Harutoyo HIRANO

This paper proposes a circulatory condition-monitoring system with an air-pack sensor for ongoing measurement of pressure signals in supine patients with cervical spinal cord injuries. The system can be used to determine pulse pressure waves, pulse beats, respiratory waves and the augmentation index (AI). In this study, the physiological significance of signals obtained via the sensor was elucidated by comparing them with signals actually measured using commercial devices. The results showed a close correspondence between the signals obtained using the proposed system and the pulse pressure waves, breathing waveforms and RR-intervals. The AI values estimated using the air-pack sensor also displayed a high level correlation with those determined from radial artery pressure waveforms. To verify the performance of the proposed system, a patient with an injury was tested while asleep. The results confirmed that the system can be used to assess circulatory states of arteriosclerosis using the estimated AI values.

This paper proposes a novel non-invasive palpable sensor to measure carotid pulse pressure. The unit consists of a pair of coil printed circuit boards, a pair of springs, and a sensing plastic chip. The distance between the boards is monitored from the displacement of the springs, and the information is converted into a voltage signal based on electromagnetic induction. In this study, carotid pulse pressures of seven healthy males were measured using the proposed sensor and a commercial pulse pressure transducer. The results showed that the correlation coefficient between the two waveforms was 0.90 or more and the carotid pulse pressure was palpable throughout with the proposed sensor. Thus we conclude that the proposed sensor enables non-invasive measurement of carotid pulse waves.

This paper proposes a noninvasive method for estimating the dynamic characteristics of arterial walls using pulse waves measured in various parts of the body by a foil-type pressure sensor. The sensor was employed to measure pulse waves based on the tonometry approach, and a method of estimating changes in arterial viscoelastic indices was proposed based on the measured pulse waves and photoplethysmograms. In order to accurately measure blood pressure, we examined suitable mechanical forces externally applied to the sensor, and found that values of 5-25 [N] yielded the best performance. We then estimated the arterial viscoelastic indices of a radial artery and a dorsal pedis artery when mechanical pain stimuli were applied to the subjects. The results suggested the estimated indices can be used to quantitatively assess vascular response caused by sympathicotonia. We thus concluded the proposed method enabled noninvasive measurement of pulse waves and estimation of viscoelastic indices.

This paper proposes a new model for estimating dynamic viscoelasticity of peripheral arterial wall using arterial pressure and photoplethysmogram. The proposed model is able to suppress the well-known pressure dependency of arterial stiffness using a log-linearization technique and estimate the changes of viscosity as well as stiffness of peripheral arterial wall induced by autonomic nervous activity. The validity of the proposal model is discussed by estimating the change of stiffness values during arm position tests and during endoscopic thoracic sympathectomies (ETSs). As results of the arm position tests, the position-dependent change of the stiffness was very little between arm positions during at rest and during loading (Up: 3.8 [%], Down: 5.6 [%]). Then, as results of the ETSs, the variation of the stiffness was significantly changed between before and during the ETS procedure (p<0.005), and between during and after the ETS procedure (p<0.025). Thus we concluded that the proposed method enabled to assess changes in the autonomic nervous activity.

This paper reports on the analysis of electric field intensity radiated from a ventricular assist device (VAD). We constructed two types of models (i.e., a VAD model without a human and one with a human) in an electromagnetic simulator (SEMCAD-X). The VAD model without a human (Model 1) consisted of the external controller, a couple of wires, and the VAD actuator in a tank (27 cm x 27 cm x 10 cm) filled with physiological saline. The VAD model with a human (Model 2) consisted of Model 1, plus the addition of a cylinder 40 cm diameter and 172 cm high (e.g., 100 MHz : relative permittivity: 66, conductivity: 0.7). This cylinder simulated a muscle in the human body. During the simulation, the maximum electric field intensity (E) to a distance three meters from these models was analysed from 30 MHz to 200 MHz. When the frequency was 30 MHz, E of model 1 was larger than E of model 2 by 1.6 dBμV/m. Therefore, there is a possibility that the human body absorbs electromagnetic waves and reduces the electric field intensity.

Implantable medical devices need to transmit information between the inside and the outside of a human body. Therefore, sufficient information needs to traverse a long communication distance but at low power. However, electromagnetic waves attenuate when information is transmitted through tissues such as muscle, skin, and various organs. In this paper, we propose a new method for wireless information transmission that uses whole-body resonance. First, we constructed a cylindrical human body model (170 mm high). Electromagnetic simulation was provided by a small implanted dipole antenna. We then examined the maximum frequency values, taking the electric and magnetic fields surrounding the human body model and dividing by the transmitting power of the antenna. The maximum frequency value was 43 MHz, which was essentially the same frequency as the theoretical value of whole-body resonance (44.1 MHz). Therefore, information may possibly transmit more efficiently using whole-body resonance.

This paper reports on the impact of setup of a ventricular assist system (VAS) and the VAS surroundings on measurement of electromagnetic noise from VAS, based on CISPR pub.11. We measured four types of electromagnetic noise. Type 1 consisted only of the VAS. Type 2 was the VAS and a human subject who gripped the VAS actuator. Type 3 was the VAS and a copper rod that connected to ground and the actuator. Type 4 was the VAS and a human who gripped the actuator and directly touched the copper rod. When the measurement frequency was 30 MHz, the electromagnetic noise of Type 2 increased by 1.6 dBμV/m, compared to the electromagnetic noise of Type 1. Electromagnetic noise of Type 3 and Type 4 also increased, by 5.2 dBμV/m and 2.6 dBμV/m, respectively, compared to electromagnetic noise of Typel. Based on these results, the setup of a VAS and its surroundings were confirmed to affect the amounts of electromagnetic noise measured.