Three-dimensional stress analysis of polypropylene leaflets for prosthetic heart valves

The effect of changing the modulus and thickness of the material in the leaflets of an artificial heart valve has been investigated. This has been achieved with a finite element model of the valve having approximately 2300 thin shell elements. The valve motion and the resulting stresses are modelled dynamically during closure, and subsequent pressurisation. The stresses decrease as the leaflets are made thicker and the modulus is increased. Local and global thickening has been investigated. The highest stresses appear at the tops of the stent posts in the regions of the commissures. When the modulus is too low, or the leaflets are too thin, the valve prolapsed.     

Survival for 145 days with a total artificial heart

A calf into which a biolized, total artificial heart (TAH) had been implanted survived for 145 days. All measured physiological parameters except central venous pressure (CVP) were back to normal one month after implantation, and thereafter the animal's physiological development was similar to that of a normal calf. The intimal weight, which was 96 kilograms at implantation, reached 190 kilogram at the end of experiment, with a daily gain rate of 0.9 kilogram per day. After the nineteenth postoperative week, signs of congestive heart failure appeared, such as high venous pressure, ascites, and enlarged liver although the calf outwardly appeared well. On postoperative day 146, the animal started foaming at the mouth, and a convulsion occurred; then, the experiment was terminated after 3,494 hours of pumping. At autopsy, there were acute bilateral bronchopneumonia involving mostly both upper lobes, pulmonary edema, slight chronic pneumonitis, and hepatomegaly. There were no serious thrombotic deposits inside the cardiac prosthesis.     

Corrected formula for the calculation of the electrical heart axis

Right brain damage results in a variety of cognitive and behavioural dysfunctions. Mutism however, has been described only with left or bihemispheric lesions involving the parietal lobe. We report an elderly man who had left faciobrachial monoparesis and concomitant mutism. His auditory-verbal comprehension was intact. MRI revealed a right parietal infarct involving the cortical and subcortical regions. Recovery from mutism during the course of treatment was abrupt and complete with no residual dysarthria. A possibility of diaschisis or impaired modulation of left hemispheric function due to right cerebral infarct, presenting as conversion reaction, is proposed for this rare association.     

Midterm results with the Sorin Monostrut heart valve prosthesis

OBJECTIVE: To monitor the hematological and clinical sequelae of a single tilting disc cardiac valve prosthesis. DESIGN: Prospective nonrandomized trial. SETTING: University teaching hospital. PARTICIPANTS: All patients receiving a single mechanical cardiac valve prosthesis were offered the Sorin Monostrut valve if they met the criteria for valve use. Seventy-five per cent of the patients entered were in New York Heart Association (NYHA) functional class III or IV. One hundred and forty-seven patients were subsequently followed at three months and then yearly after valve implantation for seven years. MAIN OUTCOME MEASURES: At one year, preoperative indexes of hemolysis were compared with three-month and one-year postoperative values. Actuarial curves for survival, freedom from cerebrovascular events and explantation were constructed for the seven-year follow-up period. RESULTS: Hemolysis, as measured by lactate dehydrogenase values, commonly occurs preoperatively, remaining significantly elevated three months and one year following valve implantation. Serum haptoglobin was normal preoperatively but was significantly low at one year. Anemia was uncommon and most patients had normal reticulocyte counts at one year. At three years, 81% of patients were in NYHA functional class I. CONCLUSIONS: Midterm results show that this valve is structurally reliable and meets all current requirements for a safe mechanical valve.     

The effects of sterilization and storage treatments on the stress-strain behavior of aortic valve leaflets

Radioisotope ventriculography was applied clinically in myelodysplastic hydromyelia in three groups of patients: two patients with normal ventricles, two with obstructive hydrocephalus, and 16 with myelodysplasia. In the myelodysplastic group, radioassay in one patient demonstrated flow of radioistope down the hydromyelic cavity. Twenty scintigraphic studies on 16 myelodysplastic patients showed hydromyelia was present in all patients with spontaneously compensated hydrocephalus but in none of those with functional ventricular shunts. This relation between the hydromyelia and disordered ventricular hydrodynamics supports the Gardner hypothesis of myelodysplasia. Radioisotope ventriculography appears a safe and useful method of diagnosing hydrosyringomyelia and evaluating treatment by means of ventricular decompression.     

