Direct measurement of human sympathetic nerve conduction velocity

We evaluated a method for direct measurement of conduction velocity (CV) in sympathetic nerves in humans using a double-recording method of skin sympathetic nerve activity (SSNA) by microneurography. SSNA in the tibial nerve was recorded simultaneously at proximal and distal sites in the popliteal fossa (short-distance study) or at the popliteal fossa and ankle (long-distance study). In both studies, CVs were determined by dividing the interelectrode distance on the skin by the difference in conduction time between the rising-phases (rising-phase analysis) or peaks of the integrated bursts (peak-to-peak analysis). The measurement using long distance and peak-to-peak analysis had the highest accuracy; it is an orthodromic conduction measurement, is unrelated to eliciting stimulus, has high temporal resolution, and is not affected by the effector organ conditions. The average CV of resting SSNA was 0.93 +/- 0.09 m/s.     

Sex difference in brain nerve conduction velocity in normal humans

Nerve conduction velocity (NCV), the speed at which impulses travel along nerves, has been extensively determined in human peripheral nerves because of its clinical utility. In contrast, almost no studies have been made of human brain NCV. We determined brain NCVs in the visual nerve pathway for 185 male and 200 female university students ages 18-25 years. In each of three independent test conditions, we found that the mean NCV of male students is about 4% faster than in females (P < or = 0.0001 for each condition). These male students also have a shorter reaction time in each of seven different RT tests than do females, even though, on the null hypothesis of equal NCVs, we would expect males to have longer RT times because of their greater physical size. Four of these comparisons are significant at or below the 0.001 level. These males also increase their NCVs with increasing age, in contrast to females. These sex differences in NCV parallel reported sex differences in age changes in white matter in the brain. These age changes may largely explain these NCV differences.     

Axotomy increases the conduction velocity of C-cells in bullfrog sympathetic ganglia

Axotomy produced an increase in the spike width and a decrease in amplitude of the afterhyperpolarization which followed the action potential in C-cells of bullfrog sympathetic ganglia. Although no change in B-cell conduction velocity was noted, C-cell conduction velocity increased significantly and approached that of B-cells. This change may reflect a process of dedifferentiation prior to the initiation of regrowth following axotomy.     

Estimation of conduction velocity of A delta fibers in humans.

Conduction velocity of A delta fibers of the human peripheral nerves was measured by using pain-related somatosensory evoked potentials following CO2 laser stimulation. It was found to be approximately 9 m/s in the forearm as well as in the lower leg. Because conventional conduction study using electric stimulation reflects only functions of large myelinated fibers related to deep proprioceptive and tactile sensations, the present noninvasive and simple, novel method is the only laboratory examination currently available to investigate physiological functions of the small diameter fibers mediating pain-temperature sensations.     

Measurement of muscle fiber conduction velocity in humans: techniques and applications

Different methods of measuring human muscle fiber conduction velocity (MFCV) are outlined. A major division can be made between invasive (needle) and noninvasive [surface electromyographic (EMG)] recording techniques. The benefits and limitations associated with the different approaches are discussed. The conduction velocity of individual muscle fibers are measurable with needle recordings on routine EMG apparatus. Velocities measured with electrical stimulation of single fibers or bundle of fibers are in general lower than recordings made during voluntary contraction. With surface EMG, an average estimate of the MFCV from many fibers and motor units can be determined with computerized data analyses--both frequency and time domain approaches. The cross-correlation method is widely used to calculate the time lag between two EMGs recorded along the muscle. Using the surface EMG-based methods, MFCV can be calculated at all contraction levels. Thus, the change in sarcolemmal function during local muscle fatigue can be assessed. Physiological factors influencing the MFCV and the utility of the MFCV estimation in clinical practice are discussed. Compared to nerve conduction velocity studies, the clinical interest in MFCV has been limited.     

Estimation of conduction velocity in bulbospinal excitatory pathways to sympathetic outflows in cat spinal cord

Experiments were performed on cats to measure the conduction velocity of the bulbospinal sympatho-excitatory axons. The lateral white matter of the cervical spinal cord and regions of the medulla were systematically explored for sympatho-excitatory points whilst recording from two sympathetic preganglionic outflows simultaneously. These were chosen a suitable distance apart to give a clear difference in latency to enable precise calculation of axonal conduction velocity between the two outflows. In addition, in a few cases conduction velocity was also measured by determining the latency shift of evoked responses, resulting from moving the stimulating electrode a known distance closer to the recording site. Conduction velocities of sympatho-excitatory axons in the spinal cord determined by these two procedures lay in the range 1.6-7.9 m/s.     

Estimation of the conduction velocity of sympathetic sudomotor C fibres in healthy subjects: study of sympathetic skin reflex.

