Selected articles from ATS - 2003,2002,2001 - American Thoracic Society

1) Effect Of Deflazacort On Pulmonary Function In Duchenne Muscular Dystrophy

Daigneault, P., Lapierre, G., Laberge, S., Vanasse, M. Service de pneumologie pdiatrique, Hopital Sainte Justine, Universit de Montral, Montral, Qubec, Canada.

RATIONALE: Duchenne muscular dystrophy (DMD) is an X-linked disorder presenting as a progressive deterioration of muscular function in young boys. Treatment is mostly supportive. Corticosteroids may help slow the progression of the disease. In previous studies, deflazacort has shown limited side effects compared to prednisone and has been used in our clinic for almost a decade. METHODS: Deflazacort was offered to patients when functional losses became apparent, usually between 6 and 9 years of age. We reviewed all patient files from our DMD clinic. 38 patients had been treated for at least one year and before loss of ambulation. All other patients (33) with enough clinical information were used as a control group. Studied variables included ability to walk, muscle strength, pulmonary function tests, presence of scoliosis, weight and height. RESULTS: Treated patients walk at a later age (p<.05). Measured strength, percent predicted forced vital capacity, inspiratory and expiratory strengths are all significantly greater in treated patients (p<.05). Incidence of scoliosis is reduced in treated patients (0%) vs untreated patients (73%). Treated boys are shorter on average, but weight for height remains unchanged. CONCLUSIONS: Deflazacort is able to delay the deterioration of lung function, prevent scoliosis, and delay loss of ambulation in patients with DMD.

2) Sleep Related Breathing Disorder in Duchenne Muscular Dystrophy

D.M. Cooper, S. Suresh, P. Wales, M. Harris. Mater Children's Hospital, Brisbane, Queensland, Australia

Duchenne muscular dystrophy is a progressive neuromuscular disease with death occurring secondary to respiratory failure. Sleep hypoventilation occurs as one of the early signs of respiratory failure.
Aim: To study the presentation of sleep related disorders in patients with Duchenne muscular dystrophy.
Method: Retrospective review of patients with Duchenne muscular dystrophy attending a tertiary paediatric sleep clinic over a 5-year period. Symptoms reported, lung function and polysomnographic indices were reviewed.
Results: Total of 34 patients with Duchenne muscular dystrophy attended our sleep clinic. Age of referral varied from 1-15years(Median 10). 20 (60%) of them reported sleep symptoms. FVC was 15-103% predicted (Median 58%). 32 progressed to have polysomnography of which 16 were normal studies. 9 had obstructive sleep apnoea(Median age 8 years). These patients subsequently had adenotonsillectomy. 7 showed varying degrees of hypoventilation/respiratory failure and non-invasive ventilation(NIV) was offered. The median FVC and age for this group were 27% and 13 years. Post NIV there was significant improvement in Respiratory disturbance index [RDI] (p=0.03).
Conclusions: The prevalence of sleep related disorders in DMD is significant. There is a bimodal presentation with obstructive sleep apnoea occurring at an earlier age and central hypoventilation occurring at the beginning of the second decade. Our group had OSAS in 23 % of patients. In patients with early stages of respiratory failure assessment with polysomnography helped in identifying sleep hypoventilation and initiating NIV. NIV is well tolerated and results in improvement of polysomnographic indices and symptoms.

4) Contribution Of Neuronal NO Synthase (NOS1) To FeNO Evidence: From Duchenne Muscular Dystrophy

H. Grasemann, F. Ratjen, H. Amthor, T. Voit, V. Straub. Children's Hospital, University of Essen, Essen, Germany

Exhaled nitric oxide (F_ENO) is increased in asthma and may reflect disease activity. However, little is known about the exact molecular and cellular source of F_ENO. There is recent evidence from genetic studies in asthma that NOS1 may contribute substantially to F_ENO (Wechsler et al, AJRCCM 2000). NOS1 protein is targeted to the surface membrane by binding to dystrophin. The absence of dystrophin in Duchenne muscular dystrophy (DMD) is accompanied by a loss of NOS1 from the sarcolemma. The aim of our study was to test whether the loss of NOS1 expression in DMD would be reflected in F_ENO. Thirteen male DMD patients (6 - 23 years of age) were compared to eleven healthy, non-smoking non-asthmatic male controls (7 - 24 years). Mean (+ SEM) F_ENO was significantly (p < 0.02) lower in DMD than in controls (7.5 + 1.4 ppb vs. 16.6 + 3.2 ppb). Low F_ENO did not result from decreased (54.4 + 5.1 % predicted) forced vital capacity (FVC) in DMD patients since restriction of FVC to 62.5 + 1.1 % of predicted normal values in five healthy subjects did not effect F_ENO. This is the first study to show that F_ENO is decreased in DMD. These findings provide further evidence that NOS1 contributes significantly to airway NO concentrations.

