Previously we showed that CO2 drive is increased in patients with obstructive sleep apnea (OSA). In the present study we would like to evaluate a possible relationship between CO2 drive and characteristics of apneas in obstructive and central sleep apnea (CSA). We compared the hypercapnic ventilatory response (HCVR) between patients with OSA and CSA. HCVR was correlated with total event time and mean event duration in both groups. 17 normocapnic patients in each group and 14 controls were studied. The apnea patients were matched for apnea-hypopnea index, age, sex, and BMI. SHCVR (slope) tended to be higher in apnea patients than in controls without statistical significancy: controls 1.65 (0.16), CSA 2.17 (0.22), OSA 2.55 (0.35) (l/min per mmHg) (P = 0.13). A significant correlation was found between HCVR and event time in CSA (0.52, P = 0.04) and between HCVR and apnea mean duration in OSA (r = 0.52, P = 0.04). We conclude that while CO2 drive was not statistically increased in both apnea types, small changes can contribute to breathing instability and may increase the total event time (in CSA) but may also shorten the apnea duration (in OSA).