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PubMed1981

Spectrin extractability from erythrocyte in Duchenne muscular dystrophies and the effect of proteases on erythrocyte ghosts.

We studied the erythrocyte membrane proteins from patients with Duchenne muscular dystrophy (DMD) using SDS-polyacrylamide gel electrophoresis. Our observations were the following: (1) The electrophoretic densitogram of freshly prepared DMD-ghosts was similar to that of controls. After the extraction of spectrin from ghosts with 1 mmol/l EDTA, pH 8.0, the unextractable spectrin remained more firmly bound in the DMD ghost residues than in controls. Extractability of spectrin from DMD ghosts was decreased about 20%. In addition, several minor bands were detected between spectrin and Band 3 in the DMD ghost residues (treated ghosts). (2) Ca2+-activated, neutral protease reacted more effectively with spectrin of DMD ghosts and ATP-depleted ghosts than with that of controls. (3) Erythrocyte actin (Band 5) of DMD ghosts was more fragile than that of controls and of ATP-depleted actin in the EDTA extracts. Gradually, partial degradation of actin was observed for three weeks at 4 degrees C. (4) The intracellular ATP level and the activities of membrane-bound (Mg2+--Ca2+) ATPases in DMD erythrocytes were unchanged. We suggest that spectrin from DMD ghosts as well as actin may be subject to increased degradation.

Actins↗
PubMed2005

Impaired primary hemostasis with normal platelet function in Duchenne muscular dystrophy during highly-invasive spinal surgery.

A defective, normal or enhanced hemostasis has been reported in Duchenne muscular dystrophy (DMD). A retrospective analysis of intra-and postoperative (up to 36 h) estimated blood losses was performed in 156 patients undergoing spinal surgery for: DMD (n = 31), idiopathic scoliosis (IS) (n = 70), poliomyelitis (n = 10), cerebral palsy (CP) (n = 28), spinal muscular atrophy (SMA) (n = 17). Platelet aggregation and bleeding times were also investigated in DMD patients. Immunohistochemistry for dystrophin was performed in platelets, megakaryocytes and blood vessels of normal tissues. DMD patients showed significantly higher intraoperative estimated blood losses (DMD: 3495+/-890 ml; IS: 2269+/-804 ml; poliomyelitis: 2582+/-1252 ml; CP: 2071+/-683 ml; SMA: 2464+/-806 ml; P < 0.05), while postoperative blood losses were similar among different groups. Higher estimated blood losses in DMD were independent of the duration of surgery, body weight, gender, age, vertebral levels or preoperative Cobb angle. DMD children had significantly prolonged bleeding times, but retained normal platelet function. From control samples dystrophin was expressed in vascular smooth muscle cells, but not in platelets. DMD appears to be characterized by immediate bleeding during highly-invasive surgery and increased bleeding time without platelet abnormalities. Considering dystrophin expression in normal vascular smooth muscle cells, these results altogether suggest a selective defect of primary hemostasis in DMD, likely to be due to impaired vessel reactivity.

Adolescent↗
PubMed2006

Scleral buckling surgery after macula-off retinal detachment: worse visual outcome after more than 6 days.

