title: Respiratory rate can be modulated by long-loop muscular reflexes, a possible factor in involuntary cessation of apnea.
abstract: BACKGROUND
  The main limiting factors determining apnea time are generally considered to be related to blood and cerebrospinal fluid chemistry. Several physiological (adaptive) mechanisms and some psychologic parameters, such as motivation, are also known to increase apnea time.
  
  
  OBJECTIVE
  We wished to study the link between peripheral muscle fatigue, the concomitant alteration of long latency (transcortical) reflexes and respiratory control.
  
  
  METHODS
  Fatigue was induced in a small hand muscle (abductor pollicis brevis) (n = 11). This muscle is sufficiently small that its fatigue and the resulting production of metabolites are unlikely to alter whole-blood biochemistry. The Hoffmann reflex, an involuntary reaction to electrical stimulation of muscle afferent sensory fibreswas studied, as was the long latency reflex (LLR) using the Dueschl method in which electrical stimulation is superimposed on a slight voluntary contraction, Different fatiguing protocols were performed, and respiratory rate continuously recorded.
  
  
  RESULTS
  The 'muscular metabolites increasing protocol' (at 50% maximum voluntary contraction, MVC) showed a significant dissociation between the decreases in the H-reflex and the LLR, compared to contraction at 25% MVC. This was associated with an increase in the respiratory rate to 148.25 (SD 11.37)% of control at 3 min (the maximum time the contraction could be sustained), whereas at 25% MVC, respiratory rate did not change during the contraction.
  
  
  CONCLUSIONS
  This suggests a peripherally mediated, central input to the respiratory centres, triggering a powerful stimulus when metabolites accumulate in muscles. We believe this to be a possible mechanism terminating extreme breath holds.
authors.affiliation: Environmental & Occupational Physiology Laboratory, Haute Ecole Paul Henri Spaak, Pôle Universitaire Bruxelles-Wallonie, Brussels, Belgium. balestra@daneurope.org
authors.forename: Costantino
authors.initials: C
authors.lastname: Balestra
authors.forename: Morgan
authors.initials: M
authors.lastname: Levenez
authors.forename: Pierre
authors.initials: P
authors.lastname: Lafère
authors.forename: Bernard
authors.initials: B
authors.lastname: Dachy
authors.forename: Mikel
authors.initials: M
authors.lastname: Ezquer
authors.forename: Peter
authors.initials: P
authors.lastname: Germonpré
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D001049:Apnea / Q000378:metabolism / Q000503:physiopathology*; D004558:Electric Stimulation / Q000379:methods; D004576:Electromyography / Q000379:methods; D005260:Female; D006181:H-Reflex / Q000502:physiology; D006225:Hand; D006801:Humans; D008297:Male; D009119:Muscle Contraction / Q000502:physiology; D018763:Muscle Fatigue / Q000502:physiology*; D018482:Muscle, Skeletal / Q000378:metabolism / Q000502:physiology*; D009475:Neurons, Afferent / Q000502:physiology; D011930:Reaction Time / Q000502:physiology; D012018:Reflex / Q000502:physiology*; D056152:Respiratory Rate / Q000502:physiology*; D055815:Young Adult