A novel apparatus for non-contact measurement of heart rate variability: a system to prevent secondary exposure of medical personnel to toxic materials under biochemical hazard conditions, in monitoring sepsis or in predicting multiple organ dysfunction syndrome

Development of a practicable non-contact bedside autonomic activation monitoring system using microwave radars and its clinical application in elderly people

We developed a practicable, non-contact, autonomic activation monitoring system using microwave radars without imposing any stress on monitored individuals. Recently, the rapid increase in the aging population has raised concerns in developed countries. Thus, hospitals and care facilities will need to perform long-term health monitoring of elderly patients. The system allows monitoring of geriatric autonomic dysfunctions caused by chronic diseases, such as diabetes or myocardial infarction (MI), while measuring vital signs in non-contact way. The system measures heart rate variability (HRV) of elderly people in bed using dual, 24-GHz, compact microwave radars attached beneath the bed mattress. HRV parameters (LF, HF, and LF/HF) were determined from the cardiac peak-to-peak intervals, which were detected by radars using the maximum entropy method. We tested the system on 15 elderly people with and without diabetes or MI (72-99 years old) from 7:00 p.m. to 6:00 a.m. at a special nursing home in Tokyo. LF/HF obtained by the system correlated significantly (R = 0.89; p < 0.01) with those obtained by Holter electrocardiography (ECG). Diabetic subjects showed significantly lower LF (radar) than non-diabetic (119.8 ± 57.8 for diabetic, 405.9 ± 112.6 for non-diabetic, p < 0.01). HF (radar) of post-MI subjects was significantly lower than that of non-MI (219.7 ± 131.7 for post-MI and 580.0 ± 654.6 for non-MI, p < 0.05). Previous studies using conventional ECG reveal that diabetic neuropathy decreases LF, and also MI causes parasympathetic attenuation which leads to HF reduction. Our study showed that average SDNN of post-MI patients is smaller than 50 ms which is known to have high mortality. The non-contact autonomic activation monitoring system allows a long-term health management especially during sleeping hours for elderly people at healthcare facilities.

Ultra-wideband sensors for improved magnetic resonance imaging, cardiovascular monitoring and tumour diagnostics

The specific advantages of ultra-wideband electromagnetic remote sensing (UWB radar) make it a particularly attractive technique for biomedical applications. We partially review our activities in utilizing this novel approach for the benefit of high and ultra-high field magnetic resonance imaging (MRI) and other applications, e.g., for intensive care medicine and biomedical research. We could show that our approach is beneficial for applications like motion tracking for high resolution brain imaging due to the non-contact acquisition of involuntary head motions with high spatial resolution, navigation for cardiac MRI due to our interpretation of the detected physiological mechanical contraction of the heart muscle and for MR safety, since we have investigated the influence of high static magnetic fields on myocardial mechanics. From our findings we could conclude, that UWB radar can serve as a navigator technique for high and ultra-high field magnetic resonance imaging and can be beneficial preserving the high resolution capability of this imaging modality. Furthermore it can potentially be used to support standard ECG analysis by complementary information where sole ECG analysis fails. Further analytical investigations have proven the feasibility of this method for intracranial displacements detection and the rendition of a tumour’s contrast agent based perfusion dynamic. Beside these analytical approaches we have carried out FDTD simulations of a complex arrangement mimicking the illumination of a human torso model incorporating the geometry of the antennas applied.

Contact-free Measurement of Heart Rate Variability via a Microwave Sensor

Measures of heart rate variability (HRV) are widely used to assess autonomic nervous system (ANS) function. HRV can be recorded via electrocardiography (ECG), which is both non-invasive and widely available. However, ECG needs three electrodes touching the body of the subjects, which makes them feel nervous and uncomfortable, thus potentially affecting the recording. Contact-free detection of the heartbeat via a microwave sensor constitutes another means of determining the timing of cardiac cycles by continuous monitoring of mechanical contraction of the heart. This technique can measure the heartbeat without any electrodes touching human body and penetrate the clothes at some distances, which in some instances may prove a practical basis for HRV analysis. Comparison of 5-minute recordings demonstrated that there were no significant differences in the temporal, frequency domains and in non-linear dynamic analysis of HRV measures derived from heartbeat and ECG, which suggested this technique may prove a practical alternative to ECG for HRV analysis.

