LAB#7
what are two key difference between cardiac muscle and skeletal muscle?
1. cardiac muscle displays autorhythmicity: skeletal muscle does not 2. Cardiac muscle has a relatively long refractory period: Skeletal muscle has a relatively short refractory period
an abnormally long p-r interval indicates a condition called
1st degree heart block
What differences would you expect to see between a diseased heart with high peripheral resistance and the healthy heart of an athlete?
A diseased heart might display blocked valves, less-pliable arteries, and a thicker myocardium. In a healthy athlete, there is an increased return of blood to the heart, and the heart may increase in size, resulting in increased stroke volume and decreased heart rate.
Explain how a person could have a normal ECG at rest, but show evidence of myocardial ischemia during exercise. Do you think all people should have regular treadmill (stress) ECG tests or only certain people? Explain
At rest, the delivery of blood to the heart may be adequate for the needs of the myocardium despite the possibility that there maybe some occlusion affection coronary blood flow. After moderate exercise, the myocardial demand for oxygen is raised so that the myocardium may become ischemic as a result of the coronary occlusion. This myocardial ischemia may thus be revealed in the ECG taken during exercise primarily as an abnormally elevated or depressed S-T segment (ventricular repolarization) that was not present during the resting ECG. Variable answer, yet regular treadmill ECG tests are highly recommended in persons over 40 years of age, or sooner if heart disease runs in the family.
On initial examination, a patient was found to have a P-R interval of 0.24 sec. A year later, the patient had a resting pulse of about 40 per min. A year after that , the patient collapsed with a pulse of 20 per min and required the insertion of an artificial pacemaker. Explain what caused this sequence of events.
At the time of the initial examination a P-R interval of 0.224 seconds defines a firs-degree AV node block. A year later the AV conduction block progressed with the patient now in third-degree Av node block as demonstrated by the appearance of ectopic pacemakers in the ventricles, the very slow rate of beat , and the lack of response to demands of exercise. An artificial pacemaker may be installed to compensate for the complete conduction block
What would occur if the left side of the heart pumped faster than the right side?
Blood would soon empty form the heart, and stroke volume would fall greatly
What is the action of each of the following ions on heart rate? Calcium: Sodium: Potassium:
Calcium: induces irregular heart rate: increases strength of contraction Sodium: induces irregular heart rate: decreases strength and rate of contraction Potassium: initially causes heart rate to decrease and then causes heart rate to become irregular : weakens cardiac contractions
What electrical event in the heart does the Pwave represent?
Depolarization of Atria
What electrical event in the heart does the QRSwave represent?
Depolarization of ventricles
Describe the pathway of conduction from the atria to the ventricles and correlate this conduction w/ the ECG waves.
Depolarization spreads through the atria producing the P wave. After a delay at the at the AV node, the depolarization the spreads down the bundle of his to the purkinje fibers and the ventricular myocardium. This produces the QRS wave. Depolarization of the ventricles in the reverse direction produces the T wave. In third-degree, or complete AV node block the ventricles are not depolarized by impulses from the atria. The atria continue to beat according to the pace set by the SA node (supraventricular) while the ventricles beat according to the pace set by an ectopic pacemaker within the ventricles, responsible for the slower rate and the lack of response to the demands of exercise that raise the atrial pacing only
Describe the pressure changes that occur within the ventricles as each ECG wave is produced, and explain how these pressure changes are related to the ECG waves
During the Wave depolarization of the atria, pressure in the ventricles changes little. During the Qto R the septum is depolarizing and starting to contract with only slight changes in the ventricular pressure. The R to S interval completes depolarization of the lateral walls of the ventricles and produces the sharp rise in ventricular pressure. The S to T segment represents the peak depolarization and contraction resulting in maximum pressure developed by ventricular fibers. During the peak of the T wave the ventricle fibers are undergoing depolarization and beginning diastole. The pressure in the ventricles during the T wave falls sharply, returning to the near zero value.
provide a cause-and-effect explanation as two how the pulse rate relates to the ECG rate. How would the relationship change if pulse were measured by palpation of the carotid artery instead off by a pulse transducer in the finger?
