T. Tamura

Monitoring of heart and respiratory rates by photoplethysmography using a digital filtering technique

An apparatus for simultaneously monitoring heart and respiratory rates was developed using photoplethysmography (PPG) and digital filters, and compared with conventional methods. The PPG signal, which includes both heart and respiratory components, was measured at the earlobe with an original transmission mode photoplethysmographic device. A digital filtering technique was used to distinguish heart and respiratory signals from the PPG signal. The cut-off frequency of the respiratory signal filter was selected automatically depending on the heart rate. Using digital filtering techniques, heart and respiratory signals were separated at rest and during exercise. The digital signal processor was employed to realize an adaptive and real-time filtering. The heart rate was calculated by the zero-crossing method and the respiratory rate from the peak interval of the filtered signal. To evaluate the newly developed monitor, an ECG for heart rate and a transthoracic impedance plethysmogram for respiratory rate were monitored simultaneously. To obtain higher heart and respiratory rates, exercise was performed on an electrical bicycle ergometer. Heart and respiratory rates calculated by the new method compare to those obtained from ECG and the transthoracic impedance plethysmogram. The maximum error of heart and respiratory rates was 10 beats/min and 7 breaths/min, respectively.

A system for monitoring temperature distribution in bed and its application to the assessment of body movement

For the assessment of body movements during sleep, a system for monitoring the temperature in bed was developed. The system consists of 16 temperature sensors and a data logger with a memory card. Fifteen of the temperature sensors were arranged in line 6 cm apart on a flat cable. The temperatures at these 15 points in the bed, and the room temperature measured by the additional sensor, were stored on the memory card at predetermined intervals. The data were transferred into a microcomputer and analysed. Changes in posture and body movement were recognizable from the changes in the temperature profile, and well visualized using a three-dimensional display of the successive temperature profiles in the bed. The time of body movement was estimated from the derivative of the temperature profile. Comparison between this estimation and the video recording showed good agreement. The linear arrangement of the sensors provides a high-resolution temperature profile during sleep.

A bed temperature monitoring system for assessing body movement during sleep

A method of monitoring and analysing temperature distribution in a patients bed during bed rest and sleep is described. The system consists of 16 temperature sensors, a solid-state recorder and a personal computer. The temperature sensors are attached on the surface of a bed mat. The temperature of the 16 measurement points are recorded and stored on a multichannel solid-state recorder, where a programmable read-only memory (PROM) is used as the memory device. The PROM is detachable from the recorder, and the temperature data is read by a computer. A two-dimensional temperature distribution pattern is obtained by interpolating the temperature between measured points. The system was effective for long-term temperature monitoring without patient discomfort, and it proved reliable and easy to use. The temperature distribution and changes in the distribution indicated body movement and hence periods of sleep.

Fully automated biosignal acquisition in daily routine through 1 month

With the goal of keeping people healthy and active, long-term at-home measurement of physiological function during daily life is valuable, and is attempted in this study. As a first trial of at-home measurements, a fully automated physiological data acquisition system was developed. This system contains unconstrained physiological parameter monitors: an ECG monitor for use during bathing, a bed temperature monitor, and a weight monitor located in the toilet seat. It also contains a computer with data acquisition programs and a data format rule. Unconstrained physiological parameter monitors and fully automatic measurement procedures provide data acquisition non-invasively and without the subjects awareness. This system has been proved by an experiment involving measurement over one month of a healthy male subject (aged 29 years) in laboratory-based facilities. The system functioned for one month of data acquisition with no operator involved. The system may be used for home health monitoring of patients and also of healthy subjects.

Detection of Physiological Parameters without Any Physical Constraints in Bed Using Sequential Image Processing.

Physiological parameters, specifically, body movement and respiratory waveform, were observed utilizing an original image sequence processing system. In this study, sequential image processing methods were used to observe both patients with acute myocardial infarction and normal subjects in bed. The results of standard differential image processing and a gradient-based method were strongly correlated with body movement of the subject. Furthermore, the respiratory waveform was detected using the gradient-based method. This image sequence processing system appears very promising for the evaluation of physical activity without any physical constraints in bed.

