Exertional heatstroke and muscle metabolism: an in vivo 31P-MRS study.
An impairment of muscle energy metabolism has been suggested as a predisposing factor for, as well as a consequence of exertional heatstroke (EHS). Thirteen young men were investigated 6 months after a well-documented EHS using 31Phosphorus Magnetic Resonance Spectroscopy (31P-MRS). The relative concentrations of ATP, phosphocreatine (PCr), inorganic phosphate (Pi), phosphomonoesters (PME), and the intracellular pH (pHi) were determined at rest, during a graded standardized exercise protocol (360 active plantar flexions) and during recovery. Also the leg tissue blood flow was determined by venous occlusion plethysmography during the MRS procedure. Sixteen age-matched healthy male volunteers served as control group. In resting muscle, there were no significant differences between the groups as regards pHi, Pi/PCr, and ATP/PCr+Pi+PME ratios. During steady state exercise conditions, effective power outputs were similar for both groups at each level of exercise: 20, 35, and 50% of maximal voluntary contraction (MVC) of the calf muscle. No significant differences were shown between the two groups in Pi/PCr, pHi, or changes of leg blood flow at each level of exercise. At 50% MVC, Pi/PCr was 0.48 +/- 0.08 vs 0.47 +/- 0.05 (P = 0.96), pHi was 6.94 +/- 0.03 vs 6.99 +/- 0.02, respectively (P = 0.13). Finally, the rate of PCr resynthesis during recovery was not significantly different between the two groups: t1/2 PCr = 0.58 +/- 0.07 vs 0.50 +/- 0.05 min, respectively (P = 0.35). Therefore, no evidence of an impairment of muscle energy metabolism was shown in the EHS group during a standardized submaximal exercise using 31P-MRS performed 6 months after an EHS.
Payen
J F
JF
Département d'Anesthésiologie, INSERM U318, Hôpital A. Michallon, Grenoble, France.
Bourdon
L
L
Reutenauer
H
H
Melin
B
B
Le Bas
J F
JF
Stieglitz
P
P
Cure
M
M
D000255:Adenosine Triphosphate / Q000378:metabolism; D000328:Adult; D005080:Exercise Test; D006359:Heat Exhaustion / Q000378:metabolism*; D006801:Humans; D007866:Leg / Q000098:blood supply; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D009119:Muscle Contraction / Q000502:physiology; D009132:Muscles / Q000378:metabolism*; D010758:Phosphorus; D012039:Regional Blood Flow
D010758:Phosphorus; D000255:Adenosine Triphosphate