Camera-based measurement of respiratory rates is reliable.

OBJECTIVES: Respiratory rate (RR) is one of the most important vital signs used to detect whether a patient is in critical condition. It is part of many risk scores and its measurement is essential for triage of patients in emergency departments. It is often not recorded as measurement is cumbersome and time-consuming. We intended to evaluate the accuracy of camera-based measurements as an alternative measurement to the current practice of manual counting. MATERIALS AND METHODS: We monitored the RR of healthy male volunteers with a camera-based prototype application and simultaneously by manual counting and by capnography, which was considered the gold standard. The four assessors were mutually blinded. We simulated normoventilation, hypoventilation and hyperventilation as well as deep, normal and superficial breathing depths to assess potential clinical settings. The volunteers were assessed while being undressed, wearing a T-shirt or a winter coat. RESULTS: In total, 20 volunteers were included. The results of camera-based measurements of RRs and capnography were in close agreement throughout all clothing styles and respiratory patterns (Pearson's correlation coefficient, r=0.90-1.00, except for one scenario, in which the volunteer breathed slowly dressed in a winter coat r=0.84). In the winter-coat scenarios, the camera-based prototype application was superior to human counters. CONCLUSION: In our pilot study, we found that camera-based measurements delivered accurate and reliable results. Future studies need to show that camera-based measurements are a secure alternative for measuring RRs in clinical settings as well.

Hybrid Optical Unobtrusive Blood Pressure Measurements.

Blood pressure (BP) is critical in diagnosing certain cardiovascular diseases such as hypertension. Some previous studies have proved that BP can be estimated by pulse transit time (PTT) calculated by a pair of photoplethysmography (PPG) signals at two body sites. Currently, contact PPG (cPPG) and imaging PPG (iPPG) are two feasible ways to obtain PPG signals. In this study, we proposed a hybrid system (called the ICPPG system) employing both methods that can be implemented on a wearable device, facilitating the measurement of BP in an inconspicuous way. The feasibility of the ICPPG system was validated on a dataset with 29 subjects. It has been proved that the ICPPG system is able to estimate PTT values. Moreover, the PTT measured by the new system shows a correlation on average with BP variations for most subjects, which could facilitate a new generation of BP measurement using wearable and mobile devices.

Calibration of Contactless Pulse Oximetry.

BACKGROUND: Contactless, camera-based photoplethysmography (PPG) interrogates shallower skin layers than conventional contact probes, either transmissive or reflective. This raises questions on the calibratability of camera-based pulse oximetry. METHODS: We made video recordings of the foreheads of 41 healthy adults at 660 and 840 nm, and remote PPG signals were extracted. Subjects were in normoxic, hypoxic, and low temperature conditions. Ratio-of-ratios were compared to reference SpO2 from 4 contact probes. RESULTS: A calibration curve based on artifact-free data was determined for a population of 26 individuals. For an SpO2 range of approximately 83% to 100% and discarding short-term errors, a root mean square error of 1.15% was found with an upper 99% one-sided confidence limit of 1.65%. Under normoxic conditions, a decrease in ambient temperature from 23 to 7°C resulted in a calibration error of 0.1% (±1.3%, 99% confidence interval) based on measurements for 3 subjects. PPG signal strengths varied strongly among individuals from about 0.9 × 10 to 4.6 × 10 for the infrared wavelength. CONCLUSIONS: For healthy adults, the results present strong evidence that camera-based contactless pulse oximetry is fundamentally feasible because long-term (eg, 10 minutes) error stemming from variation among individuals expressed as A*rms is significantly lower (<1.65%) than that required by the International Organization for Standardization standard (<4%) with the notion that short-term errors should be added. A first illustration of such errors has been provided with A**rms = 2.54% for 40 individuals, including 6 with dark skin. Low signal strength and subject motion present critical challenges that will have to be addressed to make camera-based pulse oximetry practically feasible.