PURPOSE: To determine the effect of duration of macular detachment (DMD) on visual acuity (VA) in patients with macula-off rhegmatogenous retinal detachment (RD). DESIGN: Retrospective observational case series. PARTICIPANTS: Two hundred two consecutive patients (202 eyes) with primary uncomplicated macula-off RD, preoperative VA of 10/100 or worse, a precise history of when macular function was lost, successful reattachment surgery, and a minimal follow-up of 3 months. INTERVENTION: All RDs were repaired with a primary scleral buckling procedure performed by 3 vitreoretinal surgeons. MAIN OUTCOME MEASURE: Visual acuity (best corrected and 3, 6, and 12 months postoperatively). RESULTS: Considering all eyes, the cumulative mean of the best-corrected postoperative VA (logarithm of the minimum angle of resolution [logMAR]) as a function of DMD shows a rapid worsening when DMD exceeds 6 days. Eyes were divided into 3 groups, corresponding to the DMD intervals immediate (within 10 days), delayed (11 days-6 weeks), and late (>6 weeks). Mean postoperative VAs (in logMAR) were 0.35+/-0.31 (between 20/40 and 20/50 Snellen equivalent) in eyes with DMD up to 10 days, 0.48+/-0.26 (20/60 Snellen equivalent) in the delayed group, and 0.86+/-0.30 (8/60 Snellen equivalent) in eyes with DMD longer than 6 weeks. CONCLUSIONS: The cumulative mean of the best-corrected postoperative VA (logMAR) as a function of DMD shows a rapid worsening when DMD exceeds 6 days. Our results indicate that the scleral buckling procedure should be done preferably within a 7-day DMD.

Adult↗
PubMed1992

Cognitive functions in Duchenne muscular dystrophy: a reappraisal and comparison with spinal muscular atrophy.

In order to clarify cognitive functions in Duchenne muscular dystrophy (DMD), we performed a new controlled neuropsychological study. IQ (WISC-R), verbal skills (fluency, confrontation naming and syntax comprehension) and memory abilities (BEM) were studied in two matched groups; 24 DMD children and 17 spinal muscular atrophy (SMA) children aged 12-16 yr. A significant difference appeared between the DMD and SMA patients: only in the DMD group were there significant disabilities in certain specific functions and normal scores in others. Despite similar education, the DMD children more often had significantly greater learning disabilities. There were more DMD left-handers. Verbal IQ was significantly low whereas performance IQ was at a normal level. DMD children also performed poorly in reading tasks and in some memory functions such as story recall and verbal recognition. Specific cognitive disabilities in certain DMD children, not seen in SMA children, suggest a relationship with a DMD genetic disorder.

Adolescent↗
PubMed1983

Defective myoblasts identified in Duchenne muscular dystrophy.

A defect in the proliferative capacity of satellite cells, mononucleated precursors of mature muscle fibers, was found in clonal analyses of cells cultured from Duchenne muscular dystrophy (DMD) patients. The total yield of myoblasts per gram of muscle biopsy was decreased to 5% of normal. Of the DMD myoblast clones obtained, a large proportion contained a morphological class of flat distended cells that had an increased generation time and ceased to proliferate beyond 100-1,000 cells but could be induced to fuse and form myotubes. The altered muscle phenotype was detected in all cultures from DMD patients but was rarely found among myoblasts of controls. By age 14 yr, it comprised as man as 90% of DMD myoblasts. The remaining DMD myoblast clones, which initially grew well, had severely impaired proliferative capacity upon passage and further cultivation. Eventually all myoblasts from DMD muscle tissue exhibited defective growth potential. In contrast, the fibroblast yield and proliferative capacity from DMD samples did not differ from normal. Based on these findings, we propose a hypothesis for the etiology of DMD: Dividing myoblasts are required for muscle growth and maintenance, and the limited capacity of DMD myoblasts to grow is directly related to the progressive muscle degeneration characteristic of the disease.

Adolescent↗
PubMed1998

The response of patients with Duchenne's muscular dystrophy to neuromuscular blockade with vecuronium.

