Biomedical subjects

K Toda

Publications and source records attributed to K Toda.

At least 379 records · Page 21Linked to original sources

PubMedDate not supplied

MR image and CT scan of a tuberculous abscess in the gluteus maximus muscle.

A 77-year-old man had rapidly increased intramuscular tuberculous abscess in his left buttock. Radiographs showed a bone defect in the left ischium. Postcontrast CT scanning revealed marginal enhancement. MR imaging showed low signal intensity on T1-weighted images and high signal intensity on T2-weighted images. T1-weighted MR images with Gd-DTPA enhancement showed enhancement of the wall. Bone defect and marginal enhancement on postcontrast MR images and on postcontrast CT images are image character of the intramuscular tuberculous abscess.

Abscess↗

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Histologic and scanning electron microscopic study of the glenoid labrum.

Three-dimensional fibrillar architecture of the glenoid labrum and its attachment to the glenoid rim were studied in 15 cadaveric shoulders to understand the pathophysiologic condition of various shoulder diseases. The true anatomic labrum was a narrow band located at the junction of the glenoid rim and fibrous capsule and varied considerably in size and shape. A triple-layered collagen structure of the labrum was observed by scanning electron microscopy. The thin superficial layer (articular surface) was a reticulated fibrillar network. The second layer was stratified. These two layers seem to act as a bumper against impact on the humeral head. The third, main layer of the labrum consisted of bundles of the fine fibrils densely arranged almost parallel to each other and oblique to the glenoid rim. This layer appears to act as a cushion to stabilize the shoulder joint.

Adult↗

PubMedDate not supplied

The electroretinogram of the rhodopsin knockout mouse.

The electroretinogram (ERG) of the rhodopsin knockout (rho-/-) mouse of Humphries et al. (1997) (Humphries et al., 1997) was studied for evidence of light-evoked rod activity and to describe the cone function. The rho-/- retina develops normal numbers of rod and cone nuclei, but the rods have no outer segments, and no rhodopsin is found by immunohistochemistry. The dark-adapted ERG threshold was elevated 4.7 log units above wild-type (WT) control mice, indicating that any residual rod responses were reduced >50,000-fold, consistent with a complete functional knockout. The dark-adapted rho-/- ERG had a cone waveform, and the spectral sensitivity peaked near 510 nm for both dark-adapted and light-adapted conditions, without evidence of a Purkinje shift. The light-adapted ERG b-wave amplitude of young rho-/- mice was the same as WT. The amplitude remained steady up to postnatal day P47, but thereafter it declined to only 1-2% by P80 when no cone outer segments remained. Cone b-wave threshold of dark-adapted rho-/- mice was -1.07 +/- 0.39 log cd-s/m2 (n = 17), which is 1.27 log units more sensitive than light-adapted thresholds against a rod-suppressing Ganzfeld background of 1.61 log scotopic cd/m2. This indicates that dark-adapted WT responses to still dimmer stimuli are exclusively rod driven with minimal cone intrusion. Above this cone threshold intensity, the dark-adapted b-wave of WT will be a summation of rod and cone responses. Threshold versus intensity (TVI) studies gave no evidence of a rod influence on the mouse cone b-wave.

Animals↗

PubMedDate not supplied

Development and evaluation of components for a totally implantable artificial heart system.

The authors have been developing an electrohydraulic (EH) artificial heart system for total implantation. This system consists of intrathoracic ventricles, an abdominally placed EH actuator, flexible silicone oil conduits, externally coupled transcutaneous energy transfer (TET) system, transcutaneous optical telemetry (TOT) system, internal battery, and internal control drive unit. Fitting was evaluated in chronic animal experiments as a pneumatic system in 11 goats weighing 55.2 +/- 4.2 kg and 3 calves of 52.3 +/- 1.2 kg. The longest survival time in calves was 111 days, and that in goats was 51 days. The assembled EH pump was implanted in two goats of 49 and 50 kg as an acute experiment, and 4.2-6.7 L/min of cardiac output was maintained. For the TET system, an internal coil 3 cm in diameter was implanted to make an arch covered by skin. Electric energy was transmitted from the external to the internal coil, and energy of about 20 W was carried through wires to an external load. The DC-to-DC efficiency of the system was 76-83% for 40 days. The TOT system with internal light emitting diodes and external photodiodes also was evaluated in a goat. Disalignment of up to 12 mm was tolerated. Although more improvement is necessary, most of the components showed characteristics desirable for a totally implantable system.

