| BackgroundMornitoring respiratory muscle function is very important for critically illpatients, especially the patients receiving mechanical ventilation. Although severalfactors may contribute to delayed weaning, a major determinant appears to berespiratory muscle weakness. The most frequent causes of muscle weakness incritically ill patient, which may affect both limbs and respiratory muscles, are criticalillness polyneuropathy and myopathy known as ICU-acquired weakness. It should berecognized that ICU weakness may result from alteration in muscle or nerve function,and in fact both often migrate together. Respiratory muscle dysfunction are often partof a phenomenon as critical illness polyneuropathy and myopathy. In recent years,clinicians have taken a closer look at respiratory muscle dysfunction in critically illpatients. On account of the routine muscle strength measurements just as the maximalinspiratory pressure are volitional and reqire full cooperation, reliability andrepeatability are not good enough. So a simple and effective tool to objectivelyevaluate respiratory muscle function is needed.The diaphragm is the most important respiratory muscle which is accounting forabout70%of minute ventilation in humans, so diaphragm function can reflect thewhole respiratory muscle function state. The diaphragm is only innervated by thephrenic nerve, which is why phrenic nerve stimulation enables us to analyse thediaphragm specific force output independently of the other respiratory muscles.Measurement of twitch transdiaphragmatic pressure during magnetic phrenic nerve stimulation is the commonly used method to quantitatively evaluate diaphragmaticmuscle contraction force in humans. If magnetic phrenic nerve stimulation combinedwith multi-pair esophageal electrode catheter to quantify the diaphragm compoundmuscle action potential and the latency of the phrenic nerve conduction time, whichrepresent the summated electrical activity produced by all motor units synchronouslyactivated and the phrenic nerve conduction speed. The twitch transdiaphragmaticpressure when taken in conjunction with the diaphragm compound muscle actionpotential and the latency of the phrenic nerve conduction time can be used toqualitative analysis diaphragmatic muscle dysfunction, which are helpful todistinguish between peripheral contractile failure (normal diaphragm compoundmuscle action potential amplitude, reduced twitch transdiaphragmatic pressure) andneural or neuromuscular transmission defects(both diaphragm compound muscleaction potential amplitude and twitch transdiaphragmatic pressure reduced) So itmaybe the ideal method to evaluation of diaphragmatic function comprehensively,objectively and quantitatively.ObjectivePurpose of this study was to utilize the newly designed multi-functionesophageal electrode catheter and bilateral anterolateral magnetic phrenic nervesstimulation in patients who were ready to weaning from mechanical ventilation in theintensive care unit to evaluate the diaphragm function in maximal transdiaphragmaticpressure, phrenic nerve conduction time, diaphragm compound muscle actionpotential and twitch transdiaphragmatic pressure, and compared with the healthynormal values.MethodsUsed the multi-function esophageal electrode catheter and bilateral anterolateralmagnetic phrenic nerves stimulation to evaluate the diaphragm function of healthyvolunteers and estimate the normal values of the maximal transdiaphragmaticpressure, phrenic nerve conduction time, diaphragm compound muscle actionpotential and twitch transdiaphragmatic pressure as control group. Patients were recruited if they were admitted between May to November in2013to the intensive care unit in the first affiliated hospital of Guangzhou medicaluniversity，who were intubated and mechanical ventilation, and recovered to theclinical stability states after passing the readiness to wean. Utilizing the newlydesigned multi-function esophageal electrode catheter which has feeding tube andbilateral anterolateral magnetic phrenic nerves stimulation to detect the diaphragmfunction as the aforementioned method, compared the difference between the twogroups.Results10healthy volunteers (5men and5women) age23to34years (mean age26±3)participated in the study. All of them were free of respiratory or neuromusculardisease, and all had normal lung volumes. Their maximal transdiaphragmatic pressure,phrenic nerve conduction time, diaphragm compound muscle action potential andtwitch transdiaphragmatic pressure were （71.2±32.4） cmH2O,（7.1±0.5） ms,（1.80±0.49）mV and（26.7±4.9）cmH2O respectively.14patients were recruited,1case exited because of intolerance of repetitivemagnetic stimulation, the rest of the13patients (8men and5women) age was38to76years (mean age64±12),2cases had no diaphragmatic electromyographic signalsnor twitch signals,1case had electromyographic signal but could not be elicited bymagnetic stimulation,1case had no available twitch transdiaphragmatic pressure withphrenic nerve conduction time was7.2ms and diaphragm compound muscle actionpotential was1.26mV. These4patients’s maximal transdiaphragmatic pressure werenegative. The rest of the9cases (6men and3women) age was38to76years (meanage63±15) achieved complete data were (45.1±15.5) cmH2O,(8.5±1.5) ms,(1.01±0.35) mV and (11.2±4.7) cmH2O respectively.Used Mann-Whitney U test to compare phrenic nerve conduction time of ICUpatients and normal controls, p=0.045. Used unpaired t test to compare maximaltransdiaphragmatic pressure (p=0.042), diaphragm compound muscle action potential(p＜0.001) and twitch transdiaphragmatic pressure (p＜0.001) of the two groups,, the difference was statistically significant.ConclusionNewly designed multi-function esophageal electrode catheter combined withbilateral anterolateral magnetic phrenic nerve stimulation can be used fornonvolitional comprehensive assessing diaphragm function in the critically ill.Compared with the normal volunteers, maximal transdiaphragmatic pressure,diaphragm compound muscle action potential and twitch transdiaphragmatic pressurereduced significantly with phrenic nerve conduction time prolonged of ICU patients. |
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