EXERCISE, POTASSIUM, AND MUSCLE DECONDITIONING POST-THORACIC ORGAN-TRANSPLANTATION

Although muscle deconditioning appears to significantly limit peak exercise performance post-thoracic organ transplantation, few confirmatory data exist. Potassium (K+) regulation during exercise may reflect muscle deconditioning, since both peak plasma K+ concentration ([K+]) and the increase in plasma [K+] relative to energy expenditure (Delta[K+]/W) are reduced in healthy individuals after training. This study compares Delta[K+]/W during graded exercise and the change in [K+] (Delta[K+]) during both exercise and recovery in 12 heart transplant (HT) recipients, 14 lung transplant (LT) recipients, and 7 healthy subjects. Plasma [K+] was determined from arterial blood sampled at rest; during the final 15 s of each power output; and at 1, 2, and 5 min postexercise. Peak oxygen consumption was significantly lower (P < 0.0001), whereas Delta[K+]/W was significantly higher (P < 0.002) among the HT and LT groups. When Delta[K+] during recovery was expressed relative to Delta[K+] detected during activity, no difference at 1, 2, or 5 min postexercise was detected, although the absolute fall in plasma [K+] was greater among the healthy subjects in the Ist min (P < 0.0001). The rate of Delta[K+] during recovery appears to reflect the rise seen during activity in all groups. These results suggest that [K+] regulation is altered during exercise in both HT and LT recipients and may reflect muscle deconditioning.