Contribution of po2, p50 and hb to changes in a-v o2 content during
exercise in heart failure.
Perego, Gb, Gc Marenzi, M Guazzi, P Sganzerla, E Assanelli, P Palermo,
B Conconi, G Lauri, and Agostoni.
Istituto di Cardiologia dell' Universit[grave]a degli Studi, Centro
Cardiologico Fondazione Monzino, IRCCS, Centro di Studio per le
Ricerche Cardiovascolari del CNR, Milan, Italy
APStracts 2:0426A, 1995.
Oxygen content artero-venous (O2Ct AV) differences increase during
exercise in normal subjects through several mechanisms including pO2,
p50 and haemoglobin concentration (Hb) changes. The present study was
undertaken to evaluate how much these biochemical changes are
relevant to O2Ct AV difference through exercise in patients with
heart failure. Twenty-seven patients with congestive heart failure
(10 patients in functional Class A (peak exercise VO2 > 20
ml/kg.min), 9 in Class B (20-15 ml/kg.min) and 8 in Class C (15-10
ml/kg.min) underwent a cardiopulmonary exercise test with every
minute simultaneous blood sampling from the pulmonary and systemic
arteries for determination of Hb, pO2, pCO2, pH, O2 content, Hb
saturation and lactic acid (pulmonary artery only), and calculation
of p50. Analysis of data was done at 6 exercise stages: the first at
rest, the last at peak exercise and the second to the fifth at 1/5,
2/5, 3/5 and 4/5 of oxygen consumption increase. O2Ct AV difference
at peak exercise was 14.3 +/- 2.1 ml/dl (mean +/- SD), 16.9 +/- 2.4,
and 14.7 +/- 2.1 in class A, B and C, respectively. The contribution
of Hb, p50 and pO2 changes to the increment of O2Ct AV difference
during exercise was 21, 17 and 63 %, respectively; the only
interclass difference observed was for p50, which plays a greater
role on O2Ct AV difference in class A. Hb changes act mainly at the
arterial site while p50 and pO2 at the venous site. Hb increase was
constant through the test, venous p50 increase was greater above
anaerobic threshold and venous pO2 reduction was most remarkable at
the onset of exercise; in Class C patients no venous pO2 change was
recorded in the second half of exercise. Thus, O2Ct AV difference
increase during exercise is notable in patients with heart failure
but unrelated to the severity of the syndrome. Hb, p50 and, to the
greatest degree, pO2 changes participate in the increment of O2Ct AV
difference. In class C patients the lack of pO2 reduction in the
second half of exercise suggests the achievement of a "whole body
critical venous pO2".
Received 22 March 1995; accepted in final form 15 September 1995.
APS Manuscript Number A317-5.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 6 November 95