5) Monitoring of Diaphragm Electrical Activity and Pressure in Advanced Duchenne Muscular Dystrophy

J.C. Beck, J. Weinberg, C.H. Hamnegrd, J. Olofson, G. Grimby, C. Sinderby. Department of Pediatrics, University of Montreal, Montreal, QC, Canada; Department of Neurology, Huddinge Hospital, Huddinge, Sweden; Department of Medicine, Gteborg University, Gteborg, Sweden; Department of Rehabilitation Medicine, Gteborg University, Gteborg, Sweden; Department of Medicine, University of Montreal, Montreal, QC, Canada

Due to the impaired transformations of neural respiratory activity into pressure, neural activity goes up with inspiratory muscle weakness. It is likely that in neuromuscular disorders, diaphragm pressure generation is diminished before its electrical activity (the latter representing neural activation). In order to test this hypothesis, eight patients with advanced respiratory muscle paralysis due to Duchenne Muscular Dystrophy (DMD), age 25.3 +2.2 years and vital capacity 0.4 +0.2 L, were studied during tidal breathing, maximal inspirations, maximal sniff inhalations, and cervical electromagnetically evoked diaphragm contractions. All patients but two were prescribed home mechanical ventilation (5 non-invasive and 1 tracheostomy). Transdiaphragmatic pressure (Pdi) and diaphragm electrical activity (EAdi) were measured using an esophageal catheter. Flow was also measured. During tidal breathing (tidal volume 0.20 +0.08 L, breathing frequency 25 +7, inspiratory EAdi was clearly detectable and was 12 +7 times the noise fluctuations, and represented 45 +19 % of the maximum EAdi. Mean inspiratory and sniff Pdi"s were 1.5 +1.2 and 7.6 +3.6 cmH2O, respectively (Pdi/Pdimax=18 +13%). Twitch Pdi deflections could not be detected. Twitch latency time was normal (8.2 +1.3 ms). The results of this study show that despite near complete diaphragm paralysis in advanced DMD, it is still feasible to monitor diaphragm electrical activity with an esophageal electrode array. This may open future possiblitity for long-term evaluation and neural control of mechanical ventilation in these patients.

6) Prognosis of Duchenne Muscular Dystrophy: A Decade of Mechanical Ventilation

F. Yasuma, M. Sakai, M. Konagaya, T. Kawamura. Suzuka National Hospital, Suzuka, Mie Pref., Japan; Kyoto University, Kyoto, Kyoto, Japan

[Objectives] We retrospectively analyzed the survival rate of 141 inpatients with Duchenne Muscular Dystrophy (DMD) to estimate the factors affecting their prognosis.
[Methods] The subjects were 141 Japanese inpatients with DMD (all males), who had been chronically hospitalized during the recent 23 years from 1980 to 2002. The survival rate was calculated with the Kaplan-Meier method, and the Log-Rank method was used to compare the survival rate between the subgroups younger and older than 10.6 years of age on entry (midpoint; ranging from 4.5 to 24.0), the entries before and after 1981/4/6 (midpoint; ranging from 1965/11/5 to 2000/3/29), and the subgroups treated with and without mechanical ventilation (MV). The Cox proportional-hazard regression model was used to identify independent predictors influencing the survival rate.
[Results] Ninety five patients had been dead and forty-six were alive at the end point. Although 54 patients were treated with MV and nine of them were tracheostomized, none of the rest of 87 patients was treated with MV or tracheostomy. In comparison between the subgroups, the significant differences were found in the date of entry (p=0.025) and the use of IPPV (p<0.001), but not in the age on entry (p=0.20). In the multiple regression analysis, the significant negative correlation between the survival rate and age of entry (p=0.034) and the significant positive correlation between the survival rate and use of MV (p<0.001) were found, however, the negative correlation between the survival rate and date of entry was not significant (p=0.375). Hence, the entry at younger age and MV significantly affected the prognosis.
[Conclusion] We conclude, as in the primary evidence, that the recent improved prognosis in DMD has been attributable to MV.

