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Sections of 1 Cardiology and of
2 Biostatistics,
The impact of
forearm blood flow limitation on muscle reflex (metaboreflex)
activation during exercise was examined in 10 heart failure (HF) (NYHA
class III and IV) and 9 control (Ctl) subjects. Rhythmic handgrip
contractions (25% maximal voluntary contraction, 30 contractions/min)
were performed over 5 min under conditions of ambient pressure or with
+50 mmHg positive pressure about the exercising forearm. Mean arterial
blood pressure (MAP) and venous effluent hemoglobin (Hb)
O2 saturation, lactate and H+ concentrations
([La] and
[H+], respectively)
were measured at baseline and during exercise. For ambient
contractions, the increase (
) in MAP by end exercise (MAP; i.e., the exercise pressor response) was the same
in both groups (10.1 ± 1.2 vs. 7.33 ± 1.3 mmHg, HF vs. Ctl,
respectively) despite larger [La] and
[H+] for the HF
group (P < 0.05). With ischemic
exercise, the MAP for HF (21.7 ± 2.7 mmHg) exceeded that of Ctl
subjects (12.2 ± 2.8 mmHg) (P < 0.0001). Also, for HF, [La] (2.94 ± 0.4 mmol) and
[H+] (24.8 ± 2.7 nmol) in the ischemic trial were greater than in Ctl (1.63 ± 0.4 mmol and 15.3 ± 2.8 nmol; [La] and
[H+], respectively)
(P < 0.02). Hb
O2 saturation was reduced in Ctl from ~43% in the ambient trial to ~27% with ischemia
(P < 0.0001). O2 extraction was maximized under
ambient exercise conditions for HF but not for Ctl. Despite progressive
increases in blood perfusion pressure over the course of ischemic
exercise, no improvement in Hb O2
saturation or muscle metabolism was observed in either group. These
data suggest that muscle reflex activation of the pressor response is
intact in HF subjects but the resulting improvement in perfusion
pressure does not appear to enhance muscle oxidative metabolism or
muscle blood flow, possibly because of associated increases in
sympathetic vasoconstriction of active skeletal muscle.
metaboreflex; hemoglobin oxygen saturation; lactate; hydrogen ion; pH; positive pressure
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