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Human NIBP Nano
Owner’s Guide
in the brachial artery or aorta. There may be diff erences in waveform
and in absolute level. As a consequence, interpretation of finger blood
pressure measurements with the Human NIBP Nano, in particular when
the outcome of such measurements is used as an adjunct in a patient’s
diagnosis, should be performed with care.
Comparison with intra-arterial blood
pressure
Since blood pressure readings depend on the site of measurement, a
comparison of finger arterial blood pressure and intra-arterial pressure is
also aff ected by the choice of intra-arterial pressure site. We will focus on
the finger and brachial intra-arterial measurement sites.
Finger arterial pressure
Although it is not possible to measure intra-arterial pressure in a finger
artery, there is evidence that Human NIBP Nano indeed measures finger
arterial blood pressure.
In simultaneous recordings with two finger blood pressure monitoring
devices it could be determined that the unloaded diameter determined
using the PhysioCal algorithm was close to the theoretically required
1/4–1/2 of the open diameter level [Wesseling 1995]. At this diameter the
transmural pressure is close to zero, and therefore finger cuff pressure is
equal to intra-arterial finger blood pressure.
A second basis for the assumption that the Human NIBP Nano correctly
measures finger arterial blood pressure is a phenomenon that usually
can be observed in a pressure tracing at the start of a Human NIBP
measurement.
During start-up a pressure staircase is performed to monitor finger
plethysmographic values at diff erent pressure levels. The pressure
staircase is continued until the arterial diameter changes detected by the
plethysmogram virtually disappear, provided cuff pressure is above 100
mmHg. Therefore, at the last pressure level in a pressure staircase, finger
cuff pressure is just above systolic pressure. When the continuous finger
blood pressure measurement is started immediately aft er the pressure
staircase, and when blood pressure is suff iciently stable, the systolic
pressure usually matches the cuff pressure during the last step in the
pressure staircase.
