• A Johansson, P A Oberg, and G Sedin.
• Department of Biomedical Engineering, Linköping University, Sweden.
• J Clin Monit Comput. 1999 Dec 1; 15 (7-8): 461-7.

ObjectiveA new photoplethysmographic (PPG) device for respiratory and heart rate monitoring has been evaluated in the neonatal care units at the University Children's Hospital of Uppsala, Sweden. The purpose of this study was to compare this new device with more established techniques, i.e., transthoracic impedance plethysmography (TTI) for monitoring of respiratory rate and ECG for heart rate monitoring.MethodsData were acquired continuously 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 device were compared with the ECG and the impedance plethysmogram.ResultsThe ECG recordings were of high quality in 77% of the analysed periods. In these periods, excluding periods (6%) disturbed by offset-adjustement of the PPG signal, the PPG heart signal included 1.1% (+/- 0.7% SD) false negative beats 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 synchronous with respiration included 2.7% (+/- 1.1%) false negative breaths and 1.5% (+/- 0.4%) false positive breaths. Here, 2% of the periods were discarded because of offset-adjustment. From the periods of low signal quality, two other conclusions were drawn: 1) The impedance signal contains more power 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).ConclusionsElectrode and motion artefacts seem to disturb the ECG signals and, particularly, the impedance 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 and has a small optical probe. These factors indicate further advantages of the photoplethysmographic method.

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