Cardio VIII

Question 1

Describe the 6 steps of excitation-contraction coupling when action potentials reach heart cells.

Answer 1

1. Plasma membrane gets depolarized by action potential
2. L-type calcium channels embedded in the T-tubule open in the plasma membrane
3. Calcium flows into the cytosol and binds to ryanodine receptors, which are calcium channels, on the surface of the sarcoplasmic reticulum
4. More calcium flows into the cytosol
5. Calcium binds to troponin on myofilaments
6. Contraction of actin and myosin - contraction of heart cell

Question 2

What is the relationship between action potential and calcium concentration?

Answer 2

The calcium concentration will spike when the action potential spike occurs.

Question 3

What is the timing of heart cell excitation vs contraction?

Answer 3

Mechanical activity lags behind electrical activity.

Question 4

What is electro-mechanical dissociation?

Answer 4

It is when there is electrical activity in the heart but no pulse. Activation is not the same as contraction.

Question 5

Blood pressure refers to […]

Answer 5

systemic arterial blood pressure

Question 6

Describe and draw the evolution of the left ventricular pressure and the aortic pressure over the course of a heartbeat. Label the ejection phase.

Answer 6

During the diastolic period, the left ventricular pressure is low (below aortic pressure and left atrial pressure) and rising. It then rises very suddenly during systole, peaks, and then drops down again. The ejection phase takes place when left ventricular pressure is higher than aortic pressure.

Question 7

When and why does the aortic valve open and close?

Answer 7

The aortic valve opens when the pressure of the left ventricle is higher than the pressure in the aorta. The aortic valve closes after the left ventricle pressure peaks and once it has returned below the aortic pressure.

Question 8

Draw and describe the evolution of the systemic pressure over the course of a heartbeat.

Answer 8

It will start at a diastolic pressure of 80 mm Hg and then shoot up to systolic pressure of 120 mm Hg. It will then fall down.

Question 9

What is the minimum blood pressure?

Answer 9

It is equal to the diastolic blood pressure. 80 mm Hg

Question 10

What is the maximum blood pressure?

Answer 10

It is equal to the systolic pressure. 120 mm Hg

Question 11

What is the pulse pressure?

Answer 11

It is the difference between the systolic (maximum) pressure and the diastolic (minimum) pressure. 40 mm Hg (120 - 80)

Question 12

What is mean blood pressure? How is it calculated?

Answer 12

Usually assumed to be equal to 100 mm Hg
MAP = diastolic pressure + 1/3(pulse pressure)

Question 13

The aortic pressure remains […] because of the […]

Answer 13

high because of the windkessel effect

Question 14

What is the function of the windkessel effect?

Answer 14

To maintain a high aortic pressure throughout the cardiac cycle (unlike ventricular pressure!) and provide consistent perfusion to the organs.

Question 15

Explain how the windkessel effect works, including a comparison of systole vs diastole and the relevant equations.

Answer 15

During systole, when the ventricle is contracting, the aorta will stretch to accomodate the blood and store energy like a stretched rubbber band.

During diastole, when the aortic valve is closed and the ventricular pressure is low, this stored energy in the aorta will be ejected, as the pressure upstream in the arteries will be lower than the pressure downstream and arteries have a low compliance. The pressure buildup is so high because arteries have low compliance, so a large volume of blood in the aorta means that a lot of pressure must build up, as C = dV/dP.

Question 16

Name the major methods and categories of blood pressure measurement.

Answer 16

Direct or indirect
Indirect: palpation, ascultation, oscillometry

Question 17

What is the direct method of measuring blood pressure?

Answer 17

Puncturing an artery (recall Stephen Hales)

Question 18

Measurement of blood pressure via palpation is done using the […]

Answer 18

aneroid sphygmomanometer

Question 19

Describe the setup of the aneroid sphygmomanometer and how it is used.

Answer 19

It consists of a cuff that you wrap around the patient’s arm, a valve, an inflating bulb, and an aneroid gauge. When you close the valve, you pump air into the cuff through the bulb, which sucks in air. Once the pressure in the cuff is high enough, you turn the valve slightly and the air will leak out of the cuff because the pressure in the cuff is higher than atmospheric.

Question 20

What is the difference between a mercury sphygmomanometer and an aneroid sphygmomanometer?

Answer 20

The MS gauge was filled with a liquid, mercury, while the AS gauge has no liquid in it.

Question 21

Explain how the aneroid gauge works and what blood pressure measurement method it belongs to.

Answer 21

Method: palpation (aneroid phygmomanometer)
Inside the gauge, there is a vacuum chamber with 0 pressure. So as you pump, the air pressure inside the gauge increases. This pushes down on the vacuum chamber, and this will move a lever connected to a spindle that moves the pointer on the display.

Question 22

Where on the body does the palpation method take place?

