Lambert, Edward H.

SUMMARY A case of the autoimmune form of myasthenia gravis and a case of what is probably a congenital form of myasthenia gravis were diagnosed in 2 unrelated cats. Neuromuscular weakness exacerbated by exercise was a prominent feature in both cats. Weakness was eliminated temporarily by administration of anticholinesterase drugs. Serum autoantibodies to acetylcholine receptors of skeletal muscle were present in the 1st cat and were not detected in the 2nd cat. A characteristic decrement in the amplitude of the compound muscle action potential during repetitive stimulation of the motor nerve was elicited in the 2nd cat. There was marked electromyographic improvement in response to anticholinesterase drugs. Electromyography was not performed in the 1st cat.

THE past decade has seen a number of the techniques of clinical neurophysiology come into common use in the diagnosis of neuromuscular disease. One of these is the measurement of conduction velocity of motor nerves. Conduction velocity of nerves was only of academic interest until 1948 when a simple method for making reliable measurements in man was described and proved useful as a test of nerve function. It is now a frequent subject of clinical investigation and in many laboratories measurement of conduction velocity has become a routine diagnostic procedure. A review and extension of this work by Dunn and his associates, published in this issue of Pediatrics, emphasizes the importance of such measurements to pediatrics wherein objective evidence of functional impairment of nerves is of particular importance because the clinical examination may be so unsatisfactory. Conduction velocity of peripheral nerves, measurable quickly and simply, should be standard practice in the study of neuromuscular disorders in infants and children.

Measurements of conduction velocity of the motor fibers of the ulnar nerve in the segment between the upper part of the arm and the wrist were made in 6 premature infants, 42 full-term newborn infants and 98 children up through the age of 14 years. In premature infants, 21 – 40 days before full term, values ranged from 18 to 22 meters per second with a mean of 21. Full-term newborn infants had velocities that ranged from 21 to 33 m.p.s., with a mean of 28. The values in the newborn were about one-half those of normal young adults, which range from 47 to 73 m.p.s. (mean, 60). By the age of 3 years almost all values were in the lower part of the adult range and, at 5 years, the velocities were not significantly different from those of the adult. These observations are in harmony with information about the diameter of nerve fibers during growth in man. The H-reflex could be elicited by stimulation of the ulnar nerve in almost every newborn infant. By the age of 1 year and thereafter it could rarely be elicited. Between the elbow and wrist, afferent fibers subserving this reflex conducted with a mean velocity of 30 m.p.s. Data on the action potential of the hypothenar muscles, residual latency of conduction in the ulnar nerve, latency of the H-reflex and conduction in the peroneal nerve in infants and children are compared with those on adults. Submitted on July 15, 1959

Recordings of pressure and electric potentials from Biebl loops of the duodenum of trained dogs were used to quantitate and to determine relationships among basic electric rhythm (BER), irregular bursts of spike potentials, and motor action of the duodenum. After control periods, morphine was used to stimulate rhythmic motor activity. The omnipresence of a stable, longitudinally propagated BER was demonstrated, each phase of which was detected simultaneously by electrodes arranged radially in the wall of the gut. Spike potentials were recorded whenever contraction of the gut wall was detected. The spikes occurred during a limited segment of the BER. Their number and amplitude were directly related to the strength of the contractions. Under control conditions, duodenal contractions associated with the spike potentials produced type I waves in the pressure record. Neither the spike potentials nor the type I contractions were conducted more than a few centimeters. With morphine only the latter portion of the BER showed minor changes. Incidence of spike potentials and contractions was increased. Occasionally morphine induced motor spasms, accompanied by a prolonged series of spike-like potentials and disruption of the BER.

In preparation for a study of the electric activity in the wall of the gastroduodenal junction in unanesthetized trained dogs, the pyloric portion of the stomach (antrum), the pylorus, and the first portion of the duodenum were exteriorized surgically. When the animals were fully recovered, needle electrodes were inserted into the wall of the bowel for the detection of electric activity. The pylorus was found to act as an "electric insulator" between the stomach and the duodenum. The basic electric rhythm (BER) and the fast or spike activity detected in both the pyloric canal and the duodenal bulb became attenuated in the pylorus and usually disappeared in it. The BER of the antrum had a mean frequency of 4.4 cycle/min and spike potentials sometimes were associated with it. The frequency of the BER in the duodenal bulb was the same as in the duodenum but its voltage was less and its form more irregular. Spike potentials in the bulb occurred during a greater portion of the BER and had a greater tendency to distort the BER than in the more distal duodenum.

Action potentials of single vagal afferent nerve fibers from slowly adapting pulmonary stretch receptors, transpulmonary pressure and rate of air flow were recorded in anesthetized cats with open thoraxes during varied volumes and rates of inflation and deflation of the lungs. Both discharge frequency and total transpulmonary pressure varied with lung volume and also with its rate and sign of change. Effects of acceleration of volume on discharge frequency were not observed. The receptors provide signals related to the work of breathing.