Short Term Control of BP Flashcards
Why is MAP important?
The driving force pushing blood through the circulation.
Low - syncope.
High - hypertension.
What are the baroreceptors of the arterial baroreflex?
Carotid sinus and aortic arch.
High pressure - increased firing rate.
Low pressure - decreased firing rate.
What is the arterial baroreflex?
The vagus and glossopharyngeal nerve send signals to the medullary cardiovascular centres.
Parasympathetic - vagus, decreases HR.
Sympathetic - increases HR and contractility, adrenal medulla, venoconstriction and arteriolar constriction.
What are the other inputs to the medullary cardiovascular centres?
Cardiopulmonary baroreceptors - senses central blood volume.
Central chemoreceptors - senses arterial PCO2 and PO2.
Muscle chemoreceptors - senses metabolite concentrations.
Joint receptors - senses joint movement.
Higher centres - hypothalamus and cerebral cortex.
What happens when a person stands up?
EDV, preload, SV, CO, and MAP decrease.
Arterial baroreceptors signal the decrease in MAP, by reducing the firing rate.
Sends information to medullary cardiovascular centres.
What are the effects of a person standing up?
Decreased vagal tone - less HR inhibition, increases CO.
Sympathetic activation:
Increases HR - increases CO.
Increases contractility - increases SV and CO.
Venoconstriction - increases preload, SV and CO.
Arteriolar constriction - increases TPR.
What are the first two phases of the Valsalva manoeuvre?
A forced expiration against a closed glottis.
Phase I - increased thoracic pressure is transmitted through to the aorta.
Phase II - reduces filling pressure from the veins (reduces VR, EDV, SV, CO and MAP).
Late-phase II - reduced MAP is detected by baroreceptors and increases CO and TPR.
What are the last two phases of the Valsalva manoeuvre?
Phase III - at the end of the manoeuvre, the decrease in thoracic pressure is transmitted through to the aorta.
Phase IV - VR is restored, so SV increases. However, reflex effects remain. Eventually, it returns back to normal.
What is the clinical significance of the Valsalva manoeuvre?
Tests autonomic function.
Reduced in older people, or people with autonomic neuropathy.
Increases MI risk.
How can the Valsalva manoeuvre interrupt supraventricular tachycardia?
Venous return to the LV is reduced.
Once the breath is released, there is a massive increase in VR and EDV.
Preload, SV, CO, and aortic pressure increases.
Arterial baroreceptors sense this and trigger a reflex decrease in HR.
Parasympathetic fibres innervating the pacemaker cells are activated.
