Relationship between design and control of artificial heart for protection of the right/left balance

Right/left matching in the total artificial heart (TAH) is essential to prevent fatal volume displacement into the pulmonary circuit. Measurements were made with three different sized Rostock pneumatic artificial ventricles incorporated in the Donovan mock circulatory system together with the heart driver AKT 86. First for each ventricle we determined the dependence of the maximum effective stroke volume on the systolic driving pressure and the afterload. The right ventricle (RV) is about 10% more effective than the left ventricle (LV). Control of the TAH permits different or equal frequencies for the RV and LV. For control with equal frequencies and full-to-empty regimen of one ventricle (RV-Master or LV-Master) the ratio of designed stroke volumes between RV and LV is important. This follows from the smaller efficiency of the LV and the left-to-left shunt. Otherwise a control mode with different heart rates must be used.

[The status of prazosin in therapy of chronic heart failure]

Cardiac dysfunction and neurohumoral dysregulation show that the administration of vasodilators is reasonable in a cardiac insufficiency which is therapy-refractory against glycosides and saluretics. The alpha 1-blocker prazosin is a potent substance. On the basis of haemodynamic investigations of 55 patients the acute effects are demonstrated. Depending upon the degree of the cardiac insufficiency and the sympathetic dysregulation--measured at the behaviour of the resistance--the acute effects are convincing in more than 60% of the patients. For the long-term course patients with unequivocal initial improvement are suitable. This group can undergo a satisfactory therapy for a longer time by means of a carefully increased dosage, by corrections of the application of saluretics and by short interruptions of therapy and by the change of the dilator, respectively, or by an additional administration of another vasodilator. In the total spectre of the vasodilators which are administered in cardiac insufficiency prazosin occupies one of the first places.

[Kineto- and displacement cardiography in heart valve diseases and possible diagnostic values]

With the help of the method of the kinetocardiography (KKG) inaugurated by Eddleman and the displacement cardiography (DKG) using a high fidelity changer, apart from a control group of 12 test persons with healthy heart 8 different groups of cardiac abnormalities consisting of altogether 88 patients were examined. Displacement cardiography and kinetocardiography did not significantly differ in the course of the curves. The courses of the curves for the cardiac abnormalities proved reproducible. There were significant differences in at least 6 parameters of the curves (p less than 0.05 to p less than 0.001) between the control group and each group with cardiac abnormalities. Linear correlations between the parameters of the curves and invasively gained cardial parameters confirm relations relevant to cardiac abnormalities. In future in possible computer assisted analyses of curves a better rational evaluation in controls of the curves will be the result. The value of this methodology lies in the character of the parameters confirming the cardiac abnormalities. The disadvantage consists in the absent exact quantification of the degree of severity.

[Therapeutic possibilities in terminal heart failure]

The severe and terminal cardiac insufficiency with myogenic failure and severe neurohumoral dysregulation means a problem situation in the chronically progressive or acute form of the course. The medicamentous treatment in form of the basis therapy with glycosides and saluretics may be improved by vasodilators or/and adrenergic agonists. In most cases we succeed in stabilizing the cardiovascular situation once to several times. As a rule the maximum stress only little increases. The neurohumoral dysregulation remains in different form apart from the basic disease which is no more to be corrected. Thus, in principle the vicious circle is closed. Whether the group of the so-called new inotropic and vasodilating pharmaca may essentially change the prognosis due to better influences on cardial and vascular and neurohumoral, respectively, dysfunctions, is not yet to be answered. A distinct alternative from the aspect of the cardiovascular function gives only the cardiac transplantation. The artificial heart and ventricular assist-systems, respectively, are accepted for the bridging-over up to the cardiac transplantation. The hitherto existing state of development does not yet correspond to the imaginations of a pump regulated according to the needs, disregarding material, coagulation and energy problems.

