Cardiac Output & Stroke Volume - Lecture Notes PDF

Lecture 12 What is the equation for cardiac output? - CO = HR x SV What is the resting cardiac output average? - 4.5 L/min for females - 5 L/min for males What happens to cardiac output when going from rest to exercise? - Increases - It increases to meet the oxygen demands - Blood...

Lecture 12 What is the equation for cardiac output? - CO = HR x SV What is the resting cardiac output average? - 4.5 L/min for females - 5 L/min for males What happens to cardiac output when going from rest to exercise? - Increases - It increases to meet the oxygen demands - Blood leaving the left ventricle - More delivery oxygenated blood from heart to the working skeletal muscle Why do we need cardiac output to increase during exercise? - When exercising we need more ATP, to get more ATP we need more oxygen, to get more oxygen we need to extract more oxygen from the blood coming by muscle cell, in order to get more oxygen to that muscle cell we need to deliver more, and that's where cardiac output comes into play - HR and SV must change during exercise, if it doesn’t then cardiac output doesn't change What happens to heart rate when going from rest to exercise? - Increases linearly with increasing exercise intensity - Needs to increase with intensity to meet the oxygen demand What is the average resting heart rate? - 60-70 bpm untrained What is the maximal heart rate? - 220 - age What causes the heart rate to increase? - Need to get more blood to the working skeletal muscle for more oxygen How does the heart rate increase? - The autonomic nervous system interacts with the SA node, releases ACh which is also released in synaptic cleft What happens to parasympathetic to increase heart rate? - The vagus nerve interacts with the SA node - The vagus nerve releases ACh which binds to muscarinic receptors in the heart to slow down heart rate - Causes the SA node to depolarize to resting heart rate - By slowing down this process it will increase heart rate What happens to sympathetic to increase heart rate? - Starts being used at 100 bpm - Driven by cardiac accelerator nerve that also interacts with SA node - By engaging sympathetic and cardiac accelerator to make heart rate higher than 100 bpm What is stroke volume?  - The amount of blood ejected from the heart in one contraction What happens to stroke volume when going from rest to exercise? - Increases What is systole? - The contraction phase of the cardiac cycle What is diastole? - The relaxation phase of the cardiac cycle What happens to stroke volume when exercising on an untrained person? - Peaks and plateau at 40% of VO2 max - Everything passed 40% is driven by heart rate and not stroke volume - The time has shrunk and the timing of systole and diastole go down. Diastole is reduced, the time to fill up the heart with blood decreases - The VO2 max can’t increase the amount of blood being ejected since the heart rate is too fast What is the average stroke volume at rest? - Males: 70 ml per beat - Females: 60 ml per beat What is the average stroke volume when exercising? - Males: 110 ml per beat - Females: 90 ml per beat What variables contribute to increasing the stroke volume with exercise? - Preload - Contractility - Afterload What is working against stroke volume? - Blood pressure (afterload) What is preload? - The amount of blood in the ventricle prior to contraction - Filling the chamber with more blood to get more out What is contractility? - The strength of the ventricular contraction - Greater force of myosin and actin - With the same amount of blood within the heart, contracting more will increase the amount produced What is afterload? - Aortic blood pressure - The amount of pressure in your systemic circulation that your heart has to pump against to get blood out - Working against the valve  - The blood vessels have a pressure head that has to be exceeded by our heart to get the blood to flow out of the heart and into vascular system How does exercise increase with preload? - Veno constriction - The SNS engages in the venous system that is holding the blood and causes the veins that are expanded and holding deoxygenated blood to constrict and get smaller to go up towards legs and back to heart - Skeletal muscle pump - Contracting skeletal muscle pushes blood upwards and towards the heart - Only go one direction - Respiratory pump - The diaphragm moving up and down causes a negative pressure in the thoracic cavity - The negative pressure is a suction that helps blood more upwards our heart What happens to ventricular contractility during exercise? - Increases - We want to fill the ventricular with more blood and use actin and myosin to increase the amount ejected - Want to stimulate the muscle for more contraction How does exercise increase contractility? - Sympathetic stimulation - When we engage that muscle with sympathetic activity, there is a greater amount of blood ejected - Circulating epinephrine What happens to afterload with exercise? - Decreases - The increase will decrease the amount of blood that can be ejected at any given time during exercise - It is working against that contractility and the preload How does afterload impact stroke volume? - It decreases What impact does duration of exercise have on cardiac output, stroke volume and heart rate? - Cardiac drift - Heart rate increases - Cardiac output stays the same - Stroke volume decreases - Plasma volume via sweat decreases If there is less plasma in the blood what will happen to our ability during exercise to load that ventricle with blood?  - It decreases since there isn’t has much blood - If stroke volume goes down then preload goes down - Heart rate is used for more blood to be pumped What impacts does endurance exercise training have on cardiac output? - It stays the same, they are able to exercise longer - A sedentary person and a trained person need to same amount of oxygen for the same amount of exercise How does heart rate and stroke volume influence these changes and lack of changes in cardiac output? - Heart rate decreases - Stroke volume doesn’t change How does chronic endurance exercise training increase stroke volume? - Increase in left ventricle chamber - Thicker wall with hypertrophy - Increase preload - The amount of blood that comes back into the heart increases, the skeletal pump creates a negative pressure that occurs while breathing - Increase contractility - Decrease afterload - Blood pressure will lower, isn’t working against such a big pressure head What impact does endurance training have on oxygen consumption (VO2)? ↑ VO2max = CO ↑ x a-vO2 differ (=) VO2rest = CO (=) x a-vO2 differ (=) VO2submax = CO (=) x a-vO2 differ Which of these variables contributes more to the increase in maximal oxygen consumption? - They are both equal - Occur simultaneously and equally Is the endocardium is comprised of cardiac muscle? - No What is the endocardium made up of? - Endothelial cells The thickness of the left ventricular wall is what then the right ventricular wall? - Greater than Which is not a characteristic of cardiac myocytes? - Multiple satellite cells What are the characteristics of cardiac myocytes? - Single nuclei - Fibers branching - Single fiber type Lecture 13 What is total peripheral resistance (TPR)? - Resistance - Forces that act on blood in the direction of the relative fluid flow velocity - The walls of the vessels is what causes the resistance What physiological variables affect total peripheral resistance? - Viscosity, thickness of fluid - Diameter or radius - Length of the tube, longer wall = greater resistance Which variable in the Hagen-Poiseuille equation is most affected by exercise? - Radius How is length, viscosity, and radius (TPR) of the blood vessel affected by exercise? - Length is not affected - Blood vessels don’t get longer - Viscosity is minimally affected - Sweating which causes less plasma and more RBC - Radius is affected the most - Blood vessels get bigger and smaller to accommodate more or less blood flow - Will dilate the working skeletal muscle and constrict the non working skeletal muscle (visceral) Which blood vessel type contributes the greatest amount to the regulation of TPR? - Arterioles - 70-80% of blood pressure is regulated within the arterioles What happens to TPR in the body during exercise? - Need to know the type of exercise to know if it increases or decreases - Dependent on the muscle mass activated and the intensity Why don’t we just calculate the mean blood pressure (MBP) as the sum of (SBP + DBP) /2? - The cardiac cycle isn’t split evenly - ⅓ of the time is the contraction phase - ⅔ of the time is the relaxation phase Why is it inappropriate to use the equation for mean arterial pressure (MAP) during exercise? - When we exercise the more the cardiac cycle decreases, mostly the resting phase - When exercising it is always changing and not always the ⅓ to ⅔ ration How is blood pressure regulated during rest? - Baroreceptors What is the average resting blood pressure? - 120/80 What are the two regulators for blood pressure? - Slow acting - Kidney through renin angiotensin system  - Fast acting - Baroreceptors What are baroreceptors and where are they located? - Detect pressure to keep it normal - Carotid arteries - Aortic arch How does blood pressure decrease when it is too high? - ↓ sympathetic, ↑ parasympathetic - ↓ heart rate, ↑ artery dilation How does blood pressure increase when it is too low? - ↑ Sympathetic, ↓ parasympathetic - ↑ Heart rate, ↓ artery dilation What happens to systolic, diastolic and mean arterial blood pressure with exercise? - Systolic - Increase - Diastolic - No change or slight decrease - Mean arterial blood pressure - Increase Why do baroreceptors not decrease blood pressure when exercising? - They reset to a higher limit - It will fight to maintain the blood pressure How does blood pressure change to DBP and SBP when using the equation? - ↑SBP = (↑)Q x TPR (=)or (↓small) ….CO? - (=)or(↓small) DBP = (=) Q x TPR (=) (↓small)...CO? How does blood pressure respond differently between arm exercise and leg exercise with similar workloads? - Takes the same amount of oxygen since it is the same workload - With arms, the body is dilating only ⅓ of the body and constricting ⅔ of the lower body - Higher blood pressure with arms - With legs, the body is dilating ½ of the body and constructing ½ of the lower body Where are baroreceptors located anatomically? - Carotid arteries and aortic arch What happens when baroreceptors are stretched as a result of increased blood pressure? - Increase parasympathetic nerve activity - Decrease sympathetic nerve activity - Reduce blood pressure True or false? During rest and exercise baroreceptors induced changes in blood pressure are primarily mediated by alterations in vascular conductance with only minimal contribution from cardiac output. - False