Thirty years experience with heart valve surgery: isolated mitral valve replacement

BACKGROUND: Thirty years have elapsed since the commencement of open-heart surgery in South Australia. A retrospective study was performed to evaluate mortality and complication rates and to identify factors associated with poor outcomes in all patients who underwent prosthetic mitral valve replacement during this period. METHODS: Questionnaires and personal contact have been used to generate a combined database of pre-operative and post-operative information and long-term follow-up on 938 patients who underwent isolated prosthetic mitral valve replacement at the Cardio-Thoracic Surgical Unit of the Royal Adelaide Hospital between 1963 and 1993. RESULTS: Complete survival follow-up data were obtained for 92% (865) of the patients. The Starr-Edwards valve was used in 95% (891) of the patients, a Bjork-Shiley prosthesis in 2.5% (23) of the patients, and only 24 (2.5%) other valves were inserted. The hospital mortality rate for the 30-year period was 4.7%. The mean age of the patients who underwent surgery was greater in each of the three successive decades. A long-term survival advantage was observed for patients with mitral stenosis, however, survival was significantly shorter for patients with higher New York Heart Association (NYHA) functional classifications and for patients in pre-operative atrial fibrillation. Pre-operative dyspnoea was significantly improved following mitral valve replacement. The rates of postoperative haemorrhagic and embolic complications were low by comparison with other published series. CONCLUSION: Mitral valve recipients do not regain a normalized life expectancy, but risk factors that determine long-term survival can be identified pre-operatively to aid appropriate patient selection.     

Interaction of artificial carbon pyroceram mitral valve with blood plasma

The nanocrystalline material of an artificial carbon pyroceram mitral valve obtained by sintering of 15 wt.% B₄C with crystals <10 nm that are uniformly distributed in 85 wt.% carbon with particles ～10 nm has exceptionally high chemical stability in blood plasma. The electrochemical interaction resulting from contact with a possible microadditive (for example, iron) on the valve surface is experimentally modeled by polarization induced by an external current source specially to create extreme corrosion conditions. The interaction kinetics is studied at 37 °C using anodic polarization curves. Curcumin is used as an analytical reagent for spectrophotometry of boron traces in a solution. Emissive spectroscopy is used to determine iron traces in the spume-like film formed after polarization. It is established that a chemisorbed oxygen film forms when microgalvanic elements appear at 0.4 V and stable passivation of the valve surface is observed at ～1.0 V since a low-conductive nanostructured carbon film forms. It is shown that this film results from the discharge of α-amino acids on the valve surface (amino acid residues of complex peptide chains of plasma proteins) containing heterocyclic rings. The sessile drop method shows that the valve is promptly wetted by blood plasma (wetting angle is 50 °), this also promotes the formation of a stable protective film on its surface.     

Decontamination tests of heart valve grafts with cialit

Only a small proportion of patients with carcinoma of the stomach are suitable for radical surgery. For the remainder symptomatic treatment and radiotherapy alone or in combination with chemotherapy can be used to relieve distressing symptoms of pain, nausea and vomiting, and severe anemia. In the case of radiotherapy or chemotherapy, a degree of tumor regression can be expected. There have been encouraging results recently in palliating this disease with new radiotherapy techniques, notably fast neutron irradiation.     

Acquired heart valve pathology. An update for the millennium

Two inflammatory vascular diseases often show multinucleated macrophages: Takayasu's disease and Horton's disease. Takayasu's disease is a segmentary panarteritis most prominent in the adventitia. Lesions show an inflammatory infiltrate close to the external elastic lamina. Progressive stenosis of the artery, sometimes complicated by calcifying atheroma is the typical course. Horton's disease or temporal arteritis is another segmentary arteritis. Lesions show a mixed inflammatory infiltrate partly localized in the adventitia where there are T CD4+ lymphocytes secreting II-2 and IFN-gamma and also macrophages expressing TGF beta 1, IL-6 and IL-1 beta, and partly situated in the interior part of the wall, around the internal elastic lamina, and mostly made of macrophages and giant cells which produce TNF, collagenase and nitric oxide that are responsible for destruction of the wall. The variety and subtleness of some lesions do not always make a precise diagnosis possible. But any inflammatory vascular lesion, even slight, can reveal a systemic vasculitis.     

Blood rheology in patients with native heart valve disease and after valve replacement

Patients with heart valve disease have rheologic abnormalities that are more pronounced in double valve disease than in mitral or aortic valve disease; after valve replacement surgery, the degree of rheologic abnormality is more pronounced in patients with mechanical and biological prostheses than in those with homografts and pulmonary autografts. Rheologic abnormalities seen in these patients might be related to the different incidences of thromboembolism in the presence of various valve defects and various types of prostheses.     

