title: Quantal ventilatory variability during spontaneous breathing anaesthesia.
abstract: BACKGROUND
  Cardioventilatory coupling is the triggering of inspiratory onset by preceding cardiac activity. We have observed two forms of coupling with a bimodal ('quantal') variation of respiratory period.
  
  
  METHODS
  We investigated the variables of inspiratory duration (TI), expiratory duration (TE), and tidal volume (VT) where respiratory period variation was bimodal. In 25 anaesthetized spontaneously breathing subjects we took 11 samples of recording where the variation of respiratory period was quantal.
  
  
  RESULTS
  In eight of these epochs the variation in respiratory period was associated with fluctuations in the number of heart beats per breath (entrainment ratio) with a constant time interval between inspiration and the immediately preceding heart beat (coupling interval), which we define as pattern II coupling. During pattern II coupling, the quantal variations in respiratory period were entirely caused by variation in TE, with no associated changes in either TI or VT. The other three epochs with quantal variations in respiratory period were observed in pattern III coupling, where an alternating fluctuation in both entrainment ratio and coupling interval occurs. During pattern III coupling, quantal fluctuations were observed in TE, TI, and VT.
  
  
  CONCLUSIONS
  Cross correlation analysis suggested that when pattern III was present, TI was dependent upon the preceding TE, which differs markedly from traditional views on the interaction between inspiratory and expiratory duration. VT was linearly related to TI, and so could also be determined by the preceding TE during this type of coupling.
authors.affiliation: Department of Surgery and Anaesthesia, Wellington School of Medicine, PO Box 7343, Wellington, New Zealand. peter.larsen@wnmeds.ac.nz
authors.forename: P D
authors.initials: PD
authors.lastname: Larsen
authors.forename: Y C
authors.initials: YC
authors.lastname: Tzeng
authors.forename: D C
authors.initials: DC
authors.lastname: Galletly
mesh_terms: D000328:Adult; D000768:Anesthesia, General; D005246:Feedback / Q000502:physiology*; D005260:Female; D006321:Heart / Q000502:physiology*; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D001239:Inhalation / Q000502:physiology; D008297:Male; D008875:Middle Aged; D015656:Respiratory Mechanics / Q000502:physiology*; D012815:Signal Processing, Computer-Assisted; D013990:Tidal Volume / Q000502:physiology