Time constant of inspiratory muscle relaxation in cystic fibrosis

Locomotor challenges of waterfall-climbing gobies during transitions between media

An amphidromous goby, Sicyopterus japonicus, migrates from the ocean to upstream regions of many streams and rivers in the Pacific coasts of Japan and Taiwan. Using its mouth and fused pelvic fins (pelvic sucker), this gobiid species exhibits a rock-climbing behavior and surmounts sizable waterfalls, which block the upstream movement of many of its competitors and predators. When gobies emerge from the water to commence their climbing behavior, the change in effective density (i.e., lack of buoyancy) that occurs in this transition substantially increases the force required for adhesion. Consequently, these fish must exert adhesive suction strong enough to support their body weight against gravity during climbing on the rock surface. Suction performance for adhesion and modulatory capacity of S. japonicus were evaluated with two different sets of experimental conditions: climbing on the vertical surface with no water flow, versus climbing on a 60o-inclined surface with 2 L/min flow. Individuals of S. japonicus showed 50.7% greater mean safety factor (suction force for adhesion/gravitational force) and 56.6% shorter time to reach maximum pressure differential during climbing on the 60o-inclined surface with water rushing over their bodies than during climbing on the vertical surface with no water flow. These results indicate that when climbing with drag force from flowing water, greater functional demands are imposed and therefore, S. japonicus is required to increase neuromuscular stimulation of the pelvic muscles to elevate suction performance. In addition, S. japonicus individuals at different ontogenetic stages modulate their climbing behaviors and strategies to accommodate changing functional demands as they make transitions between different inclines, as well as media, while ascending waterfalls.

Respiratory muscle function in the newborn: a narrative review

Our aim was to summarise the current evidence and methods used to assess respiratory muscle function in the newborn, focusing on current and future potential clinical applications. The respiratory muscles undertake the work of breathing and consist mainly of the diaphragm, which in the newborn is prone to dysfunction due to lower muscle mass, flattened shape and decreased content of fatigue-resistant muscle fibres. Premature infants are prone to diaphragmatic dysfunction due to limited reserves and limited capacity to generate force and avoid fatigue. Methods to assess the respiratory muscles in the newborn include electromyography, maximal respiratory pressures, assessment for thoraco-abdominal asynchrony and composite indices, such as the pressure-time product and the tension time index. Recently, there has been significant interest and a growing body of research in assessing respiratory muscle function using bedside ultrasonography. Neurally adjusted ventilator assist is a novel ventilation mode, where the level of the respiratory support is determined by the diaphragmatic electrical activity. Prolonged mechanical ventilation, hypercapnia and hypoxia, congenital anomalies and systemic or respiratory infection can negatively impact respiratory muscle function in the newborn, while caffeine and synchronised or volume-targeted ventilation have a positive effect on respiratory muscle function compared to conventional, non-triggered or pressure-limited ventilation, respectively. IMPACT: Respiratory muscle function is impaired in prematurely born neonates and infants with congenital anomalies, such as congenital diaphragmatic hernia. Respiratory muscle function is negatively affected by prolonged ventilation and infection and positively affected by caffeine and synchronised compared to non-synchronised ventilation modes. Point-of-care diaphragmatic ultrasound and neurally adjusted ventilator assist are recent diagnostic and therapeutic technological developments with significant clinical applicability.

Adhesive force and endurance of the pelvic sucker across different modes of waterfall-climbing in gobiid fishes: Contrasting climbing mechanisms share aspects of ontogenetic change

