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Journal of Human Growth and Development

Print version ISSN 0104-1282

Rev. bras. crescimento desenvolv. hum. vol.24 no.2 São Paulo  2014

 

ORIGINAL RESEARCH

 

Respiratory muscle strength of Brazilian adolescents: obtained and predicted values

 

 

Priscilla Rique FurtadoI; Tania Fernandes CamposII; Raquel Emanuele de França MendesI; Diana Amélia de FreitasI; Gabriela Suéllen da Silva ChavesI; Thalita Medeiros Fernandes de MacêdoI; Karla Morganna Pereira Pinto de MendonçaII

IPrograma de Pós-Graduação em Fisioterapia, Universidade Federal do Rio Grande do Norte - UFRN. Avenida Senador Salgado Filho, 3000, Departamento de Fisioterapia, Campus Universitário, Lagoa Nova, Natal, RN, Brasil
IIProfessora Associada, Programa de Pós-Graduação em Fisioterapia, Departamento de Fisioterapia - UFRN. Avenida Senador Salgado Filho, 3000, Departamento de Fisioterapia, Campus Universitário, Lagoa Nova, Natal, RN, Brasil

 

 


ABSTRACT

OBJECTIVES: To compare the obtained values for maximal respiratory pressures of a sample of Brazilian adolescents with the values predicted by Wilson et al. and Domènech-Clar et al.
METHODS: 156 adolescents (84 boys) aged between 12 and 17 years were assessed. Maximal respiratory pressures were assessed by a digital manometer with the adolescents in the seated position and wearing a nose clip. Maximal inspiratory and expiratory pressures were performed from residual volume and total lung capacity, respectively. Comparison of the values of maximal respiratory pressures obtained in this study with those predicted by the equations proposed by Wilson et al. and Domenèch-Clar et al., was performed by the paired Student's t test. To verify the association between these values, the Pearson's correlation test was used.
RESULTS: Mean maximal inspiratory pressure was 74,66 ± 22,95 cm H2O and 103,52 ± 25,67 cm H2O for girls and boys, respectively. Mean maximal expiratory pressure was 86,23 ± 25,92 cm H2O and 120,08 ± 27,37 cm H2O for girls and boys, respectively. The values obtained by this study did not differ and also did not significantly correlate with those predicted by the equations proposed by Wilson et al., e Domènech-Claret al.
CONCLUSIONS: The equations proposed by Wilson et al. and Domènech-Clar et al. were not successful in predicting the values for maximal respiratory pressures in the population studied, indicating the necessity of using in clinical practice reference values from a healthy population of the same ethnicity.

Key words: muscle strength, respiratory muscles, evaluation, reference values, adolescent.


 

 

INTRODUCTION

The measurement of maximal static respiratory pressures (MRP) at the mouth provides subsidies to direct the preoperative and postoperative therapeutic goals1, assess the response to respiratory muscle training and allows early muscle weakness identification in various pathological conditions2. The measurement of maximal expiratory and inspiratory pressures (MEP and MIP, respectively) are crucial to the adequate assessment of pulmonary function, and can be performed in healthy individuals of different ages, or in individuals with disorders of different origins3.4.

Several studies have been developed in order to provide reference values for MRP or formulate equations able to predict these values5,6. Thus, variables such as: age, sex, height, weight, physical activity level and ethnicity were considered, which motivated further researches with different samples in order to compare values found with predicted ones in previous studies, or to present new predicted equations2,7-11.

In 1984, Smith et al.7 highlighted the lack of studies with MR Pin adolescents and evaluated 112 individuals of different ages, among them 76 adolescents of both sexes, publishing the data as normal values. In the same year, Wilson et al.6 studied 235 subjects between 7 and 17 years, of both sexes, and provided predicted equations for MIP and MEP considering the independent variables: weight and age. Later, Szeinberg et al., in 198712, published reference values from a sample of 270 subjects aged between 8 and 40 years (243 children and adolescents). In 2003, Domènech-Clar et al.8 provided predicted equations from the assessment of 392 Spanish children and adolescents between 8 and 17 years. Similarly to the study of Wilson et al.6, the equations proposed by Domènech-Claret al.8 considered the same variables, however adding the variable height. All mentioned studies have performed the comparison between obtained and predicted values, finding differences between results.

Studies conducted in Brazil have shown that it is necessary to evaluate different populations and provide different parameters for them, once there may be differences between the characteristics of these individuals, in distinct regions of the same country9,10 and even in the same region9.

