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Section of Physiology, Istituto di Tecnologie Biomediche Avanzate, Consiglio Nazionale delle Ricerche, I-20131 Milan, Italy; Department of Physiology, Max Planck Institut für Experimentelle Medizin, D-37075 Göttingen, Germany; Laboratoire de Physiologie des Adaptations, Université de Paris V, 75014 Paris, France; and Department of Physiology, Centre Médicale Universitaire, Université de Genève, CH-1211 Geneva 4, Switzerland
Received 12 June 1996; accepted in final form 4 March 1997.
Grassi, Bruno, Claudio Marconi, Michael Meyer, Michel Rieu,
and Paolo Cerretelli. Gas exchange and cardiovascular kinetics with different exercise protocols in heart transplant recipients. J. Appl. Physiol. 82(6): 1952-1962, 1997.
Metabolic
and cardiovascular adjustments to various submaximal exercises were
evaluated in 82 heart transplant recipients (HTR) and in 35 control
subjects (C). HTR were tested 21.5 ± 25.3 (SD) mo (range
1.0-137.1 mo) posttransplantation. Three protocols were used:
protocol A consisted of 5 min of rectangular 50-W load repeated
twice, 5 min apart [5 min rest, 5 min 50 W (Ex 1), 5 min
recovery, 5 min 50 W (Ex 2)]; protocol B consisted
of 5 min of rectangular load at 25, 50, or 75 W; protocol C
consisted of 15 min of rectangular load at 25 W. Breath-by-breath
pulmonary ventilation (
E),
O2 uptake (O2),
and CO2 output
(CO2) were determined.
During protocol A, beat-by-beat cardiac
output (
) was estimated by impedance cardiography. The half times (t1/2) of the on- and
off-kinetics of the variables were calculated. In all protocols,
t1/2 values for
O2 on-,
E on-, and
CO2 on-kinetics were higher
(i.e., the kinetics were slower) in HTR than in C, independently of
workload and of the time posttransplantation. Also,
t1/2 on- was higher in HTR
than in C. In protocol A, no significant difference of t1/2 O2
on- was observed in HTR between Ex 1 (48 ± 9 s) and Ex
2 (46 ± 8 s), whereas t1/2
on- was higher during Ex 1 (55 ± 24 s)
than during Ex 2 (47 ± 15 s). In all protocols and for all variables, the t1/2 off-values were higher in HTR
than in C. In protocol C, no differences of steady-state
E,
O2, and
CO2 were observed in both
groups between 5, 10, and 15 min of exercise. We conclude that
1) in HTR, a "priming" exercise, while effective in
speeding up the adjustment of convective O2 flow to muscle fibers during a second on-transition, did not affect the
O2 on-kinetics, suggesting
that the slower O2 on- in
HTR was attributable to peripheral (muscular) factors; 2) the
dissociation between on- and
O2 on-kinetics in HTR
indicates that an inertia of muscle metabolic machinery is the main
factor dictating the
O2 on-kinetics; and 3) the
O2 off-kinetics was slower
in HTR than in C, indicating a greater alactic O2 deficit
in HTR and, therefore, a sluggish muscle
O2 adjustment.
heart denervation; oxygen uptake kinetics; exercise transients
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