Waterfall-climbing gobiids from oceanic islands use a suction-based adhesive mechanism formed by fused pelvic fins (pelvic sucker) and exhibit rock-climbing behavior during upstream migration. Although adhesion is a common feature of locomotion in these fishes, two distinct climbing styles - powerburst climbing and inching - have evolved. We compared the performance of the pelvic sucker during climbing across a range of body sizes between two species that use these different styles, collecting new data from the powerburst climber Lentipes concolor, and comparing these to published data for the inching climber Sicyopterus japonicus. Suction force for adhesion generated during continuous climbing did not differ between the species, with similar mean safety factors of 2.5-3.0. However, L. concolor engaged its pelvic sucker for a significantly longer duration of time (approximately 34 % longer per climbing cycle) than S. japonicus during continuous climbing. During sustained adhesion, both species exhibited non-linear scaling of fatigue time, with intermediate-sized individuals (e.g., large juveniles to small adults) showing the greatest endurance. However, the two species exhibited strikingly different maxima and variability in the endurance of their pelvic suckers. Maximum time to fatigue in L. concolor was less than half that of S. japonicus, but L. concolor showed more than double the variability of S. japonicus in time to fatigue. Our comparisons of these species reveal that despite differences in several aspects of their adhesive performance, some features of sucker function remain similar across climbing styles, including several related to how performance changes through ontogeny.

Clinimetric evaluation of muscle function tests for individuals with cystic fibrosis: A systematic review

Accurate testing of muscle function is essential in individuals with cystic fibrosis (CF). A literature search was conducted in MEDLINE, CENTRAL, CINAHL, PEDro, ScienceDirect and Web of Science according to PRISMA and COSMIN guidelines from inception to September 2019 to investigate the clinimetric properties of muscle tests in individuals with CF. The search identified 37 studies (1310 individuals) and 34 different muscle tests. Maximal inspiratory pressure, inspiratory work capacity and quadriceps strength measured by computerised dynamometry were identified as reliable tests of muscle function. The one-minute sit-to-stand test was found to have high reliability but its validity to measure quadriceps strength is unknown. The clinimetric properties of other routinely used tests have not been reported in people with CF. Very different measurement procedures were identified. Inspiratory muscle and quadriceps testing can be considered as reliable but high-quality studies evaluating tests of other muscles function (e.g. muscle endurance) are lacking.

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.

Adhesive force and endurance during waterfall climbing in an amphidromous gobiid, Sicyopterus japonicus (Teleostei: Gobiidae): Ontogenetic scaling of novel locomotor performance

An amphidromous sicydiine goby, Sicyopterus japonicus, exhibits rock-climbing behavior during upstream migration along rivers and streams. Using a pelvic sucker formed by fused pelvic fins, S. japonicus generates suction adhesion on the climbing surface. By measuring performance variables that correlate with successful rock-climbing capability, we evaluated scaling relationships of adhesive suction force generated by the pelvic sucker and fatigue during climbing in S. japonicus during ontogeny. In continuous climbing on the experimental 60°-inclined surface, the pelvic sucker of S. japonicus exhibited strong positive allometry in generating suction force for adhesion during ontogeny. In contrast, fatigue time of the pelvic sucker muscles for sustained adhesion scaled non-linearly with body mass during ontogeny. In addition, fatigue time and body mass showed the best fit to a quadratic regression, which predicted intermediate-sized individuals (large juveniles to small adults) to have better performance in adhesive endurance than smaller or larger individuals. Our experimental results indicate that different sizes of waterfall-climbing gobies have different performance capacities for rock climbing perhaps because of physiological differences in their pelvic muscles. In addition, our data from S. japonicus indicates that selection pressures on the locomotor capacities of waterfall-climbing gobiids vary during ontogeny.

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.

Effect of maturity and infection on the rate of relaxation of the respiratory muscles in ventilated, newborn infants

AIM

To assess the respiratory muscle time constant of relaxation (τ), an index of respiratory muscle function in ventilated newborns.

METHODS

Sixty-two infants (42 born prematurely) with a median gestational age of 29 [interquartile range (IQR) 26-37] weeks were prospectively studied. Measurement of τ was taken during spontaneous breathing on endotracheal continuous positive airway pressure prior to extubation, and τ was calculated from the reciprocal of the slope of the airway pressure decline versus time. Infants were classified as having had systemic or respiratory infection (positive microbiology) if they had any positive bacterial blood or respiratory culture prior to measurement.

