M Green

Royal Brompton and Harefield NHS Foundation Trust, Harefield, England, United Kingdom

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Publications (101)704.48 Total impact

  • M I Polkey, J Moxham, M Green
    European Respiratory Journal 02/2011; 37(2):236-7. · 6.36 Impact Factor
  • Revue Des Maladies Respiratoires - REV MAL RESPIR. 01/2006; 23(5):586-586.
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    ABSTRACT: Although breathlessness is common in chronic heart failure (CHF), the role of inspiratory muscle dysfunction remains unclear. We hypothesised that inspiratory muscle endurance, expressed as a function of endurance time (Tlim) adjusted for inspiratory muscle load and inspiratory muscle capacity, would be reduced in CHF. Endurance was measured in 10 healthy controls and 10 patients with CHF using threshold loading at 40% maximal oesophageal pressure (Poes(max)). Oesophageal pressure-time product (PTPoes per cycle) and Poes(max) were used as indices of inspiratory muscle load and capacity, respectively. Although Poes(max) was slightly less in the CHF group (-117.7 (23.6) v -100.0 (18.3) cm H(2)O; 95% CI -37.5 to 2.2 cm H(2)O, p = 0.1), Tlim was greatly reduced (1800 v 306 (190) s; 95% CI 1368 to 1620 s, p<0.0001) and the observed PTPoes per cycle/Poes(max) was increased (0.13 (0.05) v 0.21 (0.04); 95% CI -0.11 to -0.03, p = 0.001). Most of this increased inspiratory muscle load was due to a maladaptive breathing pattern, with a reduction in expiratory time (3.0 (5.8) v 1.1 (0.3) s; 95% CI 0.3 to 3.5 s, p = 0.03) accompanied by an increased inspiratory time relative to total respiratory cycle (Ti/Ttot) (0.43 (0.14) v 0.62 (0.07); 95% CI -0.3 to -0.1, p = 0.001). However, log Tlim, which incorporates the higher inspiratory muscle load to capacity ratio caused by this altered breathing pattern, was >/=85% predicted in seven of 10 patients. Although a marked reduction in endurance time was observed in CHF, much of this reduction was explained by the increased inspiratory muscle load to capacity ratio, suggesting that the major contributor to task failure was a maladaptive breathing pattern rather than impaired inspiratory muscle endurance.
    Thorax 06/2004; 59(6):477-82. · 8.38 Impact Factor
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    ABSTRACT: Impaired respiratory muscle endurance (RME) could reduce exercise tolerance and contribute to ventilatory failure. The aim of the present study was to develop a clinically-feasible method to measure RME using negative-pressure inspiratory-threshold loading. It was hypothesized that endurance time (tlim) could be predicted by normalizing oesophageal pressure-time product (PTP) per total breath cycle (PTPoes) for maximum oesophageal pressure (Poes,max); the load/capacity ratio. The corresponding mouth pressures, PTPmouth and Pmouth,max were also measured. The RME test was performed on 30 healthy subjects exposed to the same target pressure (70% of Poes,max). Eight patients with systemic sclerosis/interstitial lung disease were studied to assess the validity and acceptability of the technique. Normal subjects showed a wide intersubject variation in tlim (coefficient of variation, 69%), with a linear relationship demonstrated between log tlim and PTPoes/Poes,max (r=0.88). All patients with systemic sclerosis/interstitial lung disease had normal respiratory muscle strength, but six out of eight had a reduction in RME. In conclusion, endurance time can be predicted from the load/capacity ratio, over a range of breathing strategies; this relationship allows abnormal respiratory muscle endurance to be detected in patients. Oesophageal and mouth pressure showed a close correlation, thus suggesting that the test could be applied noninvasively.
