integrated cardiovascular responses Flashcards
Integrated cardiovascular
responses
title
Mean arterial pressure is the controlled variable
Baroreceptors
Receptors detecting blood
pressure on beat to beat basis
in carotid artery
The medulla oblongata
primary cardiovascular control centre
Baroreceptors and MAP
Baroreceptor firing frequency changes with changes in blood pressure
Baroreceptors and MAP
A fall in blood pressure causes the carotid and
aortic baroreceptors to detect a hypotensive
stimulus leading to decreases in afferent
baroreceptor nerve firing.
This reduction in neural input to the brainstem
causes a decrease in parasympathetic nerve
activity to the heart and an increase in
sympathetic outflow to the heart and vasculature.
The converse occurs with increases in blood
pressure
Mean arterial pressure is the controlled variable
Mean systemic
arterial pressure
(MAP)
=
Cardiac output
(CO)
x
Total peripheral resistance
(TPR)
Regulation of blood pressure during exercise
title
Max and Submaximal exercise tests
Maximal oxygen uptake (V̇ O2max) test = assessment of aerobic
endurance or power
Submaximal exercise tests = used to assess physiological
responses to a standardised workload
In a clinical setting exercise tests are use to help diagnose
health problems
Steady-state exercise
“the level of exercise at which the physiological responses remain relatively stable for an extended period of time”
What determines if we can maintain steady-
state exercise?
Important factors governing steady-state exercise include:
The delivery of adequate oxygen to the exercising muscles,
The ability of the cells to utilise this oxygen in the aerobic process of
energy metabolism, and
The ability to eliminate heat.
During steady-state exercise the physiological responses of ventilation
(VE), oxygen consumption ( VO2), and cardiac output (Q) are similar in
the sense that they involve four phases.
Mechanisms for control of ventilation
The initial rapid rise in ventilation is explained by central
command (that is, the motor cortex signals the respiratory control
centre to increase ventilation).
Mechanoreceptors in the muscles and limbs detect limb
movement and physical deformation, and further
supplement central command.
Mechanisms for control of ventilation
The subsequent gradual rise in ventilation may be explained
by a fine-tuning of respiratory neurons in response to
central command and feedback control from arterial
chemoreceptors positioned in the carotid and aortic bodies.
Mechanisms for control of cardiac output
The initial rapid rise in cardiac output is explained firstly by
central command, and secondly by the Starling Effect.
Input from mechanoreceptors in muscles also contribute to
the central command process by feedback control.
Chemoreceptors in muscle are mainly responsible for the
secondary gradual rise to steady state.
Metaboreflex
When exercise begins,
Muscle metabolism increases, metabolite
(e.g., lactic acid, potassium and
adenosine) accumulate in the working
muscle.
Receptors in the muscle detect this
accumulation and afferent fibres send
information to the brain (the medulla)
This increases sympathetic nerve activity
Exercise
increases
sympathetic activity
And parasympathetic
decreases
This affects heart rate &
the venules and vein
Redistribution of cardiac
output during exercise
Blood flow increases in skeletal muscle, the
skin and the heart
Skeletal Muscle:
Supply of oxygen and removal of
metabolic waste
Skin:
Dissipation of heat
Heart:
Oxygen supply (cardiac muscle extracts
almost all oxygen from blood even at rest)
Redistribution of cardiac
output during exercise
Blood flow decreases in the kidneys, digestive
tract and all other parts of the body not
directly involved in exercise.
Blood flow through the brain remains fairly
constant due to autoregulation. The fixed volume
of the cranial cavity cannot accommodate large
increases in blood flow.
Redistribution of cardiac
output during exercise
Vasodilation in muscle, the heart and in the
skin decreases peripheral resistance (local
control mechanisms and epinephrine on β2
adrenergic receptors)
The net effect of vasodilation and
vasoconstriction in the body during exercise is a
reduction in total peripheral resistance
Vasoconstriction in the rest of the body
increases peripheral resistance (increase of
sympathetic stimulation)
Summary of cardiovascular
responses to exercise
In healthy people diastolic arterial pressure
is regulated within a very narrow range
End-diastolic volume increases due to
increased venous return:
Muscle pump
Respiratory pump
Sympathetic stimulation
Cardiovascular parameters
and training
Cardiac output is larger in trained people.
Maximal heart rate is determined mainly by
age and it is not increased by training.
However, trained people have a lower heart
rate for a given workload.
Stroke volume is greater in trained people,
and it is the only way of producing a higher
maximal cardiac output in that group
