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Our objective was to evaluate the effects of 6-weeks high-resistance, low-volume inspiratory muscle strength training (IMST) on respiratory endurance, blood pressure (BP) and heart rate (HR) responsiveness to high respiratory workloads. Ten healthy young adults completed two constant-load resistive breathing tests to exhaustion (T lim ) (target pressure =65 % maximal inspiratory pressure [PI max ]; duty cycle = 0.7; breathing frequency matched to eupnea) separated by 6-weeks high-resistance (75 % maximal inspiratory pressure, PI max ), low-volume (30 inspiratory efforts/day, 5 days/week) IMST. Throughout resistive breathing trials we measured beat-to-beat changes in BP and HR, mouth pressure, inspiratory muscle work and perceived exertion. POST resistive breathing tests revealed significant gains in endurance (PRE: 362.0 ± 46.6 s vs. POST: 663.8 ± 110.3 s, p = 0.003) and increases in respiratory muscle work (PRE: -9445 ± 1562 mmHg.s vs. POST: -16648 ± 3761 mmHg.s, p = 0.069). Conversely, systolic and diastolic BP responses, HR and ratings of perceived exertion all declined. Consistent with previous observations, 6 weeks high resistance, low volume IMST lowered casual resting SBP (p = 0.002), DBP (p = 0.007) and mean arterial pressure (p = 0.001) and improved static inspiratory pressure. High resistance, low volume inspiratory muscle strength training extends respiratory endurance and attenuates BP responsiveness in healthy, recreationally-active young adults. The outcomes have implications for improved athletic performance and for attaining and/or maintaining cardiorespiratory fitness., Competing Interests: Competing Interests The authors report no competing interests., (Copyright © 2022 The Authors. Published by Elsevier B.V. All rights reserved.)

Inspiratory muscle training holds promise as a non-pharmacologic treatment that can improve respiratory muscle strength, reduce blood pressure, and improve autonomic balance in hypertensive patients. There is a gap in knowledge regarding the specific respiratory stimulus that gives rise to these favorable outcomes. We implemented five respiratory training protocols that differed in the magnitude and direction of the lung volumes and/or intrathoracic pressures generated by subjects in training. Normotensive adults were randomly assigned to each group and trained daily for 6 weeks. Pre-post and weekly measures of blood pressure showed significant declines in systolic [-8.96 mmHg (95% CI, 7.39-10.53)] and diastolic [-5.25 mmHg (95% CI, 3.67-6.83)] blood pressures for subjects who trained with large positive or negative intrathoracic pressures. Subjects who trained with modest intrathoracic pressures or large lung volumes saw no improvement in blood pressure (P > 0.3). Large intra-thoracic pressures are the specific respiratory stimulus underpinning breathing training related improvements in blood pressure., (Copyright © 2015 Elsevier B.V. All rights reserved.)

Neonates at risk for sudden infant death syndrome (SIDS) are hospitalized for cardiorespiratory monitoring however, monitoring is costly and generates large quantities of averaged data that serve as poor predictors of infant risk. In this study we used a traditional autocorrelation function (ACF) testing its suitability as a tool to detect subtle alterations in respiratory patterning in vivo. We applied the ACF to chest wall motion tracings obtained from rat pups in the period corresponding to the mid-to-end of the third trimester of human pregnancy. Pups were drawn from two groups: nicotine-exposed and saline-exposed at each age (i.e., P7, P8, P9, and P10). Respiratory-related motions of the chest wall were recorded in room air and in response to an arousal stimulus (FIO2 14%). The autocorrelation function was used to determine measures of breathing rate and respiratory patterning. Unlike alternative tools such as Poincare plots that depict an averaged difference in a measure breath to breath, the ACF when applied to a digitized chest wall trace yields an instantaneous sample of data points that can be used to compare (data) points at the same time in the next breath or in any subsequent number of breaths. The moment-to-moment evaluation of chest wall motion detected subtle differences in respiratory pattern in rat pups exposed to nicotine in utero and aged matched saline-exposed peers. The ACF can be applied online as well as to existing data sets and requires comparatively short sampling windows (∼2 min). As shown here, the ACF could be used to identify factors that precipitate or minimize instability and thus, offers a quantitative measure of risk in vulnerable populations., (Copyright © 2015 Elsevier B.V. All rights reserved.)

The neonatal rodent serves as useful and appropriate model within which to study respiratory system development. Despite an extensive literature that documents respiratory control in vitro, in vivo studies have relied upon whole body plethysmography to determine measures of respiratory frequency and tidal volume. However, plethysmography restricts access to the animal and thus, respiratory muscle electromyographic (EMG) activities have not been recorded in these studies previously. Electromyography yields accurate information about neural respiratory center output to the musculature and therefore, about the control of breathing in the intact animal. In this case, we documented neural drive to respiratory pump and upper airway muscles, electrocardiogram (ECG) and chest wall motions in rat pups up to 10 days of age noting sighs, spontaneous central apneas and hypopneas in room air and with successive increments in fractional inspired CO2 (FICO2). Our findings underscore the advantages of EMG recordings for purposes of determining the magnitude and distribution of neural drive to respiratory muscles and for characterizing the full range of breathing behaviors exhibited by rats in the early postnatal period., (Copyright © 2014 Elsevier B.V. All rights reserved.)

Upper airway muscles play an important role in regulating airway lumen and in increasing the ability of the pharynx to remain patent in the face of subatmospheric intraluminal pressures produced during inspiration. Due to the considerable technical challenges associated with recording from muscles of the upper airway, much of the experimental work conducted in human subjects has centered on recording respiratory-related activities of the extrinsic tongue protudor muscle, the genioglossus (GG). The GG is one of eight muscles that invest the human tongue (Abd-El-Malek, 1939). All eight muscles are innervated by the hypoglossal nerve (cranial nerve XII) the cell bodies of which are located in the hypoglossal motor nucleus (HMN) of the caudal medulla. Much of the earlier work on the respiratory-related activity of XII motoneurons was based on recordings obtained from single motor axons dissected from the whole XII nerve or from whole muscle GG EMG recordings. Detailed information regarding respiratory-related GG motor unit activities was lacking until as recently as 2006. This paper examines key findings that have emerged from the last decade of work conducted in human subjects. Wherever appropriate, these results are compared with results obtained from in vitro and in vivo studies conducted in non-human mammals. The review is written with the objective of facilitating some discussion and some new thoughts regarding future research directions. The material is framed around four topics: (a) motor unit type, (b) rate coding and recruitment, (c) motor unit activity patterns, and (d) a compartment based view of pharyngeal airway control., (Copyright © 2011 Elsevier B.V. All rights reserved.)