Upper airway EMG responses to acute hypoxia and asphyxia are impaired in streptozotocin-induced diabetic rats

Obstructive sleep apnoea (OSA) is a major clinical disorder that is characterised by multiple episodes of upper airway obstruction due to failure of the upper airway dilator muscles to maintain upper airway patency. The incidence of OSA is high in many endocrine disorders including both insulin-dependent and non-insulin-dependent diabetes but the reasons for this are not known. We wished to test the hypothesis that central respiratory motor output to the upper airway muscles is preferentially impaired in a rat model of diabetes mellitus. Sternohyoid (SH) and diaphragm (DIA) EMG activities were recorded in control and streptozotocin (STZ)-induced diabetic rats during normoxia, hypoxia (7.5% O₂ in N₂) and asphyxia (7.5% O₂ and 3% CO₂) under pentobarbitone anaesthesia. SH EMG responses to acute hypoxia and asphyxia were significantly impaired in STZ-induced diabetic rats compared to control animals (+47.1±5.7 vs. +11.7±1.9% during hypoxia in control and diabetic animals respectively and +56.5±7.9 vs. +15.7±5.0% during asphyxia). However, DIA EMG responses to hypoxia and asphyxia were not different for the two groups. We propose that the higher prevalence of OSA in diabetic patients is related to preferential impairment of cranial motor output to the dilator muscles of the upper airway in response to physiological stimuli.