BACKGROUND: The authors hypothesized that patients with Duchenne's muscular dystrophy (DMD) are more sensitive to nondepolarizing muscle relaxants. METHODS: Eight children with DMD and eight healthy children having orthopedic procedures were studied. Anesthesia consisted of thiopental, 60% nitrous oxide in 40% oxygen, and intravenous fentanyl and midazolam. Using electromyography, the ulnar nerve was stimulated and the electromyographic train-of-four ratio (TOFr) of the first dorsal interosseous muscle was recorded every 60 s. After baseline TOFr recording, all patients received 50 microg/kg vecuronium and the TOFr at 3 min was compared. Vecuronium (10 microg/kg) was then administered every minute until TOFr was < or =0.1. The TOFr was followed until TOFr was > or =0.01. Then 10 microg/kg of vecuronium were administered to maintain TOFr < or = 0.1. At the conclusion of the procedure, TOFr was allowed to recover to 0.25, and then neostigmine and glycopyrrolate were administered. Data are presented as medians and ranges. RESULTS: The initial dose of vecuronium resulted in greater TOFr depression in patients with DMD than in controls (0.14 vs. 0.86). Less vecuronium was needed to produce TOFr < or = 0.1 in the patients with DMD than in the control patients (55 microg/kg vs. 95 microg/kg). Recovery time for the TOFr to > or =0.1 after the initial dose was longer in the patients with DMD than in the controls (28 vs. 20 min; P = 0.03), and the maintenance dose of vecuronium was less in patients with DMD (0.6 vs. 1.3 microg x kg[-1] min[-1]; P < 0.01). The time for TOFr recovery from 0.1 to 0.25 was 36 min in the patients with DMD and 6 min in the controls (P < 0.01). After neostigmine, the TOFr was 1.0 in the controls and 0.91 (P = 0.03) in the patients with DMD. CONCLUSION: There is increased sensitivity to vecuronium from neuromuscular blockade in patients with DMD.

Adolescent↗
PubMed2005

Onset and duration of rocuronium-induced neuromuscular blockade in patients with Duchenne muscular dystrophy.

BACKGROUND: In patients with Duchenne muscular dystrophy (DMD) the response to nondepolarizing muscle relaxants is scarcely documented and conflicting. The current study was conducted to determine the time to peak effect and the time for complete spontaneous recovery after a single dose of 0.6 mg/kg of rocuronium in patients with DMD. METHODS: Twenty-four patients (12 with DMD, 12 controls, aged 10-16 yr) were studied. All patients were anesthetized with propofol and fentanyl/remifentanil. Neuromuscular transmission was monitored by acceleromyography. After induction all patients received a single dose of 0.6 mg/kg of rocuronium. The complete time course of onset and spontaneous recovery were recorded RESULTS: Significant (P < 0.01) increase in the onset times to 95% neuromuscular block was observed in DMD patients (median, 203 s; range, 90-420 s) compared with controls (median, 90 s; range, 60-195 s). The time between rocuronium administration and recovery of first twitch of the train-of-four to 90% was significantly (P < 0.01) prolonged in DMD compared with controls (median, 132 min; range, 61-209 min versus 39 min; 22-55 min). The recovery index was also significantly prolonged in the DMD group compared with controls (median, 28 min, range, 15-70 min versus 8 min; 3-14 min). CONCLUSIONS: The most striking and surprising result of this study is the delayed onset of blockade in DMD after a standard dose of rocuronium. This effect should be kept in mind in situations when a rapid airway protection is necessary in DMD patients. The documented very long recovery from rocuronium-induced block emphasizes the need for careful assessment of neuromuscular function in DMD patients.

Adolescent↗
PubMed2006

Social behavior problems in boys with Duchenne muscular dystrophy.

Duchenne muscular dystrophy (DMD) is a chronic, progressive pediatric disease that affects both muscle and brain. The objectives of the study were to examine parent reported behavior in children with DMD, investigate the influence of chronic illness, intellectual ability and etiology on behavior, and determine whether a specific behavioral profile is associated with DMD. Parental ratings of boys with DMD (n = 181) on the Child Behavior Checklist behavior scales were examined and compared to reported findings of children with other chronic illnesses, unaffected siblings of boys with DMD (n = 86), and children with cerebral palsy (CP) (n = 42). Increased ratings of general behavior problems were reported, and neither physical progression nor intellectual level contributed to behavioral ratings. Among the children with DMD, the Social Problem behavior scale had the greatest number of "clinically significant" ratings (34%). Between-group comparisons showed significantly more boys with DMD were rated as having social behavior problems than either the sibling or CP comparison groups. In addition to the increase in reported behavioral problems likely related to the effects of chronic illness, boys with DMD may be at heightened risk for specific social behavior problems. The specificity of the findings of the behavior profile in DMD may be partially due to the lack of dystrophin isoforms in the central nervous system, and not solely a reactive response to the illness.

