Lab 2 Flashcards
What are four mechanical changes that occur during the cardiac cycle?
- ventricular pressure
- ventricular volume
- aortic flow/pressure changes
- valves opening and closing
What can we see on an ECG?
P, QRA and T eaves which represent the electrical events of the heart
What do the heart sounds show?
The turbulent flow of blood due to heart valves closing
What do the carotid pulse waves show?
distension of the carotid artery during the cardiac cycle
What is the heart period?
This is the time to complete one cardiac cycle
How can we measure the heart period?
This is from the pet of one R wave to the peak of the next R wave
What is the duration of the systolic pressure?
This is the time that the ventricles are contracting
How can we measure the duration of the systolic pressure?
This is measured from the R-wave to the beginning of the second heart sound
What is the duration of the diastolic pressure?
This is the rime that the heart is relaxing
How can we calculate the duration of the diastolic pressure?
This is calculated by the heart period minus the systolic period
What is the duration of the isovolumetric contraction?
This is the time that the heart is contracting with all the valves closed
How can we measure the duration of the isovolumetric contraction?
This is measured from the R wave to the beginning of the first carotid pulse wave
What is the ejection period?
This is the time that it takes for blood to leave the ventricles
How can we measure the ejection period?
systolic period minus the IVC period
How can we calculate the heart rate?
The time in seconds divided by the heart period
60/HP
Which cells in the heart determine the heart rate/period of the cardiac cycle? Explain this
Pacemaker cells in the SA node. Each cardiac action potential (which begins the cardiac cycle) is spontaneously triggered by the SA node. The intervals between each trigger determines the duration of the heart period/cardiac cycle
How is the duration of the heart period affected by the autonomic nervous input to the heart?
The rate of firing from the SA node is determined by a balance between
- sympathetic nervous system: increase rate of firing, decreased heart period and increased heart rate
- parasympathetic nervous system: decrease rate of firing, increased heart period and decreased heart rate
Which statement is correct about the duration spent in systole
and diastole during EXERCISE:
1. Systole remains unchanged and only diastole shortens
2. Diastole remains unchanged and only systole shortens
3. They both shorten, however the same proportions of time are spent in systole (1/3) and diastole (2/3) as at rest
4. They both shorten, however diastole is shortened to a greater extent
than systole.
- They both shorten, however diastole is shortened to a greater extent than systole.
Describe what happens to the duration of diastole and systole when heart rate increases during exercise
Rest (HR=65, HP=927 ms)
Systole ≈ 300 ms
Diastole ≈ 627 ms
Systole 1/3 & Diastole 2/3
High Intensity (HR=166, HP=362 ms) Systole ≈197ms Diastole ≈ 165 ms Systole >1/2 & Diastole <1/2
Explain the mechanism(s) responsible for the changes in the duration of diastole and systole when heart rate increases during exercise
The autonomic nervous system input to the heart changes at the onset of exercise:
- there is a decrease in parasympathetic activity
- and an increase in sympathetic activity
The sympathetic nervous system innervates:
i) the SA node
ii) the conduction system
iii) the myocardium
During sympathetic stimulation of the heart:
i. The contractility of the ventricles increases
ii. The cardiomyocytes have a larger influx of calcium
iii. The calcium sensitivity of the myofilaments decreases
- All 3 are correct
How many carotid pulse waves did we measure and what were these showing?
There were 2:
- pulse wave 1: starts when the aortic valve is opening which shows the end of IVC and the start of the ejection
- pulse wave 2: starts when the aortic valve closes which shows the end of the ejection period/systole
What happens to the heart rate over a breathing cycle?
When you breathe in, there is an increase in HR and when you breathe out there’s a decrease in HR
The fluctuations in heart rate are normal physiological events and are called what?
respiratory sinus arrhythmia
What branch of the cardiac autonomic nervous system is most likely to be involved in these changes in heart rate over the breathing cycle?
This is primarily the parasympathetic NS
- PNS is active at rest so resting heart rate is less that the SA nodes intrinsic rate of firing without NS input
- there is withdrawal of the PNS
- there is the secondary impact from the sympathetic NS
Describe the Respiratory Sinus Arrhythmia
Lungs have stretch receptors which are stimulated upon inspiration and these may reflexive decrease PNS to the heart during inspiration so that the heart rate increases during expiration
What is the equation for MABP?
DP + 1/3(SP-DP)
What happens to get the diastolic reading on the blood pressure cuff?
This is the first occurrence of rhythmic sound as the blood begins to flow through the artery is the subject’s systolic blood pressure.
What happens to get the diastolic reading on the blood pressure cuff?
Continue to listen as the blood pressure cuff pressure drops and the sounds fade
Why does the pulsatile sound disappear when the pressure of the inflated cuff falls below diastolic pressure?
Because it goes from lamina blood flow (we cut off the circulation, then the first sound is blood first going through them) then it falls away when blood flow returns to normal
What is atrial fibrillation?
This is irregular beating of the heart, which may become very fast
How does an ECG of someone who has atrial fibrillation differ from that of a normal ECG?
There are no P waves because the atria is fibrillating and there are irregularly placed QRS and T waves
How does atrial fibrillation cause a reduction in cardiac output?
The SA node is not functioning properly and so the AV node has to act as the pacemaker and this is sometimes irregular so there is a decrease in HR. There is also no tipping up of the ventricle by the atria -> lower EDV and lower SV
How does atrial fibrillation cause a reduction in cardiac output?
The SA node is not functioning properly and so the AV node has to act as the pacemaker and this is sometimes irregular so there is a decrease in HR. There is also no tipping up of the ventricle by the atria -> lower EDV and lower SV
Would atrial fibrillation have a larger effect on cardiac output that at rest? Explain?
At rest: atrial contribution to filling is small and it is not very important to maintain the stroke volume.
During exercise: atrial “top-up” accounts for more EDV which is very important contribution to EDV and therefore SV. But someone with atrial fibrillation, there is no increase in HR or SV so there is no increase in CO
