Respiration physiology
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Respiration physiology · Sep 2001
Development of in vivo ventilatory and single chemosensitive neuron responses to hypercapnia in rats.
We used pressure plethysmography to study breathing patterns of neonatal and adult rats acutely exposed to elevated levels of CO2. Ventilation (VE) increased progressively with increasing inspired CO2. The rise in VE was associated with an increase in tidal volume, but not respiratory rate. ⋯ At all ages studied, LC neurons increased their firing rate by approximately 44% in response to hypercapnic acidosis (10% CO2, pH 7.0). Thus the in vivo ventilatory response to hypercapnia was not correlated with the V(m) response of individual LC neurons to hypercapnic acidosis in neonatal rats. These data suggest that CO2 sensitivity of ventilation in rats may exist in two forms, a high-sensitivity neonatal (or fetal) form and a lower-sensitivity adult form, with a critical window of very low sensitivity during the period of transition between the two (approximately P8).
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Respiration physiology · Sep 2001
Sublingual electrical stimulation of the tongue during wakefulness and sleep.
Pharyngeal obstruction in patients with obstructive sleep apnea (OSA) is thought to result from decreased upper airway muscle tone during sleep. The goal of the present study was to estimate the role of the tongue muscles in maintaining pharyngeal patency during sleep. Using non-invasive, sub-lingual surface electrical stimulation (ES), we measured tongue protrusion force during wakefulness and upper airway resistance during sleep in seven healthy subjects and six patients with OSA. ⋯ We conclude that non-invasive ES of the tongue improves flow dynamics during sleep. Combined activation of tongue protrusors and retractors may have a beneficial mechanical effect. The magnitude of responses observed suggests that in addition to the stimulated muscles, other muscles and/or forces have a substantial impact on pharyngeal patency.
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Respiration physiology · Sep 2001
Clinical Trial Controlled Clinical TrialEffects of respiratory muscle training versus placebo on endurance exercise performance.
We evaluated the effects of a 5 week (25 sessions); (30-35 min/day, 5 days/week), respiratory muscle training (RMT) program in nine competitive male cyclists. The experimental design included inspiratory resistance strength training (3-5 min/session) and hyperpnea endurance training (30 min/session), a placebo group which used a sham hypoxic trainer (n=8), and three exercise performance tests, including a highly reproducible 8 km time trial test. RMT intensity, measured once a week in terms of accumulated inspiratory pressure and the level of sustainable hyperpnea increased significantly after 5 weeks (+64% and +19%, respectively). ⋯ Heart rate, ventilation, or venous blood lactate, at equal work-rates during the incremental exercise test or at equal times during the fixed work-rate endurance test were not changed significantly across these exercise trials in either group. We propose that the effect of RMT on exercise performance in highly trained cyclists does not exceed that in a placebo group. Significant placebo and test familiarization effects must be accounted for in experimental designs utilizing performance tests which are critically dependent on volitional effort.