum of all the local tissue flows
*arterial pressure regulation is generally independent of either local blood flow control or cardiac output control


what monitors tissue needs in each tissue



what happens if arterial pressure falls below 100 mm Hg, nervous reflexes:

*increase force of heart pumping
*constrict large venous reservoirs
*generally constrict most of the arterioles throughout the body (increases arterial pressure)
*kidneys may later play important role in pressure control


define pressure gradient

pressure difference between the 2 ends of a vessel


define resistance

impediment to blood flow through the vessels


define poiseuille equation

F= (P1-P2)/R


what are the typical units for blood flow

ml/min or liters/min


what are characteristics of laminar blood flow

* streamline flow
*blood flows at a steady rate
*blood vessel is long and smooth
*blood flows in streamlines (layers)
*each layer maintains same distance from vessel wall
*central-most portion of the blood stays in the center
*each layer slips easily past surrounding layers
*velocity of fluid flowing in center is greater than that of fluid flowing towards the outer edges


what are characteristics of turbulent flow

*nonlayered flow
creases murmurs
produces more resistance than laminar flow
occurs when: flow is too great, blood passes an obstruction within the vessel, blood has to make a sharp turn, blood passes over a rough surface
*blood flows with greater resistance when eddy currents flow


when does the tendency for turbulent flow increases

*in direct proportion to velocity of blood flow
*in direct proportion to the diameter of the vessel
*in direct proportion to the density of the blood
*inversely to the viscosity of the blood


what is laminar flow directly proportional and inversely proportional with

*directly: mean velocity of blood flow in cm/sec, vessel diameter in cm, density
*indirectly: viscosity (in poise)


define blood pressure

force exerted by the blood against any unit area of the vessel wall


how is pressure measured

with a mercury manometer or with electronic transducers


what is the impediment to blood flow in a vessel



how is resistance calculated

it must be indirectly calculated from measurements of blood flow and pressure


what are the 3 main variables that determine resistance

vessel radius
blood viscosity
vessel length


what is resistance proportional to and inversely proportional to

proportional: blood viscosity and vessel length
inversely: radius (radius of blood vessel is to the fourth power)


what is the lowest arterial pressure



what is the rate of blood flow through the entire circulatory system

=cardiac output


what is the pressure difference from systemic arteries to systemic veins

100 mmHg


resistance of entire systemic circulation

100/100=1 PRU


what is the mean pulmonary arterial pressure

avg 16 mm Hg


Mean left arterial pressure

avg 2 mm Hg


what is the total pulmonary vascular resistance when cardiac output is normal at 100 ml/sec

14/100=0.14 PRU


define conductance

measure of blood flow through a vessel for a given pressure difference (usually expressed in ml/sec per ml Hg


how are arterioles, capillaries, venues, and veins arranged?

in series


what are some circulations arranged in parallel

brain, kidney, muscle, GI, skin, coronary circulation


what can occur if there is amputation of a limb or kidney that removes a parallel circuit

*reduces total vascular conductance
*reduces total blood flow
* increases total peripheral vascular resistance


what is viscosity

measure of the fluid's internal resistance


how does the viscosity of normal blood compare to that of water

viscosity of normal blood is about 3X as great as that of water


what occurs to viscosity in anemia and polycythemia

anemia: decreases viscosity
polycythemia: increases viscosity


define vascular distensibility

increase in volume/ (increase in pressure X original volume)


are arteries or veins more distensible



define vascular compliance

increase in volume/increase in pressure


what does vascular compliance tell us

tells us the total quantity of blood that can be stored in a given portion of the circulation for each mm Hg rise in pressure


how is capacitance related to elastance

inversely proportional


what happens to the elastance as the amount of elastic tissue increases in a blood vessel

elastance increases
compliance decreases


define compliance

measure of the ease with which a hollow viscus may be distended: volume change resulting from the application of a unit pressure differential between the inside and outside of the viscus


define vascular compliance

total quantity of blood that can be stored in a given portion of the circulatory system


define elastance

measure of the tendency of a hollow viscus to recoil toward its original dimensions upon removal of a distending or collapsing force


what are the 2 major factors that effect pulse pressure

stroke volume output of the heart
compliance of the arterial tree


what is the most important determinant of pulse pressure

stroke volume output of the heart


what happens to the diastolic pressure during ventricular systole

it remains unchanged


what happens during aortic valve stenosis

diameter of the aortic valve opening is reduced significantly, and the aortic pressure pulse is decreased significantly
blood flow through the aortic valve is diminished


what happens during patent ductus arteriosus

half or more of the cardiac output flows back into the pulmonary artery and lung blood vessels
diastolic pressure falls very low before next heartbeat


what happens during aortic regurgitation

the aortic valve is absent or will not close properly
aortic pressure may fall all the way to zero between heartbeats


what is the progressive reductio of the pulsations in the periphery

damping of the pressure pulses


what is the calculation for mean arterial pressure

diastolic pressure + (1/3) pulse pressure


what are factors that regulate right atrial pressure

ability of the heart to pump blood out of the right atrium/ventricle
tendency of blood to flow into the right atrium


what are factors that increase venous return

increased blood volume
increased peripheral venous pressures due to increased large vessel tone
dilation of arterioles


describe arterioles

small arteries that control blood flow to each tissue
local conditions in tissues control diameter of arterioles
arterioles are highly muscular


describe capillaries

smooth muscle fiber encircles capillary at point where it originates from a met arteriole (referred to as pre capillary sphincter)


what do slit pores do

located in capillaries
allow for rapid diffusion of water, water-soluble ions, and small solutes


what do plasmalemmal vesicles do

formed from cave-ins
play a role in endocytosis and transcytosis


what is the most important factor regulating vasomotion

concentration of oxygen in the tissues


what type of substances can diffuse readily through the capillary cell membranes

lipid soluble substances such as oxygen and CO2


why is the passage of substances through the interstitial mostly via diffusion rather than flow

because of the large number of proteoglycan filaments found in the interstitial
rivulets that allow fluid flow through the interstitial do sometimes form


what are the outward starling forces

capillary pressure and interstitial fluid colloid pressure


what are the inward starling forces

interstitial fluid pressure and capillary plasma colloid osmotic pressure


what are some factors that increase lymph flow

elevated capillary hydrostatic pressure
decreased plasma colloid osmotic pressure
increased interstitial fluid colloid pressure
increased permeability of capillaries


what is the equation for determining rate of lymph flow

interstitial fluid pressure and activity of lymphatic pump