Akira Ikarashi

A fully automated health-care monitoring at home without attachment of any biological sensors and its clinical evaluation

Daily monitoring of health condition is important for an effective scheme for early diagnosis, treatment and prevention of lifestyle-related diseases such as adiposis, diabetes, cardiovascular diseases and other diseases. Commercially available devices for health care monitoring at home are cumbersome in terms of self-attachment of biological sensors and self-operation of the devices. From this viewpoint, we have been developing a non-conscious physiological monitor installed in a bath, a lavatory, and a bed for home health care and evaluated its measurement accuracy by simultaneous recordings of a biological sensors directly attached to the body surface. In order to investigate its applicability to health condition monitoring, we have further developed a new monitoring system which can automatically monitor and store the health condition data. In this study, by evaluation on 3 patients with cardiac infarct or sleep apnea syndrome, patients’ health condition such as body and excretion weight in the toilet and apnea and hypopnea during sleeping were successfully monitored, indicating that the system appears useful for monitoring the health condition during daily living.

Development of a fully automated network system for long-term health-care monitoring at home

Daily monitoring of health condition at home is very important not only as an effective scheme for early diagnosis and treatment of cardiovascular and other diseases, but also for prevention and control of such diseases. From this point of view, we have developed a prototype room for fully automated monitoring of various vital signs. From the results of preliminary experiments using this room, it was confirmed that (1) ECG and respiration during bathing, (2) excretion weight and blood pressure, and (3) respiration and cardiac beat during sleep could be monitored with reasonable accuracy by the sensor system installed in bathtub, toilet and bed, respectively.

Assessment of Slow-breathing Relaxation Technique in Acute Stressful Tasks Using a Multipurpose Non-invasive Beat-by-Beat Cardiovascular Monitoring System

Recently, several studies revealed that daily slow-breathing exercise lowered blood pressure and increased baroreflex sensitivity. With this interesting finding, we have been contemplating to design a compact breath-controllable device for relaxation to stress reaction during daily living for home as well as ambulatory use, as a final goal, towards reduction of cognitive hemodynamic disorders, hypertension, and acute stress-induced hemodynamic disorders. The present study thereby describes, as a first step, to design a prototype system combining a compact multipurpose non-invasive beat-by-beat cardiovascular monitor developed previously with a wrist-type vibrator to make a respiration rhythm, and to assess an effect of slow-breathing relaxation on the cardiovascular hemodynamics in response to acute stressful conditions. The cardiovascular hemodynamic monitor can measure beat-by-beat systolic (SBP), mean (MBP) and diastolic (DBP) pressure in a finger based on the volume-compensation method, cardiac output (CO) by the electrical admittance method and the other hemodynamic-related parameters (e.g., total peripheral resistance (TPR=MBP/CO), heart rate (HR), respiratory rate, pulse wave velocity, etc.). The wrist-type vibrator can give various breathing rhythms quietly to a subject using a small vibration motor. The stressful tasks loaded to healthy volunteers (3 males, 23-34 yrs.) in the experiments were cold pressor and arithmetic ones as a representative of daily passive and active coping tasks, respectively, under conditions with (respiratory rate of 6 1/min) and without breath control. The results showed that the slow-breathing technique could have a significant effect on improvement of the hemodynamic changes following the acute stressful tasks, especially in the passive coping task. The prototype system combining the cardiovascular monitor with the breath controller appears to be useful and helpful in terms of self-monitoring of hemodynamic changes as well as self-care for the improvement of the cardiovascular function during daily living.

Potential for Health Screening Using Long-Term Cardiovascular Parameters Measured by Finger Volume-Oscillometry: Pilot Comparative Evaluation in Regular and Sleep-Deprived Activities

We explored the potential of health screening based on the long-term measurement of cardiovascular parameters using the finger volume-oscillometric technique. An automated instrument made simultaneous measurements of key cardiovascular parameters, including blood pressure, pulse pressure, heart rate, normalized pulse volume as an index of α-adrenalin-mediated sympathetic activity, and finger arterial elasticity. These were derived from finger photo-plethysmographic signals during application of cuff pressure. To assess the feasibility of achieving a screening function, measurements were made in ten healthy volunteers during 10 days of day-to-day living (normal condition), and carried out several times at a fixed time every day. During successive 10-day measurements, a 30-hour period of total sleep deprivation was introduced as a physiological challenge (abnormal condition). A linear discriminant analysis of the data was conducted to determine whether these two conditions could be discriminated. Periodic data collection was performed rapidly and easily, and the %-correct classifications of normal and abnormal conditions were 78.2% and 77.5%, respectively. This ability of the method to discriminate between regular and sleep-deprived activities demonstrates its potential for healthcare screening during day-to-day living. Further investigations using larger age and gender groups of subjects including patients with cardiovascular diseases under real-life situations are required.

