research activities in 2007 - CSEM

Continuous Arterial Blood Pressure Monitoring: Can the Cuff Be Got Rid of?
J. Solà I Caros
A novel family of portable arterial blood pressure monitors is under development based on the multiparametric sensing of the cardiovascular
function. Current status of research, initial experimental results and future guidelines are described here.
In clinical practice, an ever-lasting technology in the
assessment of arterial blood pressure dominates the
landscape: the so-called auscultatory technique introduced in
1905 by Korotkoff: a well trained operator places a
stethoscope over a distal artery and interprets the sequence
of sounds that occur while a cuff placed above the artery is
deflated. Although such an approach retains a secure position
in the surgery, the occasional measurements taken in this
manner can be unusually high (white coat effect) or low,
leading to false diagnoses. Consequently some individuals
may receive unneeded treatment and those actually needing it
can be lulled into a false sense of well-being hence elevating
their risk of cardiovascular disease.
Alternatives to the auscultatory technique do exist in the field
of ambulatory monitoring of blood pressure: most
epidemiologic research studies rely on automatic inflation
cuffs placed either over the brachial or radial arteries e.g. the
devices that one might acquire in a pharmacy nowadays.
Although relatively accurate, this so-called oscillometric
technique does not match with the philosophy of portable
continuous monitoring in two senses: on the one hand the
measurement periodicity must be commonly set to 30 minutes
because of the discomfort and pain associated with each
inflation event, providing thus only a partial picture of the
blood pressure evolution. On the other hand, each
measurement alters the life-style of the user and thus modifies
the blood pressure profile, especially at night.
However, the need for a continuous cuff-less blood pressure
monitor is continuously increasing in the fields of e.g.
pharmacology, clinical practice and sports.
A new family of cuff-less blood pressure monitors based on
the optical and electrical sensing of a set of cardiovascular
parameters is being explored at CSEM. The strategy consists
of non-invasively tracking the evolution of those hemodynamic
components that play a role in the establishment of the fluidic
pressure in the arteries, and from them, obtain an indirect
blood pressure estimate. From a fluidic perspective, two
hemodynamic components must be considered: the cardiac
output, i.e. the flow of blood from the left ventricle to the
systemic vessels, and the total peripheral resistance i.e. the
resistance, in a Poiseuille sense, that the systemic vessels
oppose the cardiac output.
The metrological strategies adapted inherit the know-how in
multiparametric cardiovascular monitoring acquired during
earlier research at CSEM. At the current stage an estimate of
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cardiac output is being assessed through the statistical signal
processing of bioimpedance measurements. Bioimpedance
depicts the measurement of the electrical potential differences
that are generated across the thorax of an individual through
the injection of low power AC currents on the skin surface. For
the assessment of total peripheral resistance, a new approach
based on the probabilistic information processing of infra-red
tissue absorption and bioimpedance data has been developed
and patented [1] . Both sensing techniques are inconspicuous
and imperceptible by the subjects. The approach partly relies
on the measurement of the wavefront propagation velocity of
pulse waves through the arterial tree, the so-called pulse
wave velocity.
Figure 1 shows the results of an in-vivo study realized at
CSEM labs. During the experiment, the mean arterial blood
pressure of a subject was modified while several vital
parameters were monitored with a reference device and the
CSEM prototype. In this particular experiment the novel
approach successfully tracked the variations of mean arterial
blood pressure induced to the subject.
MAP [mmHg]
160
140
120
100
80
60
CO [l/min]
TPR [mmHg.s/mL]
8
6
4
2
1
0
0 5 10
Time [min]
15 20
PORTAPRES
CSEM
Figure 1: Experimental dynamic cardiovascular responses estimated
during a period of 25 minutes by a reference device (PORTAPRES)
and CSEM technique.
Returning to the initial question of being able to achieve
continuous blood pressure monitoring without the cuff, the
results obtained by CSEM biomedical sensing technology
suggest this goal may be achieveable, at least under certain
constraints. The research is still in progress.
[1] J. Solà I Caros, “Method for the continuous non-invasive and
non-obstrusive monitoring of blood pressure”, EP07123934.7,
2007