Exam 6 - Arterial Blood Pressure Monitoring Flashcards
Arterial Blood Pressure
- Measure of force of blood on arterial walls
- Result of pressure generated by beating heart and resistance
- Flow and pressure is pulsatile (systolic and diastolic)
- Not the same in all points of arterial tree
Effect of gravity on MAP
- If standing: lower above heart….higher below heart
- Heart level is standard reference - Laying down is same throughout
- Same at all vertical points
MAP
- Avg pressure in system during systole AND diastole
- Reflects: Driving pressure
Peak pressure
Compliance of large arteries
- Reflects: Driving pressure
Estimation of MAP
- (1/3)(SBP) + (2/3)(DBP)
- MAP assumes 60 bpm (in reality HR is not fixed)
- Diastolic fluctuates all the time
- May not be true reflection of MAP under certain conditions
Actual MAP
- (CO)(SVR) + CVP
- determined by area under curve per given cardiac cycle
- obtained via invasive monitoring
- display is averaged over several cardiac cycles
Why MAP is good assessment tool
- MAP is same in all parts of arterial tree
- Not significantly affected by overshoot, artifact, dampening
- PVR and SVR can be calculated using MAP
- Gives approx pressure within systemic and cerebral cap beds
Pressure waves
- precedes actual flow of blood (ECG-Pulse delay)
- Pressure wave: 10 m/s
- Blood flow: 0.5 m/s
- Can affect pressure wave form shape due to reflection
5 components of pressure wave form
1 - Anacrotic limb (ascending limb) (systolic upstroke)
2 - Systolic peak
3 - Dicrotic limb (descending limb) (diastolic decline)
4 - Dicrotic notch (Aortic valve closes)
5 - End Diastole
Physiology of true pressure wave
Phase 1 - Inotropic component
- Aortic valve opens, steep upstroke, early systole
Phase 2 - Volume displacement curve
- blood into aorta, fills out and maintains pressure
- Round due to continued ejection, blood displacement, distention of arterial walls
- May see anacrotic notch (change from inotropic to displacement)
- Low SV (curve narrow w/ low amplitude)
Phase 3 - Late systole and Diastole
- sloping decline (runoff > input) , dicrotic notch (start of diastole)
dP/dT
- Slope of lines on pressure wave from curves
- change in pressure over change in time
High amplitude inotropic spike
- increased pressure generation
- increased acceleration of blood flow
- HYPERDYNAMIC (anemia, AI)
- increased reflection of pressure waves (vasoconstriction)
- may want to remove volume
- slope is quick to rise
Decreased amplitude of inotropic spike
- Myocardial depression (ischemia, CM)
- hypovolemia
- decreased reflections (vasodilation)
- may want to add volume
- hypotensive
Effects of pressure waves
1 - Gravitational effects (standing, laying down)
2 - Reflected waves
- preceded blood flow, bounce off arterioles and back, additive
- pulse pressure greater as you move down arterial tree
- usually results in overestimating actual wave
3 - Physiological effects
- Age, hyper/hypotension, hypovolemia, arrhythmia,
- Vessels get stiffer over time
- Kids have bigger dicrotic notch
Pulse pressure
- difference between systolic and diastolic pressure
- High PP can be predictor of heart problems
- >60 is abnormal - Low PP can mean poor heart function (more common)
- <40 is abnormal
High PP causes
- Calcification of Aorta
- Atheroslerosis
- Aortic Dissection
- Endocarditis
- AI
- Anemia
- Pregnancy
- Anxiety
- Heart block
- Hypertension
