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* From the Ludwig Boltzmann-Institute for Environmental Pulmonology and Pulmonary Department, City Hospital Lainz, (Drs. Koessler, Wanke, Winkler, Nader, and Zwick), and the Department of Neuropsychiatry for Children, University (Dr. Toifl), and the Pediatric Department, Danube Hospital (Dr. Kurz), Vienna, Austria.
Correspondence to: Wolfgang Koessler, MD, City Hospital Lainz, Pulmonary Department, Wolkersbergenstr 1, A-1130 Vienna, Austria; e-mail: Kow{at}khl.pul.magwien.gv.at
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Abstract |
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Patients and methods: Twenty-seven patients with NMDs (Duchenne’s muscular dystrophy, 18 patients; spinal muscular atrophy, 9 patients) underwent 24 months of IMT. Patients were divided into three groups according to their vital capacity (VC) values. VC was measured as the parameter for the respiratory system involvement of the disease. Maximal inspiratory pressure (PImax) was assessed as the parameter for respiratory muscle strength, and the results of the 12-s maximum voluntary ventilation test (12sMVV) were assessed as the parameter for respiratory muscle endurance. Pulmonary and inspiratory muscle function parameters were assessed 6 months before training, at the beginning of training, and then every 3 months.
Results: The PImax values improved in group A (VC, 27 to 50% predicted) from 51.45 to 87.00 cm H2O, in group B (VC, 51 to 70% predicted) from 59.38 to 94.4 cm H2O, and in group C (VC, 71 to 96% predicted) from 71.25 to 99.00 cm H2O. The 12sMVV values improved in group A from 52.69 to 69.50 L/min, in group B from 53.18 to 62.40 L/min, and in group C from 59.48 to 70.5 L/min. For all three groups, there was a significant improvement of PImax (p < 0.007) and 12sMVV (p < 0.015) until the 10th month when a plateau phase was reached with no decline in the following month until the end of training.
Conclusion: With IMT, respiratory muscle function can be improved in the long term of up to 2 years.
Key Words: inspiratory muscle training • long-term effects • neuromuscular disorders
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Introduction |
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The goal of our study was to answer the following questions:
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Materials and Methods |
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The diagnosis of the disease was made between 3 and 5 years of age on clinical, enzymatic, electromyographic, and muscle biopsy criteria. All patients were free from respiratory tract infections and had no symptoms or signs of inspiratory muscle fatigue, which are the obligatory indications for rest.9 No patient complained of sleep disturbance, daytime hypersomnolence, or morning headaches, and none had had an episode of acute respiratory failure requiring endotracheal ventilation. Capillary blood collected from an earlobe was used to analyze blood gases. No patient was hypercapnic, and all had normal PO2 values. Informed consent was obtained from all subjects, and the study was approved by the Human Subject Committee of the City Hospital Lainz.
Training Apparatus
The training apparatus (E. Biegler Co; Mauerbach, Austria) that
we used and the training itself were described in detail in our
previous study.2
Each patient had his own training
apparatus and trained at home. It enabled the patient to do resistive
breathing maneuvers against variable inspiratory resistance for
endurance training or maximal static inspiratory efforts against almost
occluded resistance for strength training. Pressure was measured with a
± 300 cm H2O differential pressure transducer
(model 142 PC; Honeywell; Freeport, IL). To provide a visual control of
the performance, we used a visual feedback system. During endurance
training, there was a light-emitting diode display whereby the patients
were shown breath by breath the inspiratory airflow actually achieved
in arbitrarily chosen units, and they were shown the minimal
inspiratory flow they had to reach during each inspiration. Patients
were also shown whether they had achieved the minute ventilation value
level while breathing against the inspiratory resistance. During
the 1-min breathing cycle, if the minimal airflow value was not
achieved more than twice, a warning signal on the training apparatus
would be shown to the patient, and the cycle had to be repeated. The
same happened if the desired minute ventilation level was not achieved.
During muscle strength training, the visual feedback system shows the minimal inspiratory pressure that had to be achieved and the actual inspiratory pressure that was reached.
Lung Function and Respiratory Muscle Function Parameters
Ventilatory function and inspiratory muscle function were
evaluated 6 months before training, at the beginning of the training,
in the first month of training, then every 3 months, and at the end of
training after 24 months. We used the 12-s maximum voluntary
ventilation (12sMVV) test as the parameter for respiratory muscle
endurance, and maximal inspiratory mouth pressure (PImax)
as the parameter for respiratory muscle strength. All measurements were
made with the patient in the sitting position. The VC and the 12sMVV
test were measured three times on a computerized spirometer (Jaeger;
Würzburg, Germany). The best trial for the 12sMVV test was used
for further analysis. The patient used a flanged mouthpiece, which was
held in the mouth behind the lips and firmly gripped by the teeth. This
mouthpiece also was used for training at home.10
The best
of 10 PImax maneuvers was used for the analyses.
The baseline lung function parameters of the three patient groups are shown in Table 1 . The expected normal values are those reported by Quanjer et al.11 In patients with scoliosis, arm span was used to determine the percent predicted values according to the method of Johnson and Westgate.12 PImax was measured by using the training apparatus. Ten maximal static inspiratory efforts against the almost occluded resistance were performed. An interval of 30 to 40 s was allowed between each maneuver, and the highest pressure obtained was used for further analyses.
