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Número atual: Dezembro 2016 - Volume 23  - Número 4


Avaliação da força muscular respiratória e capacidade funcional em pacientes com fibrose cística

Evaluation of respiratory muscle strength and functional capacity in patients with cystic fibrosis

Cássio Magalhães da Silva e Silva1; Adriele Mascarenhas Araujo2; Anna Lúcia Lima Diniz da Silva3; Valdívia Alves de Sousa3; Mansueto Gomes Neto4; Micheli Bernadone Saquetto1

DOI: 10.5935/0104-7795.20160035

1. Fisioterapeuta, Professor Assistente da Universidade Federal da Bahia - UFBA
2. Fisioterapeuta, Residência em Fisioterapia em UTI e Emergência - SESAB
3. Fisioterapeuta, Hospital Especializado Octávio Mangabeira - SESAB
4. Fisioterapeuta, Professor Adjunto da Universidade Federal da Bahia - UFBA

Endereço para correspondência:
Cássio Magalhães da Silva e Silva
Instituto de Ciências da Saúde - ICS
Av. Reitor Miguel Calmon, s/n
Salvador - BA CEP 40110-100

Recebido em 17 de Junho de 2016.
Aceito em 28 Novembro de 2016.


Objetivo: Correlacionar a força muscular respiratória e a capacidade funcional em pacientes com FC. Métodos: Estudo transversal em adultos com fibrose cística. Os dados amostrais foram catalogados no Microsoft Office Excel 2007 e as variáveis analisadas pelo SPSS versão 20.0 através do teste t de Student e do coeficiente de Spearman. O nível de significância adotado foi p < 0,05. Resultados: Foram avaliados 35 pacientes com fibrose cística (44,6 ± 19,0 anos), grande parte dos pacientes de FC (n=26) não apresentaram fraqueza da musculatura inspiratória (PImáx -90,7 ± 27,4 cmH2O). Não foi encontrada estatística significativa apenas entre os pacientes adultos e idosos. Houve correlação positiva entre PImáx, PEmáx e teste de caminhada de 6 minutos (TC6) nos participantes com fraqueza muscular respiratória e nos idosos. Houve diferença estatisticamente significativa entre as médias da distância percorrida no TC6 e das pressões respiratórias máximas com a média do que foi previsto para estas variáveis. Conclusão: Todos os grupos apresentaram limitação da força respiratória e da capacidade funcional. As correlações entre as pressões respiratórias com o TC6 foram baixas e pequenas nos adultos e indivíduos sem fraqueza muscular respiratória; moderadas à alta nos idosos; pequenas à moderada nas mulheres; pequenas e negativas nos homens; e, altas naqueles com fraqueza muscular respiratória.

Palavras-chave: Fibrose Cística, Músculos Respiratórios, Tolerância ao Exercício


During the last three decades, due mainly to early diagnosis, the implementation of treatment programs and the creation of specialized centers, the life expectancy of patients with cystic fibrosis (CF) born in developed countries has increased.1 However, life expectancy of these patients is related to the severity and evolution of lung impairment associated with this disease.2

Respiratory changes of CF consist of pneumothorax, hemoptysis, nasal polyps and progressive chronic obstructive pulmonary disease, whose progression is the main cause of morbidity and mortality in patients with CF.2-5 The most relevant functional alterations include airflow obstruction, air trapping, and ventilatory deficiency. The evolution pattern of these alterations is characterized by a predominance of obstructive ventilatory disorder with early reduction of small airway flows and late impairment of forced vital capacity (FVC), whereas the total pulmonary capacity (TPC) is usually slightly increased, normal or reduced.5-7

Due to the respiratory conditions, the evaluation of respiratory muscle strength is an important parameter in clinical and functional respiratory practice, since respiratory muscles are responsible for the proper functioning of the respiratory system, and they maintain the adequate ventilation for gas exchange and consequent maintenance of activities of daily life.

The assessment of exercise tolerance and physical fitness of patients with CF is a sensitive measure to analyze the impact of this disease on daily activities, particularly in individuals at severe stages of the pathology.8

The 6-minute walk test (6MWT) assesses the functional capacity of healthy individuals or those with chronic diseases who cannot perform an ergometric. The 6MWT is a submaximal test that allows the assessment of the respiratory, cardiac and metabolic tracts, that is widely applied in physical rehabilitation programs and in treatment of patients with cardiopulmonary diseases.9-14

In patients with CF, muscle weakness and functional impairment associated with malnutrition are factors that limit physical capacity.15-17


The objective of the study was to analyze respiratory muscle strength and functional capacity of patients with cystic fibrosis.



