Abstract
The effect of length on tension generation by the human diaphragm has previously only been described using single bilateral phrenic nerve stimuli, but in peripheral skeletal muscle the length tension relationship is dependent on the frequency of stimulation (Rack & Westbury J Physiol(Lond) 1969;204:443-60). We therefore studied 8 healthy volunteers using paired supramaximal bilateral phrenic nerve stimuli (Yan et al Eur Resp J 1993;6:211-8). Stimuli were given anteriorly using two 40mm coils each of which was powered by 2 Magstim 200 stimulators. Each pair of stimulators was linked by a BiStim module which allowed a minimum of 3 stimuli to be given at the following interstimulus intervals; 999ms (1 Hz), 100ms (10 Hz), 50ms (20 Hz), 33ms (30 Hz) and 10ms (100 Hz), and at the following lung volumes; RV, FRC, 1/3 IC, 2/3 IC and TLC. Results are shown in the figure; 50 ms and 33 ms were similar to 10 ms and are therefore omitted for clarity. Increasing lung volume caused the greatest reduction in the Pdi elicited by stimuli 100ms apart (ie 10 Hz). We conclude that the length-tension relationship of the diaphragm is frequency dependent. Given that phrenic nerve firing rates in vivo are approximately 10 Hz this may contribute to impaired diaphragm function in patients who are hyperinflated. (Graph Presented) LUNG VOLUME (%VC).
| Original language | English |
|---|---|
| Journal | Thorax |
| Volume | 51 |
| Issue number | SUPPL. 3 |
| Publication status | Published - 1 Dec 1996 |