Laser Doppler Flowmeter (LDF) non-invasively measures cutaneous blood flow in surface capillaries and gives instantaneous and continuous readings. Previous researchers have compared LDF to Muscle Sympathetic Nerve Activity, catecholamine release and electrocardiogram (EKG) R-R interval variability (gold standard measures of autonomic change) and found it to be a highly reliable and sensitive measure of systemic autonomic tone. In this current study we sought to validate (i.e., demonstrate accuracy) of the LDF to measure systemic autonomic changes in subjects in which the autonomic system was activated by head-tilt and ice hand plunge, as compared to the gold standard, EKG R-R interval. Researchers in the field have intimated that the LDF holds promise to be more accurate than the EKG in this assessment. We desire to validate the use of LDF in measuring autonomic tone so we can later use it to evaluate the effect of osteopathic manipulation techniques on autonomic tone. We tested the feasibility of our protocol on 4 volunteers and gathered preliminary data. The subjects filled out a health questionnaire that screened for underlying autonomic dysfunction, and they tolerated the procedures well without complications or complaints. Due to the large variability in subjects' autonomic tone even at rest, and lack of a steady baseline in our few volunteers at this point, we will need to increase our sample size as well as alter our inclusion criteria to only those subjects that demonstrate a steady baseline autonomic tone in order to expect to find a significant difference in autonomic tone during rest vs. after autonomic activation. However, even with the preliminary data we can appreciate a difference in autonomic tone between subjects at rest and after autonomic activation using the LDF. Further, at the beginning of the study we did not appreciate the difficulty of simultaneously measuring and integrating the EKG R-R interval with the LDF, but have since purchased new software and measuring devices that will ensure success on this endeavor. Ultimately, this study shows that it is feasible to validate the use of LDF in measuring autonomic change in subjects using this protocol and the LDF shows promise to be used in future studies evaluating the physiologic effects of Osteopathic manipulation techniques.
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