The cross-sectional area of the upper airway is known to be lung volume dependent. If, and to what extent, lung volume variables correlate to nocturnal obstructive apnoeas and oxygen desaturations independently of other factors known to affect lung volumes and sleep disordered breathing is still unclear. A total of 92 subjects were examined by ambulatory recording of nocturnal obstructive apnoeas and desaturations. Sixty-nine of the subjects had a history of snoring and 23 were healthy subjects without complaints of snoring and daytime sleepiness. All subjects performed static and dynamic spirometry for measurements of lung volumes. To evaluate the correlation between lung volume variables and apnoea index (AI) and oxygen desaturation index (ODI), simple and multiple regression analysis was performed. Expiratory reserve volume (ERV) was found to be lower in subjects with snoring and apnoeas (ERV = 1.0 l) than in non-snoring subjects (ERV = 1.7 l), (P<0.001). Forced expiratory volume in 1 sec (FEV1)/vital capacity (VC) was slightly, but significantly (P = 0.031), lower in subjects with snoring and nocturnal apnoeas and desaturations. In the multiple regression analysis ERV was found to be independently correlated to both AI (R2=0.13; P=0.001) and ODI (R2 = 0.11; P = 0.002). Multiple regression analysis also revealed that ERV, body mass index (BMI) and habitual smoking together accounted for 43% of the variation in AI and 48% of the variation in ODI. We find a significant independent association between ERV and nocturnal obstructive apnoea and oxygen desaturation frequency. Our results indicate that ERV is correlated to these events to a similar extent, as is obesity.

No abstract

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.

The same questionnaire and study design was used in two surveys of asthma among all the children attending the 9-y compulsory school in Sundsvall in 1985 (n = 10527) and 1995 (n = 9165). A detailed questionnaire was distributed by post to the parents of all children who had answered in the affirmative to a simple screening question on asthmatic symptoms at the beginning of the autumn term. The questionnaire contained detailed questions on symptoms and asthma management. Our findings indicated a moderate increase in reported asthma-like symptoms and physician-diagnosed asthma between 1985 and 1995. The severity of symptoms was unchanged, despite a large community-based asthma campaign and a tenfold increase in the number of children receiving inhaled steroids. A validation analysis included an interview by a physician, a skin prick test, determination of specific IgE antibodies and spirometry. The oral interviews suggested that undertreatment was common. Many children had adequate medication at home, but this medication was not used properly. Finally, all 13-14-y-old children also replied to written and video questionnaires from the International Study of Asthma and Allergies in Childhood (ISAAC). It is likely that differences in study design explained the much higher prevalence of wheezing in this part of the study.