Lab 2 - Cardiac Cycle Flashcards
Explain the difference between electrical and mechanical events in the heart?
Electrical events = ECG (created by signals that control the timing of heartbeats for example the SA node, the AV node and the conduction pathway).
Mechanical events = the actual physical actions that pump blood due to pressure and flow changes (contraction/systole and relaxation/diastole).
(+ Vavular events = heart sounds)
What mechanical event occurs at the start of ventricular diastole?
Ventricular diastole = ventricular filling
AV valve opens allowing for ventricular filling to begin
What are the electrical and mechanical events that occur during ventricular diastole?
Electrical - phase of ventricular repolarisation (T wave on ECG) following systole to allow for the cardiac cells to reset to prepare for the next heart beat. After the T wave there is a prolonged period of no electrical activity as the heart relaxes.
Mechanical - Isovolumetiric ventricular relaxation then AV valve open allowing for passive ventricular filling and then in late diastole there is atrial contraction for the remaining 10% of CO to fill the ventricle to EDV.
What happens to atrial and ventricular pressure during ventricular diastole?
Atrial Pressure - as blood fills the atria pressure rises. Once pressure becomes greater than ventricular pressure the AV valve opens causing blood to flow from atria to ventricle and atrial pressure drops. In late diastole the atria depolarised and pressure increases during contraction.
Ventricular Pressure - when the semilunar valves close the ventricles relax without change volume so pressure drops a lot. Once AV valve opens ventricular pressure remains low as the ventricles fill passively with blood. Pressure rises slightly due to the extra blood during atria contraction. Overall ventricular pressure is low.
What mechanical event occurs at the start of ventricular systole (contraction)?
AV valves close so pressure increases in ventricles and cause the semilunar valves to open for ejection of blood.
Semilunar valves open - aortic valve and pulmonary valve - shunting blood from ventricles to either the lungs or to the body.
What are the electrical and mechanical events that occur during ventricular systole?
Electrical events = ventricular depolarisation = QRS complex
Mechanical = AV valves close increasing pressure and preventing back flow. Isovolumetric contraction for a brief moment increasing pressure and then causing the semilunar valves to open and blood ejected into arteries.
How does an increase in cardiac sympathetic nervous activity effect the electrical and mechanical events that occur during a cardiac cycle?
Electrical Events: It increases the heart rate by speeding up the firing rate of the SA node, reducing the time between action potentials. It also enhances conduction speed through the AV node.
Mechanical Events: It strengthens ventricular contraction (increased contractility), resulting in more forceful ejection of blood, and shortens the duration of systole. This leads to increased stroke volume and cardiac output.
How does an increase in cardiac sympathetic nervous activity affect the relative amount of time spent in diastole and in systole?
They both shorten but diastole (time for heart to relax and fill) is shortened to a greater extend than systole.
What is the thoracic cage?
Chest area from which each valve sound is best heard
How do you work out Heart period?
Heart period is the time taken for one complete cardiac cycle.
It is measured from R-wave to R-wave.
How do you work out duration of systolic period?
Systolic period is the time that the ventricles are contracting.
Measured from R-wave to the beginning of the second heart sound.
How do you work out duration of diastolic period?
Diastolic period is the time that the heart is relaxing.
It is calculated by heart period - systolic period or from the beginning of the second heart sound to the peak of the following R wave.
How do you work out duration of isovolumic contraction period (IVC)?
IVC is the time that the heart is contracting with all valves closed.
Measured from R wave to the beginning of the first carotid pulse wave.
How do you work out duration of ejection period ?
Ejection period id the time that blood is leaving the ventricles
Calculated by systolic period - IVC period or from the beginning of the first carotid pulse wave to the beginning of the second heart sound
How do you work out heart rate?
Heart rate is the number of beats per minute.
It is worked out by 60 divided by your heart period in SECONDS.
Which cells in the heart determine heart rate/period of cardiac cycle?
Pacemaker cells - SA node
How is the duration of the heart period affected by autonomic nervous input to the heart?
The rate of firing from the SA node is determined by the balance between the PSNS and SNS.
SNS increases the rate of firing therefore increasing HR whereas, PSNS decreases the rate of firing therefore decreases HR.
Which mechanical and or electrical events are used to measure the systolic and diastolic period?
Electrical:
Systolic = QRS complex
Diastolic = T wave
Mechanical:
Systolic - from closure of AV valves to the closure of the semilunar valves
Diastolic - from the closure of semilunar valves to the closure of AV valves (diastolic longer).
What is rpm?
revolutions per minute - used for bpm
What happens to D and S duration when heart rate increases during exercise and why?
Decrease in PSNS activity and an increase in SNS activity means that both D and S shorten but D shortens at a greater amount.
What three places does the SNS act on / innervate?
The SA node
The conduction System
The myocardium
What is pulsatile sound?
Pulsatile sound refers to a rhythmic sound that follows the pattern of a pulse or heartbeat. It is often characterized by a regular, rhythmic pulsation corresponding to the heartbeat.
What does an increase in sympathetic nervous system activity cause on the SA node?
Increased pace/firing of action potenitals therefore reduction in heart period (increased heart rate)
What does an increase in sympathetic nervous system activity cause on the conduction system?
increase in conduction velocity leading to better synchronised contraction
