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

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 ((V) over dotE), O-2 uptake ((V) over dotO(2)), and CO2 output ((V) over dotCO(2)) were determined. During protocol A, beat-by-beat cardiac output ((Q) over dot) 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 for (V) over dotO(2) on-, (V) over dotE on-, and (V) over dotCO(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) over dot on- was higher in HTR than in C. In protocol A, no significant difference of t(1/2) (V) over dotO(2) on- was observed in HTR between Etc 1 (48 +/- 9 s) and Ex 2 (46 +/- 8 s), whereas t(1/2) (Q) over dot on- was higher during Ex 1 (55 +/- 24 s) than during Ex 2 (47 1 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-state (V) over dotE, (V) over dotO(2), and (V) over dotO(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 O-2 flow to muscle fibers during a second on-transition, did not affect the (V) over dotO(2) on-kinetics, suggesting that the slower (V) over dotO(2) on- in HTR, was attributable to peripheral (muscular) factors; 2) the dissociation between (Q) over dot on- and (V) over dotO(2) on-kinetics in HTR indicates that an inertia of muscle metabolic machinery is the main factor dictating the (V) over dotO(2) on-kinetics; and 3) the (V) over dotO(2) off-kinetics was slower in HTR than in C, indicating a greater alactic O-2 deficit in HTR and, therefore, a sluggish muscle (V) over dotO(2) adjustment.