Contribution to the physiology of capillary resistance in the human.

Abstract

Abstract This study on 450 healthy subjects during a period of four years is warranted by recent advances in the physiology of capillary resistance which offer new viewpoints for the understanding and interpretation of this phenomenon. 1.1. Diurnal variations (decrease of capillary resistance as the day advances) seem to be connected with the diurnal rhythm of adrenocortical activity. 2.2. The daily fluctuations of capillary resistance have an individual trait: some persons show wide fluctuations, others minor ones. They seem to be related to similar fluctuations of adrenocortical activity due to variations in the strain factor of everyday life. 3.3. To the known possible causes of seasonal variation (dietary deficiency, infections) two factors may be added: physical activity and sunshine. In the described experiments, these two factors were found to play the predominant, if not the exclusive, role. 4.4. There are people with high and others with medium or low capillary resistance, which is characteristic of the individual, and the fluctuations occur about this average individual level. Particular attention was given to the surprisingly large group of individuals (18.3 per cent) with low levels of capillary resistance. Insamuch as local differences in skin texture as well as allergic and other pathologic conditions were ruled out as possible causes, and since a correlation with the body build was found, a constitutional factor is postulated. 5.5. Any gross change in the routine of life may cause the capillary resistance to deviate temporarily from the individual level. 6.6. The human capillary stress response to various forms of stress may show four patterns: increase of capillary resistance, decrease, biphasic reaction, and no change. Essentially the human response is identical with that found in various animal species. It is postulated, for the time being as a working hypothesis, that these patterns of stress response reflect individual differences in the balance mechanism of the two hormones involved, corticoids and the somatotropic hormone. 7.7. A harmless and feasible form of stress was found in ultraviolet light, which, when applied under standard conditions, is very suitable for studying the human capillary stress response. 8.8. Knowledge of the individual capillary resistance level, the physiologic fluctuations, and the capillary stress response is essential for any study dealing with problems connected with capillary resistance.