Technical and methodological procedures for respiratory muscles study in different populations.
Children, respiratory muscles, amyotrophic lateral sclerosis, neuromuscular diseases.
Introduction: Respiratory muscles play a major role in pulmonary ventilation, functionally dividing into three groups: the diaphragm, the rib cage and the abdominal muscles. In clinical practice, the strength of this musculature is measured by pressures generated mainly in voluntary and non-invasive maneuvers, such as through the maximum inspiratory and expiratory pressures (PImax and PEmax, respectively) and sniff nasal inspiratory pressure (SNIP). In addition to PEmax to measure strength of expiratory muscles, the literature provides nasal expiratory pressure (SNEP) as an alternative to complement PEmax. In respiratory and neuromuscular pathologies, we observe respiratory muscle weakness, which implies a decrease in pressure and the consequent appearance of ventilatory symptoms. Aims: 1) Analyze the reliability of the SNIP maneuver in a single evaluation and determine the number of maneuvers necessary to reach the maximum SNIP peak in healthy children from 6 to 11 years of age; 2) Establish the reference values for maximum respiratory pressures in healthy children of the same age group; 3) Observe the difference in nasal respiratory pressure measurements (SNIP and SNEP), as well as evaluate the relaxation rates (MRR, 1/2RT and τ) and contractile properties (MRPD and CT) of the respiratory muscles in different positions in individuals with Amyotrophic Lateral Sclerosis (ALS). Materials and Methods: 1) This cross-sectional study included 121 healthy children with normal lung function, in which 12 to 20 SNIP maneuvers were performed, with 30 seconds of rest between each maneuver. Reliability was tested using the intraclass correlation coefficient (ICC), standard error of measurement (SEM), minimum detectable change (MDC) and Bland-Altman analysis for concordance. 2) A minimum of three tests were performed for each maximum respiratory pressure, PImax and PEmax, on 121 healthy children, with a minimum duration of the maneuver of 1.5 seconds with a plateau of 1 second and a 1-minute rest between the tests. A stepwise multiple linear regression analysis was applied for PImax and PEmax taking into account the correlations observed with the independent variables: age, weight and sex. 3) In a sample of 17 patients with ALS, SNIP and SNEP were evaluated in two different positions (seated and supine with a 30º elevation), as well as the surface electromyographic activity of the respiratory muscles in both maneuvers. Variables corresponding to relaxation rates and contractile properties of the respiratory muscles were extracted from the SNIP and SNEP curves. Results: 1) The ICC and corresponding confidence interval (CI) between the highest measure and the first reproducible maneuver were 0.752 (0.656–0.824), SEM=10.37 cmH2O, and MDC=28.74 cmH2O. For children aged 6 to 7 years, the ICC was 0.669 (0.427–0.822), SEM=10.76 cmH2O and MDC=29.82 cmH2O; for children aged 8 to 11 years, the ICC was 0.774 (0.662–0.852), SEM=9.74 cmH2O, and MDC=26.05 cmH2O. For girls, the ICC was 0.817 (0.706–0.889), SEM=9.40 cmH2O and MDC=26.05 cmH2O; for boys, the ICC was 0.671 (0.487–0.798), SEM=11.51 cmH2O, and MDC=31.90 cmH2O. Approximately 80% of the total sample reached the highest SNIP before the 10th maneuver. 2) There was a statistically significant difference for PImax between genders (p = 0.006), but the same did not occur with PEmax (p = 0.051). Comparisons of pressures between ages showed statistically significant differences in PImax (p <0.001) and PEmax (p = 0.01) according to the established age groups. The independent variables height, weight, age and sex were positively correlated with PImax, but age and sex persisted in the equation (PImax = 24.630 + 7.044 * age + 13.161 * sex). PEmax was positively correlated with height, weight and age, making up the equation the variables age in girls and weight in boys (PEmax (girls) = 55.623 + 4.698 * age, and PEmax (boys) = 82.617 + 0.612 * weight). 3) We observed that there are no statistically significant differences between the variables in different positions, however, we found a moderate effect size for the TC, MRR, τ and ½ TR of the SNIP, moderate also for the SNEP peak and large for the MRR of SNEP. Conclusions: 1) SNIP demonstrated moderate reliability between the maneuvers in children aged 6 to 11 years; older children and girls reached the SNIP peak faster. Finally, results indicated that 12 maneuvers were sufficient for healthy children aged 6 to 11 years to achieve the highest SNIP peak. 2) This study determined new reference equations for maximal respiratory pressures in healthy children aged 6-11 years, including variables such as age, sex and weight, using all the methodology recommended by ATS / ERS and BSPT. 3) The results have not yet been discussed.