Elimination of spurious absent sweat response in QSWEAT recordings.

INTRODUCTION: Forearm QSWEAT recordings are occasionally absent in females, likely due to high skin resistance. METHODS: We identified consecutive subjects with no sudomotor abnormalities but absent/markedly reduced QSWEAT forearm volume, and repeated QSWEAT at the same site after gentle abrasion. RESULTS: QSWEAT volumes were absent for 4 subjects and markedly reduced for the other 4 (median 0.01, IQR 0-0.03). After gentle skin abrasion, repeat volumes were significantly higher for all subjects and became normal in 7 of 8 subjects. DISCUSSION: Skin abrasion restores QSWEAT volumes in previously absent/markedly reduced site suggesting that skin preparation using abrasion is more effective.

Effect of position on valsalva maneuver: supine versus 20 degree position.

Blood pressure changes in response to the Valsalva maneuver (VM), which reflect the integrity of the baroreflex that regulates blood pressure. Performing this maneuver in the standard supine position often prevents adequate venous preload reduction, resulting in a rise rather than a fall in blood pressure, the "flat-top" Valsalva response. We determined whether performing the VM at a 20 degree angle of head-up tilt (20 degrees ) improves preload reduction, thereby reducing the frequency of flat-top responses, improving reflex vasoconstriction, and increasing the Valsalva ratio. One hundred thirty patients were evaluated in a prospective study. Each patient performed the VM in both supine and 20 degrees positions.Flat-top responses were present in 18% of subjects when supine. Twenty degree angle of head-up tilt position reduced the flat-top response by 87%. The components of the response that are dependent on preload reduction (Valsalva ratio and phases II_E, II_L, and IV) also showed significant improvement with 20 degrees .A 20 degree angle of tilt is sufficient to reduce venous preload, decreasing flat-top response rate and improving the Valsalva ratio and the morphology of the VM. We recommend this modification for laboratory evaluation of the VM, whenever a flat-top response is seen.