Electrical excitation of the cardiac fibers (ECG tracing) results in their mechanical contraction (pulse). More rapid discharge of the SA node, more rapid conduction of impulses, and a faster rate of contraction all result in an increased cardiac rate with exercise. The reverse occurs while resting. Increased cardiac rates are mainly due to shortening of the ventricular diastole and only secondarily due to a shortening of the ventricular diastole and only secondarily due to shortening of ventricular systole
The electrical synapses between adjacent myocardial cells are called ?
Gab junctions
What happens to the beating of the atria and ventricles during third-degree AVnode block? Why does this occur?
In third-degree AV node block non of the impulses from the atria reach the ventricles. No longer subservient to the SA node rhythm, the ventricle fibers beat at a much slower rate (20-45 beats per min) and do not respond to any demands from the cardiovascular control center in the medulla oblongata. The atria however, are still responding to the medulla and will continue to beat at a normal pace (sinus rhythm).
What was the effect of increasing flow tube radius on flow rate and flow volume ?
Increasing flow tube radius had the effect of increasing flow rate and flow volume
Describe what is meant by "laminar flow" and "turbulent flow." Before you inflate the cuff, which term more closely describes the blood flow in the brachial artery? Explain.
Laminar or "layered" flow of blood through the arteries occurs when all parts of the fluid move smoothly in the same direction, parallel to the axis of the vessel. Blood in the central axial stream moves the fastest, and blood closer to the artery wall moves more slowly. By contrast, turbulent flow occurs when some parts of the fluid move in radial and circumferential direction, churning and mixing the blood, which may cause vibrations and sounds. Blood flow in the brachial artery before the cuff is inflated is mostly laminar, and so is smooth and silent
the ECG wave completed just before the end of ventricular diastole is the _______ wave
P
Suppose a person had paroxysmal atrial tachycardia, producing "palpitations." Describe this condition, and propose ways that the condition might be treated.
Paroxysmal atrial tachycardia is also known as supraventricular tachycardia in which an ectopic focus above the ventricles results in spontaneous rapid running of the heart (150-250 beats per min)that begins and ends abruptly. The ectopic focus extrasystoles often produce a subjective feeling in the chest called palpitations. This condition is often treated successfully with digitalis . Digitalis decreases the excitability of the AV node and thus maintains the ventricular rate within the normal range, despite the excitability that may be occurring in the atria
The ECG wave that occurs at the beginning of ventricular systole is _______ wave
QRS
Which ECG wave must occur before the ventricles can contract?
QRS
How might a regular program of aerobic exercise influence the resting blood pressure? Explain your answer
Regular aerobic exercise should lower the resting blood pressure. Exercise often results in a lowering of the resting cardiac rate and an increase in the resting stroke volume. Athletes ave a greater degree of inhibition of the SA node by the vagus nerve and an increased blood volume. Working together these factors increase in cardiac output , improve the delivery of oxygen to the tissues and result in a lowered blood pressure´
The pacemaker region of the heart is the
SA node
leads I,II, and III are collectively called the
Standard limb
Compare supraventricular tachycardia with ventricular tachycardia in terms of its nature, ECG pattern, and seriousness.
Supraventricular tachycardia is characterized by an abrupt rapid atrial beat that drives a rapid ventricular beat for short intervals for periods of time. The ECG is normal in appearance and the ventricles are able to pump blood during this brief condition. In ventricular tachycardia however, the ventricles are not paced by the atria but rather by excitable ectopic foci in the ventricles that cause the ECG to have widened and distorted QRS complexes that can mask normal P waves. Ventricular tachycardia is more serious because it can degenerate into ventricular fibrillation and because the ventricular pumping is very erratic
The ECG wave that occurs at the end of systole and at the beginning of diastole is the _____ wave
T
Which ECG wave must occur before the ventricles can relax?
T wave
an abnormally fast rate of beat is called ______ ; an abnormally slow rate is called _____
Tachycardia, bradycardia
What property makes the normal pacemaker region of the heart function as a pacemaker? Explain.
The SA node fibers serve as the pacemaker region of the heart because they open special ion channels and undergo spontaneous depolarization faster than any other fibers in the heart. Consequently, the SA node sets the pace, generating AP's that are rapidly conducted to other myocardial cells via intercalated discs (gap junctions). Although capable of spontaneous depolarization, other myocardial cells depolarize at a slower rate and thus normally follow the SA node rhythm. The depolarized cells of the atria respond first by contracting as a unit, followed shortly by the ventricles that similarly depolarize and contract. Furthermore, the SA node pace is influenced by autonomic neurotransmitters ACH (slows) and norepinephrine (speeds), and by epinephrine (speeds).
