Breathing Problems

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Mechanism of CO2    Retention in Patients With Neuromuscular Disease*
[Clinical    Investigations: Control Of Breathing]
Misuri, Gianni MD; Lanini, Barbara MD; Gigliotti, Francesco MD; Iandelli, Iacopo MD; Pizzi, Assunta MD; Bertolini, Maria Grazia RT; Scano, Giorgio MD, FCCP
*From the Fondazione Don C. Gnocchi, ONLUS, Pozzolatico (Firenze), Italy.
Manuscript received February 26, 1999; revision accepted September 21, 1999.
This study was supported by a grant from MPI of Italy.
Correspondence to: Giorgio Scano, MD, FCCP, Section of Respiratory Disease, Fondazione Don C. Gnocchi, ONLUS, Pozzolatico, Via Imprunetana, Pozzolatico (Firenze), CAP 50020 Italy; e-mail: riabrfi@tin.it
Abstract

Background: In many studies of patients with muscle weakness, chronic hypercapnia has appeared to be out of proportion to the severity of muscle disease, indicating that factors other than muscle weakness are involved in CO2 retention. In patients with COPD, the unbalanced inspiratory muscle loading-to-strength ratio is thought to trigger the signal for the integrated response that leads to rapid and shallow breathing and eventually to chronic hypercapnia. This mechanism, although postulated, has not yet been assessed in patients with muscular dystrophy.
Abbreviations: Eldyn = dynamic lung elastance; Eldyn (%Pplsn) = elastic load per unit of inspiratory muscle force; FRC = functional residual capacity; LGD = limb-girdle dystrophy; MD = myotonic dystrophy; MEP = maximal expiratory pressure; MIP = maximal inspiratory pressure; NMD = neuromuscular disease; NS = not significant; Pi = mean inspiratory driving pressure; P0.1 = mouth occlusion pressure; Ppl = pleural pressure; Pplsn = pleural pressure during a sniff maneuver; Rf = respiratory frequency; RL = lung resistance; RSB = rapid and shallow breathing; TE = expiratory time; TI = inspiratory time; TTOT = total time of respiratory cycle; VC = vital capacity; [latin capital V with dot above]E = minute ventilation; VT = tidal volume; Zrs = impedance of the respiratory system
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Materials and Methods
Subjects
Twenty consecutive patients (10 men) with a mean age of 47.6 years (range, 23 to 67 years) were studied: 11 patients with limb-girdle dystrophy (LGD), 3 with Duchenne muscular dystrophy, 2 with amyotrophic lateral sclerosis, 1 with Charcot-Marie-Tooth syndrome, 1 with Becker muscular dystrophy, 1 with MD, 1 with facioscapulohumeral dystrophy, and no respiratory complaints. Nine were ambulatory, and 11 were wheelchair bound. The standard criteria were used to select patients. 20,21

None of the patients had a scoliosis nor any abnormalities on chest radiograph nor obvious abnormalities in diaphragm placement. Five patients were current mild smokers (<=5 pack-years).

Seventeen normal subjects matched for age (range, 26 to 62 years; mean, 41.5 years) and sex (8 men) were studied as a control group. The study was approved by the local ethics committee, and the subjects gave their informed consent.

The anthropometric characteristics of the patients are shown in Table 1.
Functional Evaluation

Routine spirometry, obtained with the patients seated in a comfortable armchair, was measured as previously described. 13,16,22 Functional residual capacity (FRC) was measured by the helium dilution technique. The normal values for lung volumes were those of the European Community for Coal and Steel. 23 Arterial blood gas tensions were measured with a blood gas analyzer (IL-1304; Instrumentation Laboratory; Milan, Italy).
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Protocol All subjects were tested in the morning. Before the experiment, the subjects were well acquainted with the laboratory and equipment. An arterial blood sample and lung function tests were performed, and then changes in volume, flow, and Ppl were recorded. Finally, the respiratory muscle strength tests were performed in each patient.