[Noninvasive monitoring of pneumatically driven blood pumps based on measurements of air volume flow in the drive hose]

A computer-assisted measuring system for the noninvasive control of pneumatically driven blood pumps in the artificial total heart replacement and in assist-systems is described. Air volume current measurements with heat wire anemometer in the driving tube underlie as principle. The technique takes into consideration losses of valves, depending upon driving parameters and central circulatory parameters. The dependences established base on measurements at the circulation model. The methods demonstrated allow to qualitatively characterize the signals of the air volume current in the driving tube and approximatively to determine central circulatory parameters on the basis of comparative measurements at the circulation model. Animal-experimental experiences confirm the necessary application of such systems for the measurement of the cardiac output and for the control of the pumping function of pneumatically driven blood pumps. Analyses at the circulation model let expect a measuring error for the volume of output smaller than 20%. By increased measuring exactness of the heat wire anemometer this error can be diminished. For final evidence concerning the measuring exactness animal-experimental investigations and comparisons with reference techniques are provided.

[Catheter problems in the use of ventricular cardiovascular assist systems]

The prerequisite for efficient assist-ventricles and impulses in the pulsatile pumping function are sufficiently dimensioned afflux and flowing off connections. In systematic investigations on the hydraulic circulation model the cannulas from an internal parameter of 12 mm with a total length of the connection distance to the inflow and outflow valve, respectively, at the bypass ventricle of 30 cm proved sufficient for performing a volume of output of 5-6 l/min in clinic-relevant filling pressures in a hypodynamic circulatory situation. Connection cannulas for the heart-lung machine used in routine work are not sufficient in periodic filling and ejection processes in the pulsatile pumping function for an effective decompression and effective increase of the cardiac output. In case of an ECG-triggered mode of action of the ventricular assist-system an increase of frequency up to 130/min in after that incomplete filling of the assist-ventricle does not remarkably restrict the effectiveness of the assist-system.

[Pressure measurements of pneumatically driven artificial ventricles]

In the mock circulation are investigated methods for pressure measurement developed especially for the application on artificial ventricles. They require the in-vivo-confirmation in the long-term experiment. An exact analysis of the pressure curves gives information about the absolute measuring values and also about the function of the pump itself, such as about the points of reaching the final positions of the pump membrane. Via a control related to this in the "full stroke" mode with ejection of the complete stroke volume, when the stand-still times of the membrane are minimized, in addition to this the atrial pressures and the cardiac output can be determined. Eventual non-linearities in the lower pressure region (less than or equal to 0.5 kPa) are not essential in the measurement of the ventricular pressure with amplitudes of 20-25 kPa on the left side and are not investigated in detail.

[Possibilities of using cardiovascular assist systems and the artificial heart]

The mechanical support of the cardiovascular circulation of the reversibly or irreversibly damaged natural heart is possible in a different way. Beginning with the balloon pulsation with limited haemodynamical efficacy the application of left-or right-ventricular assist-systems finally leads to the biventricular assistance, when there are signs of the global cardiac dysfunction and an ability of recovery the heart function is assumed. The trend to use assist-systems over longer periods is perceptible also in patients in terminal phases of chronic cardiac diseases. Thus the importance of artificial hearts is increasing which are to be regarded as biventricular assist-system in orthotopic position. For a short-time use the up to now developed blood pumps, drives and regulation units are suited in few centres of the world. The orthotopic implantation of artificial hearts permits as second step the transplantation of a suitable donor heart. The heart transplantation guarantees high success rates and a cardiac function adapted according need. The demands on the long-term implantation of artificial hearts are at present so high that the majority of the specialists at the present stage of the development has a sceptical attitude to the long-term use.

[Therapeutic principle of organ replacement--artificial organs]

The natural or artificial replacement of organs provides the aimed influence on terminal phases of organ diseases. The hitherto obtained solutions for the replacement in diseases of kidneys, the heart, the lungs, the pancreas and the liver are developed in a different way. For the natural replacement of organs ameliorations in the fields of recipient conditioning, immunotherapy, prophylaxis against infections in operative and technical prerequisites given are subject of further efforts. The complex of problems artificial replacement of organs in the sense of the influence on global and partial organ dysfunctions organ-related reveals different consideration and development. The most advanced perfectioning is existing for the artificial kidney. The elementary and relatively high need of replacement of organs is another challenge to medical and technological sciences.

