Gas exchange and cardiovascular kinetics with different exercise protocols in heart transplant recipients

Abstract

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 Cconsisted of 15 min of rectangular load at 25 W. Breath-by-breath pulmonary ventilation (V˙e), O2 uptake (V˙o 2), and CO2 output (V˙co 2) were determined. During protocol A, beat-by-beat cardiac output (Q˙) was estimated by impedance cardiography. The half times ( t 1/2) of the on- and off-kinetics of the variables were calculated. In all protocols, t 1/2 values forV˙o 2 on-,V˙e on-, andV˙co 2 on-kinetics were higher (i.e., the kinetics were slower) in HTR than in C, independently of workload and of the time posttransplantation. Also, t 1/2 Q˙ on- was higher in HTR than in C. In protocol A, no significant difference of t 1/2 V˙o 2on- was observed in HTR between Ex 1 (48 ± 9 s) and Ex 2 (46 ± 8 s), whereas t 1/2Q˙ on- was higher during Ex 1 (55 ± 24 s) than during Ex 2 (47 ± 15 s). In all protocols and for all variables, the t 1/2 off-values were higher in HTR than in C. In protocol C, no differences of steady-stateV˙e,V˙o 2, andV˙co 2 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 theV˙o 2 on-kinetics, suggesting that the slower V˙o 2 on- in HTR was attributable to peripheral (muscular) factors; 2) the dissociation between Q˙ on- andV˙o 2 on-kinetics in HTR indicates that an inertia of muscle metabolic machinery is the main factor dictating theV˙o 2on-kinetics; and 3) theV˙o 2 off-kinetics was slower in HTR than in C, indicating a greater alactic O2 deficit in HTR and, therefore, a sluggish muscleV˙o 2 adjustment.