Laboratory for Physiology ECG Cardiovascular System and Exercise

Before, during and after exercise Introduction a. Today we will look at how the cardiovascular system responds to accommodate the increased metabolic demands of the skeletal muscles during exercise b. To do this you will record your subjects: ECG Blood Pressure Skin temperature Before, during and after exercise

Introduction Exercise for this lab is going to be a step test where the subject will step up and down at a rate of about 22-23 steps/minute for 9 minutes This is a quick pace and should cause a good cardiovascular response in most people Every 3 minutes you will record your subjects ECG, Skin Temp and systolic BP. Overall you should have 7 measurements when you are done: Parameters at rest After 3 minutes of exercise After 6 minutes of exercise After 9 minutes of exercise Immediately Post-excercise Recovery period: 2 mins post exercise Recovery period: 5 mins post exercise

Potential problems Sweating causes electrodes to come loose Solution: Tape the ECG electrodes in place with water proof tape and fan to keep cool Noise in the recording due to movement during the exercise stage Solution: Try to minimize movement of the cables by taping them in place on the carts. Taking the subjects BP during exercise 2 Ways: Feel pulse. Blow up the cuff until you can’t feel the pulse any longer. This is approx SBP. Inflate cuff and gradually release pressure and watch for the pot that the needle starts to beat. Record this as SBP Whichever method you chose you should PRACTICE each BEFORE you start the lab exercise.

Expected Results When a person exercises the normal homeostatic mechanisms’ that serve to maintain BP are over-ridden by the brain so that the demands of the exercising tissues can be met When a person starts exercising inputs to the CVCC from the higher brain cause INCREASED Sympathetic activity DECREASED Parasympathetic activity

Which has FOUR effects on the cardiovascular system INCREASED HR INCREASED Stroke Volume (SV) and Cardiac Output (CO) of the heart Re Distribution of Blood flow and Vasoconstriction of the arterioles is caused by the increased Sympathetic activity HEAT

INCREASED HR HR is controlled by the pace maker cells in the SA node These cells receive both sympathetic and parasympathetic inputs Para SLOWS HR Symp SPEEDS up HR At rest Para tends to dominate generating a resting HR of ~70-80 bpm As you exercise the CVCC under the influence of higher brain centers adjusts the balance between Symp and Parasympathetic such that there is a decrease in Parasympathetic and an increase in Sympathetic activity PARASYMPATHETIC HR SYMPATHETIC

INCREASED Stroke Volume (SV) SV is the volume of blood ejected by the LV contraction SV depends to a large degree on the force of contraction of the heart Force of contraction = SV Heart musculature receives input from the Sympathetic nervous system which acts to adjust the force of contraction (contractility) of the heart muscle Increased Sympathetic inputs during exercise induce an INCREASE in the force of contraction which in turn INCREASES stroke volume Sympathetic Activity = Force of contraction = SV

INCREASED Cardiac output (CO) The volume of blood pumped/unit time. CO is determined by the product of HR+SV and so can be calculated using the formula: CO=HR X SV During exercise HR + SV = CO ***This means that during exercise more blood is being delivered to the arterial system/unit time which is reflected as an increase in systolic BP During exercise CO is not distributed evenly to all the organs of the body. Rather it is directed to where it is needed most (i.e. the active muscles) This selective redistribution of blood during exercise is achieved by the COMBINED AFFECTS of 1. The INCREASED sympathetic activity 2. Release of local vasodilators (CO2, Lactic acid) in the exercising muscles. Redistributed bloodflow is the 3rd effect seen during exercise.

Re Distribution of Blood flow and Vasoconstriction of the arterioles is caused by the increased Sympathetic activity This decrease in blood flow to the skin yields a DECREASE in skin temperature The muscles are initially also vasoconstricted but as they exercise they release local vasodilators (CO2, Lactic Acid) leading to increased blood flow. Vasodilation of the vasculature that supply these muscles DECREASES resistance to blood flow in these vessels so blood is directed away from the vasoconstricted vessels in the skin and other parts of the body and rather directed towards the vasodilated vessels in the muscles where it is needed.

HEAT During sustained exercise heat builds up in the body THUS a decrease in blood flow to the skin causes the core body temperature to rise. This rise in BT is sensed by temperature sensors in the hypothalamus which activates a part of the sympathetic system called the SYMPATHETIC CHOLINERGIC VASODILATOR SYSTEM. The SCVS acts to selectively dilate the blood vessels in the skin This increased blood flow to the skin allows for increased heat loss across the skin During the early stages of exercise skin temp DECREASES due to DECREASED blood flow but during sustained exercise skin temperature INCREASES as the SCVS is activated and blood flow is re directed to the skin. During this lab you should watch for these changes in skin temp, HR and SBP.

HINTS: Tape the thermistor to the finger Tape electrodes to the chest Make sure temp is stable BEFORE starting to exercise This may take 5-10 minutes! Tape electrodes to the chest Clip cables to subjects clothing to minimize movement Tape cables to cart to minimize movement of cables during exercise BEFORE your subject starts exercising, test to make sure you are getting good readings on the Biopac and practice taking their SBP If subjects HR exceeds their calculated max HR they should slow their exercise rate but NOT STOP If the subject can’t complete the exercise then they may voluntarily stop but try to do your best to keep going.

Enjoy the lab HAVE FUN DO NOT RUSH!!!!! QUESTIONS? Enjoy the lab HAVE FUN DO NOT RUSH!!!!!