The tension-time index of the diaphragm revisited in quadriplegic patients with diaphragm pacing

Stefano Nava, Fiorenzo Rubini, Ercole Zanotti, Dario Caldiroli

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The fatigue threshold of the human diaphragm, index of its endurance and fatigability, corresponds, during spontaneous breathing, to a tension-time index (TTdi = Pdi/Pdi(max) x TI/Ttot (i.e., the inspiratory time over the total breath duration) of 0.15 to 0.18. We studied three quadriplegic patients with diaphragm pacing in order to reassess this threshold in patients in whom the contribution of the other respiratory muscles is lacking. Transdiaphragmatic pressure (Pdi) was obtained from the difference between gastric (Pga) and esophageal (Pes) pressures while the electromyograms (EMG) of both hemidiaphragms were recorded with surface electrodes. Four runs at different TTdi were performed on different days in each subject, varying either the Pdi developed per breath, changing the frequency of stimulation, or the TI/Ttot. The time of fatigue was defined when Pdi decreased during the trials by 35% from baseline. No evidence of transmission fatigue (i.e., decline in action potential amplitude) was observed. The TTdi at which fatigue occurred in all the quadriplegic patients was around 0.10 to 0.12, well below the values previously described. After fatigue had occurred, the force recovery during the force-frequency curve was not complete after 2 h at low frequencies, whereas at high frequencies it was fully complete at 30 min. We conclude that when respiration is accomplished only by the diaphragm, without the contribution of the other respiratory muscles, the fatigue threshold is lower than previously reported.

Original languageEnglish
Pages (from-to)1322-1327
Number of pages6
JournalAmerican Journal of Respiratory and Critical Care Medicine
Issue number4
Publication statusPublished - 1996

ASJC Scopus subject areas

  • Pulmonary and Respiratory Medicine


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