Exercise Physiology and Cardiac Output Flashcards
Cardiac Output (CO)
The volume of blood the heart pumps through the circulatory system in a minute. It is detrmibed by stroke volume and heart rate
Stroke Volume (SV)
The amount of blood expelled by the left ventricle of the heart in one contraction.
Mean Arterial Pressure (MAP)
An average arterial pressure which is influenced by the CO and the total peripheral vascular resistance.
Starling’s Law
The more the ventricles fill with blood, the more force the heart can generate for contraction. This expels more blood from the LV, so volume of blood entered the ventricle basicallly equal to blood that exits.
Cardiac Output (CO) Formula
CO = Stroke Volume (SV) x Heart Rate (HR).
Normal Cardiac Output at Rest
Approximately 5 litres of blood per minute.
Cardiac Output Calculation Example
Left ventricle: End Diaastolic V - End Systolic V = SV
75 bpm x 70 mL = 5250 mL/min.
(HR x SV)
What CO tells us?
A measure of heart performance. This info is needed because Cardiac Output changes
Sympathetic Nervous System
Increases ventricular contractility by adrenaline, pushing against srterial pressue (afterload)
Parasympathetic Nervous System
Decreases heart rate by acetylcholine.
Preload
The amount of blood in the ventricles before contraction. Increases dur to increased heart rate as a result of adrelanines action on the SAN.
How and why is the volume of the blood that can enter the ventricles limited?
By a transpaent memrane surrounding the heart that reduces friction of the hearts movement and prevents it enlarging and stretching too much.
If preload icreases, CO increases. Why?
If more blood enters ventricles, they contract more (starlings law), so more blood leaves the ventricles, increasing CO.
Afterload
The pressure the ventricles must overcome to eject blood.
Blood Flow Distribution at Rest
Digestive tract and liver receive ~27% of cardiac output, muscles 21%, and kidneys ~20%.
Blood Flow During Exercise
Muscles can receive as much as 85% of cardiac output.
Vasoconstriction
The tightening of smooth muscle cells around arterioles to restrict blood flow to certain organs during exercise. As a result they recieve near the same volume of blood as at rest, since SV and CO are increased during exercise.
Vasodilation
The widening of arterioles supplying blood to the skeletal muscle system so they receive greater blood volume than at rest.
How does vasoconstirction occur?
Arteriole walls change diameter as they are made of smooth muscle. Alo pre capilliary sphincters (at junction of capilliaries) can close, so oxyenated blood is directed into larger arterioles and not capilliaries (causing cold fingers).
Normal Heart Rate at Rest
Between 60 and 100 bpm.
Increased Heart Rate and Cardiac Output During Exercise
Can go up to 130-150 bpm because the body needs more oxygen. Stroke volume (volume of blood pumped out) also increases.
Average Blood Pressure
The mean arterial pressure (MAP) changes depending on activity.
MAP, Mean Arterial Pressure
Average pressure in arteries. Tells us how much blood the heart is pumping and how it may be changing.
Gives us the average blood pressure in the circulator system.
How to meaure MAP
Pressure gauge and stethoscope together
