A pilot study to measure upper extremity H-reflexes following neuromuscular electrical stimulation therapy after stroke.

Upper extremity (UE) hemiparesis persists after stroke, limiting hand function. Neuromuscular electrical stimulation (NMES) is an effective intervention to improve UE recovery, although the underlying mechanisms are not fully understood. Our objective was to establish a reliable protocol to measure UE agonist-antagonist forearm monosynaptic reflexes in a pilot study to determine if NMES improves wrist function after stroke. We established the between-day reliability of the H-reflex in the extensor carpi radialis longus (ECRL) and flexor carpi radialis (FCR) musculature for individuals with prior stroke (n=18). The same-day generation of ECRL/FCR H-reflex recruitment curves was well tolerated, regardless of age or UE spasticity. The between-day reliability of the ECRL H-reflex was enhanced above FCR, similar to healthy subjects [20], with the Hmax the most reliable parameter quantified in both muscles. H-reflex and functional measures following NMES show the potential for NMES-induced increases in ECRL Hmax, but confirmation requires a larger clinical study. Our initial results support the safe, easy, and efficacious use of in-home NMES, and establish a potential method to measure UE monosynaptic reflexes after stroke.

Comparison of linear regression and probit analysis for detecting H-reflex threshold in individuals with and without spinal cord injury.

A major challenge to understanding spinal reflex organization in health and disease is identifying sensitive measures of reflex excitability. The purpose of this study was to determine whether linear regression or probit analysis techniques are more sensitive for detecting H-reflex and M-wave threshold and for identifying differences in H-reflex threshold in individuals with and without spinal cord injury (SCI). Soleus H-reflex recruitment curves were generated in 9 individuals with SCI and 20 able-bodied individuals. H-reflex and M-wave threshold was estimated using three different methods, two that used linear regression of H-reflex peak-to-peak amplitude and one that used probit analysis of quantal H-reflexes. Results indicate that in both groups all three techniques were equally sensitive for detecting H-reflex but not M-wave threshold. When H-reflex threshold was normalized to M-wave threshold, different techniques provided different estimates of H-reflex threshold. However, between-group differences (SCI vs. able-body) in H-reflex and M-wave threshold were not affected by the measurement techniques that were compared in this study. We conclude that these techniques provide equally sensitive estimates of H-reflex but not M-wave threshold in persons with and without SCI. Hence, caution should be used when interpreting normalized and non-normalized values of H-reflex threshold.