Cardioventilatory coupling and inter-breath variability in children referred for polysomnography.

Measures of respiratory variability including cardioventilatory coupling (CVC), were examined in 8 Down syndrome (DS), 4 Prader Willi syndrome (PWS) and 42 non-syndromic children (median age 7 years) referred for diagnostic polysomnography. Inspiratory onsets (I) and corresponding ECG R waves were determined, I-I, R-R and R-I intervals derived, and ventilatory frequency (f), standard deviation of f (SDf), coefficient of variation of f (CVf), median I-I and kurtosis and skewness I-I calculated. Proportional Shannon Entropy of the RI(-1) interval (SHα) was measured to quantitate CVC. SHα varied with age (p=0.02), oxygen saturation (p<0.05) and PWS diagnosis (p=0.001) in Stage 4 but not REM sleep. SDf and CVf varied with sleep state (p<0.00001) as did kurtosis I-I (p<0.0001) and skewness I-I (p=0.004). Ventilatory frequency decreased with age in REM sleep (p=0.03) and increased in obese children in REM (p=0.02) and Stage 4 sleep (p=0.004). Sleep state influences respiratory variability in children and CVC may confer a physiological advantage in children with PWS.