Voluntary blood pressure control using continuous systolic blood pressure biofeedback.

1. Ability to alter blood pressure (BP) acutely with continuous systolic (SBP) BP biofeedback was assessed in volunteers using a new non-invasive finger BP monitor. 2. Reliability of finger BP measurement was demonstrated in six hypertensive subjects (21-60 years), by beat-to-beat comparison with brachial intra-arterial BP over 90 min. Wide variation of BP was achieved by physiological manoeuvres. Mean error of finger BP was -3.0/-2.2 mmHg with intra-subject s.d. of 7.2/5.4 mmHg. 3. Thirteen normotensives (21-51 years) were paid to undergo 30 trials of SBP biofeedback in six sessions over 3 weeks. The SBP trend was displayed on a monitor with appropriately 'shaped' targets; each trial consisted of BP-raising and -lowering periods of 45 and 90 s respectively with intervening 45 s baselines. 4. Nine subjects raised BP, on analysis of the last 10 trials, by an average of 18.8 mmHg while five of the 13 successfully lowered BP by an average of 10.0 mmHg. BP lowering was best achieved by diminishing respiratory rate and depth, and muscular relaxation. 5. Demonstration of large BP reductions in five of 13 normotensives using strategies applicable to longer training sessions warrants further investigations in hypertensive subjects, focusing on mediating mechanisms and transfer of effect beyond the laboratory.

Osmoregulation of the cane toad, Bufo marinus, in salt water.

Adult cane toads, B. marinus, survived in salinities up to 40% sea-water (SW). Pre-exposure to 30, then 40% SW, increased the survival time of toads in 50% SW. Plasma from toads acclimated to salt water is hyperosmotic to the environment--a result of increased plasma sodium, chloride and urea concentrations. When toads were placed in tap-water and 20% SW, all significant changes to plasma sodium, chloride, urea and osmotic pressure occurred within the first 2 days of exposure. When toads were placed in 30 and 40% SW environments, the increases in plasma sodium and chloride concentrations occurred within the first 2 days of exposure while urea and total osmotic pressure continued to rise until some time between 2 and 7 days exposure.