In vivo cardiac phase response curve elucidates human respiratory heart rate variability.

Recovering interaction of endogenous rhythms from observations is challenging, especially if a mathematical model explaining the behaviour of the system is unknown. The decisive information for successful reconstruction of the dynamics is the sensitivity of an oscillator to external influences, which is quantified by its phase response curve. Here we present a technique that allows the extraction of the phase response curve from a non-invasive observation of a system consisting of two interacting oscillators--in this case heartbeat and respiration--in its natural environment and under free-running conditions.

Why life oscillates--biological rhythms and health.

A multitude of biological rhythms have been identified in the whole organism as well as within each living cell. Some of these rhythms reflect adaptations to our environment, while others run on their own. Recent evidence shows that these rhythms and their interaction might be more important not only for recreation but also for our health.

Physiological considerations about life cycles of universities.

In Austria, a new federal law concerning university reorganization (UG 2002) has led to the former university medical faculties in Vienna, Innsbruck and Graz becoming independent medical universities, despite warnings by competent persons that this could have negative consequences. One logical consequence for example, is a certain isolationist trend that will eventually lead to medicine withdrawing into a kind of "splendid isolation", physically separated, even, from the rest in brand new buildings. The splitting of each of the three Austrian universities, which included Medical Faculties, into a new Medical University and a 'Rest University', has led to the growth of two daughter cells each now larger in terms of administration than the former university.

Physiological considerations about a statement by Gaius Petronius.

In my inauguration speech on November 8, 1989 as Rector of the Karl-Franzens-University in Graz (1) I have warned not to split off the Medical Faculty as a separate Medical University "...

Noninvasive assessment of vascular function.

Impaired arterial compliance contributing to increased blood pressure and cardiac workload is well accepted as a major factor in cardiovascular disease. Information on local arterial compliance is obtained when analyzing the deformation of selected arterial segments under stress. A more global measure of arterial compliance is obtained by analyzing the arterial pulse by so-called pulse wave analysis.

Classification of sudden infant death (SID) cases in a multidisciplinary setting. Ten years experience in Styria (Austria).

Objective: Sudden infant death syndrome (SIDS) remains a challenge for health professionals despite decreasing rates in recent years. The figures for different areas and time periods are hardly comparable, because of differences in postmortem investigations and classification criteria. In 1992, the European Society for the Study and Prevention of Infant Deaths (ESPID) proposed a classification for any sudden and unexpected death in infancy.

Microvibrations: an interrelation between heart beat, muscle tremor and resting muscle tone.

The phenomenon of microvibrations was described by Rohracher in Vienna in the 1950s. Microvibrations consist of oscillationns in the frequency range of 7 to 13 Hz which can be observed on the surface of the body during a complete muscle relaxation. We had the opportunity to study the changes of microvibrations and physiological tremor under the condition of weightlessness in the Russian Space Station MIR during the so called "Austromir" project and the following Russian long term flights including the record flight of cosmonaut Polyakow.

[Karl E. Hammerschmidt. Humanist, natural scientist and pioneer in anesthesia].

Karl Eduard Hammerschmidt was born in Vienna in 1801. There are indications that after studying law he passed on to studies in medicine and surgery in Vienna, though it has to be said there is no trace of his attaining any qualification. After this he worked in various scientific sectors and in recognition of his achievements he was accepted as a member of the Kaiser Leopold Academy of Researchers in Natural Sciences in Bonn.

Temporal disparity between reduction of cot death and reduction of prone sleeping prevalence.

According to several reports sudden infant death rates have decreased significantly after public campaigns aimed at reducing the incidence of sleeping in a prone position. The Styrian population (1.2 million inhabitants), who have been studied from 1984, also showed a significant drop in the incidence of cot death during 1989 (from 2/1000 to 1/1000%).

Effects of an eight-day space flight on microvibration and physiological tremor.

Microgravity was used to study accelerometrically recorded microvibration (MV) and postural tremor (PT) at reduced muscle tone on one cosmonaut before, during, and after an 8-day space flight on the Russian Mir station. MV of the relaxed forearm in the 1 g environment showed the typical 7- to 13-Hz resonance oscillations triggered by the heart beat. In 0 g, these pulsations shifted to below 5 Hz and the waveform became similar to an ultralow frequency acceleration ballistocardiogram.

