title: Gas exchange and cardiovascular kinetics with different exercise protocols in heart transplant recipients.
abstract: 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 (VE), O2 uptake (VO2), and CO2 output (VCO2) were determined. During protocol A, beat-by-beat cardiac output (Q) 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 VO2 on-, VE on-, and VCO2 on-kinetics were higher (i.e., the kinetics were slower) in HTR than in C, independently of workload and of the time post-transplantation. Also, t1/2 Q on- was higher in HTR than in C. In protocol A, no significant difference of t1/2 VO2 on- was observed in HTR between Ex 1 (48 +/- 9 s) and Ex 2 (46 +/- 8 s), whereas t1/2 Q 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 VE, VO2, and VCO2 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 VO2 on-kinetics, suggesting that the slower VO2 on- in HTR was attributable to peripheral (muscular) factors; 2) the dissociation between Q on- and VO2 on-kinetics in HTR indicates that an inertia of muscle metabolic machinery is the main factor dictating the VO2 on-kinetics; and 3) the VO2 off-kinetics was slower in HTR than in C, indicating a greater alactic O2 deficit in HTR and, therefore, a sluggish muscle VO2 adjustment.
authors.affiliation: Section of Physiology, Istituto di Tecnologie Biomediche Avanzate, Consiglio Nazionale delle Ricerche, Milan, Italy. grassi@itba.mi.cnr.it
authors.forename: B
authors.initials: B
authors.lastname: Grassi
authors.forename: C
authors.initials: C
authors.lastname: Marconi
authors.forename: M
authors.initials: M
authors.lastname: Meyer
authors.forename: M
authors.initials: M
authors.lastname: Rieu
authors.forename: P
authors.initials: P
authors.lastname: Cerretelli
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D002245:Carbon Dioxide; D002302:Cardiac Output; D002320:Cardiovascular Physiological Phenomena; D015444:Exercise; D005260:Female; D016027:Heart Transplantation; D006801:Humans; D007700:Kinetics; D008297:Male; D008875:Middle Aged; D010101:Oxygen Consumption; D011184:Postoperative Period; D011659:Pulmonary Gas Exchange; D012119:Respiration; D013997:Time Factors
chemical_list: D002245:Carbon Dioxide