Studies of Neuromuscular Function in the Newborn: 1. A Comparison of Myoneural Function in the Full Term and the Premature Infant

Abstract

The evoked surface muscle action potential (MAP) of seventeen newborn infants ranging between 34 and 42 weeks gestational age was studied by a variation of the repetitive stimulation technique of HARVEY and MASLAND. Those infants of less than 38 weeks gestational age at the time of testing were designated as premature. The subjects were stimulated for 15 seconds at rates of 1, 2, 5, 10, 20 and 50 impulses per second (IPS). The voltages of the MAP's were measured before, during, and after the series of impulses. There was no significant change in MAP observed during or after 1 and 2 IPS. At 5 and 10 IPS, 5 and 8 infants respectively, showed at least a 10% facilitation during the series. At 20 IPS, 12 of 17 of the infants showed a decrement during the stimulation. Only the prematures showed post-tetanic exhaustion ranging from 5 to 35 seconds. This finding clearly demarcated the prematures from their more mature counterparts. At 50 IPS, all of the infants showed a decrement during the series of impulses. In general, the prematures declined more than the more mature infants. After the 50 IPS series, almost all of the subjects showed post-tetanic exhaustion ranging up to 10 minutes. It is concluded that newborn infants have less neuromuscular reserve than do adults. Prematures, in turn, have even less reserve than do their more mature counterparts. Some practical applications for the use of the techniques and standards evolved are discussed.

Keyword

Muscle Action Potential (MAP) - Repetitive Stimulation - Impulses Per Second (IPS) - Facilitation - Decrement - Post-Tetanic Exhaustion