Advantages of continuous measurement of cardiac output 24 hours a
day.
Montani, Jean-Pierre, H. Leland Mizelle, Bruce N. Van Vliet, and
Thomas H. Adair.
Department of Physiology and Biophysics, University of Mississippi
Medical Center, Jackson, Mississippi, U.S.A. 39216-4505, Division of
Basic Medical Science, Faculty of Medicine, Memorial University of
Newfoundland, Canada, A1B 3V6
APStracts 2:0083H, 1995.
To test the hypothesis that measurement of cardiac output continuously
24 hours a day would provide a better day-by-day reproducibility of
the daily average cardiac output than acute measurements, we
developed a computer-assisted method to monitor cardiac output
continuously using an electromagnetic flow transducer. Because the
diastolic aortic flow, which is used as a zero flow reference, can
drift significantly with electromagnetic flow probes, automatic
tracking of the diastolic flow baseline was considered essential for
long-term measurements. To accomplish this, the analog pulsatile flow
signal was digitally converted and processed by an IBM PC to correct
for signal drift on a beat-per-beat basis. Using this computerized
system in 19 chronically instrumented dogs, we compared the values of
cardiac output during 5 consecutive control days, measured either for
20 hours each day (allowing 4 hours for special care), or for 30
minutes in the morning when the trained dogs were required to lie
quietly in their cages. The results show that the coefficient of
variation of the 5 daily averages in cardiac output for each
individual dog was 3 times smaller when cardiac output was measured
20 hours each day (2.9 0.3 % vs. 9.7 1.0 %). Whole day coefficients
of variation were also smaller for mean arterial pressure, heart
rate, stroke volume and total peripheral resistance. Because of this
greater day-by-day reproducibility, continuous monitoring of cardiac
output is likely to be more sensitive to small changes in cardiac
output induced by experimental protocols.
Received 22 November 1994; accepted in final form 1 March 1995.
APS Manuscript Number H1034-4.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 21 March 1995.