Effect of controlled extracorporeal blood cooling on ultrafiltration-induced blood volume changes during hemodialysis.

Considerable amounts of heat may be lost or gained through the extracorporeal circuit during hemodialysis and influence the hemodynamic stability of the dialysis patient. The effects of two levels of extracorporeal heat flux (Jtherm in W) on blood pressures and ultrafiltration-induced blood volume changes were studied in eight patients on conventional hemodialysis. Treatments were controlled automatically for mild to medium Jtherm of either -13.

Characterisation of arm microvibration recorded on an accelerometer.

Microvibration (MV) of the freely hanging and firmly supported lower arm was studied (n = 8) using two accelerometers, one located over muscle tissue (brachioradialis muscle) and one over bony tissue (processus styloideus). Measurements were made in the completely relaxed arm (REST), during arterial occlusion (CUFF) and during mild handgrip (GRIP), first with the arm relaxed and hanging beside the chair and then repeated with the arm supported in a special rest. At REST.

Lipoprotein(a) inhibits collagen-induced aggregation of thrombocytes.

Lipoprotein(a) [Lp(a)] is known to interact with human platelets in vitro. In the present study the effect of physiological concentrations of Lp(a) on platelet aggregation was studied. Freshly prepared gel-filtered platelets from healthy donors were incubated for 30 minutes at 37 degrees C with various concentrations of Lp(a); aggregation was triggered with ADP, thrombin, and collagen.

Instrumentation for assessment of tremor, skin vibrations, and cardiovascular variables in MIR space missions.

A versatile and simple to use biomedical instrumentation for noninvasive examinations of cosmonauts at the Russian MIR space station was developed. It consists of a comfortable sensor jacket to assess signals from the body surface, a precision hand dynamometer to produce muscular and cardiovascular loads, and a small interactive microprocessor unit that controls the examination and stores measurement data. The sensor jacket includes highly sensitive piezo-resistive accelerometers, pulse sensors, an ECG system, and a skin-mountable mechanical vibrator.

Indirect measurement of blood pressure without a cuff.

This review covers the following topics: the palpation of the arterial pulse, the method of tonometry, the relation between blood pressure, arterial diameter and pulse wave velocity, the frequency dependence of the components of the pulse wave velocity, the influence of the state of the vascular smooth muscles on the pulse wave velocity, a special method to measure radial pulsations of the pulmonary artery, the so-called pulse transmission function and, finally, the influence of gravity on the arterial pulses.

Age, time, entropy, and biological optimality--some remarks on the general problem of biological optimization.

The purpose of this paper is to look from a very general viewpoint to the interaction of factors which contribute to the process of aging. Life time is the most significant period for an individual. Several theories try to explain the process of aging by genetic determinants, by genetic or metabolic defects, by immunologic failure or by other reasons.

Analysis of left ventricular contractile behaviour during atrial fibrillation.

Objectives: The purpose of this study was to explore the physiology underlying the beat-to-beat variations of ventricular function during atrial fibrillation (AF).

Methods: Left ventricular pressure, and its first derivative (LVdP/dtmax, an index of contractility, and aortic blood velocity (and its integral AVI, an ejection index), were recorded using cathetermounted transducers in 15 patients with AF during cardiac catheterisation. Transfer function modelling was used to examine the influence of preceding intervals on LVdP/dtmax, and of LVdP/dtmax on AVI.

Heart rate variability as a prognostic tool in cardiology. A contribution to the problem from a theoretical point of view.

Background: Recent clinical studies have proposed standard deviation of heart rate as a diagnostic tool for the outcome of cardiac infarction. Mathematical analysis of heart rate variability shows that heart rate is influenced by different frequency components derived from different parts of the autonomous nervous system. In the experimental part of this study, we investigated the possibility of calculating a variable describing the parasympathetic branch of the autonomous nervous system exclusively.

Arm tremor and precision of hand force control in a short and long term flight on the MIR-Space-Station.

To determine whether long and short time exposure of man in 0g alters normal physiological tremor patterns we recorded arm tremor using an accelerometer as well as hand forces and tremor during constant isometric contraction using a load cell. Arm tremor was decreased during both flights in amplitude and frequency. Shortly after the long term flight arm tremor amplitude was increased, indicating adaptive changes in the tonic reflex loop.