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J Appl Physiol 86: 1785-1792, 1999;
8750-7587/99 $5.00
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Vol. 86, Issue 6, 1785-1792, June 1999

Respiratory energetics during exercise at high altitude

Fabio Cibella1, Giuseppina Cuttitta1, Salvatore Romano1, Bruno Grassi2, Giovanni Bonsignore1, and Joseph Milic-Emili3

1 Istituto di Fisiopatologia Respiratoria del Consiglio Nazionale delle Ricerche, Palermo 90146; 2 Istituto di Tecnologie Biomediche Avanzate del Consiglio Nazionale delle Ricerche, Milan, Italy 20100; and 3 Meakins-Christie Laboratories, McGill University, Montreal, Quebec, Canada H2X 2P2

The purpose of this study was to assess the effect of high altitude (HA) on work of breathing and external work capacity. On the basis of simultaneous records of esophageal pressure and lung volume, the mechanical power of breathing (Wrs) was measured in four normal subjects during exercise at sea level (SL) and after a 1-mo sojourn at 5,050 m. Maximal exercise ventilation (VEmax) and maximal Wrs were higher at HA than at SL (mean 185 vs. 101 l/min and 129 vs. 40 cal/min, respectively), whereas maximal O2 uptake averaged 2.07 and 3.03 l/min, respectively. In three subjects, the relationship of Wrs to minute ventilation (VE) was the same at SL and HA, whereas, in one individual, Wrs for any given VE was consistently lower at HA. Assuming a mechanical efficiency (E) of 5%, the O2 cost of breathing at HA and SL should amount to 26 and 5.5% of maximal O2 uptake, whereas for E of 20% the corresponding values were 6.5 and 1.4%, respectively. Thus, at HA, Wrs may substantially limit external work unless E is high. Although at SL VEmax did not exceed the critical VE, at which any increase in VE is not useful in terms of body energetics even for E of 5%, at HA VEmax exceeded critical VE even for E of 20%.

chronic hypoxia; respiratory muscles; muscle efficiency; work of breathing


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