Do the competition rules of synchronized swimming encourage undesirable levels of hypoxia?

Recent anecdotal reports that some synchronized swimmers have become dizzy or disorientated towards the end of their performance, and in the worst cases fainted underwater, have caused concern. However, the rules of synchronized swimming encourage slow performance of compulsory figures, and an analysis of the competition placings and duration of underwater sequences showed that the highest rankings were gained by slowly performed compulsory figures and free programmes containing a long underwater sequence. The combination of breath-holding and the vigorous exercise involved suggests that some of the symptoms complained of by the swimmers might be due to hypoxia.

Effect of pregnancy on pressure-volume relationships in circulation of rabbits.

Mean circulatory filling pressure (MCFP) has been measured after vagally induced cardiac arrest in 11 nonpregnant and 10 near-term pregnant rabbits, anesthetized with pentobarbital sodium. MCFP was 6.1 +/- 0.

The effect of carotid sinus pressure changes on mean circulatory filling pressure in the anaesthetized rabbit.

The effect on mean circulatory filling pressure (MCFP) of changes in pressure within the vascularly isolated carotid sinus has been studied in anaesthetized rabbits. With the sinus exposed to arterial pressure (102 +/- 6 mm Hg; mean +/- SEM) MCFP was 6.18 +/- 0.

Contribution of the hindlimb vasculature to systemic resistance responses to carotid sinus pressure changes in the rabbit.

The effects on the vascular resistance of the skinned hindlimb of changes in pressure within the vascularly isolated carotid sinus have been compared with those on systemic vascular resistance in the same rabbits. With the hindlimb perfused at arterial pressure a reduction of sinus pressure from 200 mm Hg to 40 mm Hg increased hindlimb vascular resistance by only 50% compared with an increase of 100% in systemic vascular resistance. Although cardiac output was unaltered, blood flow to the hindlimb increased by 24%.