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The paper reviews findings in humans regarding interindividual differences in sympathetic nerve activity. Data come predominantly from microneurographic multi- or single fibre recordings of sympathetic nerve activity in healthy subjects. Findings relate to interindividual differences in muscle sympathetic nerve activity (MSNA) during resting conditions and in response to surprising sensory stimuli. At rest there are marked interindividual differences in the number of multiunit MSNA bursts. At the single fibre level the differences are because of more vasoconstrictor fibres being active in subjects with high than in subjects with low number of bursts. There are inverse relationships between (i) sympathetic burst incidence and cardiac output (CO) and (ii) between sympathetic burst incidence and vascular responsiveness to noradrenaline. Both findings contribute to explaining the absence of correlation between resting levels of MSNA and blood pressure. Surprising visual, somatosensory or auditory stimuli of sufficient strength cause a short lasting inhibition of MSNA in approx. 50–60% of healthy subjects. In subjects who display significant inhibition, the stimulus-induced blood pressure increase is smaller than in subjects without inhibition. The underlying mechanism may be related to fear of blood/injury. It is concluded that analysis of interindividual differences in sympathetic activity improves the understanding of central nervous control of the circulation. [ABSTRACT FROM AUTHOR]

Abstract Aim: Surprising sensory stimuli causing arousal are known to evoke short-lasting activation of human sympathetic activity in skin but not in muscle nerves. In fact, anecdotal observations suggest that muscle sympathetic activity may be inhibited. To test this hypothesis, the effects of surprising somatosensory (electrical skin pulses) or visual (flash) stimuli on multiunit muscle sympathetic activity were studied in 36 healthy subjects, aged 19–71 years. Methods: The stimuli were given either 200 or 400 ms after the R-wave of the electrocardiogram. Dummy stimuli, consisting of trigger pulses without sensory stimuli, served as controls. Results: On a group basis, a single sensory stimulus of either type attenuated the amplitude of one or two sympathetic bursts, while no such effects occurred after dummy stimuli. Individually, the inhibition was evoked by at least one stimulus modality or delay in 16 subjects, whereas in three subjects no significant inhibition occurred. Electrodermal signs of skin sympathetic activation were present in all subjects. Compared with one, five repeated electrical skin pulses induced only minor additional inhibition of muscle sympathetic activity, indicating marked habituation of the neural response. In nine subjects, the experiments were repeated once and in three subjects twice (with intervals of 2–3 months); in 11 of the12 subjects, the sympathetic effects were reproducible. In the group of subjects without significant sympathetic inhibition the stimuli induced a small, transient increase of mean blood pressure, which was not present in the group with sympathetic inhibition. Conclusion: The finding that different sensory stimuli induce similar effects that habituate markedly on repetition suggests that the inhibition of muscle sympathetic activity is because of arousal. The interindividual differences in sympathetic and blood pressure effects may be part of interindividual differences in behavioural responses... [ABSTRACT FROM AUTHOR]

Objective: To evaluate (1) if laboratory tests may be a useful complement in diagnosing palmar hyperhidrosis and (2) if such tests can be used in the follow up examination of treatment effects.Methods: Repeated measurements of evaporation and conductance were made in glabrous skin on hands and compared with subjective estimates of the degree of sweating in 20 control subjects and 20 patients with a history of palmar hyperhidrosis. In addition, 17 patients were monitored for up to 6 months after treatment of the hands with botulinum toxin A.Results: Before treatment, evaporation in the palms was higher in the patients than in the control subjects but skin conductance did not differ between the groups. After treatment both evaporation and skin conductance decreased markedly in the patients and then slowly returned towards pretreatment values.Conclusions: Measurements of evaporation, but not skin conductance, may be a useful objective adjunct when diagnosing palmar hyperhidrosis. Both methods can, however, be used to monitor intraindividual changes of sweating over time. [Copyright &y& Elsevier]

Abstract Aim: Congestive heart failure (CHF) and obstructive sleep apnoea syndrome (OSAS) are both associated with an intense sympathoexcitation, including an increased muscle sympathetic nerve activity (MSNA). We have studied the firing characteristics of single vasoconstrictor fibres to the muscle vascular bed in CHF and OSAS patients, at rest and during transient sympathoexcitatory stimuli, to elucidate the mechanisms by which vasoconstrictor output is augmented in these conditions. Results: The main alternatives for augmenting sympathetic output are an increased firing frequency of individual nerve fibres and an increased recruitment of nerve fibres. Starting with the frequency alternative, the inherent bursting character of MSNA provides two possibilities to increase the firing of individual fibres: (1) by increasing the proportion of neural bursts in which the fibre is active (increased firing probability) and (2) by increasing the number of spikes a fibre generates per burst (increased multiple within-burst firing). At rest and in cardiac sinus rhythm, an increased firing probability is seen in both CHF and OSAS patients, whereas increased multiple within-burst firing is found in OSAS but not in CHF. In response to transient sympathoexcitatory stimuli (such as pre-mature heart beats), both patient groups show marked shifts towards multiple within-burst firing. Thus, both mechanisms for augmenting discharge frequency are operating in these two pathological conditions, but the firing characteristics at rest differ significantly. During recording sessions in sympathoexcited patients, we have encountered vasoconstrictor fibres that are active almost exclusively during periods of transient sympathoexcitation, while being virtually silent at rest. This suggests that recruitment of previously inactive vasoconstrictor fibres, the second main alternative for increasing vasoconstrictor output, contributes to transient sympathoexcitatory responses in these patients.... [ABSTRACT FROM AUTHOR]