Mechanical stability of elastomeric polymers for blood pump applications

As a series of studies on the mechanical properties of materials used in cardiac prostheses, static and dynamic characteristics and stability of five kinds of elastomeric polymers have been studied by uniaxial tensile and fatigue tests in air at room temperature and in saline solution at 37 degrees C. Of all materials tested in this study, Texin MD85A, a segmented polyether polyurethane, has the lowest flexibility under static and dynamic conditions, with relatively high strength. Hexsyn, a polyolefin rubber, is highly flexible with little stress relaxation. However, this material has very low tensile strength and short elongation, and shows unstable change in the elastic modulus during cyclic deformation. Avcothane 51, a copolymer of polyurethane and silicon, has unstable mechanical properties and gradually stiffens upon cyclic deformation. On the other hand, Biomer, a segmented polyether polyurethane, has high flexibility and shows the most stable behavior during cyclic deformation regardless of test environment. Toyobo TM5, a similar segmented polyurethane to Biomer, has higher strength and ductility than Biomer, although its static and dynamic flexibility are slightly worse and less stable than those of Biomer. These results indicate that Biomer and Toyobo TM5 are more suitable for flexible components of cardiac prostheses.

Spinal cord monitoring: basic principles and experimental aspects

Spinal cord monitoring, based on spinal cord potentials recorded close to the conus medullaris and evoked by stimulating rostral spinal cord, has been extensively used clinically in Japan. To understand how such spinal cord evoked potentials (SCEP) reflect injurious effects on the spinal cord, we carried out the following animal experiments. The effects of spinal cord distraction, compression, and combined compression and hypotension or hypoxia were examined. We found that there is a critical point of compression or distraction of the spinal cord at which SCEP amplitude decreases significantly. Acute hypotension concomitant with moderate compression increases the risk of insult to the cord. Accordingly, we believe that repetitive monitoring and rapid feedback to the surgeon are indispensable to intraoperative spinal cord monitoring. Furthermore, hypotension should be carefully avoided whenever symptoms of spinal cord compression occur. A comparative study of SCEP and spinal SEP indicates that both potentials can substitute for each other, although the sensitivity of the SCEP for detecting hazardous effects is higher.

Redundant nerve roots in patients with degenerative lumbar spinal stenosis

Extensive fundamental and clinical investigations have been performed concerning redundant nerve roots (RNR) and the pathogenesis of cauda equina claudication (CEC) in degenerative lumbar canal stenosis (DLCS). These investigations consisted of (1) anatomic observations on RNR in 117 fixed cadaveric specimens, (2) myelographic study in 117 patients with or without DLCS, (3) operative observation on neural elements with special reference to the cauda equina in 56 DLCS patients (including a postoperative follow-up), and (4) electrophysiologic tests using spinal cord action potential recording under walking load preoperatively and intraoperative measurement of nerve conduction velocity of RNR. The RNR have neuronal losses resulting from a longer duration stenosis that suggests a sort of friction neuritis. Complicated factors contribute to the pathogenesis of CEC and the development of root gripping, such as the magnitude of RNR, the extent of the stenosis, a narrowed sac, age-dependent axial shortening of the spinal canal, and dynamic or postural factors. In cases with severe RNR, satisfactory operative results can be obtained only after thorough decompression with dural incision.

[Left ventricular thrombus formation and cuspal fusion of the prosthetic valve during left heart bypass: their pathophysiological significance and echocardiographic observations]