    European Respiratory Journal 03/2002; 19(2):232-9. · 6.36 Impact Factor
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    ABSTRACT: Anecdotal observations suggest that low frequency fatigue, as judged by a fall in twitch tension, is more difficult to achieve in the diaphragm than nonrespiratory muscle but this hypothesis has not previously been directly tested. We studied 7 subjects by performing incremental repetitive contraction loading protocols of the diaphragm and quadriceps. We measured twitch transdiaphragmatic pressure (Tw Pdi) and twitch quadriceps tension (Tw Q) during both muscle contraction and relaxation phases during the run. Unpotentiated and potentiated Tw Pdi and Tw Q were measured before and at 20, 40, and 60 minutes after the run. During the run, greater activation of the quadriceps was achieved; for example, at 70% of maximal voluntary effort the interpolated Tw Q was 12.5% of the relaxation phase Tw Q (implying activation of 87.5%) compared with 29.4% (i.e., 70.6% activation) for the diaphragm (p = 0.05). A significantly greater fall in Tw Q than Tw Pdi was observed (unpotentiated Tw Pdi at 20 minutes 94% baseline versus Tw Q 59% baseline, p = 0.007). Low frequency fatigue in humans is more difficult to generate in the diaphragm than in the quadriceps muscle due in part to reduced central activation.
    Beiträge zur Klinik der Tuberkulose 02/2002; 180(1):1-13. · 2.06 Impact Factor
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    ABSTRACT: Diaphragm strength can be assessed from twitch gastric (TwPgas), twitch oesophageal (TwPoes), and twitch transdiaphragmatic pressure (TwPdi) in response to phrenic nerve stimulation. This requires the passage of balloon catheters, which may be difficult. Changes in pressure measured at the mouth during phrenic nerve stimulation avoid the need for balloon catheters. We hypothesized that pressures measured at the tracheal tube during phrenic stimulation, could also reflect oesophageal pressure change as a result of isolated diaphragmatic contraction and, therefore, reflect diaphragm strength. We aimed to establish the relationship between twitch tracheal tube pressure (TwPet), TwPoes, and TwPdi in patients in the supine and sitting positions. The phrenic nerves were stimulated magnetically bilaterally, in 14 ICU patients while supine and on another occasion while sitting up at 45 degrees. In the sitting position mean TwPoes was 9.1 cm H2O and TwPet 11.3 cm H2O (mean(SD) difference -2.2 (SD 1.5)). In the supine position mean TwPoes was 8.1 cm H2O and TwPet 9.9 cm H2O (mean difference -1.8 (2.2)). The difference between TwPoes and TwPet was less at low twitch amplitude; less than +/- 1 cm H2O below a mean twitch height of 8 cm H2O supine and 10 cm H2O sitting. Sitting TwPet was related to TwPoes r2=0.93 and TwPdi r2=0.65 (P<0.01). Supine TwPet was related to TwPoes r2=0.84 and TwPdi r2=0.83 (P<0.01). The mean within occasion coefficient of variation while sitting was TwPet=13.3%, TwPoes=13.9%, TwPdi=11.2%, and supine TwPet=11.6%, TwPoes=14.6%, TwPdi=11.8%. We conclude that TwPet reflects TwPoes during diaphragmatic stimulation and is worthy of further study to establish its place as a guide to the presence of respiratory muscle strength and fatigue.
    BJA British Journal of Anaesthesia 01/2002; 87(6):876-84. · 4.24 Impact Factor
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    ABSTRACT: The aim of this study was to measure inspiratory pressure-generating capacity in patients presenting with acute asthma, as it has been suggested that inspiratory muscle fatigue may contribute to breathlessness and acute respiratory failure. Descriptive study. Emergency departments of two inner-city hospitals. Fifty-one patients with acute asthma, and 45 patients without respiratory disease who served as control subjects. Measurements and results: Maximum inspiratory pressure-generating capacity was measured soon after presentation by the sniff nasal inspiratory pressure (SNIP) method. The mean (SD) SNIP was 110 cm H(2)O (23 cm H(2)O) in men with asthma (mean for control subjects, 126 cm H(2)O [25 cm H(2)O]; p < 0.05) and 80 cm H(2)O [24 cm H(2)O] in women with asthma (mean for control subjects, 105 cm H(2)O (26 cm H(2)O); p < 0.01). In a second study of simultaneous SNIP and intrathoracic pressure measurements in a group of patients with acute asthma (n = 10) and control subjects (n = 11), the effect of airways obstruction on SNIP was assessed. The measurement of sniff esophageal pressure was more negative than SNIP by approximately 16% in asthmatic patients and by 4% in control subjects. Taking account of the likely effect of airways obstruction on SNIP, the reduction in inspiratory pressure-generating capacity that was observed in these patients with moderately severe acute asthma was minor and was consistent with the modest hyperinflation observed. This study did not find evidence of inspiratory muscle weakness or fatigue in patients with moderately severe acute asthma presenting to the emergency department.
