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  • 1
    Digitale Medien
    Digitale Medien
    Functional development of the parasympathetic innervation of the sino-auricular node in newborn rabbits, cats and guinea pigs (1983)
    Springer
    Pflügers Archiv 398 (1983), S. 73-77 
    Details
    ISSN: 1432-2013
    Schlagwort(e): Ontogenesis ; Autonomic nervous system ; SA-node ; Rabbit ; Cat ; Guinea pig
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary The effects of supramaximal vagus nerve stimulation on heart rate were studied in newborn rabbits, cats and guinea pigs. The analysis of the stimulus-effect curve revealed that the carlier proposed relationship: logI f/I o=H·f (I o is the steady state PP-interval before andI f during stimulation,f is the stimulus frequency, andH the slope of the line) accurately summarizes the relation in rabbits, while with minor deviations it also holds for newborn cats and guinea pigs. Thus, the vagus effect for each nerve and animal is characterized by the slope of the line,H. In rabbits and cats the vagus effect decreased during the first postnatal week to about 1/3 and 1/5 of the initial value at birth. Guinea pigs, however, did not show such a postnatal change of the vagus effect. In comparison with rabbits and cats these animals are born at a relatively late ontogenetic stage. Therefore, we hypothesized that the decrease in vagus effect is related to the stage of development and occurs mainly before birth in this species.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00584717
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  • 2
    Digitale Medien
    Digitale Medien
    Effects of endotoxin infusion on mean systemic filling pressure and flow resistance to venous return (1996)
    Springer
    Pflügers Archiv 431 (1996), S. 741-747 
    Details
    ISSN: 1432-2013
    Schlagwort(e): Endotoxin ; Venous return ; Systemic filling pressure ; Vascular resistance ; Stressed volume
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract Mean systemic filling pressure (P sf) is an indicator of the filling state of the systemic circulation. Cardiac output (Q′) is related linearly to the difference betweenP sf and central venous pressure (P cv), according to:Q′ = (P sf −P cv)/R sf, whereR sf is the flow resistance downstream from the sites where blood pressure is equal toP sf In 16 anaesthetized pigs we evaluatedP sf,R sf andQ′ during baseline conditions, continuous endotoxin infusion and after subsequent fluid loading.P sf andR sf were determined from simultaneous measurements ofQ′ andP cv at seven levels of lung inflation. The following results were obtained.P sf was 8.1 ±1.8 mm Hg (mean ± SD) during baseline conditions, increased after endotoxin infusion to 9.9 ± 3.2 mm Hg (P = 0.04) and remained the same after infusion of 18 ml · kg−1 of Ringer's lactate.R sf increased from 0.34 ± 0.07 to 0.80 ± 0.34 mm Hg · ml−1 · s by endotoxin and decreased after fluid infusion to 0.58 ± 0.14.Q′ changed inversely proportional toR sf (P = 0.001).R sf changes were highly correlated with the changes in total systemic flow resistance (R S) (P 〈 0.001). Endotoxin caused haemoconcentration and a decrease in plasma volume. The stability ofP sf during endotoxin infusion and after volume loading indicate that the stressed volume was well maintained and changes in blood volume are compensated by changes in nonstressed volume. The increase inR sf can be attributed to arteriolar vasoconstriction, venous vasoconstriction and haemoconcentration.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02253838
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  • 3
    Digitale Medien
    Digitale Medien
    Effects of local nerve cooling on conduction in vagal fibres shed light upon respiratory reflexes in the rabbit (1992)
    Springer
    Pflügers Archiv 421 (1992), S. 280-282 
    Details
    ISSN: 1432-2013
    Schlagwort(e): Vagal A and C fibres ; local nerve cooling ; conduction block ; compound action potential ; respiratory reflexes ; rabbit
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract In ten vagus nerves the effect of local cooling on the compound action potential was studied in the temperature range of 34 to 0 °C in spontaneously breathing, anaesthetized rabbits. The mean temperature at which the myelinated (A) fibres were completely blocked, was 10.2±2.4 °C (mean ± S.D.). In nine nerves, local vagus cooling to 0 °C failed to block all non-myelinated (C) fibres. In one nerve, total blocking occurred at 2.0 °C. We conclude that in the rabbit, the earlier found increase in tonic activity of the diaphragm following lung inflation or deflation during bilateral local vagus cooling to a temperature between 8 and 0 °C is due to afferent impulses in vagal C fibres.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00374839
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  • 4
    Digitale Medien
    Digitale Medien
    Quantitative effect of vagal stimulation on heart interval in newborn and older rabbits (1971)
    Springer
    Pflügers Archiv 325 (1971), S. 61-76 
    Details
    ISSN: 1432-2013
    Schlagwort(e): Neonatal Heart ; Vagal Stimulation ; Sino-Auricular Node ; Heart Interval ; Neonatales Herz ; Vagusreizung ; Sinusknoten ; Herz-Intervall