The echocardiographic findings during left ventricular assist of a heart of a 36-year-old woman who underwent mitral valve replacement were described. Blood was bypassed from the left atrium to the aorta. Echocardiography demonstrated that the pulmonary and tricuspid valves functioned with each heart beat, but that the aortic and prosthetic mitral valves did not open, and the left ventricular wall did not contract. In the left ventricular cavity, there was a mobile and amorphous thrombus which correlated with dynamic intracavitary micro-echoes ("moya moya" echoes). With higher left atrial pressure, the left ventricular motion increased slightly, and the left ventricular dimension gradually decreased. These findings were interpreted as follows: (1) desired results were attained from the previous powerful assist, or (2) the most optimum pressure of the left atrium in relation to the left ventricle was relatively high. It has not yet been determined which is actually the case. The "moya moya" and thrombus echoes were decreased. The general condition of the heart appeared to be improved, but the prosthetic valve motion was not observed. Contrast study via an echocardiographically-guided catheter inserted retrogradely into the left ventricular cavity revealed prosthetic valve stenosis. Fusion of its cusps by fibrin was confirmed on repeat surgery. Although the patient's condition allowed removal of the left ventricular assist device after surgery, the patient died of progressive infection. Optimum powerful assist should be performed while the formation of thrombi and cuspal adhesions is being prevented by other methods, or a more mild assist may be desirable.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of immersion in cholesterol-lipid solution on the tensile and fatigue properties of elastomeric polymers for blood pump applications

Tensile and fatigue properties were studied on three kinds of segmented polyether polyurethanes developed for blood pump applications. To study the effects of plasma constituents, specimens were immersed in a cholesterol-lipid solution whose composition is similar to that of plasma. The results obtained were compared with those observed in a saline solution which had been reported previously. Immersion in the cholesterol-lipid solution has influence on the mechanical properties of Toyobo TM5 polyurethane and Avcothane 51: Its effect is enhanced by cyclic deformation. Cholesterol-lipids change the mechanical characteristics of Avcothane 51 more remarkably than those of Toyobo TM5 polyurethane possibly because the former contains about 10% silicone. On the other hand, there is little effect of the constituents of the cholesterol-lipid solution on the static and dynamic mechanical properties of Biomer, although moisture and cyclic deformation have some influence on the mechanical characteristics.

Microvasculature of the mouse epididymis, with special reference to fenestrated capillaries localized in the initial segment

The blood supply, microvasculature, and ultrastructure of the capillaries in the epididymis in adult mice were regionally examined. The epididymal duct of the initial segment is surrounded with a dense network of fenestrated capillaries running just under the epithelium. The other segments have loose networks of nonfenestrated capillaries running in the interductal connective tissue. The fenestration of capillaries in the initial segment was markedly reduced in frequency immediately after cutting the efferent duct. In adult mice which were subjected to cutting of the efferent duct neonatally, the dense capillary network did not develop, and fenestrated capillaries were absent in the initial segment. We interpret our results to indicate that the fenestrated capillaries in the initial segment provide for absorption of the testicular fluid and that their development is dependent upon the testicular fluid entering the epididymal duct.

Interruption of the luminal flow in the epididymal duct of the corpus epididymidis in the mouse, with special reference to differentiation of the epididymal epithelium

The efferent duct or the epididymal duct at the border between the caput and corpus epididymidis was cut or ligated in mice at the following stages: birth, 20 days, and 60 days of age. The epididymal duct of the corpus epididymidis was observed at 60 days of age after neonatal or juvenile operation and 4 weeks after the adult operation. After efferent duct interruption, the epididymal duct in the corpus possessed abundant PAS-positive material with no spermatozoa in the lumen, and the principal cells of the epithelium contained PAS-positive inclusions which were considered to be formed due to absorption of the PAS-positive material secreted by the principal cells in the caput epididymidis. Especially after interruption at the border between the caput and corpus epididymidis in juvenile mice, the epithelium of the epididymal duct in the corpus was much taller with peculiar pale, vacuolated cells. These cells were considered as abnormally differentiated forms of the principal cells. The occurrence of the PAS-positive inclusions and peculiar pale cells varied in frequency according to the level and age of interruption of the epididymal duct. The results suggest that the luminal contents produced in the proximal region of the duct may exert an influence on the differentiation of the principal cells of the epididymal duct.