Thirty-five patients were recruited from a convenience sample by consecutive sampling to participate in a cross-sectional study, which was conducted between August and October 2014 at the CF referral center of a specialized and public hospital, in the city of Salvador, Bahia, Brazil. Individuals of both sexes, older than 18 years, with diagnosis of CF who participated in the physiotherapy program and who signed the free and informed consent form were included. Patients with cognitive alterations, hearing and visual disabilities, orthopedic limitations, and lack of interest in participating in the study and who did not sign the informed consent form were excluded.

This study was approved by the Research Ethics Committee of the Faculty of Medicine of the Federal University of Bahia - UFBA, and received the registration number 731.684. The ethical principles ofthe Helsinki Declaration were fulfilled.18


At the beginning of data collection, the socio-demographic status (age, sex, marital status, profession, race) was recorded on an evaluation form. Weight was measured by a digital scale (Magna 150kg, G-Life, CA4000, São Paulo, Brazil), and height by a measuring tape of 150cm. Measurements of maximum respiratory pressures and the required rest variables to perform the 6MWT were also recorded.

The maximum respiratory pressure was measured by an analogue manovacuometer (WIKA, model 611.10, São Paulo, Brazil), with 10 cmH2O sensitivity interval and a range -150 to +150 cmH2O. To measure the maximum inspiratory pressure (MIP), the patient sat and was instructed to slowly exhale and, when in residual volume, a mouthpiece was connected between their lips, the nasal cavity was simultaneously closed by a clip, and the patient was requested to try his most intense and deepest inspiration out of the manovacuometer. To measure maximum expiratory pressure (MEP), the patient remained in the sitting position, and was requested to slowly inhale until total pulmonary capacity (TPC) was reached. Immediately after TPC, the manovacuometry mouthpiece was connected between the patient's lips and the nasal passage was occluded with a clip, so that the patient could try a rapid and intense expiration. Both pressures were alternately measured three times with two minutes of rest between each measurement. A variation of 10% was accepted and only the highest value was analyzed, even though all measurements were recorded in the evaluation form. In between the MIP and MEP measurements, there was an interval of five minutes.19 The reference values of MIP and MEP for the Brazilian population are approximately 100 cmH2O and 110 cmH2O, respectively.20

The evaluator then recorded the patient's heart rate (HR, bpm) and peripheral oxygen saturation (SpO2,%) values with a portable pulse oximeter (Contec MED CMS-50D, Commercial Society, Hebei, China ), blood pressure (BP, mmHg) with an automatic arm pressure device (OMRON, model HEM-7113, Dalian, China), respiratory rate (RR, ipm) and degree of dyspnea and fatigue with a modified Borg scale. Then the participant was taken to an outdoor 30-meter length flat corridor, with marks every 3 meters, to perform the 6MWT.

Before the beginning of the 6MWT, the participant was instructed to walk, and not to jump or run and, if he felt any discomfort, the test could be interrupted, but the test time would continue. The researcher stayed at one end of the corridor, where every minute he signaled the time remaining to the end of the test, as well as offering a verbal encouragement in a neutral voice ("You're doing well!" and "Carry on!"). After six minutes, counted by a chronometer, the patient was instructed to stop and the total distance from the starting to the stopping point was measured.21 At the end of the test and three minutes later, the values of the HR, FR, SpO2, PA and modified Borg scale variables were measured, the evaluator again checked the same variables.15 The mean distance of the 6MWT is 576m for men and 494m for women.16

Statistical analysis

The statistical analysis was performed with the complete sample of patients, as well as with subgroups as male and female, patients older and younger than 60 years of age. All variables were evaluated as means and standard deviations. The sample data were compiled in Microsoft Office Excel 2007 and the variables were analyzed by the statistical package SPSS version 20.0. Student's t-test was used for the subgroup comparisons. The Spearman coefficient was used to test the correlations between MIP and MEP, MIP and 6MWT, and MEP and 6MWT of patients above and below 60 years of age, and female and male patients. These correlations were interpreted as very weak ("r" up to 0.25), weak ("r" between 0.26-0.49), moderate ("r" between 0.50-0.69), strong ("r" Between 0.70-0.89) and very strong ("r"above 0.90), according to the reference values described by Domholdt.22 The established level of significance was p<0.05.


