title: Deterministic recurrences of sequential F-wave latencies.
abstract: OBJECTIVE
  Historically, F-waves have been classified by various linear descriptors like persistence, latency, duration, amplitude, chrono-dispersion and number of repeater waves. But because physiological signals are notoriously nonlinear in nature, the objective of this study was to apply modern nonlinear methodology to F-waves sequences to assess the presence of underlying deterministic structures. Subtle changes in these sensitive markers could give early warnings for neurological problems.
  
  
  METHODS
  F-waves were elicited in the left abductor pollicis breivs muscle by supra-maximally stimulating the median nerve percutaneously at the wrist. Approximately 200 stimuli were applied (0.5 Hz) to three subjects for at least four trials each. F-wave latencies were measured and assembled into sequences in proper order. Recurrence quantification analysis (RQA) was applied to these F-wave sequences from different dimensional perspectives. Controls were constructed by randomly shuffling the ordered sequences. RQA has a theoretical mathematical foundation and practical performance record on numerous other physiological systems.
  
  
  RESULTS
  Recurrence analysis showed that sequential F-waves form recurrent patterns with parallel trajectories with deterministic and laminated structures. These features could be destroyed by randomizing the sequential orders of F-waves, upholding the hypothesis that sequences of F-waves are deterministically formed from underlying physiological rules.
  
  
  CONCLUSIONS
  F-wave time series are fully amenable to recurrence analysis which provides a higher-dimensional perspective on the physiological dynamic. The recurrent patterns are complex, but not random, meaning that physiological rules dominate the sequence of F-waves. Disease processes within the central or peripheral nervous system may alter F-wave patterns. If so, RQA potentially may be a diagnostic tool to help discern subtleties between altered deterministic rules operating in disease.
authors.affiliation: Hines VAH, Hines, IL 60141, USA. morris.fisher@med.va.gov
authors.forename: M A
authors.initials: MA
authors.lastname: Fisher
authors.forename: J
authors.initials: J
authors.lastname: Chawla
authors.forename: C L
authors.initials: CL
authors.lastname: Webber
mesh_terms: D000200:Action Potentials / Q000502:physiology; D000328:Adult; D004558:Electric Stimulation; D004568:Electrodiagnosis / Q000379:methods*; D006801:Humans; D008475:Median Nerve / Q000502:physiology; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000294:innervation / Q000502:physiology; D009422:Nervous System Diseases / Q000175:diagnosis* / Q000503:physiopathology*; D009431:Neural Conduction / Q000502:physiology*; D010525:Peripheral Nerves / Q000502:physiology*; D010523:Peripheral Nervous System Diseases / Q000175:diagnosis / Q000503:physiopathology; D011237:Predictive Value of Tests; D011930:Reaction Time / Q000502:physiology; D012018:Reflex / Q000502:physiology*; D012680:Sensitivity and Specificity; D012815:Signal Processing, Computer-Assisted; D013933:Thumb / Q000294:innervation / Q000502:physiology; D013997:Time Factors