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Biomedical subjects

J H Sneek

Publications and source records attributed to J H Sneek.

5 recordsLinked to original sources
PubMed1986

Arterial pressure and heart period in the conscious rabbit: diurnal rhythm and influence of activity.

Mean-arterial pressure (MAP), heart period (HP) and the level of physical activity were measured in conscious rabbits and averaged over one-hour periods during 14 consecutive days. Serial autocorrelation coefficients and serial crosscorrelation coefficients were computed, to analyse periodicity. Measurements were started immediately after implantation of the cannula (group A, n = 11) or 10-46 days after implantation of the cannula (group B, n = 6). In the course of 14 days, in group A, MAP decreased 9 mmHg and HP increased 21 ms (P less than 0.05). In group B, MAP decreased and HP increased in a similar way. Percentage activity did not show a trend. Significant diurnal rhythms were found. MAP and percentage activity reached the lowest values at noon, and the highest late in the evening. HP reached the highest values at noon and the lowest late in the evening. MAP and HP fluctuated exactly in antiphase. This suggests a common origin for both rhythms. During physical activity MAP was 10-15 mmHg higher and HP was 35-40 ms shorter than during rest. These differences did not show a trend or a diurnal variation. In individual animals MAP and HP varied greatly from hour to hour. These biological variations in MAP and HP as well as the influence of activity should be taken into account when conclusions are drawn from short-term measurements.

Animals↗
PubMed1982

Cardioplegia in the presence or absence of calcium.

The effect of the Bretschneider procedure of myocardial protection on the recovery of dog hearts in the postischemic phase after 90 min of aortic occlusion was studied. In one series of experiments, Bretschneider's calcium-free cardioplegic solution HTP was used; in a second series, 5 X 10(-5) M CaCl2 was added to this solution. The coronary system was perfused with cardioplegic solution (6 degrees C) for 6 min at the onset and for 1 min after 30 and 60 min of ischemic arrest. Functional recovery of the heart and plasma creatine kinase activity during the postischemic phase were not significantly different in the two groups of dogs. It is concluded that low temperature, mode of administration, and composition of Bretschneider's cardioplegic solution HTP protect the heart against the potential danger of exposure to a calcium-free solution.

Animals↗
PubMed1982

Cardiac function, fiber shortening, and dynamic geometry.

Many models for the study of the pump function of the heart emphasize the importance of cardiac geometry and detailed dimensional data. Because of the lack of accurate measuring techniques, approximate geometries such as shells of revolution have been applied. In this study, methods are presented that measure the dynamic geometry of the working, isolated canine heart by means of ultrasound-velocity tomography techniques. In addition, cardiac dimensions, intramural deformations, and fiber shortening have been measured dynamically in the in situ canine heart throughout the cardiac cycle with implanted radiopaque markers and biplane roentgen techniques. Results of regional contraction and relaxation patterns are presented. Epicardial fiber shortening between apex and base were computed and found to be dependent on the duration of the preceding RR interval.

Animals↗
PubMedDate not supplied

Continuous 24-hour intra-arterial blood pressure recording in the conscious unrestrained rabbit.

A measuring system is described for the long-term continuous beat-to-beat measurement of mean aortic pressure and heart period (interval between beats) in the conscious unrestrained rabbit. Pressures and heart periods were collected in hourly histograms. The histograms were summed into day (0800-2000 h), night (2000-0800 h) and 24-hour histograms. Separate histograms were formed for resting and active periods. From each histogram the mean value, standard deviation, fifth percentile, 50th percentile and 95th percentile were calculated and stored on a floppy disc together with the histograms. Off-line, histograms and their descriptive parameters were plotted and sent to a HP1000 computer for bulk storage and further analysis. The measuring system is capable of handling up to eight animals simultaneously for an indefinite period. The design functioned properly in the long-term measurement (more than 4 weeks) of mean level and variability of arterial pressure and heart period. The measuring system is useful in the study of arterial blood pressure behaviour after sino-aortic denervation and in the evaluation of drug effects in conscious animals.

Animals↗