Basic concept for implantation technique of total artificial heart in humans: a review from cadaver implantations

To develop the application technique of the total artificial heart in humans, it is important to establish a concept about the implantation procedures. Based on cadaver experiments with various types of prosthetic ventricles, some aspects in solving the surgical difficulties were described. Special interest was directed to the geometric topography, the optimal design of the prosthetic ventricles, and the possible surgical solution. Under consideration of spatial differences, especially from that of experimental animals, a proposal was made to place the left and right artificial ventricle with the goal of avoiding compression of the inflow tract or obstruction of the outflow. The design of the connection parts and the angles of the inflow and outflow tracts of the artificial ventricles is essential for good results.

[Therapy of chronic heart failure with vasodilators]

The chronic heart insufficiency is essentially characterized by a disturbed regulative function of the peripheral circulation. These processes taking place within efforts for compensation close the chain of the vicious circle. The vasodilators with their different principles of effect affect in various places of the vegetative nervous system up to the smooth musculature of the vessels and modulate the peripheral part of the cardiovascular system. Via a changed behaviour of the impedance also with the arterial vasodilation the ejection behaviour of the insufficed hearts changes. With the increase of the ejection fraction the filling pressure can decrease, also when only the arterial branch of the periphery of the vessels is influenced. In case of an additional vasodilation of the capacity vessels greater influences of the preload are present. As a rule after the full use of the conventional therapy with digitalis and saluretics is resorted to the adjuvant therapy with vasodilators. Good experiences in the therapy of chronic heart insufficiency are present above all for hydralazine and prazosin as well as increasingly also for captopril, when vasodilating and at the same time positively inotropic medicaments are disregarded. In future, depending upon haemodynamic and neurohumoral (PNA, PRAA) findings in problematic cases and aimed additional adjuvant therapy will be aspired to.

[Mono- or combination therapy with myocardial and coronary active drugs in ischemic heart disease]

The medicamentous treatment of the ischaemic heart disease with nitrates, beta-receptor blockers and calcium antagonists takes into account the in the ideal case evident pathomechanism and the essential principles of the effect of these groups of pharmaca. Apart from the influence on way of life and environmental factors at first the monotherapy is tried. As a rule, in individually possible full use of the dose a large part of the patients can sufficiently be improved. As to "conventional therapy", however, from the first the concerning the therapeutic mechanism favorable combination beta-receptor blocker and nitrates is understood. The increasing interest in calcium antagonists aprt from the increased application of these pharmaca in monotherapy led to the question of the combination with beta-receptor blockers and nitrates. Taking into consideration the different spectres of action of the calcium antagonists particularly in unstable angina pectoris, especially under haemodynamically controlled conditions a combination of three remedies is to be discussed. With regard to this there are no sufficient clinical experiences. At present there are no sufficient evidences for the superiority of this combination therapy.

[Pathophysiological investigations on the function of artificial hearts]

The mode of action of artificial hearts is in a wide range variable and to be adapted to different conditions of the circulatory systems. The direct regulative function of the peripheral circulation is restricted by the rigid ability of artificial hearts bound to motor drive parameters. Their great dependence on pre- and afterload already in normal calves presumes a harmonized functional capacity of the right and left ventricle. As to the situation in potential recipients of artificial hearts with considerably disturbed macro- and microhaemodynamics there are problems for the choice of suitable conditions of motor drive, in order to favour a right-left balance and an adequate volume. The substitution of the natural regulators by suitable sensors and the regulation of the artificial hearts according to haemodynamic controls and pump parameters, respectively, is necessary to achieve a balanced adequate ventricular function. This complex is subject of an intensive research.

[Experiences with the Rostock artificial heart]

A totally artificial heart--the Rostock totally artificial heart (Rostock TAH) was implanted in calves. We can give the following deductions after 27 examinations: -- The Rostock TAH was tested successfully in endurance test about 7 months; it show no sign of wear. -- The surgical technique of the implantation was standardised and a successful experimentation is possible. -- The longest survival time was 15 days. The hemodynamic early results were very good in 3 other animals. -- Modifications of the Rostock TAH were taken up relating to the dimensions of the artificial ventriculi and by mounting a screw cap for avoiding an air embolism. -- Adaption tests in the corpse show that the present form of the artificial heart is not ideal for a possible application in man. -- The problem is still existing in developing a suitable drive system locates intrathoracically. The present drive and control system on a pneumatic base is qualified only for the animal experiment but not for a possible application in man.

