Janek Mann

Respiratory Rate and Flow Waveform Estimation from Tri-axial Accelerometer Data

There is a strong medical need for continuous, unobstrusive respiratory monitoring, and many shortcomings to existing methods. Previous work shows that MEMS accelerometers worn on the torso can measure inclination changes due to breathing, from which a respiratory rate can be obtained. There has been limited validation of these methods. The problem of practical continuous monitoring, in which patient movement disrupts the measurements and the axis of interest changes, has also not been addressed. We demonstrate a method based on tri-axial accelerometer data from a wireless sensor device, which tracks the axis of rotation and obtains angular rates of breathing motion. The resulting rates are validated against gyroscope measurements and show high correlation to flow rate measurements using a nasal cannula. We use a movement detection method to classify periods in which the patient is static and breathing signals can be observed accurately. Within these periods we obtain a close match to cannula measurements, for both the flow rate waveform and derived respiratory rates, over multi-hour datasets obtained from wireless sensor devices on hospital patients. We discuss future directions for improvement and potential methods for estimating absolute airflow rate and tidal volume.

Simultaneous Activity and Respiratory Monitoring Using an Accelerometer

Simultaneous monitoring of respiratory function and activity level would be of benefit in the monitoring of chronic conditions such as chronic obstructive pulmonary disorder (COPD), but is ill-addressed by existing methods. Current solutions for monitoring respiratory function are obtrusive and not suitable for pervasive monitoring in the home, while existing activity monitors, not equipped to measure parameters of respiration, do not differentiate between causes of sedentary behaviour. Previous work has validated a method for obtaining angular rates of breathing motion of the chest wall using a tri-axial accelerometer against nasal pressure. We have used this method to perform respiratory monitoring during periods of low activity while simultaneously monitoring activity using a single wireless device. We observe that the optimal placement for respiratory monitoring does not preclude successful activity monitoring. We propose an activity monitoring algorithm based on direct estimation of motion energy observed by the device. We show favourable comparison against three commercial activity monitors validated against indirect calorimetry during a programme of exercise activities in healthy subjects.

Validation of a new non-invasive automatic monitor of respiratory rate for postoperative subjects

BACKGROUND Respiratory rate is an important measurement in patient care but frequently poorly assessed. We set out to develop a simple non-invasive device to reliably measure respiratory movements and estimate respiratory rate, in clinical circumstances. METHODS Respiratory movement was detected with an encapsulated tri-axial accelerometer (Orient speck) and the data transmitted wirelessly to a computer for analysis. We studied subjects after gynaecological surgery who received opioid analgesia, and compared the derived signal with a signal from nasal cannula using directly matched breaths and within the same 5 min epoch. We analysed the signals for 5 min epochs over a 15 h recording period. RESULTS For matched breath analysis, the instantaneous respiratory rates matched within 2 bpm on 86% of occasions. A similar match was found between epoch averages of the respiratory rate. The mean absolute difference between the respiratory rate measured by nasal cannula and Orient speck was 0.6 bpm. The Orient speck generated reliable measures of respiratory rate every 5 min in 95.4% of epochs. CONCLUSIONS The Orient speck provides a reliable measure of respiratory rate at frequent intervals in subjects receiving patient-controlled morphine analgesia after surgery.

Characterization of breathing patterns during patient-controlled opioid analgesia

BACKGROUND Respiratory rate is an important measurement in patient care, but accurate measurement is often difficult. We have developed a simple non-invasive device to measure respiratory movements in clinical circumstances, with minimal interference with the patient. We investigated respiratory patterns in patients receiving postoperative morphine analgesia to assess the capacity of the device to detect abnormalities. METHODS We studied subjects during self-administered opioid analgesia after major gynaecological surgery, and related the derived signals with a signal from a nasal cannula. Respiratory movement signals were transmitted wirelessly to a recorder from two encapsulated tri-axial accelerometer (RESpeck) sensors. We analysed the signals using two different sensor placements, each for 30 min. The nasal cannula signal was used to classify breathing patterns as obstructive or non-obstructed. RESULTS We studied 20 patients for a mean duration of 49 min each. Breathing patterns were very variable, between and within patients. The median breathing rates ranged from 6.4 to 19.5 bpm. Breathing was partly obstructed in 10 patients, and six patients had repeated cycles of obstruction and transient recovery. In these patients, we found a consistent and statistically significant pattern of changes in chest wall movement, with increased abdominal and decreased rib cage movement during obstruction. In patients with slow respiratory rates, breath-to-breath times were highly variable. CONCLUSIONS In undisturbed subjects receiving patient-controlled morphine analgesia after surgery, abnormal breathing patterns are extremely common. Cyclical airway obstruction is frequent and associated with a typical pattern of changes in chest wall movement.

Prospeckz-5 -- A Wireless Sensor Platform for Tracking and Monitoring of Wild Horses

This paper addresses the use of on-body sensors for tracking and monitoring Retuerta wild horses (one of the oldest horse breeds in Europe) over a 12-month period in the Doñana National Park, Andalusia, Spain. The challenges are outlined and the design of the Prospeckz-5 platform, which is used in both the sensor node on the horses and in the base stations for gathering data, is described. Results are presented for tests on the performance of the antenna and the solar cell array charger ahead of deployment on the horses in Spain.

Performance Evaluation of the VB-TDMA Protocol for Long-term Tracking and Monitoring of Mobile Entities in the Outdoors

The Virtual Beacon-Time Division Multiple Access (VB-TDMA) communication protocol has been proposed in [12] for a growing class of applications which require GPS tracking of autonomous mobile entities in the outdoors, and the long-term continuous monitoring of their contextual information using wireless sensors. Examples include monitoring animal behaviour in their natural habitat over the annual cycle, tracking shipping containers during their life-cycle of transit, loading/unloading and storage, and the handling of high-value packages during transportation. This paper employs simulations to evaluate the network performance of the VB-TDMA communication protocol in a representative scenario involving wild horses attached with collars, each containing a custom-designed platform with a three-axis accelerometer, a GPS module and ancillary electronics and battery, which uploads wirelessly to static base-stations, its position (sensed thrice an hour) and a summary of its activities between uploads. The simulations benefited from movement models derived from real data obtained from a long-term deployment of the collars on wild horses in the Donana National Park in south-west Spain. Comparisons with other MAC protocols have demonstrated the superior performance of the VB-TDMA protocol over a range of metrics for the representative example. An enhanced version of the VB-TDMA protocol - a multi-hop variant - is introduced for low latency requirements and was simulated for an urban scenario of bicycles fitted with sensors for crowd-sourcing spatio-temporal air quality information along the route of travel which is uploaded to the server when within range of static base-stations, for cases where low latency data upload is a requirement to enable access to the latest air quality information.

Wireless monitoring of post-operative respiratory complications

Respiratory complications may occur in post-operative patients but are often difficult to detect due to the lack of a well-tolerated and reliable monitoring method. We have developed a wireless accelerometer-based device that measures chest wall rotations due to breathing and has been shown to provide an accurate measure of respiratory rate in a clinical setting, when validated against rates obtained from nasal pressure. This paper describes a method for detecting instances of respiratory problems due to physical airway obstruction and central nervous system (CNS) respiratory depression using a combination of nasal pressure and chest wall rotation signals in gynaecological patients during the first night after surgery. Waxing and waning of breath amplitude and irregularity of breath length are found to be useful indicators. A clinical study involving 19 post-operative patients shows that the proposed method is able to detect and distinguish between both forms of respiratory complications.