Appearance of peculiar multivesicular bodies in the principal cells of the epididymal duct after efferent duct cutting in the mouse

Ligation of the efferent duct in the mouse results in appearance of PAS-positive inclusions in principal cells in the duct of the epididymal body, and the inclusions are considered to be formed by absorption of the luminal PAS-positive material produced in the epididymal head (ABE et al., 1982a). For better understanding of the significance of the inclusions, this study examined morphologic changes in the principal cells after efferent duct cutting, by light and electron microscopy. Electron microscopy revealed that the principal cells containing PAS-positive inclusions are characterized by a nipple-like protrusion--micropapilla--on the luminal surface and by peculiar multivesicular bodies in the supranuclear cytoplasm. The micropapilla, 1-2 micron in height, contains ductules of 0.2-0.5 micron thickness which extends from its tip to the multivesicular bodies. The multivesicular bodies, measuring up to 10 micron in diameter, are larger toward the nucleus. They contain numerous vesicles, 40-100 nm in diameter, and an amorphous material that is similar to the luminal material of the epididymal duct. In addition, larger multivesicular bodies are heterogenous in structure and possess bundles of tubules 40 nm thick. There are dense bodies in the basal cytoplasm under the nucleus which appear to be transformed from the multivesicular bodies. In summary, occurrence of the micropapilla and the giant multivesicular bodies are considered to represent an activated breakdown of the material ingested from the duct lumen.

Design of pusher-plate-type left ventricular assist device based on mechanical analyses

A permanently implantable left ventricular assist device (LVAD) pump of the pusher-plate type was designed based on mechanical analyses. A series of three different segmented polyether polyurethanes was utilized for the diaphragm, cannulae, and their blood-contacting surfaces, considering each material's characteristics. The span and thickness of the pump diaphragm were determined so as to minimize the stress developed by the bending and blood pressure forces. The inflow and outflow cannulae were designed using fundamental equations that describe the operation of a piston-type reciprocating pump. The pump diameter was determined considering the required flow for the average Japanese person. In vitro and in vivo experiments showed good pump performance, which satisfied the design specifications. No failure was observed in the designed diaphragm. The Hall effect sensor incorporated in the pump was very useful in monitoring the cardiac output of the pump.

Asymptomatic leiomyosarcoma of maxillary sinus accompanied by primary mucocele

A case of asymptomatic leiomyosarcoma of the maxillary sinus accompanied by primary maxillary mucocele is presented together with a review of the literature. The manifestation and symptoms, pathology in special reference to electron microscopic findings, treatment and prognosis, and origin of this tumor are discussed. Initially, this tumor should be treated by extensive surgical excision, but long-term follow-up is essential in the light of this high rate of local recurrence, and radical neck surgery is indicated for metastatic nodal disease.

Spinal cord monitoring as a clinical utilization of the spinal evoked potential

For the purpose of monitoring spinal cord function, evoked spinal cord potential was observed by recording electrodes in the subarachnoid space at the level of the conus medullaris and stimuli delivered to the rostral spinal cord from the epidural space. A specially designed, flexible tube-type electrode was used for both recording and stimulating. The spinal cord evoked potential consisted of an initial spike followed by polyphasic waves. The peak amplitude change was considered to be the main indicator of events that would potentially be hazardous to spinal cord function. Two hundred and twenty-nine operations were monitored by the recording electrode. Six of the patients experienced postoperative neurologic complications. During operation, the peak amplitudes of the evoked potentials diminished to less than 50% of the control values. Simultaneous monitoring of evoked potential revealed that this method was more sensitive than the wake-up test. No complications resulted from the application of this method. Thus, monitoring is a sufficiently sensitive, safe, and reliable method to be useful during aggressive surgery in the spine and spinal cord.

Circulation control of experimental and clinical profound left ventricular failures by automatic left ventricular assist system

It is desirable that circulation control of the patient using a left ventricular assist device (LVAD) should be achieved appropriately and safely. We have developed an automatic LVAD system, which can maintain the normal circulation irrespective of the severity of heart failure and can restore the failing heart by decreasing the bypass flow (BF) through the LVAD as the heart recovers. The main part of the control-drive unit is an automatic level control (ALC) system for left atrial pressure (LAP) and total flow (TF). Profound left ventricular failure (LVF) was made by complete interception of blood supply to the extent of 50% (5 goats) and 70% (5 goats) of the LV free wall. The air-driven diaphragm-type LVAD was implanted between LA and aorta. At the beginning of LVAD pumping, BF tended to be very high to keep LAP at the preset level (0-5 mmHg) and to maintain TF at somewhat higher level (120-140 ml/kg/min). The recovering heart was able to decrease LAP gradually. Since the LAP was set at a certain level, the ALC of LAP decreased BF to maintain LAP at the preset level. During the recovering stage from LVF, preset level of LAP was gradually raised while checking the pulmonary function. When natural heart output exceeded 100 ml/kg/min, LVAD was removed. The 50% LVF group recovered between 17 hours and 3 days, and 70% LVF group between 6th and 16th postoperative day. This LVAD system was then applied to the postoperative profound LVF in a MVR patient whose entire circulation was maintained normal during 14 day pumping. The failed heart gradually recovered and the pump was successfully removed. We consider that the decompression of LV will prevent overextension of impaired myocardium and simultaneously accelerate the solid scar formation. And gradual increase of LV work will promote the compensation ability of the residual myocardium. Continuous LVAD assistance can therefore earn time for the impaired myocardium to recover while maintaining normal circulation.

