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Respiratory physiology and oxygen therapy
P39 Ventilatory Response Amongst Scuba Divers and Non-Divers
  1. CMN Earing1,
  2. DJ McKeon2,
  3. H-P Kubis1
  1. 1School of Sport, Health and Exercise Science, Bangor
  2. 2University, Bangor, Wales, Respiratory Department, Ysbyty Gwynedd, BCUHB, Bangor, Wales

Abstract

Purpose To investigate the ventilatory response to CO2 in hyperoxia, hypoxia, and during exercise amongst experienced scuba divers and matched controls.

Methods Three studies were performed comparing the ventilatory response to CO2 of experienced scuba divers with non-diving matched controls. The first study measured the ventilatory recruitment threshold (VRT) during CO2 rebreathing in hyperoxia of experienced divers (n=10) and controls (n=10); the second study investigated the CO2 sensitivity in rest and exercise using CO2 rebreathing in hyperoxia at a workload designed to mimic the load of diving with scuba divers (n=11) and controls (n=11). The third study examined the respiratory drive of scuba 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) aimed to assess the combined response to hypercapnia and moderate hypoxia.

Results Experienced divers possessed a higher VRT (P<0.05) coinciding with the accumulation of 7%insCO2(pCO2cap =53.20±2.20 mm Hg) during CO2 rebreathing compared to controls with VRT occurring at 6%insCO2(pCO2cap =44.72±1.74 mm Hg). 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 x mmHg-1]) and controls (rest: 2.08±0.71; exercise: 2.05±0.98 [l/min x mmHg-1]) while differences in sensitivity remained between the groups (P<0.05). Inspiration of the four test gas mixtures revealed there was no contribution of the tested oxygen pressures to the difference in ventilatory sensitivity to CO2 between divers and controls.

Conclusion Divers possess a lower ventilatory response to CO2 which was not affected by exercise or the tested oxygen pressures suggesting an adaptation of central CO2 sensitivity.

Key Words Diving, hypercapnia, hypoxia, chemo sensitivity, exercise

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