Level of consciousness as a conditioning factor of F wave generation in stroke patients Elisabeth Chroni a, * , George Katsoulas a , Andreas A. Argyriou a , George C. Sakellaropoulos b , Panagiotis Polychronopoulos a , George Nikiforidis b a Department of Neurology, University of Patras Medical School, P.O. Box 1045, 26504 Rion-Patras, Greece b Department of Medical Physics, University of Patras Medical School, Rion-Patras, Greece Accepted 22 October 2005 Available online 4 January 2006 Abstract Objective: The current study aimed to investigate whether the level of consciousness influenced the F wave generation, as an independent factor. Methods: Forty three patients with acute stroke were divided according to their level of consciousness in two groups; to those with Glasgow scale (GCS) score 3–7 indicating coma (group I) and those with GCS score 8–15 (group II). A series of 40 electrical stimuli were delivered to the ulnar nerve bilaterally in order to obtain F waves. The following variables were estimated and then compared between groups: F persistence, F wave latency, amplitude and duration. All studies were performed within 3 days from the onset of the stroke symptoms. Results: The main finding to emerge was the significantly reduced F wave persistence in the group of patients with low GCS score as opposed to patients allocated in the group with GCS score 8–15. This result is referred to F waves obtained from both the affected and unaffected limb. F wave minimum latency was also prolonged in the group with low GCS score, whilst the comparison of all other F wave variables revealed no significant differences between groups I and II. F wave persistence measurements did not differ between the affected and unaffected sides. Stroke location and type (ischemic or hemorrhagic) were not associated with alterations of F wave measurements. Conclusions: Our results on stroke patients suggest that generation of F waves, expressed by the F wave persistence is associated with the level of consciousness. Significance: F wave study may be useful as an objective measure in documenting the severity of consciousness impairment. q 2005 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved. Keywords: Level of consciousness; Glasgow scale; Stroke; F waves 1. Introduction F waves are late muscle responses elicited by backfiring of antidromically stimulated motor neurons. Their measure- ments are helpful in evaluating motor conduction along the entire length of the peripheral axons, including the most proximal segment (Kimura, 2001). F wave study has become part of the routine neurophysiological investigation of peripheral nerves (Fisher, 1992; Mesrati and Vecchierini, 2004; Panayiotopoulos and Chroni, 1996) and has been proven to be particularly useful in diagnosis of polyneuro- pathies. Furthermore, on research grounds mainly, changes of F wave parameters also have long been described in central nervous system (CNS) diseases such as Parkinson, ALS and stroke (Abbruzzese et al., 1985; de Carvalho et al., 2002; Fisher, 1992). Several studies have focused on F wave abnormalities recorded from limbs affected by upper motor neuron diseases during acute, but mainly chronic phases. Increased F wave amplitude, duration or frequency that have been observed in spasticity, were attributed to imbalance of central impulses in favor of excitatory resulting in enhanced anterior horn cells excitability (Eisen and Odusote, 1979). In contrast, during the initial Clinical Neurophysiology 117 (2006) 315–319 www.elsevier.com/locate/clinph 1388-2457/$30.00 q 2005 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.clinph.2005.10.018 * Corresponding author. Tel./fax: C30 2610 993949. E-mail address: echroni@yahoo.com (E. Chroni).