    Chest 09/2001; 120(3):757-64. · 7.13 Impact Factor
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    ABSTRACT: In the critically ill, respiratory muscle strength usually has been assessed by measuring maximum inspiratory pressure. The maneuver is volitional, and results can be unreliable. The nonvolitional technique of bilateral anterolateral magnetic stimulation of the phrenic nerves, producing twitch transdiaphragmatic pressure, has been successful in normal subjects and ambulatory patients. In this study we used the technique in the intensive care unit and explored the measurement of twitch endotracheal tube pressure as a less invasive technique to assess diaphragmatic contractility. Clinical study to quantify diaphragm strength in the intensive care unit. Patients from three London teaching hospital intensive care units and high-dependency units. Forty-one intensive care patients were recruited. Of these, 33 (20 men, 13 women) were studied. Esophageal and gastric balloon catheters were passed through the anaesthetized nose, and an endotracheal tube occlusion device was placed in the ventilation circuit, next to the endotracheal tube. Two 43-mm magnetic coils were placed anteriorly on the patient's neck, and the phrenic nerves were stimulated magnetically. On phrenic nerve stimulation, twitch gastric pressure, twitch esophageal pressure, twitch transdiaphragmatic pressure, and twitch endotracheal tube pressure were measured. Forty-one consecutive patients consented to take part in the study, and twitch pressure data were obtained in 33 of these. Mean transdiaphragmatic pressure was 10.7 cm H2O, mean twitch esophageal pressure was 6.7 cm H2O, and mean twitch endotracheal tube pressure was 6.7 cm H2O. The mean difference between twitch esophageal pressure and twitch endotracheal tube pressure was 0.02 cm H2O. Correlation of the means of twitch endotracheal tube pressure to twitch esophageal pressure was 0.93, and that for twitch endotracheal tube pressure to transdiaphragmatic pressure was 0.78. Transdiaphragmatic pressure can be measured in the critically ill to give a nonvolitional assessment of diaphragm contractility, but not all patients can be studied. At present, the relationship of twitch endotracheal tube pressure to transdiaphragmatic pressure is too variable to reliably represent a less invasive measure of diaphragm strength.
    Critical Care Medicine 08/2001; 29(7):1325-31. · 6.12 Impact Factor
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    ABSTRACT: Exercise intolerance is a feature of chronic heart failure (CHF). We hypothesized that excessive loading of the respiratory muscle pump might contribute to exertional breathlessness. One marker of excessive muscle-loading is slowing of maximum relaxation rate (MRR) and, therefore, to test our hypothesis, we investigated the effect of exhaustive treadmill walking on inspiratory muscle MRR in patients with CHF. We studied eight stable patients with mild-moderate CHF walking on a treadmill until termination because of severe dyspnea. Inspiratory muscle MRR was determined from esophageal pressure (Pes) change during submaximal sniffs (Sn) before and immediately after exercise to a mean (SD) minute ventilation of 77 () L/min. For comparison, nine healthy subjects performed a similar protocol; exercise was terminated either by severe dyspnea or when minute ventilation reached 100 L/min. There were no significant differences in terms of heart rate, respiratory rate, tidal volume, or inspiratory duty cycle at cessation of exercise. The mean slowing of Sn Pes MRR in the first minute after termination of exercise in the CHF group was 22.4% and in the normal control group it was 2.8% (p < 0.01). Our data show that slowing of inspiratory muscle relaxation rate occurs in patients with CHF walking to severe breathlessness. We conclude that severe loading of the inspiratory muscles is a feature of exertional dyspnea in CHF.