What is the difference between the effective refractory period and the relative refractory period?
The effective refractory period is the period of time between the beginning of the cardiac AP and the middle of phase 3. The relative refractory period is the period of time between the effective refractory period and phase 4.
Were the blood pressure measurements different when they were taken in the standard sitting position, reclining, and standing up? Explain what might have caused any differences observed.
The position of the arm directly affects the measurement of diastolic pressure partially due to the effect of gravity. When the arm is below the heart level the diastolic pressure measured by the cuff is raised. When the arm is positioned above the heart level, the diastolic pressure is lowered. This helps to explain why the cuff should be placed at the heart level on the arm of the subject during blood pressure measurements. The greatest drop in diastolic pressure should occur immediately upon standing. Theoretically, the greatest drop in diastolic pressure should be read when the subjects lying down or immediately upon standing with activation of the baroreceptors reflex response. However, there are many factors that can vary results from the expected--- such as anxiety, sympathetic drive, respiratory movements (laughter), and others .
How is the pulse pressure calculated, and how does it value relate to the pulse? Also, describe how the mean arterial pressure is calculated and explain its significance.
The pulse pressure is systolic minus diastolic pressure. As the blood pressure rises from diastolic to systolic values within an artery, the rise in hydrostatic pressure against the artery wall causes the artery to expand somewhat. This is the "pulse" you feel when you press your finger against the outside of an artery. In this way, the pulse pressure causes the pulse. The mean arterial is equal to the diastolic pressure plus one-third of the pulse pressure. The mean arterial pressure represents the combined systolic and diastolic pressure head that drives the blood from the arterial tree into the blood capillaries
Describe the cardiac cycle
The right side of the heart pumps blood to the lungs so that blood can take up oxygen.This blood is then returned to the heart, pumped by the left side of the heart to the rest of the body, and then returned the right side of the heart again.
Define Starling's Law
When the rate at which blood returns to the heart changes, the heart will adjust its output to match the change in flow
what could cause an increase in the peripheral resistance in blood vessel?
a clogged artery
The parasympathetic nervous system releases the neurotransmitter ____________
acetylcholine
stimulation equipment from the pump mechanic screen- flow tube between middle and right beakers
artery
Describe the regulatory mechanisms that produce an increase in cardiac rate during exercise. Explain how theses changes affect the ECG
at the beginning of the exercise, there is a decrease in the activity of the parasympathetic (vagus) innervation of the heart. This causes an increase in cardiac rate that is further raised during greater levels of exercise by increased sympathetic nerve (cardiac) activity. As a result of the faster rate the period of diastole is shortened sp that the time between T wave of one ECG tracing and the P wave of the next tracing is significantly reduced. At higher heart rates the increased conduction velocity shortens the period of systole as shown by a decrease in the QRS-T interval
Stimulation equipment from Pumps Mechanics screen - fluid in left beaker
blood coming from the lungs
stimulation equipment from the pump mechanic screen- fluid in right beaker
blood going to the rest of the body
The conducting tissue of the heart located in the interventricular septum is the
bundle of his
The arterial blood pressure is directly proportional to two factors : the_______ and the ______
cardiac output , total peripheral resistance
pacemaker cells
cells in the sinotrial node
isovolumetric contraction
contraction that occurs when the volume of blood in the ventricles remains constant
vagus nerves
cranial nerves that deliver parasympathetic input to the heart
the parasympathetic nervous system _______ heart rate.
decreases
digitalis
decreases heart rate: blocks conduction of atrial impulses to the ventricles
pilocarpine
decreases heart rate: mimics ACH
What electrical event in the heart does the Twave represent?
depolarization of ventricles
The last Korotkoff sound occurs when the cuff pressure equals the _______ pressure
diastolic
How do you think the arterial blood pressure, and mean arterial pressure would change during exercise? explain
during exercise the increase in heart rate and stroke volume (cardiac output) cases the systolic pressure more that it raises the diastolic pressure. However, both pressures can rise to as high as 200/100 mmHg. The pulse pressure (systolic minus diastolic) in this case would increase to 100 mmHg while the mean arterial pressure (1/3 puts pressure plus diastolic pressure) would rise accordingly. The exercise- induced vasodilation causes the diastolic pressure to rise the least.
