GAS-EXCHANGE AND CARDIOVASCULAR KINETICS WITH DIFFERENT EXERCISE PROTOCOLS IN HEART-TRANSPLANT RECIPIENTS

Metabolic and cardiovascular adjustments to various submaximal exercis es were evaluated in 82 heart transplant recipients (HTR) and in 35 co ntrol subjects (C). HTR were tested 21.5 +/- 25.3 (SD) mo (range 1.0-1 37.1 mo) posttransplantation. Three protocols were used: protocol A co nsisted 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)]; pr otocol B consisted of 5 min of rectangular load at 25, 50, or 75 W; pr otocol C consisted of 15 min of rectangular load at 25 W. Breath-by-br eath pulmonary ventilation ((V) over dotE), O-2 uptake ((V) over dotO( 2)), and CO2 output ((V) over dotCO(2)) were determined. During protoc ol A, beat-by-beat cardiac output ((Q) over dot) was estimated by impe dance cardiography. The half times (t(1/2)) of the on- and off-kinetic s of the variables were calculated. In all protocols; t(1/2) Values fo r (V) over dotO(2) on-, (V) over dotE on-, and (V) over dotCO(2) on-ki netics 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-va lues were higher in HTR than in C In protocol C, no differences of ste ady-state (V) over dotE, (V) over dotO(2), and (V) over dotO(2) were o bserved in both groups between 5, 10, and 15 min of exercise. We concl ude that 1) in HTR, a ''priming'' exercise, while effective in speedin g up the adjustment of convective O-2 flow to muscle fibers during a s econd on-transition, did not affect the (V) over dotO(2) on-kinetics, suggesting that the slower (V) over dotO(2) on- in HTR, was attributab le to peripheral (muscular) factors; 2) the dissociation between (Q) o ver 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-kinetic s was slower in HTR than in C, indicating a greater alactic O-2 defici t in HTR and, therefore, a sluggish muscle (V) over dotO(2) adjustment .