Animals↗

PubMedDate not supplied

Development of an electrohydraulic total artificial heart at the National Cardiovascular Center, Osaka, Japan.

The authors have been developing an electrohydraulic total artificial heart with a basic concept placing the blood pumps and an electrohydraulic energy converter separately, in the thorax and the abdominal region, respectively, to minimize anatomic constraints. Major problems of the system were a high energy consumption of 56 W at 6 L/min output and an insufficient maximum output of 6.7 L/min. The energy converter was redesigned to overcome these problems. A three phase, 4 pole brushless DC motor, which has maximum efficiency of 79% at a motor rotation of 2500 rpm with a load of 0.1 Nm, was developed for the new energy converter. Flow-channel design of the regenerative oil pump was optimized, which resulted in increasing the maximum flow rate at one directional motor rotation from 18 to 29 L/min. In vitro performance of the electrohydraulic total artificial heart was evaluated in a mock circulation with physiologic pressure conditions. Maximum output was increased to 10.7 L/min at a pump rate of 120 bpm and energy consumption of the motor at 6 L/min output was reduced to 18 W. Based upon these favorable results, the system is now being assembled for chronic animal implantation.

Animals↗

PubMedDate not supplied

Heat generation and hemolysis at the shaft seal in centrifugal blood pumps.

The heat and hemolysis around a shaft seal were investigated. Materials were original pumps (Nikkiso HMS-15:N-original, and 3M Delphin:D-original), vane-removed pumps (Nvane(-), Dvane(-)), and a small chamber with a shaft coiled by nichrome wire (mock pump). The original pumps were driven at 500 mmHg and 5 L/min, and vane-removed pumps were driven at the same rotation number. An electrical powers of 0, 0.5, 2, and 10 W was supplied to the mock pumps. In vitro hemolytic testing showed that hemolytic indices were 0.027 g/100 L in N-original, 0.013 in Nvane(-), 0.061 in D-original, and 0.012 in Dvane(-). Measurement of heat with a thermally insulated water chamber showed total heat within the pump of 8.62 and 10.85 W, and heat at the shaft seal of 0.87 and 0.62 W in the Nikkiso and Delphin pumps, respectively. Hemolysis and heat generation of mock pumps remained low. The results indicate that the heat generated around the shaft seal was minimal. Hemolysis at the shaft-seal was considerable but not major. Local heat did not affect hemolysis. It was concluded that the shaft-seal affected hemolysis, not by local heat but friction itself.

Animals↗

PubMedDate not supplied

Development and in vivo evaluation of an implantable left ventricular assist system with an impedance based monitoring and control system.

We have developed an implantable pneumatically driven diaphragm left ventricular assist system (LVAS) for small adults, and an electric impedance based monitoring and control system (Z system). In this Z system, measurement of electric impedance of the blood chamber is performed by charging an alternating current with a constant amplitude between two metal connectors without compromising anti-thrombogenicity. Automatic calibration was performed periodically by measuring trough values of impedance in the blood chamber for several beats while the blood pump was in a full-fill state under preset driving conditions. For precise control of the fill-to-empty (F/E) drive, an automatic trigger level adjustment method was developed. This method is an automatic searching algorithm that identifies the volume change of the last ejection or filling by the Z system and settles the next trigger level to maintain a definite stroke volume. In chronic in vivo evaluation, this LVAS was used in 13 adult goats. The pump was installed between the LV apex and the descending aorta and was placed in the abdominal wall. Pump output ranged from 2.5 to 5.8 L/min, and the Z system provided good monitoring. The F/E drive was achieved satisfactorily by this Z system. The physical condition of the goats was excellent for as long as 19 weeks. Hematologic, hepatic, and renal functions were within the normal range, and no prominent thromboembolic symptoms were observed. A new mobile control drive unit with this Z system is being developed. We conclude that this LVAS with the Z system is promising for long-term use in a clinical setting.

