Age-related Variation of Respiratory Chemosensitivity in Monozygotic Twins1,2

To examine age-related variations in respiratory chemosensitivity to hypoxia and hypercapnia, the magnitudes of within-pair variances for ventilatory responses to hypoxia and hypercapnia were measured in 38 pairs of male monozygotic twins. Mean values for the slope factor of end-tidal Po2-ventilation hyperbola (A) were larger in Group I (13 pairs with a mean age of 16.3 ± SD 0.9 yr) than those in Group II (12 pairs with a mean age of 29.8 ± 6 yr), and Group III (13 pairs with a mean age of 46 ± 7.2 yr). The slope factors for end-tidal Pco2-ventilation line (S) were similar among the 3 groups. Within-pair variances for A, A/body surface area (BSA), and (asymptote for ventilation when end-tidal Po2 is infinite) were larger in Groups II and III than in Group I. Within-pair variances for S and S/BSA were also larger in Groups II and III than in Group I, whereas within-pair variances for B (intercept with end-tidal Pco2) were similar among the 3 groups. These results indicate that variations for respiratory ch...