The effect of wrist size on the orthodromic median sensory nerve action potential

Abstract

A number of studies have demonstrated that the amplitude of sensory nerve action potential (SNAP) is higher in females than in males. 12224,6,10312 The mechanism for this is not clearly e~tab1ished.l~ Bolton and Carter' suggested that finger circumference affected the amplitude of antidromic SNAPs but found no relationship between wrist circumference and the amplitude of orthodromic median and ulnar SNAPs. SNAP amplitude may be expected to relate mainly to the distance between the nerve and the recording electrodes-a known property of a charged body in a conducting medium. It is therefore conceivable that gender differences in wrist size may partly explain the gender difference in SNAP amplitude. We therefore studied the effect of physical size of the wrist and finger on the amplitude of the orthodromic median SNAP in a group of normal male and female volunteers. METHODSOrthodromic median SNAPs were recorded from the right wrist after stimulating digit 2 of 37 female volunteers (mean age = 29.3, SD = 6.77, range 19-42 years) and 25 male volunteers (mean age = 31.7, SD = 6.50, range 22-43 years). Palm temperature, conduction velocity ( C V ) , and thickness, width, and circumference of the wrist and the volume and length of the index finger were also measured from the tested arm. The multiple physical measures of wrist size were unified by modeling the wrist cross-section area (CSA) as an ellipse (Fig.

Antidromic vs orthodromic sensory median nerve conduction studies

“…Obviously, other types of electrodes would yield equally good results provided they are consistently used in any study requiring comparison among subjects. The orthodromic SNAP is of smaller amplitude than the antidromic one and its amplitude but not its latency is affected by wrist size (Lim et al, 1995). However, this is apparently also the case with antidromic recording, where amplitude of the finger SNAP was found to be inversely proportional to the circumference of the finger (Bolton and Carter, 1980; as well as to the thickness of the wrist Chira-Adisai et al, 1999).…”