Right ventricular conductance to establish closed-loop pacing.

Innovations in pacing technology, which include the addition of rate-responsive features to programmable pacemakers, can improve the quality of life of patients suffering from sick sinus syndrome. Among the strategies providing rate-adaptive cardiac pacing, the most attractive is the physiological restoration of closed-loop chronotropic control. This paper describes how autonomic nervous system (ANS) control information is extracted from dynamic measures of myocardial contractile performance obtained from unipolar conductance measurements using the stimulation electrode in the right ventricular cavity. The pacemaker uses the ANS information to modulate pacing rate and restore normal physiological control of heart rate. A new algorithm, regional effective slope quantity (RQ), for isolating the ANS signal was developed. The resulting signal, ventricular inotropic parameter (VIP), is a normalized parameter proportional to the strength of the ANS inotropic signals to the myocardium. The efficacy of the ANS control concept was evaluated in multi-centre studies. Patients with AV block and VIP-controlled pulse generators performed defined exercise protocols. The ANS-controlled pacing rate and the spontaneous sinus rate were closely correlated. Blood pressure and subjective patient reports further indicated that good control of the cardiovascular circulation was achieved.

Autonomic nervous system controlled closed loop cardiac pacing.

A multicenter clinical study is presented, which focuses on the reestablishment of closed loop cardiac control in patients with chronotropic insufficiency. Using the information about sympathetic tone contained in the myocardial contractility, it is possible to reconnect the heart rate to the physiological control mechanisms. Intracardiac impedance is measured with the ventricular electrode and the ventricular inotropic parameter (VIP) is derived from that. The VIP serves directly as input to the control of heart rate by the pacemaker. Over 200 patients have received autonomic nervous system (ANS) controlled pacemakers. The patient-pacemaker system was investigated in different ways. This included standard exercise tests, long-term studies of every day activities over 24 hours, psychological, and pharmacological challenges. To prove the validity of the approach we specifically looked at (1) the appropriateness of changes in paced heart rate with sympathetic tone during exercise, (2) the correlation between heart rate and sinus rate, if detectable, and (3) the correlation between the echocardiographically determined preejection period (PEP) and the VIP controlled heart rate.

[Measuring intracardiac impedance for the determination of sympathetic nerve activity in frequency-adapted electrostimulation--Part 2: Clinical results]. / Intrakardiale Impedanzmessung zur Bestimmung der Sympathikusaktivität bei frequenzadaptiver Elektrostimulation--Teil 2: Klinische Ergebnisse.

The results of a multicenter clinical study involving patients receiving the first ANS controlled rate adaptive pacemaker are presented. In the patients with primary or secondary chronotropic insufficiency, it is possible to reestablish the closed loop control system that includes the baroreceptors, the medulla oblongata, the cardiac output and the mean arterial blood pressure. This system serves to keep the blood pressure constant in the face of changing demands on the circulation. Utilizing intracardiac impedance measurements, the myocardial contractility can be determined, which contains information about the current sympathetic tone, and thus represents an excellent physiological input for a rate adaptive mechanism. The results presented are taken from a study population of over 200 patients. The objective evaluation of this new approach was performed echocardiographically, by ergometry and 24-hour Holter monitoring.

[Physiologic frequency adaptation of cardiac pacemakers using systolic time intervals]. / Zur physiologischen Frequenzanpassung von Herzschrittmachern mittels systolischer Zeitintervalle.

Of the parameters in consideration for control of physiological rate responsive pacing special interest is directed to stroke volume. In search of indirect parameters which are correlated to stroke volume it is demonstrated on principle that systolic time intervals could be used. From the relation ejection time versus pre-ejection time (LVET/PEP) which is known for its correlation to stroke volume a simple algorithm is derived which is based on the realization that PEP is related to the reciprocal of cardiac output. First investigations with patients demonstrated the possibility of the computation of heart rate from PEP only, with good physiological significance.

[Pressure measurements of pneumatically driven artificial ventricles]. / Druckmessungen an pneumatisch betriebenen künstlichen Ventrikeln.

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.

[Diagnostic and therapy-assessing studies of gingival capillary function by photoplethysmography (preliminary report)]. / Diagnostische und therapiebewertende Untersuchungen der Kapillarfunktion der Gingiva mittels Fotoplethysmorgraphie (Vorläufige Mitteilung).

