ROENTGENKYMOGRAPHIC DETERMINATION OF CARDIAC OUTPUT IN SYNCOPE INDUCED BY GRAVITY

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Abstract
The cardiac outputs of 8 individuals were detd. during quiet standing by the roentgenkymographic method. Three of these individuals showed no cardiovascular embarrassment during a 20-min. standing period, 4 consistently showed signs of oncoming syncope during this period and one subject was embarrassed but did not faint. The non-fainters showed only insignificant changes in stroke and cardiac outputs while the fainters showed a marked decrease in these functions under the same conditions. If no marked movement occurred, the stroke outputs just before syncope were 25-35% less than at the beginning of the standing period, while the cardiac outputs had diminished 21-43%. In the presence of considerable muscular contractions (convulsions) the stroke and cardiac outputs were increased by approx. the same amts. The development of syncope in quiet standing is considered to be due primarily to the absence of adequate muscular contraction which results in a diminished venous return and a secondary vasomotor failure.

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