7) Longitudinal Modeling Of Lung Function In Duchenne's Muscular Dystrophy (DMD)

R G Norman ^1,2, M A Scott ², I N Cabrera ³, K Axen ³, F Haas ¹, K I Berger ¹. Depts of ¹Pulm/Crit Care Med & ³Rehab Med, NYU Med School, ²NYU Steinhardt School of Ed.

Longitudinal modeling of lung function in DMD is complicated by a mixture of both growth and decline in lung function within each subject and an unknown point of separation between these phases (change point). Linear mixed effects (LME) models can be used assuming a fixed change point for all cases, however, this assumption may be incorrect. This abstract describes an extension of linear mixed effects modeling in which random change points are integrated into the model as parameters and estimated using an EM algorithm.
METHODS: Data from pulmonary function tests performed during routine medical care in 56 patients with DMD were collected from medical records. From 1 to 24 (median = 6) tests were performed on each subject over ages ranging from 5 to 39. A standard LME model incorporating age and height terms was extended to include model parameters for possible change point values (ages 12, 14 and 16). LME models were fit using the NLME library in S plus. The new random change point model was implemented with a generalized EM algorithm using custom code. The goodness of fit of the new model was compared to fixed change point LME models using the -2 log likelihood criterion.
RESULTS: The random change point model provided a better fit (-2LL =110.6) than fixed change points of 12 (-2LL=143.4), 14 (-2LL=114.7) or 16 (-2LL=152.9). The model indicates an average increase of 0.09 liters/year during the growth phase and a decline of .13 liters/year following the change point. Height was not significant in any model, once all of the other controls and random effects were in place. The distribution of change points is 27.8% for age 12, 61.2% for age 14 and 11.0% for age 16.
CONCLUSIONS: The technique described allows for estimation of lung function during both growth and decline with simultaneous estimation of the change point between these phases. Model fit is better than other standard techniques and does not require the assumption of a fixed change point. This model can be used as a prognostic indicator in DMD.

8) Forced Oscillatory (IOS) Assessment of Pulmonary Function and Bronchodilator Response in Children with Neuromuscular Disorders

G.D. Sharma, M. Cooper, H. Arora, L.A. Lester, M.D. Goldman. Rush-Presbyterian-St.Luke Medical Center, Chicago, IL; Univ.of California Los Angeles, Los Angeles, CA

Children with neuromuscular disorders (NMD) associated weakness can develop reactive airway disease secondary to aspiration and gastro-esophageal reflux. These patients are often unable to perform spirometry maneuver due to inadequate effort and inability to perform forced and prolonged exhalation. We used the Impulse Oscillation System (IOS, Jaeger) to measure pulmonary function and response to beta2-agonist bronchodilator (BD) in 5 children (age 6-14 yrs) with NMD. Clinical diagnoses included spinal muscular atrophy, Duchenne muscular dystrophy, and myotonic dystrophy. All children had clinical history suggestive of dysphagia and/reflux and had signs and symptoms suggestive of reactive airway disease. We also assessed 9 asthmatic children (age 3-10 yrs) who were unable to perform spirometry. All children underwent IOS testing (triplicate tests of 20-30 sec duration) before and after a dose of nebulized BD. Measurements included resistance at 5-35 Hz, integrated low frequency reactance (AX) between 5 hz and resonant frequency (Fres). In NMD patients, mean values for pre-bronchodilator AX, resistance at 5Hz, resistance at 20Hz, were 16.41, 7.07, 5.32 cm H20/l/s and corresponding figures for post-bronchodilator were 8.73, 6.06, and 4.54 (p 0.068, n=5). Similar results for asthmatic children showed a significant change after bronchodilator (p< 0.05). This technique allows determination of bronchodilator responsiveness in children unable to perform spirometry and has potential usefulness in assessment of NMD in whom an unexpected airway obstruction and reversibility was observed.

9) Effect of a Specific Respiratory Muscle Training in mdx Mouse on Function and Proteins Structure of the Diaphragm

S. Matecki, F. Rivier, G. Hugon, G. Gayraud, A. Michel, C. Prefaut, D. Mornet, M. Ramonatxo. Laboratoire de Physiologie des Interactions, Service Central de Physiologie Clinique, Hpital Arnaud de Villeneuveve, Montpellier, France; Unite de Recherche UI28, IFR 24, Groupe Muscles et Pathologies, Institut-Bouisson-Bertrand, Montpellier, France; Unite U454, Laboratoire de Pharmacologie, Facult de Pharmacie, Montpellier, France

