Lab 2

Question 1

What are four mechanical changes that occur during the cardiac cycle?

Answer 1

• ventricular pressure
• ventricular volume
• aortic flow/pressure changes
• valves opening and closing

Question 2

What can we see on an ECG?

Answer 2

P, QRA and T eaves which represent the electrical events of the heart

Question 3

What do the heart sounds show?

Answer 3

The turbulent flow of blood due to heart valves closing

Question 4

What do the carotid pulse waves show?

Answer 4

distension of the carotid artery during the cardiac cycle

Question 5

What is the heart period?

Answer 5

This is the time to complete one cardiac cycle

Question 6

How can we measure the heart period?

Answer 6

This is from the pet of one R wave to the peak of the next R wave

Question 7

What is the duration of the systolic pressure?

Answer 7

This is the time that the ventricles are contracting

Question 8

How can we measure the duration of the systolic pressure?

Answer 8

This is measured from the R-wave to the beginning of the second heart sound

Question 9

What is the duration of the diastolic pressure?

Answer 9

This is the rime that the heart is relaxing

Question 10

How can we calculate the duration of the diastolic pressure?

Answer 10

This is calculated by the heart period minus the systolic period

Question 11

What is the duration of the isovolumetric contraction?

Answer 11

This is the time that the heart is contracting with all the valves closed

Question 12

How can we measure the duration of the isovolumetric contraction?

Answer 12

This is measured from the R wave to the beginning of the first carotid pulse wave

Question 13

What is the ejection period?

Answer 13

This is the time that it takes for blood to leave the ventricles

Question 14

How can we measure the ejection period?

Answer 14

systolic period minus the IVC period

Question 15

How can we calculate the heart rate?

Answer 15

The time in seconds divided by the heart period

60/HP

Question 16

Which cells in the heart determine the heart rate/period of the cardiac cycle? Explain this

Answer 16

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

Question 17

How is the duration of the heart period affected by the autonomic nervous input to the heart?

Answer 17

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

Question 18

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.

Answer 18

4. They both shorten, however diastole is shortened to a greater extent than systole.

Question 19

Describe what happens to the duration of diastole and systole when heart rate increases during exercise

Answer 19

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

Question 20

Explain the mechanism(s) responsible for the changes in the duration of diastole and systole when heart rate increases during exercise

Answer 20

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

Question 21

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

Answer 21

1. All 3 are correct

Question 22

How many carotid pulse waves did we measure and what were these showing?

Answer 22

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

Question 23

What happens to the heart rate over a breathing cycle?

Answer 23

When you breathe in, there is an increase in HR and when you breathe out there’s a decrease in HR

Question 24

The fluctuations in heart rate are normal physiological events and are called what?

Answer 24

respiratory sinus arrhythmia

Question 25

What branch of the cardiac autonomic nervous system is most likely to be involved in these changes in heart rate over the breathing cycle?

Answer 25

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

Question 26

Describe the Respiratory Sinus Arrhythmia

Answer 26

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

Question 27

What is the equation for MABP?

Answer 27

DP + 1/3(SP-DP)

Question 28

What happens to get the diastolic reading on the blood pressure cuff?

Answer 28

This is the first occurrence of rhythmic sound as the blood begins to flow through the artery is the subject’s systolic blood pressure.

Question 29

What happens to get the diastolic reading on the blood pressure cuff?

Answer 29

Continue to listen as the blood pressure cuff pressure drops and the sounds fade

Question 30

Why does the pulsatile sound disappear when the pressure of the inflated cuff falls below diastolic pressure?

Answer 30

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

Question 31

What is atrial fibrillation?

Answer 31

This is irregular beating of the heart, which may become very fast

Question 32

How does an ECG of someone who has atrial fibrillation differ from that of a normal ECG?

Answer 32

There are no P waves because the atria is fibrillating and there are irregularly placed QRS and T waves

Question 33

How does atrial fibrillation cause a reduction in cardiac output?

Answer 33

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

Question 33

How does atrial fibrillation cause a reduction in cardiac output?

Answer 33

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

Question 34

Would atrial fibrillation have a larger effect on cardiac output that at rest? Explain?

Answer 34

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