    American Journal of Respiratory and Critical Care Medicine 05/2001; 163(6):1400-3. · 11.04 Impact Factor
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    ABSTRACT: Anterior magnetic stimulation (aMS) of the phrenic nerves is a new method for the assessment of diaphragm contractility that might have particular applications for the clinical assessment of critically ill patients who are commonly supine. We compared aMS with existing techniques for measurement of diaphragm weakness and fatigue in 10 normal subjects, 27 ambulant patients with suspected diaphragm weakness and 10 critically ill patients. Laboratory and intensive care unit of two university hospitals. Although aMS was not demonstrably supramaximal in normal subjects, the mean value of twitch transdiaphragmatic pressure (Tw Pdi) obtained at 100% of stimulator output, 23.7 cmH2O, did not differ significantly from that obtained with bilateral supramaximal electrical stimulation (ES), 24.9 cmH2O, or bilateral anterior magnetic phrenic nerve stimulation (BAMPS), 27.3 cmH2O. A fatiguing protocol produced a 20 % fall in aMS-Tw Pdi and a 19% fall in BAMPS-Tw Pdi; the fall in aMS-Tw Pdi correlated with the fall in BAMPS-Tw Pdi (r2 = 0.84, p = 0.03) indicating that aMS can detect diaphragm fatigue. In ambulant patients aMS agreed closely with existing measures of diaphragm strength. The maximal sniff Pdi correlated with both the aMS-Tw Pdi (r2 = 0.60, p < 0.0001) and the BAMPS-Tw Pdi (r2 = 0.65, p < 0.0001) and the aMS-Tw Pdi was a mean (SD) 2.2 (4.3) cmH2O less than BAMPS-Tw Pdi. In addition, aMS correctly identified diaphragm dysfunction in patients studied on the ICU. We conclude that aMS is of clinical value for the investigation of suspected diaphragm weakness.
    Intensive Care Medicine 09/2000; 26(8):1065-75. · 5.54 Impact Factor
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    ABSTRACT: Many critically ill patients develop significant skeletal muscle weakness in the Intensive Care Unit (ICU), which ultimately may cause difficulties in weaning from mechanical ventilation and a protracted, expensive ICU stay. Reliable monitoring of muscle strength in this environment is difficult. The purpose of this study was to develop a reproducible, nonvolitional method of measuring adductor pollicis (AP) muscle function by magnetic stimulation of the ulnar nerve (MSUN) that could be applied to patients in the ICU and operating theater (OT). Fifty subjects (32 healthy control subjects [12 of whom were elderly], 12 ICU patients with critical illness [mean APACHE II score 20], and six otherwise healthy patients requiring minor surgery in the OT) received MSUN. In 12 of the normal subjects electrical stimulation of the ulnar nerve (ESUN) and MSUN were compared and AP twitch tension (Tw AP) and surface electromyogram (EMG) were measured. Close agreement was found between supramaximal Tw AP (median [95% CI] for MSUN 6.3 N [5-7.2 N] and ESUN 6.9 N [5.2-7.8 N] [p = NS]). Median (95% CI) values with MSUN for the 20 young and 12 elderly control subjects were 6.9 N (5. 3-7.4 N) and 7.1 N (4.4-9.8 N). Median (95% CI) Tw AP for the ICU group was 4.2 (2.2-6.7 N) and for the OT group was 5.8 (4-9.1 N). Tw AP was significantly reduced in ICU patients compared with age-matched controls (p = 0.01). MSUN can be used to measure neuromuscular function in both the laboratory and clinical settings including the ICU.
    American Journal of Respiratory and Critical Care Medicine 08/2000; 162(1):240-5. · 11.04 Impact Factor
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    ABSTRACT: The function of the diaphragm and other respiratory muscles during exercise in chronic obstructive pulmonary disease (COPD) remains controversial and few data exist regarding respiratory muscle pressure generation in this situation. The inspiratory pressure/time products of the oesophageal and transdiaphragmatic pressure, and the expiratory gastric pressure/time product during exhaustive treadmill walking in 12 patients with severe COPD are reported. The effect of noninvasive positive pressure ventilation during treadmill exercise was also examined in a subgroup of patients (n=6). During free walking, the inspiratory pressure/time products rose early in the walk and then remained level until the patients were forced to stop because of intolerable dyspnoea. In contrast, the expiratory gastric pressure/time product increased progressively throughout the walk. When patients walked the same distance assisted by noninvasive positive pressure ventilation, a substantial reduction was observed in the inspiratory and expiratory pressure/time products throughout the walk. When patients walked with positive pressure ventilation for as long as they could, the pressure/time products observed at exercise cessation were lower than those observed during exercise cessation after free walking. It is concluded that, in severe chronic obstructive pulmonary disease, inspiratory muscle pressure generation does not increase to meet the demands imposed by exhaustive exercise, whereas expiratory muscle pressure generation rises progressively. Inspiratory pressure support was shown to substantially unload all components of the respiratory muscle pump.
