Novel whole body plethysmography system for the continuous characterization of sleep and breathing in a mouse

Abstract

Sleep is associated with marked alterations in ventilatory control that lead to perturbations in respiratory timing, breathing pattern, ventilation, pharyngeal collapsibility, and sleep-related breathing disorders (SRBD). Mouse models offer powerful insight into the pathogenesis of SRBD; however, methods for obtaining the full complement of continuous, high-fidelity respiratory, electroencephalographic (EEG), and electromyographic (EMG) signals in unrestrained mice during sleep and wake have not been developed. We adapted whole body plethysmography to record EEG, EMG, and respiratory signals continuously in unrestrained, unanesthetized mice. Whole body plethysmography tidal volume and airflow signals and a novel noninvasive surrogate for respiratory effort (respiratory movement signal) were validated against simultaneously measured gold standard signals. Compared with the gold standard, we validated 1) tidal volume (correlation, R(2) = 0.87, P < 0.001; and agreement within 1%, P < 0.001); 2) inspiratory airflow (correlation, R(2) = 0.92, P < 0.001; agreement within 4%, P < 0.001); 3) expiratory airflow (correlation, R(2) = 0.83, P < 0.001); and 4) respiratory movement signal (correlation, R(2) = 0.79-0.84, P < 0.001). The expiratory airflow signal, however, demonstrated a decrease in amplitude compared with the gold standard. Integrating respiratory and EEG/EMG signals, we fully characterized sleep and breathing patterns in conscious, unrestrained mice and demonstrated inspiratory flow limitation in a New Zealand Obese mouse. Our approach will facilitate studies of SRBD mechanisms in inbred mouse strains and offer a powerful platform to investigate the effects of environmental and pharmacological exposures on breathing disturbances during sleep and wakefulness.

Rodent models of sleep apnea

“…Historically, apneas in rodents have been described as exclusively central events and the upper airway anatomy of mice and rats is more stable than the upper airway of humans. Although the recent work by Hernandez et al (2012) suggests that obese mice can demonstrate flow limitation of the upper airway, it is still unclear whether clinically relevant obstructive apneas occur in sleeping rodents. A potential approach to addressing the question of whether or not rodents have obstructive events would be to utilize diaphragm and/or intercostal EMGs to measure respiratory effort simultaneously with airflow measurements.…”

“…Additionally, leptin-deficient ob/ob mice have defects in upper airway neuromechanical control which is reversed with leptin administration (Polotsky et al, 2012), which suggests that leptin protects against upper airway obstruction in obese mice, and that mice deficient in leptin may be vulnerable to the development of obstructive apnea. In a follow-up study, Hernandez et al (2012) used plethysmography and polysomnography to obtain short-term characterization of sleep and breathing in the New Zealand obese mouse. With adaptation of an infant blood pressure cuff, respiratory movement was estimated and compared to signals of airflow to determine whether reduced upper airway flow occurred in the presence or absence of respiratory movement.…”

Sleep Apnea Research in Animals. Past, Present, and Future

“…The actual demonstration of OSA in rodents was made possible by the development of a plethysmography system by Hernandez and colleagues (13) in 2012. Their system built upon existing technology to measure respiration in unrestrained mice, but with modifications, including continuous measurements of breathing, tidal volume, and respiratory effort.…”

0008 Chemogenetic Stimulation of the Hypoglossal Neurons Improves the Upper Airway Patency

“…The EMG GG was rectified, and a 100 ms time constant was applied to compute the moving average (LabChart Pro 7). Respiratory effort was monitored with a sensing bladder wrapped around the mouse as previously described 35 . DREADD infected mice (n = 13) were treated with clozapine-N-oxide (CNO, 1 mg/kg in saline i.p.)…”