35 patients were included and evaluated, and their sociodemographic data is described in table 1.

The comparison between the values of respiratory pressures and the distance of the 6MWT of those younger and older than 60 years of age, there was no statistically significant difference, as shown in Table 2.

When the values of respiratory pressures and distance walked on the 6MWT are compared between the female and the male patients, a statistically significant difference was found, as shown in Table 3.

Mean of the distance covered in the 6MWT (480.7 ± 74.3) by the patients with cystic fibrosis was lower than the mean of the predicted distance (625.3 ± 115.5) for these individuals, with a statistically significant difference between them (p<0.001). It also occurred with respiratory pressures, where the mean values of MIP (79 cmH2O) and MEP (79 cmH2O) were lower than the predicted values (95 cmH2O and 98 cmH2O, respectively), whose comparison yielded statistically significant differences of MIP (p=0.005) and MEP (p=0.002).

Among the adults (up to 60 years of age), a weak correlation was found between MIP and MEP (r=0.403 / p=0.057), MIP and 6MWT (r=0.383 / p=0.720), and MEP and 6MWT (r=0.213 / p=0.847). However, among the elderlies (above 60 years of age), there was positive and statistically significant correlation between MIP and MEP (r=0.617 / p=0.04), MIP and 6MWT (r=0.767 / p= 0.014), and MEP and 6MWT (r=0.707 / p=0013).

Regarding the genders, the best correlation was evidenced among females, for whom moderate correlation was found between MIP and MEP (r=0.536 / p=0.002), weak correlation between MIP and 6MWT (r=0.406 / p= 0.768), and weak correlation between PEM and 6MWT (r=0.215 / p=0.969). Among the male population, the correlations were very weak and negative between MIP and MEP (r=-0.254 / p=0.08), MIP and 6MWT (r=-0.229 / p=0.87), and MEP and 6MWT (r=-0.297 / p=0.277).


All patients with CF has limitations of functional capacity and of respiratory muscle strength for those with MIP lower than 60 cmH2O.19 There was a statistically significant difference between the mean distance covered in the 6MWT and the mean predicted distance for these individuals, as well as between the mean and predicted values of respiratory pressures. When respiratory pressures were correlated one to another and to the 6MWT, adults (younger than 60 years of age) and individuals without respiratory muscle weakness had low and small correlations, whereas the elderlies (older than 60 years of age) the correlation ranged from moderate to strong. The women had weak to moderate correlations, whereas men had negative and weak correlations. And participants with respiratory muscle weakness had strong correlations.

The performance of any muscle can be analyzed by its strength, endurance and resistance to fatigue. The measurement of these characteristics makes it possible to obtain significant information for the functional evaluation of respiratory muscles. MIP and MEP produced in the mouth during static and forced respiration are considered a surrogate measure of respiratory muscle strength.20

The age related muscular changes affect the respiratory muscles function, with an important reduction of about 25% in the strength of the diaphragm of the elderlies, when compared to young adults, which can lead to respiratory fatigue during exercise.23 Vasconcellos et al.24 measured the respiratory muscle strength and functional capacity of sedentary elderly women and showed a positive and significant correlation between the walk distance (443.5 ± 49.6 m) and inspiratory muscle strength (-55.6 ± 21.0 cmH2O). In our research, as well as the authors cited, we observed a significant correlation between 6MWT and MIP, but, opposed to their findings, we observed a positive correlation between the walk distance of the 6MWT and expiratory muscle strength for all the elderly population.

The MIP measured in females over 60 years of age was higher than the inspiratory muscle strength of the sedentary elderly women in the study by Vasconcellos et al.24, if the only parameter is the walk distance of the 6MWT. This can be explained since the patients with CF in our sample attend physical therapy sessions and, some of them, Pilates.