The cellular mechanisms induced by a beneficial respiratory muscle training in children with Duchenne Muscular Dystrophy (DMD) are unknown. The aim of this study was thus to investigate the functional effect induced by a specific respiratory muscle training in mdx mouse diaphragm. In 10 mdx mouse, we reproduced by hypercapnic stimulation of ventilation (8% CO2), during 6 weeks/ 30 min per day, a specific respiratory muscle training. 10 mdx mice served as controls. Diaphragmatic force frequency relationships showed that this specific respiratory training improves the tetanic force production of the diaphragm (8.0 + 0.5 N/cm2 in the control group and 9.5 + 0.7 N/cm2 in the training group at 120 Hz) but not endurance. We found no difference between the groups in diaphragm muscular fiber type and in citrate synthase activity. Western blot analysis of diaphragm showed: 1) an over-expression of alpha-dystrobrevin in training group compared to control group (8100+710 versus 6100+520 arbitrary units, p<0.01) and a decrease in utrophin expression in training group compared to control group (2100+320 versus 3100+125 arbitrary units, p<0.05). In conclusion, The overexpression of alpha-dystrobrevin which seems have more a signalling than a mechanical role in muscle could be interpreted as an important pathway to improve muscular function and could be seen as a possible way for therapeutic intervention in patient with DMD.

10) A Randomised Controlled Comparison Of Cough Inexsufflation (MI-E), Non-Invasive Ventilation (NIV), And Physiotherapy Assistance (PAC) On Peak Cough Flow (PCF) In Children And Adolescents With Neuromuscular Disease

M CHATWIN, E ROSS, A H NICKOL, M I POLKEY & A K SIMONDS. Sleep and Ventilation Dept, Royal Brompton and Harefield NHS Trust, London, UK

Recurrent chest infections are a major cause of morbidity and mortality in patients with neuromuscular disease (NMD). Both inspiratory and expiratory muscle weakness can produce a decrease in PCF. Subjects 10 patients age range 10-17 (median 14) years; diagnoses included: spinal muscular atrophy, Duchenne and congenital muscular dystrophy. The following indices of respiratory muscle strength were assessed: sniff nasal inspiratory pressure (SNIP) (meanSD, cmH₂O) 2613, PI_max 2214, whistle mouth pressure (P_mow) 1910, PE_max 1911 and PCF of 13253L/min in patients and 10 age matched controls; SNIP 9717, PI_max 10330, P_mow 11538, PE_max 9738 and a PCF of and 534128L/min. Methods The MI-E (JH Emerson Co) was compared to traditional methods of cough enhancement: PAC and NIV assisted cough. PCF was measured using a pneumotachograph attached to a full-facemask. Subjects performed an unassisted cough (UAC) and the following in a random order: PAC; NIV; MI-E and exsufflation alone (E) assisted coughs. Results See graph for patient group. All interventions improved PCF and were well tolerated. There was a significant increase in PCF in both the patient and control Groups, with E and MI-E (*P<0.01). Conclusion The greatest PCF was achieved with a combination of insufflation-exsufflation.

11) A Randomised Controlled Comparison Of Cough Inexsufflation (MI-E), Non-Invasive Ventilation (NIV), And Physiotherapy Assistance (PAC) On Peak Cough Flow (PCF) In Adults With Neuromuscular Disease (NMD)

M CHATWIN, A H NICKOL, E ROSS, N MUSTFA, M I POLKEY & A K SIMONDS Sleep and Ventilation Department, Royal Brompton Hospital, and Respiratory Muscle Laboratory, Kings College Hospital, London, UK

Recurrent chest infections are a major cause of morbidity and mortality in patients with NMD. Both inspiratory and expiratory muscle weakness can produce a decrease in PCF. Subjects 14 patients age range 18-56 (median 27) years; diagnoses included: spinal muscular atrophy, Duchenne and congenital muscular dystrophy. The following indices of respiratory muscle strength were assessed: sniff nasal inspiratory pressure (SNIP) (meanSD cmH₂O) 2419, PI_max 2518, whistle mouth pressure (P_mow) 1915, PE_max 2016 and PCF of 15472L/min in patients and 11 aged matched controls: SNIP 9229, PI_max 10333, P_mow 14551, PE_max 121 39 and a PCF of and 631139L/min. Methods The MI-E (JH Emerson Co) was compared to traditional methods of cough enhancement; PAC and NIV assisted cough. PCF was measured using a pneumotachograph attached to a full-facemask. Subjects performed an unassisted cough (UAC) and the following in a random order: PAC; NIV; MI-E and Results See graph for patient results. There was a significant increase E and MI-E (*P<0.01), but no change in PCF in the control group. Conclusion The greatest increase in PCF was achieved with a combination of insufflation and exsufflation.

