Skin sympathetic neuroeffector response is attenuated dose-dependently by systemic prostaglandin E1 injection in humans

Role of sympathetic nerve activity in the process of fainting

Syncope is defined as a transient loss of consciousness and postural tone, characterized by rapid onset, short duration, and spontaneous recovery, and the process of syncope progression is here described with two types of sympathetic change. Simultaneous recordings of microneurographically-recorded muscle sympathetic nerve activity (MSNA) and continuous and noninvasive blood pressure measurement has disclosed what is going on during the course of syncope progression. For vasovagal or neurally mediated syncope, three stages are identified in the course of syncope onset, oscillation, imbalance, and catastrophe phases. Vasovagal syncope is characterized by sympathoexcitation, followed by vagal overcoming via the Bezold-Jarisch reflex. Orthostatic syncope is caused by response failure or a lack of sympathetic nerve activity to the orthostatic challenge, followed by fluid shift and subsequent low cerebral perfusion. Four causes are considered for the compensatory failure that triggers orthostatic syncope: hypovolemia, increased pooling in the lower body, failure to activate sympathetic activity, and failure of vasoconstriction against sympathetic vasoconstrictive stimulation. Many pathophysiological conditions have been described from the perspectives of (1) exaggerated sympathoexcitation and (2) failure to activate the sympathetic nerve. We conclude that the sympathetic nervous system can control cardiovascular function, and its failure results in syncope; however, responses of the system obtained by microneurographically-recorded MSNA would determine the pathophysiology of the onset and progression of syncope, explaining the treatment effect that could be achieved by the analysis of this mechanism.

Altered sympathetic thermoregulation in patients with hypothalamic dysfunction following resection of suprasellar tumors

In patients with suprasellar tumors, both the tumor and its surgical resection may produce hypothalamic dysfunction including thermoregulatory disturbances. We quantitated skin sympathetic nerve activity using microneurography in eight patients with hypothalamic dysfunction following resection. Skin sympathetic nerve activity, skin blood flow (by laser Doppler flowmetry), sweating, blood pressure, and pulse rate were monitored during changes of core (tympanic) temperature in the patients and seven healthy controls. Core temperature was decreased by 0.3 degrees C and increased by 0.5 degrees C relative to baseline using a cooling/heating blanket. The increase in sympathetic nerve activity in response to cooling did not differ between controls and patients (41.0+/-13.1 vs. 38.1+/-7.7 bursts [min degrees C](-1)), but an increase upon heating in controls (45.1+/-5.4 bursts [min degrees C](-1)) was absent in the patients (-26.0+/-17.5 bursts [(min degrees C](-1)). Skin blood flow during heating increased significantly in controls but not in patients (35.6+/-14.6 vs. 15.8+/-5.8 ml [min 100 g tissue degrees C](-1)). The patients thus showed impaired heat loss during body temperature elevation. Microneurography proved to be a sensitive measure of hypothalamic autonomic function.

Reflex responses to insertion of the intubating laryngeal mask airway, intubation and removal of the ILMA

We studied 21 patients (ASA 1 or 2) to investigate the skin vasomotor reflex (SVmR) and haemodynamic responses to insertion of an intubating laryngeal mask airway (ILMA), tracheal intubation using the ILMA and removal of the ILMA. Anaesthesia was induced with fentanyl, midazolam, vecuronium and nitrous oxide. A size 4 ILMA was inserted using the standard technique, and a silicone reinforced tracheal tube (7.5 mm, ID) was passed through it. After confirming successful intubation, the ILMA was removed using the stabilizing rod. The three procedures were performed at approximately one-minute intervals. Insertion of the ILMA, intubation and removal of the ILMA all significantly reduced the skin blood flow on the ring finger in all patients. The mean amplitudes of the SVmR were 0.46 (SD 0.29), 0.54 (0.32) and 0.68 (0.21) respectively. The magnitude of the SVmR and the haemodynamic changes induced by removal of the ILMA were significantly larger than those accompanying the other two procedures. Use of the ILMA for intubation and removal of the ILMA produces three stimuli and the removal of the ILMA produces the greatest response.

Effects of increased ambient temperature on skin sympathetic nerve activity and core temperature in humans

The strength of sympathetic vasoconstrictor nerve traffic to the skin has an important role in human thermoregulation since it controls heat loss from the skin by constricting or dilating cutaneous blood vessels. This study sought to clarify the time relationship between a reduction of the vasoconstrictor activity induced by elevating the ambient temperature (Ta), and subsequent change of core temperature (Tty). For this purpose, we recorded peroneal skin sympathetic nerve activity (SSNA), laser Doppler skin blood flow, skin and core (tympanic) temperatures in 11 subjects while increasing Ta from 15 to 30 degrees C during approximately 30 min. We observed a significant suppression of SSNA 7.7 min after Ta rise with marked interindividual variations. Tty displayed an increase with a peak after 8.2 min followed by a successive decrease, which became significant 14 min after the Ta rise. The rate of decrease of vasoconstrictor SSNA correlated both with the rate of decrease of Tty (P<0.01) and the magnitude of the Tty decrease (P<0.0005). A cross-correlogram between SSNA and Tty showed a peak at 7 min (r=0.52). We conclude that a Ta rise-induced reduction of skin vasoconstrictor nerve traffic leads to a core temperature decrease after 7-8 min.

Skin sympathetic outflow in Buerger's disease

To clarify if sympathetic outflow is altered in Buerger's disease (thromboangitis obliterans, TAO), we measured skin sympathetic nerve activity (SSNA) in TAO patients, and observed the sweating and vasoconstrictive responses during resting and with activating maneuvers. Multiunit postganglionic sympathetic activity was recorded in a skin fascicle of the tibial nerve innervating the skin of the sole (glabrous skin) and peroneal nerve innervating the skin of the dorsum pedis (hairy skin) from five TAO patients and five healthy subjects simultaneously with skin blood flow and sweat expulsion. TAO patients showed significantly less vasoconstrictor SSNA than healthy subjects (17.0+/-1.9 vs. 31.5+/-5.8 bursts/min, P<0.001). Moreover, we found no relationship between vasoconstrictor SSNA and skin blood flow in some patients, while they were well correlated in healthy subjects. There was no evidence for increased sympathetic activity in TAO patients, and no hypersensitive relationship was found between SSNA and skin blood flow. These observations suggested that these TAO patients exhibiting no relationship between skin blood flow reduction and vasoconstrictor activity might not respond to sympathectomy, which is generally expected to result in an increase in skin blood flow. The absence of increased sympathetic nerve activity provides further indirect evidence of a local vascular abnormality in TAO.