    European Respiratory Journal 05/2000; 15(4):649-55. · 6.36 Impact Factor
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    Critical Care 01/2000; 3:1-1. · 4.93 Impact Factor
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    ABSTRACT: The effect of Cushing's syndrome on respiratory muscle strength is unknown. Therefore, we studied 10 consecutive patients with severe Cushing's syndrome. The respiratory muscles were assessed using maximal inspiratory and expiratory mouth pressures (MIP, MEP), maximal sniff transdiaphragmatic pressures (max sniff Pdi), and maximal sniff esophageal pressures (max sniff Pes). Maximal quadricep strength was also assessed. The patients demonstrated an overall mean MIP 92 cm H(2)O, SD 19 (mean 105% of predicted; SD, 23%), mean MEP 134 cm H(2)O, SD 35 (mean 99% of predicted; SD, 25%), mean max sniff Pdi 107 cm H(2)O, SD 12 (mean 78% of predicted; SD, 10%) and mean max sniff Pes of 92 cm H(2)O, SD 11 (mean 92% of predicted; SD, 11%). Quadriceps muscle strength was reduced in all 10 patients: mean 26 kg, SD 9 (mean 49% of predicted strength, SD 21%). Respiratory muscle weakness was not found, despite the presence of severe quadriceps impairment. We conclude that major weakness of the respiratory muscles is not usual in Cushing's syndrome.
    American Journal of Respiratory and Critical Care Medicine 12/1999; 160(5 Pt 1):1762-5. · 11.04 Impact Factor
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    ABSTRACT: Functional magnetic stimulation (FMS) of the thoracic nerve roots to simulate cough has been suggested as a treatment approach in patients unable to voluntarily activate the abdominal muscles. However, factors that could influence the efficacy of FMS in clinical use have not been evaluated. In the present investigation we studied train length, posture, and frequency to determine the optimal stimulation protocol. We also evaluated the use of a valve at the mouth to enhance glottic function and investigated whether lung volume at the time of stimulation would influence the tension generated by the abdominal muscles. Studies were performed using a Magstim rapid stimulator augmented by four booster packs in nine healthy subjects; we measured the change in gastric (DeltaPga(FMS)), esophageal (DeltaPes(FMS)), and mouth pressure and expiratory flow. With our apparatus pressure generation was maximized by having a train length of at least 300 ms and a frequency of 25 Hz. Posture and valve use were not important determinants of DeltaPga(FMS) or DeltaPes(FMS). Lung volume exerted only a minor influence on DeltaPga(FMS), but the ratio DeltaPes(FMS):DeltaPga(FMS) was increased at TLC compared with FRC. Expiratory flow was increased by adopting a seated posture and using an occlusion valve with an opening threshold close to the maximum DeltaPes(FMS) generated by the stimulus train; however, expiratory flow was susceptible to interference from glottic incoordination. Representative results (with train length 600 ms, 25 Hz, and 100% power, seated) were mean DeltaPga(FMS), 166 cm H(2)O; mean DeltaPes(FMS), 108 cm H(2)O; and mean expiratory flow, 311 L/min. We confirm that FMS of the abdominal muscles can generate a substantial positive intra-abdominal and intrathoracic pressure and, consequently, expiratory flow in normal subjects.
