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Physiology Workshop 2: Cardiovascular Physiology

BIOM20002, semester 2, 2024

Cardiovascular Workshop

Contents

In this workshop, you will learn more about the principles behind basic cardiovascular physiology, such as the maintenance of blood pressure and heart rate.

The following workshop activities will cover these learning objectives:

● Understand the function of, and mechanisms behind, the baroreflex. Predict the baroreceptor reflex response to a decrease in arterial blood pressure.

● Define and calculate cardiac output (CO), and describe the factors that affect CO.

● Define and understand cardiac cycle, systole and diastole, and be able to define end systolic volume (ESV), end diastolic volume (EDV), stroke volume (SV) and ejection fraction (EF).

● Define venous return (VR) and describe the factors that can alter venous return.

● Understand the relationship between myocardial fibre length, EDV, cardiac contractility, and SV. Describe how changes in EDV affect SV and CO (Frank-Starling law).

● Provide examples of chemical signalling molecules that alter HR, and the mechanism in which they act.  

● Define systolic arterial pressure and diastolic arterial pressure. Given systolic and diastolic arterial pressures, calculate pulse pressure and mean arterial pressure (MAP).

● Understand how MAP relates to cardiac output (CO) and total peripheral resistance (TPR).

● Define vasoconstriction and vasodilation. Understand the major local factors that affect total peripheral resistance (TPR).  

● Define myogenic autoregulation and explain its significance in the local regulation of blood flow

● Understand the role of the autonomic nervous system (sympathetic nerve activity (SNA) and parasympathetic nerve activity (PSNA) in the control of blood pressure, heart rate, heart contractility and cardiac output.

● Explain the equation that regulates blood flow to pressure gradient and resistance of the system. Understand how each variable is impacted as one variable changes.

● Understand how blood pressure is affected in various illnesses and situations.

Simulation 1: Baroreceptor Reflex Part I

Recommended readings:

· StatPearls: Physiology, Baroreceptors: https://www.ncbi.nlm.nih.gov/books/NBK538172/ 

· StatPearls: Physiology, Cardiovascular: https://www.ncbi.nlm.nih.gov/books/NBK493197/ 

· Autoregulation of organ blood flow: https://cvphysiology.com/blood-flow/bf004 

Click on the following link: https://justphysiology.com/Modules/view/750

· Add variables for Stroke volume, cardiac output, TPR, MAP and blood brain flow

1. State Ohm’s law and the physiological mean arterial pressure (MAP) equations. ( 2 marks)

2. Determine the baseline: (2 marks)

a) 10mins lying (not changing any other parameters)  

i. Calculate MAP from systolic blood pressure (SBP) and diastolic blood pressure (DBP) using the values below:

SBP = 120 mmHg

DBP = 80 mmHg

ii. Compare that to the ‘actual’ value using the values in the simulation                (1 mark)

iii. How similar are they? Always keep in mind that calculations are only estimations of the measured values.            (1 mark) 

3. Determine the ‘Normal’ response to standing: (5.5 marks)

a) Stand for 10mins (all other fields kept as default (do not change values)

i. Which parameters immediately change upon lying (within the first 2 minutes), and in what direction: increased/decreased? Input values in table below.

Table 1 : At the end of two minutes   

ii. Explain why these changes occurred during the change of positioning.            (5 marks)

4. Consider the immediate impact of standing on both sympathetic nerve activity (SNA) and total peripheral resistance (TPR).   

a) How would you predict the change in SNA to impact TPR? (1 mark) 

b) What actually happened to TPR in the first 5 minutes of standing? (1.5 marks). Please include in your answer any values that can help explain this answer.

c) Fill in the table below: (you may need to export table into a spreadsheet)            (8 marks) 

d) What is “Autoregulation”? Describe two forms of blood vessel autoregulation in systemic circulation. Be sure to include details about stimuli and response.  ( 3 marks)

e) Provide a possible explanation for the observation of changes in the TPR. ( 3 marks) (~100 words)

f) What might happen to TPR if there was no myogenic response upon standing? (Consider plotting TPR vs Brain Blood flow for your own understanding) (2 marks)

g) Would you see the same response in TPR if the person was passively tilted, rather than standing up actively? Why / why not? (2 mark)

h) We know that cardiac output (CO) is related to heart rate (HR) and stroke volume (SV), so why didn’t SV change in the same direction/shape as HR? (Consider plotting stoke volume (SV) vs HR to aid understanding)    (3 marks)

i) What happened to these measured parameters at 5 minutes of standing (e.g., increased / decreased further, returned to baseline, etc)? (2 marks)

j) What are the potential mechanisms that caused these changes? (3 mark)

k) What is the relationship between CO and HR? Why does an increase in HR lead to a decrease in CO? (Consider plotting SV vs HR)         ( 2 marks)

5. What would happen if the baroreflex is clamped? (Clamping is holding something steady/not allowing it to change)

Restart the simulation and set it for 10mins lying for baseline measurements. Then, turn the carotid clamp on at 95mmHg and set the simulation for 10mins lying.

a) What are the changes you noticed with just the clamp being on? (2 marks)

6. Then, with the carotid clamp on at 95mmHg, set the simulation for 20mins standing. Reference data points collected in your responses.

a)  How similar/different are these results compared to when the clamp was off?            (2 marks) 

b)  Explain the mechanism/s behind this similarity/difference? (1.5 marks)