Optimal continuous positive airway pressure in patients with obstructive sleep apnoea: role of craniofacial structure

Although nasal continuous positive airway pressure (CPAP) is effective in i mproving nocturnal obstructive apnoea, daytime sleepiness and well-being in patients with obstructive sleep apnoea syndrome (OSAS), not all patients t olerate this treatment. Since optimal CPAP titration is essential to mainta in compliance. it is important to elucidate the factors that help to determ ine the optimal pressure. However. the determinants of the optimal CPAP lev el are controversial. The subjects comprised 27 Japanese male patients with OSAS who underwent st andard polysomnography (PSG), pulmonary function tests. arterial blood gas analysis, cephalometry and CPAP titration. Twenty normal controls also unde rwent cephalometric analysis. The apnoea-hypopnoea index (AHI), mean oxygen saturation (mean SaO(2)) and the lowest SaO(2)during sleep were found to be 54(.)7 +/- 22(.)6, 89(.)0 +/ -5(.)6%, and 69(.)7 +/-9(.)0%, respectively by PSG. The mean optimal CPAP w as 9(.)6 +/-1(.)8cmH(2)O. The cephalometric angles (SNA, SNB and NSBa) were similar to those found in the control subjects, but MP-H. and PNS-P were s ignificantly longer than those in the control subjects as shown by cephalom etry. The optimal CPAP was correlated with the mean SaO(2) (P < 0(.)0001), neck circumference (P <0(.)05) and three cephalometric variables (NSBa: P < 0.01, MP-H: P <0(.)05, PNS-P: P <0(.)05). Multiple. step-wise, regression a nalysis showed that the mean SaO(2) and NSBa were independent variables tha t best predicted the optimal CPAP. These variables accounted for 57(.)5% of the total variance (R-2=0(.)575, P <0(.)001). Optimal CPAP was closely correlated with oxygen desaturation during sleep. However: the craniofacial structure had additional effects such as an indep endent factor in determining the optimal CPAP level.