Effects of diaphragmatic control on the assessment of sniff nasal inspiratory pressure and maximum relaxation rate

Effects of diaphragmatic control on multiparametric analysis of the sniff nasal inspiratory pressure test and inspiratory muscle activity in healthy subjects

BACKGROUND

We investigated the influence of diaphragmatic activation control (diaphC) on the relaxation rate, contractile properties and electrical activity of the inspiratory muscles of healthy subjects. Assessments were performed non-invasively using the sniff inspiratory pressure test (SNIP) and surface electromyography, respectively.

METHODS

Twenty-two subjects (10 men and 12 women) performed 10 sniff maneuvers in two different days: with and without diaphC instructions. For the SNIP test with diaphC, the subjects were instructed to perform intense activation of the diaphragm. The tests with the best SNIP values were used for analysis.

RESULTS

The maneuver with diaphC when compared to the maneuver without diaphC exhibited significant lower values for: SNIP (p <0.01), maximum relaxation rate (MRR) (p <0.01), maximum rate of pressure development (MRPD) (p <0.01), contraction times (CT) (p = 0.02) and electrical activity of the sternocleidomastoid (SCM) (p <0.01), scalene (SCL) (p = 0.01) and intercostal (CI) (p = 0.03) muscles. In addition, the decay constant (tau, τ) and relaxation time (½ RT) did not present any changes.

CONCLUSION

The diaphragmatic control performed during the SNIP test influences the inspiratory pressure and the contractile properties of inspiratory muscles. This occurs due to changes in the pattern of muscle recruitment, which change force velocity characteristics of the test. Thus, instruction on diaphC should be encouraged for better performance of the SNIP test and for evaluation targeting the diaphragm muscle activity.

Normal range of values for contractility and relaxation parameters of inspiratory muscles in healthy children: An exploratory study

OBJECTIVES

To estimate normal range of values for the contractility and relaxation parameters of inspiratory muscles and compare them by sex, age, nutritional status and level of physical activity in healthy children.

WORKING HYPOTHESIS

We hypothesized that healthy children present similar range of values for the contractility and relaxation parameters of inspiratory muscles.

STUDY DESIGN

Exploratory study conducted between 2017 and 2018.

PATIENT-SUBJECT SELECTION

Healthy children aged 6 to 11 years without history of respiratory, cardiac, cerebrovascular or neuromuscular disease as well as no nasal congestion, influenza or known septum deviation were included.

METHODOLOGY

Anthropometric, spirometry and respiratory muscle strength data were assessed. Maximum rate of pressure development (MRPD), maximum relaxation rate (MRR), time constant of decay curve (τ), contraction time (CT) and half-relaxation time (½ RT) were calculated from the nasal inspiratory pressure curve.

RESULTS

The sample was composed of 110 children (55 boys) with 1.045 as mean z-BMI-score. MRPD range of values was 8.09% to 10.86% rise/10 ms, MRR range of values was 8.09% to 10.86% fall/10 ms, τ range of values was 36.41 to 49.88 ms, CT range of values was 200 to 276 ms, ½ RT range of values was 117.5 to 148 ms and MRPD/MRR range of values was 0.71 to 1.04. The contractility and relaxation parameters did not present significant differences among children when compared by sex, age, nutritional status, or level of physical activity groups (P > .05).

CONCLUSIONS

The contractility and relaxation parameters present similar values among children and they are not influenced by age, sex, nutritional status or physical activity level.

Reference values of sniff nasal inspiratory pressure in healthy children

OBJECTIVE

To determine reference values of sniff nasal inspiratory pressure (SNIP) in healthy children.

METHODS

This cross-sectional observational study included healthy children aged 6 to 11 years of both sexes. The volunteers underwent a pulmonary function test to rule out respiratory disorders. Respiratory muscle strength was measured using maximal inspiratory pressure (MIP) and maximal expiratory pressure (MEP), respectively, with MIP close to functional residual capacity (FRC) and residual volume, while MEP to total lung capacity. SNIP was performed through the nostril contralateral to the occlusion, close to FRC. Two 6-minute walk tests were performed to assess functional exercise capacity.

RESULTS

The sample comprised 121 healthy children (62 girls); 54% presented body mass index (BMI) percentile less than 85th and 46% more than equal to 85th percentile, higher than expected. SNIP values were similar between sexes (91.1 ± 21.0 cmH₂ O in girls and 87.7 ± 19.4 cmH₂ O in boys; P = .36) as well as the means of lower limits of normal (56.88 cmH₂ O for girls and 56.66 cmH₂ O for boys). Girls presented SNIP measurements larger than those of the MIP of FRC (P < .0001), while boys presented similar mean values for both. We found a positive correlation between SNIP and BMI percentile (r = .25, P = .04) in girls, unlike boys, in whom no correlation was observed.

CONCLUSIONS

SNIP reference values and mean lower limits of normal were defined for healthy children aged 6 to 11. BMI percentile seems to positively influence the inspiratory muscle strength measured by SNIP in girls only.

Multiparametric Analysis of Sniff Nasal Inspiratory Pressure Test in Middle Stage Amyotrophic Lateral Sclerosis

The relaxation rates and contractile properties of inspiratory muscles are altered with inspiratory muscle weakness and fatigue. This fact plays an important role in neuromuscular disorders patients and had never been extensively studied in amyotrophic lateral sclerosis (ALS). In this cross-sectional study, these parameters were investigated non-invasively through nasal inspiratory sniff pressure test (SNIP) in 39 middle stage spinal onset ALS subjects and compared with 39 healthy controls. ALS patients were also divided into three subgroups according to a decline in their percentage of predicted forced vital capacity (FVC_%pred) as well as a decline in the ALS functional rating scale score and its respiratory subscore (R-subscore) in order to determine the best parameter linked to early respiratory muscle weakness. When compared with healthy subjects, middle stage ALS subjects exhibited a significantly lower (p < 0.0001) maximum relaxation rate and maximum rate of pressure development (MRPD), as well as a significantly higher (p < 0.0001) tau (τ), contraction time, and half-relaxation time. The results from receiver operating characteristic curves showed that MRPD (AUC 0.735, p < 0.001) and FVC_%pred (AUC 0.749, p = 0.009) were the best discriminator parameters between ALS patients with ≤30 and >30 points in the ALS functional rating scale. In addition, 1/2RT (AUC 0.720, p = 0.01), FVC_%pred (AUC 0.700, p = 0.03), τ (AUC 0.824, p < 0.0001), and MRPD (AUC 0.721, p = 0.01) were the parameters more sensitive in detecting a fall of three points in the R-subscore. On the other hand, MRPD (AUC 0.781, p < 0.001), τ (AUC 0.794, p = 0.0001), and percentage of predicted of SNIP (AUC 0.769, p = 0.002) were the parameters able to detect a fall in 30% of the FVC_%pred in middle stage ALS patients. The contractile properties and relaxation rates of the diaphragm are altered in middle stage spinal onset ALS when compared with healthy subjects. These parameters are able to discriminate between those middle stage ALS subjects with early decline in inspiratory muscle function and those who not.