title: Diver respiratory responses to a tunable closed-circuit breathing apparatus.
abstract: Respiratory impedance of closed-circuit underwater breathing apparatus (UBA) is comprised of resistive, elastic, and inertial elements in series. Impedance is at a minimum when a UBA operates at its resonant frequency (f(n)). This study investigated the respiratory responses of 12 male U.S. Navy divers to changes in the f(n) of a simulated closed-circuit UBA. Respiratory effort, breathing comfort and ventilatory parameters were assessed during open- and closed-circuit breathing at rest and while exercising at 75 W on a bicycle ergometer in the dry at 1 atm abs. During closed-circuit breathing, the f(n) of the system was adjusted to different frequencies between 0.2 Hz and 0.4 Hz (12 and 24 breaths/min) by varying UBA inertance. When the simulated UBA was switched from open to closed-circuit breathing the subjects changed their breathing frequency in a direction toward the f(n) of the system and attempted to maintain minute ventilation constant by adjusting tidal volume. Results suggest that when divers breathe on a closed-circuit system with different f(n)'s they attempt to improve breathing comfort and reduce respiratory effort by adopting a breathing pattern that reduces their peak-to-peak mouth pressures.
authors.affiliation: Naval Medical Research Institute, Bethesda, Maryland 20889-5607, USA.
authors.forename: D M
authors.initials: DM
authors.lastname: Fothergill
authors.forename: D D
authors.initials: DD
authors.lastname: Joye
authors.forename: N A
authors.initials: NA
authors.lastname: Carlson
mesh_terms: D000328:Adult; D002138:Calibration; D004242:Diving / Q000502:physiology*; D004867:Equipment Design; D005080:Exercise Test; D006801:Humans; D008297:Male; D012119:Respiration / Q000502:physiology*; D014939:Work of Breathing / Q000502:physiology