Sten Skoglund

POST-TETANIC POTENTIATION OF H-REFLEXES IN HUMAN INFANTS.

Abstract H-reflexes occurring in various muscles and their reaction to tetanic stimulation, previously studied in adults, have been investigated in newborn infants. It was found that contrary to adults most muscles in the infants have easily elicitable H-reflexes which show post-tetanic potentiation shortly after birth. It is concluded that a combination of such studies and detemination of conduction velocities in motor and sensory nerves might allow an assessment of neural maturation. The results are correlated with similar investigations carried out in kittens.

POSSIBLE FACTORS INFLUENCING THE DEMONSTRATION OF POST-TETANIC POTENTIATION OF THE H-REFLEX AS STUDIED IN THE CAT.

Abstract A study of possible factors influencing the demonstration of post-tetanic potentiation (PTP) of H-reflexes was performed in cats and kittens. Monosynaptic reflexes were elicited by surface stimulation of mixed nerves and recorded either by surface electrodes or silver pins in the muscles. The results were controlled by appropriate nerve sections and stimulation of bared nerve trunks and recording from peripheral nerves or roots. It was found that the sensory fibers have a lower threshold than the motor fibers, which explains why the H-reflex is obtained before th M-response. Tetanization of a peripheral nerve lead to changes in threshold which were not restricted to the region of stimulation when testing with submaximal stimulus strength. Since that has to be used to demonstrate H-reflexes, the M-response is reduced and accordingly the antidromic volley up the motor fibers. The H-reflex may then appear enhanced after a tetanization because it is counteracted by a smaller antidromic volley. These mechanisms can lead to the appearance of a “false” PTP. It is concluded that the only safe way to demonstrate a PTP of the H-reflex is to use test stimuli weak enough not to set up any M-response.

An Improved Method for Experimental Angiography

An improved method for experimental angiography is presented. It is based on a high concentration of contrast medium in the circulating blood giving a fairly constant visualisation of the cardiovascular system for some period of time. (1) One single dose of 5–10 ml/kg body weight of a solution of thorium dioxide (25% Thorotrast) given intravenously creates a blood concentration of contrast medium sufficient to visualise the heart, arteries, veins and the small branches for about 2 hours and for a longer time the liver, spleen and kidneys. (2) The blood concentration remains fairly constant from 30 minutes up to one hour as determined by densitometry and measurements of the radioactivity of thorium dioxide in blood samples taken at intervals after the injection of 10 ml/kg body weight in a cat. During this period the radiographs are in all probability strictly comparable. (3) The method presented is compared with the conventional one for angiography and found superior for experimental work on animals.