Intermittent hypoxia reduces upper airway stability in lean but not obese Zucker rats

Abstract

Obstructive sleep apnea involves intermittent periods of airway occlusions that lead to repetitive oxygen desaturations. Exposure to chronic intermittent hypoxia (IH) in rats increases diurnal blood pressure and alters skeletal muscle physiology. The impact of IH on upper airway muscle function is unknown. We hypothesize that IH exposure increases upper airway collapsibility in rats due to alterations of the muscles surrounding the upper airway. Lean and obese rats were exposed to cyclic alterations in O(2) levels (20.6%-5%) every 90 s, 8 h/day for 6 days/wk for 12 wk. Following the exposure period, arterial pressure was recorded via the tail artery in conscious unrestrained rats. Mean arterial pressure was increased in lean IH but not in obese IH-exposed Zucker rats (P < 0.05). The pharyngeal pressure associated with airway collapse (P(crit)) was measured under anesthesia during baseline conditions and then during supramaximal stimulation of the hypoglossal nerve (cnXII). Baseline P(crit) was more positive (more collapsible) in lean but not obese rats following 12 wk of IH (P < 0.05), while supramaximal stimulation of cnXII increased airway stability (decreased P(crit)) in both lean and obese Zucker rats following IH to levels that were similar to their respective room air controls. The in vitro peak tension and the expression of the individual myosin heavy chain isoforms from the upper airway muscles were unaltered following IH. We conclude that IH leads to increases in baseline collapsibility in lean Zucker rats exposed to IH by nonmyogenic mechanisms.

Structural and Functional Properties of an Upper Airway Dilator Muscle in Aged Obese Male Rats

“…Fibre type transformation (oxidative to glycolytic) and decreased SDH activity were seen in aged obese sternohyoid muscle, consistent with previous reports for this muscle in aged rats [5,9] and other aged upper airway muscles [10], while increased GPDH activity was observed in keeping with a previous report in aged rat [5]. Interestingly, there was no evidence of increased lipid peroxidation (a marker of oxidative stress in tissues) in aged obese sternohyoid muscle, though this has been reported in limb muscle of older rats [11,12].…”

“…Retropharyngeal fat pads may predispose to airway obstruction, and aging of airway musculature may weaken their ‘splinting’ action on the upper respiratory tract. Previous studies on the aged Fisher rat [4] and the Zucker fatty rat [5,6] have examined these factors in isolation and found no effect on peak force production, but the combination of these factors may overwhelm the working muscle. Therefore, we decided to study the structure and function of an upper airway dilator muscle (sternohyoid) in young lean and old obese male rats.…”

Vitamin D3 intake modulates diaphragm but not peripheral muscle force in young mice

“…Once the desired intensity was achieved, the destain was removed, the gel was washed with ddH2O, and the staining was visualized and quantified (BioRad GelDoc EZ system, ImageLab software). MHC I, IIb, IIa, and IIx distribution was determined on the basis of migration, per previously described methods (25). Statistical analysis.…”

Dim light at night interacts with intermittent hypoxia to alter cognitive and affective responses

“…During this treatment, mice were moved to custom-designed Plexiglas chambers (31 cm ϫ 19 cm ϫ 18 cm) with a raised floor (6.5 cm); 10 mice were placed in one chamber at a time (30). Oxygen levels were controlled by connecting the cages via a regulator system to compressed air and nitrogen tanks.…”