Adolescent↗
PubMed2001

Prediction of progression of spinal deformity in Duchenne muscular dystrophy: a preliminary report.

STUDY DESIGN: Discriminatory power was statistically estimated for multiple combinations of risk indicators for the progression of spinal deformity in Duchenne muscular dystrophy (DMD). OBJECTIVE: To differentiate DMD cases in which spinal deformity will rapidly and severely progress from those with lesser progression of spinal deformity. SUMMARY OF BACKGROUND DATA: Early surgical intervention using instrumentation has recently been advocated for DMD patients to prevent the progression of spinal deformity. However, early determination of cases needing surgical intervention is difficult because of variations in the severity of the clinical courses of DMD patients. METHODS: Charts and spinal radiographs of 12 DMD patients were reviewed retrospectively. Patterns of progression in spinal deformity were classified into three types according to Oda's classification. Discriminant analysis was conducted to categorize the patients into either a severe progression group (type-1 and type-2 patients) or a less severe progression group (type-3 patients and patients without spinal deformity) on the basis of four predictors: 1) vital capacity at the age of 10 years, 2) the age at which ambulation ceased, 3) curve pattern of spinal scoliosis, and 4) Cobb angles of spinal scoliosis at the age of 10 years. RESULTS: Eleven of the twelve DMD patients showed spinal deformity. Three were classified as type 1, six were classified as type 2, and two were classified as type 3. The remaining patient showed no spinal deformity. Multiple discriminant analysis correctly predicted the severity of the clinical course of 91.7% of the DMD patients. Vital capacity at age 10 was found to be the strongest predictor among the variables. CONCLUSIONS: Through multiple discriminant analysis, the clinical course of spinal deformity in DMD patients was correctly predicted in 92% of subjects. This method would be useful to determine early which DMD cases need surgical intervention for treatment of spinal deformity.

Child↗
PubMed2006

Rocuronium 0.3 mg x kg-1 (ED95) induces a normal peak effect but an altered time course of neuromuscular block in patients with Duchenne's muscular dystrophy.

BACKGROUND: In patients with Duchenne's muscular dystrophy (DMD) recovery from neuromuscular block is delayed. It has been assumed that this is because of a higher potency of muscle relaxants in this patient cohort. We determined the peak effect, and the time course of action of rocuronium 0.3 mg x kg(-1) (ED(95)) in DMD patients. METHODS: Twenty-four patients (12 with DMD and 12 controls; aged 10-18 years) were studied. All patients were anesthetized with propofol and fentanyl/remifentanil. Neuromuscular transmission was monitored by acceleromyography. After induction all patients received a single dose of rocuronium 0.3 mg x kg(-1). The complete time course of action as onset, peak effect and spontaneous recovery was recorded. RESULTS: The onset time (s) to maximum block was significantly (P < 0.01) prolonged in DMD patients (median: 315; range: 120-465) compared with controls (195, 75-270). The peak effect (% twitch depression relative to baseline) was not different between the groups (DMD: 59-100; controls: 28-100). In the DMD group, recovery was significantly (P < 0.01) delayed compared with controls at all recorded time points. The clinical duration (min) was 40.3 (22-89) in the DMD group vs 9.8 (6-17) in the control group (P < 0.01). CONCLUSIONS: The similar peak effect in both groups does not confirm the thesis of rocuronium having a higher potency in DMD patients. The documented very long recovery after the ED(95) of rocuronium emphasizes the need for careful assessment of neuromuscular function in DMD patients.

