P065 Heart Rate and Heart Rate Variability in paediatric sleep disordered breathing: Is LF a proxy for vascular motor tone

In children, sleep disordered breathing (SDB) is associated with changes in cardiac and vascular remodeling and hence may alter cardiac rhythm. Heart rate variability (HRV) measured during different sleep stages and at discreet times across the night, where vascular tone is known to change, provides an opportunity to better understand the effect of SDB on the cardiac function. 50 children diagnosed with SDB and 51 healthy children underwent overnight polysomnography to determine sleep staging. HRV (mean NN, SDNN, RMSSD, LF, HF, and LF:HF) was determined for the following segments pre-sleep; 3 slow wave sleep and 3 segments during rapid eye movement sleep (SWS1, SWS2, REM3, REM2, REM1). Children with SDB demonstrated higher heart rate (decreased mean NN) in all sleep segments. All HRV variables were similar between groups pre-sleep and REM3 and SWS3. LF and LF:HF were significantly lower in SWS1&2 and REM1 while as were SDNN and rMSSD were lower in the SDB group in REM1&2. LF remained low in the SDB group but rose to pre sleep levels in the control group. Children with SDB have increased heart rate across the night even when HRV is similar between the groups. This suggests intrinsic changes to the cardiac components that determine heart rate. The HRV difference between groups was greatest post acrophase (body temperature dropping) and post nadir (body temperature rising) of the circadian cycle. We propose that impaired peripheral vascular control and sustained cardiac remodelling may underlie the heart rate and HRV changes observed in children with SDB.