Factors Affecting Responses of the Inspiratory Center to Electrical Stimulation1

Journal/Book: Reprinted from THE AMERICAN JOURNAL OF PHYSIOLOGY Vol. 172 No. 3 March 1953. 1953;

Abstract: From the Department of Physiology Harvard Medical School Boston Massachusetts Received for publication August 18 1952. 1 This research was supported by a Public Health Service grant from the National Institute of Neurological Diseases and Blindness. 2 Harold Scharper Memorial Fellow National Paraplegia Foundation. SUMMARY The responses of a medullary area corresponding to what is usually called the inspiratory center to graded electrical stimulation are shown (fig. 1). The diaphragm was found to be more intrinsically rhythmic than the intercostal mechanisms. Vagotomy increased the electrical excitability of the center (fig. 2). Stimulation of the vagus decreased it (fig. 3). Administration of CO2 had little effect on the electrical excitability of the center although it increased respiratory rhythmicity (fig. 4). Occlusion of the carotid arteries increased the response of the center to electrical stimulation (fig. 5). Sectioning the dorsal columns in the cervical region decreased the electrical excitability of the center presumably due to removal of excitatory proprioceptive impulses (fig. 6). Section or block of dorsal roots T1 and C8 bilaterally in vagotomized animals led to respiratory failure in four out of six animals presumably by interruption of an inspiratory-excitatory pathway which has been described as running through the stellate ganglia (fig. 7). Section of other dorsal roots had no significant effect. In the discussion it is pointed out that the nervous control of respiration consists of at least five interrelated feedback systems which might be expected when interconnected to form an unstable whole and show oscillation. Thus the respiratory center would not have to be intrinsically rhythmic. Looking at the nervous control of respiration in this way may be more fruitful than a mere concern with any possible rhythmicity of an isolated part of the mechanism. ___MH

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