Background
Asthma is considered the world’s most common chronic respiratory disease. It affects 334 million people of all ages and is the 14th most important disorder in the world in terms of its extent and duration of disability [
1]. It is characterized by a chronic inflammation of the airways, limiting the expiratory airflow, which produces intermittent hyperinflation and adaptations in the thoracic cage to move the trapped air, with reduced costal mobility [
2‐
4].
The evaluation of thoracic mobility allows us to quantify the functional consequences and the degree to which asthma is controlled [
3]. Photogrammetry is one of the tools available for this evaluation, providing a kinematic analysis of respiratory movements, but it requires special equipment and training, and the computerized analysis of images requires additional time per patient, increasing its cost and minimizing its clinical applicability [
5‐
7]. Thoracic perimetry is used in a clinical context, expressed as the Thoracic Index (TI), because it is a low-cost and easy-to-apply technique. In a review of the literature, however, no studies were found that evaluated the TI’s psychometric properties in adults with stable asthma [
8‐
11].
Having reliable and valid measuring tools in a clinical setting allows the clinician to provide an objective evaluation and diagnosis, and to undertake appropriate interventions to improve the respiratory mechanics compromised by asthma [
2]. They are also useful in a research context for demonstrating the results of physiotherapeutic interventions, decreasing the likelihood that the effects obtained will be influenced by any variability in the measurements [
9].
For these reasons, it is necessary to evaluate the psychometric properties of the tests used in clinical practice, using tests and measurements of proven validity and reproducibility as test comparators. The reliability and validity of the TI are tested against a photogrammetric analysis of the breathing cycle. This will allow an improved evaluation of the respiratory mechanics in asthma. It will also allow the control of the disease to be monitored and the provision of an evidentiary basis for intervention programs to control symptoms, prevent complications, and improve the functionality and quality of life of this population [
12,
13].
The objective of this study was to evaluate the intra- and inter-evaluator reliability of TI measurements, and the convergent validity between the TI and photogrammetric analysis in a population of asthmatic adults.
Discussion
Within the established reliability, the limits to agreement were narrower at all the measurement levels than those reported by Malaguti et al. [
9], who evaluated the reproducibility of thoracic cirtometry in people with COPD. This result can be attributed to the standardization of all the conditions within the protocol. The limits were considered acceptable both for the intra-evaluator and inter-evaluator agreements, using the maximum and average values with an average of differences close to zero, thus demonstrating control of measurement bias, possibly resulting from the session where the evaluators were trained and the participants were familiarized with the measurements.
In both studies, the limits were narrowest at the xiphoid level and widest apart at the abdominal level. Malaguti et al. [
9] attributed the greater variability at the abdominal level to differences in the breathing patterns of each participant at maximum inhalation. In addition, when analyzing the variability at the abdominal level in the seated position, the distribution of the pulmonary volumes should be taken into consideration. Lee et al. [
32] concluded that subtle changes in the trunk position of healthy adults can alter the configuration and movement of the thoracic wall, as well as the distribution of the respiratory volume, changes that can be attributed to modifications in muscular activation [
33].
These modifications in the neck and trunk muscles are related to the double function of these muscles in the respiratory cycle and postural control [
34,
35], especially at the abdominal level. Postural adjustments in a seated position can influence breathing patterns due to the alternation of these functions. Small postural changes can favor the predominance of either the postural or the respiratory function [
33,
36]. Thus, despite having a standardized seated posture for every participant, small postural adjustments may have influenced the variability of the measurements.
Romei et al. [
6] found that costal kinematics in healthy adults are significantly affected by the trunk position. A gradually increasing inclination of the trunk leads to a progressive reduction in rib cage displacement and an increasing abdominal contribution leads to tidal volume. These findings may also explain the variable TI measurements for individual subjects, and indicate aspects of intra-subject measurements that can generate random errors outside the evaluator’s control.
In addition, the measurement of costal mobility has been used to determine the effectiveness of physiotherapeutic interventions for people with asthma. Burianová et al. [
37] evaluated the effect of physiotherapeutic treatment on thoracic mobility and reported a statistically significant improvement with total increments of between 1.5 cm and 2.1 cm for men at the level of the fourth rib and xiphoid level, respectively, and of 2 cm for women at both levels. The findings of this study, however, suggest that changes under 2.1 cm cannot be considered clinically significant, as they can represent randomization given the variability of measurements for either the evaluated subject or the evaluator rather than the effect of the intervention, which is highly relevant in the clinical practice of physiotherapy.
With regard to reproducibility, a wide IC of 95% was found at every level, which should be analyzed in light of the participants’ pathological condition. In asthma, hyperinflation takes place during the crisis. When the disease recedes, breathing patterns may vary from person to person [
38]. Thus, greater variations in costal mobility may appear in asthma patients than in people with COPD, which could explain the lesser reproducibility at the axillary level in this study compared to Malaguti et al. [
9].
The intra-evaluator reproducibility of between acceptable and good may be attributable to the influence of sex over mobility. Romei et al. [
6] showed that the abdominal contribution to tidal volume is less among women, so including subjects of both sexes in this study may have introduced an additional source of variability. The participants’ posture during the evaluation constitutes another influential factor. Verschekelen et al. [
39] described a greater contribution of the superior costal level when respiratory maneuvers were carried out at the vital capacity level in a standing position compared to measurements at the vital capacity level in a supine position. These findings could also explain the variability in the results at the axillary level.