To the best of our knowledge, the predicted equations and parameters of normality offered by Wilson et al.6 and Domènech-Clar et al.8 have been the most widely used as reference in the evaluation of respiratory muscle strength of adolescents from different nationalities. However, comparative studies using a sample of Brazilian adolescents were not found.

Thus, the aim of this study is to compare the values found with those predicted by Wilson et al.6 and Domènech-Clar et al.8 and to verify if the predicted values are suitable to be used in a population of Brazilian adolescents.

 

METHODS

This is a cross-sectional study conducted in accordance with the Declaration of Helsinki and approved by the Research Ethics Committee of Federal University of Rio Grande do Norte (UFRN), protocol number 278/2009. Sample calculation was conducted according to the formula to estimate the mean supplied by the Laboratory of Epidemiology and Statistics13 resulting in 14 boys and 12 girls for each age group assessed.

The subject's selection was made from a list of public and private schools in the city of Natal provided by the 1st Regional Education Directorate (DIRED). By a previous contact, a letter explaining the study was delivered to parents and/or guardians, accompanied by an informed consent form and a respiratory questionnaire, composed of nine questions regarding respiratory symptoms, validated for diagnosis of respiratory diseases. This is recommended by The American Thoracic Society and Division of Lung Diseases14. Inclusion criteria were: aged between 12 and 17 years15, be eutrophic16; do not have chronic lung, neuromuscular or cardiovascular disease, as well as reporting the use of medications that might interfere in the performance during assessments17; neurological damage or inability to understand the guidelines for using the manovacuometer3,17; recent upper airway, chest or abdominal trauma; acute middle ear infection; abdominal hernia; glaucoma or retinal detachment3; fever in the three previous weeks3 and flu and/or cold in the week prior to the procedure; or have past history of smoking; thoracic deformity3; or a score of 7 or higher on the standardized questionnaire of the American Thoracic Society and Division of Lung Diseases ATS-DLD-78-C14.

Individuals excluded were those unable to perform the necessary procedures and those who declined to participate; exhibited acute respiratory tract disease during the collection period; missed class during the evaluation period at their school; displayed values lower than 80% of those predicted for Peak Expiratory Flow (PEF), Forced Vital Capacity (FVC), Forced Expiratory Volume (FEV), Forced Expiratory Volume in the first second (FEV1) and the FEV1/FVC ratio, as well as values less than 70% of those predicted for mean Forced Expiratory Flow between 25 and 75% of the FVC curve (FEF25 75%) - in accordance with ATS18 criteria. The measures proposed by Mallozi19 were used as reference values.

On the scheduled day, each adolescent underwent anthropometric assessment. The Anthro Plus software from the World Health Organization (WHO) automatically provided the nutritional status.

Heart rate and peripheral oxygen saturation were verified with the purpose of monitoring the adolescent for possible interruption of the evaluation before complications. The instruments used were a Visomat® Handy IV digital sphygmomanometer (UEBE Medical Gmb H, Germany) and an Onyx® II 9550 Pulse Oximeter (Nonin Medical, Plymouth-MN, United States of America).

In order to avoid air escape, all measurements were performed with the adolescent using a nose clip and instructed to properly adjust their lips around the mouthpiece8. Because this was an effort-dependent test, the examiner provided verbal encouragement during assessments. The adolescents remained seated with their heads in a neutral position.

Spirometry

Spirometry was performed using a hand held One Flow FVC digital spirometer (Clemente Clark International - England)

Initially, the adolescents performed three respiratory cycles at tidal volume, and then they were instructed to perform one maximum ins-piration (indicated by a predetermined gesture), close their mouth firmly around the mouthpiece and, following a minimum pause, make a vigorous maximum expiration. The maneuvers produced flow - volume and time-volume curves that, for its use in the interpretation, should be in accordance with the acceptability and reproducibility criteria recommended by the American Thoracic Society20: realization of a maximum inspiration before the beginning of the test; a minimum pause (1-2 seconds); expiration with maximum effort; satisfactory test duration (6 seconds); and the lack of artifacts.

A minimum of three and maximum of eight maneuvers were executed. Of these, three were acceptable, and the best two did not exhibit a maximum difference of 0.150 L between them, with the better of the two tests chosen. A one-minute rest was permitted between each maneuver18.