    American Journal of Respiratory and Critical Care Medicine 09/1999; 160(2):513-22. · 11.04 Impact Factor
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    ABSTRACT: Reduced respiratory muscle strength has been reported in chronic heart failure (CHF) in several studies. The data supporting this conclusion come almost exclusively from static inspiratory and expiratory mouth pressure maneuvers (MIP, MEP), which many subjects find difficult to perform. We therefore performed a study using measurements that are less dependent on patient aptitude and also provide specific data on diaphragm strength. In 20 male patients and 15 control subjects we measured MIP and MEP as well as esophageal and transdiaphragmatic pressure during maximal sniffs (Sn Pes, Sn Pdi) and cervical magnetic phrenic nerve stimulation (Tw Pdi). In a subgroup the response to paired phrenic nerve stimulation (pTw Pdi) at interpulse intervals from 10 to 200 ms (5 to 100 Hz) was also determined. As expected, MIP was significantly reduced in the CHF group (CHF, 69.5 cm H(2)O; control, 96.7 cm H(2)O; p = 0.01), but differences were much less marked for Sn Pes (CHF, 95.2 cm H(2)O; control, 104.8 cm H(2)O; p = 0.20) and MEP (CHF, 109.1 cm H(2)O; control, 135.7 cm H(2)O; p = 0.09). Diaphragm strength was significantly reduced (Sn Pdi: CHF, 123.8 cm H(2)O; control 143.5 cm H(2)O; p = 0.04. Tw Pdi: CHF, 21.4 cm H(2)O; control, 28.5 cm H(2)O; p = 0.0005). Paired phrenic nerve stimulation suggested a trend to increased twitch summation at 5 to 20 Hz in CHF, although this did not reach significance. We conclude that mild reduction in diaphragm strength occurs in CHF, possibly because of an increased proportion of slow fibers, but overall strength of the respiratory muscles remains well preserved.
    American Journal of Respiratory and Critical Care Medicine 09/1999; 160(2):529-34. · 11.04 Impact Factor
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    ABSTRACT: The purpose of this study was to establish the phrenic nerve conduction time (PNCT) for magnetic stimulation and further assess the relatively new technique of anterior unilateral magnetic stimulation (UMS) of the phrenic nerves in evaluating the diaphragm electromyogram (EMG). An oesophageal electrode was used to record the diaphragm compound muscle action potential (CMAP) elicited by supramaximal percutaneous electrical phrenic nerve stimulation (ES) and UMS from eight normal subjects. The oesophageal electrode used for recording the CMAP was positioned at the level of the hiatus and 3 cm below. The diaphragm CMAP was also recorded from chest wall surface electrodes in five subjects. All of the phrenic nerves could be maximally stimulated with UMS. A clear plateau of the amplitude of the CMAP was achieved for the right and left phrenic nerves. The mean amplitudes of the CMAP recorded from the oesophageal electrode were, for the right side, 0.74+/-0.29 mV (mean+SD) for ES and 0.76+/-0.30 mV for UMS with maximal power output, and for the left side 0.88+/-0.33 mV for ES and 0.80+/-0.24 mV for UMS. PNCT measured by the oesophageal electrode with ES and UMS with maximal output were, for the right side, 7.0+/-0.8 ms and 6.9+/-0.8 ms, respectively, and for the left side 7.8+/-1.2 ms and 7.7+/-1.3 ms, respectively. However, the CMAP recorded from chest wall surface electrodes with UMS was unsuitable for the measurement of PNCT. The results suggest that unilateral magnetic stimulation of the phrenic nerves combined with an oesophageal electrode can be used to assess diaphragmatic electrical activity and measure the phrenic nerve conduction time.
    European Respiratory Journal 03/1999; 13(2):385-90. · 6.36 Impact Factor
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    ABSTRACT: Diaphragm paralysis is a recognized complication of neuralgic amyotrophy that causes severe dyspnoea. Although recovery of strength in the arm muscles, when affected, is common, there are little data on recovery of diaphragm function. This study, therefore, re-assessed diaphragm strength in cases of bilateral diaphragm paralysis due to neuralgic amyotrophy that had previously been diagnosed at the authors institutions. Fourteen patients were recalled between 2 and 11 yrs after the original diagnosis. Respiratory muscle and diaphragm strength were measured by volitional manoeuvres as maximal inspiratory pressure and sniff transdiaphragmatic pressure. Cervical magnetic phrenic nerve stimulation was used to give a nonvolitional measure of diaphragm strength: twitch transdiaphragmatic pressure. Only two patients remained severely breathless. Ten of the 14 patients had evidence of some recovery of diaphragm strength, in seven cases to within 50% of the lower limit of normal. The rate of recovery was variable: one patient had some recovery after 2 yrs, and the rest took 3 yrs or more. In conclusion, in most patients with diaphragm paralysis due to neuralgic amyotrophy, some recovery of the diaphragm strength occurs, but the rate of recovery may be slow.