12) Use Of The Mechanical In/Exsufflator (MIE) In Pediatric Patients With Neuromuscular Disease And Impaired Cough

L.J. Miske, E. Hickey, S. Kolb, H.B. Panitch, Philadelphia, PA

Impaired cough secondary to neuromuscular disease (NMD) can cause serious respiratory complications including atelectasis, pneumonia, small airway obstruction and acidosis. These problems can be avoided by the use of the MIE, a device that delivers a positive pressure insufflation followed by an expulsive exsufflation, thereby simulating a normal cough. Use of the MIE in adults with impaired cough results in improved cough flows and enhanced airway clearance. There are, however, no reports of use of the MIE in children. We retrospectively reviewed the medical records of 42 patients (25 males) with NMD and impaired cough in whom MIE was initiated to determine its safety, tolerance and effectiveness. The median age at initiation of MIE use was 16.2 yrs (range: 3 mos to 28.7 yrs). Diagnoses included: Duchenne Muscular Dystrophy (DMD) (n=15), Spinal Muscular Atrophy (n=14), Myopathy (n=8), Other NMD (n=5). Mechanical ventilation via tracheostomy was used by 22 patients, 18 received non-invasive ventilatory support and 2 required no ventilatory support. Appropriate inspiratory and expiratory pressures were determined clinically in the Pulmonary Function Laboratory or hospital. Duration of use was 11.6 ± 9.5 (range 0-39) mos. One infant died from her disease before using it at home. Four patients chose not to continue with MIE: 2 felt it was ineffective and 2 preferred other devices. Two others reported complications: 1 with DMD developed PVC's during MIE use, and one parent felt her infant with SMA did worse. Chronic atelectasis resolved in 4 patients after beginning MIE and 4 patients have experienced a reduction in frequency of pneumonias. We conclude that in 85% of our population the use of a MIE was safe, tolerated and effective in preventing long term pulmonary complications

13) Ventilatory Responses To Hypercapnia In mdx Adult Mice

S. Matecki, A. Michel, S. Jaber, C. Prefaut, M. Ramonatxo, Montpellier, France

Nightly hypoventilation with hypercapnia and hypoxemia are characteristics periodically observed in Duchenne muscular dystrophy (DMD). This ventilatory control alteration may be due to the lack of dystrophin.
To investigate the role of dystrophin in the ventilatory response, we analyzed the magnitude and pattern of breathing responses to hypercapnia (8% CO₂, 21% O₂, 71% N₂) in adult mdx mice and their wild-type littermates (C57). Ventilation, breath duration, and tidal volume were measured using whole-body plethysmography. We did not find significant difference between mdx and C57 mice in breathing frequency (325 ± 63 versus 320 ± 49 cycles per minute), tidal volume (25,9 ± 6 versus 25 ± 5 l/g) and minute ventilation (8.5 ± 3 versus 8.0 ± 1.8 ml/g/min). However, in mdx mice, mean inspiratory to total time of the respiratory cycle (Ti/Ttot) was significantly weaker (0.43 ± 0.03 versus 0.54 ± 0.02).
In conclusion, as minute ventilation was the same in the two groups, differences observed in response to hypercapnic stimulus, seem more an adaptation of ventilatory control secondary to respiratory muscle weakness than an alteration of ventilatory control. Moreover, this hypercapnic stimulus could therefore be useful for evaluating the effects of specific respiratory training of respiratory muscle of mdx mice by hyperventilation as recommended in DMD children.

14) Increased Stiffness In Diaphragm And Bicepsfemoris Muscles Of Young -Sarcoglycan Deficient Mice

Nisha Patel ¹, Suneal R. Jannapureddy ¹, Imran Chaudhry ¹, Michael Lopez, Eva Engvall ², and Aladin M. Boriek ¹. Department of Medicine ¹, Baylor College of Medicine, Houston, TX 77030. Burnham Institute ², La Jolla, CA 92037.

