The reflex tachycardia elicited by rapid i.v. infusions of a blood substitute was studied in 21 chronic cats with spinal sections at C 8. All animals could breathe spontaneously. The day after section the average resting heart rate (HR) and arterial pressure (AP) were 109 beats/min and 98/67 mmHg, respectively. Vagal blockade with atropine (0.5-0.7 mg/kg iv) was performed prior to each infusion, increasing the average HR to 127 beats/min. In 39 infusions in 21 cats the average increase in HR was 10 beats/min (range from -6 to +22 beats/min). A tachycardia was observed in all but five trials, four of which were obtained in two cats that subsequently responded with a tachycardia. In seven animals the neural circuit mediating the response was partially or totally interrupted by section of several thoracic dorsal roots (T 1-T 4 or T 1-T 6) and of the spinal cord at the inferior level of these sections (between T 6 and T 7). The tachycardia response was progressively reduced and finally abolished by these procedures. These experiments indicate that spinal neural mechanisms are likely to contribute to the phenomenon first described by Bainbridge.
|Title of host publication||American Journal of Physiology|
|Number of pages||5|
|Publication status||Published - 1976|
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