Automatic classification of activity and apneas using whole body plethysmography in newborn mice

Abstract

An increasing number of studies in newborn mice are being performed to determine the mechanisms of sleep apnea, which is the hallmark of early breathing disorders. Whole body plethysmography is the method of choice, as it does not require immobilization, which affects behavioral states and breathing. However, activity inside the plethysmograph may disturb the respiratory signal. Visual classification of the respiratory signal into ventilatory activity, activity-related disturbances, or apneas is so time-consuming as to considerably hamper the phenotyping of large pup samples. We propose an automatic classification of activity based on respiratory disturbances and of apneas based on spectral analysis. This method was validated in newborn mice on the day of birth and on postnatal days 2, 5, and 10, under normoxic and hypoxic (5% O(2)) conditions. For both activity and apneas, visual and automatic scores showed high Pearson's correlation coefficients (0.92 and 0.98, respectively) and high intraclass correlation coefficients (0.96-0.99), supporting strong agreement between the two methods. The present results suggest that breathing disturbances may provide a valid indirect index of activity in freely moving newborn mice and that automatic apnea classification based on spectral analysis may be efficient in terms of precision and of time saved.

Breathing without CO2Chemosensitivity in ConditionalPhox2bMutants

“…Breathing variables of P2-P9 pups were measured noninvasively in unanaesthetized, unrestrained pups using whole-body flow barometric plethysmography as described previously (Matrot et al, 2005;Ramanantsoa et al, 2006). Breathing variables of P22 and adult mice were measured using a larger whole-body flow barometric plethysmograph (Dauger et al, 2003).…”

“…Breathing variables were continuously monitored after a 7 min familiarization period in the plethysmograph chambers. Activity periods, which typically included exploratory movements, grooming, and sniffing, were detected based on large disturbances in the respiratory signal caused by the combined effects of positional changes and changes in breathing pattern (Matrot et al, 2005). Breathing variables were analyzed over activity-free periods, which represented Ͼ80% of recording Figure 1.…”

A human mutation in Phox2b causes lack of CO 2 chemosensitivity, fatal central apnea, and specific loss of parafacial neurons

“…Breathing movements were recorded noninvasively in unanaesthesized, unrestrained pups within 20 min after delivery, using whole-body flow barometric plethysmography as described (43,44). A constant bias flow (200 ml/min) prevented CO2 and water accumulation and ambient temperature drifts over time.…”

“…After 5 min in room air, the pups were exposed to hypercapnic (8% CO 2/21% O2/71% N2) air, followed by 10 min in air. Apnoeas, defined as ventilatory pauses longer than twice the duration of the preceding breath, were determined by using an automatic classification method (43). Breathing variables [breath duration (T TOT), tidal volume (VT), and ventilation (VE) calculated as VT/TTOT] were measured on apnea-free periods.…”

Neural control of breathing: insights from genetic mouse models

“…Automatic methods that rely on spectral analysis for apnea detection facilitate phenotype determination in large numbers of mutant animals (51). As a rule, respiratory signals must be processed automatically to achieve reasonably high-throughput physiological screening of newborn mutant pups and to improve the identification of genetic factors involved in early respiratory-control disorders (32).…”