Alpha-sarcoglycan (SG) is a transmembrane protein of the dystrophin- associated complex. Absence of SG causes a form of limb-girdle muscular dystrophy. We hypothesized that SG contributes to force transmission in muscles. We used bicepsfemoris and diaphragm muscles of 8 normal mice (weight: 23.6 7.2 g; age: 43.5 15.9 days old) and 7 SG deficient mice (weight: 17.8 2.6 g; age: 32.3 2.4 days old). After anesthetizing the mouse, either the diaphragm or bicepsfemoris muscle was excised and submerged in Krebs-Ringer solution bubbled with 95% O₂ - 5% CO₂. Length-tension relationships along and transverse to muscle fibers were determined by passively lengthening and shortening the muscle in the direction of the muscle fibers (AF) as well as transverse to the fibers (TF) in an in-vitro biaxial apparatus. At a tension of 5 g/cm, the extensibility ratios () in the bicepsfemoris of the control mice were greater than SG deficient mice (+/+ AF = 1.17 0.13, -/- AF = 1.12 0.09; +/+ TF = 1.16 0.12, -/- TF = 1.12 0.05; p < .05). Similarly, in the diaphragm, was greater in control mice compared to knockouts (+/+ AF = 1.45 0.14, -/- AF = 1.21 0.07; +/+ TF = 1.15 0.17, -/- TF = 1.10 0.09; p < .05). During biaxial loading of the diaphragm, controls were more extensible than SG null mice (+/+ BA = 1.40 0.17, -/- BA = 1.15 0.12; p < .05). These data suggest increased muscle stiffness in these SG deficient mice.

15) Presentation Of Respiratory Failure In Neuromuscular Disease Children

S. Sritippayawan, S. Kun, T.G. Keens, S.L. Davidson Ward, Los Angeles, CA

Ideally, home mechanical ventilation (HMV) should be initiated non-emergently in children with progressive neuromuscular disease (NMD) and respiratory failure (RF) after discussion of the options with patients/families. However, HMV was emergently initiated in 43/52 (82%) NMD patients with RF without prior discussion of the options with patients/families. Only 9/52 (17%) had HMV initiated non-emergently following such discussion. Were there missed opportunities to discuss the options prior to initiating HMV in the emergent patients? To answer this, we documented the presentation of RF in 52 progressive NMD patients (age between 0-24 yr old; 26% female). The time from onset of weakness to HMV varied from 0 in some of the congenital patients to >10 yrs in Duchenne muscular dystrophy. 24/52 (46%) patients required HMV following RF with pneumonia. Prior to HMV, 11/43 (26%) of the emergent and 5/9 (56%) of the non-emergent group, had PFT done; all were abnormal. Prior to HMV, 9/43 (21%) of the emergent and 7/9 (77%) of the non-emergent group, had PSG done; all but one were abnormal. 27/39 (69%) patients, whose hospitalization data were available, had 1 episode (range: 1-10) of pneumonia prior to HMV. In the emergent group, there were opportunities for discussion of the options prior to HMV in all 43 patients, which could have occurred during 72 hospitalizations for pneumonia, 9 pre-operative evaluations, 32 abnormal PFT, and 15 abnormal PSG. We conclude that most NMD children had HMV emergently initiated after pneumonia with RF without prior discussion with the patients/families. We speculate that opportunities for discussion of the options prior to HMV were missed or ineffective in the emergent HMV group.

18) Isometric Contractile Properties Of Alpha-Sarcoglycan Deficient Diaphragm During Uniaxial And Biaxial Loading

I. Chaudhry, M. Lopez, A. Jain, E. Engvall, A. Boriek, Houston, TX, La Jolla, CA

-sarcoglycan is a transmembrane protein and lack of it causes limb-girdle muscular dystrophy. -sarcoglycan may involve in force transmission from the cytoskeleton to the extracellular matrix. We investigated in vitro contractile properties of the -sarcoglycan-deficient mouse diaphragm. The diaphragm is pressurized in vivo, and we thus quantitatively characterized contractile properties under biaxial loads. METHODS. Muscles from 7 normal 129SV mice (weight: 17.36 ± 4.66 g; age: 30 ± 13 d) and 8 -sarcoglycan-deficient 129SV mice (weight: 17.56 ± 1.66 g; age: 30 ± 11 d) were used. The left costal diaphragm was excised and stimulated at 100 Hz preceded by twitches under the presence of uniaxial, 1 g biaxial and 2 g biaxial loading (BAL) conditions. RESULTS. Muscle stress was depressed in -sarcoglycan-deficient as compared to normal diaphragm at (a) uniaxial load, 41.63±2.02 N/cm² vs. 30.49±1.06 N/cm² (b) 1 g BAL, 46.89±1.62 N/cm² vs. 32.96±1.56 N/cm² (c) 2 g BAL, 44.94±1.71 N/cm² vs. 32.22±1.46 N/cm². Furthermore, transverse stress altered muscle stress in normal mice (uniaxial 41.85±1.71 N/cm² vs. 1 g BAL 47.77±1.45 N/cm²) but the effect was negligible in -sarcoglycan-deficient mice (uniaxial 30.49±1.06 N/cm² vs. 1 g BAL 32.96±1.56 N/cm²). CONCLUSION: Disruption of the sarcoglycan complex causes depression in diaphragm maximal tetanic stress. Furthermore, compared to controls, passive transverse stress did not appear to alter contractile force depression in the -sarcoglycan deficient diaphragm.

