Ventilatory response to CO2 in patients with snoring, obstructive hypopnoea and obstructive apnoea.
Obstructive sleep apnoea (OSA) is caused by an obstruction of the upper airway. Sufficient sensitivity to CO2 in the respiratory centre is known to be a critical factor for adequate tone in the upper airway muscles. The hypothesis of this study is, therefore, that the ventilatory response to CO2 is reduced in patients with OSA. Twenty-six patients who suffered from snoring, 19 snoring patients with obstructive hypopnoea (OH) and 33 snoring patients with obstructive apnoea (OA), were studied. The control group consisted of 25 subjects from a random sample with no history of snoring or daytime sleepiness. Tests of the hyperoxic and hypoxic ventilatory response to CO2 were performed, as well as static and dynamic spirometry. Subjects in the OA group displayed a higher hyperoxic (VE/FetCO2hy = 12.6 l min-1/%) and hypoxic (VE/FetCO2ho = 15.7 l min-1/%) ventilatory response to CO2 than patients with obstructive hypopnoea (VE/FetCO2hy = 8.6 l min-1/%; VE/FetCO2ho = 15.2 l min-1/%), snorers (VE/FetCO2hy = 8.4 l min-1/%; VE/FetCO2ho = 12.7 l min-1/%) and non-snorers (VE/FetCO2hy = 7.6 l min-1/%; VE/FetCOho = 9.6 l min-1/%). Multiple regression analysis reveals that neck circumference, apnoea index, oxygen desaturation index, PCO2 and sex (male gender) are correlated with VE/FetCO2hy (R2 = 0.43). Multiple regression analysis also reveals that ERV (expiratory reserve volume) and sex (male gender) are correlated with VE/FetCO2ho (R2 = 0.21). Arguing against the hypothesis, patients with OSA displayed an increased hyperoxic and hypoxic ventilatory response to CO2. Nocturnal apnoea frequency and the obesity factor in OSA may have contributed to these results.