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

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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.