98 ELECTROMYOGRAPHY 109. Lin ZY, Chen JDZ, McCallum RW, Parolisi S, Shifflett J, 126. Dickens EJ, Hirst GD, Tomita T. Identification of rhythmi- Peura D. The prevalence of electrogastrogram abnormalities cally active cells in guinespig stomach. J Physiol (London) in patients with non-ulcer and H. pylori infection: results of H. 1999;514:515–531. pylori eradication. Dig Dis Sci 2001;46(4):739–745. 127. Ordog T, Ward SM, Sanders KM. Interstitial cells of Cajal 110. Stern RM, Koch KL, Leibowitz HW, Lindblad I, Shupert C, generate slow waves in the murine stomach. J Physiol 1999; Stewart WR. Tachygastria and motion sickness. Aviat 518:257–269. Space Environ Med 1985;56:1074–1077. 128. Hanani M, Freund HR. Interstitial cells of Cajal—their role 111. Koch KL, Tran TN, Stern RM, Bringaman S, et al.Gastric in pacing and signal transmission in digestive system. Acta myoelectrical activity in premature and term infants. J Physiol Scand 170;177–190. Gastrointest Motil 1993;5:41–47. 129. Lin ZY, Sarosiek I, Forster J, McCallum RW. Association 112. Koch KL, Bringaman S, Tran TN, Stern RM. Visceral between baseline parameters of the electrogastrogram and perceptions and gastric myoelectrical activity in healthy long-term symptom improvement in gastroparetic patients women and in patients with bulimia nervosa. Neurogastro- treated with gastric electrical stimulation. Neurogastroen- netrol Motil 1998;10:3–10. terol Motil 2003;15:345–346. 113. Hathaway DK, Abell T, Cardoso S, Heartwig MS, Gebely S, Gaber AO. Improvement in autonomic and gastric function Reading List following pancreas-kidney versus kidney-alone transplan- tation and the correlation with quality of life. Transplanta- Stern RM, Koch KL. Using electrogastrography to study motion tion 1994;57:816. sickness. In: Chen JDZ, McCallum RW, editors. Electrogastro- 114. Gaber AO, Hathaway DK, Abell T, Cardoso S, Heartwig MS, graphy: Principles and Applications. New York: Raven Press; Gebely S. Improved autonomic and gastric function in pan- 1994. p 199–218. creas-kidney vs. kidney-alone transplantation contributes to quality of life. Transplant Proc 1994;26:515. See also GASTROINTESTINAL HEMORRHAGE; GRAPHIC RECORDERS. 115. Cashion AK, Holmes SL, Hathaway DK, Gaber AO. Gastro- paresis following kidney/pancreas transplant. Clin Trans- plant 2004;18:306–311. 116. Levanon D, Chen JDZ. Electrogastrography: its role in managing gastric disorders. (Invited Review). J Pediatr ELECTROMAGNETIC FLOWMETER. See Gastroenterol Nutr 1998;27:431–443. FLOWMETERS, ELECTROMAGNETIC. 117. Chen JDZ, Co E, Liang J, Pan J, Sutphen J, Torres-Pinedo RB, Orr WC. Patterns of gastric myoelectrical activity in human subjects of different ages. Am J Physiol 1997;272: G1022–G1027. ELECTROMYOGRAPHY 118. Liang J, Co E, Zhang M, Pineda J, Chen JDZ. Development of gastric slow waves in preterm infants measured by elec- CARLO DE LUCA trogastrography. Am J Physiol (Gastrointest Liver Physiol) Boston University 1998;37:G503–G508. Boston, Massachusetts 119. Levy J, Harris J, Chen J, Sapoznikov D, Riley B, De La Nuez W, Khaskeberg A. Electrogastrographic norms in children: toward the development of standard methods, reproducible INTRODUCTION results, and reliable normative data. J Pediatr Gastroen- terol Nutr 2001;33(4):455–461. Electromyography is the discipline that deals with the 120. Cucchiara S, Riezzo G, Minella R, et al. Electrogastrography detection, analysis, and use of the electrical signal that in non-ulcer dyspepsia. Arch Disease Childhood 1992;67(5): emanates from contracting muscles. 613–617. This signal is referred to as the electromyographic 121. Ravelli AM, Ledermann SE, Bisset WM, Trompeter RS, (EMG) signal, a term that was more appropriate in the Barratt TM, Milla PJ. Gastric antral myoelectrical activity past than in the present. In days past, the only way to in children wit chronic renal failure. In: Chen JDZ, capture the signal for subsequent study was to obtain a McCallum RW, editors. Electrogastrography: Principles ‘‘graphic’’ representation. Today, of course, it is possible to and Applications. New York: Raven Press; 1994. p 411– 418. store the signal on magnetic tape, disks, and electronics 122. Devane SP, Ravelli AM, Bisset WM, Smith VV, Lake BD, components. Even more means will become available in the Milla PJ. Gastric antral dysrhythmias in children wit near future. This evolution has made the graphics aspect of chronic idiopathic intestinal pseudoobstruction. Gut 1992; the nomenclature a limited descriptor. Although a growing 33:1477–1481. number of practitioners choose to use the term ‘‘myoelectric 123. Forster J, Damjanov I, Lin ZY, Sarosiek I, Wetzel P, McCal- (ME) signal’’, the term ‘‘EMG’’ still commands dominant lum RW. Absence of the interstitial cells of Cajal in patients usage, especially