Aims: 

Upper airway muscle dysfunction is implicated in obstructive sleep apnoea (OSA). Agents that improve respiratory muscle performance may be useful as an adjunct therapy. The aim of this study was to examine the effects of superoxide scavengers on rat pharyngeal dilator muscle contractile properties.

Methods: 

Adult male Wistar rats were killed humanely and isometric contractile properties of isolated strips of sternohyoid muscle were examined in aerated physiological salt solution at 35°C in vitro. Muscles were incubated in tissue baths under hyperoxic (95%O₂/5%CO₂) or hypoxic (95%N₂/5%CO₂) conditions in the absence (control) or presence of the antioxidants: Tiron (10mM) or Tempol (10mM). Force-frequency relationship was determined in response to supra-maximal stimulation (10-100Hz, 300msec).

Results: 

Under hyperoxic conditions, both Tiron and Tempol significantly increased sternohyoid muscle force and caused a left-shift in the force-frequency relationship. Thus peak force was 17 ± 2, 22 ± 2* 27 ± 1* N/cm² for control (n = 9), Tiron (n = 8) and Tempol-incubated (n = 9) muscles (*p < 0.01 ANOVA). The EF50 ie stimulus frequency producing 50% of peak force was 66 ± 4Hz for control, 56 ± 4* for Tiron and 49 ± 2* for Tempol, p < 0.01 ANOVA. Sternohyoid muscle force was significantly lower in hypoxia compared to hyperoxia for all groups. Tempol-incubated muscles generated significantly more force than control muscles in hypoxia at stimulus frequencies ranging from 60-100Hz.

Conclusions: 

This study illustrates that superoxide scavengers increase upper airway muscle force and protect against hypoxia-induced decreases in muscle performance. We conclude that antioxidant therapy may be beneficial in the treatment of OSA.

Supported by the Health Research Board of Ireland and University College Dublin.