Non-contact detection of myocardium's mechanical activity by ultrawideband RF-radar and interpretation applying electrocardiography

Electromagnetic waves can propagate through the body and are reflected at interfaces between materials with different dielectric properties. Therefore the reason for using ultrawideband (UWB) radar for probing the human body in the frequency range from 100 MHz up to 10 GHz is obvious and suggests an ability to monitor the motion of organs within the human body as well as obtaining images of internal structures. The specific advantages of UWB sensors are high temporal and spatial resolutions, penetration into object, low integral power, and compatibility with established narrowband systems. The sensitivity to ultralow power signals makes them suitable for human medical applications including mobile and continuous noncontact supervision of vital functions. Since no ionizing radiation is used, and due to the ultralow specific absorption rate applied, UWB techniques permit noninvasive sensing with no potential risks. This research aims at the synergetic use of UWB sounding combined with magnetic resonance imaging (MRI) to gain complementary information for improved functional diagnosis and imaging, especially to accelerate and enhance cardiac MRI by applying UWB radar as a noncontact navigator of myocardial contraction. To this end a sound understanding of how myocardial's mechanic is rendered by reflected and postprocessed UWB radar signals must be achieved. Therefore, we have executed the simultaneous acquisition and evaluation of radar signals with signals from a high-resolution electrocardiogram. The noncontact UWB illumination was done from several radiographic standard positions to monitor selected superficial myocardial areas during the cyclic physiological myocardial deformation in three different respiratory states. From our findings we could conclude that UWB radar can serve as a navigator technique for high and ultrahigh field magnetic resonance imaging and can be beneficial preserving the high resolution capability of this imaging modality. Furthermore it can potentially be used to support standard electrocardiography (ECG) analysis by complementary information where sole ECG analysis fails, e.g., electromechanical dissociation.

Optical Vibrocardiography: A Novel Tool for the Optical Monitoring of Cardiac Activity

We present an optical non-contact method for heart beat monitoring, based on the measurement of chest wall movements induced by the pumping action of the heart, which is eligible as a surrogate of electrocardiogram (ECG) in assessing both cardiac rate and heart rate variability (HRV). The method is based on the optical recording of the movements of the chest wall by means of laser Doppler interferometry. To this aim, the ECG signal and the velocity of vibration of the chest wall, named optical vibrocardiography (VCG), were simultaneously recorded on 10 subjects. The time series built from the sequences of consecutive R waves (on ECG) and vibrocardiographic (VV) intervals were compared in terms of heart rate (HR). To evaluate the ability of VCG signals as quantitative marker of the autonomic activity, HRV descriptors were also calculated on both ECG and VCG time series. HR and HRV indices obtained from the proposed method agreed with the rate derived from ECG recordings (mean percent difference <3.1%). Our comparison concludes that optical VCG provides a reliable assessment of HR and HRV analysis, with no statistical differences in term of gender are present. Optical VCG appears promising as non-contact method to monitor the cardiac activity under specific conditions, e.g., in magnetic resonance environment, or to reduce exposure risks to workers subjected to hazardous conditions. The technique may be used also to monitor subjects, e.g., severely burned, for which contact with the skin needs to be minimized.

Non-contact respiratory monitoring system using a ceiling-attached microwave antenna

Using a microwave antenna attached to the room ceiling, we conducted non-contact monitoring of respiratory chest wall motions of subjects in bed and covered by a soft comfortable bedding, to measure the vital signs of patients under nursing care in a welfare institution. Long-term vital sign monitoring using electrodes places a heavy burden on monitored individuals. Our non-contact respiratory monitoring system comprises a 1,215 MHz-microwave radar (LDR-1), antenna box attached to the ceiling, and personal computer with analyzing software. The system was tested on eight healthy volunteers (mean age, 25 years; range, 21-44 years) and eight elderly volunteers with some disorders (mean age, 69 years; range, 66-75 years). Respiratory rates of subjects measured using this system correlated with rates measured using respiration sensors (r=0.97, P<0.001 for healthy volunteers, r=0.98, P<0.0001 for elderly volunteers). The system could monitor subtle changes in respiratory rate, and monitoring respiratory rate increases caused by disorders such as pneumonia will be possible.