title: Divers revisited: The ventilatory response to carbon dioxide in experienced scuba divers.
abstract: OBJECTIVE
  To investigate the ventilatory response to CO2 in hyperoxia, hypoxia, and during exercise amongst experienced scuba divers and matched controls.
  
  
  METHODS
  Two studies were performed. The first investigated the CO2 sensitivity in rest and exercise using CO2 rebreathing in hyperoxia at a workload typical for diving with divers (n = 11) and controls (n = 11). The second study examined the respiratory drive of divers (n = 10) and controls (n = 10) whilst breathing four different gas mixtures balanced with N2 (ambient air; 25% O2/6% CO2; 13% O2; 13% O2/6% CO2) to assess the combined response to hypercapnia and moderate hypoxia.
  
  
  RESULTS
  Exercise at a load typical for diving was found to have no effect on the ventilatory sensitivity to CO2 in divers (rest: 1.49 ± 0.33; exercise: 1.22 ± 0.55 [l/min × mmHg(-1)]) and controls (rest: 2.08 ± 0.71; exercise: 2.05 ± 0.98 [l/min × mmHg(-1)]) while differences in sensitivity remained between the groups. Inhalation of the four gas mixtures revealed the tested oxygen pressures caused no significant alteration in the ventilatory sensitivity to CO2 in divers and controls.
  
  
  CONCLUSIONS
  Experienced divers possess a lower ventilatory response to CO2 which was not affected by exercise or the tested oxygen pressures suggesting a dominant adaptation of central CO2 sensitivity.
authors.affiliation: School of Sport, Health and Exercise Sciences, Bangor University, Gwynedd, Wales LL57 2PZ, UK; Cardio-Respiratory and Vascular Department, Countess of Chester Hospital, NHS Foundation Trust, Chester, England CH2 1UL, UK. Electronic address: christopher.earing@nhs.net.
authors.forename: Christopher Matthew Norton
authors.initials: CM
authors.lastname: Earing
authors.affiliation: Respiratory Department, Ysbyty Gwynedd, BCUHB, Penrhosgarnedd, Gwynedd, Wales LL57 2PW, UK.
authors.forename: Damian John
authors.initials: DJ
authors.lastname: McKeon
authors.affiliation: School of Sport, Health and Exercise Sciences, Bangor University, Gwynedd, Wales LL57 2PZ, UK.
authors.forename: Hans-Peter
authors.initials: HP
authors.lastname: Kubis
mesh_terms: D000328:Adult; D002245:Carbon Dioxide / Q000097:blood; D004242:Diving / Q000502:physiology*; D015444:Exercise / Q000502:physiology; D005541:Forced Expiratory Volume / Q000502:physiology; D006801:Humans; D006935:Hypercapnia / Q000097:blood / Q000503:physiopathology*; D000860:Hypoxia / Q000097:blood / Q000503:physiopathology; D008297:Male; D009043:Motor Activity / Q000502:physiology; D010313:Partial Pressure; D014797:Vital Capacity / Q000502:physiology; D055815:Young Adult
chemical_list: D002245:Carbon Dioxide
keywords: Chemosensitivity; Diving; Exercise; Hypercapnia; Hypoxia