    European Respiratory Journal 03/1999; 13(2):379-84. · 6.36 Impact Factor
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    ABSTRACT: The purpose of this study was to establish the phrenic nerve conduction time (PNCT) for magnetic stimulation and further assess the relatively new technique of anterior unilateral magnetic stimulation (UMS) of the phrenic nerves in evaluating the diaphragm electromyogram (EMG).An oesophageal electrode was used to record the diaphragm compound muscle action potential (CMAP) elicited by supramaximal percutaneous electrical phrenic nerve stimulation (ES) and UMS from eight normal subjects. The oesophageal electrode used for recording the CMAP was positioned at the level of the hiatus and 3 cm below. The diaphragm CMAP was also recorded from chest wall surface electrodes in five subjects.All of the phrenic nerves could be maximally stimulated with UMS. A clear plateau of the amplitude of the CMAP was achieved for the right and left phrenic nerves. The mean amplitudes of the CMAP recorded from the oesophageal electrode were, for the right side, 0.74±0.29 mV (mean±sd) for ES and 0.76±0.30 mV for UMS with maximal power output, and for the left side 0.88±0.33 mV for ES and 0.80±0.24 mV for UMS. PNCT measured by the oesophageal electrode with ES and UMS with maximal output were, for the right side, 7.0±0.8 ms and 6.9±0.8 ms, respectively, and for the left side 7.8±1.2 ms and 7.7±1.3 ms, respectively. However, the CMAP recorded from chest wall surface electrodes with UMS was unsuitable for the measurement of PNCT.The results suggest that unilateral magnetic stimulation of the phrenic nerves combined with an oesophageal electrode can be used to assess diaphragmatic electrical activity and measure the phrenic nerve conduction time.
    European Respiratory Journal 01/1999; 13(2):385 - 390. · 6.36 Impact Factor
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    ABSTRACT: The purpose of the study was to compare electrical stimulation (ES) and cervical magnetic stimulation (CMS) of the phrenic nerves for the measurement of the diaphragm compound muscle action potential (CMAP) and phrenic nerve conduction time. A specially designed esophageal catheter with three pairs of electrodes was used, with control of electrode positioning in 10 normal subjects. Pair A and pair B were close to the diaphragm (pair A lower than pair B); pair C was positioned 10 cm above the diaphragm to detect the electromyogram from extradiaphragmatic muscles. Electromyograms were also recorded from upper and lower chest wall surface electrodes. The shape of the CMAP measured with CMS (CMS-CMAP) usually differed from that of the CMAP measured with ES (ES-CMAP). Moreover, the latency of the CMS-CMAP from pair B (5.3 +/- 0.4 ms) was significantly shorter than that from pair A (7.1 +/- 0.7 ms). The amplitude of the CMS-CMAP (1.00 +/- 0.15 mV) was much higher than that of ES-CMAP (0.26 +/- 0.15 mV) when recorded from pair C. Good-quality CMS-CMAPs could be recorded in some subjects from an electrode positioned very low in the esophagus. The differences between ES-CMAP and CMS-CMAP recorded either from esophageal or chest wall electrodes make CMS unreliable for the measurement of phrenic nerve conduction time.
    Journal of Applied Physiology 01/1999; 85(6):2089-99. · 3.48 Impact Factor

Publication Stats

2k Citations
704.48 Total Impact Points

Institutions

  • 2011
    • Royal Brompton and Harefield NHS Foundation Trust
      • Respiratory Medicine
      Harefield, England, United Kingdom
  • 2001
    • ICL
      Londinium, England, United Kingdom
  • 1985–2001
    • King's College London
      • Division of Asthma, Allergy and Lung Biology
      Londinium, England, United Kingdom
  • 2000
    • The Bracton Centre, Oxleas NHS Trust
      Дартфорде, England, United Kingdom
  • 1998–2000
    • Sahlgrenska University Hospital
      Goeteborg, Västra Götaland, Sweden
  • 1997–2000
    • The Kings College
      Alabama, United States
  • 1991–1998
    • National Heart, Lung, and Blood Institute
      Maryland, United States
  • 1996
    • Kingston College United Kingdom
      Londinium, England, United Kingdom
  • 1995
    • Royal Society of Medicine
      Londinium, England, United Kingdom
  • 1993
    • The Heart Lung Center
      Londinium, England, United Kingdom