Response of epididymal duct to the temporary depletion of spermatozoa induced by testicular irradiation in mice

The mouse epididymal duct can be histologically divided into five segments (I-V), and the principal cells in segment II appear to secrete periodic acid-Schiff (PAS)-positive material into the lumen. In this study, male dd-mice received one, two, or four 800-R doses of radiation beginning at age 50 days. Mice receiving multiple doses were irradiated at 1-week intervals. After irradiation, marked depletion of spermatozoa, or aspermia, occurred in the epididymal duct for 2 to 16 weeks after a latency period of 3 to 4 weeks according to the times of irradiations. During oligospermia or aspermia, PAS-positive inclusions appeared in the principal cells in segment IV. The inclusions occupied a supranuclear position and appeared as round granules and globules measuring 2-15 micron in diameter, and increased in number, size, and staining intensity with time. They disappeared after reappearance of spermatozoa. The findings suggest that PAS-positive material may bind to spermatozoa and, if not bound, is reabsorbed by the principal cells in segment IV and deposited as intracellular inclusions, and the principal cells in segment IV are capable of digesting the accumulated PAS-positive material.

Tubule-containing inclusions in the epithelial cells of the mouse epididymal duct

The mouse epididymis, consisting of a head, body and tail, was examined by electron microscopy. The principal cells of the epididymal duct in the epididymal body have rod-shaped inclusions, 0.3 to 1.0 microns in diameter and 2 to 5 microns in height. The inclusions contain a bundle of tubules, about 40 nm in diameter, with a wall about 6 nm in thickness. The tubules are regularly arranged in a hexagonal pattern. A goniometric study of the inclusions shows evidence that the wall of the tubules consists of filament-like subunits which run parallel to each other and are inclined at about 25 degrees to the axis of the tubules, forming loose spirals. The inclusions occasionally contain material similar to that in the lysosomal bodies. These inclusions were observed in every epididymis examined, and seem to be related to the specific functions of the principal cells in the epididymal body.

Appearance of peculiar epithelial cells in the epididymal duct of the mouse ligated epididymis

The mouse epididymis was ligated at the junction of the head and body at 20 to 30 days or 90 days of age, and examined by light and electron microscopy 30 days after ligation. In the normal mouse, the lumen of the duct in the corpus epididymidis was distended with abundant spermatozoa and PAS-positive material. In the epididymis ligated at 20 to 30 days, the duct of the corpus was decreased in diameter and contained no spermatozoa and little PAS-positive material in the lumen. Peculiar pale, vacuolated cells appeared scattered or clustered in the epithelium in this region. The cells often formed intercellular cysts. The vacuoles and intercellular cysts had long microvilli on their inner surface. In the epididymis ligated at 90 days, few or no pale cells were seen in the epithelium of the duct. These findings imply that the differentiation of the epithelial cells is dependent on the luminal contents of the epididymal duct.

Response of the epididymal duct in the corpus epididymidis to efferent or epididymal duct ligation in the mouse

Different parts of the epididymal duct were ligated when mice were 90 days old. The mice were killed 1--4 weeks later. PAS-positive materials appeared in the epithelial cells of Segment IV (corpus epididymidis) after ligation of the efferent ducts or at Segment II (middle part of caput) but not when the ligature was distal to Segment II. The inclusions were seen as early as 1 week after ligation and became increased in size and number with time.