Lecture 31 - Baroreflex Flashcards
What is Systolic BP:
Max. pressure exerted in arteries when blood is ejected into them during systole (heart contracting phase).
what is diastolic BP
Min. pressure within arteries when blood draining off into remainder of vessels during diastole (heart relaxing/filling phase).
what is pulse pressure
A measure of strength of pressure wave (= Difference between Systolic & Diastolic BP)
what is mean arterial pressure (MAP)
Average pressure responsible for driving blood forward into tissues throughout cardiac cycle.
how do you measure MAP
o Diastolic BP + 1/3 pulse pressure
o Flow = change in pressure/resistance
o Flow = cardiac output (CO)
o Resistance = sum of peripheral resistance (TPR)
o Therefore, pressure = CO x TPR
factors that affect MAP
o Physiological variables
Stroke volume (SV)
Heart rate (HR)
TPR
o Measurable variables
Diastolic pressure
Pulse pressure
Frank-starling mechanism (stroke volume)
o Increase volume of blood in ventricle –> increased stretch on muscle wall
o Increased muscle stretch –> increased force of contraction
o Increased force of contraction –> increased SV
Frank-starling mechanism (cardiac output)
o Increased end diastolic volume (left ventricle)
o Increases force of contraction
o Increased SV
o Increases CO
The cardiac cycle
o atrial systole begins
o atrial systole ends, atrial diastole begins
o ventricular systole – first phase
o ventricular systole – second phase
o ventricular diastole – early
o ventricular diastole – late
posture and baroreflex
o venous pressure highest at standing
o then walking (6km/h)/running (10km/h)
o then lowest at slow walking (3km/h)
baroreflex response to orthostatic hypotension
o decreased skeletal muscle pump
o decreases venous return
o decreases SV
o decreases CO
o decreases MAP
o activates baroreflex
measuring blood pressure
o cuff pressure > 120 mm Hg = no blood progresses through arterial segment under cuff, no sound detected
o cuff pressure < 80 mm Hg = arterial flow past region of cuff is continuous, no sounds are audible
o cuff pressure between 80 and 120 = spurts of blood transverse artery segment under cuff with each heartbeat and Korotkoff sounds are heard
what is systolic arterial pressure measurement
120 mm Hg
what is diastolic arterial pressure measurement
80 mm Hg
What are Korotkoff sounds
o Two theories
o Result of fluid turbulence
o Result of arterial wall oscillations