Adult↗

PubMedDate not supplied

Development of an intravenous axial flow pump for temporary right heart assist.

In clinical settings, quick application systems with easy access for circulatory support are desired. For left heart assist, an intraarterial axial flow pump (Hemopump) has been developed and applied to clinical cases. However, no simple way has been proposed for right heart assist. We have developed an intravenous axial flow pump for temporary right heart assist and have reported its hemodynamic effect. In this study, in vivo evaluation of this system was performed. The pump system consists of an outflow cannula, an impeller that was newly developed for intravenous use, and a driving system for the Hemopump. A prototype pump demonstrated 3.2 L/min of maximal flow at a pressure differential against 40 mmHg at a pump speed of 28,000 rpm in mock circulation. Application to goats is as follows. A 14 mm low porosity graft was anastomosed to the infrarenal inferior vena cava (IVC). The pump system was inserted into the IVC through the graft and advanced to the right heart using balloon catheter guidance under fluoroscopy, and the tip of the cannula of the pump was positioned at the main pulmonary artery. In acute experiments, this system provided effective right heart assist under induced pulmonary stenosis and induced biventricular failure with left ventricular assist. Chronic animal experiments were performed for as long as 4 hr using adult goats weighing 51-54 kg. There were no difficulties in pump insertion. In one goat, the drive shaft was broken because of kinking of the shaft inside the body, caused by failure in securing the pump. Levels of platelet counts and plasma hemoglobin were acceptable, and there was no prominent damage to heart tissues. In conclusion, an intravenous axial flow pump introduced through a peripheral vein is practicable for temporary right heart assist.

Animals↗

PubMedDate not supplied

Improvement in antithrombogenicity in a centrifugal pump with self wash-out structure for long-term use.

Antithrombogenicity in the initial (NCVC-1) centrifugal pump (CP) developed at our institute is provided by a central balancing hole in an impeller that promotes self wash-out blood flow (Sf) around the impeller. The current CP (NCVC-2) was ameliorated to obtain better antithrombogenicity, where the balancing hole diameter was widened to improve Sf velocity (Vsf), and the edge of a thrust bearing (TB) was rounded to minimize flow separation. Effects of the modifications were assessed in in vitro and in vivo studies. The Vsf of the NCVC-1 and the NCVC-2 evaluated by Doppler velocimeter were 12.8 and 22.1 cm/sec, respectively. Flow around the TB visualized by a light cutting method confirmed less flow stagnation in the NCVC-2. In vivo antithrombogenicity of the CPs was investigated in three goats. A pulsatile VAD (P-VAD) was installed paracorporeally between the left atrium and the aorta. After 3 weeks, the P-VAD was exchanged for the NCVC-2 and the NCVC-1 in sequence. Each CP was driven for 1 week and disassembled. No anticoagulation was used, except for heparin injection at pump exchange. Thrombus at the TB was found in the two NCVC-1s, and two little thrombi were on the impeller of another NCVC-1, whereas a thrombus smaller than 1 mm3 at the TB was noted in one NCVC-2. These results indicate that the NCVC-2 has better antithrombogenicity and Sf around the impeller and the TB.

Animals↗

PubMedDate not supplied

Acute phase responses of vasoactive hormones to non pulsatile systemic circulation.