Adolescent↗
PubMed1979

Erythrocyte spectrofluorometric abnormalities in Duchenne patients and carriers. A new approach to carrier detection.

Duchenne muscular dystrophy (DMD) is a disorder whose pathogenesis is attributed, according to the most recent theories, to generalized membrane abnormalities, including red cell membrane. The study of erythrocyte ghosts in patients affected by DMD showed alterations in ion transport and in various enzymatic activities. Employing a spectrofluorometric method using 1-anilino-8-naphthalene sufonate (1.8-ANS) we have tried to characterize the erythrocyte ghosts of DMD patients, definite DMD carriers and normal controls, matched for age and sex. We found an increase of membrane polarity in DMD and definite DMD-carrier erythrocyte ghosts. Using this new method we were able to: - confirm by means of a different technique the previous observations of many authors on erythrocyte ghost alterations in DMD - find a new technique useful in detecting the DMD carriers. It is noteworthy that in such a way the detection rate of definite DMD carriers was higher than with the CPK test.

Adult↗
PubMed1993

Impact of genetic counselling after neonatal screening for Duchenne muscular dystrophy.

In a pilot neonatal screening programme for Duchenne muscular dystrophy (DMD) conducted in the Canadian province of Manitoba, a cohort of eight affected males was identified between 1 January 1986 and 31 December 1989. Demographic information, knowledge of DMD, reproductive outcome, and attitudes to prenatal diagnosis and neonatal screening for DMD were obtained through questionnaires distributed in May 1992 to the eight sets of parents of index cases, two high probability carrier aunts, and one high probability carrier sister. Personal interviews were subsequently conducted in the summer of 1992. Although there is overall consensus among the families in favour of routine neonatal screening for DMD, five of seven subsequent pregnancies reported in six women were not monitored by prenatal diagnosis and have resulted in the birth of two affected boys. In a comparable time interval, prenatal diagnosis was acceptable to carrier females whose affected male relatives were traditionally diagnosed at four or five years. We conclude that, although molecular genetic analysis now allows for precise diagnosis of DMD, highly accurate carrier testing and prenatal diagnosis, very early DMD carrier identification, and genetic counselling after the identification of DMD males in a population based neonatal screening programme may not be an effective way of decreasing the number of repeat cases of DMD within families or the overall population frequency of DMD.

Adolescent↗
PubMed1996

Resting energy expenditure and energy substrate utilization in children with Duchenne muscular dystrophy.

The high prevalence of obesity at an early stage of Duchenne muscular dystrophy (DMD) could result not solely from reduced physical activity, but may also involve low resting energy expenditure (REE), abnormal nutrient utilization, or overfeeding. We hypothesized that the dramatic muscle mass loss in DMD should reduce the REE. REE was measured by indirect calorimetry in 13 9-13-y-old DMD boys (5 obese, 8 nonobese) and 9 male age-matched controls. Muscle mass was estimated from 3-d creatinine excretion in urine. Daily energy intake was estimated from 7-d diet records. In the nonobese DMD group (NODMD) the muscle mass was reduced by 71%, and the REE was 13% lower than in controls (47.5 versus 54.6 kcal.h-1, p < 0.05). Postabsorptive respiratory quotients appeared higher in both DMD groups than in the controls; however, the difference was significant only for the NODMD group (0.88 versus 0.83, p < 0.05). Respiratory quotients were not different between the two DMD groups. Diet records were not contributive in revealing a different dietary behavior between groups. Our results suggest that: 1) muscle mass loss in DMD is associated with a low REE, 2) low postabsorptive fat utilization might occur at an early stage of the disease, and 3) obesity is not associated with an increase in fat utilization in DMD. This study warrants further research to test low REE and low fat utilization as risk factors in developing obesity in DMD.

