Journal of applied physiology
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The purpose of the study was to determine the influence of neuromuscular electrical stimulation (NMES) current intensity and pulse width applied to the right elbow flexors on the discharge characteristics of motor units in the left biceps brachii. Three NMES current intensities were applied for 5 s with either narrow (0.2 ms) or wide (1 ms) stimulus pulses: one at 80% of motor threshold and two that evoked contractions at either ∼10% or ∼20% of maximal voluntary contraction (MVC) force. The discharge times of 28 low-threshold (0.4-21.6% MVC force) and 16 high-threshold (31.7-56.3% MVC force) motor units in the short head of biceps brachii were determined before, during, and after NMES. ⋯ NMES did not significantly influence the discharge characteristics of tracked single-threshold motor units. However, a qualitative analysis indicated that there was an increase in the number of unique waveforms detected during and after NMES. The findings indicate that activity of motor units in the left elbow flexors can be modulated by NMES current and pulse width applied to right elbow flexors, but the effects are not distributed uniformly to the involved motor units.
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Combined optogenetic activation of the retrotrapezoid nucleus (RTN; a CO2/proton-activated brainstem nucleus) with nearby catecholaminergic neurons (C1 and A5), or selective C1 neuron stimulation, increases blood pressure (BP) and breathing, causes arousal from non-rapid eye movement (non-REM) sleep, and triggers sighs. Here we wished to determine which of these physiological responses are elicited when RTN neurons are selectively activated. The left rostral RTN and nearby A5 neurons were transduced with channelrhodopsin-2 (ChR2(+)) using a lentiviral vector. ⋯ Overall (all ChR2(+) rats combined), ΔV̇e correlated with the number of ChR2(+) RTN neurons whereas arousal probability correlated with the number of ChR2(+) catecholaminergic neurons. In conclusion, RTN neurons activate breathing powerfully and, unlike the C1 cells, have minimal effects on BP and have a weak arousal capability at best. A5 neuron stimulation produces little effect on breathing and BP but does appear to facilitate arousal.
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Both transient receptor potential ankyrin 1 (TRPA1) and vanilloid 1 (TRPV1) receptors are abundantly expressed in bronchopulmonary C-fiber sensory nerves and can be activated by a number of endogenous inflammatory mediators. A recent study has reported a synergistic effect of simultaneous TRPA1 and TRPV1 activations in vagal pulmonary C-fiber afferents in anesthetized rats, but its underlying mechanism was not known. This study aimed to characterize a possible interaction between these two TRP channels and to investigate the potential role of Ca(2+) as a mediator of this interaction in isolated rat vagal pulmonary sensory neurons. ⋯ This potentiating effect was eliminated when either AITC or Cap was replaced by non-TRPA1 and non-TRPV1 chemical activators of these neurons, demonstrating the selectivity of the interaction between these two TRP channels. Furthermore, when Ca(2+) was removed from the extracellular solution, the synergistic effect of Cap and AITC on pulmonary sensory neurons was completely abrogated, clearly indicating a critical role of Ca(2+) in mediating the action. These results suggest that this TRPA1-TRPV1 interaction may play a part in regulating the sensitivity of pulmonary sensory neurons during airway inflammatory reaction.
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Pharyngeal collapsibility during sleep increases primarily due to decline in dilator muscle activity. However, genioglossus EMG is known to increase during apneas and hypopneas, usually without reversing upper airway obstruction or inspiratory flow limitation. The present study was undertaken to test the hypothesis that intense activation of the genioglossus fails to prevent pharyngeal obstruction during sleep, and to evaluate if sleep-induced changes in tongue muscle coordination may be responsible for this phenomenon. ⋯ In sleeping OSA patients, genioglossal activity may increase during obstructed breathing to levels that exceed substantially those required to prevent pharyngeal collapse during wakefulness. In contrast, coactivation of retractors is deficient during sleep. These findings suggest that sleep-induced alteration in tongue muscle coordination may be responsible for the failure of high genioglossal EMG activity to alleviate flow limitation.
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Recent studies showed that nasal high flow (NHF) with or without supplemental oxygen can assist ventilation of patients with chronic respiratory and sleep disorders. The hypothesis of this study was to test whether NHF can clear dead space in two different models of the upper nasal airways. The first was a simple tube model consisting of a nozzle to simulate the nasal valve area, connected to a cylindrical tube to simulate the nasal cavity. ⋯ For the anatomically based model, there was complete tracer-gas removal from the nasal cavities within 1.0 s. The level of clearance in the nasal cavities increased by 1.8 ml/s for every 1.0 l/min increase in the rate of NHF. The study has demonstrated the fast-occurring clearance of nasal cavities by NHF therapy, which is capable of reducing of dead space rebreathing.