Answer 22

The cuff is wrapped around the upper arm, but the pulse used is from the radial artery.

Question 23

Describe how and at what point a reading is obtained via the method of palpation. What type of reading can you get?

Answer 23

After the cuff has been pumped, the pressure in the cuff drops gradually. While the pressure is higher in the cuff than in the artery, you won’t feel a radial pulse. Once the cuff pressure is low enough that the arterial pressure pulses are higher than that, you will feel a pulse, and it is at this point that you take the reading.
You can only get a reading of the systolic blood pressure, not the diastolic blood pressure, by this method.

Question 24

The method of ascultation is done using a […]

Answer 24

stethescope

Question 25

What is the procedure used to measure the blood pressure by ascultation?

Answer 25

You pump up a cuff (just like in palpation) and then use a stethescope on the arm to listen for korotkoff sounds.

Question 26

Korotkoff sounds come from […]

Answer 26

blood pressure (NOT the heart itself)

Question 27

WIthout using a cuff, when might you hear Korotkoff sounds? Why?

Answer 27

Never. Without constriction from the cuff, the blood flow is laminar (smooth). It is only when you use the cuff that you can get turbulent blood flow, which will create the sounds.

Question 28

Using the auscultation method, when do you hear Korotkoff sounds and why? What measurements can you get from this method?

Answer 28

You hear Korotkoff sounds between when the cuff is first lower pressure than the arterial pressure purlses and when the cuff pressure is lower than the arterial pressure at all points of the cardiac cycle. The point where the Korotkoff sounds start is when the systolic pressure is measured, and the point where they stop is when the diastolic pressure is measured.

Question 29

Measurement of blood pressure via the oscillometric method is done using a […]

Answer 29

machine with a pressure detector

Question 30

Explain how the oscillometric method of measuring blood pressure works and what measurements it takes.

Answer 30

This method uses oscillations in the cuff pressure to determine blood pressure (it does not use Korotkoff sounds, but they can be heard). The machine looks at the slope of the lines created by the cuff oscillations and uses the upward portion to calculate the systolic pressure and the downward portion to calculate the diastolic pressure

Question 31

In which methods of blood pressure measurement do you hear Korotkoff sounds?

Answer 31

Ascultation and oscillometric

Question 32

What generates the blood pressure?

Answer 32

It comes from the fact that once every heartbeat, there’s a contraction of the ventricular muscle that kicks the blood pressure up, and from the Windkessel effect, which keeps the blood flowing through the aorta even when the ventricle is relaxed.

Question 33

Explain why arterial blood pressure is so important to the rest of the body.

Answer 33

The blood pressure is the pressure in the aorta or the large arteries. As you move down the tree, it falls. This blood pressure is therefore in control of the perfusion pressure that drives the circulation of blood throughout the entire vascular tree.

Question 34

What is the mathematical relationship between arterial blood pressure and flow?

Answer 34

Since flow = perfusion pressure/R and arterial pressure is responsible for perfusion pressure, flow can be expressed as follows:
Flow = MAP/R
Where MAP = mean arterial pressure

Question 35

What is total peripheral resistance?

Answer 35

It is the combined resistance of all the organs. This is the pressure that the left ventricle pressure has to work against.

Question 36

What is the formula for total peripheral resistance? Explain where this formula came from.

Answer 36

TPR = MAP/CO
Perfusion pressure is output - input pressure, which for the cardiovascular system is mean arterial pressure (left arterial pressure) - right arterial pressure. However, the pressure of the right atrium is low enough to be negligible.
The flow to the system is the cardiac output.
Therefore, TPR = MAP/CO

Question 37

Mean arterial blood pressure depends on what factors? Explain why (mathematically).

Answer 37

It depends on 3 factors: heart rate, stroke volume, and total peripheral resistance
Recall that cardiac output = stroke volume x heart rate.
MAP = CO x TPR
MAP = HR x SV x TPR

Question 38

What is the value of pulmonary perfusion pressure? How is this calculated?

Answer 38

Pulmonary perfusion pressure = 10 mm Hg

Mean pulmonary artery pressure = 15 mm Hg
Pulmonary vein pressure = 5 mm Hg
15 - 5 = 10 mm Hg

Note that here, the perfusion pressure cannot be approximated using the arterial pressure as it can in the systemic circulation because there is a much smaller difference between the two values in the pulmonary circulation.

Question 39

How does the pulmonary vascular resistance compare to the systemic resistance? Explain why.

Answer 39

The flow of blood to the lungs is the same as the flow to the system (same CO for left and right heart). The lungs use a lower pressure to manage way more flow (10 mm Hg perfusion pressure vs 100 mm Hg for systemic) - the pulmonary resistance is therefore 10 x smaller than the resistance of the other organs in the body.