FAMILIAL RESPIRATORY CHEMOSENSITIVITY DOES NOT PREDICT HYPERCAPNIA OF PATIENTS WITH SLEEP-APNEA-HYPOPNEA SYNDROME

The mechanisms of hypercapnia observed in some patients with sleep apnea-hypopnea syndrome (SAHS) are not known. In chronic obstructive lung disease (COLD), hypercapnic and hypoxic ventilatory responses (HCVR/HVR) are decreased in normal family members of hypercapnic patients compared with those of non-hypercapnic patients. This suggests a familial (presumably genetic) diminished chemosensitivity predisposing to hypercapnia. In this study we investigated the possibility of a similar mechanism in SAHS. Based on Pa(CO2), 29 patients with polysomnographic evidence of SAHS were divided into those with chronic hypercapnia (Pa(CO2) greater-than-or-equal-to 45 mm Hg, n = 13) and those with normocapnia (Pa(CO2) < 45 mm Hg, n = 16). We studied healthy adult (greater-than-or-equal-to 17 yr) immediate family members of these patients. Family members were required to have normal spirometry and be on no medications. In Group I, there were 32 family members of hypercapnic patients and in Group II, 26 family members of normocapnic patients. In Group I, the mean (+/- SD) of age (yr) was 36 +/- 12, weight (kg) 82 +/- 22, FEV1 (L) 3.1 +/- 0.8, VCO2 (ml/min) 228 +/- 63, slope (L/min) of HCVR 2.0 +/- 0.8, and slope (L/min/1% saturation) of HVR -1.20 +/- 0.82. Respective values in Group II were 34 +/- 14, 83 +/- 16, 3.2 +/- 0.8, 233 +/- 63, 2.0 +/- 1.0, and -1.34 +/- 1.20. There were no statistically significant differences in measured variables between the two groups. Furthermore, there were no significant correlations between Pa(CO2) of patients and slopes of HCVR or HVR of their family members. In contrast, the mean values of slopes of HVR (-0.32 versus -1.15 L/min/1% saturation) and HCVR (1.04 versus 2.31 L/min) were significantly lower in hypercapnic patients compared with normocapnic patients. Our results do not support the hypothesis that familial diminished chemosensitivity to hypercapnia or hypoxemia could explain hypercapnia in patients with SAHS.