Assessment of gait parameter in hemiplegic patients by accelerometry

A portable microprocessor-based data acquisition system was used to measure the acceleration of joints during walking in ambulatory subjects and to evaluate temporal and spatial parameters of the gait. The system consists of two triaxial accelerometers and a microdata logger with removable memory. After examination, the recorded data are downloaded to a personal computer to analyze the gait cycle, power spectrum, and attractor of two sites. Experiments were performed on 28 hemiplegic patients of different Brunnstrom stages (Br. stages). The orthogonal accelerations at the head of the fibula were measured when walking at a normal speed. The gait cycle for a subject of a low Br. stage was significantly larger than that for a high Br. stage. The frequency distribution of gait for a low Br. stage subject was significantly smaller than that for a high Br. stage. The attractors of normal subjects and unaffected sites were simple figures with small variance, while those of affected sites were complex forms with large variance. The attractor changes simple form with higher Br. stage. Thus, the authors could estimate the rehabilitation effect from the attractor. This monitor may permit a quantitative evaluation of the recovery of paralyzed patients, both in hospital and at home.

Assessment of bed temperature monitoring for detecting body movement during sleep: comparison with simultaneous video image recording and actigraphy

This study was designed to assess changes in bed temperature as an index of body movement. Changes in the temperature of the bed or mattress were used to estimate motility and number of awakenings, and total time in bed. Simultaneous temperature records, video image recordings and actigraphic data were obtained from 12 young adults for three consecutive nights. Significant agreement of time in bed and body movement among the three measurements was found. Intra-individual variability was low for time in bed. In a second study, 10 healthy elderly subjects used a temperature monitor at home for four consecutive nights. The time in bed was 8.1 h, a little longer than for the younger adults, but not markedly different. These studies show the potential usefulness of bed temperature monitoring as an index of sleep behaviour. Although the precise sleep index could not be observed, behaviour could be evaluated simply.

Photoplethysmographic measurement of heart and respiratory rates using digital filters

A monitor. for simultaneous recording of heart and respiratory rates has been developed using photoplethysmography (PPG) and digital filters. PPG signal includes both heart and respiratory synchronous components. Digital filtering technique was employed to differentiate between those. With increasing heart and respiratory rates, the cut-off frequency o f filter was changed empirically. Obtained signals agreed with those obtained with ECG and thermistor. The digital filtering technique may provide on-line monitor for heart and respiratory rates.

Effect of Loud Sound Exposure on the Cochlear Blood Flow

The effect of loud sound exposure on cochlear blood flow was studied in the guinea pig by the laser Doppler method. Fourteen guinea pigs with normal Preyer reflex were anesthetized and tracheotomy was performed. A tracheotomy tube was connected to a ventilator and the experiment was performed with artificial ventilation. After exposure of the tympanic bulla and complete removal of the mucosa, a probe of a laser Doppler flowmeter was attached to the lateral wall of the basal turn of the cochlea. A specially-designed ear piece connected with a speaker was inserted into the external ear canal and loud sound (10 kHz at 120 dB SPL) was delivered to the ear for 30 min. Thirteen of the 14 exposed guinea pigs showed a prompt decrease in cochlear blood flow at the onset of the sound exposure and 12 of the 13 guinea pigs showed a prompt recovery of the cochlear blood flow after the cessation of the sound exposure.

A solid-state ambulatory physical activity monitor and its application to measuring daily activity of the elderly

An ambulatory acceleration monitor was developed and used to evaluate physical activity in the elderly. The ECG and accelerations at the wrist, waist, and ankle were recorded, and the heart rate and frequency and amplitude of accelerations per unit time were evaluated in both working and retired elderly women performing normal daily activities. The heart rate closely paralleled wrist acceleration. The behaviour patterns of the subjects could be differentiated by time interval signals and histogram distributions. This system appears to be an effective method of understanding and describing the characteristic activities of the elderly in a quantitative and objective fashion.