Ventilatory responses to hypercapnia and hypoxia in elite breath-hold divers

It was recently hypothesized that elite breath-hold divers may display blunted ventilatory responses to hypoxia and/or hypercapnia (Ferretti et al., J. Appl. Physiol. 70: 794-802, 1991). To test his hypothesis, the following measurements were made on three elite breath-hold divers (members of the same family), and on 9 healthy untrained control subjects (C): (1) Steady-state pulmonary ventilation (V̇E) at rest in the supine posture while breathing room air or normoxic CO2-enriched mixtures. (2) Breath-by-breath V̇E changes (ΔV̇E), with respect to baseline conditions, after 4 breaths of 100% O2, under the following conditions: normoxia (PIOjavax.xml.bind.JAXBElement@3754e586 = 146 Torr) at rest (NR); normoxic exercise (60 watt on a bicycle ergometer) (NE); hypoxia (PIOjavax.xml.bind.JAXBElement@513ab0b6 = 77 Torr) at rest (HR); hypoxic exercise (HE). The results were as follows: (1) In hypercapnic experiments V̇E (normalized per unit of body surface area) was significantly lower in the divers than in C (4.32±0.04 [x±SD] L·min-1·m-2 vs. 5.31±0.62 at FICOjavax.xml.bind.JAXBElement@7a2349d4=1.5%; 5.21±0.17 vs. 7.72±1.39 at FICO2=3%; 8.86±0.76 vs. 13.14±2.27 at FICO2=5%), as well as than in subjects described by previous authors as being characterized by 'low CO2 sensitivity'. (2). The 100% O2-breathing maneuvers did not induce significant ΔV̇E both in NR and in HR, whereas peak ΔV̇E were -6.73±1.38 L·min-1 (divers) vs. -5.24±3.10 (C) in NE, and -17.39±4.92 (divers) vs. -17.25±6.32 (C) in HE (no significant differences). It is concluded that the divers, compared to C, had a blunted ventilatory response to hypercapnia, but not to hypoxia. The former may represent an adaptive or genetically inherited phenomenon. © 1994.