Acute phase responses of vasoactive hormones to the rapid conversion of a systemic flow pattern from pulsatile or non pulsatile mode to the reverse were assessed in 20 goats weighing 45-69 kg. A total left heart bypass was instituted under general anesthesia, with pulsatile and non pulsatile pumps interposed in the circuit in parallel, and the systemic flow mode was rapidly and bidirectionally converted from the pulsatile mode or non pulsatile mode to the reverse. Vasoactive hormone levels and hemodynamics were evaluated before and after 5 min of conversion. No significant difference was observed between the modes either in blood flow or systemic vascular resistance, while the mean aortic pressure was significantly higher in the non pulsatile mode than the pulsatile mode (106.7 +/- 2.4 versus 99.9 +/- 3.5 mmHg). Among various vasoactive hormone levels evaluated, only norepinephrine showed a significant difference between the modes, where concentration in the non pulsatile mode was significantly higher than the pulsatile mode (391.0 +/- 60.7 versus 309.4 +/- 42.5 pg/ml). No correlation was found between the absolute values of mean aortic pressure and norepinephrine level, whereas a significant reciprocal correlation was detected between the magnitude of inter-mode differences in these two parameters. In conclusion, a non pulsatile systemic circulation does not exert significant influence on vasoactive hormone levels, except for slight increase in norepinephrine with a reciprocally correlated increase in mean aortic pressure. It is deduced that activity of the sympathetic nervous system represented by norepinephrine level is higher in the non pulsatile mode than the pulsatile mode, and the baroreceptor reflex functions in an acute phase after flow mode conversion.

Acute-Phase Reaction↗

PubMedDate not supplied

How does the sympathetic nervous system behave during non pulsatile circulation?

Non pulsatile circulation is commonly applied to clinical cardiopulmonary bypass or circulatory assist. However, influences of non pulsatile circulation on sympathetic nerve activity, which plays an important role in circulatory control, have not been elucidated. In this study the renal sympathetic nerve activity (RSNA) was recorded for the first time in goats, whose heart rate and size are similar to humans', and the difference during pulsatile and non pulsatile circulation was evaluated. Total left heart bypass was instituted in eight adult goats under general anesthesia. A pneumatic pulsatile pump and a centrifugal non pulsatile pump were incorporated in parallel so that pulsatile circulation and non pulsatile circulation could be instantly converted to the other. The pumping rate was set at 90/min regardless of the native heart rate during pulsatile circulation and the mean aortic pressure was maintained constant at the conversion of circulatory mode. The original signals of RSNA were integrated and defined as the mean RSNA. The mean RSNA and the mean aortic pressure were averaged every 30 sec and quantified during pulsatile circulation and non pulsatile circulation. The pulse synchronized burst of RSNA during pulsatile circulation immediately disappeared and the mean RSNA significantly increased up to 120% of pre depulsation level after changing the circulatory mode to non pulsatile circulation. Reverse conversion of circulatory mode from non pulsatile circulation to pulsatile circulation decreased the mean RSNA to 79%. The results suggest that vasotonus may be affected in its periodicity as well as its quantity by the loss of pulsation during the initial phase after depulsation.

Animals↗

PubMedDate not supplied

Long-term cardiopulmonary support with a composite artificial heart-lung system.

A novel cardiopulmonary support (CPS) system as a long-term total substitute for the natural heart and lung was designed and evaluated. The CPS system is composed of a ventricular assist device (VAD) and a newly developed compact artificial lung (AL). The pneumatic VAD was originally developed in the authors' institute and has proven durable and antithrombogenic in over 120 clinical uses. The AL, with 1.2 m2 membrane surface area and 140 ml priming volume, consists of a special gas exchange membrane where not only are micropores blind-ended to prevent serum leakage, but the blood contacting surface is treated with heparin binding to ease systemic anticoagulation. Chronic animal experiments of total CPS were carried out in three goats weighing from 28 to 36 kg. Venoarterial bypass was instituted with the CPS system in which all venous blood was drawn from both the right atrium and ventricle and returned to the aorta. No systemic anticoagulation was conducted except for heparin added fluid infusion from pressure lines. One animal survived for 2 weeks without any device related problems until electively euthanized. Blood flow rate ranged between 3.2 to 4.5 L/min, O2 transfer between 120 to 220 ml/min, and CO2 removal between 60 to 210 ml/min. No substantial changes were found in platelet count or other coagulation factors. These results indicate that the system has the ability to be used for long-term CPS, such as a bridge to lung or heart-lung transplantation.

