Journal of applied physiology
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Randomized Controlled Trial Clinical Trial
Intense exercise stimulates albumin synthesis in the upright posture.
We tested the hypothesis that an elevation in albumin synthetic rate contributes to increased plasma albumin content during exercise-induced hypervolemia. Albumin synthetic rate was measured in seven healthy subjects at 1-5 and 21-22 h after 72 min of intense (85% peak oxygen consumption rate) intermittent exercise and after 5 h recovery in either upright (Up) or supine (Sup) postures. Deuterated phenylalanine (d(5)-Phe) was administrated by a primed-constant infusion method, and fractional synthetic rate (FSR) and absolute synthetic rate (ASR) of albumin were calculated from the enrichment of d(5)-Phe in plasma albumin, determined by gas chromatography-mass spectrometry. ⋯ In contrast, FSR and ASR of albumin were unchanged in Sup (3.9 +/- 0.4 to 4.0 +/- 1.4%/day and 74.2 +/- 8.9 to 85.3 +/- 23.9 mg albumin. kg body wt(-1). day(-1) at control and 22 h of recovery, respectively). Increased albumin synthesis after upright intense exercise contributes to the expansion of greater albumin content and its maintenance. We conclude that stimuli related to posture are critical in modulating the drive for albumin synthesis after intense exercise.
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Randomized Controlled Trial Clinical Trial
Role of expiratory flow limitation in determining lung volumes and ventilation during exercise.
We determined the role of expiratory flow limitation (EFL) on the ventilatory response to heavy exercise in six trained male cyclists [maximal O2 uptake = 65 +/- 8 (range 55-74) ml. kg-1. min-1] with normal lung function. Each subject completed four progressive cycle ergometer tests to exhaustion in random order: two trials while breathing N2O2 (26% O2-balance N2), one with and one without added dead space, and two trials while breathing HeO2 (26% O2-balance He), one with and one without added dead space. ⋯ With HeO2 (compared with N2O2) breathing during heavy and maximal exercise, 1) HeO2 increased maximal flow rates (from 20 to 38%) throughout the range of vital capacity, which reduced EFL in all subjects during tidal breathing, 2) the gains of the ventilatory and inspiratory esophageal pressure responses to added dead space increased over those during room air breathing and were similar at all exercise intensities, 3) EELV was lower and end-inspiratory lung volume remained near 90% of total lung capacity, and 4) VT was increased relative to room air breathing. We conclude that EFL or even impending EFL during heavy and maximal exercise and with added dead space in fit subjects causes EELV to increase, reduces the VT, and constrains the increase in respiratory motor output and ventilation.
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Randomized Controlled Trial Clinical Trial
Susceptibility to periodic breathing with assisted ventilation during sleep in normal subjects.
Assisted ventilation with pressure support (PSV) or proportional assist (PAV) ventilation has the potential to produce periodic breathing (PB) during sleep. We hypothesized that PB will develop when PSV level exceeds the product of spontaneous tidal volume (VT) and elastance (VTsp. E) but that the actual level at which PB will develop [PSV(PB)] will be influenced by the DeltaPCO2 (difference between eupneic PCO2 and CO2 apneic threshold) and by DeltaRR [response of respiratory rate (RR) to PSV]. ⋯ PB developed in five subjects on PAV at amplification factors of 1.5-3.4. It failed to occur in seven subjects, despite PAF of up to 7.6. We conclude that 1) a PCO2 apneic threshold exists during sleep at 1.5-5.8 Torr below eupneic PCO2, 2) the development of PB during PSV is entirely predictable during sleep, and 3) the inherent susceptibility to PB varies considerably among normal subjects.
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Randomized Controlled Trial Clinical Trial
Effect of sodium in a rehydration beverage when consumed as a fluid or meal.
To investigate the impact of fluid composition on rehydration effectiveness, 30 subjects (15 men and 15 women) were studied during 2 h of rehydration after a 2.5% body weight loss. In a randomized crossover design, subjects rehydrated with water (H2O), chicken broth (CB: 109.5 mmol/l Na, 25.3 mmol/l K), a carbohydrate-electrolyte drink (CE: 16.0 mmol/l Na, 3.3 mmol/l K), and chicken noodle soup (Soup: 333.8 mmol/l Na, 13.7 mmol/l K). Subjects ingested 175 ml at the start of rehydration and 20 min later; H2O was given every 20 min thereafter for a total volume equal to body weight loss during dehydration. ⋯ Urine osmolality was higher in the CB and Soup trials than in the CE trial. Urinary sodium concentration was higher in the Soup and CB trials than in the CE and H2O trials. These results provide evidence that the inclusion of sodium in rehydration beverages, as well as consumption of a sodium-containing liquid meal, increases fluid retention and improves plasma volume restoration.
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Randomized Controlled Trial Clinical Trial
Apnea and periodic breathing in bed-sharing and solitary sleeping infants.
Mother-infant bed sharing, compared with the solitary sleeping condition, has recently been associated with several physiological and behavioral effects. Because the physiological effects of bed sharing may also include respiratory changes, we compared the incidence of central and obstructive apneas and periodic breathing in bed-sharing and solitary sleeping infants. Twenty routinely bed-sharing mother-infant pairs and fifteen routinely solitary sleeping pairs slept for 3 nights in a sleep laboratory. ⋯ In both groups, there was a significantly higher frequency of periodic breathing events on the bed-sharing night than on the solitary night. These findings demonstrate that the bed-sharing environment can have a significant impact on respiratory control in the infant. Evidence is also presented to suggest that routine bed sharing may result in subtle neurophysiological and/or developmental differences in infants.