Deep peroneal motor nerve conduction velocity distribution and correlation between nerve conduction groups and the number of innervated muscle fibers

In this study, the distribution of peroneal-nerve conduction velocity was studied in 17 normal subjects, using the collision method. Paired supramaximal stimuli with predetermined interstimulus intervals (ISI) were applied at distal and proximal points of peroneal nerve and the resultant compound muscle action potentials (CMAPs) were recorded. The change in CMAP amplitudes and areas with ISI were deduced, and the relative number of fibers corresponding to each conduction velocity group (CVG) were computed. Conduction velocities of the peroneal motor nerve innervating the Extensor Digitorum Brevis (EDB) muscle were found to be in the range of 28-52 m/s and CVG innervating the greatest number appears to be in 40-48 m/s range, which consists of 70% of all fibers. These results show that, compared with the median motor nerve, deep peroneal motor nerve that innervates the EDB muscle consist of slow fibers.     

Correlation of motor nerve conduction velocity and number of innervated muscle fibers

Distal and proximal motor (M) responses were recorded from the "Abductor Pollicis Brevis" (APB) muscle by using the collision method; median motor nerve was stimulated at distal (elbow) and proximal (wrist) regions in a concurrent manner. The delay between two stimuli (ISI: Inter-stimulus Interval), beginning at 9 ms, was decreased by 0.1 ms steps, until the proximal potential completely disappeared. Areas of M responses recorded for each ISI were calculated. Because the area difference between two subsequent ISIs is proportional to the number of muscle fibers innervated by the conduction velocity group at that interval, the relative numbers of muscle fibers for each velocity group were calculated. The results show that the motor nerve conduction velocities belonging to the innervating APB muscle vary between 38 m/s and 57 m/s; the conduction velocity of the group innervating the greatest number of muscle nerves was found to be 55-57 m/s, which comprised 10% of all fibers.     

Videodensitometric ejection fractions from intravenous digital subtraction left ventriculograms: correlation with conventional direct contrast and radionuclide ventriculography

Forty-three patients who had undergone direct-contrast ventriculography were submitted to intravenous digital subtraction ventriculography and first-pass radionuclide ventriculography to compare the left ventricular ejection fractions obtained by each method. Ejection fractions were calculated by the area-length method from the direct contrast ventriculograms, by both area-length and videodensitometric methods from the digital subtraction ventriculograms, and by count densitometry from the radionuclide ventriculograms. Satisfactory correlations were found between values obtained by the late mask resubtracted videodensitometric method and the radionuclide method (r = 0.85) and by the digital ventriculographic area length method and direct-contrast method (r = 0.88). Videodensitometric methods may be an alternative way to estimate left ventricular ejection fractions accurately without reliance on geometric assumptions about the shape of the left ventricular cavity.     

The association between preterm newborn hypotension and hypoxemia and outcome during the first year

Ninety-eight newborn infants, less than 34 weeks at birth, were studied to examine the relationship between newborn hypotension and hypoxemia and brain damage. Heart rate, blood pressure and oxygen tension were recorded continuously during the 96 h following delivery. Outcome measures included neuropathology in children who died, and motor and cognitive development at one year corrected age in children who survived. There were 22 children with a minor and 27 with a major abnormal outcome. There was a relationship between newborn hypotension, newborn hypoxemia and low birth weight, and a major abnormal outcome. The probability of a major abnormal outcome increased from 8% in newborns with no hypotension or hypoxemia, to 53% in children with both hypotension and hypoxemia. These findings support the contention that combinations of sustained newborn hypotension and hypoxemia are important factors in the development of brain damage, accounting for a major abnormal outcome.     

The effect of bupivacaine on compound action potential parameters of sciatic nerve fibers

The aim of this study was to document the effects of the local anesthetic agent bupivacaine on individual fibers of peripheral nerve. To accomplish this objective, compound action potentials (CAPs) were recorded from isolated frog sciatic nerves treated with bupivacaine for seven individual concentration levels. Numerical and fast Fourier transform (FFT) analysis were performed on these recordings. The areas, latency periods, maximum and minimum derivatives, and power spectrums of the CAPs were computed. The results show that the area and the absolute values of maximum and minimum derivatives decrease linearly as bupivacaine concentration increases. The power spectrum of the CAPs, which resides in the 0-1000 Hz interval, initially shifts to higher frequencies then returns to lower frequency region again with increasing bupivacaine concentration. Due to this result, it is thought that bupivacaine inhibits nerve fibers in a dose-dependent manner. It primarily affects the fibers having the least myelin sheets (motor fibers), then it begins to depress the fast conducting (neurosensorial) fibers as the bupivacaine concentration increases, and finally blocks the unmyelinated C-fibers.