Advances in Reflective Oxygen Saturation Monitoring With a Novel In-Ear Sensor System: Results of a Human Hypoxia Study

Abstract

Pulse oximetry is a well-established, noninvasive photoplethysmographic method to monitor vital signs. It allows us to measure cardiovascular parameters, such as heart rate and arterial oxygen saturation, and is considered an essential monitoring tool in clinical routine. However, since many of the conventional systems work in transmission mode, they can only be applied to the thinner or peripheral parts of the body, such as a finger tip. This has the major disadvantage that, in case of shock-induced centralization and a resulting drop in perfusion, such systems cannot ensure valid measurements. Therefore, we developed a reflective in-ear sensor system that can be worn in the ear channel like a headphone. Because the sensor is integrated in an ear mold and positioned very close to the trunk, reliable measurement is expected even in case of centralization. An additional advantage is that the sensor is comfortable to wear and has considerable resistance to motion artifacts. In this paper, we report on hypoxia studies with ten healthy participants which were performed to analyze the system with regard to the detection of heart rate and arterial oxygen saturation. It was shown earlier that, due to the high signal quality, heart rate can easily be detected. Using the conventional calculation principle, based on Beer-Lambert's law combined with a single-point calibration method, we now demonstrate that the detection of arterial oxygen saturation in the human ear canal is possible using reflective saturation sensors.

The human ear canal: investigation of its suitability for monitoring photoplethysmographs and arterial oxygen saturation

“…The finding of our results were different from the results presented by Vogel and Venema [8,9], as the sensor design, placement in the ear canal and the choice of the LED wavelengths were different that those described by the above mention authors. Hence, by further decomposing the ear canal PPG signal, valuable clinical information regarding cardiovascular function might be extracted.…”

“…The results presented showed that the determination of oxygen saturation in the ear canal is feasible. However, when creating a global calibration curve from all the measurements, the accuracy level was reported to be unacceptable for use in SpO2 measurements [9]. Moreover, the quality of the PPG signals and accuracy of SpO2s, acquired from the auditory canal during conditions of compromised peripheral perfusion has not yet been investigated or published.…”

In-ear photoplethysmography for central pulse waveform analysis in non-invasive hemodynamic monitoring

“…SNR calculations were performed in accordance with the description given in Section 2.2. Analogously to previous studies [2], a lower limit of 0.5 Hz was chosen for the useful PPG signal bandwidth. With respect to the upper limit, we performed SNR calculations for two different threshold values.…”

Individualized biomonitoring in heart failure – Biomon-HF “Keep an eye on heart failure – especially at night”

“…For a detailed description of these first results, the interested reader is referred to the publications written by the Biomon-HF project members thus far [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. Figure 4 Overview of full electronic clinical study data management system implemented in Biomon-HF.…”

“…In the previous work, it could be demonstrated that measurement of heart rate (HR), arterial oxygen saturation (SpO 2 ), and respiratory-related information can be performed with reliable accuracy [7,8]. As these results were obtained under laboratory conditions, in Biomon-HF, the in-ear sensor is studied in a clinical sleep laboratory and atrial fibrillation study setting.…”