Craniofacial morphology, head posture, and nasal respiratory resistance in obstructive sleep apnoea: an inter-ethnic comparison

The aim of this study was to measure craniofacial morphology and nasal respiratory resistance (NRR) in Malay, Indian and Chinese subjects with obstructive sleep apnoea (OSA). The sample consisted of 34 male subjects, 27-52 years of age (Malay n = 11, which included five mild and six moderate-severe OSA; Indian n = 11, which included six mild and five moderate-severe OSA; and Chinese n = 12, which included six mild and six moderate-severe OSA) diagnosed using overnight polysomnography. After use of a decongestant, NRR was recorded using anterior and posterior rhinomanometry. Standardized lateral cephalometric radiographs were used to record linear and angular dimensions. Malay subjects with moderate-severe OSA had a shorter maxillary (sp-pm) and mandibular (gn-go) length when compared with a mild OSA reference sample (P < 0.05). The hyoid bone was located more caudally in the Chinese moderate-severe subjects (hy-NL, hy-ML)(P < 0.05), and may be a useful diagnostic indicator for severity in this racial group. No pattern of differences for NRR was seen between the moderate-severe and mild OSA subjects. The consistently lower values for nasopharyngeal resistance in all the moderate-severe subjects when compared with the mild group may indicate that some compensation at this level of the airway had taken place. Strong positive correlations between craniocervical angulation (NL/OPT) and total airway resistance and the turbulent component of flow (k(2)) suggest that head posture is sensitive to fluctuations in airway resistance (P < 0.01).