MJ Mador, A Rodis, UJ Magalang and K Ameen
Division of Pulmonary and Critical Care Medicine, State University of New York at Buffalo, New York, USA.

Brief supramaximal stimulation of the phrenic nerves (twitch) is considered a promising technique to detect diaphragmatic fatigue in humans. However, the most commonly employed methodology (transcutaneous stimulation) is technically difficult. Cervical magnetic stimulation is a recently described technique that is potentially simpler and may obviate some of the problems inherent with transcutaneous stimulation. The purpose of this study was to determine the ability of cervical magnetic stimulation to evaluate diaphragmatic function. Accordingly, we measured transdiaphragmatic pressure (Pdi) during transcutaneous and cervical magnetic stimulation of the phrenic nerves before and after a potentially fatiguing task; inspiratory threshold loading to task failure. During threshold loading, subjects generated approximately 60% of their maximal esophageal pressure with each breath until they could no longer reach the target pressure. At least 10 twitches were obtained during both transcutaneous and magnetic stimulation before and 10, 30, 60, and 120 min after threshold loading. Control twitch Pdi was significantly larger during magnetic stimulation compared with transcutaneous stimulation: 39.3 +/- 3.0 (mean +/- SE) versus 27.4 +/- 2.3 cm H2O, p < 0.0005. This increase in twitch Pdi was solely due to the esophageal component. Following threshold loading, a significant reduction in transcutaneous twitch Pdi was seen in only three of the 10 subjects. Mean transcutaneous twitch Pdi fell only slightly from 27.4 +/- 2.3 during control to 25.1 +/- 2.2 cm H2O at 10 min after loading (p < 0.004). In contrast, magnetic twitch Pdi was significantly reduced in nine of the 10 subjects following threshold loading. Mean magnetic twitch Pdi fell from 39.3 +/- 3.0 during control to 31.1 +/- 3.0 cm H2O at 10 min after loading (p < 0.0001). The average fall in twitch Pdi post-loading (expressed as a percentage of the control value) was significantly greater for magnetic stimulation compared with transcutaneous stimulation: 21.0 +/- 3.1 versus 7.8 +/- 2.9%, p < 0.0001. In summary: (1) in the fresh state, twitch Pdi is larger with magnetic stimulation compared with transcutaneous stimulation, and (2) transcutaneous and cervical magnetic twitch Pdi are affected differently by threshold loading to task failure.

This article has been cited by other articles:

				S. Verges, O. Lenherr, A. C. Haner, C. Schulz, and C. M. Spengler Increased fatigue resistance of respiratory muscles during exercise after respiratory muscle endurance training Am J Physiol Regulatory Integrative Comp Physiol, March 1, 2007; 292(3): R1246 - R1253. [Abstract] [Full Text] [PDF]

				T. M. Hemmerling and F. Donati Neuromuscular blockade at the larynx, the diaphragm and the corrugator supercilii muscle: a review: [Blocage neuromusculaire du larynx, du diaphragme et du muscle sourcilier : une revue] Can J Anesth, October 1, 2003; 50(8): 779 - 794. [Abstract] [Full Text] [PDF]

				F. Series and G. Ethier Assessment of upper airway stabilizing forces with the use of phrenic nerve stimulation in conscious humans J Appl Physiol, June 1, 2003; 94(6): 2289 - 2295. [Abstract] [Full Text] [PDF]

				T.J. Kufel, L.A. Pineda, R.G. Junega, R. Hathwar, and M.J. Mador Diaphragmatic function after intense exercise in congestive heart failure patients Eur. Respir. J., December 1, 2002; 20(6): 1399 - 1405. [Abstract] [Full Text] [PDF]

				T. M. Hemmerling, J. Schmidt, C. Schurr, G. Breuer, and K. E. Jacobi A Comparison Between Anterior and Posterior Monitoring of Neuromuscular Blockade at the Diaphragm: Both Sites Can Be Used Interchangeably Anesth. Analg., October 1, 2002; 95(4): 940 - 943. [Abstract] [Full Text] [PDF]

				W.D-C. Man, Y-M. Luo, N. Mustfa, G.F. Rafferty, J-C. Glerant, M.I. Polkey, and J. Moxham Postprandial effects on twitch transdiaphragmatic pressure Eur. Respir. J., September 1, 2002; 20(3): 577 - 580. [Abstract] [Full Text] [PDF]

				ATS/ERS Statement on Respiratory Muscle Testing Am. J. Respir. Crit. Care Med., August 15, 2002; 166(4): 518 - 624. [Full Text] [PDF]

				M. J. Mador, S. Khan, and T. J. Kufel Bilateral Anterolateral Magnetic Stimulation of the Phrenic Nerves Can Detect Diaphragmatic Fatigue Chest, February 1, 2002; 121(2): 452 - 458. [Abstract] [Full Text] [PDF]

				Y. M. Luo, N. Hart, N. Mustfa, R. A. Lyall, M. I. Polkey, and J. Moxham Effect of diaphragm fatigue on neural respiratory drive J Appl Physiol, May 1, 2001; 90(5): 1691 - 1699. [Abstract] [Full Text] [PDF]

				M. JEFFERY MADOR, T. J. KUFEL, and L. A. PINEDA Quadriceps and Diaphragmatic Function after Exhaustive Cycle Exercise in the Healthy Elderly Am. J. Respir. Crit. Care Med., November 1, 2000; 162(5): 1760 - 1766. [Abstract] [Full Text]

				M. JEFFERY MADOR, T. J. KUFEL, and L. PINEDA Quadriceps Fatigue after Cycle Exercise in Patients with Chronic Obstructive Pulmonary Disease Am. J. Respir. Crit. Care Med., February 1, 2000; 161(2): 447 - 453. [Abstract] [Full Text]

				M. JEFFERY MADOR, T. J. KUFEL, L. A. PINEDA, and G. K. SHARMA Diaphragmatic Fatigue and High-intensity Exercise in Patients with Chronic Obstructive Pulmonary Disease Am. J. Respir. Crit. Care Med., January 1, 2000; 161(1): 118 - 123. [Abstract] [Full Text]

				Y M Luo, M I Polkey, R A Lyall, and J Moxham Effect of brachial plexus co-activation on phrenic nerve conduction time Thorax, September 1, 1999; 54(9): 765 - 770. [Abstract] [Full Text]

				P. D. HUGHES, M. I. POLKEY, M. LOU HARRIS, A. J. S. COATS, J. MOXHAM, and M. GREEN Diaphragm Strength In Chronic Heart Failure Am. J. Respir. Crit. Care Med., August 1, 1999; 160(2): 529 - 534. [Abstract] [Full Text]

				Y. M. Luo, M. I. Polkey, L. C. Johnson, R. A. Lyall, M. L. Harris, M. Green, and J. Moxham Diaphragm EMG measured by cervical magnetic and electrical phrenic nerve stimulation J Appl Physiol, December 1, 1998; 85(6): 2089 - 2099. [Abstract] [Full Text] [PDF]

				T. Similowski, C. Straus, V. Attali, A. Duguet, and J.-P. Derenne Cervical magnetic stimulation as a method to discriminate between diaphragm and rib cage muscle fatigue J Appl Physiol, May 1, 1998; 84(5): 1692 - 1700. [Abstract] [Full Text] [PDF]