Fast and Robust Real-Time Estimation of Respiratory Rate from Photoplethysmography

Respiratory rate (RR) is a useful vital sign that can not only provide auxiliary information on physiological changes within the human body, but also indicate early symptoms of various diseases. Recently, methods for the estimation of RR from photoplethysmography (PPG) have attracted increased interest, because PPG can be readily recorded using wearable sensors such as smart watches and smart bands. In the present study, we propose a new method for the fast and robust real-time estimation of RR using an adaptive infinite impulse response (IIR) notch filter, which has not yet been applied to the PPG-based estimation of RR. In our offline simulation study, the performance of the proposed method was compared to that of recently developed RR estimation methods called an adaptive lattice-type RR estimator and a Smart Fusion. The results of the simulation study show that the proposed method could not only estimate RR more quickly and more accurately than the conventional methods, but also is most suitable for online RR monitoring systems, as it does not use any overlapping moving windows that require increased computational costs. In order to demonstrate the practical applicability of the proposed method, an online RR estimation system was implemented.This research was supported by the National Research Foundation of Korea (NRF) grants funded by the Ministry of Science, ICT & Future Planning (MSIP) (NRF-2015M3C7A1065052 and 2015R1A2A1A15054662)

Confounding effects of heart rate, breathing rate, and frontal fNIRS on interoception

Recent studies have established that cardiac and respiratory phases can modulate perception and related neural dynamics. While heart rate and respiratory sinus arrhythmia possibly affect interoception biomarkers, such as heartbeat-evoked potentials, the relative changes in heart rate and cardiorespiratory dynamics in interoceptive processes have not yet been investigated. In this study, we investigated the variation in heart and breathing rates, as well as higher functional dynamics including cardiorespiratory correlation and frontal hemodynamics measured with fNIRS, during a heartbeat counting task. To further investigate the functional physiology linked to changes in vagal activity caused by specific breathing rates, we performed the heartbeat counting task together with a controlled breathing rate task. The results demonstrate that focusing on heartbeats decreases breathing and heart rates in comparison, which may be part of the physiological mechanisms related to “listening” to the heart, the focus of attention, and self-awareness. Focusing on heartbeats was also observed to increase frontal connectivity, supporting the role of frontal structures in the neural monitoring of visceral inputs. However, cardiorespiratory correlation is affected by both heartbeats counting and controlled breathing tasks. Based on these results, we concluded that variations in heart and breathing rates are confounding factors in the assessment of interoceptive abilities and relative fluctuations in breathing and heart rates should be considered to be a mode of covariate measurement of interoceptive processes

Recent development of respiratory rate measurement technologies

Respiratory rate (RR) is an important physiological parameter whose abnormity has been regarded as an important indicator of serious illness. In order to make RR monitoring simple to do, reliable and accurate, many different methods have been proposed for such automatic monitoring. According to the theory of respiratory rate extraction, methods are categorized into three modalities: extracting RR from other physiological signals, RR measurement based on respiratory movements, and RR measurement based on airflow. The merits and limitations of each method are highlighted and discussed. In addition, current works are summarized to suggest key directions for the development of future RR monitoring methodologies

Ein Verfahren zur störungsarmen Erfassung der Pulsfrequenz unter Bewegungsbedingungen

Es wurde das SNR bei den Methoden EKG, PPG, IPG und Druck zur Messung der Pulsfrequenz bei Bewegung des Nutzers untersucht. Dann wurde ein mobiler PPG-Stirnbandsensor entwickelt, womit die Gliedmaßen frei beweglich bleiben. Ein Signalkoppelmodell beschreibt die Entstehung von zwei PPG-Signalen ausgehend vom Herzschlag als gemeinsame Signalquelle mittels Übertragungsfunktionen, welche vom Messort, der Physiologie und der Ankopplung abhängig sind. Nutz- und Störsignalanteile sollen sich additiv überlagern. Ein zweistufiger adaptiver Algorithmus schätzt und entfernt den Störsignalanteil aus dem PPG.Methods as the ECG, IPG, PPG or blood-pressure as sensors for heart rate measurements were compared while in motion. We aimed to develop a novel approach for an alternative heart-rate-monitor including a software algorithm for suppressing interfering signals. PPG-sensor showed good properties and a low SNR in motion. By using transfer functions between 2 sensor-signals an algorithm to extract the origin pulse signal from a strongly disturbed pulse signal was developed. It was possible to estimate the original form of the PPG-signal during movements like head shaking