Training Protocol
At home, patients had to perform both resistive breathing
maneuvers and maximal static inspiratory efforts. Training was
performed with the patient in the sitting position, and a noseclip was
used. Inspiratory resistive breathing training consisted of 10 loaded
breathing cycles of 1-min duration each, with 20-s intervals between
them. The level of the inspiratory resistance was adjusted in the
hospital every 3 months so that 70 to 80% of the PImax
value had to be generated with each breath. Thus, each patient had to
correctly complete 10 resistive breathing cycles twice a day. The
number of correctly and incorrectly performed exercises was stored by
the apparatus to enable the physician to check the training of the
patient. An incorrect test result represents a failure of the patient
to achieve the target pressure or flow levels, or a failure to perform
the total number of exercise cycles at all. Fifteen minutes before the
resistive breathing training, the patients had to perform 10 maximal
static inspiratory efforts and reach a certain minimal pressure value,
which was at least 90% of the maximally generated inspiratory pressure
that had been determined in the hospital. This value also was
determined and was adjusted in the hospital in each follow-up. A 20-s
interval between the maneuvers was allowed. If the minimal pressure
values were not achieved, this maneuver had to be repeated until a
total of 10 maneuvers were performed correctly.
Patients had to perform strength and endurance training twice daily, but if they could not perform the prescribed number of exercises, they were not excluded from our study.
Statistical Analysis
We used the rank-sum test for statistical analyses, a
nonparametric test to check the median differences between different
groups or different points of time.
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Results |
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Discussion |
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As far as we know, this is the first study that analyzed the long-term effects of a 24-month IMT program in patients with NMDs. During this time, periodic measurements of lung function parameters and respiratory muscle function parameters, like inspiratory muscle strength and endurance, were performed.
One of the main problems of NMDs is the progressive impairment of inspiratory muscle function. This leads to fatigue and eventually to respiratory failure, which is the most important cause of death in these patients.13 Therefore, it seems logical to use respiratory muscle training to improve inspiratory muscle function and to delay the early onset of respiratory failure in patients with NMDs. In the literature, the role of IMT has been controversial in patients with NMDs. In some studies2 6 14 in which inspiratory resistive loaded breathing was used, muscle strength and endurance increased. But in these studies, the training period often lasted not more than a few weeks, so there is no evidence that these effects would continue over a long period. In other studies,15 16 only endurance increased, and there was no improvement in muscle strength. The reason could be that the intensity of training was too low, because there was no control of training intensity. Respiratory muscles seem to exhibit similar adaptations to training to those of other skeletal muscles, provided that the training follows the basic training principles for any other striated muscle with regard to intensity, duration of the stimulus, and the specifics of the training.17 However, it also has been argued18 that IMT is hazardous since it may accelerate fatigue in the respiratory muscles by overwork.
We could show that IMT, combined with visual feedback, improved respiratory muscle strength and endurance even in the long term, provided that the patient’s ventilatory function was not severely impaired.2 The visual feedback allows proper monitoring of the training intensity, so that sufficient training could be carried out and its positive effects on respiratory muscles could be explained.
Although the advantage of improved inspiratory muscle function is obvious, it is certainly not easy to motivate especially young patients for the training. Respiratory muscle training is considered cumbersome, boring, and without immediate reward, so that it is very unlikely that many patients will use it long enough to reap the benefits.19 As a reward, our training equipment identifies incorrect exercises, so that they can be repeated without much waste of time and patients can complete their exercises quickly. A further advantage is that training can be done at home without abandoning close monitoring of the exercises. This complies with the ideal that patients with NMDs should be treated as outpatients, while keeping admissions to the hospital to a minimum.20 In our three patient groups, there was no difference in the number of correctly performed maneuvers in strength and endurance training, which means that the motivation to perform IMT is not influenced by the severity of the disease.
In addition to improvement in respiratory muscle function, there were also positive effects on lung function. In previous studies, it has been shown that during the growth phase VC increases normally and is identical to its predicted value.21 The plateau phase generally occurs between 10 and 12 years of age when the VC stabilizes, and then VC decreases as the disease progresses and is complicated by orthopedic deformities.21
It has been a great challenge to stabilize VC, or at least to retard its decline by IMT. We have shown that IMT leads to a stabilization of VC, which is important because VC is regarded as a predictor of the need for mechanical ventilation.22 It may be argued that PImax and 12sMVV test results increase due to a learning effect rather than indicating a real increase in strength and endurance.14 17 However, an increase due to learning should be most marked between the initial measurements, but such a change was not found. There was a continuous rise in 12sMVV test results in all patient groups until the plateau was reached after 10 months.
The results of our study have shown beneficial effects of respiratory muscle training on 12sMVV test results and PImax measurements during a 2-year period. Therefore, long-term IMT in patients with NMDs is justified.
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Footnotes |
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Received for publication July 11, 2000. Accepted for publication April 9, 2001.
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This article has been cited by other articles:
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  I. Yeldan, H N. Gurses, and H. Yuksel Comparison study of chest physiotherapy home training programmes on respiratory functions in patients with muscular dystrophy Clinical Rehabilitation, August 1, 2008; 22(8): 741 - 748. [Abstract] [PDF]
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 J van der Palen, T D Rea, T A Manolio, T Lumley, A B Newman, R P Tracy, P L Enright, and B M Psaty Respiratory muscle strength and the risk of incident cardiovascular events Thorax, December 1, 2004; 59(12): 1063 - 1067. [Abstract] [Full Text] [PDF]
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