Increased variability in respiratory parameters heralds obstructive events in children with sleep disordered breathing

Sleep disordered breathing (SDB) is characterized by repeated episodes of central or obstructive apneas, disturbing respiratory patterns. The purpose of this study is to quantify respiratory variability associated with apneic/hypopneic events by computing respiratory parameters and thoraco-abdominal asynchrony (TAA) over sleep periods preceding the occurrence of obstructive events in children with SDB. One minute artifact-free epochs of ribcage (RC) and abdominal (AB) signals were extracted from the respiratory inductive plethysmograph (RIP) channel of the PSG prior to the onset of each obstruction. Breath-by-breath values of TAA were computed using a Hilbert transform based technique that measures the phase shift between the RC and AB signals. In addition, the following parameters were computed breath-by-breath from the RC signal: inspiratory time (Ti), expiratory time (Te), total time (Ttot), and the inspiratory duty cycle (DC=Ti/Ttot). Standard deviation of the parameters (SD-TAA, SD-Ti, SD-Te, SD-Ttot, SD-DC) over each 1 min epoch were calculated and averaged over each subject with respect to sleep stage. For comparison, similar measures were computed from within quiet breathing periods of each subject. We found that breaths immediately before apnea/hypopneas were associated with a high degree of variability in respiratory timing and TAA. The proposed variability analysis of RIP signals may be useful for detecting acute epochs of respiratory instability in children with SDB.