RESULTS

Measurement of τ was taken at a median post-natal age of 6 (IQR 3-29) days. The median τ was higher in premature infants [17.4 (IQR 7.7-28.3) sec/cmH₂ O] compared to term infants [6.8 (IQR 4.4-8.7) sec/cmH₂ O, p < 0.001]. The median τ was higher in infants who had had positive microbiology [17.6 (IQR 9.9-29.1) sec/cmH₂ O] compared to infants with negative microbiology [8.0 (IQR 6.3-17.9) sec/cmH₂ O, p = 0.034]. τ was related to gestational age (r = -0.265, p = 0.003) and weight at measurement (r = -0.269, p = 0.002).

CONCLUSION

Respiratory muscle function in ventilated newborns is negatively affected by prematurity and previous systemic or respiratory infection.

Body composition and lung function in children with cystic fibrosis and meconium ileus

The aim of this study was to explore whether history of meconium ileus (MI) at birth in children and adolescents with cystic fibrosis (CF) adversely affects body composition and lung function in later life. Data of children and adolescents with CF who underwent spirometry and DXA as part of their routine care were analyzed. Associations between MI (explanatory variable) and areal bone mineral density (total body less head-TBLH aBMD), lean tissue mass (LTM), and fat mass (FM) (outcomes) were assessed using general linear models. Potential relationships of TBLH aBMD, LTM, and FM with FEV₁ (additional outcome) were also explored. One hundred and one subjects with CF (mean age 14 ± 3 years) were included, 19 (18.8%) of whom had history of MI. Negative associations were demonstrated between history of MI and FEV₁ (P = 0.04), TBLH aBMD (P = 0.03), and FM (P < 0.01) but not between history of MI and LTM (P = 0.07) after adjustment for other variables. Lung function was positively associated with TBLH aBMD (P < 0.01) and LTM (P = 0.02) but not with FM (P = 0.20).

CONCLUSION

Among children and adolescents with CF, those with history of MI have lower bone mineral density, FM, and lung function. What is Known: • Among children and adolescents with cystic fibrosis, those with history of meconium ileus in the neonatal period are at risk of having lower body mass index percentile and FEV ₁ percent predicted. What is New: • Children and adolescents with cystic fibrosis and history of meconium ileus have decreased bone mineral density and fat mass compared to patients without such history. • Lower lung function in children with MI coexists with suboptimal bone mineral density.

Relaxation Rate of the Respiratory Muscles and Prediction of Extubation Outcome in Prematurely Born Infants

BACKGROUND

Accurate prediction of extubation outcome could result in a significant reduction of respiratory morbidity in premature neonates.

OBJECTIVES

To assess whether the respiratory muscle time constant of relaxation (τ) predicted extubation outcome in mechanically ventilated, premature infants.

METHODS

Forty-six mechanically ventilated infants with a median gestational age of 26 (interquartile range [IQR] 25-29) weeks were prospectively studied. τ was calculated from the reciprocal of the slope of the decline in airway pressure as a function of time. Measurements of τ were done during 5-10 min of a spontaneous breathing test (SBT) prior to extubation. During the first and last minute of the SBT, τ1 and τ2, respectively, were assessed, and the difference between them was calculated (Δτ).

RESULTS

The median τ2 was significantly higher in infants whose extubation failed (20.7 [IQR 12.9-34.7] s/cm H2O) than in infants whose extubation succeeded (8.2 [IQR 6.2-17.8] s/cm H2O, p = 0.002). The median Δτ was significantly higher in infants whose extubation failed (10.3 [IQR 4.4-23.9] s/cm H2O) than in infants whose extubation succeeded (-1.63 [IQR -5.7 to 0.3] s/cm H2O, p = 0.001). Extubation failure was associated with τ2 (p = 0.011) and Δτ (p = 0.010) after correcting for postmenstrual age, patent ductus arteriosus, and intraventricular haemorrhage. Receiver operator characteristic curve analysis demonstrated that Δτ predicted extubation failure with an area under the curve of 0.937. A Δτ of +1.02 s/cm H2O predicted extubation failure with 94% sensitivity and 83% specificity.

CONCLUSIONS

The respiratory muscle time constant of relaxation during an SBT was significantly greater in infants whose extubation failed and could be used to predict extubation outcome in prematurely born infants.