3 Theory of Operation
3.1 Physiology of wave reflection
Figure 17: Arteries of the upper body
The Uscom BP+ monitor has been developed using Pulse Wave Oscillometric
technology (referred to as
BP+
) and a scientific understanding of pressure wave
propagation in the arterial system. The arteries most relevant to BP+
measurement technique are shown in Figure 17.
The theory of wave reflections implies that the pressure at any location in the
arterial tree can be considered to be the sum of forward- and backward-going
pressure waves.
The initial forward-going pressure wave is generated by the contraction of the
heart’s left ventricle. Backward-going pressure waves are created when the
forward-going pressure wave encounters a change in the properties and
geometry within the arterial system. At such a point, the forward-going wave is
partly reflected, creating the backward-going pressure wave. There are multiple
reflection sites within the human arterial system.
3.2 Blood Pressure Measurement
The Cardiovascular monitor is designed to measure pressure-related information
from the upper arm using an inflatable cuff. As shown in Figure 18, the pressure
wave generated by the heart can be considered to take two paths to the upper
arm cuff, generating what are known as the incident wave and reflected wave.
•
The incident wave travels from the heart, through the ascending aorta,
subclavian artery and brachial artery to reach the cuff.
•
The reflected wave travels from the heart, through the ascending aorta,
aortic arch and down the descending aorta to the effective reflection site
in the abdominal aorta. At this location, some of the forward-going wave
is reflected and travels back up the descending aorta, through the
subclavian and brachial arteries before arriving at the cuff.
Measurement should be performed on the left arm. In cases where left-arm
measurement is contraindicated, measurement from the right arm can be
performed. Validation has only been performed on the left arm. As with all
oscillometric blood pressure measurements due to the additional complexity of
the wave path to the right brachial artery, results from the right arm will differ and
are not directly comparable with left-arm results.
Heart
Left brachial artery
Left subclavian artery
Brachiocephalic trunk
Left common carotid artery
Right common carotid artery
Right subclavian artery
Right brachial artery
Abdominal descending aorta
Common iliac arteries
Thoracic descending aorta
Ascending aorta
Aortic arch
Page 21 of 31
BP+ User Manual (R7)
