Autonomic nervous system function among individuals with acute musculoskeletal injury.

OBJECTIVE: To determine differences in peripheral and cardiovascular autonomic function between individuals with acute musculoskeletal injury (<1 week) and healthy controls. METHODS: Autonomic cardiovascular modulation, baroreceptor sensitivity, skin conductance, and peripheral skin temperature were obtained in 6 subjects with acute musculoskeletal injury and 6 age- and sex-matched controls. Power spectral analysis was performed on both beat-to-beat R-R intervals and continuous systolic blood pressure (SBP) peaks. Baroreceptor sensitivity was derived using both heart rate and blood pressure spectral analysis components. RESULTS: The SD of R-R intervals was significantly different for the acute injury group relative to controls (49.8 +/- 10.5 vs 76.8 +/- 12.7 ms; P < .01). Continuous SBP peaks and skin conductance (sympathetic vasomotor and sudomotor indices, respectively) were significantly higher (59.6 +/- 6.7 vs 23.8 +/- 6.4 mm Hg2 /Hz, and 3.87 +/- 1.04 vs 2.19 +/- 0.3 mhos; P < .01, respectively) and baroreceptor sensitivity lower (0.97 +/- 0.07 vs 1.10 +/- 0.08 mm Hg; P < .02) in the acute injury group compared with controls. Regression analysis revealed a significant relationship between skin conductance and continuous SBP peaks (r = 0.75; P < .01). CONCLUSIONS: These findings suggest that interaction between cutaneous and vasomotor sympathetic neurons in response to acute musculoskeletal injury, reflected as increased afferent input from sensitized nociceptors and other sensory neurons, results in alterations in autonomic function.

Comparison of tibial nerve H-reflex excitability after cervical and lumbar spine manipulation.

BACKGROUND: Previous investigations indicate that spinal manipulation leads to short-term attenuation of alpha-motoneuron excitability, when assessed by means of the Hoffmann reflex. Past studies, however, are limited to regional effects, such as lumbar manipulation effects on lumbar alpha-motoneuron activity. OBJECTIVE: This study compared and contrasted the effects of cervical and lumbar spine manipulation on the excitability of the lumbar alpha-motoneuronal pool in human subjects without low back pain, and compared the effects of cervical (nonregional) and lumbar (regional) spinal manipulation on lumbar alpha-motoneuron pool excitability in healthy subjects. The specific aim of this study was to determine if the inhibitory effects on the lumbar alpha-motoneuron pool associated with spinal manipulation are limited to the specific region in which the manipulative procedure is applied, or if rostral (cervical) manipulation can also influence caudal (lumbar) motoneuron excitability. METHOD: Thirty-six nonpatient human subjects were used to study the effect of cervical and lumbar spinal manipulation on the amplitude of the tibial nerve Hoffmann reflex, recorded from the gastrocnemius muscle. The Hoffmann reflex (H-reflex) technique allows for an indirect index of motoneuron pool excitability by means of peripheral nerve Ia-afferent fiber stimulation. Reflexes were recorded before and after spinal manipulative procedures. RESULTS: Lumbar spinal manipulation, as measured by amplitude changes of the tibial nerve H-reflex, attenuated lumbar alpha-motoneuronal activity. Suppression of motoneuronal excitability was significant (P <.05) but transient, with a return to baseline within 60 seconds after manipulation. Cervical spinal manipulation had no significant effect on lumbar motoneuron activity. CONCLUSION: These data indicate that the inhibitory effects of spinal manipulation on motoneuronal excitability are regional, rather than global.