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Biomedical subjects

A Dittmar

Publications and source records attributed to A Dittmar.

71 records · Page 4Linked to original sources
PubMed1977

High-sensitivity device for continuous measurements of tissue O2 uptake.

An analysis system for continuous measurements of O2 uptake by rat diaphragm during several hours is described. The tissue was set in a chamber where a medium was flowing at a known and constant flow rate, temperature, and partial pressure of oxygen (PO2). The decrease in PO2 of the medium was measured with a Clark O2 cathode at the outlet of the chamber. To increase the sensitivity of the system and the signal-to-noise ratio of the measurements, a sweeping device was designed. It provided homogenization of the medium in the chamber. The main characteristics of this analysis system are a) a sensitivity of +/-0.2% of the mean PO2 value of the perfused medium, +/-0.8% of the mean O2 uptake of rat diaphragm, b) a linearity of +/-1.75% in the range of 0+/-200 Torr, c) a stability of +/-0.38% of the initial PO2 value, and d) a time constant of 8 min 30 s. This type of system can be used for high-sensitivity measurements of O2 uptake of any tissue after adaptation of the chamber and of the medium flow rate.

Animals↗
PubMedDate not supplied

Relationships between performance and skin resistance evolution involving various motor skills.

The aim of this article was to question the classical inverted-U curve relationship between activation and performance. It was hypothesized that changes in performance were related to both activation and the degree of skill difficulty, suggesting a more complex relation. Fifty-one subjects took part in one of three experiments requiring sensory and motor anticipation abilities. They were divided into three different groups, each performing one particular anticipation task. Skin resistance was continuously recorded during task performance. This autonomic variable is well known to be a reliable index in predicting activation variations. The first task, carried out in a seated position, was to intercept a moving spot on a computer screen by pressing the space bar on the keyboard. The second task, performed standing, required subjects to intercept a moving table tennis ball with palm of the hand, by extending the forearm and the arm. The third task, executed in movement was performed on a volley-ball ground. The aim was to hit a ball to reach a moving human target, using the forearm-blow technique. Results showed that 90.9% of subjects'performance in Experiment 1 was related to skin resistance tonic level variations, thus establishing a strong relationship between performance and arousal. Subjects' performance (43.8%) in Experiment 2 was related to skin resistance tonic level variations, whereas only 12.5% of performance was related to this variable in Experiment 3. In conclusion, tonic level variations can only account for success or failure in the first experiment. Conversely, success or failure were dependent upon information processing, decision making, and motor execution in the third experiment. The second experiment, requiring intermediate abilities, was found to show intermediate results. The role of skin resistance tonic level fluctuations and their use in the study of sporting performance are discussed, suggesting that arousal/performance relationships do not correspond to a simple inverted-U curve in complex motor skills requiring a steady level of arousal.

Adolescent↗
PubMedDate not supplied

Measurements of effective thermal conductivity during hyperthermia: a comparison of experimental and clinical results.

Temperature and effective thermal conductivity (including the convective effects due to tissue blood flow) profiles have been mapped both within a perfused phantom model containing a differentially perfused pseudo-tumour and in patients undergoing microwave (915 MHz) hyperthermia. These measurements demonstrate the influence of differential thermal characteristics of tumour vs. normal tissue on the temperature distributions obtained during hyperthermia. Effective thermal conductivity was measured using a self-heated thermistor probe, and temperature profiles were measured by means of conventional thermocouples and fibre-optic temperature probes. Measurements of effective thermal conductivity obtained in patients prior to microwave hyperthermia, and temperature profiles obtained once steady-state treatment conditions had been attained, show a strong relation between the effective thermal conductivity profile and the ability to obtain therapeutic temperatures without excessive heating of intervening tissues. These observations were confirmed in phantom experiments, demonstrating that this perfused phantom is a more realistic physical model than the conventional unperfused gels usually employed as physical models for hyperthermia experiments. These results demonstrate that tissue thermal clearance is an important determinant of treatment temperature fields, independent of and in addition to the SAR distribution of the particular applicator. Effective thermal conductivity measurements of the different tissues constituting the volume to be heated could be an important index in the planning and optimization of treatment strategies.

Clinical Protocols↗
PubMedDate not supplied

Internal temperature variations during the sleep-wake cycle in the rat.

This study attempted to explain the variations of internal (brain and subcutaneous) temperature in the rat as a function of sleeping and waking. Temperature variations in cerebellum and hypothalamus were related to the changes in local cerebral blood flow (CBF) measured chronically with a thermal clearance method. CBF was stable and at a high level during slow wave sleep (SWS), decreased at the beginning of each wake (W) and paradoxical sleep (PS) phase, but tended to overshoot at the end of the PS phase. Subcutaneous temperature was related to the whole body thermogenesis (VO2) and to the sensible heat loss by radiation, convection and conduction. VO2 increased during W, decreased and plateaued during SWS, and was at a minimum level during PS. Sensible heat loss decreased during W, increased during SWS, and generally rose abruptly during PS. These variations in body and brain heat gain and heat loss are in agreement with the local temperature variations during sleeping and waking. The concomitant variations in vigilance states and internal temperature led to an apparent close relationship between the circadian rhythms of these variables, although their exact degree of liaison was not established.

Animals↗
PubMedDate not supplied

Comparison of continuous microperfusion and cold storage for pig heart preservation.

The aim of this study was to compare two methods of hypothermic heart preservation. Isolated hearts of pigs were preserved in cold cardioplegic solution (St. Thomas Hospital solution) either by simple storage or continuous microperfusion (with a new perfusion device) for 6 hours (group I, n = 12), 12 hours (group II, n = 12) and 24 hours (group III, n = 12). After storage, the myocardial function was studied for 60 minutes under nonworking conditions with an ex vivo functional testing system. Hearts preserved 24 hours by cold storage (group III) showed ventricular compliance and mean spontaneous left ventricular developed pressure significantly lower than hearts preserved by microperfusion (respectively, 63 +/- 47 versus 14 +/- 18 mm Hg and 16.8 +/- 22.0 versus 83 +/- 33 mm Hg). After 12 hours (group II) of preservation, mean left ventricular developed pressure was higher in microperfused hearts compared to immersed hearts (respectively, 133.3 +/- 39.0 versus 83.1 +/- 27.0 mm Hg, p < 0.05), whereas after 6 hours of preservation, no functional difference was observed between the microperfused and the immersed hearts. Hearts were also studied using myocardial biopsy specimens taken at the end of the preservation. The biopsy specimens were analyzed for high-energy phosphates. After 6 hours of preservation, the microperfusion group showed higher levels of adenosine triphosphate and total adenine nucleotides (adenosine triphosphate + adenosine diphosphate + adenosine monophosphate) (respectively, 4.60 +/- 0.5 mumol/gm and 5.98 +/- 0.5 mumol/gm fresh tissue) versus the cold storage group (respectively, 3.10 +/- 0.4 mumol/gm and 3.75 +/- 0.4 mumol/gm).(ABSTRACT TRUNCATED AT 250 WORDS)

Adenine Nucleotides↗