Normal values for the hypercapnic ventilation response: effects of age and the ability to ventilate

Normal values reported for the hypercapnic ventilation response (HCVR) vary considerably, but the reported normal values have come from studies containing small sample sizes and/or the subjects were young or of unidentified age. We speculated that age has a major effect on HCVR due to the generally lower maximal ventilation (VEmax) of elderly subjects. Therefore, we performed a large study to more accurately define the normal range and to reveal any effects which age and sex might have on HCVR. We studied 181 normal subjects (69 males, 112 females) between the ages of 20 and 93 years. Prior to measuring HCVR we measured forced expired volume in 1 s (FEV1) and forced vital capacity to establish whether lung function was normal and to obtain an estimate of VEmax. Results for the entire group revealed a significant correlation between FEV1 and HCVR [HCVR = 0.51 + (0.33 FEV1), r = 0.43, p < 0.001], so it is clear that the ability to ventilate can influence HCVR. We also found a significant correlation between age and HCVR [HCVR = 2.08-(0.01.age), r = 0.34, p < 0.001]. The mean HCVR for our male group (1.86 +/- 0.54 l/min.mm Hg) was significantly higher (p < 0.001) than that for the females (1.37 +/- 0.60) even though their mean ages were similar (41.3 vs. 41.7 years, respectively). We expect that this difference in HCVR was due to the higher FEV1 in males compared to females (3.82 vs. 2.83 liter, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)