Development of non-invasive and ambulatory physiological monitoring systems for ubiquitous health care

Ubiquitous healthcare is very important subject not only as an effective scheme for early diagnosis of cardiovascular and other diseases, but also for prevention and control of such diseases. For this purpose, we have developed two kinds of non-invasive physiological monitoring systems. One is the systems utilizing furniture and furnishings in home to detect biosignals under daily life, and the other is portable systems for ambulatory monitoring of physiological valuables including blood pressure, cardiac output, posture change, walking speed, and so on.. In this paper, structure and performance of these systems are briefly described.

An optimal spot-electrodes array for electrical impedance cardiography through determination of impedance mapping of a regional area along the medial line on the thorax.

Electrical impedance or admittance cardiography is a simple method for non-invasive, continuous measurement the stroke volume and cardiac output. For the electrical impedance cardiography, the band-electrodes array proposed by Kubicek et al has been widely used, and various spot-electrodes array have been experimented in search of a less uncomfortable and equally reliable electrodes array that is easier to attach. From the uniformity of current distribution on the thorax, we have reinvestigated focusing on the measurement of contour maps of static and pulsatile components of a regional area along the medial line on the frontal part of the thorax. Consequently, the appropriate electrodes locations for current injection were determined as the back of an ear and on the lower abdomen, while those for voltage pick-up was on the medial portion at the level of clavicle and on the portion above the xiphisternum. Preliminary comparison experiments between the cardiac output values obtained by the electrical impedance cardiography and by a pulse dye-densitometry showed a fairy good agreement

Experimental and Numerical Study on Optimal Spot-electrodes Arrays in Transthoracic Electrical Impedance Cardiography

Transthoracic electrical impedance (or admittance) cardiography is a simple technique for the non-invasive and continuous monitoring of stroke volume or cardiac output by detecting the electrical impedance of a thorax which is roughly assumed to be a two-compartment coaxial cylindrical model composed of the aorta and its surrounding thoracic tissues. A tetra-polar band-electrodes method by Kubicek et al. has been widely used for the detection of the electrical impedance. However, this band-electrodes attachment makes a subject troublesome. Replacement of the band- to a spot-electrodes array is therefore highly required for practical use. In our previous reports, we have confirmed that a thorax is nearly assumed as an electrical cylinder model when a pair of current injection spot-electrodes are placed far from the thorax like a placement of the forehead - left medial knee or the mastoid process - lower right abdomen, and that the changes in current distributions associated with cardiac blood ejection are roughly homogeneous around the medial line of the thorax. The present study concerns with determination of an optimal spot-electrodes array for voltage pick-up through the detailed measurements of pulsatile components of the thoracic impedance along the medial line of the thorax using an 11times2 channels impedance mapping system. Additionally, we have investigated the influence of blood volume change in the heart itself by a finite element method. From these experimental and numerical investigations, it was suggested that the impedance change due to the blood volume change in the aorta without that in the heart can mainly be detected between the level of the clavicle and that of the xiphisternum. Consequently, an optimal electrodes-location for voltage pick-up was to be determined as the medial portion at the level of the clavicle and the portion above the xiphisternum.

An Improved Local Pressurization-Cuff Technique for Non-invasive Digital Arterial Pressure by the Volume-Compensation Method: Its Performance and Evaluation of Accuracy

The volume-oscillometric and volume-compensation methods, previously developed by us, are a useful and helpful means for non-invasive measurement of blood pressure. These methods are usually applied for digital arterial pressure measurement. During the continuous measurement of finger arterial pressure by the volume-compensation method, a band-type cuff wrapped around the finger has been conventionally used. However, this causes venous blood congestion at the distal portion of the cuff site due to occlusion of all veins under the cuff, resulting in uncomfortable and painful feeling for a subject. In order to reduce such congestion, we have previously designed a disk-type cuff unit for local pressurization to the digital artery. This local pressurization-cuff technique needs practice in proper attachment of the cuff unit: It is important to correctly place the cuff just above the digital artery concerned. It is therefore necessary to facilitate the determination of a proper cuff-position for practical use. To address this practical problem, the present study describes a definite method of this determination based on the nonlinear nature of arterial pressure-volume characteristics. We have also investigated the cuff-pressure transmission through the tissue by a finite element method. From the experimental and numerical investigations, we have developed the determination method together with a new cuff unit. To evaluate accuracy of the blood pressure measurement with this method, comparison experiments with the direct measurement of radial artery were made using healthy volunteers under informed consent. The results clearly indicate that a proper cuff-attachment could be easily achieved by this determination method and that the indirect finger arterial pressure showed good agreement with the direct radial artery pressure. The present technique with the volume-compensation method seems available for long-term as well as ambulatory arterial pressure monitoring.

