Disturbances in blood pressure and volume
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What is the skeletal muscle pump?
Tonic contraction for posture Limits venous pooling Rhythmic contraction of toes and calves etc also effective Venous valves
What is the respiratory pump?
Deeper breathing when standing promotes venous return and limits venous pooling
What do both pumps aid?
Increase in CVP - increase in EDV, SV, CO and ABP Prevent oedema
What does hypertension increase the risk of?
Heart failure Stroke Congestive heart failure
What is congestive heart failure?
Arises from: myocardial infarction chronic hypertension Systolic contraction of ventricular muscle is weak Ejection fraction is low Ventricles, atria and venous vessels are over filled/distended Large EDV but low SV CO and ABP are low
What is the baroreceptor response in someone with congestive heart failure?
Increased sympathetic activity Decreased parasympathetic activity Ventricular contractility increases with little effect Retention of water by kidney
How can we test baroreceptor reflexes?
IV injection of vasoconstrictor causes baroreflex bradycardia IV injection of vasodilator causes baroreflex tachycardia
How can we test cardiac and vascular components of the baroreceptor reflex?
Cannulate the carotid artery Change sinus pressure and record afferent nerve activity In humans, neck cuff mimics changes in ABP
What changes occur in hypertension?
Set point of the baroreceptor reflex changes Output of symapthetic nerve activity from CNS is chronically raised
What changes occur in congestive heart failure?
Set point of baroreceptor reflex is not changed Baroreflex sensitivity is reduced Volume receptor reflex also reduced