The Role Of The Autonomic Nervous System On Vascular Function During A Passive Limb Movement Test

Background: Cardiovascular diseases (CVD) cause an estimated 17.9 million deaths globally every year, with over 83 million people in the United States having one or more forms of CVD. Vascular dysfunction is often a prerequisite in the development of CVD. The passive limb movement (PLM) test has recently been developed to assess vascular function and identify early signs of vascular dysfunction. However, the role of the autonomic nervous system, which can act on the vasculature to alter assessment outcomes, during the PLM test response is not known. Purpose: The purpose of this study was to elucidate the contribution of the autonomic nervous system, via muscle sympathetic nerve activity (MSNA), on vascular function measures during the PLM test. Methods: We assessed 5 (1M/4F) healthy, premenopausal adults aged 20±2yr. Hemodynamic responses via Doppler ultrasound, and MSNA responses via microneurography, to PLM in a room temperature condition and during a cold pressor test (CPT) were assessed in a randomly assigned order. A single PLM (sPLM) movement and a continuous PLM (cPLM) were performed in each condition. Stages were defined as baseline, sPLM, and cPLM. Results: No significant differences were observed in MSNA across conditions (MSNA burst frequency, p=0.31; MSNA burst incidence, p=0.57) or stage (MSNA burst frequency, p=0.62; MSNA burst incidence, p=0.57). There was a main effect of stage for blood flow response, expressed as area under the curve for 60s (BFAUC60), with baseline being different than cPLM (p=0.04). There was a main effect of stage for vascular conductance response(VCAUC60), with baseline being different than cPLM (p=0.02). During theCPT, a strong correlation between ^BFaverage and ^MSNA burst incidence was observed (r=-0.94; p=0.02). Conclusion: We were unable to detect differences in MSNA during the CPT, and therefore were unsuccessful in identifying the role of MSNA on CPT. However, it seems as though PLM may act independently of MSNA as we observed differences in vascular responses between conditions.