Monitoring of heart and respiratory rates in newborn infants using a new photoplethysmographic technique

Objective. A new photoplethysmographic (PPG) device for respiratory and hea rt rate monitoring has been evaluated in the neonatal care units at the Uni versity Children's Hospital of Uppsala, Sweden. The purpose of this study w as to compare this new device with more established techniques, i.e., trans thoracic impedance plethysmography (TTI) for monitoring of respiratory rate and ECG for heart rate monitoring. Methods. Data were acquired continuousl y for 8-hours in each of 6 neonates. The signals were analysed for periods of 30 seconds, in which the heart and respiratory signals from the PPG devi ce were compared with the ECG and the impedance plethysmogram. Results.The ECG recordings were of high quality in 77% of the analysed periods. In thes e periods, excluding periods (6%) disturbed by offset-adjustement of the PP G signal, the PPG heart signal included 1.1% (+/- 0.7% SD) false negative b eats and 0.9% (+/- 0.6%) false positive beats. In periods with an impedance signal of high quality (29% of total time), the part of the PPG signal syn chronous with respiration included 2.7% (+/- 1.1%) false negative breaths a nd 1.5% (+/- 0.4%) false positive breaths. Here, 2% of the periods were dis carded because of offset-adjustment. From the periods of low signal quality , two other conclusions were drawn: 1) The impedance signal contains more p ower in the respiratory range than the corresponding PPG respiratory signal . 2) The breaths are easier to identify in the PPG respiratory signal than in the impedance signal (subjective measure). Conclusions. Electrode and mo tion artefacts seem to disturb the ECG signals and, particularly, the imped ance signals. During periods of high quality ECG and impedance signals, the new optical device produces signals of equal quality to these traditional methods, and is in some cases even better. The new device is non-invasive a nd has a small optical probe. These factors indicate further advantages of the photoplethysmographic method.