APPLICATION OF A CERVICAL STIMULATING APPARATUS FOR BILATERAL TRANSCUTANEOUS PHRENIC-NERVE STIMULATION

Transcutaneous bilateral phrenic nerve stimulation (tPNS) is frequentl y used to assess diaphragmatic function in humans. Commonly, stimulati on is performed with hand-held electrodes; however, these are unsuitab le for studies requiring repeated PNS and where recruitment of rib cag e and neck muscles may shift the probes in relation to the nerves. In this study we describe the design of a cervical neck brace and electro de probes that maintain stimulating electrodes in constant position re lative to the phrenic nerves and facilitates studies requiring repeate d maximal PNS. The effectiveness of the apparatus was examined by 1) r eviewing the reproducibility of the transdiaphragmatic pressure respon se to 0.1 ms tPNS (PdiT) at relaxed functional residual capacity in fo ur subjects studied on 25 +/- 8 (SD) occasions (greater than or equal to 24 h apart) over a 4-yr period, and 2) measuring peak-to-peak ampli tude of the left and right diaphragmatic compound muscle action potent ials (surface electrodes) during two prolonged studies (38 +/- 9 min) in each subject, when tPNS was performed during repeated submaximal an d maximal inspiratory efforts. PdiT was reproducible in each subject w hen measured repeatedly within a single study [coefficient of variatio n (CV) of 3.8 +/- 0.8%] and over separate days (CV of 11.5 +/- 3.5%). The peak-to-peak amplitudes of the left and right compound muscle acti on potentials were also reproducible (CV of 8.4 +/- 4.3 and 8.4 +/- 2. 9%, respectively) and independent of the degree of effort. The apparat us appears effective for the maintenance of maximal stimulation under varied conditions for long periods and provides reproducible measureme nts of PdiT both within and between studies.