PHY3171 Lecture 1: CVS homeostasis
10 Feb 2019
School
Department
Course
Professor
1/03/18
CARDIOVASCULAR RESPONSE TO STRESS L1
CHALLENGES TO CARDIOVASCULAR HOMEOSTASIS
Changes in blood volume/central blood volume
Reduced
- Haemorrhage, head-up tilt, standing, crucifixion
- Lower body negative pressure
Increased
- Blood transfusion
- Head-out water immersion (compresses lower body, pushes blood up, ↑ venous return)
- Lower body positive pressure
Changes in energy/organ blood flow requirements
- Exercise: muscle requirement of oxygen, diving: conserve oxygen
- Pain → fight or flight response: less blood flow to unnecessary areas
Haemorrhage = Maintenance of adequate arterial pressure + perfusion of brain and heart in the face
of ↓ cardiac output
Blood Transfusion = The opposite challenge, as cardiac output ↑
Exercise = ↑ delivery of oxygen + nutrients (via increased blood flow) to exercising muscles
Diving = Conservation of oxygen by ↓ blood flow to non-essential organs
BASIC PRINCIPLES
Whole organism
– MAP = CO x TPR
– You can also have the opposite of TPR – total peripheral conductance
Local organ
– Organ blood flow = Arterial pressure x Organ vascular conductance
Cardiac output
– CO = HR x SV
– ↑ Contractility and ventricular end-diastolic volume
are different
↑ ventricular end-diastolic volume
• Frank-Starling Law
• As the heart fills more during diastole
• Cardiomyocytes get stretched
• Stretching brings more crossbridges interlined
• More actin is available to form crossbridges with
myosin heads
• Therefore, greater force of contraction
↑ contractility
• SV you get for any given level of cardiac filling
• Governed by activity of sympathetic nerves
PRESSURE CHANGES THROUGHOUT THE CIRCULATION
– In large arteries we have highly pulsatile pressure
o Goes up during systole and down during diastole
– As we move through circulation, pulsatility + mean pressure is gradually reduced
Document Summary
Head-out water immersion (compresses lower body, pushes blood up, venous return) Exercise: muscle requirement of oxygen, diving: conserve oxygen. Pain fight or flight response: less blood flow to unnecessary areas. Haemorrhage = maintenance of adequate arterial pressure + perfusion of brain and heart in the face of cardiac output. Blood transfusion = the opposite challenge, as cardiac output . Exercise = delivery of oxygen + nutrients (via increased blood flow) to exercising muscles. Diving = conservation of oxygen by blood flow to non-essential organs. You can also have the opposite of tpr total peripheral conductance. Organ blood flow = arterial pressure x organ vascular conductance. Contractility and ventricular end-diastolic volume are different. Ventricular end-diastolic volume: frank-starling law, as the heart fills more during diastole, cardiomyocytes get stretched, stretching brings more crossbridges interlined, more actin is available to form crossbridges with myosin heads, therefore, greater force of contraction.
