Effect of small vs large muscle mass endurance training on maximal oxygen uptake in organ transplanted recipients

Maximal oxygen consumption (V̇O_2max) is impaired in heart (HTx), kidney (KTx), and liver (LTx) transplanted recipients and the contribution of the cardiovascular, central, and peripheral (muscular) factors in affecting V̇O_2max improvement after endurance training (ET) has never been quantified in these patients. ET protocols involving single leg cycling (SL) elicit larger improvements of the peripheral factors affecting O₂ diffusion and utilization than the double leg (DL) cycling ET. Therefore, this study aimed to compare the effects of SL-ET vs DL-ET on V̇O_2max. We determined the DL-V̇O_2max and maximal cardiac output before and after 24 SL-ET vs DL-ET sessions on 33 patients (HTx = 13, KTx = 11 and LTx = 9). The DL-V̇O_2max increased by 13.8% ± 8.7 (p < 0.001) following the SL-ET, due to a larger maximal O₂ systemic extraction; meanwhile, V̇O_2max in DL-ET increased by 18.6% ± 12.7 (p < 0.001) because of concomitant central and peripheral adaptations. We speculate that in transplanted recipients, SL-ET is as effective as DL-ET to improve V̇O_2max and that the impaired peripheral O₂ extraction and/or utilization play an important role in limiting V̇O_2max in these types of patients. Novelty: SL-ET increases V̇O_2max in transplanted recipients because of improved peripheral O₂ extraction and/or utilization. SL-ET is as successful as DL-ET to improve the cardiorespiratory fitness in transplanted recipients. The model of V̇O_2max limitation indicates the peripheral factors as a remarkable limitation to the V̇O_2max in these patients.

Impaired systemic oxygen extraction in treated exercise pulmonary hypertension: a new engine in an old car?

Ambrisentan in 22 patients with pulmonary hypertension diagnosed during exercise (ePH) improved pulmonary hemodynamics; however, there was only a trend toward increased maximum oxygen uptake (VO₂max) secondary to decreased maximum exercise systemic oxygen extraction (Ca-vO₂). We speculate that improved pulmonary hemodynamics at maximum exercise “unmasked” a pre-existing skeletal muscle abnormality.