Estimating exercise stroke volume from the asymptotic oxygen pulse
in humans.
Whipp, Brian J, Michael B Higgenbottam, and Frederick C Cobb.
Department of Physiology, St George's Hospital Medical School,
Cranmer Terrace, London SW17 0RE, UK, Division of Cardiology,
Department of Medicine, Duke Medical Center and Durham Veterans'
Administration Medical Center, Durham, North Carolina, USA
APStracts 3:0359A, 1996.
Noninvasive techniques have been devised to estimate cardiac output ()
during exercise to obviate vascular cannulation. But while these
techniques are noninvasive, they are commonly not non-intrusive to
subjects' spontaneous ventilation and gas-exchange responses. We
hypothesized that the exercise stroke volume (SV) and hence might be
accurately estimated simply from the response pattern of two
standardly-determined variables: O2 uptake (O2) and heart rate (HR).
Central to the theory is the demonstration that the product of and
mixed venous O2 content is virtually constant during steady-state
exercise. Thus, from the Fick equation: O2 = .CaCO2 - k, the O2 pulse
(O2-P) = SV.CaCO2 - (k/HR). As CaO2 is usually relatively constant in
normal subjects during exercise, O2-P should change hyperbolically
with HR, asymptoting at SV.CaO2. And as the asymptotic O2-P = the
slope (S) of the linear O2-HR relationship, exercise SV may be
predicted to be S/CaO2. We tested this prediction in 23 normal
subjects who underwent a 3-min incremental cycle-ergometer test, with
direct determination of CaO2 and CO2 from indwelling catheters. The
predicted SV closely reflected the measured value (r = 0.80). We
therefore conclude that, in normal subjects, exercise stroke volume
may be estimated simply as five times the slope of the linear O2-HR
relationship (where 5 1/CaO2).
Received 11 August 1995; accepted in final form 15 July 1996.
APS Manuscript Number A880-5.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 21 August 1996