Familial respiratory chemosensitivity does not predict hypercapnia of patients with sleep apnea-hypopnea syndrome

Abstract

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 PaCO2, 29 patients with polysomnographic evidence of SAHS were divided into those with chronic hypercapnia (PaCO2 greater than or equal to 45 mm Hg, n = 13) and those with normocapnia (PaCO2 less than 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 PaCO2 of patients and slopes of HCVR or HVR of their family members.(ABSTRACT TRUNCATED AT 250 WORDS)