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

• Objective.A new photoplethysmographic (PPG) device for respiratoryand heart rate monitoring has been evaluated in the neonatal care units at theUniversity Children's Hospital of Uppsala, Sweden. The purpose of thisstudy was to compare this new device with more established techniques, i.e.,transthoracic impedance plethysmography (TTI) for monitoring of respiratoryrate and ECG for heart rate monitoring.Methods.Data were acquiredcontinuously for 8-hours in each of 6 neonates. The signals were analysed forperiods of 30 seconds, in which the heart and respiratory signals from the PPGdevice were compared with the ECG and the impedance plethysmogram.Results.The ECG recordings were of high quality in 77% of the analysed periods.In these periods, excluding periods (6%) disturbed by offset-adjustement ofthe PPG signal, the PPG heart signal included 1.1% (±0.7% SD) falsenegative beats and 0.9% (±0.6%) false positive beats. In periods withan impedance signal of high quality (29% of total time), the part of the PPGsignal synchronous with respiration included 2.7% (±1.1%) falsenegative breaths and 1.5% (±0.4%) false positive breaths. Here, 2% ofthe periods were discarded because of offset-adjustment. From the periods oflow signal quality, two other conclusions were drawn: 1) The impedance signalcontains more power in the respiratory range than the corresponding PPGrespiratory signal. 2) The breaths are easier to identify in the PPGrespiratory signal than in the impedance signal (subjective measure).Conclusions.Electrode and motion artefacts seem to disturb the ECGsignals and, particularly, the impedance signals. During periods of highquality ECG and impedance signals, the new optical device produces signals ofequal quality to these traditional methods, and is in some cases even better.The new device is non-invasive and has a small optical probe. These factors indicate further advantages of the photoplethysmographic method.

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