Pattern of respiratory-induced changes in fingertip blood volume measured by light transmission

Abstract

Respiratory-induced fluctuations in heart rate and arterial blood pressure have been intensively investi-gated, but there is little information on the effect of respiration on peripheral blood volume. In the cur-rent study, blood volume changes in the finger, ob-tained by light transmission measurements, were measured during regular breathing (6 s periods) and long breathing (12 s periods). Respiratory chest-cir-cumference changes were simultaneously measured in order to associate the pattern of tissue blood vol-ume change with the respiratory cycle. Sixteen sub-jects were studied, and in fourteen finger blood vol-ume increased during inspiration and decreased during expiration in the long-breathing periods. In all 14 subjects the start of blood volume decrease was significantly delayed from the start of expiration by mean ± SD 1.00 ± 0.65 s (p < 0.001, range 0 -2.3 s). The start of blood volume increase was significantly delayed from the end of expiration by 3.45 ± 1.76 s (p < 0.005). In eight, finger blood volume started to in-crease more than 2 s before the start of inspiration. For the 6 s breathing period, blood volume decreased during inspiration in five examinations, and in-creased in seven. The increase in peripheral blood volume during inspiration could be attributed to the higher abdominal pressure during inspiration, and to the decrease in sympathetic activity during inspira-tion and the subsequent vasodilatation. The decrease in peripheral blood volume during inspiration is probably due to the negative thoracic pressure dur-ing inspiration and its mechanical effect on thoracic vessels.