the systemic arterial blood pressure Flashcards
pulse pressure
pulse pressure = systolic pressure - diastolic pressure
mean arterial pressure
MAP = Pdias + 1/3(Psys - Pdias)
systolic BP is related to :
SV and aortic elasticity
diastolic BP related to:
TPR, aortic elasticity and HR
decreased aortic distensibility
A decrease in aortic elasticity leads to an increase in SBP
Normally, elastic aorta takes up kinetic energy from blood during systole & dampens the rise in pressure.
Inelastic aorta can cause systolic hypertension in the elderly
Hard arteries reduce the baroreceptor response
increase in heart rate
increase in HR will increase mean arterial pressure- due to lack of ‘run off’
the effect of Systemic Vascular Resistance
The resistance vessels are innervated by SNS nerve terminals that cause vasoconstriction when active.
The SVR increase accounts for ~80% of the compensatory response to a fall in MAP under resting conditions (i.e., the cardiac component contributes ~20%).
Describe the sensors for detecting pressure in the cardiovascular system and the integration centres in the CNS that respond to input from these sensors.
general:
Survival requires that pressure be maintained in the arterial system at all times.
The cardiovascular system includes two distinct pathways for monitoring and maintaining arterial pressure.
- ) Baroreceptor reflex, fast activating and helps compensate for short-term pressure changes
- ) Slow-activating system manipulates mean arterial pressure through changes in circulating blood volume by modifying renal function
baroreceptors- 2 main groups:
2 groups providing ‘the integrator’ – located in medulla with info about pressure and flow in CVS
- ) High pressure baroreceptors in carotid sinus and aortic arch.
- ) Low pressure cardiopulmonary receptors
the carotid and aortic baroreceptors as the primary means of detecting changes in MAP
They monitor pressure indirectly by responding to arterial wall stretch.
They are bare sensory receptors buried in the elastic layers of the aorta, carotid sinus
Information from the sinus travels back to the brain (afferent limb) via the glossopharyngeal nerve CNIX
Information from the arch travels back on CN X - the vagus nerve
function of baroreceptors
In the absence of stretch baroreceptors are inactive.
As MAP increases, nerve endings are stretched – leading to a graded potential – if deformation (stretch) is high an Action potential triggers, the higher the pressure the higher the frequency. The level hence drops during diastole when pressure is lower.
To enable a more nuanced response stretch sensitivity varies from one nerve ending to the next, thereby allowing for responsiveness over a wide pressure range.
The carotid baroreceptors have a response threshold of around 50 mm Hg and saturate at 180 mm Hg.
The aortic baroreceptors operate over a range of 100 to 300 mm Hg, meaning that they are usually inactive under resting conditions. In practice, this means that the carotid baroreceptors bear the brunt of responses to moment-by-moment changes in blood pressure.
preload
Preload refers to a load that is applied to a myocyte and establishes muscle length before contraction begins. In the LV, preload equates with the volume of blood entering the chamber during diastole (EDV), which is dependent on end-diastolic pressure (EDP).
cardiopulmonary baroreceptors
Found in lower pressure regions of the cardiovascular system. They provide the CNS with info about the ‘fullness’ of the CVS – their role is hence about modulating renal function.
However, because fullness correlates with ventricular preload, they also have a role in maintaining MAP.
Anatomically they are similar to the high pressure ones – the are also free nerve endings, they are found in the vena cava, pulmonary arteries and veins and the atria.
Info is conveyed back to CNS on Vagal afferents.
the 2 populations of baroreceptors in the atria
A receptors respond to tension that develops in the atrial wall during contraction. B receptors are sensitive to atrial wall stretching during filling. B receptors are also involved in raising HR when central venous pressure (CVP) is high, a response known as the Bainbridge reflex.
central integrator
These afferents converge on medulla, where the info is ‘compared’ to preset values and a ‘decision’ is made about the nature of the compensatory response.
The medulla is composed of a collection of nuclei that comprise the cardiovascular centre. Arterial pressure is a product of CO and systemic vascular resistance, (MAP = CO × SVR), and the control centres adjust both parameters simultaneously.
