Responses of the sino-atrial node to change in pressure in the sinus node artery

The sino-atrial node area was perfused selectively through the right atrial artery in 76 dogs. The relationship between changes in the blood pressure in this artery and sinus node rhythmicity was studied in 56 hearts in which the major blood supply to the sinus node artery came from the right atrial artery. A reciprocal relation was observed between changes of blood pressure in the sinus node artery and the sinus rate. Some characteristics were: (1) The negative chronotropic effect induced by raising the blood pressure was linearly related to the Degrees of pressure change and more prominent than the positive chronotropic effect induced by reducing the pressure. (2) This relationship was most prominent in a limited range between 20 and 100 mm Hg. (3) Dichloroisoproterenol, atropine, hexamethonium, reserpine and vagotomy did not modify these responses. It is concluded that this localized mechanosensitivity of the sinus node to changes in arterial pressure may be responsible for the regulation of the heart rate in the lower range of blood pressure and that complete regulation of the heart rate is achieved physiologically in combination with the reflexes through the carotid and aortic nerves.

Involvement of the central nervous system in vibration syndrome

In order to clarify the involvement of the central nervous system (CNS) in vibration syndrome (VS), patients with VS and age-matched controls were given a questionnaire and neurophysiological tests on auditory brainstem response (ABR), event-related potential (P300), short-latency somatosensory evoked potentials (SLSEP), and blink reflex (BR). Twenty-eight patients with a mean age of 56.3 (SD = 3.01, range 48-65) years from western Japan were examined. They had been on sick leave for an average of 6.13 (SD = 3.2, range 1-13) years at the time of the testing. Almost all were experiencing Raynaud's phenomenon in the winter of 1990-1991. They were not suffering from diseases or injuries which might have affected the CNS function. These patients were divided into two subgroups, one with more symptoms related to the CNS, especially memory and judgment (n = 13, group A), and the other with fewer symptoms (n = 15, group B). Normal controls with an average age of 55.8 (SD = 4.8, 48-65) years were people from the same area who met similar criteria. The ABR parameters of the patients were slightly, but not significantly, delayed compared with those of the controls. The SLSEP and BR parameters of the patients were not delayed. The latencies of P300 in group A were significantly delayed compared with those in the controls. The findings suggest that VS involves the cognitive and attention functions of the cerebral higher function, but not the conduction function in the auditory and somatosensory ascending tract and facial nerve reflex tract in the brainstem.