APTA Annual Conference Abstracts

PT 2011: The Annual Conference and Exposition of the APTA, June 8 - 11, 2011

The Evaluation of Inspiratory Muscle Function and Impacting Characteristics in Stable Adults With Cystic Fibrosis


Robert L. Dekerlegand*1, Kento Kamiyama1, Kathrynne Mulhern1, Victoria Milano1, Ryan Ciesielski1, Eric Cohen1, Mary Jane Myslinski2
1. Rehabilitation and Movement Sciences, UMDNJ-SHRP and Rutgers University; 2. Rehabilitation and Movement Sciences, UMDNJ-SHRP

PURPOSE: The purpose of this systematic review is to evaluate inspiratory muscle function (IMF) in stable adults with cystic fibrosis (CF) and identify characteristics that impact IMF.
BACKGROUNDS/SIGNIFICANCE: Cystic Fibrosis (CF) is a progressive multi-system disease characterized by excessive production of thickened exocrine secretions. Pulmonary secretions obstruct airflow and predispose the individual to recurrent respiratory infections. Inflammation associated with chronic infections results in progressive airflow limitation, impaired gas exchange, decreased pulmonary function, and ultimately respiratory failure over the disease course. The work of breathing (WOB) is elevated in individuals with CF due to increased airway resistance, ventilatory inefficiency and an elevated ventilatory demand. Elevated WOB and ventilatory demand exceeding inspiratory muscle capacity may limit functional capacity and quality of life, and contribute to respiratory failure and the sensation of dyspnea. An imbalance can occur from excessive loads placed on the inspiratory muscles and/or the presence of inspiratory muscle dysfunction. Impaired IMF has been documented in chronic obstructive pulmonary disease (COPD) and is related to nutritional status, disease severity, hyperinflation, inflammation, corticosteroids, and oxidative stress. Inspiratory muscle training (IMT) can positively impact IMF in individuals with COPD and decrease dyspnea. Conflicting reports exist in the limited research on IMF and IMT in individuals with CF. Knowledge of IMF in adults with CF will provide a better understanding of the nature of the disease across the lifespan and identify individuals who may benefit from therapeutic interventions to enhance IMF.
SUBJECTS: Not applicable.
METHODS AND MATERIALS: The systematic review was conducted between September 2009 and June 2010 using the PubMed, CINAHL (1982 - present), and Medline (1950 - present) databases. Keywords included: inspiratory muscle, respiratory muscle, maximal inspiratory pressure, skeletal muscle, diaphragm, and cystic fibrosis. Cross-sectional and cohort studies whose primary purpose included evaluating IMF in stable human adults (mean age > 18 years) with CF as compared to a control group or predicted values were included in the review.
ANALYSES: Each article was evaluated to determine methodological quality. The assimilated literature was discussed to determine the effect of CF on measures of IMF.
RESULTS: Fifteen articles were located that met the inclusion criteria. Extreme heterogeneity of subjects was noted in all included studies. Maximal inspiratory pressure (MIP) was measured in 14 articles reflecting inspiratory muscle strength. Three of these articles also measured sustained MIP (SMIP) as a measure of inspiratory work capacity. The majority of group mean values for MIP were normal or above normal. Three articles reported decreased MIP. SMIP values were all decreased. Diaphragmatic strength was assessed in one article which demonstrated weakness in this muscle. Standard measures of inspiratory muscle endurance were not evaluated. Significant correlations were found between IMF and corticosteroids, nutritional status, hyperinflation, peripheral muscle strength, and forced expiratory volume in one-second (FEV1).
CONCLUSIONS: The effect of CF on IMF in stable adults is unclear. IMF was shown to be decreased, normal, or above normal in the included studies based on group mean values. Normal or increased inspiratory muscle strength was found in the majority of studies as measured by MIP. Preservation of MIP is hypothesized to result from a selective training effect secondary to the chronically elevated WOB. However, extreme heterogeneity existed in disease severity and decreased inspiratory muscle strength was found in some individuals and not others. In contrast, inspiratory muscle work capacity (i.e. SMIP) appears to be diminished in stable adults with CF. Inspiratory muscle dysfunction may result from muscle wasting, mechanical disadvantage, or altered muscle contractile properties. Decreased inspiratory muscle function in adults with CF is suspected to be related to: 1. disease severity, 2. hyperinflation, 3. nutritional status, 4. peripheral muscle weakness and 5.corticosteroids. Future research is needed to confirm the significance of IMF in CF over the course of the disease and should include homogenous sample populations. If present, an imbalance between IMF and WOB may negatively impact quality of life, mortality, functional capacity, lung transplant outcomes, and severity of exacerbations as the disease progresses. This knowledge may identify individuals who may respond to therapeutic interventions to enhance IMF.
KEYWORDS: Cystic Fibrosis, Inspiratory Muscle Function, Respiratory Muscle Function

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*First author