48
Human NIBP Nano
Owner’s Guide
1. As the cuff pressure is increased in the pressure staircase at
start-up, the amplitudes of the plethysmogram signal and total
transmitted light increase as blood is pushed out from beneath the
cuff . At ‘1’ the greatest plethysmogram signal is detected and the
corresponding cuff pressure is ‘set’.
2. At this cuff pressure, the shape of the plethysmogram waveform is
analyzed and the servo setpoint is adjusted accordingly. The servo
loop is then closed and finger arterial pressure measurements are
taken.
3. Following 10 heart beats, the servo loop is reopened and a cuff
pressure is applied that is halfway between diastolic and systolic
pressures. Shapes of several plethysmogram waveforms are
analyzed and the servo setpoint is adjusted to a slightly higher
level. At ‘3’ the servo loop is closed and there is a decrease in the
amount of blood beneath the cuff leading to a small increase in the
level of transmission.
Interruptions due to Auto calibration (or ‘AutoCal’) occur less and less
frequently, until a 70 beat interval (roughly 1 minute) is established.
Example of a normal AutoCal
During a normal AutoCal the blood pressure measurement is interrupted
immediately aft er the detection of the systolic phase of the heart beat.
The first pressure level is located between diastolic and systolic finger
arterial pressure. The shape and amplitude of the plethysmogram are
analyzed and also compared with previous AutoCal periods. If the end-
diastolic phase of the plethysmogram has the correct shape, an additional
measurement of the plethysmogram is performed at diff erent cuff
pressure level to confirm that the determination of the unloaded volume
is indeed optimal. The PhysioCal algorithm also checks that the unloaded
diameter is not too close to the fully collapsed state of the finger artery.