Manovacuometry

After 10 minutes of rest, the same examiner conducted the assessment of maximal respiratory pressures. MRP were assessed using an MVD 300 digital manometer (Globalmed®, Porto Alegre - RS, Brazil). A disposable biological filter (Vida Tecnologia Biomédica, São Paulo - SP, Brazil) was attached to a Rescal adaptor which connects the system with the ambient air. This was coupled to a rigid and flattened plastic mouthpiece (Globalmed®, Porto Alegre - RS, Brazil) with a 2-mm wide hole on its upper surface.

The evaluation was performed with the manometer connected to a laptop (Compac Presario CQ50-113BR). The computer software provided the subject with visual feedback, and auditory feedback was given by the examiner. MRP measurement was performed in accordance with the method proposed by Souza3.

Initially, adolescents randomly selected the first MRP to be assessed. To assess MIP the adolescents were instructed to perform three respiratory cycles at tidal volume and then perform a maximum expiratory effort up to approximately the residual volume (RV). The adolescents indicated the maximum effort by a predetermined gesture. At that moment they were instructed to perform a maximal inspiration (until approximate total lung capacity - TLC). Instructions were similar for MEP assessment, except participants first performed a maximal inspiration and then maximal expiration following occlusion of the orifice. During this measurement the examiner manually supported the adoles-cents'cheeks21.

A maximum of nine maneuvers were performed for each MRP assessment8. Of these, at least three had to be acceptable (without leaking, with a duration of at least 2s and sustained for 1s), from which a minimum of two were required to be reproducible (with a difference between them of no more than 10% of the highest value). The better of these two values was selected8. However, the last measurement could not be the highest, and another measurement was taken when this occurred. A one-minute rest was permitted between each maneuver, with five minutes allowed between MIP and MEP assessments.

The equipment used in this investigation only directly supplies peak pressure values (the highest value during the maneuver)22. As such, sustained pressure values were determined by examining the pressure versus time curve provided by the manometer software.

Analysis of data

Data were analyzed using SPSS statistics software version 17.0, with a significance level of 5%. Data normality was verified by the Kolmogorov-Smirnov test. Descriptive statistics are expressed as mean and standard deviation.

One-way analysis of variance (ANOVA), followed by the Bonferroni post hoc test, was used to determine whether there was a significant difference in MRP according to age and sex. Non-paired Student's t-test was applied to verify inter-gender differences. Unpaired Student's t-test was used to establish the existence of differences between the mean MIP and MEP values obtained in the present study and those from the equations proposed by Wilson et al.6 and Domènech-Claret al.8 The Pearson's correlation test was performed to verify the association between those values. Levene's test was performed to assess the homogeneity of variances (homoscedasticity). The lower limit of normal (LLN) was calculated by subtracting a value two times greater than the standard deviation of the measurements from mean MRP3.

 

RESULTS

244 questionnaires were returned, 28 teenagers were not included in the sample for non-compliance with one of the inclusion criteria. Among the 216 adolescents selected, 60 were excluded (3 refused to take part, 39 were not classified as eutrophic, 13 did not meet criteria established by spirometry and 5 were unable to perform acceptable and reproducible manovacuometer maneuvers among the maximum number of nine measurements), resulting in a total sample of 156 subjects, 84 boys and 72 girls. Table 1 describes the anthropometric variables, expressed as mean and standard deviation.

MIP and MEP values had normal distribution with a significant level of p = 0,49 and p = 0,55, respectively. ANOVA indicated no significant difference between respiratory muscle strength and age (12-17 years) with a P value of 0,18 for MIP and 0,749 for MEP.

Table 2 describes the means obtained for maximal respiratory pressures in boys and girls. This table also shows the lower limits of normal of the adolescents assessed.

Table 3 shows the inexistence of significant difference for comparison of maximal respiratory pressure values found with the ones predicted by the equations proposed by Wilson et al.6 and Domènech-Clar et al.8

The dispersion graphs of MRP values found and those predicted in equations proposed by Wilson et al.6 and Domènech-Clar et al.8 are shown in figures 1 and 2, respectively. Obtained values of MIP and MEP in both sexes had low coefficients and did not present significant correlation with the values predicted by Wilson et al.6 and Domènech-Claret al.8

 

DISCUSSION

When comparing the values found for maximal respiratory pressures from a sample of 156 healthy Brazilian adolescents with the values predicted by Wilson et al. (1984)6 and Domenèch-Clar et al. (2003)8 it was verified that the equations proposed by these authors were not able to predict respiratory muscle strength of Brazilian adolescents.

