Assuming that along the pulmonary arteries, mathematical expectations of branching are equal to matrix (Ei,j; i: parent branch class, j: daughter branch class number), we made computer drafts of patterns of pulmonary arterial branching trees from the published data of canine pulmonary arterial casts with the "Monte Carlo methods" by FORTRAN, calculating from these data, the numbers of branches, size and resistance of the trees. We also analyzed blood flow distribution in a pulmonary branch according to the pathlength from the entrance of the tree. The graphics of the trees were similar to the original arterial casts, and numbers of the branches were nearly the same as the previous reported values. Calculated resistance was reasonable. The rate of blood flow per unit vessel in the short pathlength group was calculated as 1.5 times that of the long pathlength group of the same diameter. We believe that our method of describing the branching pattern matrix (Ei,j) provides a reasonable simulation of complex branching patterns such as pulmonary arteries and a useful means to analyze local hemodynamics.

Animals↗

PubMedDate not supplied

Right ventricular failure during clinical use of a left ventricular assist device.

The purpose of this study is to describe the authors' clinical experience of RVF during LVAD pumping and to delineate the effect of LVADs on RV function, with special reference to the level of myocardial recovery. Pneumatically driven LVADs were used on a total of 13 postoperative cases for 18 hours to 70 days (mean, 9.9 days). The RVF, which was defined as increased right atrial pressure (RAP greater than or equal to 20 mmHg) during LVAD pumping, were experienced in four cases (two ischemic, two valvular). Duration of the RVF ranged from 3 hours to 8 days (mean, 3.0 days) and the maximum RAP ranged 22-30 mmHg (mean, 27 mmHg). The effects of LVAD pumping on the RV function were delineated during serial pump on-pump off studies in two cases with RVF and three cases without RVF, in relation to off/on ratio of the systolic aortic pressure (AOP off/on), which worked as an indicative parameter of myocardial recovery. Each pair of on/off data were assigned to four groups according to AOP off/on and complication with RVF, and mean percentage changes of mRAP and PAP were compared. The RAP of RVF cases were significantly increased by 16% with the LVAD pumping when the AOP off/on was below 0.7, whereas PAP invariably decreased in most cases. The results indicated that the LVAD suppressed the RV function before the myocardial recovery and when the heart was complicated with RVF.

Equipment Design↗

PubMedDate not supplied

Continuous monitoring of autonomic nerve information for the control of an artificial heart.

To drive an artificial heart system optimally, information from the autonomic nervous system may be needed; however, it is very difficult to monitor autonomic nerve discharges continuously. In this study, we propose a new automatic control algorithm for a total artificial heart (TAH) using fluctuations in the circulatory system. It was reported that fluctuations in hemodynamics reflect ongoing information from the autonomic nervous system. A Mayer wave at 0.1 Hz was reported to reflect sympathetic information. We observed fluctuations in vascular resistance, which can be measured during use of an artificial heart. Four adult goats were used for the experiments. Through a left thoracotomy, hemodynamic parameters were measured during chronic animal experiments. All time series data were recorded on magnetic tape. Quantitative analysis, statistics, and spectral analysis were carried out on a computer through an analog-digital (AD) converter. A Mayer wave peak was clearly recognized in all goats in the spectrum of vascular resistance. A band pass filter was used to convert this information to automatic control. Time series curves of the Mayer wave of vascular resistance were provided, and compared with the time series curve of the cardiac output. After a change in the Mayer wave, increase in cardiac output was observed. This phenomenon may be interpreted as sympathetic nervous control of changes in cardiac output. These results suggest that an artificial heart may be controlled by the measurement of the Mayer wave of vascular resistance, making it possible to control an artificial heart with neural information.

Algorithms↗

PubMedDate not supplied

Origin of chaos in the circulation: open loop analysis with an artificial heart.

To develop the optimal automatic control algorithm for an in vivo artificial heart system, investigation of the basic characteristics of the cardiovascular system may be important. The clinical significance of chaotic dynamics in the cardiovascular system has attracted attention. The circulation is a so-called complex system with many feedback circuits, making it very difficult to investigate the origin of chaos within the system. In this study, we investigated the origin of chaos by open loop analysis with an artificial heart (which has no fluctuation in pumping rate or contraction power) in chronic animal experiments with healthy adult goats. As a result, in the artificial heart circulatory time series data, low dimensional deterministic chaos was discovered by nonlinear mathematical analysis, suggesting the importance of blood vessels in the chaotic dynamics of the cardiovascular system. To investigate the origin of chaos further, sympathetic activity was directly measured in animals with artificial hearts. Chaotic dynamics was also recognized in sympathetic action potentials, even during artificial heart circulation. Coupling of the nonlinear information between blood vessels and sympathetic activity was suggested by analysis of mutual information. In chaotic dynamics, the central nervous system (CNS) played an important role through sympathetic activity. These findings may be useful for the development of an automatic control algorithm for an artificial heart.

Algorithms↗

PubMedDate not supplied

Development of an implantable artificial anal sphincter by the use of the shape memory alloy.

