title: Dyspnea during exercise in hyperbaric conditions.
abstract: BACKGROUND
  Length-tension and force-velocity characteristics of respiratory muscles and hyperinflation are the likely determinants of dyspnea in subjects exercising under hyperbaric conditions. We hypothesize that hyperinflation plays a minor role and that the reduced velocity of shortening of the respiratory muscles modulates dyspnea for any given pleural pressure.
  
  
  METHODS
  We studied five normal subjects who performed an incremental exercise test on a cycloergometer in both normobaric (SL) and hyperbaric (4 ATA) conditions. We measured breathing pattern, inspiratory pleural pressure swing (Pessw), Delta Pes (i.e., the difference between the most and the less negative pleural pressures during tidal breathing), and dyspnea intensity (Borg score). End-expiratory lung volume (EELV) changes were evaluated by measuring changes in inspiratory capacity. Mean inspiratory flow (VT/TI) was used as an index of velocity of shortening of respiratory muscles.
  
  
  RESULTS
  Compared with SL, at 4 ATA, peak exercise ventilation (VE) (84.5 vs 62.2 L x min(-1)) and VT/TI (2.99 vs 2.16 L x s)(-1) were lower, Pessw (30.9 vs 38.6 cm H2O) and Delta Pes (43.8 vs 62.2 cm H2O) were higher, and Borg score was not different (7.60 vs 8.20 au). EELV decreased progressively during exercise but remained higher than at SL. Borg score was greater for a same VE and lower for a same Delta Pes. VT/TI was lower for a same Pessw. The differences in EELV between SL and 4 ATA did not relate with the concurrent changes in Borg score.
  
  
  CONCLUSIONS
  The results confirm our hypothesis that during exercise in hyperbaric conditions, decreased velocity of shortening of respiratory muscles modulates pressure-induced increases in dyspnea, with hyperinflation playing a minor role.
authors.affiliation: Dipartimento di Medicina Interna, Unita Funzionale di Medicina Iperbarica, University of Florence, Firenze, Italy. r.duranti@dmi.unifi.it
authors.forename: Roberto
authors.initials: R
authors.lastname: Duranti
authors.forename: Lorenzo
authors.initials: L
authors.lastname: Bonetti
authors.forename: Paolo
authors.initials: P
authors.lastname: Vivoli
authors.forename: Tommaso
authors.initials: T
authors.lastname: Benedetti
authors.forename: Barbara
authors.initials: B
authors.lastname: Binazzi
authors.forename: Pierantonio
authors.initials: P
authors.lastname: Laveneziana
authors.forename: Giorgio
authors.initials: G
authors.lastname: Scano
mesh_terms: D000328:Adult; D004417:Dyspnea / Q000503:physiopathology*; D015444:Exercise / Q000502:physiology*; D005080:Exercise Test; D006801:Humans; D006931:Hyperbaric Oxygenation; D008297:Male; D012129:Respiratory Function Tests; D012132:Respiratory Muscles / Q000503:physiopathology