Are adult transcranial Doppler systems suitable for application in neonates?

UNLABELLED: Transcranial Doppler systems have not been available for monitoring of cerebral blood flow velocities in neonates because of potential hazardous effects of energy output from standard instruments developed for adult application. Aim of the study was to test commercially available transcranial Doppler instruments for their applicability in neonates and to develop guidelines for adaptation for safe neonatal use. Energy output of five commercially available transcranial Doppler instruments was measured with a hydrophone system and a radiation force balance. At the highest setting and at the nominal 10% attenuation level, five out of five and two out of five instruments, respectively, had an energy output above the recommended limits. Power reduction was not linear in one instrument. Evaluation of safety devices (alarm, freeze mode, energy reduction facilities, display of energy values) showed that none of the tested instruments had an optimal setting for safe neonatal application. CONCLUSION: Commercially available transcranial Doppler instruments should be evaluated critically for their energy output prior to their application in neonates. Special software for neonatal application of transcranial Doppler systems should be developed in order to provide extremely low energy output levels and devices for indication of duration of Doppler insonation and energy output.

Effects of treadmill exercise protocol with constant and ascending grade on levelling-off O2 uptake and VO2 max.

In order to investigate the effect of an exercise protocol on the levelling-off O2 uptake and VO2 max values, ten male subjects aged 28 +/- 5 yrs, height 1.8 +/- 0.05 m, body mass 76 +/- 6 kg performed two treadmill exercise protocols: 1) constant grade (CG) of 5%, with increasing running speed starting at 6 km.h-1 and increments of 2 km.h-1 every 3 minutes. 2) ascending grade (AG) starting at 0% and increments of 5% every 3 minutes, with constant running speed of 5 km.h-1. During each protocol oxygen uptake (VO2), pulmonary ventilation (VE), tidal volume (Vt), and breathing rate (BR) as well as blood lactate concentration (La) and heart rate (HR) were measured. In CG a levelling-off phenomenon of VO2 in all cases was observed. Aerobic capacity expressed as VO2 max in CG was 46.2 +/- 6.0 ml.min-1.kg-1. In contrast, VO2 max was 35% higher in AG (62.6 +/- 7.2 ml.min-1.kg-1). The behaviour of VO2 indicates a lower efficiency with increasing work load in AG as compared to CG. Regarding maximum performance it can be concluded that VO2 in CG seems to be limited by a mechanical or neuromuscular constraint on the depth of breathing, which is confirmed by a distinct flattening of Vt. The levelling-off of the VO2 in CG, something which is not observed in AG, can be explained plausibly this way.

[The effect on wound healing of venous leg ulcers of a two-layered polyurethane foam wound dressing]. / Beeinflussung des Heilungsverlaufs von venösen Ulcera cruris durch eine zweischichtige Polyurethan-Schaumstoff-Wundauflage.

To demonstrate the effect of a two-layered polyurethane foam wound dressing (Lyomousse) on the healing of venous leg ulcers a comparative study in 41 patients (24 treated, 17 controls) was performed. For a quantification of the process of healing a computer-assisted morphometric procedure was used. This method is based on a Polaroid-photograph of the ulceration which is transferred in digital form by means of a digitizing equipment. From the digital data the primary variables area, perimeter and maximal diameter of the ulceration are calculated. For quantitative comparison the relative changes as well as the rate of the changes of the primary variables were used. The statistical comparison of the treated group and the control group showed a highly significant (p less than 0.001) promotion of wound healing for the therapy with the synthetic foam dressing using the relative changes as an indicator, and a significant (p less than 0.05) increase in the rates of changes, indicating an acceleration of healing. This therapeutical advantage can be drawn back to specific characteristics of the synthetic material, assuring a water vapour saturated micro-environment at the surface of the wound and reducing this way the detrimental effect of heat loss due to evaporation onto the healing process.

Single cuff comparison of two methods for indirect measurement of arterial blood pressure: standard auscultatory method versus automatic oscillometric method.

With the introduction of automatic oscillometric systems for indirect measurement of arterial blood pressure (e.g. DINAMAP), the problem of correspondence between that method and the standard auscultatory method arose. For an exact and valid comparison of two methods, for physiological and methodological reasons, both measurements have to be performed simultaneously and using only one single cuff. Applying a methodological approach fulfilling these preconditions and offering in addition the advantage of a graphic documentation of the individual measurement cycles, we were able to investigate both methods in a sample of 216 comparative experiments. We found a mean difference (auscultatory method minus oscillometric method) between the methods (bias) of -0.82 mm Hg (-0.109 kPa) for systolic pressure, 1.25 mm Hg (0.166 kPa) for diastolic pressure and 1.00 mm Hg (0.133 kPa) for mean pressure. Except for systolic pressure, the differences were statistically significant (paired t-test and analysis of variance). We also obtained a significant negative correlation between the differences and the average of both pressure values (decreasing error with increasing pressure) and a significant negative correlation between differences and heart rate (decreasing differences with increasing heart rate). The conclusions drawn from the comparative study are that, although the oscillometric method exhibited a tendency to higher systolic and lower diastolic measurement values compared to the auscultatory method, both methods are well comparable and the differences are below the level of physiological and clinical significance.