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary In two groups of young rabbits, aged 0–5 and 9–23 days, the effect on the heart interval of stimulation of the right and left vagal nerves separately was investigated at frequencies of 1, 2, 4, 8 and 16 stimuli per second. Up to and including 8 stimuli per second, this is well described by log10 (I f /I o )=Hf, orI f =I o L f =I o e hf , whereI o andI f are the heart intervals before and during stimulation respectively at frequencyf, L is a lengthening factor,H=log10 L andh=2.3026 H. Thus each increase in vagal stimulation multiplies the heart interval by a constant factor. the response as defined by H were estimated for both right and left vagal nerves in 15 rabbits, and right or left only in 7 others. The responses varied considerably in individual rabbits and were much larger for almost all in the younger group. The effects of right compared with left stimulation, and of deviations of observed from fitted interval ratios, are studied in detail. Some other mathematical forms given in the literature for the response curves are discussed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00587492
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  • 5
    Digitale Medien
    Digitale Medien
    Mean systemic filling pressure as a characteristic pressure for venous return (1985)
    Springer
    Pflügers Archiv 405 (1985), S. 226-233 
    Details
    ISSN: 1432-2013
    Schlagwort(e): Venous return ; Systemic filling pressure ; Lung volume ; Central venous pressure ; Arterial pressure ; Capillary pressure ; Venous capacity function
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract Guyton's theory on venous return, implying a linear relationship between blood flow and central venous pressure, was tested in an intact circulation after thoracotomy and airtight chest closure. In eleven Yorkshire pigs (approx. 10 kg) we measured flow in the pulmonary artery and aorta and pressure in the central veins and aorta during pentobarbital anesthesia and mechanical ventilation. To change central venous pressure different lung volumes were randomly applied at intervals of 5 min in a series of inspiratory hold procedures of 7.2 s. During these short periods hemodynamic steady state circumstances were met without involvement of cardiovascular control mechanisms. We confirmed the linear relationship between venous return and central venous pressure and derived mean systemic filling pressure from the regression equation. Mean systemic filling pressure was on average 10.5±2.3 (SD) mm Hg. The time dependent changes during the inspiratory hold procedure showed that the increase in central venous pressure was the primarily dependent variable, followed by a decrease in venous return and right ventricular output. After a delay of 2–4 heart beats also a decrease in left ventricular output and aortic pressure occurred. Subsequently, the lower venous return during inspiratory hold was mainly sustained by the lower aortic pressure, but nevertheless fulfilled the linear relationship mentioned above. For analysis of flow and pressure changes in the systemic circulation during changes of central venous pressure a tube of constant flow resistance was used as a conceptual model. Consequently, the point where mean systemic filling pressure exists during normal flow conditions was predicted at a characteristic location in the peripheral venous system. Downstream from this point blood pressure will rise and vessel capacity will be filled up during increases in central emptying vessel capacity partially.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00582565
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  • 6
    Digitale Medien
    Digitale Medien
    Tidal variation of pulmonary blood flow and blood volume in piglets during mechanical ventilation during hyper-, normo- and hypovolaemia (1993)
    Springer
    Pflügers Archiv 424 (1993), S. 255-265 
    Details
    ISSN: 1432-2013
    Schlagwort(e): Ventilatory cycle ; Lung blood volume ; Cardiac output ; Right ventricular function ; Hypervolaemia ; Normovolaemia ; Hypovolaemia ; Squeezing
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract Effects of changes in blood volume on changes in pulmonary blood flow and pulmonary blood volume during the ventilatory cycle during mechanical ventilation with a positive end-expiratory pressure of 2 cm H2O were determined in six pentobarbital anaesthetized, curarized pigs weighing about 10 kg. Haemodynamic variables were analysed for each cardiac cycle in eight ventilatory cycles in four consecutive series under hyper-, normo- and hypovolaemic conditions. Cardiac output was highest in hypervolaemia. Compared with normo- and hypovolaemia, it decreased less during inflation, due to a smaller rise in central venous pressure and presumably a larger filling state of the venous system. The smaller decrease in right ventricular output in hypervolaemia coincided with a larger fall in transmural central venous pressure (right ventricular filling pressure), due to right ventricular action at a higher, less steep part of its function curve. The difference between right ventricular-output (electromagnetic flow measurement) and left ventricular-output (pulse contour) indicated changes in pulmonary blood volume. In hypervolaemia less blood shifted from the pulmonary circulation into the systemic system during inflation than in normo- and hypovolaemia. This difference can be explained by two mechanisms namely, the smaller fall in input into the pulmonary vascular beds and a smaller pulmonary vascular volume decrease as a result of transmural pressure fall at a steeper part of the pressure-volume curve.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00384351
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