Adolescent↗
PubMed1989

Genetic abnormalities in Duchenne and Becker dystrophies: clinical correlations.

Duchenne muscular dystrophy (DMD) and Becker muscular dystrophy (BMD) are two allelic forms of an X-linked muscle disorder exhibiting phenotypic heterogeneity. We studied 49 individuals clinically diagnosed as having classic DMD, female DMD, mild DMD "outliers," and BMD. The patients' DNA was analyzed and alterations detected were correlated with particular phenotypes. We found that 14 of 32 classic DMD patients have an internal deletion in the same, relatively small, region of the gene; therefore this region may undergo deletions at a higher rate than the remainder of the gene. We could detect no alterations in the DNA in the remaining 18 patients. Selected patients from both groups failed to show muscle dystrophin. Seven of 11 patients with a mild DMD or BMD phenotype showed deletions at the 5' end of the gene. The other 4 patients failed to show deletions. Three of the patients with both a mild phenotype and a deletion at the 5' end had normal or low amounts of a dystrophin of smaller molecular weight. Patients with classic DMD who had a detectable deletion had a milder clinical course than those without. Contrary to a previous report, no patient in the population of clinically precisely defined DMD boys showed a deletion at the 5' end; thus, the outlier and BMD patients may be genetically different from boys with classic DMD. This correlation may be of diagnostic and prognostic significance.

Adolescent↗
PubMed1995

[Clinical significance of dystrophin positive fibers in Duchenne muscular dystrophy].

Dystrophin is a protein product of the Xp 21 gene which is defective in patients with Duchenne muscular dystrophy (DMD). In immunohistochemical staining of dystrophin, the majority of DMD muscle fibers show negative staining. Nevertheless, biopsy specimens from DMD patients labeled with many different antibodies may show a small number of fibers which are clearly dystrophin positive. This very small percentage of dystrophin-positive fibers (DPF) probably represents somatic reversion, suppression of the DMD gene mutation or alternating splicing of dystrophin mRNA. To determine the significance of isolated DPF in muscle specimens of DMD patients, we examined 30 DMD muscle specimens, aged 4 years to 16 years, by the use of monoclonal antibody against the C-terminal region of dystrophin. Additionally, muscle specimens from 2 normal human controls and 2 mice with X-linked muscular dystrophy were used for positive and negative controls, respectively. Muscle specimens from DMD patients and mdx mice showed almost totally negative dystrophin staining in most of their muscle fibers, but in 20 patients, three was a trace of isolated DPF ranging from 0.06% to 0.77%. DMD patients with no isolated DPF seemed to have higher functional disability. In the whole group of 30 patients, a significant negative correlation was found between the abundance of DPF and clinical functional grading (r = -0.85, p < 0.0001, based on linear regression). It is suggested that even the very low concentrations of dystrophin found in DMD patients may have a favorable functional significance.

Adolescent↗
PubMed1997

[Abnormal metabolism of fatty acids and ketone bodies in Duchenne muscular dystrophy, and the effect of biotin on these abnormalities].

It has been reported that serum levels of ketone bodies often elevate in patients with Duchenne muscular dystrophy (DMD). The cause of this abnormal metabolism, however, has not been elucidated. In this study, serum levels of ketone bodies were measured in the early morning in patients with DMD, congenital muscular dystrophy and cerebral palsy. Serum free fatty acids (FFA), glucose, and thickness of subcutaneous fat were also measured. Ketone bodies elevated in most DMD patients, but not elevated in patients with the other disorders. Hyperketonemia in the DMD patients was accompanied by elevation of the FFA level, but no correlation was seen between hyperketonemia and the creatine kinase level or the severity of muscle involvement. No differences were found between DMD patients and others in the levels of FFA, glucose and thickness of subcutaneous fat. These results indicate that DMD patients are more prone to ketosis than the others. The effect of biotin administration (2 mg/day) on hyperketonemia also was investigated in 11 patients with DMD. The levels of total ketone bodies decreased by biotin administration for 2 weeks. These data suggest that the utilization of FFA and ketone bodies may be impaired in DMD patients. Biotin treatment will be useful for improving the abnormal metabolism of ketone bodies in DMD patients.

