The effect of diet-induced obesity on sleep and breathing in female mice.

Obesity and male sex are main risk factors for sleep-disordered breathing (SDB). We have shown that male diet-induced obesity (DIO) mice develop hypoventilation, sleep apnea, and sleep fragmentation. The effects of DIO on breathing and sleep architecture in females have not been investigated. We hypothesized that female mice are less susceptible to the detrimental effects of DIO on sleep and SDB compared to males. Female DIO-C57BL/6J and lean C57BL/6J mice underwent 24-hour metabolic studies and were exposed to 8% CO2 to measure the hypercapnic ventilatory response (HCVR), and sleep studies. Ventilatory response to arousals was calculated as ratio of the average and peak minute ventilation (VE) during each arousal relative to the baseline VE. Breathing stability was measured with Poincaré plots of VE. Female obesity was associated with decreased metabolism, indicated by reduced oxygen consumption (VO2) and CO2 production (VCO2). VE in 8% CO2 and HCVR were significantly attenuated during wakefulness. NREM sleep duration was reduced in DIO mice, but REM sleep was preserved. Ventilation during NREM and REM sleep was augmented compared to lean mice. Arousal frequency was similar between groups. Obesity increased the frequency of spontaneous arousals, whereas the apnea index was 4-fold reduced in DIO compared to lean mice. Obesity decreased pre- and post-apnea arousals. Obese mice had more stable breathing with reduced ventilatory response to arousals, compared to lean females. We conclude that obese female mice are protected against SDB, which appears to be related to an attenuated CO2 responsiveness, compared to the lean state.