• Riccardo Colombo, Andrea Marchi, Beatrice Borghi, Tommaso Fossali, Roberto Rech, Antonio Castelli, Alberto Corona, Stefano Guzzetti, and Ferdinando Raimondi.
• From the Anesthesiology and Intensive Care Unit, Azienda Ospedaliera "Luigi Sacco" - Polo Universitario, Università degli Studi di Milano, Milano, Italy (R.C., A.M., B.B., T.F., R.R., A. Castelli, A. Corona, F.R.); and Department of Emergency, Azienda Ospedaliera "Luigi Sacco" - Polo Universitario, Università degli Studi di Milano, Milano, Italy (S.G.). Current position: Anesthesiology and Intensive Care Unit, Istituto Clinico Humanitas IRCCS, Rozzano, Italy (A.M., F.R.).
• Anesthesiology. 2015 Aug 1;123(2):336-45.

BackgroundNovel pulse photoplethysmographic-derived indices have been proposed as tools to measure autonomic nervous system (ANS) modulation in anesthetized and awake patients, but nowadays their experimental validation is lacking. The authors aimed to investigate the ability of pulse photoplethysmographic amplitude (PPGA), ANS state (ANSS), and ANSS index (ANSSi) to measure changes of ANS modulation in response to sympathetic stimulation.MethodsTen awake healthy volunteers underwent two passive head-up tilts at 45° and 90°. The heart rate variability (HRV) and systolic arterial pressure variability were analyzed in the frequency domain as a measure of ANS modulation directed to the heart and the vessels. HRV, baroreflex sensitivity, and pulse photoplethysmographic indices were measured at baseline and after tilt maneuvers. The agreement between HRV-derived indices and pulse photoplethysmographic indices was assessed using Bland-Altman plots.ResultsPPGA, ANSS, and ANSSi changed significantly during the study protocol. Head-up tilt decreased PPGA and ANSS and increased ANNSi. There was a good agreement between ANSSi and baroreflex sensitivity explored in the high-frequency band (bias, 0.23; 95% CI, -22.7 to 23.2 normalized units) and between ANSSi and the sympathovagal modulation directed to the heart (bias, 0.96; 95% CI, -8.7 to 10.8 normalized units).ConclusionsIn controlled experimental conditions, novel pulse plethysmographic indices seem to estimate the changes of the sympathetic outflow directed to the vessels and the sympathovagal balance modulating heart rate. These indices might be useful in the future to monitor the fluctuation of sympathetic activity in anesthetized patients.

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