Although the differences are not significant, there was weak correlation without statistical significance between the values found in the current study and the predicted ones by both studies6,8. According to Parreira et al.9, to assert that there is concordance between found and predicted maximal respiratory pressures values it is necessary that these measures do not show statistical difference and present a significant correlation.

During the last years, several studies have comparatively analyzed maximal respiratory pressures and highlighted the discrepancies observed between found and predicted values in different age groups7,9-11. Such fact has been attributed to methodological differences, to the quantity and quality of samples evaluated, to equipments and techniques used, besides geographical, social and anthropometric differences of the individuals9.

With regard to technique's aspects, it is argued that the use of a nose clip and a flanged mouthpiece contribute to reduce the risks of air escape and consequently avoid the under estimation of the real values measured for maximal respiratory pressures10. This aspect may justify the possible underestimation of the obtained values by the study of Wilson et al.6 in which a nose clip has not been used. Another aspect to be considered, is the examiner support of the cheeks during the expiratory efforts which according to Clanton and Diaz21 aims to ensure that the pressure exerted by the respiratory muscles is transmitted to the device instead of staying stuck in the oral cavity by distention of the cheeks and air concentration in that area. In the study of Domenèch-Clar et al.8 the adolescents performed MEP with their hands over their cheeks, while in the current study the examiner supported the adolescents' cheeks. Studies with the aim to investigate differences in results regarding this aspect were not found; however it is possible that this methodological factor might interfere in the results.

The results show that the mean values of MRP in boys were significantly higher than those observed in girls. Similar findings have been reported in several studies performed with samples of children6,12, adolescents7,8, and adults2,6,9,10. The most accepted explanation for this difference involves the existence of greater amount of lean body mass in boys, which is even greater after puberty8, and to the fact that, in general, the males are more physically active23. In females, hormonal changes play an important role in puberty and during the menstrual cycle may interfere in MRP measures as it was verified by Silva et al.24 These authors commented on the existence of a positive influence of estradiol and progesterone hormones on the respiratory muscle strength in the luteal phase.

Considering the learning effect, a minimum of 3 and a maximum of 9 maneuvers were performed in the current study to achieve 3 acceptable and 2 reproducible maneuvers11. Domenèch-Clar et al.8 used a similar parameter. However, Wilson et al.6 did not establish a maximum limit, it was only determined the performance of at least 3 maneuvers. In 1997, a study conducted by Wen et al.25 stated that a larger number of maneuvers could determine more effectively there spiratory muscle weakness. In opposition to this perspective, Smyth et al.7 stated that in clinical practice the performance of successive repetitions of these maneuvers can be impractical in the assessment of patients. In addition, a recent study when comparing the number of maximal respiratory pressures maneuvers performed, observed that there was no difference in the perceived exertion rate of children who performed up to five or more than five maneuvers26.

One important difference to be considered among maximal respiratory pressures studies consists of the ethnic differences. Several authors emphasized the differences in MRP values of individuals from different nationalities, and even in the same region of a country5,9-11. Nevertheless, references of studies that compared MRP values obtained in a sample of Brazilian adolescents with the predicted values by previous studies from other nationalities were not found. This theme was only previously studied in populations of children and adults27,28. Such fact highlights the importance of this study to contribute to the advancement of investigation of MRP values that can be used as reference.

A limiting factor in the present study was the absence of hormonal evaluation which would allow a better understanding of the puberty changes influences in respiratory muscle strength during adolescence. Another aspect that may limit the interpretation of the findings of the current study is the divergence observed between the age groups evaluated in previous studies, as well as the lack of information about the characteristics of samples evaluated which would allow more appropriate comparisons.

 

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Manuscript submitted Aug 01 2013
Accepted for publication Dec 28 2013

 

 

Instituição: Departamento de Fisioterapia da Universidade Federal do Rio Grande do Norte (UFRN), Natal, Rio Grande do Norte, Brasil.
Fonte financiadora: projeto executado com recursos próprios. O presente estudo é parte de uma dissertação de mestrado denominada "Equações preditivas para as pressões respiratórias estáticas máximas de adolescentes brasileiros", defendida em Natal na Universidade Federal do Rio Grande do Norte (UFRN) - Programa de Pós-Graduação em Fisioterapia, em 2012.
Corresponding author: kmorganna@ufrnet.br