Ventilatory efficiency and exercise tolerance in 101 healthy volunteers

The ventilatory equivalent for CO2 defines ventilatory efficiency largely independent of metabolism. An impairment of ventilatory efficiency may be caused by an increase in either anatomical or physiological dead space, the latter being the most important mechanism in the hyperpnoea of heart failure, pulmonary embolism, pulmonary hypertension and the former in restrictive lung disease. However, normal values for ventilatory efficiency have not yet been established. We investigated 101 (56 men) healthy volunteers, aged 16-75 years, measuring ventilation and gas exchange at rest (n = 64) and on exercise (modified Naughton protocol, n = 101). Age and sex dependent normal values for ventilatory efficiency at rest defined as the ratio ventilation:carbon dioxide output ((V) over dot(E):(V) over dotCO(2)), exercise ventilatory efficiency during exercise, defined as the slope of the linear relationship between ventilation and carbon dioxide output ((V) over dot(E) vs (V) over dotCO(2) slope), oxygen uptake at the anaerobic threshold and at maximum ((V) over dotO(2AT), (V) over dot O-2max respectively) and breathing reserve were established. Ventilatory efficiency at rest was largely independent of age, but was smaller in the men than in the women [(V) over dot(E):(V) over dotCO(2) 50.5 (SD 8.8) vs 57.6 (SD 12.6) P < 0.05]. Ventilatory efficiency during exercise declined significantly with age and was smaller in the men than in the women (men: ((V) over dot(E) vs (V) over dotCO(2) slope = 0.13 x age; 19.9; women: (V) over dot(E) vs (V) over dot CO2 slope = 0.12 x age + 24.4). The (V) over dot(2AT) and (V) over dot O-2max were 23 (SD 5) and 39 (SD 7) ml O-2 . kg.min(-1) in the men and 18 (SD 4) and 32 (SD 7) in the women, respectively, and declined significantly with age. The (V) over dot O-2AT was reached at 58 (SD 9)9% (V) over dot O-2max. Breathing reserve at the end of exercise was 41% and was independent of sex and age. It was concluded from this study that ventilatory efficiency as well as peak oxygen uptake are age and sex dependent in adults.