On the relation between cardiodynamics and heartbeat perception.

The mediation of heartbeat perception by cardiodynamic parameters was investigated by experimentally introducing changes in heart performance. Twenty-five subjects (14 women, 11 men) underwent bicycle ergometric exercises (0-75 W) at different tilt angles (90 degrees-0 degree). After each of the 31 tilt/exercise phases, the following measures of cardiac performance were taken using impedance cardiography: stroke volume, Heather Index (as an indicator of contractile force), heart rate, and an estimate of the momentum of the ejected blood mass. Additionally, a heartbeat perception task was performed. The different tilt/exercise combinations induced profound changes in all cardiodynamic measures. The correlation between heartbeat perception and cardiodynamic parameters was highest for "momentum" (r = .67) and for stroke volume (r = .59). From our data, we infer that intraindividually occurring changes in cardiac perception are mediated partially by characteristics of heart dynamics and that the source of these interoceptive signals lies in the heart or in its close vicinity.

[Effect of body posture on heart rate and cardiocirculatory parameters in stress--implications for frequency-adapted pacemaker systems]. / Einfluss von Körperposition auf Herzfrequenz und kardiozirkulatorische Parameter unter Belastung--Implikationen für frequenzadaptierende Schrittmachersysteme.

In order to study the influence of body position on cardiodynamics and the consequences for the regulation of rate-adaptive pacing, we examined variations of cardiocirculatory parameters with passive graded tilt from the erect to the supine position (90 degrees, 75 degrees, 60 degrees, 45 degrees, 30 degrees, 0 degrees) in 25 healthy subjects of both sexes under resting conditions and under conditions of exercise on a bicycle ergometer. Using impedance cardiography combined with phonocardiography, it was possible to record heart rate, cardiac output, contractility (Heather index), and left-ventricular ejection time (LVET). Under the condition of rest, some parameters showed evident tilt dependency: tilting from erect to supine induced a decrease of heart rate (85.1 to 65.7 bpm), an increase of stroke volume (84.4 to 111.4 ml), and a prolongation of LVET (255.8 to 330.3 ms). Cardiac output and the index of contractility were not changed by this manipulation, however. Tilting under the condition of exercise clearly had less influence on all cardiodynamic parameters than tilting under the condition of rest. The only significant increase of heart rate (89.4 to 109.2 bpm), cardiac output (10.4 to 13.1 l/min), and Heather index (24.2 to 29.8 ohm/s2) was found between 30 degrees or 15 degrees, respectively, and the supine position. Thus, in addition to indicators of physical activity, body position respective stroke volume should be taken into consideration. Consequently, rate-adaptive pacing may guarantee optimal physiological hemodynamics.

Computerized Mackworth vigilance clock test.

A computerized vigilance test, the Mackworth clock test, is described. The program runs on IBM-compatible XT and AT computers with a graphics adapter.

[Cardiodynamic determinants of heart perception]. / Kardiodynamische Determinanten der Herzwahrnehmung.

Subjective perception of one's heartbeat is augmented by psychological factors (stress, fear) as well as by physiological influences (e.g., physical work). It is still unclear on which cardiac or circulatory parameters the "signal" for cardiac perception is based. In this study, the relation between cardiac performance and the ability to perceive one's heartbeat was investigated. Sixteen healthy subjects (8 female, 8 male, aged from 21 to 31 years) participated. Cardiac activity was varied by a combination of passive tilt and physical work on a bicycle ergometer. Subjects had to perform physical work (0, 25, 50, 75, 100 W) on the bicycle at seven different angles (90 degrees, 75 degrees, 60 degrees, 45 degrees, 30 degrees, 15 degrees, 0 degrees). A cardiac perception test was carried out after each load. The following cardiodynamic parameters were measured: stroke volume, contractility, and heart rate. The mean correlation coefficient between cardioceptive performance and cardiodynamic parameters was .62 for stroke volume, .45 for contractility, and .12 for heart rate. Obviously, a remarkable relation exists between the mass and--to a lesser degree--the velocity of ejected blood and cardiac perception. From this we infer, tentatively, that the subjectively perceivable heartbeat stimulus is generated by mechanical events that occur close to the left ventricle.

[Changes in the cardiac dynamics in passive tile to the supine position--impedance cardiography measurements]. / Veränderungen der Kardiodynamik bei passivem Kippen in die Waagrechte--Impedanzkardiographische Messungen.

Passive tilt is an effective means to manipulate cardiodynamic processes. While there is a large amount of literature available concerning cardiac function with upright tilt, passive tilt into the supine position is poorly investigated. There is evidence that adapting processes to the new position do not show analogy in both conditions. In this study we investigated cardiodynamic changes occurring with passive-graded tilt from the upright position to 20 degrees headdown tilt. Twenty healthy students of both sexes participated in the study. Using impedance cardiography combined with phonocardiography it was possible to acquire stroke volume, heart rate, Heather index, and systolic time intervals. The whole procedure was repeated to test the reliability of impedance data. There was no steady augmentation of stroke volume. Between 90 degrees and 60 degrees stroke volume remained stable and showed only little change between 60 degrees and 30 degrees. Between 30 degrees and the supine position there was a steep increase of stroke volume. Tilting into the upright position apparently has a different effect. The onset of heart rate decline preceded the increase of stroke volume. It is concluded that only little changes of stroke volume/preload are necessary to induce vagal response. In the 30 degrees position both cardiac output and Heather index were minimal; this may be due to decreased sympathetic output. Systolic time intervals showed volume dependancy. Correlations between the first and second part of the study were high for all variables.