The long-term increase of baseline and reflexly augmented levels of human vagal-cardiac nervous activity induced by scopolamine.

We tested the hypothesis that transdermal scopolamine increases vagal-cardiac nervous outflow over the long term in 16 healthy young men. Twenty-four hours after application of one scopolamine patch, the average RR interval was increased by 13% and the average standard deviation of the RR interval (taken as an index of the level of vagal-cardiac nervous activity) was increased by 31%. Baroreceptor-cardiac reflex responsiveness (as reflected by prolongation of RR interval provoked by graded neck suction) also was increased substantially. These findings suggest that vagal-cardiac nervous activity can be augmented pharmacologically in man on a long-term basis. Since vagal outflow influences cardiac electrical properties in an important way, these findings may have therapeutic implications.

Transdermal scopolamine in the prevention of motion sickness: evaluation of the time course of efficacy.

This study evaluated the time course of efficacy of transdermal scopolamine in the prevention of motion sickness induced by exposure to coriolis stimulation in a rotating chair. We measured levels of efficacy, quantified side effects and symptoms, and determined inter- and intra-subject variability following use of transdermal scopolamine. The response to transdermal scopolamine was highly variable, although overall we recorded a 40% improvement (p less than 0.05) in test scores 16-72 h after application of the transdermal system. This variability could not be explained solely by the levels of scopolamine present in the blood. The improvement was not due to the artifactual repression by scopolamine of selected symptoms of motion sickness. An unexpectedly high incidence of side effects was reported. It was concluded that the therapeutic use of transdermal scopolamine be evaluated individually and that individuals be cautioned that subsequent usage may not always be effective.

The endocrine and metabolic responses to space flight.

The absence of hydrostatic forces, which results in body fluid shifts, and the absence of deformation forces on normally load-bearing tissues, appear to cause the principal disturbances found during and after space flight in the cardiovascular, fluid and electrolyte, erythropoietic, musculoskeletal, and metabolic systems. These alterations produce reduced body fluid volume, reduced musculoskeletal mass, and alterations in basal metabolism, resulting in the following consistent findings of space flight: weight loss, altered body composition, decreased orthostatic tolerance, and a compromised ability to deal with physical activity after returning from a space-flight environment. Specific changes include alterations in hydration status, resulting in a relative dehydration, loss of body calcium stores with a concomitant increase in urinary hydroxyproline, skeletal muscular atrophy, and a negative energy balance after prolonged space flight. Numerous endocrine changes have been determined during space flight, but more sensitive assay developed recently will allow careful determination of other hormone levels, and measurement of some of the primary changes that occur during the first hours of space flight. These results will be integrated into a working systems model of the physiologic response to weightlessness.