title: Photoplethysmographic signals to predict the success of lumbar sympathetic blockade for lower extremity pain.
abstract: OBJECTIVE
  A prospective, observational study to investigate how photoplethysmography (PPG) signals change during lumbar sympathetic blockade (LSB), and whether these changes can predict sympathetically mediated pain (SMP).
  
  
  METHODS
  Patients with unilateral lower extremity pain and self-reported cold hyperalgesia underwent LSB. Bilateral temperature and PPG signals (AC and DC) were recorded. Power spectrum analysis (PSA) was performed.
  
  
  RESULTS
  Of the total patient cohort (n = 38), eight patients (22.1%) had excellent pain-relief after LSB and were determined to have SMP. In all patients, the PPG AC signal changed immediately after drug administration, before any temperature change. DC signals decreased slowly in a linear fashion. PSA of DC signals showed significantly lower low-frequency/high-frequency (LF/HF) ratios in the SMP group than the sympathetically independent pain group, both before and after LSB. A cut-off value of 2.92 for LF/HF resulted in sensitivity, specificity and positive predictive values for SMP of 75.0%, 76.7% and 3.21 [1.5, 6.9], respectively.
  
  
  CONCLUSIONS
  PPG may be used as an early indicator of a successful LSB and could also be helpful in diagnosing SMP.
authors.affiliation: Department of Anaesthesia and Pain Medicine, Korea University Anam Hospital, Seoul, Republic of Korea Department of Biomedical Engineering, College of Medicine, Seoul National University, Seoul, Republic of Korea thregi@hanmail.net.
authors.forename: Soo Young
authors.initials: SY
authors.lastname: Park
authors.affiliation: Department of Biomedical Engineering, College of Medicine, Seoul National University, Seoul, Republic of Korea.
authors.forename: Hyun Jae
authors.initials: HJ
authors.lastname: Baek
authors.affiliation: Department of Biomedical Engineering, College of Medicine, Seoul National University, Seoul, Republic of Korea.
authors.forename: Kwang Suk
authors.initials: KS
authors.lastname: Park
authors.affiliation: Department of Anaesthesia and Pain Medicine, Seoul National University Hospital, Seoul, Republic of Korea.
authors.forename: Yong Chul
authors.initials: YC
authors.lastname: Kim
mesh_terms: D000328:Adult; D000368:Aged; D003080:Cold Temperature; D005260:Female; D006801:Humans; D006930:Hyperalgesia / Q000188:drug therapy*; D035002:Lower Extremity / Q000294:innervation; D008161:Lumbosacral Region / Q000294:innervation*; D008297:Male; D008875:Middle Aged; D010146:Pain / Q000188:drug therapy*; D017156:Photoplethysmography / Q000379:methods*; D011446:Prospective Studies; D013565:Sympatholytics / Q000627:therapeutic use*; D014664:Vasodilation / Q000187:drug effects
chemical_list: D013565:Sympatholytics
keywords: Lumbar sympathetic blockade; photoplethysmography; power spectrum analysis; sympathetically mediated pain