19) Non-Invasive Assessment Of Respiratory Muscle Fatigue In Children

L.T. Mulreany, D.J. Weiner, J. McDonough, H.B. Panitch, J.L. Allen, Philadelphia, PA

BACKGROUND. The tension-time index (TTI) is the dimensionless product of (i) the ratio of mean transdiaphragmatic pressure (Pdi) to maximal transdiaphragmatic pressure (Pdi_max) and (ii) the ratio of inspiratory time (TI) to total respiratory cycle time (TTOT). The TTI is one measure of diaphragmatic fatigue. The invasive nature of the test (requiring esophageal and gastric pressure transducers) has limited its usefulness in children. A non-invasive measurement (TTmus), based on mouth occlusion pressure 100 milliseconds after the onset of inspiration (P₁₀₀), extrapolated to mean inspiratory pressure (PI), and maximal inspired pressure measured at the mouth (MIP), has been found to correlate well with the TTI [Ramonatxo, J Appl Physiol. 1995; 78:p646]. This measurement likely reflects fatigue of all inspiratory muscles rather than just the diaphragm. There are, as yet, only limited data using this technique in children. METHODS. We measured lung function and TTmus in 22 children. Subjects were grouped as controls (n=12), having obstructive lung disease (n=8, including CF, bronchiectasis, and asthma), or having restrictive lung diseases (n=2, muscular dystrophy and an unspecified myopathy). Inspiratory flow was occluded for 250 milliseconds with a balloon in the inspiratory limb that was inflated during exhalation. Data were collected for 3 minutes during quiet breathing using a computerized system. TTmus was calculated from P₁₀₀, MIP at functional residual capacity, TI, and TTOT as previously described. RESULTS. TTmus was significantly higher in subjects with restrictive lung disease (TTmus=0.199 ± 0.12, p<0.05 by ANOVA), and was higher in obstructive patients (TTmus=0.122 ± 0.07) than in controls (TTmus=0.067 ± 0.03). Most of the variation of TTmus was due to variation in PI /MIP and not due to variation in TI/TTOT. CONCLUSION. Children with lung diseases, especially restrictive diseases, may be at higher risk for respiratory muscle fatigue which may predispose to respiratory insufficiency. Non-invasive measurement of TTmus may detect early respiratory muscle fatigue. As such, further study is warranted to evaluate the clinical utility of this measurement in children.

20) Regenerative Potential Of Dystrophin-Deficient Muscles With Advanced Disease: Implications For Gene Therapy In The Dystrophic Diaphragm

G.H. Guibinga, S. Ebihara, J. Nalbantoglu, G. Karpati, B.J. Petrof, Montreal, PQ, Canada

Duchenne muscular dystrophy (DMD) and its murine homolog (mdx) are caused by defects in the dystrophin gene. Adenoviral vectors (AdV) represent a potential method for restoring a functional dystrophin gene in this setting. Immature regenerating myofibers are the principal target for AdV in muscle, and this is likely related at least in part to greater expression of the Coxsackie/adenovirus attachment receptor (CAR). However, spontaneous regeneration is reduced in dystrophin-deficient muscles with advanced pathology. Therefore, in the current study we have sought to evaluate the regenerative potential of dystrophin-deficient diaphragm and limb muscles with advanced pathology. First, the soleus muscle of 14-17 mo old mdx mice was injected with notexin, a substance which induces transient necrosis followed by vigorous regeneration in normal muscle. Five days after notexin delivery to mdx mice, marked overexpression of CAR was found, and AdV containing a dystrophin minigene (AdV-Dys) was injected into the regenerating muscle. At 50 days after AdV-Dys delivery, improved force-generating capacity and protection against high-stress lengthening contractions was observed as compared to an untreated muscle. Given the phenotypic resemblance between the diaphragm of adult mdx mice and DMD, we then determined the functional impact of notexin administration on the mdx diaphragm. An effective regenerative response was also observed, as evidenced by widespread embryonic myosin heavy chain staining at day 5 and no functional deficit compared to untreated muscle at 60 days. These results suggest that regeneration can be effectively induced in the dystrophic diaphragm, and this strategy may facilitate molecular therapeutic intervention with adenoyiral vectors in DMD.