In the sense of relation pathology, the local peripheral blood supply plays a decisive role also in periodontal diseases. Thus, the differentiation of local circulatory disturbances is of great importance in diagnosis and early detection as well as in therapeutical decisions. Photoplethysmography is well suited for this purpose, especially in evaluating the curves by determining the time of inclination and the plateau index (if necessary, with resort to the nitrangin test). The indicated method also permits to assess the success of therapeutical measures.

[Objectification of gingival blood-supply disorders by photoelectric plethysmography (author's transl)]. / Zur Objektivierung von Durchblutungsstörungen der Gingiva mittels Foto-Plethysmographie.

The measuring method described in this paper is used to photoelectrically detect the volume pulsation of the gingival border. The method, which is remarkable for its ease of application, enables both the original pulse and its first differential derivation to be recorded reliably. Evaluation of the pulse cure is by the time of inclination and by the recently introduced "plateau index". Results of studies conducted by Kötzschke et al. show that the plateau index allows to clearly distinguish between normal subjects and parodontopathy patients including those where the disease is in its early stage. This measuring method may be used for objectifying therapeutical measures. Using the "nitroglycerin test", it was possible to show that parodontopathies are very frequently accompanied by functional blood-supply disorders.

[Assessment of the coronary circulation regulation by means of the so-called isometric contraction index]. / Die Beurteilung der Herz-Kreislauf-Regulation mit dem sog. Anspannungsindex

The index of isometric contraction formed from the quotient period of isometric contraction in the erect position by period of isometric contraction in lying position gives the possibility to separate between cardially sufficient and cardially insufficient patients with adequately disturbed regulation of the cardiac circulation. The recognition of early stages of the disturbed left-ventricular function is possible. The use of an adequate exact technique in gaining the primary data is to be presumed. Corrections of the frequency of the index of isometric contraction do not improve the evidence. In the borderline region of the index of isometric contraction with values between 1.03 and 1.1 in questionable cases a further differentiation into still normal or already latent insufficient will do by the analysis of the trend of the index of isometric contraction after the application of medicaments. The determination of the change of the direction of the index of isometric contraction after peroral application of nitroglycerin would be justifiable in routine work after the recognition of the initiaction increases in patients with latent heart insufficiency, in patients with a healthy heart it decreases. The clinical value of the index of isometric contraction as a simple test of the circulatory function is highly to be estimated.

[Objectivation of the cardiac insufficiency load index--a comparison between spiroergometry and stretch-index]. / Zur Objektivierung der Kardialen Belastungsinsuffizienz--ein Vergleich zwischen Spiroergometrie und Anspannungsindex

It was shown that reduction in exercise capacity because of latent heart insufficiency could be significantly demonstrated by the so-called pre-ejection index PI, measured under conditions of rest. On the other hand, normals did not show any significant interrelation between PI and parameters related to exercise capacity, obtained by spiroergometric measurements. The pre-ejection index PI is a non-invasive parameter which compares the pre-ejection period in upright and supine posture. Since spiroergometric measurements could not be made under vita-maxima conditions, PI values were compared with parameters of submaximal exercise. Exercise was performed on the bicycle ergometer, with oxygen consumption and heart rate being recorded. Measuring results also revealed that by means of the pre-ejection index the necessity and effectiveness of glycoside medication may be objectively defined. Measuring techniques are described and statistically processed data are presented.

[New, non-invasive index for recognition of the early stages of cardiac insufficiency]. / Ein neuer nichtinvasiver Index zur Erkennung von Frühstadien der Herzinsuffizienz

Proceeding from the highly significant correlation of the pre-ejection period (PEP) with usual measures of contractility a new non-invasive index is given which allows to recognize a decrease in left ventricular contractile adaptability and, therefore, to diagnose early stages of heart failure. The so-called pre-ejection index is based on measuring the pre-ejection period in upright and supine posture under resting conditions. By means of series of measurements with 30 normal subjects and 30 patients with latent heart insufficiency is demonstrated that a highly significant separation of the two groups is possible. A newly developed so-called thermistor pulse transducer is described which is essential for an easy application technique. Suggestions are presented for determination of the pre-ejection index by means of a single channel E.C.G. apparatus and for automatic digital data acquisition.