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B Gunnar Wallin

Publications and source records attributed to B Gunnar Wallin.

14 recordsLinked to original sources
PubMed2006

Regulation of sympathetic nerve traffic to skeletal muscle in resting humans.

An overview is given of microneurographic studies of resting vasoconstrictor traffic in human muscle nerves (muscle sympathetic nerve activity = MSNA). In multiunit recordings, the activity consists of synchronized bursts of vasoconstrictor impulses, the outflow of which is under potent arterial baroreflex control. In agreement with this, the bursts always display cardiac rhythmicity and occur during temporary reductions of blood pressure. Burst occurrence shows a close inverse correlation to variations of diastolic blood pressure whereas the correlation to the strength of the bursts is weak or absent, suggesting that the mechanisms controlling the two parameters are not identical. These dynamic characteristics are similar in all subjects despite large, reproducible, interindividual differences in number of bursts. Such interindividual differences probably have a genetic origin, and since discharge frequencies in single vasoconstrictor fibers are similar in subjects with few and many bursts, the differences in multiunit activity are likely to be due to a higher number of active fibers in subjects with many bursts. The interindividual differences in multiunit activity are not associated with differences in resting blood pressure levels. Recent studies have revealed (a) an inverse relationship between resting levels of cardiac output and MSNA and (b) evidence of reduced vascular responsiveness to noradrenaline in subject with many sympathetic bursts at rest. These findings suggest that the vasoconstriction induced by the sympathetic impulses is balanced or reduced by these factors, which thereby contribute to the poor relationship between the mean number of sympathetic bursts and the blood pressure level.

Blood Pressure↗
PubMed2005

Normal nerve conduction velocity and vibrotactile perception thresholds in computer users.

OBJECTIVES: A literature report described significantly raised vibration threshold within the territory of the median nerve in a group of office workers and concluded that the results indicated a change in the function of large sensory fibres. The aim of the present cross-sectional study was to compare vibrotactile perception thresholds and nerve conduction measurements in the upper extremity between female computer users (secretaries) and female non-users (nurses). METHODS: Eighty-two secretaries, aged 25-65 (median 44) years and 35 nurses, aged 24-57 (median 46) years went through nerve conduction measurements on the dominant hand and also a vibration threshold test with readings over the hand at five sites which tested cutaneous innervation of the median, ulnar, and radial nerves. RESULTS: There was no significant difference in any parameter of the nerve conduction testing and there was no significant difference in any parameter of the vibration threshold test between secretaries and nurses. The numerical differences between groups were small and in both directions and thus do not indicate a power problem. CONCLUSIONS: We saw no signs of early neural deficits of large sensory fibres in subjects who intensively use computer keyboard equipment.

Adult↗
PubMed2005

Bicycle ergometer test to obtain adequate skin temperature when measuring nerve conduction velocity.

OBJECTIVE: To achieve optimal diagnostic accuracy, measurements of nerve conduction velocity require standardised tissue temperatures. To warm an extremity to a desired temperature that remains constant during the measurement may be difficult, especially in subjects with low finger temperatures. The aim of this study was to investigate if a submaximal bicycle ergometer test before the examination would be a useful method of obtaining high and stable finger temperatures during nerve conduction studies in the hand. METHODS: 114 women aged 25-65 (median 44) performed a bicycle ergometer test on an electrically braked bicycle ergometer (Siemens-Elema) before they underwent a nerve conduction test. RESULTS: Before cycling, the mean finger temperature was 28.1 degrees C (range 20.5-35.4 degrees C) and 15 min after the test 35.1 degrees C (range 30.3-36.9 degrees C). The levels remained almost constant throughout the nerve conduction examination, which had a duration of approximately 25 min. CONCLUSIONS: A bicycle ergometer test proved to be a simple and effective method of raising hand temperature.

Adult↗
PubMed2004

Evaluation of objective methods to diagnose palmar hyperhidrosis and monitor effects of botulinum toxin treatment.

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.

Adolescent↗
PubMed2003

Resting discharge of human muscle spindles is not modulated by increases in sympathetic drive.

There is evidence in experimental animals that, in addition to receiving fusimotor drive, muscle spindles are subject to modulation by the sympathetic nervous system. We examined the validity of this idea in human subjects by recording from muscle spindles in the relaxed ankle and toe extensor muscles during a strong and sustained physiological activation of muscle sympathetic outflow. Unitary recordings were made from 20 primary and 17 secondary muscle spindle afferents via a tungsten microelectrode inserted percutaneously into the peroneal nerve in 10 awake, healthy subjects seated with the legs supported in the extended position. ECG, blood pressure, respiration and calf circumference were also recorded. The majority of the muscle spindles were spontaneously active at rest; a background discharge was induced in four silent spindles by vibrating the tendon. A sustained increase in muscle vasoconstrictor activity, an increase in calf volume and a fall in pulse pressure were produced by subjects performing a 30-40 s maximal inspiratory breath-hold. Despite this strong increase in muscle sympathetic outflow no significant changes occurred in the discharge of either primary or secondary muscle spindle afferents, measured as a change in mean frequency and variability over sequential 5 s epochs and compared with the preceding period of rest. Strong chemoreceptor-driven sympathetic bursts during sustained expiratory breath-holds also failed to modulate the firing of 14 spindle endings. We conclude that a sustained, physiological increase in muscle sympathetic activity causes no detectable change in muscle spindle firing, lending no support to the concept that the sympathetic nervous system can influence the sensitivity of human muscle spindles directly.

Adolescent↗
PubMed2003

Arousal increases baroreflex inhibition of muscle sympathetic activity.