A new design for a totally artificial heart: the ellipsoid heart (author's transl)]

Thromboembolic complications represent the main limiting factor in cardiac replacement by totally artificial hearts in calves at present. Thrombus formation within artificial hearts is caused by the appearance of stagnation areas. The ellipsoid heart eliminates stagnation areas by virtue of its production as a one-piece membrane. The heart is driven pneumatically and functions as a diaphragmatic blood pump. The stroke volume is 178 cm3 and the maximal cardiac output 15.8l/Min. Three acute experiments demonstrated a high degree of haemodynamic efficiency without compression of, or interference with surrounding structures, especially the inferior vena cava or the right atrium.     

In vivo evaluation of the Lillehei-Kaster heart valve prosthesis

Three decomposition products of Morazone (ingredient of the pharmaceutical preparation Rosimon-Neu) were observed following heat treatment in acid medium (hydrochloric or tartaric acid). These products were isolated by TLC and identified as bis-antipyryl-methane, phenmetrazine and 4-hydroxymethyl-antipyrine by mass spectrometry and IR-spectroscopy and 1H-nuclear magnetic resonance. Morazone and the metabolite phenmetrazine may be extracted from alkaline urine using chloroform, however acid hydrolysis (pH 1) of the urine before alkaline extraction will improve the sensitivity of detection of morazone by producing the metabolite phenmetrazine in addition to bis-antipyrylmethane. The metabolite 4-hydroxymethyl-antipyrine is barely detectable by TLC from alkaline extraction of urine.     

Acoustic classification of the state of artificial heart valves

Transthoracic acoustic signals from BSCC (Bj?rk-Shiley convexo-concave) mechanical heart valves implanted in human patients were processed to determine if the valves had separated outflow struts. For normal valves with intact outflow struts it is demonstrated that a time-windowed spectral analysis reveals the resonant frequency of the vibrating strut. The strut, which is set into vibration when the valve closes during each cardiac cycle, has a resonant frequency that varies among valves but usually is between 7000 and 8000 Hz. The signal processing technique is based on the hypothesis that the strut's resonant waveform has a smaller decay rate than interfering signals and noise generated upon closure by other mechanical components of the valve. A time window can be selected that optimizes the outflow strut's signal-to-interference ratio. It is shown that the absence of the resonant frequency in the 7000- to 8000-Hz interval is an indication that one of the strut's legs has separated from the valve's flange. This separation of one leg appears to precede the valve's failure that occurs if the other leg also separates from the flange, a state referred to as OSF (outlet strut failure). Acoustic data recorded from 18 clinical patients with implanted valves, that were later explanted and examined, formed the database for this study. Of the 18 valves 9 were SLS (single-leg separated) and 9 were intact (both legs of the outflow strut still attached to the valve's flange). The time-windowed spectral process correctly identified the states of all 18 valves.(ABSTRACT TRUNCATED AT 250 WORDS)     

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.     

Results of heart valve replacement: especially on the selection criteria for valve prostheses and on a new anticoagulation regimen

Since March 1981 till the end of 1987, a total of 76 artificial heart valves were implanted in 72 patients. Heart valve prostheses were selected individually according to the patient's needs rather than assigning a single model to every patient. Postoperatively patients were placed on an anticoagulation therapy regimen consisting of reduced-dose warfarin (prothrombin time maintained at 30% of the control) and a small dose (81 mg/day) aspirin. During this period no bioprosthesis was implanted. For aortic valves, Starr-Edwards caged-ball valves were used in 53.1% and St. Jude Medical (SJM) valves in 37.5%. For mitral valves, SJM valves were used in 68%. No mechanical valve failure and no thrombosed valve was encountered. There was one patient-prosthesis missmatch. The incidence of thromboembolism for the entire series was 5/181.2 patient-years. There was 1-2/181.2 patient-years incidence of hemorrhagic complications. These figures were comparable to the ones with conventional warfarin therapy. No intracranial hemorrhage was encountered. Our selection criteria for artificial heart valves and our method of anticoagulation were discussed in detail. We conclude that at present there is no single prosthesis which satisfies all the varying needs of every patient, and the prosthesis which is best suited to that particular patient should be selected. We are generally happy with our current method of postoperative anticoagulation and will continue with this regimen.