What do the valves in the Pump Mechanics screen do?
ensure that blood is flowing in only one direction
How do a frog heart and a human heart differ in their responses to temperature? Why?
frogs are poikilothermic; humans are homeothermic
the sympathetic nervous system ______ heart rate.
increases
epinephrine
increases heart rate and strengthens contraction
Atropine
increases heart rate: inhibits ACH
If the viscosity of blood were to increase, what could you do to keep the flow rate "normal"?
increasing the radius or decreasing the tube length
The scientific terms for insufficient blood flow to the heart muscle is
ischemia
stimulation equipment from the pump mechanics screen- middle beaker
left side of the heart
The sympathetic nervous system releases the neurotransmitter ____________
norepinephrine
the specific nerve that, when stimulated , causes a decrease in the cardiac rate is the ________
parasympathetic
What happens in each of the five phases of cardiac muscle depolarization? Phase 0- phase 1- phase 2- phase 3- phase 4-
phase 0- rapid upswing in membrane potential; sodium ions enter cardiac cell Phase 1- membrane potentials falls slightly , then rebounds as potassium flow out of the cell decreases and calcium flows into the cell Phase 2- "the plateau phase"- when the membrane remains in a depolarized state ; potassium channels stay closed ; calcium channels stay open Phase 3- internal potential falls, significant amounts of potassium flow out of the cell, calcium flow into the cell decreases, membrane repolarizes until the resting potential is reached Phase 4- period of resting potential until the next depolarization
Which variable had the strongest effect on fluid flow?
radius
The scientific name of the device used to take a blood pressure reading is the
sphygmomanometer
The nerve that increases the rate of discharge of the SA node is a ______ nerve
sympathetic
When blood pressure measurements are taken, the first sound of Korotkoff occurs when the cuff pressure equals the _______ pressure
systolic
sinotrial node
the "pacemaker" of the heart: where the cardiac cells with the fastest contraction rates join together
cardiac output
the amount of blood each ventricle pumps per minute
stroke volume
the amount of blood pumped to the body per contraction per ventricle
ventricular ejection
the ejection of blood near the end of systole during which ventricular pressure rises and then begins to decline
When the heart is externally stimulated just after the start of the contraction cycle, why does this have no effect on heart rate?
the heart is in a refractory period
Temperature
the heart rate in the frog would increase with increased temperature and decrease with decreased temperature; however, the human heart is not affected by environmental temperatures unless the temperatures are extreme
autorhythmicity
the heart's ability to trigger its own contractions
explain why the SA node generates AP's at a frequency of approx. 100 beats per min even though avg. resting heart rate is 70 beats per min
the parasympathetic nervous system which slows down heart rate has slightly more influence on heart rate than the sympathetic nerves system, which speeds up heart rate
End Systolic Volume (ESV)
the volume of blood in the heart at the end of ventricular contraction
End Diastolic Volume (EDV)
the volume of blood in the heart at the end of ventricular relaxation
The sounds of Korotkoff are produced by
turbulent blood flow
stimulation equipment from the pump mechanic screen- flow tube between left and middle beakers
vein
systole
ventricular contraction
diastole
ventricular relaxation
How are the Korotkoff sounds produced? When do you hear the first Korotkoff sound? When do you hear the last Korotkoff sound? Explain why this is true of the first and last sounds.
vibrations heard through a stethoscope due to the turbulent flow of blood through a partially compressed brachial artery cause Korotkoff sounds. The narrowing of the lumen creates turbulent blood flow and the vibrations produced are characterized as Korotkoff sounds. The first Korotkoff sound is heard when the pressure in the sphygmomanometer cuff is lowered so that the brachial artery is only partially compressed (the cuff pressure is equal to the systolic pressure) thereby permitting the initial turbulent glow out of the distal portion of the cuff. The last Korotkoff sound is heard as the flow of blood throughout the cuff is no longer compressed by the cuff and laminar flow is restored (diastolic pressure) and no more sounds are detected
