title: Pulse Photoplethysmographic Analysis Estimates the Sympathetic Activity Directed to Heart and Vessels.
abstract: BACKGROUND
  Novel 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.
  
  
  METHODS
  Ten 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.
  
  
  RESULTS
  PPGA, 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).
  
  
  CONCLUSIONS
  In 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.
authors.affiliation: 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.).
authors.forename: Riccardo
authors.initials: R
authors.lastname: Colombo
authors.forename: Andrea
authors.initials: A
authors.lastname: Marchi
authors.forename: Beatrice
authors.initials: B
authors.lastname: Borghi
authors.forename: Tommaso
authors.initials: T
authors.lastname: Fossali
authors.forename: Roberto
authors.initials: R
authors.lastname: Rech
authors.forename: Antonio
authors.initials: A
authors.lastname: Castelli
authors.forename: Alberto
authors.initials: A
authors.lastname: Corona
authors.forename: Stefano
authors.initials: S
authors.lastname: Guzzetti
authors.forename: Ferdinando
authors.initials: F
authors.lastname: Raimondi
mesh_terms: D000328:Adult; D017704:Baroreflex / Q000502:physiology*; D001794:Blood Pressure / Q000502:physiology*; D001808:Blood Vessels / Q000294:innervation / Q000502:physiology; D005260:Female; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D008297:Male; D017156:Photoplethysmography / Q000379:methods*; D017779:Sympathetic Fibers, Postganglionic / Q000502:physiology*; D018667:Tilt-Table Test / Q000379:methods