Effects of spinal anesthesia on resting metabolic rate and quadriceps mechanomyography

Previous work by our group has shown by mechanomyography (MMG) that resting muscle is mechanically active. Ten patients having spinal anesthesia for surgery, which paralyses muscle below the waist, were studied to help determine whether resting-muscle mechanical activity plays a significant role in resting metabolism, and to further determine if the phenomenon is neurally mediated. Resting metabolic rate (RMR) by indirect calorimetry, and mid-anterior thigh MMG by accelerometer, were recorded before and during spinal anesthesia. Spinal anesthesia produced a 25% decrease in oxygen uptake (mean ± standard deviation: pre-spinal 228 ± 76; during spinal 171 ± 67 ml min⁻¹; P < 0.001) and 37% decrease in mean absolute MMG signal amplitude (pre-spinal-anesthetic 10.6 ± 3.9; during spinal: 6.7 ± 3.5 mm s⁻²; P < 0.001). Decreased oxygen uptake in individuals correlated with decreased resting-muscle mechanical activity (R = 0.624; P = 0.05). Paralysis of muscle below the waist reduced RMR and resting-muscle mechanical activity.