In this study, we developed and assessed an artificial anal sphincter driven by an shape memory alloy actuator (AS-SMA). The performance characteristics of the device were analyzed with a measurement system. Assessment showed that the AS-SMA could generate a pressure of 55 mm Hg at an atmospheric temperature of 36 degrees C, and displacement of the SMA actuator was 7.5 mm when the temperature of the SMA plate was 55 degrees C. To evaluate opening and closing, we studied a piglet colostomy model, in which the AS-SMA was implanted around the colostomy in the extraperitoneal space. Flow control tests using living porcine intestine revealed that the AS-SMA could maintain fecal continence against an intestinal pressure of 75 mm Hg. The high pressure zone corresponding to the location of the device was demonstrated in a manometric examination. For 6 days after surgery, we activated the AS-SMA twice a day and observed the bowel movements. The animal experiment indicated that the AS-SMA is able to control the bowel movements of patients with fecal incontinence if several problems, such as burning of tissue around the device and compression injury of the intestine, are resolved.

Alloys↗

PubMedDate not supplied

Automatic monitoring system for artificial hearts using self organizing map.

This study presents an automatic monitoring system for artificial hearts. The self organizing map (SOM) was applied to monitoring and analysis of an aortic pressure (AoP) signal measured from an adult goat equipped with a total artificial heart. In the proposed system, two different SOMs were used to detect and classify abnormalities in the measured AoP signal. In the first stage, an ordinary SOM, taught with only normal AoP data, was used for detection of abnormalities on the basis of the quantization error in the real-time monitoring task. In the second stage, a supervised SOM was used for classification of abnormalities. The supervised SOM can be regarded as an ordinary SOM with an extra class vector for solving the classification problem. The class vector is assigned to every node in the second SOM as an output weight learned according to Kohonen's learning rule. The effectiveness of detection and classification of abnormalities using these two SOMs was confirmed.

Animals↗

PubMedDate not supplied

Classical but effective techniques for estimating cardiovascular dynamics.

Explore the source record for details and available documents.

Animals↗

PubMedDate not supplied

Fundamental rhythm of sympathetic nerve discharges in animals with total artificial hearts.

To evaluate the effect of total artificial heart replacement on the autonomic nervous system, sympathetic neurograms were analyzed by power spectrum and coherence function. Two pneumatically driven, sac type ventricular assist devices were implanted as biventricular bypasses (BVB) in adult, mongrel dogs. After initiation of BVB pumping, the natural heart was electrically fibrillated to form a BVB TAH model. Renal sympathetic nerve activity (RSNA) was recorded using a bipolar electrode attached to the left renal sympathetic nerve. RSNA was amplified and integrated by use of an R-C integrator. Power spectra of the RSNA and values of squared coherence between the arterial pressure wave form and the RSNA were calculated by computer. In animals with total artificial hearts (TAHs), coherence at the cardiac rhythm frequency was decreased, and coherence at the TAH pumping rhythm frequency was increased. These results indicate that the arterial pulse wave observed in TAH animals contributed to the sympathetic neurogram.

Animals↗

PubMedDate not supplied

The newly designed univalved artificial heart.

A univalved artificial heart (AH) powered electromagnetically in the frequency range of 1-30 Hz was developed to obtain a totally implantable AH. This small sized AH consisted of a vibrating tube, coils, magnets, and a jellyfish valve as an outlet AH valve. The fluid mechanical, hemodynamic, and hematologic properties were evaluated in a mock circulation and 10 animal experiments using adult goats. This vibrating electromagnetic AH could generate more than 10 L/min as an output volume, with 10 Hz vibration using 20 volts supplied voltage. It could also provide two kinds of flow and pressure patterns, in constant-peak and periodic-peak patterns. The values of free hemoglobin remained within acceptable limits. The authors concluded that this new type of pump was useful as a totally implantable AH, ventricular assist, or organ assist system.

Blood Flow Velocity↗

PubMedDate not supplied

Real time sound spectral analysis for early detection of thrombosed Björk-Shiley standard disc valves.

Clinical usefulness of sound spectral analysis (SSA) in early detection of thrombosed Bjork-Shiley standard tilting disc prostheses (B-SP) was evaluated. Among a total of 365 B-SP, nine valves developed thrombosis. These included seven MVR and two AVR, and replacement of the affected valves was performed in all cases. Thrombus formation was localized at the minor strut in two cases in which the SSA demonstrated preoperative abnormalities of only opening clicks. In four cases, thrombus formation was noted at both minor and major struts, and the SSA showed abnormalities both on opening and closing clicks. In two cases with pannus formation, no abnormalities were found by SSA. As the thrombi were seen on the minor strut during surgery in all cases with thrombosed valves, the minor strut is considered as the preferred, and probably initial area of thrombus formation, and the diagnosis therefore could be made by abnormal findings on opening clicks. In conclusion, the SSA was found to be a useful diagnostic tool for early detection of thrombosis of B-SP, because the opening clicks of the tilting disc valves were often too low in amplitude for abnormalities to be detected by auscultation.

Adult↗