Variability of electrophrenic diaphragm twitch stimulation over time in normal subjects.
Transcutaneous electrophrenic twitch stimulation is a potentially powerful way to assess diaphragm contractile function in response to interventions which may alter respiratory muscle strength and endurance. At present, the variability of the transdiaphragmatic twitch pressure (Pdi(T)) over a several hour period is not well described. The present study examines the reproducibility of Pdi(T) amplitude and the twitch occlusion technique of assessing maximum transdiaphragmatic pressure (Pdi(max)) in seven normal adults stimulated intermittently every hour for a total 4-h period. In one subject, data were obtained on two occasions separated by a 2-month interval. Among all subjects, the Pdi(T) amplitude expressed as a percentage of the Pdi(max) was highly reproducible over 4 h (coefficient of variation 5.3). Peak Pdi(T) was inversely related to graded voluntary Pdi (r = -0.0996) and the relationship was virtually identical over 4 h (r = - 0.999, P = 0.96). These data show that Pdi(T) at functional residual capacity and the twitch occlusion relationship are highly reproducible.