Does handgrip exercise training increase forearm ischemic vasodilator responses in patients receiving hemodialysis?

Abstract

In patients receiving hemodialysis, exercise capacity is extremely limited. Although vasodilation is one of the key phenomena for blood perfusion into working skeletal muscles during exercise, it is not clear whether the vasodilator capacity is increased after physical training in this population. We attempted to clarify whether handgrip exercise training increases forearm vasodilator responses to arterial occlusion, and to determine the relationship between muscle contraction function and the vasodilator responses in patients receiving hemodialysis. Eight patients and 7 age-matched healthy controls were tested. The patients participated in handgrip training four times a week for 6 weeks. Before and after the training the maximum muscle strength and endurance were measured with a handgrip dynamometer, and the forearm vasodilator responses to 3-minute arterial occlusion were measured by the near infrared spectroscopy technique. Maximum strength and endurance were significantly lower in the patients than in the controls. Maximum strength (from 183+/-84 to 228+/-92 Newtons, p<0.05) and endurance (from 19+/-6 to 31+/-8 sec, p<0.05) were both increased after the training in the patients. Vasodilator responses estimated by the ratio of the maximum value of oxyhemoglobin after relief of arterial occlusion to its minimum value before the relief were significantly smaller in the patients compared with those in the controls (132+/-20 vs 161+/-27%, p<0.05). In contrast to the findings in muscle function, the decreased vasodilator responses were not improved after the training (141+/-17%). Additionally, no improvement in the vasodilator responses was observed in the parameters estimated by oxygen saturation. These data suggest that exercise capacity increased by physical training is produced by the functional improvement of skeletal muscles per se, but not by alterations in blood perfusion for oxygenation of the muscles in patients receiving hemodialysis.