[Relevance of lactate determination in sports medicine]. / Relevanz der Laktatbestimmung in der Sportmedizin).

In the last years increasing attention has been paid to specific changes of muscle metabolism during physical exertion in the diagnosis of physical performance. Lactate resp. lactic acid, being the terminal product of anaerobic glycolysis, has gained a central position in that field of sports medicine. Measuring lactate concentration level in arterialized capillary blood (drawn from the earlobe) one can investigate both the onset of anaerobic-lactic energy production during increasing work load (aerobic-anaerobic transition) and the maximal amount of anaerobic energy formation during short periods of exhausting work. In this way, using suitable work load protocols, the aerobic capacity (endurance capacity) on the one hand and the anaerobic capacity on the other hand can be determined. Therefore the most prominent components of energy production in working muscle and physical performance in general are accessible by measurement of blood lactate concentration level.

Training-dependent changes of red cell density and erythrocytic oxygen transport.

Prolonged endurance training causes a decreased O2 affinity of Hb, which is due to an increase in erythrocyte 2,3-diphosphoglycerate (2,3-DPG) concentration. Possible mechanisms were studied in 20 males with varying degrees of fitness. Training status was tested by ergometry. Red cell density and O2 transport parameters were determined before this test. The O2 tension at 50% O2 saturation of Hb (P50) was higher in the more fit subjects (+1.3 mmHg) and the 2,3-DPG concentration was higher (+2.3 mumol/g Hb) in this group. The mean density was significantly lower in fit subjects (1.1002 g/ml) as compared with less fit subjects (1.1056 g/ml), indicating a lower mean age. Density distribution curves show that in the fit subjects more young erythrocytes were in blood and that the very old erythrocytes were missing. After correction for the differences in the density distribution, no differences in the P50 value and 2,3-DPG concentration between less fit and fit subjects were found. Therefore, the decreased Hb-O2 affinity after training can be explained by the presence of more young erythrocytes in the blood of trained subjects. The magnitude of this effect correlates with the training status.

Serum FSH, LH, and testosterone in humans after physical exercise.

The serum levels of FSH, LH, and testosterone were determined by radioimmunoassay in 63 men before, during, and after maximal and submaximal physical short- and long-term exercise (800-n running, climbing, 36-k cross-country skiing). In the 800-meter run, significant elevations of FSH, LH, and testosterone were observed, while in all other field and laboratory test (climbing, 36-km cross-country skiing, maximal stepwise bicycle and treadmill ergometry, 90-min submaximal bicycle ergometry) the hormone levels remained unchanged or were decreased. In contrast to FSH and LH, which did not show any clear modification with duration or intensity of exercise or with the state of training, changes of testosterone in the endurance field test (36-km cross-country skiing) seemed to be training dependent. In highly endurance-trained subjects, there was an increase and in less well-trained subjects a decrease of testosterone for equal distances and intensities of exercise.

TSH, T3, rT3 and fT4 in maximal and submaximal physical exercise.

The response of various thyroid hormone parameters to maximal physical exercise (MPE) was investigated in 14 medium and long distance runners and 13 divers. The effects of submaximal long time physical exercise (SMPE) was examined in seven divers. The TSH-level decreases significantly during MPE and slightly rises again after the end of the exercise. In SMPE, however, TSH continuously rises until 15 min after the end of the exercise. The T3 level rises significantly in MPE and falls below the initial value 15 min after the exercise finishes, during SMPE it remains practically unchanged and slightly decreases after the finish. In MPE, the rT3 level does not change and slightly decreases after termination, while the fT4 level continuously decreases from the beginning till 15 min after the exercise period. The latter two parameters do not show any change in SMPE. As possible reasons for the changes of TSH levels a decrease (MPE) or an increase (SMPE) of pituitary secretion might play a role. Furthermore, in MPE the rise in T3 level might be related to hemoconcentration, and the decrease in fT4 level to an elevated cellular utilization.

[Regression analysis of the heart rate increase in children during linearly increasing work load on a bicycle ergometer]. / Regressionsanalyse der Herzfreqauenzzunahme von Kindern bei linear ansteigender Belastung am Fahrradergometer.

E. A. Müller (1950) has introduced a procedure for the measurement of the "Leistungspulsindex" (LPI) based on the determination of a linear regression between heart rate increase and work load. For this purpose the work load on a bicycle ergometer is increased in proportion to time (about 10 W/min) and the heart rate is recorded continuously. We have performed measurements in children (10--11 years of age) and found that the above mentioned regression is markedly nonlinear and can be described best by two overlapping linear regression lines with different slopes (b11 and b12). We propose that under these conditions the regression coefficient b11 of the first part of the relation can be assumed as LPI. In our analysis we found the linear part of the heart rate to increase between the end of min 2 and min 6 (+/- 1.4) of the experiment in boys. In girls we found the linear part of the regression only until min 3.8 (+/- 1.4). One consequence of our results is related to the calculation of the PWC170 by linear extrapolation which appears to be impossible in all cases in which the relation between work load and heart rate is nonlinear. It seems possible to relate that part of the heart rate increase where the slope suddenly changes to the endurance limit.

