The Effects of Breathing He–O₂ Mixtures on Maximal Oxygen Consumption in Normoxic and Hypoxic Men

Abstract

The hypothesis that the ventilatory resistance to O2 flow (RV) does limit maximal O2 consumption (V̇O2 max) in hypoxia, but not in normoxia, at least in non‐athletic subjects, was tested. RV was reduced by using He–O2 mixtures. V̇O2, max was measured during graded cyclo‐ergometric exercise in eight men (aged 30 ± 3 years) who breathed N2–O2 and He–O2 mixtures in normoxia (inspired oxygen fraction (FI,O2= 0.21) and hypoxia (FI,O2= 0.11). O2 consumption, expired and alveolar ventilations (V̇E and V̇A, respectively), blood lactate and haemoglobin concentrations, heart rate and arterial oxygen saturation (Sa,O2) were determined at the steady state of each work load. Arterial O2 and CO2 partial pressures (Pa,O2) and Pa,CO2, respectively) were measured at rest and at the end of the highest work load. Maximal V̇E and V̇A were significantly increased by He—O2 breathing in normoxia (+27 and +18%, respectively), without significant changes in Pa, O2, Sa, O2V̇O2, max In hypoxia, V̇E and V̇A increased (+31 and +24%, respectively), together with Pa,O2 (+17%), Sa, O2 (+6%) and V̇O2, max (+14%). The results support the hypothesis that the role of RV in limiting V̇O2,max is negligible in normoxia. In hypoxia, the finding that higher V̇E and V̇A values during He–O2 breathing led to higher V̇O2,max values suggests a greater role of RV as a limiting factor. It is unclear whether the finding that the V̇O2 max values were the same during He–O2 and N2–O2 breathing in normoxia is due to a non‐linear response of the O2 transfer system, as previously proposed.

Acute respiratory muscle unloading by normoxic helium–O2 breathing reduces the O2 cost of cycling and perceived exertion in obese adolescents

“…Previous studies carried out on . V O 2 peak with normoxic helium breathing in normal subjects observed no changes (Esposito and Ferretti 1997), an increase (Brice and Welch 1983;Powers et al 1986) or a decrease (Murphy et al 1969) of the variable. The present study does not allow further insights into the possible reasons for these conflicting results.…”

“…Also the calibration of the pneumotachograph was carried out by utilizing the experimental gas mixture (AIR or He-O 2 ). The possibility of this technical limitation was not mentioned in the studies by Brice and Welch (1983), Chiappa et al (2009), Esposito and Ferretti (1997), Louvaris et al (2012), Murphy et al (1969), Powers et al (1986).…”

Air to Muscle O2Delivery during Exercise at Altitude

“…The drop in Sao 2 that occurs with exercise in hypoxia is inversely related to HVR, explaining why sojourners with high HVR may perform better at extreme altitude (Schoene et al, 1984). In addition, replacing the N 2 -O 2 gas mixture by helium-O 2 (both with a Fio 2 ¼ 0.11) allowed increases in V Emax by 31%, Pao 2 by 17%, Sao 2 by 6%, and Vo 2max by 14% (Esposito and Ferretti, 1997), thus emphasizing the impact of hyperventilation on O 2 transport and exercise capacity in hypoxia. (Sutton et al, 1988).…”

An analysis of performance in human locomotion

“…Attention is centered on blood flow, which provides most of the limit to _ VO 2max . The above differences of course have led to markedly different experimental conceptions in testing di Prampero's (Bringard et al 2010;Esposito and Ferretti 1997;Ferretti et al 1997a, b; but see also Brink-Elfegoun et al 2007) and Wagner's (Knight et al 1993;Richardson et al 1995a, b;Schaffartzik et al 1993) _ VO 2max limitation models. Both models have drawbacks, but they share a great advantage with respect to other approaches proposed so far: i.e.…”