Yoshiaki Katahira

Effect of left ventricular assistance on sympathetic tone.

To determine the effect of left ventricular assist device (LVAD) pumping on sympathetic tone, renal sympathetic nerve activity (RSNA) was detected in acute animal experiments. Our TH-7B pneumatically driven, sac-type ventricular assist device was used in 7 adult mongrel dogs. RSNA was detected by the use of bipolar electrodes attached to the left renal sympathetic nerve. RSNA was amplified and integrated by use of an R-C integrator circuit. The area of the integrated nerve discharge per unit time was calculated in the computer system and expressed as RSNA per unit time. During LVAD pumping, RSNA decreased with increase in blood pressure, with an increase in pulmonary artery flow, and with a decrease in left atrial pressure. These data suggest that LVAD has an effect on the sympathetic nervous system which is mediated by the aortic and cardiopulmonary baroreflex system.

An automatic control algorithm for the optimal driving of the ventricular-assist device

A new method of keeping one of the most suitable driving conditions for regulating the outflow volume from the ventricular-assist device (VAD) is presented. The experimental results from a mock circulatory system have shown that the relationship between the stroke volume and the systolic duration of the VAD can be specified by the combination of characteristic curves of the positive and negative drive pressures. The optimal operating point on the characteristic curve has been defined as the point at which thrombosis on the blood-contacting surface and hemolysis due to mechanical damage can be avoided and at which the driving energy can be minimized. The present analysis shows that the optimal operating point is the vertex of the triangular figure obtained from the characteristic curve. The algorithms for keeping the optimal operating point and for regulating the stroke volume are given.<<ETX>>

Fundamental Rhythm of Sympathetic Nerve Discharges in Animals with Total Artificial Hearts

To evaluate the effect of total artificial heart replacement on the autonomie 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.

Experimental and clinical evaluation of a sack-type ventricular assist device and drive system

A newly designed ventricular assist device and driving system, including an automatic control system, is presented. The blood-contacting surfaces of the blood pump are coated with either Cardiothane or Cardiomat. The system was tested in experiments on goats, whereby only one of fifteen animals showed sudden thrombus formation after 34 pumping days. The system was also applied in three clinical cases for durations of 18 h, 2 days, and 5 days. In two of the cases, weaning could not be performed because of continued bleeding, and the other patient is still alive. No gross findings of thrombus formation were observed in any of the cases, except for a thin circular thrombus at the junction of the connectors and the sack of the blood pump.

A mobile communications system for home-visit medical services: The Electronic Doctor's Bag

In the present study, “Electronic Doctors Bag” which is a tele-healthcare tool for home-visit medical service using the mobile communications environment has been proposed and evaluated by preliminary experiments. It was shown that its basic function was sufficiently evaluated by a few doctors and nurses but further improvement in portability and operability is required on the basis of much more opinions of medical and nursing professionals.

Spiral systolic blood flow in the ascending aorta and aortic arch analyzed by echo-dynamography

Using echo-dynamography, systolic blood flow structure in the ascending aorta and aortic arch was investigated in 10 healthy volunteers. The blood flow structure was analyzed based on the two-dimensional (2D) and 1D velocity vector distributions, changing acceleration of flow direction (CAFD), vorticity distribution, and Doppler pressure distribution. To justify the results obtained in humans, in vitro experiments were done using straight and curved tube models of 20mm diameter. The distribution of the CAFD showed a spiral staircase pattern along the flow axis line. In addition, the changes in the velocity profile in the short-axis direction, 2D distribution of the vorticity, and velocity vector distribution on the aortic cross-section plane, all confirmed the presence of systolic twisted spiral flow rotating clockwise toward the peripheral part of the ascending aorta. The rotation cycle of this spiral flow correlated inversely with the maximum velocity of the aortic flow, so that this cycle was shorter in early systole and longer in late systole. The model experiments showed similar results. The spiral flow seemed to be produced by several factors: (i) anterior shift of the direction of ejected blood flow due to the anterior displacement of the projection of the aorta; (ii) accelerated high pressure flow ejected antero-upward; (iii) inertia resistance at the peripheral boundary of the sinus of Valsalva; and (iv) reflection caused by the concave spherical structure of the inner surface of the basal part of the aorta. Because the main spiral flow axis line nearly coincided with the center line of the aorta, it is concluded that the occurrence of the spiral flow plays an important role in maintaining the blood flow direction passing through the cylindrical curved aortic arch and thus in keeping the most effective ejection as well as in dispersing the shear stress in the aortic wall.

