Transcript Cardiovascular responses to acute exercise PPT

Cardiovascular
Responses to Acute
Exercise
Cardiovascular response: heart rate
anticipatory response; activity response;
increased blood pressure; vasoconstriction;
vasodilation
The Goal of the CV system
is
To meet the increased demands needed to perform exercise
To meet such demands the following come into play:
Heart rate (HR)- beats per minutes
Stroke volume (SV) – Amount of blood pumped from the ventricles
in one beat
Cardiac 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 vessels
Blood flow
Resting Heart Rate (RHR)
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 HR
heart rate increases linearly from about 60 bpm
to a maximum of about 200 bpm
Steady-State HR
HR increases until it reaches a
plateau, when rate of work is
held constant at sub-maximal
intensity
Optimal 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
Maximum HR (MHR)
Highest HR value achieved in an
all-out effort to the point of
exhaustion
Remains constant from day to day
but decreases with age
Approximated by: HRmax= 220-age
or HRmax = 208- (0.7 x age)
Stroke Volume (SV)
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 contractility
Aortic 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 Trained Vs Untrained
• Trained individuals have a larger SV then
untrained as you can see from the graph!
venous return
 Increased
(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.
3.
Blood is returned
through the veins to
the heart and enters
the atria
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
2. Blood then moves from the atria
to the ventricles causing the
myocardium (cardiac muscle) in
the ventricles to stretch
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!!!
The Muscle thoracic Pump Helps Venous Return
 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
What causes SV to increase during exercise?
 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
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/min
When 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
Changes in Q (Cardiac Output) and SV
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!
Cardiac Output and Intensity
• Here you can
see the linear
relationship
between
exercise
intensity and Q
• This individuals
Qmax is around
24L/Min
Changes in HR, SV, and Q with Changes in Posture and Exercise
SV changes are due
to changes in venous
return, ventricular
contractility and
peripheral resistance
HR and
activity/exercise
intensity have a linear
relationship
Q and
activity/exercise
intensity have a linear
relationship
Blood
Pressure
 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 Response to Exercise
Systolic- Maximum
pressure
DiastolicMinimum 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
Blood Flow
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 Cont
SYSTEMIC BLOOD DISTRIBUTION
VASCULAR SHUNT
blood is redistributed towards active skeletal muscle during exercise
and 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 CONTROL
VASODILATION
• 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
Vascular Shunt
Below is a diagram showing how pre capillary sphincters along with
vasoconstriction and vasodilation help shunt the blood to active areas of the
body.
Relative to total blood volume
Absolute