A photoelectric plethysmograph is described that performs a frequency analysis of the peripheral volume pulse wave using a portable computer. It was used to determine how the pulse shape varied with age using 54 subjects in three age groups, 10-29, 30-59, and 60-89 years. The youngest group had a larger power in the second harmonic, (normalized to the fundamental), with p less than 0.05 than the older two groups. The decrease of power in the harmonics of the peripheral pulse wave with age may be a useful noninvasive measure of aging and vascular disease.

Although discharge of many sympathetic nerves decreases substantially on transection of the spinal cord in cats, firing of splenic and mesenteric postganglionic nerves continues unabated (R. L. Meckler and L. C. Weaver, Brain Res. 338: 123-135, 1985; R. D. Stein and L. C. Weaver. J. Physiol. Lond. 396: 155-172, 1988). Therefore, ongoing sympathetic outflow directed to the splanchnic circulation was proposed to be less dependent on supraspinal excitatory drive than that directed to other vascular beds. Blockade or transection of cervical spinal pathways in chloralose-anesthetized cats significantly decreased firing of gastric, hepatic, adrenal, and lumbar chain sympathetic nerves. Discharge of gastric and hepatic nerves decreased as much as that of adrenal and lumbar chain nerves; therefore, sustained discharge in the absence of bulbospinal excitation is not a characteristic of all sympathetic nerves innervating the splanchnic circulation. In contrast, discharge of the preganglionic greater splanchnic nerves was not decreased after spinal transection, although it changed from a rhythmic to an asynchronous pattern. This provocative finding suggests that rhythmicity of preganglionic discharge may be important for effective synaptic transmission to some postganglionic neurons, since postganglionic gastric, hepatic, and adrenal nerve firing decreased in the presence of sustained but asynchronous preganglionic input.