Room air dilution of heliox given by facemask.

OBJECTIVES: To measure the extent of dilution of helium-oxygen (heliox) by room air when given via high concentration reservoir mask to spontaneously breathing subjects. Substantial dilution of heliox by room air under these circumstances might alter its physical properties sufficiently to negate any potential clinical benefit in obstructive respiratory failure. DESIGN: Healthy volunteers breathing different concentrations of helium in oxygen via two different masks in a randomised crossover design. SETTING: Operating theatre in a university hospital. PATIENTS AND PARTICIPANTS: Six healthy volunteers. INTERVENTIONS: The concentrations of helium, nitrogen and oxygen were measured in the trachea of each volunteer using a mass spectrometer during normal breathing, hyperventilation and hypoventilation. MEASUREMENTS AND RESULTS: During normal breathing of Heliox21 (79% helium) via a standard non-rebreathe reservoir mask, within subject median percentage tracheal helium was 37.2% (range 29.3-52.2%) and nitrogen was 41.7% (27.4-49.4%). Air entrainment was affected by changes in breathing pattern: tracheal nitrogen concentration was greater during hyperventilation (55.4%; range 49.4-63.5%) and less during hypoventilation (33.1%; range 24.6-39.6%, p=0.043). Tracheal nitrogen could be almost completely abolished by administering heliox via a tightly fitting cushioned facemask, even during hyperventilation (2.2%; range 0.6-6.1%, p=0.028). CONCLUSIONS: Heliox administration via a standard high-concentration reservoir mask leads to significant dilution by room air. For the full potential benefits of heliox to be realised in spontaneously breathing patients, it should be administered via a system that achieves a gas tight seal, with no leaks between the delivery device and the surroundings.

Lack of effects of guanfacine on executive and memory functions in healthy male volunteers.

RATIONALE: Guanfacine is an alpha2-adrenergic receptor agonist that has been shown to have beneficial effects on working memory and attentional functions in monkeys and in patients with attention deficit hyperactivity disorder. OBJECTIVES: The aim of this study was to further investigate the cognitive-enhancing properties of guanfacine using an established battery of tasks measuring executive and memory functions. METHODS: Sixty healthy male volunteers were randomised into three groups. Cognitive testing was performed from +2 to +4 h after double-blind administration of a single oral dose of 1 or 2 mg of guanfacine or placebo. RESULTS: Systolic blood pressure was significantly reduced by both doses of guanfacine at the end of the testing session. There were no statistically significant effects on any of the cognitive measures. Two trend effects were observed with poorer performance on digit span backward and slower 'Go' reaction times after guanfacine. CONCLUSION: This study found no improvement of prefrontal memory or executive functions after guanfacine. Negative effects on blood pressure and trend effects on digit span backward and go reaction time indicate a mild sedative effect of guanfacine at these doses, possibly via mechanisms of autoreceptor down-regulation.