The inter-evaluator reproducibility in this project was similar to that of Malaguti et al. [
9]. The ICCs were acceptable at the axillary level and good at the xiphoid and abdominal levels, with 95% IC. Muscular activation of the upper limbs may have contributed to lesser reproducibility at the axillary level. In healthy subjects, elevating the arm during everyday activities increases ventilatory activity, as the muscles implicated in the positioning of the arm decrease their participation in respiration, thus affecting the mechanics of the ventilatory effort [
40]. These adjustments may apply to the present study, which could explain the acceptable reproducibility at the axillary level.
The intra- and inter-evaluator reproducibility was lower at the axillary level, which is considered below the clinically acceptable level. This level is based on the application of the measurements in clinical trials. In these studies the variability of group means is related to sample size. For that reason a 0.70 reliability threshold is appropriate [
41].
On the other hand, the use of 0.7 threshold in the clinical scenario, would be limited due that the random variability of patient is greater that in clinical trial conditions. Additionally, intra- and inter-evaluator reproducibility was classified as clinically acceptable in xiphoid and abdominal levels. However, at the xiphoid level there was better inter-evaluator reproducibility than intra-evaluator, a finding that we consider a random effect because no clinical reasons are identified for such differences; and in any case, these differences do not represent changes in the decision to use or not the TI in the clinical or research context.
With regard to the external convergence construct validity, the analysis using the maximum value and the average of the two instances of the TI measurement and photogrammetry showed a correlation of between moderate and high at every level. The confidence intervals were wide at the three levels.
This positive correlation between the kinematic and TI analyses is based on the fact that both tests were evaluating the same construct: costal mobility, and the maneuvers used in the two cases are similar. Costal mobility results from the distensibility of tissue, and it could be inferred that both methods measure this biomechanical property at the three levels. Previous studies [
9] have suggested that distensibility is greatest at the abdominal level, which could explain the high correlation observed in this study at that level.
The lesser correlation at the costal level (axillary and xiphoid) can be understood beginning with the modifications to the distribution of air in this area, responding to individual breathing patterns and the consequences of intermittent hyperinflation. In asthma, hyperinflation is considered intermittent, as it appears during crises and disappears during inter-crisis periods [
38]. With regard to the type of pattern used, it was considered relevant to evaluate the correlation by allowing each subject to spontaneously maximize his/her respiration, which allowed for modified distributions of the volume of air in each test.
The consequences of hyperinflation with regard to the distribution of air in the rib cage have been studied by other authors [
3], and it has been established that the volume of trapped air moves principally to the upper costal level, thus reducing distensibility [
33]. This, together with the pathologic increased time taken to empty a lung of air and the local limitation to respiratory flow, produces hyperinflation in the other regions of the lung in patients with asthma [
42].
The results of this study suggest that TI reliability and validity are similar when using measurements of the maximum and average values. The maximum value corresponds to a greater effort by a person to move lung volumes and capacities into and out of the rib cage, while the average value illustrates the typical form of costal mobility when the subject is requested to exert a greater-than-baseline respiratory effort [
43].
For the above reasons, the TI can be used in clinical practice with people who can perform maximally at just one attempt, as well as those who require two or more attempts to obtain a result. In either case, a standardized protocol that includes every level of measurement should be considered, with an emphasis on explaining the maneuver and the commands or requests that are most effective at eliciting maximum force.
Some factors in the evaluation of the TI are outside the control of the evaluator, for example, sex, dynamic postural adjustments, breathing pattern, and muscular activation during the test [
6], but they should be considered in the clinical setting when the effects of the disease or the results of the evaluation and the physiotherapeutic management are being analyzed. The evaluation of the effects of an intervention on costal mobility should include all these factors and should always be analyzed keeping in mind that statistically significant changes should be reflected in an improvement of the clinical condition.
Within the limits of the study, it was found that the TI’s psychometric properties were established for adults with stable asthma, for which reason the results are limited to people with these characteristics. It is recommended that the psychometric properties of these evaluations be assessed with other age groups, at different phases of the disease, and with other pathologies.
The TI measurements and measurements of costal kinematics were taken after requesting maximum respiratory force. However, lung volumes and capacities were not measured objectively using tools such as plethysmography. Thus, it was not possible to standardize the exact quantifiable volume when the measurements were taken. It is recommended that lung volumes and capacities be quantified using plethysmography to decrease variability in TI measurement in future research.
Conclusions
Based on our review of the literature, this is the first study to evaluate the reliability and validity of perimetry in adults with stable asthma. Many works have demonstrated changes to respiratory mechanics in people with asthma, so this kind of evaluation should be routine for asthma patients.
The quality of the measurement techniques determines the quality of the research results and the decisions for the clinical management of these patients, and studies of reliability and validity help avoid errors in interpreting variables before and after interventions. In this study, the good reliability can be attributed to the standardization of the test and the use of a special session for familiarization. Nonetheless, it is important to remember that some aspects could not be controlled by the evaluator such as the subject’s sex and his/her dynamic postural adjustments.
A moderate to high correlation was found between the costal mobility variables, and the validity of the external convergent construct for the TI was established. This correlation stems from the fact that the same construct (costal mobility) was evaluated for both tests, and it depends on the distensibility of tissues. The elements that affect this correlation and that are not susceptible to control are individual breathing patterns and the consequences of the pathology for respiratory mechanics.
It can be concluded that the TI is a valid and reproducible measurement that can be used by health professionals during the physical examination of the thorax to evaluate thoracic mobility in adults with asthma, thus broadening their analysis of the respiratory mechanics in each case. This test can also be applied in controlled clinical trials to determine the effectiveness of therapeutic interventions for optimizing respiratory force in people suffering from this pathology.