title: Severity of Myasthenia Gravis Influences the Relationship between Train-of-four Ratio and Twitch Tension and Run-down of Rat Endplate Potentials.
abstract: BACKGROUND
  Train-of-four ratio (TOFR) is often used to evaluate muscle relaxation caused by neuromuscular-blocking agents (NMBAs). However, it is unknown whether TOFR reliably correlates with the first twitch tension (T1) in patients with myasthenia gravis (MG). By using rat models of experimental autoimmune MG (EAMG), the authors verified the hypothesis that the severity of MG influences the relationship between TOFR and T1.
  
  
  METHODS
  EAMG rats were divided into sham, moderate MG, and severe MG groups. Isometric twitch tension of the hemidiaphragm was elicited by phrenic nerve stimulation with and without use of the NMBA rocuronium to measure TOFR and T1, and run-down of endplate potentials was estimated in the three groups. Changes around the neuromuscular junction in EAMG rats were investigated by observation of electron micrographs.
  
  
  RESULTS
  With similar attenuation of T1, TOFR was significantly (n = 6) different among the three groups in the presence of 50% inhibitory concentrations of rocuronium (IC50). Run-down in the sham group was significantly (n = 8) greater with exposure to IC50, whereas that in the severe MG group was statistically insignificant. Width of the primary synaptic cleft in the severe MG group was significantly (n = 80) greater than that in the other groups.
  
  
  CONCLUSIONS
  Severity of MG influences the relationship between TOFR and T1, together with changes in run-down of endplate potentials and those around the neuromuscular junction in rats. TOFR may, therefore, not be an accurate indicator of recovery from NMBAs in MG patients.
authors.affiliation: From the Departments of Anesthesiology (K.T., T.N., Y.T., M.Y.) and Traumatology and Critical Care Medicine (E.N.), Sapporo Medical University School of Medicine, Sapporo, Hokkaido, Japan.
authors.forename: Kazunobu
authors.initials: K
authors.lastname: Takahashi
authors.forename: Tomohisa
authors.initials: T
authors.lastname: Niiya
authors.forename: Yukimasa
authors.initials: Y
authors.lastname: Takada
authors.forename: Eichi
authors.initials: E
authors.lastname: Narimatsu
authors.forename: Michiaki
authors.initials: M
authors.lastname: Yamakage
mesh_terms: D000732:Androstanols / Q000008:administration & dosage; D000818:Animals; D003964:Diaphragm / Q000503:physiopathology; D004195:Disease Models, Animal; D019706:Excitatory Postsynaptic Potentials / Q000502:physiology*; D005260:Female; D009157:Myasthenia Gravis / Q000503:physiopathology*; D009469:Neuromuscular Junction / Q000503:physiopathology; D061886:Neuromuscular Monitoring / Q000379:methods* / Q000706:statistics & numerical data; D003473:Neuromuscular Nondepolarizing Agents / Q000008:administration & dosage; D051381:Rats; D011917:Rats, Inbred Lew; D000077123:Rocuronium; D012720:Severity of Illness Index; D009435:Synaptic Transmission / Q000502:physiology
chemical_list: D000732:Androstanols; D003473:Neuromuscular Nondepolarizing Agents; D000077123:Rocuronium