Dyspnea during exercise in hyperbaric conditions.
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.
Duranti
Roberto
R
Dipartimento di Medicina Interna, Unita Funzionale di Medicina Iperbarica, University of Florence, Firenze, Italy. r.duranti@dmi.unifi.it
Bonetti
Lorenzo
L
Vivoli
Paolo
P
Benedetti
Tommaso
T
Binazzi
Barbara
B
Laveneziana
Pierantonio
P
Scano
Giorgio
G
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