Adolescent↗
PubMed1990

A tetrodotoxin- and Mn2(+)-insensitive Na+ current in Duchenne muscular dystrophy.

Muscle myotube cultures were obtained from normal and Duchenne muscular dystrophy (DMD) biopsies by using an explant technique. The current-voltage (I/V) curve of the whole sodium (Na+) current (INa) in normal myotubes was similar to that obtained from DMD myotubes. However, the inactivation curve of the whole INa was different in normal myotubes when compared to that obtained from DMD myotubes. Addition of 10(-4) M tetrodotoxin (TTX, a fast INa blocker) decreased the whole INa in both preparations. The inorganic calcium (Ca2+) blocker manganese (Mn2+) completely blocked the remaining TTX-resistant INa of normal myotubes and decreased this current in DMD myotubes leaving behind a TTX- and Mn2(+)-insensitive INa that was insensitive to the Ca2+ blocker desmetoxyverapamil ((-)D888). The slow inward barium current (IBa) of both normal and DMD myotubes was blocked by Mn2+ and (-)D888. However the kinetics of the slow channel in normal myotubes was different from that of DMD myotubes. This study demonstrates the presence of a TTX- and Mn2(+)-insensitive INa in DMD myotubes. This channel may contribute to the increase of intracellular Na+ [( Na]i) in DMD and allow Ca2+ to enter the cells through the Na(+)-Ca2+ exchanger, thus contributing to calcium loading.

Adolescent↗
PubMed2001

Inspiratory flow reserve in boys with Duchenne muscular dystrophy.

Patients with advanced muscular dystrophy frequently develop ventilatory failure. Currently respiratory impairment usually is assessed by measuring vital capacity and the mouth pressure generated during a maximal inspiratory maneuver (PI,max), neither of which directly measures ventilatory capacity. We assessed inspiratory flow reserve in 26 boys [mean (SD) age 12.8 (3.8) years] with Duchenne muscular dystrophy (DMD) without ventilatory failure and in 28 normal boys [mean (SD) age 12.6 (1.9) years] by analyzing the ratio between the largest inspiratory flow during tidal breathing (V'I,max(t)) and during a forced vital capacity maneuver (V'I,max(FVC), (V'I,max(t)/V'I,maxFVC). We have compared this ratio with the forced vital capacity FVC and PI,max measured at functional residual capacity. Mean PI,max was -90(30)cmH2O, average 112% (range 57-179%) of predicted values in control boys and -31(11)cmH2O, average 40% predicted values in DMD boys (control vs DMD, P < 0.001). FVC was reduced in DMD boys [59(20)% predicted values vs 86(10)% predicted values in controls, P < 0.01]. Absolute V'I,max(FVC) was strongly related to FVC in both control and DMD boys; V'I,max(FVC) (expressed as FVC. s(-1)) was not related to PI,max in either group. The mean V'I,max(t)/V'I,max(FVC); ratio was higher in DMD 0.22 (0.08) than in controls 0.12 (0.03) (P < 0.001) indicating a reduction in inspiratory flow reserve in DMD. Inspiratory flow reserve was within the normal range in 8 of 19 DMD patients with PI,max less than 50% of predicted values. We conclude that measurement of inspiratory flow reserve (V'I,max(t)/V'I,maxFVC ratio) provides a simple and direct assessment of dynamic inspiratory muscle function which is not replicated by static measurement of PI,max or vital capacity and might be useful in assessment of respiratory impairment in boys with Duchenne muscular dystrophy. Follow-up studies are required to establish whether measures of inspiratory flow reserve are of clinical value in predicting subsequent ventilatory failure.

Adolescent↗