Ventilatory responses to exercise and carbon dioxide in elderly and younger humans

Summary

The present investigation examined the relationship between CO₂ sensitivity [at rest (S _R) and during exercise (S _E)] and the ventilatory response to exercise in ten elderly (61–79 years) and ten younger (17–26 years) subjects. The gradient of the relationship between minute ventilation and CO₂ production (Δ$\dot V$ _E/Δ$\dot V$CO₂) of the elderly subjects was greater than that of the younger subjects [mean (SEM); 32.8 (1.6) vs 27.3 (0.4); P<0.01]. At rest, S _R was lower for the elderly than for the younger group [10.77 (1.72) vs 16.95 (2.13) 1 · min⁻¹ · kPa⁻¹; 1.44 (0.23) vs 2.26 (0.28) 1 · min⁻¹ · mmHg⁻¹; P<0.05], but S _E was not significantly different between the two groups [17.85 (2.49) vs 19.17 (1.62) l · min⁻¹ · kPa⁻¹; 2.38 (0.33) vs 2.56 (0.21) 1 · min⁻¹ · mmHg⁻¹]. There were significant correlations between both S _R and S _E, and Δ$\dot V$ _E/Δ$\dot V$CO₂ (P<0.05; P<0.001) for the younger group, bot none for the elderly. The absence of a correlation for the elderly supports the suggestion that Δ$\dot V$ _E/Δ$\dot V$CO₂ is not an appropriate index of the ventilatory response to exercise for elderly humans.