title: [Variability of pulse signal frequency obtained using nocturnal pulse oximetry in patients with sleep apnoea/hypoapnoea syndrome].
abstract: BACKGROUND
  The measurement of central tendency (MCT) is a non-linear analysis technique which applied to second order differences diagrams enables the degree of variability to be quantified in a data series. In the present study an attempt is made to quantify and characterise the changes in heart rate obtained by pulse oximetry in patients with a clinical suspicion of sleep apnoea/hypoapnoea syndrome (SAHS) using the MCT and to evaluate its diagnostic use.
  
  
  METHODS
  A total of 187 patients were included in the study, on whom a nocturnal polysomnographic and pulse oximetry study was performed. To evaluate the variability of the heart rate the MCT applied to graphs of second order differences obtained from the heart rate record.
  
  
  RESULTS
  Patients with SAHS had a higher heart rate variability than patients without SAHS (0.449 vs. 0.666, P<0.001. In the multivariate analysis, the heart rate, the minimum saturation and the desaturation index of 4% were independently associated with the heart rate variability. As a diagnostic method, the MCT of the heart rate gives a sensitivity of 69.3%, a specificity of 77.6% and a diagnostic precision of 72.7%
  
  
  CONCLUSIONS
  Patients with SAHS have a greater variability in heart rate during the night, evaluated by applying the MCT of the heart rate to diagrams of second order differences. As a screening method, the MCT applied to the heart rate has a moderate sensitivity and specificity.
authors.affiliation: Servicio de Neumología, Hospital Universitario del Río Hortega, Valladolid, España. fsas@telefonica.net
authors.forename: Félix
authors.initials: F
authors.lastname: del Campo Matía
authors.forename: Roberto
authors.initials: R
authors.lastname: Hornero Sánchez
authors.forename: Carlos
authors.initials: C
authors.lastname: Zamarrón Sanz
authors.forename: Daniel
authors.initials: D
authors.lastname: Alvarez González
authors.forename: J
authors.initials: J
authors.lastname: Víctor Marcos Martín
mesh_terms: D005260:Female; D006339:Heart Rate; D006801:Humans; D008297:Male; D008875:Middle Aged; D010092:Oximetry / Q000295:instrumentation*; D017286:Polysomnography; D012720:Severity of Illness Index; D020181:Sleep Apnea, Obstructive / Q000175:diagnosis*