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 the 12 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 to stress.

Adult↗
PubMed2003

Pathological sympathoexcitation: how is it achieved?

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. Although it seems reasonable to assume that recruitment may also contribute to the resting level of MSNA in CHF and OSAS, this issue is difficult to resolve in microneurographic studies. CONCLUSION: In conclusion, pathological sympathoexcitation appears to depend on both recruitment and increased firing frequency. A shift towards multiple within-burst firing, at rest or in response to transient stimuli, may constitute a risk factor per se as it entails neural volleys with high instantaneous firing frequencies and consequently higher release of neurotransmitters.

Action Potentials↗
PubMed2003

Remote sessions and frequency analysis for improved insight into cerebral function during pediatric and neonatal intensive care.

A project involving recording and analysing EEG together with cardiovascular signals and temperature has been initiated. The aim of this project is to establish difficulties and possibilities involved with implementing a system for remote sessions and analysing EEG in correlation with other physiological signals. One objective is to find indicators of cerebral function during postasphyxia neonatal intensive care and pediatric cardiopulmonary bypass surgery with hypothermia. Remote sessions for joint interpretation have been carried out between pediatricians and clinical neurophysiologists, and EEG has been analyzed using frequency analyzing tools. One result is the discovery of reversible spectral changes coinciding with blood pressure falls, which may indicate loss of autoregulation function. This finding is one outcome from initial use of a system, developed during the project to facilitate communication about, and analysis of the recorded signals. Thus, already from a limited number of remote sessions and the use of basic signal processing techniques, important results have been achieved and better insight has been gained of how cerebral function is affected by cardiopulmonary bypass surgery. In this paper, we present our experiences from introducing a system for remote consultations, and evaluate the use for such a system in the current applications.

Algorithms↗
PubMed2002

Inhibition of human muscle sympathetic activity by sensory stimulation.

Surprising sensory stimuli causing arousal are known to evoke short-lasting activation of human sympathetic activity in skin but not in muscle nerves; anecdotal observations suggest that there may even be an inhibition of muscle sympathetic nerve activity (MSNA). To test this hypothesis we recorded multiunit MSNA in the peroneal nerve in 19 subjects aged 19-71 years, while sensory stimuli, consisting of either an electrical skin stimulus to a finger or a visual flash, were delivered repeatedly with intervals of approximately 20 s. The stimuli were given either 200 or 400 ms after the R wave of the electrocardiogram. Dummy stimuli, consisting of trigger pulses without sensory stimulation served as controls. Electrical skin resistance reductions were monitored from the palm of a hand as electrodermal signs of arousal-induced cutaneous sympathetic activity. On a group basis both types of sensory stimuli attenuated the amplitude of one or two bursts of MSNA, 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. Skin resistance responses were evoked in all subjects. Some subjects responded to one, others to both stimulus modalities, and electrical stimuli were more effective than visual stimuli in causing MSNA inhibition as well as skin resistance reduction. On the other hand, electrodermal signs of arousal were equally common in subjects with and without inhibitory responses. We suggest that the MSNA inhibition evoked by sensory stimuli is an arousal effect which varies markedly between individuals.

Adult↗
PubMed2002

Interindividual differences in sympathetic and effector responses to arousal in humans.

Surprising sensory stimuli have been found to attenuate one or two sympathetic discharges in human muscle nerves of some, but not all subjects, an effect suggested to be due to arousal. The aims of the present study were: (1) to provide evidence for or against an arousal mechanism by searching for evidence of habituation, and (2) to investigate if the presence or absence of inhibitory response is reproducible. To this end we recorded peroneal muscle sympathetic nerve activity (MSNA), electrocardiogram (ECG), finger blood pressure and changes of skin electrical resistance in 17 awake healthy subjects, while sensory stimuli consisting of five electrical pulses were delivered to a finger. The electrical pulses were triggered on five consecutive R waves of the ECG after a delay of 200 ms. Dummy stimuli, consisting of five trigger pulses without electrical pulses were used as controls, and the interval between two successive stimuli (real or dummy) was 30 s. On a group basis, the stimuli attenuated two initial and one late MSNA bursts. On an individual basis, significant attenuation of one or two initial bursts occurred in eight subjects, whereas in nine subjects there was no significant inhibition. In nine subjects the experiments were repeated once and in three subjects they were repeated twice. The effects on MSNA were reproducible in 11 of the12 subjects. In the group of subjects without significant MSNA inhibition the stimuli induced a small, transient increase in mean blood pressure, which was not present in the group with significant MSNA inhibition. Heart rate did not change in either group. In conclusion, the inhibitory effect on MSNA of five repeated electrical pulses to a finger is largely similar to that previously shown for one pulse, i.e. there is rapid habituation of the response, compatible with an arousal-induced effect. The inhibitory responsiveness shows marked interindividual differences, which are reproducible over several months and associated with different effects on blood pressure.

Adult↗
PubMed2002

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.

Adult↗
PubMed2002

Firing properties of single postganglionic sympathetic neurones recorded in awake human subjects.

For over three decades, the technique of microneurography has allowed us to record sympathetic neural outflow directly from postganglionic axons in awake human subjects. But because sympathetic axons are clustered within a nerve fascicle, such recordings have been limited to the analysis of multi-unit neural activity. To improve the information content of intraneural recordings, we developed the single-unit approach, in which focal recordings can be made from a single C-fibre via a high-impedance tungsten microelectrode. In this review, we describe our methodology for analyzing unitary sympathetic activity and discuss the similarities in the firing properties of individual muscle vasoconstrictor, cutaneous vasoconstrictor and sudomotor neurones.

Action Potentials↗