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.

Photoplethysmography imaging (PPGI) and infrared thermography imaging (IRTI) are contactless camera-based measurement methods for monitoring a wide range of basic vital parameters. In particular, PPGI enhances the classical contact-based photoplethysmography. Approved evaluation algorithms of the well-established PPG method can easily be adapted for detection of heart rate, heart rate variability, respiration rate (RR), respiratory variability (RV), and vasomotional activity with PPGI. The IRTI method primarily records temperature distribution of the observed object, but information on RR and RV can also be derived from IRTI by analyzing the development of temperature distribution in the nasal region. The main advantages of both monitoring methods are unobtrusive data acquisition and the possibility of assessing spatial assignment between vital parameters and body region. Hence, these methods enable long-term monitoring or the monitoring of effects with special local characteristics. Because the two systems supplement each, a combined hybrid application is proposed and its feasibility discussed.

Acute circulatory disorders are commonly associated with systemic inflammatory response (SIRS) and sepsis. During sepsis, microcirculatory perfusion is compromised leading to tissue hypoperfusion and potentially to multiple organ dysfunction. In the present study, acute lung injury (ALI), one of the major causes leading to SIRS and sepsis, was experimentally induced in six female pigs. To investigate the progress of body temperature distribution, measurements with a long-wave infrared camera were carried out. Temperature centralization was evidenced during ALI owing to impairments of peripheral perfusion. In addition, statistical analysis demonstrated strong correlations between (a) standard deviation of the skin temperature distribution (SD) and shock index (SI) (p<0.0005), (b) SD and mean arterial pressure (MAP) (p<0.0005), (c) ΔT/Δx and SI (p<0.0005), as well as between (d) ΔT/Δx and MAP (p<0.0005). For clarification purposes, ΔT/Δx is a parameter implemented to quantify the spatial temperature gradient. This pioneering study created promising results. It demonstrated the capacity of infrared thermography as well as of the indexes, SD and ΔT/Δx, to detect impairments in both circulation and tissue perfusion.

Vital parameter monitoring of term and preterm infants during incubator care with self-adhesive electrodes or sensors directly positioned on the skin [e.g. photoplethysmography (PPG) for oxygen saturation or electrocardiography (ECG)] is an essential part of daily routine care in neonatal intensive care units. For various reasons, this kind of monitoring contains a lot of stress for the infants. Therefore, there is a need to measure vital parameters (for instance respiration, temperature, pulse, oxygen saturation) without mechanical or conductive contact. As a non-contact method of monitoring, we present an adapted version of camera-based photoplethysmography imaging (PPGI) according to neonatal requirements. Similar to classic PPG, the PPGI camera detects small temporal changes in the term and preterm infant's skin brightness due to the cardiovascular rhythm of dermal blood perfusion. We involved 10 preterm infants in a feasibility study [five males and five females; mean gestational age: 26 weeks (24-28 weeks); mean biological age: 35 days (8-41 days); mean weight at the time of investigation: 960 g (670-1290 g)]. The PPGI camera was placed directly above the incubators with the infant inside illuminated by an infrared light emitting diode (LED) array (850 nm). From each preterm infant, 5-min video sequences were recorded and analyzed post hoc. As the measurement scenario was kept as realistic as possible, the infants were not constrained in their movements in front of the camera. Movement intensities were assigned into five classes (1: no visible motion to 5: heavy struggling). PPGI was found to be significantly sensitive to movement artifacts. However, for movement classes 1-4, changes in blood perfusion according to the heart rate (HR) were recovered successfully (Pearson correlation: r=0.9759; r=0.765 if class 5 is included). The study was approved by the Ethics Committee of the Universal Hospital of the RWTH Aachen University, Aachen, Germany (EK 254/13).

Homecare is healthcare based on the principle “outpatient before inpatient,” with the aim of moving at least some care-delivery to the home. But reliable determination of vital signs at home requires new, smart sensors, which can be used by the patients themselves. We present a novel pulse oximetry sensor worn in the ear channel. It was previously shown that measurement of heart rate, arterial oxygen saturation and related respiratory information can be performed with reliable accuracy under laboratory conditions. The present study explores the clinical feasibility of the sensor system for cardiovascular monitoring during sleep, with the aim to diagnose sleep apnea. For this, human trials were performed in a sleep laboratory including patients with a clinical suspicion of sleep apnea. Besides a general analysis of the sensor's signal quality during sleep, the evaluation focuses on heart rate dynamics and time-variant oxygen saturation. In addition, several methods to derive respiration rate from photoplethysmographic signals are examined and discussed. Results from the in-ear sensor are compared with standard polysomnography monitoring and demonstrate that this novel system allows long-term nocturnal measurement of heart rate, oxygen saturation and respiratory rate with sufficient accuracy.