The aim of this study was to establish a simple method for estimating the conduction velocity (CV) of post-ganglionic sympathetic sudomotor C fibres (SSFCV) in the upper and lower limbs by simultaneously measuring the sympathetic skin reflex (SSR) in two distant sites. Fifty healthy volunteers were studied. SSRs were recorded with standard surface electrodes applied to both proximal (axilla and crural line) and distal sites for each limb (hand and foot). The CV of the efferent branch of the SSR was calculated by dividing the difference in the latencies of the response from two recording sites by the distance between the sites (axilla-hand for upper limb; crural line-foot for lower limb). Day-to-day reproducibility and intra-individual variability of the SSFCV were calculated. For the upper limbs, the SSFCV in the axilla-hand tract was 2.0+/-0.3 m/sec (range 1.6-2.4 m/sec). For the lower limb, the SSFCV in the crural line-foot tract was 1.4+/-0.4 m/sec (range 1.2-1.6 m/sec). Mean intra-individual variability of the SSFCV for the upper and lower limbs was 0.11 and 0.09, respectively. The coefficient of variation of the SSFCV for the upper and lower limbs was 5.1% and 5.4%, respectively. Our data show that this simple and non-invasive method can reliably be used to measure the CV of the sympathetic sudomotor fibres, in suitable temperature conditions, and may be useful when investigating the physiological functions of peripheral nerves in patients with peripheral neuropathies.     

Orthostatic tolerance, cerebral oxygenation, and blood velocity in humans with sympathetic failure

BACKGROUND AND PURPOSE: Patients with orthostatic hypotension due to sympathetic failure become symptomatic when standing, although their capability to maintain cerebral blood flow is reported to be preserved. We tested the hypothesis that in patients with sympathetic failure, orthostatic symptoms reflect reduced cerebral perfusion with insufficient oxygen supply. METHODS: This study addressed the relationship between orthostatic tolerance, mean cerebral artery blood velocity (V(mean), determined by transcranial Doppler ultrasonography), oxygenation (oxyhemoglobin [O(2)Hb], determined by near-infrared spectroscopy), and mean arterial pressure at brain level (MAP(MCA), determined by finger arterial pressure monitoring [Finapres]) in 9 patients (aged 37 to 70 years; 4 women) and their age- and sex-matched controls during 5 minutes of standing. RESULTS: Supine MAP(MCA) (108+/-14 versus 86+/-14 mm Hg) and V(mean) (84+/-21 versus 62+/-13 cm. s(-1)) were higher in the patients. After 5 minutes of standing, MAP(MCA) was lower in the patients (31+/-14 versus 72+/-14 mm Hg), as was V(mean) (51+/-8 versus 59+/-9 cm. s(-1)), with a larger reduction in O(2)Hb (-11. 6+/-4 versus -6.7+/-4.5 micromol. L(-1)). Four patients terminated standing after 1 to 3.5 minutes. In these symptomatic patients, the orthostatic fall in V(mean) was greater (45+/-6 versus 64+/-10 cm. s(-1)), and the orthostatic decrease in O(2)Hb (-12.0+/-3.3 versus -7.6+/-3.9 micromol. L(-1)) tended to be larger. The reduction in MAP(MCA) was larger after 10 seconds of standing, and MAP(MCA) was lower after 1 minute (25+/-8 versus 40+/-6 mm Hg). CONCLUSIONS: In patients with sympathetic failure, the orthostatic reduction in cerebral blood velocity and oxygenation is larger. Patients who become symptomatic within 5 minutes of standing are characterized by a pronounced orthostatic fall in blood pressure, cerebral blood velocity, and oxygenation manifest within the first 10 seconds of standing.     

The conduction velocity of the descending spinal pathway to the renal sympathetic nerve in the cat

The conduction velocity of the descending spinal excitatory pathway to the renal sympathetic nerve was measured in five chloralose-anaesthetised, spinal cats (C1 transection). Electrical stimuli were delivered to the dorsolateral funiculus at three levels between segments C3 and T6, and responses recorded from the ipsilateral renal nerve. Spinal conduction velocity was calculated as 4.4 +/- 0.4 m/s (mean +/- SEM), from the latency difference of renal nerve volleys to stimulation at different cord levels. A contralateral pathway to the renal nerve was identified: this also ran in the dorsolateral funiculus, and crossed below segment T5. It conducted at 4.1 and 7.9 m/s (two cats). Renal preganglionic conduction velocity (greater splanchnic nerve) was 4.1 and 5.0 m/s (two cats). As the renal sympathetic nerve is functionally homogeneous, these conduction velocity measurements are of a functionally-defined sympathoexcitatory pathway.     

A simple method for estimating conduction velocity of the spinothalamic tract in healthy humans.