Both genders had shorter distances of the 6MWT then the predicted reference values of CF patients, what certain consequences on low functional capacity and limitation for performing activities of daily life. Similarly, Ziegler et al.25 found that 73.2% of the 41 adolescent and adult patients with CF of their sample walked shorter 6MWT distances than the normal distance predicted. However, unlike our study, Chetta et al.26 analyzed 25 adult patients (15 women, aged 18-39 years) diagnosed with CF, have shown normal exercise capacity in the walk distance of the 6MWT (629 ± 49 m).

It was observed that the male and female patients presented low MIP and MEP values when compared to the reference value for this population (p<0.05), and there was a positive correlation between these variables only at the women group. The predicted values were obtained from the MIP and MEP reference equation for men and women, based on their mean age.20

Nonetheless, it was observed that the MIP measured on both genders was high, what could not determine respiratory muscle weakness, even though these values are below the reference value for males (84.1% of the predicted value) and females (80, 4% of the predicted value) with cystic fibrosis. Accordingly, Zanchet et al.27 showed mean values of respiratory pressures above the reference values for individuals with cystic fibrosis and his justification is that 55% of their sample had not yet presented pulmonary function impairment.

It is expected that, given men have greater respiratory muscle strength, they have better functional capacity than women.28,29 This was observed in our study, once the male subjects presented higher mean values for all variables when compared to the female subjects, confirming the findings of the literature for MIP, MEP and walk distance. However, there was no significant correlation between the 6MWT and the gender. Similarly, Pereira et al.,15 who compared functional performance during the 6MWT of 55 patients with cystic fibrosis with 115 healthy individuals, with a mean age of 12.2 ± 4.3 years and 11.3 ± 4.3 years respectively, found that sex has no influence on walk distance of the 6MWT, whose correlations occur only with age, weight and height.

A high MIP (> 80cmH2O) or a high MEP (> 90cmH2O) exclude significant inspiratory or expiratory weakness, in which the evidence that a person has a low MIP, this value should be less than 60% of the predicted value, which in turn must be based on variables such as gender, age, body weight and height; values above 60 cmH2O clinically exclude the possibility of respiratory muscle weakness.7 In our study, the most patients had MIP above 60 cmH2O, what excluding the possibility of respiratory muscle weakness. However, in the individual analysis of the sample, 9 patients had MIP lower than or equal to 60 cmH2O, for whom there was statistically significant differences between the MIP, MEP and 6MWT variables.

Regarding functional capacity, the gradual reduction of physical fitness associated with inactivity begins a vicious cycle in which the worsening of dyspnea is related to increasingly smaller physical efforts, seriously impairing the quality of life.24 Therefore, a widely used test for assessing submaximal exercise capacity in patients with pulmonary disease and heart failure has been the 6MWT which is also indicated for the assessment of recovery after therapeutic interventions.21

Enright and Sherrill21 emphasized that the walk distance of the 6MWT is an important predictor of morbidity and mortality of patients with pulmonary and / or cardiovascular diseases, especially those who have walked less than 300 meters. However, although a few participants needed to stop and rest to complete the test, and the distances the patients in our study walked were lower than the reference value, all these individuals walked more than 300m in the 6MWT, showing that in our study sample, patients did not present an increased risk of morbidity and mortality due to cystic fibrosis.

Ziegler et al.,25 whose sample consisted of individuals with cystic fibrosis with a mean age of 23.7 ± 6.5 years, observed that the walk distance of the 6MWT did not significantly correlate with BMI, age, MEP, MIP, SpO2 at rest, dyspnea at the start of the test, and dyspnea at the end of the test. However, in our study, there was a positive correlation between the 6MWT with MIP and MEP for elderly individuals and those with MIP less than 60 cmH2O.

The limitation of this study is the lack of evidence in the literature to be used as background to the discussion of the sample we studied.


In this context, we conclude that respiratory muscle weakness was evident only in the group with MIP < 60 cmH2O of the studied population, but all groups presented limitation of respiratory muscle strength and functional capacity.

Regarding the comparisons between the means of the walk distance of the 6MWT and the maximum respiratory pressures with the mean of the predicted values for these variables, it was observed that there was a statistically significant difference.

The correlations among respiratory pressures and the correlations between these pressures with the 6MWT were low and weak in adults and individuals without respiratory muscle weakness, moderate to strong in the elderly population, weak to moderate in women, weak and negative in men, and strong in those with respiratory muscle weakness.


We acknowledge the help and assistance of all participants with cystic fibrosis of the HEOM referral hospital.


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