21) Response Of Dystrophin-Deficient Skeletal Muscle To Ischemia/Reperfusion-Induced Oxidative Stress

R. W. R. Dudley, W. -K. Cho, S. N. Hussain, S. Mohammed, L. Lands, and B. J. Petrof. Respiratory Division, Royal Victoria Hospital, Meakins-Christie Laboratories, McGill University Health Center, Montreal, Canada.

Mutations in the gene encoding the cytoskeletal protein dystrophin cause Duchenne Muscular Dystrophy (DMD), but the precise mechanism by which lack of dystrophin leads to muscle destruction with attendant respiratory failure remains unresolved. It has been postulated that free radicals may play a role in this process, and displacement of neuronal nitric oxide synthase (nNOS) from the sarcolemma to the cytosol has been implicated. Here we used hindlimb tourniquet application to subject the tibialis anterior (TA) of adult dystrophic (mdx; n=7) and normal control mice (C57B16; n=7) to ischemia-reperfusion (I/R) injury, a model of in vivo oxidative stress. Evans blue dye (EBD), a low molecular weight tracer, was injected i.v. to determine the level of sarcolemmal damage after I/R. Glutathione analysis and immunoblotting for protein carbonyls were used as markers of overall oxidative stress, while 3-nitrotyrosine formation was used as an indicator of nitrosative stress. Within each mouse strain, I/R caused significant increases in EBD uptake and protein carbonyls as well as a significant decrease in total glutathione, but no differences were seen between the mdx and control mice. However, mdx muscles demonstrated increased protein tyrosine nitration after I/R. In particular, a protein band of ~58 kDa showed a 37393% (p<0.05) increase in 3-nitrotyrosine immunoreactivity in mdx, while increasing by only 10313% in controls. Our results suggest that dystrophic muscles of adult mdx mice are not abnormally vulnerable to sarcolemmal injury and certain oxidative modifications following I/R, but do display increased susceptibility to protein tyrosine nitration relative to controls. We speculate that nNOS displacement to the cytosol in mdx muscle may play a role in this enhanced 3-nitrotyrosine formation.

22) Long-Term Effects of Nocturnal Noninvasive Ventilation in Children with Neuromuscular Disorders (NMD)

U. Mellies, R. Ragette, C. Schwake, T. Voit, H. Teschler. University of Essen, Children's Hospital, Essen, Germany; Ruhrlandklinik, Department of Pneumology and Sleep Medicine, Essen, Germany

Objective: Aim of the study was to investigate the long-term impact of nocturnal non-invasive ventilation (NIV) on sleep, sleep disordered breathing (SDB) and respiratory function in children with NMD. Methods: Thirty patients (12.3 4.1 years) with various inherited NMD were treated with NIV for respiratory failure (RF, n=14) or symptomatic SDB (n=16). Patients were prospectively followed over 25.3 12.7 month. In addition 10 succesfully treated patients were studied before and after 3 nights withdrawal from NIV. Results: NIV normalized nocturnal gas exchange in all patients and diurnal gas exchange in patients with RF. The effects persisted long-term: nocturnal transcutaneous PCO2 improved from (baseline vs. latest control) 53.7 9.9 to 41.6 4.8 mmHg, diurnal PaCO2 from 56.4 9.5 to 42.8 2.6mmHg (p <0.001 for all). NIV improved respiratory disturbance index, arousals from sleep, nocturnal heart rate (p <0.01 for all) and sleep architecture (p <0.05). Vital capacity decreased in five adolescents with Duchenne muscular dystrophy -183 111 ml/year but remained stable ( +8 78 ml/year) in 25 children with other conditions. Peak inspiratory pressure increased slightly in all NMD (from 2.5 1.3 to 2.8 1.2 kPa, p <0.05). Three nights withdrawal from NIV resulted in prompt deterioration of SDB and gas exchange back to base-line but could be instantly normalized by resumption of NIV. Conclusion: There is sufficient evidence that NIV has favourable long-term impact on sleep disordered breathing and respiratory function in children with NMD. NIV is indicated in children with symptomatic SDB or respiratory failure.