University:
Western Sydney University
Course:
MEDI 2003 | Clinical Sciences 2
Academic year:

2024
Views:

419

Pages:

4
Author:

Mariam A. A.

Arterial pressure and its control Learning objectives: • Recognise that blood pressure is kept relatively constant through the operation of the arterial baroreflex and cardiac baroreflex, both of which are negative feedback loops • Define the components of the arterial baroreflex: baroreceptors - nucleus tractus solitarius (NTS) - caudal ventrolateral medulla (CVLM) - rostral ventrolateral medulla (RVLM) - muscle sympathetic nerve activity (MSNA) • To define the components of the cardiac baroreflex: baroreceptors - nucleus tractus solitarius (NTS) - nucleus ambiguous (NA) and dorsal motor nucleus of the vagus (DMX) cardiac parasympathetic nerve activity Arterial pressure ✓ The high pressure (peak ~ 120 mmHg) within the arteries required to perfuse the tissues of the body ✓ Determined by the pumping of the heart (cardiac output) and the resistance of the blood vessels ✓ Cardiac output = stroke volume x heart rate ✓ Cardiac output = 70 ml x 70 min-1 = 4.9 l min-1 ✓ The arterioles provide most of the peripheral resistance ✓ The arterioles provide most of the peripheral resistance ✓ Venous pressure is lower than arterial pressure Measurement of systolic and diastolic pressures by auscultation Mean arterial pressure is the average pressure over the cardiac cycle (beat-beat) Because of the hydrostatic pressure on standing, mean arterial and venous pressures are higher in the foot than in the head Accordingly, arterial pressure is measured in the supine (recumbent) position - at heart level The gut is highly vascularized: changes in diameter of its arterioles have a large effect on total peripheral resistance Skeletal muscle is highly vascularized: changes in diameter of its arterioles have a large effect on total peripheral resistance ✓ Total peripheral resistance is largely determined by the arteriolar diameter in the muscle vascular beds, controlled by muscle sympathetic vasoconstrictor drive ✓ Sympathetic nerve terminals release noradrenaline (norepinephrine), which acts on adrenergic a receptor to cause contraction of the smooth muscle ✓ Blood flow through the arterioles causes release of nitric oxide (NO) from the endothelium ✓ NO causes vasodilatation, counteracting the neutrally mediated vasoconstriction: pharmacological blockade of NO production increases means BP by ~20mmHg Arterial pressure is controlled continuously (beat-beat): ✓ Sympathetic vasoconstriction ✓ Sympathetic and parasympathetic (cardiac vagal) effects on heart rate and stroke volume ✓ The control system (the baroreflex) is a negative feedback loop: an increase in arterial pressure brings about a decrease in arterial pressure (and vice versa), maintaining a constant (set) level ✓ Fluctuations in blood pressure are buffered by the baroreflex: falls in blood pressure result in increases in heart rate and sympathetic vasoconstrictor drive