Photoplethysmographic (PPG) waveforms are used to acquire pulse rate (PR) measurements from pulsatile arterial blood volume. PPG waveforms are highly susceptible to motion artifacts (MA), limiting the implementation of PR measurements in mobile physiological monitoring devices. Previous studies have shown that multichannel photoplethysmograms can successfully acquire diverse signal information during simple, repetitive motion, leading to differences in motion tolerance across channels. In this paper, we investigate the performance of a custom-built multichannel forehead-mounted photoplethysmographic sensor under a variety of intense motion artifacts. We introduce an advanced multichannel template-matching algorithm that chooses the channel with the least motion artifact to calculate PR for each time instant. We show that for a wide variety of random motion, channels respond differently to motion artifacts, and the multichannel estimate outperforms single-channel estimates in terms of motion tolerance, signal quality, and PR errors. We have acquired 31 data sets consisting of PPG waveforms corrupted by random motion and show that the accuracy of PR measurements achieved was increased by up to 2.7 bpm when the multichannel-switching algorithm was compared to individual channels. The percentage of PR measurements with error ≤ 5 bpm during motion increased by 18.9% when the multichannel switching algorithm was compared to the mean PR from all channels. Moreover, our algorithm enables automatic selection of the best signal fidelity channel at each time point among the multichannel PPG data.

This is the first study to demonstrate the feasibility of a reconstruction algorithm to improve oxygen saturation estimates on a dataset with MAs and concomitant hypoxia.

The costs of pressure injury treatments continue to rise with a steadily aging population and consistent pressure injury incidence rates. Evidence suggests that the bioimpedance of living tissues changes in response to continuous pressure loading and may be useful as an indicator for the onset of pressure injuries. Therefore, the development of a low-cost, accurate, and portable sensor capable of measuring the bioimpedance of human skin has practical significance in the development of pressure injury prevention devices. This paper reports the design and characterization of a system for measuring skin impedance based on the AD5933 impedance analyzer. The sensor was tested for accuracy via measurements of a simplified electrical equivalent skin model. Long duration measurement stability was assessed over 24 hours and skin measurement repeatability was performed on the volar forearm. The power consumption was measured both during idle and when transmitting data for each major component. The sensor demonstrated accuracies similar to those reported for other AFE's used in conjunction with the AD5933. Additionally, the sensor shows good stability over long measurement durations as well as good repeatability when measuring the skin bioimpedance on the volar forearm. Power consumption was as expected and future suggestions for lowering the overall circuit power consumption and size are presented.

Objective: Rises in the incidence of pressure ulcers are increasingly prevalent in an aging population. Pressure ulcers are painful, are associated with increased morbidity and mortality, increase the risk for secondary infections and inpatient stay, and adds $26.8 billion annually to the healthcare costs of the USA. Evidence suggests that a change in the bioimpedance of living tissue in response to continuous local contact pressure can be a useful indicator for the onset of pressure injuries. Approach: Thirty-five Sprague Dawley rats were subjected to various skin pressures for differing periods of time via a surgically inserted steel disk and an externally applied magnet. Contact pressure and bioimpedance were measured and correlated with tissue loading intensity and compared to clinical ulcer grading. Main results: Moderate relationships between bioimpedance changes and tissue loading intensity were found. Stronger correlations were found by utilizing a combination of bioimpedance and phase angle. Thresholds were applied to the bioimpedance parameters and the usefulness of bioimpedance in classifying different ulcer stages is demonstrated. Significance: These results indicate that bioimpedance may be useful as an early indicator of pressure ulcer formation and has practical significance in the development of early pressure injury detection devices.