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C&P12 Blood Pressure Measurements
Mechanical work equation for the heart
Work = pressure x stroke volume
Law of Laplace [sphere]
P = 2T / R or
T = (P x R) / 2
(pressure, tension, radius)
MAP of tall man standing (head, heart, feet)
Head: 52 mmHg
Heart: 90 mmHg
Feet: 203 mmHg
Relationship of MAP, CO, PVR
MAP = CO x PVR
Width of BP cuff compared to diameter of the arm
Width should be 20% larger than the diameter of the arm.
Modern BP cuffs are considered what & how do they work
-As BP decreases the needle oscillates (integrated electronics)
Drawbacks of automated oscillometers to measure BP (x2)
-2 min minimum interval
-Fails at BP < 50 mmHg
Identify the BP measuring device & explain how it works
-Uses LED plethysmography at fingertip & inflatable cuff to measure continuous BP at fingertip
Rate NS infuses in an arterial line
Frequency range for invasive BP monitor
0 to 40 Hz
Placing art line in brachial artery
a BAD idea
Resonance in art lines & how to prevent
Always occurs due to the inertia of the fluid column but as long as it is >40 Hz it does not interfere with the quality of the reading.
-Kept above 40 Hz by using stiff, short tubing.
Dampening in art lines & impact
Occurs with an air bubble or clot (they absorb the higher frequencies)
-usually negligible to MAP reading
PA catheter waveforms