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Cardiovascular Responses to Acute
ExerciseCardiovascular response: heart rate anticipatory response; activity response; increased blood pressure; vasoconstriction; vasodilation
To meet the increased demands needed to perform exerciseTo meet such demands the following come into play:
Heart rate (HR)- beats per minutesStroke volume (SV) – Amount of blood pumped from the ventricles
in one beatCardiac output (Q) - The amount of blood that is pumped by the
heart per unit time, measured in litres per minute (l/min). Blood pressure (BP) - is the pressure exerted by circulating blood
upon the walls of blood vesselsBlood flow
The Goal of the CV system is
Typically RHR = 60-80 bpm (beats per minute)
Pre-exercise HR usually increases above normal resting values
This is an anticipatory rise and is not a reliable estimate of RHR - RHR must be taken sometime
before exercise
Increases in HR are due to the sympathetic nervous system (SNS) releasing adrenaline.
Once exercise has started the increase in carbon dioxide (CO) and lactic acid in the body is detected by the chemoreceptors; signals are then sent back to the SNS and more adrenaline
is released this further increases HRheart rate increases linearly from about 60 bpm
to a maximum of about 200 bpm
Resting Heart Rate (RHR)
HR increases until it reaches a plateau, when rate of work is held constant at sub-maximal
intensityOptimal HR for meeting the
circulatory demands at that rate of work
The lower the steady-state HR at each exercise intensity, the
greater the cardiorespiratory fitness
Steady-State HR
Highest HR value achieved in an all-out effort to the point of
exhaustionRemains constant from day to day
but decreases with ageApproximated by: HRmax= 220-age
or HRmax = 208- (0.7 x age)
Maximum HR (MHR)
SV is the amount of blood pumped from the ventricles in one beat (specifically the left one)SV is a major determinant of cardiorespiratory
endurance capacity at near-maximal and maximal exercise intensities
The fitter you are the greater your SV generally!Resting SV is normally around 70-90ml
(0.07 -0.09L)In general males have a bigger SV than females
SV values are determined by:
Volume of venous blood returned to the heart Ventricular dispensability
Ventricular contractilityAortic or pulmonary artery pressure
Stroke Volume (SV)
stroke volume rises during the initial stages of work and then levels off until near maximal
levels where it slightly declines due to decreased ventricular
filling time
in early exercise the increase is related to increases in both HR and SV. Later increases are due
to HR only assuming that SV levels out
Stroke Volume (SV)
• Trained individuals have a larger SV then untrained as you can see from the graph!
Stroke Volume Trained Vs Untrained
Increased venous return (preload) (the muscle pump and respiratory pump help with venous return during exercise):
extent to which ventricle fills with blood and stretches and subsequently contracts more forcefully: Frank-Starling mechanism
1. Blood is returned through the veins to the heart and enters the atria 2. Blood then moves from the atria
to the ventricles causing the myocardium (cardiac muscle) in the ventricles to stretch
3. The greater the venous return the more blood that enters the ventricles, the greater the myocardium is stretched. The further it is stretched the stronger and more forceful the contract will be
You can mimic preload by stretching an elastic band, the further the stretch the
elastic band the greater the distance it will travel when
you release it!!!
During exercise the muscle pump functions to return blood to the heart, or increase venous return; the muscles contract and squeeze the veins to push blood back up to the heart
the thoracic or respiratory pump serves the same function, i.e, as you breath in and out this compresses veins in the chest and abdomen to increase venous return to the heart
The Muscle thoracic Pump Helps Venous Return
SV values can also increase due to increased ventricular contractility from neural stimulation from the sympathetic nerve (from the Central Nervous
System CNS)SV values can increase also due to decreased total peripheral resistance in
the blood vessels due to vasodilation of blood vessels in exercising skeletal muscle
What causes SV to increase during exercise?
Cardiac Output (Q)
Q is the amount of blood pumped from the heart every minute (litres per minute) and is the product of: HR x SV As HR and SV increase therefore so does Q during exercise, to a maximum!Resting Q is about 5.0 L/min, but does vary with size of person .
There is a linear relationship between Q and exercise intensity up to 20-40 L/minWhen level of exercise exceeds 40% to 60% of maximal exercise capacity, SV either plateaus or increases at a much slower rate
Further increases in Q at this point are due to increases in HR
As you can see in a trained and untrained individual their SV starts to plateau at a HR of around 120bpm, but Q still increases this is due to increases in HR. However an Elite individuals SV capacity is greater than untrained individuals!
Changes in Q (Cardiac Output) and SV
Cardiac Output and Intensity• Here you can
see the linear relationship between exercise intensity and Q
• This individuals Qmax is around 24L/Min
HR and activity/exercise intensity have a linear relationship
SV changes are due to changes in venous return, ventricular contractility and peripheral resistance
Q and activity/exercise intensity have a linear relationship
Changes in HR, SV, and Q with Changes in Posture and Exercise
Cardiovascular Endurance Exercise: ◦ Systolic Blood Pressure (SBP) increases in direct proportion to increase in exercise intensity
◦ As exercise begins the baroreceptors found in the aortic and carotid arteries detect a decrease in blood pressure specifically SBP
◦ The central nervous system (CNS) responds by constricting (vasoconstriction – narrowing of the blood vessel lumen) blood vessels and increasing SBP and further increases HR
◦ Eventually the CNS detects that SBP needs to be reduced and is reduced via the vasodilation of the vessels. The CNS will continue to attempt to regulate BP throughout exercise until maximal
levels are reached
◦ Diastolic Blood Pressure (DBP) does not change significantly (may even decrease)
◦ Therefore little change in Mean Arterial Pressure (MAP) which is a product of both SBP and DBP
Resistance Exercise:◦ Can exaggerate BP as high as 480/350 bpm
◦ Some BP increases can be attributed to the Valsalva maneuver (performed by attempting to forcibly exhale while keeping the mouth and nose closed)
Blood Pressure
Blood Pressure Response to Exercise
Systolic- Maximum pressureDiastolic- Minimum pressure
Blood Pressure Response to Exercise Continued
McArdle et al., Exercise Physiology, Lippincott, 2001
Blood Pressure Responses
• As exercise intensity increases SBP in both arms and legs increases in a linear fashion
• Small or little changes in DAP
Acute changes in Q and BP during exercise allow for increased total blood flow to the body.
Blood flow patterns change in transition from rest to exercise – blood must be redistributed to other areas such as muscle this is often called a vascular shunt
Through Sympathetic Nervous System (SNS), blood is redirected to active areas during exercise
SNS activity cause the vasoconstriction (narrowing of vessels) and vasodilatation (widening of vessels) of blood vessels. Also pre capillary
sphincters open and close to allow for blood to either travel in or away from a certain area of the body.
This causes blood to be redirected to other areas of the body during exercise.
Blood Flow
SYSTEMIC BLOOD DISTRIBUTION VASCULAR SHUNT
blood is redistributed towards active skeletal muscle during exerciseand away from inactive organs
as body heat builds up some blood flow is shifted to the skin to help maintain internal temperatures within acceptable limits
VASOMOTOR CONTROLVASODILATION• dilation of arterioles and opening
of precapillary sphincters increases blood flow to active muscle
VASOCONSTRICTION• constriction of arterioles and
closure of precapillary sphincters reduces blood flow to inactive organs
Blood Flow Cont
Below is a diagram showing how pre capillary sphincters along with vasoconstriction and vasodilation help shunt the blood to active areas of the body.
Vascular Shunt
Relative to total blood volume
Absolute