[The artificial heart - wishful thinking or alternative?]

The development of the highly specialised cardiological diagnostics furthered the morphological and functional analysis of the congenital and acquired heart diseases. Parallel to this the therapeutic repertoire of the cardiosurgery increased. Successful animal-experimental investigations with artificial hearts and survival times up to several months allow as a justified aim the imagination that the artificial heart by all means may be an alternative to the heart transplantation also in man. This high aim demands further intensive work concerning the optimum form of artificial hearts, better qualities of the material, miniaturised units of motion and regulation with a possibly implantable or at least easily portable source of energy.

[The use of sodium nitroprusside (Nipruton) in ischemia-related acute heart insufficiency]

By controlled vasodilation with nitroprusside sodium we succeed in improving the negative haemodynamic effects of the pumping insufficiency in myocardial ischamia. Increased filling pressures decrease, volumes of output increase in clearly decreased oxygen consumption of the myocardium. The influence on the time volume of the heart depends on the height and reaction of the filling pressure on nitroprusside sodium. In normal LVEDP the time volume of the heart decreases by nitroprusside sodium. The local function of the heart may clearly be improved under nitroprusside sodium in ischaemia. Altogether the hitherto got results in man are not homogeneously interpreted. Problems result from in form of therapy necessary frequent controls of the filling pressures and volumes of output as well as from the possible decrease of the time volume of the heart and the critical reduction of the perfusion pressure. According to own results of experiments on animals the sequelae of ischaemia may be reduced under the infusion of nitroprusside sodium. The restricted regional function of the heart is particularly improved. An obligatory judgment concerning the temporarily restricted use of nitroprusside sodium in the pumping insufficiency conditioned by ischaemia is not yet possible. A complicating effect have the individually different dose-effect-relations as well as not foreseeable haemodynamic results as a sequel of the basic disease in the complicated myocardiac infarction which is to be regarded as indication.

[Therapeutic principles of drug-induced cardiac debit with vasodilators]

For the haemodynamically controlled preload reduction (LVEDP and ZDV) as well as the afterload reduction (arterial blood pressure) with volume of output taken into consideration in the first place glycerol trinitrate, nitroprusside sodium, alpha-blockers, hydralazine, prazosine and nitrates are used. The medication is given in acute and chronic pumping insufficiency. The distance between therapeutic effect wanted and unfavourable influences due to critically reduced preload and coronary perfusion as well as reduced volume of output is close. The haemodynamic analysis of actual situation of the disease as well as regular controls are necessary. The effects of the long-term therapy in chronic pumping insufficiency with peroral effective vasodilators are still unsatisfactory.

[The effect of cardiovascular hypertrophy on the work capacity of hypertensive patients]

Hypertensive persons with pathological ECG in rest compared with healthy persons and hypertensives with normal ECG in rest show a significantly decreased physical efficiency. In hypertensives in stage II disturbances in form of references to a stress heart insufficiency, to a stress coronary insufficiency and a circulatory dysregulation are the cause of the disturbed function of the circulation. Thus the pathological ECG in rest in the hypertensive is an important diagnostic and prognostic criterion for practice.

[Behavior of cardiopulmonary function in hypertonics under ergometer load]

In 56 male hypertensive patients a complex cardiopulmonary functional diagnosis was performed in rest and under ergometer load. The total functional capacity of the hypertensive patients is decreased already in the early stage and also in juvenile age, compared with healthy persons. Furthermore disturbances of the regulations of the minute output of the heart, hypertensive stress reactions, disturbances of the coronary blood supply and disturbed functions of the myocardium are provable.

[Importance of continuous recording of vascular resistance]

The behaviour of resistance in the periphery of the circulation and in the organic regions underlies different influences. Depending on the function of the organs, on the situation of heart and circulation and on the therapeutic influences the vascular resistance changes. To the study of the dynamics of the behaviour of resistance particularly the continuous electronic recognition is suitable. The gain of time and information is great. Especially for the determination of the coronary perfusion in different functions of heart and circulation the continuous registration of the vascular resistance is necessary. Its importance was as an example demonstrated for the left-ventricular ejection resistance and for the left- and right-coronary influx resistance.