Data Analysis
Volume and time components of the respiratory cycle, RL, and Eldyn were averaged in each patient over 30 consecutive breaths. Eldyn was expressed both as an actual value and as a percent of Pplsn, an index of the balance between the elastic load of the lung relative to the maximal inspiratory force available. Single and stepwise multiple regression analyses were performed to assess relationships between variables. The statistical analysis we carried out considers the dependency of a variable (eg, the level of PaCO2) on a series of independent variables. The effect of each variable on PaCO2 was evaluated independent of the effect of all other variables. In a multivariate analysis, a rule of thumb is to limit the number of variables as a function of the number of patients.28 Thus, multiple regression analysis with stepwise selection of the independent variables was carried out relating PaCO2 to functional variables. The proportion of total variance in the dependent variable accounted for by the predicted variables is reported as the square of the correlation coefficient (r2). Single regression analysis was performed using Pearson’s single correlation coefficient. Comparisons between groups were made using the Mann-Whitney U test. A value of p < 0.05 was considered as the threshold of statistical significance. Data are presented as mean ± SD unless otherwise specified. .
Results

Clinical, anthropometric, and respiratory function characteristics of the patients (and control subjects) are shown in Table 1. As shown in Table 1, vital capacity (VC) was reduced in 11 patients, as was total lung capacity in 9. The means of MIP (47.8 ± 28.3 cm H2O; range, 11 to 127 cm H2O; p = 0.00001) and MEP (49.5 ± 26.2 cm H2O; range, 15 to 104 cm H2O; p = 0.00002) were significantly lower than in control subjects. In 11 patients and 10 patients, the values of MIP and MEP, respectively, were lower than the mean – 2 SD of the value calculated for the control subjects. Arterial blood gases were normal in all but eight patients in whom PaCO2 was considered to be high (>= 45 mm Hg) and in three patients in whom PaCO2 was low (< 80 mm Hg). In some of the patients, and particularly in patients 12 and 14, in whom PaCO2 was normal, a high level of ventilation was found.
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Discussion
We have found that in patients with NMD, Eldyn (%Pplsn) is the strongest predictor of the variance in PaCO2. Increased Eldyn (%Pplsn) was associated with a decreased TI, which truncates VT, thereby leading to chronic CO2 retention (PaCO2).
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References
1 Begin R, Bureau MA, Lupien L, et al. Control of breathing in Duchenne’s muscular dystrophy. Am J Med 1980; 69:227-234
2 Kilburn KH, Eagen JT, Sieker HO, et al. Cardiopulmonary insufficiency in myotonic and progressive muscular dystrophy. N Engl J Med 1959; 261:1089-1096

CANADA

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CANADA
This page contains information and support for people with Myotonic Dystrophy in Canada

National Center for Myotonic Dystrophy Opens in Canada The William Singeris National Centre for Myotonic Dystrophy (Dec 2004)

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The William Singeris National Centre for Myotonic Dystrophy was officially opened Monday December 20 2004 with a commitment of $ 237,700.00 over five years by Phil and Megan Singeris and their family of supporters. Inspired by their 2 year old son William who has Congenital Myotonic Dystrophy, Phil and Megan wanted to do something to help others suffering from this little known disease. A fundraising gala was held in April 2004 with the goal of raising $30,000.00. When the final results came in, the astonishing total of over $60,000.00 was realized! The Centre based in London at Children’s Hospital of Western Ontario and Children’s Health Research Institute will for the first time in Canada, document and track all children born in Canada with Myotonic Dystrophy and follow their development and treatments for five to ten years.This data will not only form a critical foundation for development and testing of treatments that could eventually lead to a cure, but will also provide much needed information to parents and prospective parents of children with this disease to help base family decisions on more solid facts. Led by Dr. Craig Cambell, Paediatrician at Children’s Hospital of Western Ontario and Associate Scientist, Children’s Health Research Institute, the research process has already begun. “Information and questionnaires will be sent to every paediatrician in Canada each month asking for reports on any child with Myotonic Dystrophy,” said Dr. Campbell. “In addition to medical information and annual development testing, we will look at quality of life measures for both the child and family. The Child Health and Well- being Program at Children’s Health Research Institute has one of the best known research groups in Canada to study such impact on children and their families”. Thank you to Phil, Megan, Stephanie and especially William Singeris for an amazing gift to children all over Canada!
Links
 

The Muscular Dystrophy Association of Canada can be very helpful. Here is their link: http://www.mdac.ca/
http://users.auracom.com/smdi/muscular.htm (other links)
Dr. Jack Puymirat

The Promise of Gene Therapies for Muscular Dystrophies
Cataracts, muscle weakness in the hands, feet, and face, and a decreasing ability to relax contracted muscles are among the symptoms of myotonic dystrophy, which hits one in every 500 people in Qu?bec. But researchers, including Dr. Puymirat, are closer than ever to discovering effective new therapies.