title: Predictors of increased PaCO2 during immersed prone exercise at 4.7 ATA.
abstract: During diving, arterial Pco(2) (Pa(CO(2))) levels can increase and contribute to psychomotor impairment and unconsciousness. This study was designed to investigate the effects of the hypercapnic ventilatory response (HCVR), exercise, inspired Po(2), and externally applied transrespiratory pressure (P(tr)) on Pa(CO(2)) during immersed prone exercise in subjects breathing oxygen-nitrogen mixes at 4.7 ATA. Twenty-five subjects were studied at rest and during 6 min of exercise while dry and submersed at 1 ATA and during exercise submersed at 4.7 ATA. At 4.7 ATA, subsets of the 25 subjects (9-10 for each condition) exercised as P(tr) was varied between +10, 0, and -10 cmH(2)O; breathing gas Po(2) was 0.7, 1.0, and 1.3 ATA; and inspiratory and expiratory breathing resistances were varied using 14.9-, 11.6-, and 10.2-mm-diameter-aperture disks. During exercise, Pa(CO(2)) (Torr) increased from 31.5 +/- 4.1 (mean +/- SD for all subjects) dry to 34.2 +/- 4.8 (P = 0.02) submersed, to 46.1 +/- 5.9 (P < 0.001) at 4.7 ATA during air breathing and to 49.9 +/- 5.4 (P < 0.001 vs. 1 ATA) during breathing with high external resistance. There was no significant effect of inspired Po(2) or P(tr) on Pa(CO(2)) or minute ventilation (Ve). Ve (l/min) decreased from 89.2 +/- 22.9 dry to 76.3 +/- 20.5 (P = 0.02) submersed, to 61.6 +/- 13.9 (P < 0.001) at 4.7 ATA during air breathing and to 49.2 +/- 7.3 (P < 0.001) during breathing with resistance. We conclude that the major contributors to increased Pa(CO(2)) during exercise at 4.7 ATA are increased depth and external respiratory resistance. HCVR and maximal O(2) consumption were also weakly predictive. The effects of P(tr), inspired Po(2), and O(2) consumption during short-term exercise were not significant.
authors.affiliation: Department of Anesthesiology, Duke University Medical Center, Durham, NC 27710, USA.
authors.forename: A D
authors.initials: AD
authors.lastname: Cherry
authors.forename: I F
authors.initials: IF
authors.lastname: Forkner
authors.forename: H J
authors.initials: HJ
authors.lastname: Frederick
authors.forename: M J
authors.initials: MJ
authors.lastname: Natoli
authors.forename: E A
authors.initials: EA
authors.lastname: Schinazi
authors.forename: J P
authors.initials: JP
authors.lastname: Longphre
authors.forename: J L
authors.initials: JL
authors.lastname: Conard
authors.forename: W D
authors.initials: WD
authors.lastname: White
authors.forename: J J
authors.initials: JJ
authors.lastname: Freiberger
authors.forename: B W
authors.initials: BW
authors.lastname: Stolp
authors.forename: N W
authors.initials: NW
authors.lastname: Pollock
authors.forename: P O
authors.initials: PO
authors.lastname: Doar
authors.forename: A E
authors.initials: AE
authors.lastname: Boso
authors.forename: E L
authors.initials: EL
authors.lastname: Alford
authors.forename: A J
authors.initials: AJ
authors.lastname: Walker
authors.forename: A C
authors.initials: AC
authors.lastname: Ma
authors.forename: M A
authors.initials: MA
authors.lastname: Rhodes
authors.forename: R E
authors.initials: RE
authors.lastname: Moon
mesh_terms: D000222:Adaptation, Physiological; D000328:Adult; D000403:Airway Resistance; D001274:Atmospheric Pressure; D002245:Carbon Dioxide / Q000097:blood*; D004242:Diving / Q000009:adverse effects*; D015444:Exercise; D045853:Exhalation; D005260:Female; D006801:Humans; D006935:Hypercapnia / Q000097:blood / Q000209:etiology* / Q000503:physiopathology; D007101:Immersion; D001239:Inhalation; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D010100:Oxygen / Q000097:blood; D010101:Oxygen Consumption; D010313:Partial Pressure; D016684:Prone Position; D012123:Pulmonary Ventilation; D012126:Respiratory Dead Space; D012143:Respiratory Physiological Phenomena; D012307:Risk Factors; D015854:Up-Regulation; D055815:Young Adult
chemical_list: D002245:Carbon Dioxide; D010100:Oxygen