Animals↗

PubMedDate not supplied

Power of the fatigue resistant in situ latissimus dorsi muscle.

To evaluate the in situ latissimus dorsi muscle as an actuator for circulatory assistance, 1) muscle power was analyzed in animal experiments, and 2) muscle weight was measured in human cadavers. Three adult goats underwent 12 week preconditioning. The insertion of the latissimus dorsi muscle was then connected to a spring and a tension transducer in series. The stroke length was measured with a photosensor without power loss. With contraction of muscles under various loads, tension-length relationships at end contraction and end relaxation were obtained and the maximum area of a square drawn within both lines was assumed to be maximum external power. Good fatigue resistance and the highest maximum external power of 3.16 Watts/kg at 120 min was derived from preconditioned latissimus dorsi muscle in burst frequency of 50 Hz. Muscle weight in 42 human cadavers was negatively correlated with age (r = 0.56) and was expected to be 221.6 g in patients aged 45 years. According to these data, the power of a human preconditioned latissimus dorsi muscle was estimated as 0.7 Watts. It was concluded the power of in situ preconditioned latissimus dorsi muscles was appropriate for right heart assistance or counterpulsation for left heart assist.

Aged↗

PubMedDate not supplied

An approach to reducing hemolysis in an axial-flow blood pump.

In an attempt to decrease hemolysis caused by an axial-flow blood pump, we studied whether specific speed (Ns) at a design point (determined by flow in m3/min, pump head in m, and pump speeds in rpm), should be kept within the existing engineering standard range (1000 < Ns < 2500) or whether pump speed should be reduced to a minimum (Ns < 1000). Four pumps (A: 14,000 rpm, B: 18,000 rpm, C: 22,000 rpm, and D: 26,000 rpm), each with an impeller 11.8 mm in diameter, were designed to accommodate a flow rate of 5 L/min and a pressure head of 100 mmHg. At this design point, the Ns of each pump was calculated as A:758, B:974, C:1191, and D:1407. Pump performance was observed, and the total efficiency of each pump was calculated. The hemolysis index (HI) was calculated after simultaneous testing in duplicate of all four pumps using fresh goat blood (anticoagulated with citrate-dextrose solution) in a closed mock-loop circuit. Total efficiency of each pump was calculated as A:49%, B:50%, C:45%, and D:22%. In the first hemolytic test, HIs were measured as A:0.066, B:0.18, and C:0.13; a water seal failed in pump D. In the second test, HIs were B:0.077, C:0.0499, and D:0.12; a bearing failed in pump A. It is concluded that a lower level of hemolysis is associated with a pump speed in the minimum range at the design point, even though Ns is outside the standard range.

Animals↗

PubMedDate not supplied

Set-up, improvement, and evaluation of an electrohydraulic total artificial heart with a separately placed energy converter.

The authors have been developing an electrohydraulic total artificial heart (TAH) system with a separately placed electrohydraulic energy converter to minimize anatomic constraints in the pericardial space. Improvements to the system and current status of the development are reported. The energy converter was miniaturized to improve implantability, and its thickness was reduced to 54 mm. System efficiency was increased by suppressing rush current at the time of motor reversal. Maximum cardiac output of the TAH system was 9 L/min, and maximum system efficiency increased to 10%. The blood pump system was implanted easily in the body of a 57 kg calf, and no significant temperature rise on the energy converter surface was observed. As the next step, main components were integrated into a total system. The transcutaneous energy transfer system could supply power to the TAH without a decline in pump performance, and the internal battery could support the system at 6.5 L/min of cardiac output for 1 hour without a decrease in cardiac output. The authors consider the TAH system with a separately placed energy converter the most promising approach to development of a TAH for smaller sized patients.

Animals↗

PubMedDate not supplied

Development of a precise controller for an electrohydraulic total artificial heart. Improvement of the motor's dynamic response.

