Helium has a higher thermoconductivity and heat capacity than nitrogen. However, heat loss during respiration is mainly due to water vaporization, and the extra loss while breathing heliox amounts to, by our estimation, an extra 2.5%, unlikely of significance in adults. None of the stud-ies reported hypothermia or subjective feelings of cold by the patients.
Heliox improves certain respiratory (surrogate) parameters in some asthmatic patients during an attack, but not in others. Heliox may offer benefits in patients with acute asthma within the first hour of use, but its advantages become less apparent beyond 1 h, as most conventionally treated patients improve to similar levels, with or without it. The effect of heliox may be more pronounced in more severe cases. Since there is insufficient data, future studies should focus on whether heliox can reduce tracheal intubation rate; the duration of mechanical ventilation, intensive care, and hospital lengths of stay; and mortality. In addition, future investigators should also improve on the levels of allocation concealment, prevent air entrainment during heliox administra-tion, consider the use of higher heliox flow to compensate for its lower nebulizing efficiency, and allow a period for washout of the test gas before spirometry is performed to minimize the effects of helium on such measurements Cialis Australia.
Study objective: For the 2002 Winter Olympic Games, athletes were required to submit objective evidence of asthma or exercise-induced bronchoconstriction (EIB) for approval to inhale a P2-agonist. Eucapnic voluntary hyperventilation (EVH) was recommended as a laboratory challenge that would identify airway hyperresponsiveness (AHR) consistent with EIB. The objective was to compare the change in FEV1 provoked by EVH with that provoked by exercise in cold weather athletes.
Design: Spirometry was measured before and for 15 min after challenges. The two challenges were performed in random order at least 24 h apart.
Setting: EVH was performed in the laboratory at 19°C, and exercise took place in the field in the cold (2°C, 45% relative humidity).
Participants: Thirty-eight athletes (25 female subjects; median age, 16 years).
Interventions: For the EVH, athletes inhaled dry air containing 5% carbon dioxide for 6 min at a target ventilation equivalent to 30 times baseline FEV1. Exercise was performed by cross-country skiing, ice skating, or running for 6 to 8 min.
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Measurements and results: AHR consistent with EIB was defined as > 10% fall in FEV1 from baseline after challenge. Eleven athletes were exercise positive (EX+) [FEVX fall, 20.5 ± 7.3%], and 17 athletes were EVH positive (FEVX fall, 14.5 ± 4.5%) [mean ± SD]. Of 19 subjects with AHR, 58% were identified by exercise and 89% were identified by EVH. EVH identified 9 of 11 subjects who were EX+ and a further 8 subjects with potential for EIB. The average ventilation during EVH was 28 times FEVX.