Bauhaus-Universität Weimar

Handbook for the Physiological Laboratory. Text
Burdon-Sanderson, John Scott E. Klein Michael Foster T. Lauder Brunton
arterial pressure and in the frequency of the contractions of the 
heart, are not necessarily dependent on the mechanical effect of 
the respiratory movements on the heart, inasmuch as they persist 
when these movements are abolished ; and that they have their 
primary source in the vasomotor and cardiac-inhibitory centres, 
which act rhythmically, not because they are subject to any 
rhythmical excitation, but because they have periods of waxing 
and waning activity which correspond to those of the respiratory 
centre. A very little consideration shows that this inference 
carries the admission, that the cardiac-inhibitory centre and the 
vasomotor centre act alternately, for it can be seen in every tra¬ 
cing that the increase of arterial tension determined by increased 
^ • * 
vascular tonus, alternates with the retarded pulse and diminished 
tension produced by “ vagus excitation.” In other words, the 
phase of maximum activity of the inhibitory centre always co¬ 
incides with that of minimum activity of the vasomotor centre. 
The experiment by which it is proved that the respiratory phases 
of arterial pressure and pulse frequency are independent of the 
thoracic movement, consists in curarizing a dog by the injection 
into the venous system of a dose of solution of curare only just 
sufficient to paralyse the respiratory muscles (5 to 10 millig. for 
a dog of 10 lbs. weight), and observing graphically the changes 
of arterial pressure which occur during the gradual extinction of 
the respiratory movements, with the aid of the apparatus described 
above. The tracings, figs. 259-261, show what is observed at three 
different stages of curarization. Curve 259 was drawn w hen the 
animal's muscles were still active. It may be regarded as normal. 
Curve 260* corresponds to a period at which each inspiration and 
expiration is represented by a scarcely perceptible contraction 
and dilatation of the chest. Curve 261 to a still later condition, in 
which the inspiratory movements are indicated by a mere vibra¬ 
tion of the lever, produced (as w7as observed at the time) by 
momentary contraction of certain inspiratory muscles which 
were not >et completely paralysed. We learn from these obser¬ 
vations, that during the gradual extinction of the respiratory 
movements, the intervals between them correspondingly lengthen ; 
and that at first the variations of arterial pressure and pulse fre¬ 
quency exhibit the characters which closely correspond to those 
they exhibit normally. Subsequently, the ascents and descents of 
the mercurial column become much more gradual, and the 
* In fig. 260 the notches in the lower tracing represent rudimentary inspirations 
and expirations. The expiratory movements, e e e, are only traceable, however, in 
the last half of the tracing ; they follow the inspiratory, i i i, at an interval of about 
five mill. = l£ sec. In fig. 261, the expiratory movements are wholly indistinguish¬ 
able. All the tracings of this series are reduced one-half to save space. The distance 
between the respiratory and arterial tracing is also diminished for the same reason.


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