Assessment of Stress-Induced Hemodynamic Responses Using Multipurpose Non-invasive Continuous Cardiovascular Monitoring System

In order to develop a simple and reliable assessment method of the stress induced psychosomatic and hemodynamic responses against various stress situations, especially for evaluating of the effectiveness of stress reduction methods, a multipurpose non-invasive continuous cardiovascular monitoring system was developed. The monitoring system could measure beat-by-beat finger blood pressure (SBP, MBP, DBP based on the volume-compensation method), cardiac output (CO, electrical admittance method), total peripheral resistance (TPR=MBP/CO), and the other hemodynamic related parameters (e.g. RR-interval, respiratory rate, pulse wave velocity, etc.). As controlled stress conditions, the human subjects would be exposed to the various stresses such as flash video display, electrical stimulation and so on. In this study, after 5 minutes resting, the stress induced hemodynamic responses were measured during 10-min presentation of floating vertical stripes image using 5 healthy subjects. The image presentation was discontinued when the subject gave his/her self-assessment due to considerable discomfort. The results showed that although BP increased during the presentation in all the subjects, there observed two types of cardiovascular responses; one is a type of increase in CO (or of almost unchanging or decrease in TRP), and the other of increase in TPR. These results strongly suggested that the detection of the change in TPR might be an important factor for the evaluation of stress conditions. Further investigations would be required for the reasons why these two types were observed in the same stressful condition.

A New Cuff Unit for Measuring Instantaneous Blood Pressure at the Finger Artery by Local Pressurization

A new cuff unit for measuring instantaneous blood pressure at the finger based on the volume-compensation method by local pressurization is developed, and its characteristics are evaluated. Results of measurement indicated that, the finger artery could be completely compressed using the local pressurization cuff, and the cuff-pressure controller is suitable for BP measurement in human. Also, the comparative measurements between the present cuff unit and the conventional band-type cuff indicated that, the venous congestion from the present unit is greatly reduced. Therefore, the present cuff unit is capable of non-invasively measuring instantaneous blood pressure at the finger artery in long term. The volume-compensation and Penaz methods are useful and helpful for the non-invasive measurement of instantaneous blood pressure (BP) on a beat-by-beat basis. In these methods, a band cuff which is wrapped around the finger is usually used. During the measurement, the cuff pressure is continuously controlled between diastolic and systolic pressure, and consequently it occludes all veins under the cuff. This causes blood pooling or venous congestion distal to the cuff site, resulting in discomfort for the subject. This is a serious problem, especially in long term BP monitoring (1~3). In order to reduce the congestion, many attempts are carried out. Imholtz et a1. (1) have tried to relieve the discomfort due to venous congestion by alternating between two fingers, an index and a middle finger, every 30 min. This may help reduce discomfort, but it does not essentially remove the venous congestion. There has been a proposal to use a superficial temporal artery as a measuring site for BP monitoring, hoping to prevent venous congestion and let the subject move hands freely (2). Although this approach is successful in overcoming these problems, great care is needed to attach the disk cuff firmly and accurately over the temporal artery. Also, Nakagawara et al (4) developed a local pressurization cuff unit for a finger artery pressure monitoring system based on the volume compensation method (5). The cuff unit consists of a disk-type cuff for local pressurization to the finger artery, a cuff-holding clip to ensure a firm attachment of the cuff with some local supporting points, and a photo-plethysmographic sensor. Since a local pressurization disk-type cuff is used and only part of the cuff-holding clip contacts with skin of the finger during measurement, the venous congestion is greatly reduced. But, little discomfort is still remained when using the unit because the finger is pinched by the cuff-holding clip which is made from aluminum. Also, the adjustment of the unit is not easy when searching the optimum detect position at the finger. In this paper, a newly developed solid type cuff unit for the non-invasive measurement of instantaneous blood pressure (BP) at the human finger based on the volume-compensation method is introduced, and its characteristics is evaluated.