In an electrohydraulic total artificial heart developed at the National Cardiovascular Center (Osaka, Japan), two blood pumps are pushed alternatively by means of the bidirectional motion of a brushless DC motor for pump systole and diastole. Improvement in the dynamic response of the motor is very important to obtain better pump performance; this was accomplished by using power electronic simulation. For the motor to have the desired dynamic response, it must be commutated properly and the damping ratio (zeta), which represents transient characteristics of the motor, must lie between 0.4 and 0.8. Consequently, all satisfactory specifications with respect to power consumption must be obtained. Based on the simulated results, the design criteria were determined and the precise controller designed to reduce torque ripple and motor vibration, and determine motor stop time at every direction change. In in vitro tests, evaluation of the controller and dynamic response of the motor was justified in terms of zeta, power consumption, and motor stop time. The results indicated that the power consumption of the controller and the input power of the motor were decreased by 1.2 and 2.5 W at zeta = 0.6, respectively, compared to the previous system. An acceptable dynamic response of the motor, necessary for the reduction of torque ripple and motor vibration, was obtained between zeta = 0.5 and zeta = 0.7, with an increase in system efficiency from 10% to 12%. The motor stop time required for stable motor reoperation was determined to be over 10 msec, for a savings in power consumption of approximately 1.5 W. Therefore, the improved dynamic response of the motor can contribute to the stability and reliability of the pump.

Biomedical Engineering↗

PubMedDate not supplied

Influence of non pulsatile systemic circulation on tissue blood flow and oxygen metabolism.

Influence of non pulsatile systemic circulation on oxygen metabolism was examined regarding tissue perfusion in 12 adult goats weighing from 46 to 55 kg. Under general anesthesia, a flow character, changeable total left heart bypass circuit consisting of pulsatile and non pulsatile pumps was installed through a left thoracotomy. Systemic flow was converted from pulsatile to non pulsatile in 7 of 12 animals, and in the reverse order in the other 5, by changing the driving pump. Esophageal mucosal blood flow was determined by a colored microsphere method that estimated tissue blood flow at the pre capillary level. Esophageal intramucosal pH was evaluated with a silicone balloon tonometer catheter surgically placed in the submucosal space. Hemodynamic and arterial blood gas parameters were unchanged at flow mode conversion. Although oxygen delivery was comparable between pulsatile and non pulsatile circulation, oxygen extraction ratio was lower and venous oxygen saturation was higher in non pulsatile than pulsatile circulation. Although statistically not significant, serum lactate level tended to be higher with non pulsatile circulation. No difference was observed in esophageal mucosal blood flow between pulsatile and non pulsatile circulation, whereas intramucosal pH, which strongly correlated with arterial pH regardless of the flow mode, was significantly lower under non pulsatile than pulsatile conditions. In conclusion, systemic oxygen uptake is less efficient in non pulsatile than pulsatile circulation in the setting of an acute experiment using animals, which may be accounted for by the disparity between the pre capillary blood flow and actual tissue oxygen metabolism.

Animals↗

PubMedDate not supplied

Importance of metabolic function of the natural lung evaluated by prolonged exclusion of the pulmonary circulation.

It is generally considered that the natural lung metabolizes various vasoactive substances through the pulmonary circulation. However, the influences of bypassing or eliminating the pulmonary circulation have not been fully elucidated, especially for prolonged periods. In this study, we performed total cardiopulmonary bypass and exclusion of the pulmonary circulation for up to 336 hr in awake goats to clarify the importance of the metabolic function of the lung. In seven adult goats, biventricular bypass with a pulsatile ventricular assist system was first established. After 2 weeks, the biventricular bypass was converted to total cardiopulmonary bypass without anesthesia. Adequate gas exchange and perfusion support were achieved in all animals. However, the institution of total cardiopulmonary bypass led to marked decreases in the mean aortic pressure and systemic vascular resistance, and they remained low thereafter. The arterial levels of prostaglandin E2 and norepinephrine, which are inactivated naturally through the pulmonary circulation, increased remarkably. These results indicate that the natural lung plays an important role in controlling systemic circulation by metabolizing various vasoactive substances. Understanding the non respiratory function of the natural lung is of prime importance for advancement of lung and heart-lung support.

Animals↗