Real-time cardiac output estimation of the circulatory system under left ventricular assistance

A method for indirect and real-time estimation of the cardiac output of the circulatory system supported by the left ventricular assist device (LVAD) is proposed. This method has low invasiveness and is useful for clinical applications of the LVAD since it needs only two measurements: the rate of blood outflow from the LVAD and the aortic pressure. The method is based on a system identification technique for the time-series model of the cardiovascular system and requires less computational time than other methods with similar estimation accuracy. Hence, the method could be implemented in a personal computer system and realize online, real-time estimation of the instantaneous outflow rate of the natural heart. Results obtained in vitro using a mock circulatory system and in vivo using an adult goat show that the method can yield a fairly high correlation coefficient between the true stroke volume of the natural heart and its estimate of more than 0.99 (in vitro) or 0.95 (in vivo). The estimation method thus appears suitable for clinical use.<<ETX>>

Estimation of the following Cardiac Output Using Sympathetic Tone and Hemodynamics for the Control of a Total Artificial Heart

A sympathetic neurogram is potentially useful for the development of a real time total artificial heart (TAH) control system. We used sympathetic tone and hemodynamic derivatives to estimate the following cardiac output in acute animal experiments using adult mongrel dogs. Moving averages of the mean left atrial pressure and mean aortic pressure were used as parameters of the preload and afterload, respectively. Renal sympathetic nerve activity (RSNA) was employed as a parameter of sympathetic tone. Equations for the following cardiac output were calculated using multiple linear regression analysis of the time series data. A significant correlation was observed between the estimated and following measured cardiac output. These results suggest the potential usefulness of the sympathetic neurogram for the real time TAH automatic control system.

Physiological basis and clinical significance of left ventricular suction studied using echo-dynamography

BACKGROUND The existence as well as the exact genesis of left ventricular suction during rapid filling phase have been controversial. In the present study, we aimed at resolution of this problem using noninvasive and sophisticated ultrasonic methods. The clinical meaning was also documented. METHODS Ten healthy male volunteers were examined by 2D echocardiography and echo-dynamography which enables us to obtain detailed instantaneous data of blood flow and wall motion simultaneously from the wide range of the left ventricle. The correlation of blood flow and wall motion was also studied. RESULTS Rapid ventricular filling was divided into 2 phases which had different physiology. The early half (early rapid filling: ERF) showed the effect which was alike drawing a piston. This was proved by the shape of the velocity of inflow and the basal muscle contraction which actively assisted extension of the relaxed apical and central parts of the left ventricle, giving the negative pressure which causes the ventricular suction. The later half (late rapid filling: LRF) showed the turning of the fundamental flow and the squeezed basal part just like the sphincter in addition to the expansion of the apical and central portions of the left ventricle, and all of these cooperatively augmented the suction effect. CONCLUSION Ventricular suction does exist to help ventricular filling. Simultaneous appearance of the contraction in the basal part and the relaxation or extension in the apical part during the post-ejection transitional period was made to occur the suction in the LV. And it can be said that the suction appeared in the late stage of systole as the one of the serial systolic phenomena.

Need for radiation safety education for interventional cardiology staff, especially nurses

Objective Cardiac interventional radiology (IR) can cause radiation injury to the staff who administer it as well as to patients. Although education in the basic principles of radiation is required for nurses, their level of radiation safety knowledge is not known. The present study used a questionnaire protocol to assess the level of radiation safety knowledge among hospital nurses. Methods and results A questionnaire to assess the level of training and current understanding of radiation safety was administered to 305 nurses in 2008 and again to 359 nurses in 2010. Our study indicates that nurses had insufficient knowledge about radiation safety, and that a high percentage of nurses were concerned about the health hazards of radiation. Moreover, more than 80% of the nurses expressed an interest in attending periodic radiation safety seminars. Annual radiation protection training for hospital staff (including nurses) is important. Conclusions Our results suggest that nurses do not have sufficient knowledge of radiation safety and should receive appropriate radiation safety training. Many had a minimal understanding of radiation and thus had significant concerns about the safety of working with radiation. Periodic radiation safety education/training for nurses is essential.