Resistance respiratory muscle training (RRMT) increases respiratory muscle and swimming performance at depths down to 17 msw. It is unknown if RRMT improves swimming performance at greater depths and if the improvements are associated with a reduced work of breathing (WOB), altered respiratory mechanics and/or improved respiratory muscle performance. Eight male subjects (30.3 +/- 6.0 years) were tested swimming underwater in a hyperbaric chamber at 37 m of depth against a pre-determined load (70% VO(2)) until exhausted. End expiratory lung volume (EELV) was determined by subtracting inspiratory capacity from total lung capacity throughout the swims. The mechanical WOB on the lung was calculated as the integrated product of the transpulmonary pressure and ventilatory flow. Maximal expiratory (P EMAX) and inspiratory pressures (P IMAX) were measured pre- and post-RRMT. RRMT was performed every 30 s against spring loaded inspiratory and expiratory valves 30 min/day, 5 days/week, for 4 weeks. RRMT increased P (IMAX) and P (EMAX) by 40% (110 +/- 11 cmH2O (SD) vs. 155 +/- 22, p < 0.001) and 30% (148 +/- 33 cmH2O vs. 192 +/- 49, p < 0.001), respectively, respiratory endurance by 75% (19.7 +/- 15.4 min vs. 34.4 +/- 27.3, p = 0.010), and swimming endurance by 87% (26.4 +/- 9.7 min vs. 49.4 +/- 21.6, p = 0.004). The longer swimming time was associated with reduced V(E) and V(A) (p < 0.001), f(b) (p < 0.001), V(CO(2)) (p < 0.001) and WOB (p < 0.001). There were no changes in EELV post-RRMT. These results suggest the improved exercise performance post-RRMT was associated with stronger respiratory muscles, a decreased f b, and a reduced WOB.

No abstract

The effects of [+/-]-2,5-dimethoxy-4-iodoaminophentamine, a serotonin(2A/2C) receptor agonist, on pharyngeal airflow mechanics were examined in isoflurane-anesthetized lean and obese Zucker rats. The pharyngeal pressure associated with flow limitation, maximum inspiratory flow, oronasal resistance, genioglossus muscle activity, and arterial blood pressure (BP) were measured before and after the intravenous administration of the agonist. A robust activation of the genioglossus muscle in all lean and obese rats was associated with decreased upper airway (UA) collapsibility (p < 0.05), unchanged maximum flow, and increased oronasal resistance (p < 0.05) in both groups. The changes in UA mechanics and BP after the drug were similar in lean and obese rats. The serotonin agonist had no effect on UA mechanics in a group of paralyzed (pancuronium bromide) rats, despite similar elevations in BP. There was a smaller decrease (p < 0.05) in UA collapsibility that was also associated with increased upstream resistance when the drug was administered after bilateral hypoglossal nerve transection. We conclude that systemic administration of a serotonin(2A/2C) receptor agonist improves UA collapsibility predominantly, but not exclusively, via stimulation of the hypoglossal nerves and also increases upstream resistance, at least in part, through activation of nonhypoglossal motoneuronal pools innervating the UA muscles.

No abstract

Obstructive sleep apnea involves intermittent periods of airway occlusions that lead to repetitive oxygen desaturations. Exposure to chronic intermittent hypoxia (IH) in rats increases diurnal blood pressure and alters skeletal muscle physiology. The impact of IH on upper airway muscle function is unknown. We hypothesize that IH exposure increases upper airway collapsibility in rats due to alterations of the muscles surrounding the upper airway. Lean and obese rats were exposed to cyclic alterations in O(2) levels (20.6%-5%) every 90 s, 8 h/day for 6 days/wk for 12 wk. Following the exposure period, arterial pressure was recorded via the tail artery in conscious unrestrained rats. Mean arterial pressure was increased in lean IH but not in obese IH-exposed Zucker rats (P < 0.05). The pharyngeal pressure associated with airway collapse (P(crit)) was measured under anesthesia during baseline conditions and then during supramaximal stimulation of the hypoglossal nerve (cnXII). Baseline P(crit) was more positive (more collapsible) in lean but not obese rats following 12 wk of IH (P < 0.05), while supramaximal stimulation of cnXII increased airway stability (decreased P(crit)) in both lean and obese Zucker rats following IH to levels that were similar to their respective room air controls. The in vitro peak tension and the expression of the individual myosin heavy chain isoforms from the upper airway muscles were unaltered following IH. We conclude that IH leads to increases in baseline collapsibility in lean Zucker rats exposed to IH by nonmyogenic mechanisms.