The Effects of Circumferential Air-Splint Pressure on Flexor Carpi Radialis H-Reflex in Subjects without Neurological Deficits

Abstract

The purposes of this study were to investigate the effects of circumferential pressure on flexor carpi radialis (FCR) H-reflex in subjects without neuromuscular deficits and to evaluate the skin's contribution to this effect. FCR H-reflex was assessed in 43 subjects by measuring the peak-to-peak amplitude change before, during, and after circumferential pressure was applied to the forearm. Twelve H-reflexes (H/M ratio: M = 25%, SD = 14) were recorded before pressure application to obtain a baseline value (Hbaseline) to which all data were compared. A pneumatic 15 to 20-cm air splint inflated to 51–60 mmHg provided the pressure around the forearm. H-reflex recordings were taken at 1, 3, and 5 min. during (Hpressure) and after pressure application. A second smaller study (placebo), in which the air splint was inflated to 0 mmHg, was conducted in 5 subjects to ensure that changes in reflex amplitudes were not a result of cutaneous effects. Two types of responses were observed in the FCR H-reflex following pressure application. One group of subjects significantly increased in H-reflex amplitude while another group decreased in H-reflex amplitude when compared to Hbaseline Regression analysis found that Hmax explained 37.2% of the variance when controlling for Hbaseline. Subjects with larger Hmax showed an increase in Hpressure while subjects with lower Hmax showed decreases in Hpressure. The placebo study revealed no differences in H-reflex amplitude from baseline values, implying that skin stimulation from the air splint has no role in the effects observed. The dichotomous result indicates that pressure influences the upper extremity differently than it does the lower extremity in certain individuals. Clinicians, using circumferential pressure as a therapeutic modality to lower muscle activity of the upper extremity, need to be cognizant that pressure may have contrasting effects on their patients.