OBJECTIVES: The object of this study was to establish a method for estimating the conduction velocity (CV) of the spinothalamic tract (STT) in relation to clinical application. METHODS: The CV of the STT was estimated by an indirect method based on that reported by Kakigi and Shibasaki in 1991 (Kakigi R, Shibasaki H. Electroenceph clin Neurophysiol 80 (1991) 39). Laser-evoked potentials (LEP) were measured in 8 subjects following hand (LEPH) and foot (LEPF) laser stimulation. The conduction times recorded at the scalp (P340, P400 and N150 potentials) were considered as the summation of peripheral and central components. The peripheral conduction times were calculated by measuring the latency of the electrical cutaneous silent period (from the same stimulus site of LEPs), corrected for F- and M-wave latency values. RESULTS: The CV of the STT ranged between 8.3 and 11.01 m/s and its mean value was found to be approximately 9.87+/-1.24 m/s. The CV of the STT obtained by the N150 latencies overlapped that obtained by the P340/P400 latencies. CONCLUSIONS: Our data suggest that our method appears appropriate and useful for practical clinical purposes, furnishing an additional tool for investigating the physiological function of small-fiber pathways.     

Spinal motor preparation in humans

This study examined the influence of preparatory 'set' on the modulation of monosynaptic reflex excitability immediately prior to the initiation of a voluntary movement. Six subjects performed 3 tasks which varied the level of preparatory set according to the availability of temporal and event anticipation. A choice reaction-time task restricted both temporal and event anticipation; a simple reaction-time task restricted temporal anticipation while allowing event anticipation; and a coincidence-timing task permitted both temporal and event anticipation. The response for all tasks performed was ankle plantarflexion. The excitability of the monosynaptic reflex was examined by eliciting H reflexes to the right soleus muscle at 50 msec intervals over the final 400 msec preceding the initiation of voluntary muscle contraction. All 3 tasks showed an initial depression and later increase in the H reflex amplitude. The onset of reflex facilitation was the same for the choice and simple reaction-time tasks, commencing 74 msec prior to voluntary muscle contraction. However, the coincidence-timing task showed an earlier onset of reflex facilitation. Reflex facilitation preceded voluntary muscle contraction by 130-337 msec during the performance of this task. Thus, it appears that the modulation of monosynaptic reflex excitability is not time-locked to the onset of voluntary muscle contraction, but rather is controlled by the preparatory set of the subject. The modulation of reflex excitability represents a separate, though necessary, stage in the organization and initiation of voluntary movement.     

Neural conduction velocity in patients on hemodialysis

Fourteen patients with chronic glomerulonephritis and with Alport's syndrome were treated. Haemodialysis was performed 2--3 times weekly. The duration of treatment was from 10 months to 9 years. Serum levels of electrolytes, urea and creatinine were determined, the neurological condition was examined and nerve conduction velocity was measured in the lower and upper extremities. The determinations were done before and after haemodialysis. Subclinical manifestations of polyneuropathy were demonstrated with reduced motor-nerve conduction velocity in the lower extremities. A direct effect of single haemodialysis was far from uniform: usually the conduction velocity increased after haemodialysis and in some cases it decreased. There was no correlation between the serum levels of electrolytes, urea and creatinine and motor-nerve conduction velocity.     

Nerve conduction velocity in juvenile rheumatoid arthritis

Motor and sensory nerve conduction velocities (NCV) were recorded in several nerves of a total of 99 patients with juvenile rheumatoid arthritis (JRA), and the results were compared to those obtained for two reference groups, one consisting of healthy children and the other of 30 children with different articular manifestations. The JRA and the affected reference group were not found to differ significantly from each other. NCV values were systematically slightly higher and the distal median nerve latencies slightly shorter in the patients with JRA than in the healthy reference group. Several measurement values differed from each other significantly. Some patients with JRA showed slightly decreased NCVs in individual nerves, but manifest mononeuropathy was not found. The results show that complications of peripheral nervous system origin do not typically occur in association with JRA.     

Axonal conduction velocity and perikaryal size

The recent identification of brisk-transient units with alpha cells in the cat's retina provided a direct opportunity to test the widely held belief that larger cells give rise to larger axons, and smaller to smaller. Alpha-cell perikarya increase substantially in size over the first 2 mm from the center of the area centralis. In one cat a map was obtained of the receptivefield centers of all brisk-transient units in the region of the area centralis together with their antidromic latencies to optic tract stimulation. The map was then brought into approximate register with a map of all the alpha cells of the region. The correspondence was controlled by the placement and subsequent identification of electrolytic lesions. Thus perikaryal size could be rather directly compared with axonal conduction latency. The expected relation was verified under singularly uniform circumstances.