in clinical environments. with gastroparesis and correlation with clinical findings. An example of the EMG signal can be seen in Fig. 1. J Gastrointest Sur 2005;9:102–108. Here the signal begins with a low amplitude, which when 124. Lin ZY, Chen JDZ. Advances in electrical stimulation of the expanded reveals the individual action potentials asso- gastrointestinal tract. Crit Rev Biomed Eng 2002;30(4–6): 419–457. ciated with the contractile activity of individual (or a small 125. Abell T, McCallum RW, Hocking M, Koch K, Abrahamssion group) of muscle fibers. As the force output of the muscle H, LeBlang I, Lindberg G, Konturek J, Nowak T, contraction increases, more muscle fivers are activated and Quigley EMM, Tougas G, Starkebaum W. Gastric electrical the firing rate of the fibers increases. Correspondingly, the stimulation for medically refractory gastroparesis. Gastro- amplitude of the signal increases taking on the appearance enterology 2003;125:421–428. and characteristics of a Gaussian distributed variable. ELECTROMYOGRAPHY 99 Guided by the work of Inman et al. (5), in the mid-1940s to the mid-1950s several investigations revealed a mono- tonic relationship between the amplitude of the EMG signal and the force and velocity of a muscle contraction. This significant finding had a considerable impact: It dra- matically popularized the use of electromyographic studies concerned with muscle function, motor control, and kine- siology. Kinesiological investigations received yet another impetus in the early 1960s with the introduction of wire electrodes. The properties of the wire electrode were dili- gently exploited by Basmajian and his associates during the next two decades. In the early 1960s, another dramatic evolution occurred in the field: myoelectric control of externally powered prostheses. During this period, engineers from several countries developed externally powered upper limb pros- theses that were made possible by the miniaturization of electronics components and the development of lighter, more compact batteries that could be carried by amputees. Figure 1. The EMG signal recorded with surface electrodes loca- Noteworthy among the developments of externally pow- ted on the skin above the first dorsal interosseous muscle in the ered prostheses was the work of the Yugoslavian engineer hand. The signal increases in amplitude as the force produced by the muscle increases. Tomovic and the Russian engineer Kobrinski, who in the late 1950s and early 1960s provided the first examples of such devices. The novice in this field may well ask, why study elec- In the following decade, a formal theoretical basis for tromyography? Why bother understanding the EMG sig- electromyography began to evolve. Up to this time, all nal? There are many and varied reasons for doing so. Even knowledge in the field had evolved from empirical and a superficial acquaintance with the scientific literature will often anecdotal observations. De Luca (6,7) described a uncover various current applications in fields such as mathematical model that explained many properties of the neurophysiology, kinesiology, motor control, psychology, time domain parameters of the EMG signal, and Lindstrom rehabilitation medicine, and biomedical engineering. (8) described a mathematical model that explained many Although the state of the art provides a sound and rich properties of the frequency domain parameters of the EMG complement of applications, it is the potential of future signal. With the introduction of analytical and simulation applications that generates genuine enthusiasm. techniques, new approaches to the processing of the EMG signal surfaced. Of particular importance was the work of HISTORICAL PERSPECTIVE Graupe and Cline (9), who employed the autoregressive moving average technique for extracting information from Electromyography had its earliest roots in the custom the signal. practiced by the Greeks of using electric eels to ‘‘shock’’ The late 1970s and early 1980s saw the use of sophis- ailments out of the body. The origin of the shock that ticated computer algorithms and communication theory to accompanied this earliest detection and application of decompose the EMG signal into the individual electrical the EMG signal was not appreciated until 1666 when an activities of the muscle fibers (10–12). Today, the decom- Italian, Francesco Redi, realized that it originated from position approach promises to revolutionize clinical elec- muscle tissue (1). This relationship was later proved by tromyography and to provide a powerful tool for Luigi Galvani (2) in 1791 who staunchly defended the investigating the detailed control schemes used by the notion. During the ensuing six decades, a few investigators nervous system to produce muscle contractions.