Abstract
The tachycardia which accompanies hypoxia is usually thought to be due to medullary stimulation and increased sympathetic activity. The present results indicate that an intact sympathetic pathway from medulla to spinal cord is not essential to the normal pattern of heart rate changes during hypoxia and re-oxygenation.
Eight subjects with complete cervical spinal cord transection were studied. They were given 10 per cent. oxygen to breathe for 3 minutes, and the hypoxia was then abruptly relieved by switching to 100 per cent. oxygen. Heart rate and ventilation were recorded throughout, and blood pressure was measured intermittently. The heart rate increased by an average of about 10 beats per minute, and decreased rapidly to normal after an average delay of 18.8 seconds from the first breath of oxygen. Neither the extent nor the timing of these changes was significantly different from those found previously by a similar technique in normal subjects. The changes in heart rate were not consistently linked to changes in ventilation or in blood pressure.
Possible mechanisms for the heart-rate changes have been considered in the light of these results and those in normal subjects. If the site of action is medullary, the efferent pathway must be vagal; alternatively the action must be on the sympathetic system below the lesion, or a direct effect on the cardiovascular system.
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Jennett, S. The response of heart rate to hypoxia in man after cervical spinal cord transection. Spinal Cord 8, 1–13 (1970). https://doi.org/10.1038/sc.1970.2
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DOI: https://doi.org/10.1038/sc.1970.2
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