[Biomedical technique in physiology (author's transl)]. / Biomedizinische Technik in der Physiologie (demonstriert an zwei Projektbeispielen).

On the basis of two examples of projects being realized in the department of physiology in Graz the use of engineering methods in physiological research is demonstrated. The first example presents a survey of the use of system-theoretical methods for the investigation of overall regulation of circulation under working conditions. Using two test-signals (impulse input, random input) for experimental identification, the impulse response of heart-rate to changes in work load was obtained. The impulse responses of the volunteers were then characterized by a set of three parameters, allowing statistical evaluation, classification for diagnostic means and verification of hypotheses. The second example deals with an investigation of the signal structure of ultrasound-CW-Doppler-systems. Basing on the general Doppler-principle, which is already in use in angiology it was tried to quantify the determinants of the audio-signal, describing it by statistical functions and by experiments on simple models (tube-models). The goal of the experiments is a quantitative assessment of volume-flow and an enhancement of information about the scattering medium (rheological properties of blood).

[Significance and tasks of work physiology (author's transl)]. / Bedeutung und Aufgaben der Arbeitsphysiologie Projekte der Arbeitsgruppe für Arbeitsphysiologie.

In the department of physiology in Graz the projects in the field of work physiology are concerned with basic and applied research. Currently the interest is focussed mainly on problems of exercise physiology. By a system analysis of the cardiorespiratory system the influence of exercise on respiration and circulation is examined. Furthermore routine methods for testing the training condition of athletes are being developed.

[Investigations of the validity of e.a. müller's "leistungspulsindex" (author's transl)]. / Untersuchungen zur Aussagefähigkeit des Leistungspulsindex nach E. A. Müller.

In order to obtain a critical review of E.A. Müller's "Leistungspulsindex", we worked out a functional representation of that index, using a simple physiologic-mathematic model of the oxygen transport system. We found that the LPI is influenced by the economy of the oxygen transport system and that it is inversely proportional to stroke volume, caloric coefficient, and to the efficiency of muscular work. Based on the theoretic analysis we tried to interpret the results of an investigation carried out with pupils of an coeducative intermediate school (years of birth 1964, 1965, 1966). We obtained statistically significant correlations (p less than 0.1%) between LPI and parameters characterizing performance capacity (PWC170, heart rate at 100 W work load) and between LPI and body weight. The results of both the theoretic and experimental investigation indicate a dependence of the LPI on factors influenced by physical training processes, but no evidence was found, however, on an interrelationship between LPI and congenital factors of physical performance.

[Ergospirometric studies on patients with diabetes mellitus and the effect of biguanides on physical performance]. / Ergospirometrische Untersuchungen bei Patienten mit Diabetes mellitus und der Einfluss der Biguanide auf die körperliche Leistungsfähigkeit.

24 diabetic patients had submaximal exercise testing before, and 4 days after, biguanide treatment. Biguanide treatment resulted in a significantly decreased exercise capacity. This is explained by increased anaerobic energy production, which results in a decrease of the performance of an individual.

Method for the analysis of the entrainment between heart rate and ventilation rate.

A digital computer program was developed which allows to continuously represent the relation between heart rate and ventilation rate. Using this program, experiments in anesthetized rabbits were performed. We found periods of synchronization, periods of transient entrainment and escape, and periods of complete desynchronization. By testing the respective roles for the entrainment mechanism of ventilation rate and heart rate it was found that spontaneous adjustments of the ventilation rate play a more pronounced role. Thus, as soon as spontaneous or induced variations of the heart rate and/or the ventilation rate shift both rhythms close to synchronization, variations of the ventilation pattern, which seem to be of reflex nature, tend to induce entrainment.

[Method for the continuous measurement of the phase relation between heart beat and respiration (author's transl)]. / Zur Methodik der kontinuierlichen Bestimmung der Phasenbeziehung zwischen Herzschlag und Atmung

A simple method for the continuous analysis of the phase relation between heart beat and respiration is described. By means of an analog computer the timing of the R wave of the ECG within the respiratory cycle is graphically displayed. In contrast to other investigations, the onset of the inspiration is used as starting signal. The results obtained with the analog computer were completed by a digital computer program, which allowed in addition to calculate histograms of the events. In order to evaluate our method we used an analog model of two coupled oscillators. Responses obtained at different coupling characteristics were compared with measurements in four subjects. The results indicate a mutual interaction between heart action and respiration as cause of the coupling of these two systems.