The effects of waterbeds on heart rate in preterm infants.

The purpose of this study was to investigate the effects of waterbeds on heart rate (HR) in preterm infants. Subjects were 22 medically stable preterm infants. Across a 10-day study, HR was determined for a 1-hour period on each day. Baseline HRs with infants on the standard incubator mattress were obtained on the first 2 days of the study. They were then placed on the waterbed for 4 days. They were then returned to the incubator mattress and studied for 4 more days. Infants served as their own controls among baseline, on-waterbed (On-WB) and off-waterbed (Off-WB) periods. HR was determined by using a heart beat counting feature of the neonatal cardio-respiratory monitors. Analysis of variance revealed significant HR variability among subjects. There was no difference between baseline HR and on-waterbed HR. The HR increased when infants were transferred back to the standard mattress. The possibility that theophylline acted as a confound existed because doses were changed and levels varied for some subjects within the study period. Eight infants responded to the waterbed with lower HR during the On-WB period compared to the baseline (mean reduction = 5.7 bpm). The findings that HRs rose when the infants were returned to the incubator mattress are similar to those of a previous study. The subjects' reactivity to changes in treatment condition continues to confound the question as to whether waterbed therapy effects a reduction in HR. Since waterbeds have consistently resulted in soothing effects such as improved sleep and lowered activity, failure to produce a concomitant reduction in HR warrants attention toward other factors that may be determinants of heart rate. The high variability within and among subjects raises questions as to the usefulness of the HR variable for determining energy costs.