Abstract
Respiratory-induced fluctuations in heart rate and arterial blood pressure have been intensively investigated, but there is little information on the effect of respiration on peripheral blood volume. In the current study, blood volume changes in the finger, obtained by light transmission measurements, were measured during regular breathing (6 s periods) and long breathing (12 s periods). Respiratory chest-circumference changes were simultaneously measured in order to associate the pattern of tissue blood volume change with the respiratory cycle. Sixteen subjects 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 increase more than 2 s before the start of inspiration. For the 6 s breathing period, blood volume decreased during inspiration in five examinations, and increased 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 inspiration and the subsequent vasodilatation. The decrease in peripheral blood volume during inspiration is probably due to the negative thoracic pressure during inspiration and its mechanical effect on thoracic vessels.
Highlights
Respiratory-induced fluctuations in heart rate—respiratory sinus arrhythmia—and similar fluctuations in arterial blood pressure have been intensively investigated, but in only a few studies the pattern of the change during inspiration and during expiration was investigated
In 14 out of the 16 long-breathing period examinations (12 s each, including 5 s pause), tissue blood volume increased during inspiration and decreased during expiration
An inverse pattern was found for the long breathing periods: the tissue blood volume in the finger decreased during inspiration and increased during expiration
Summary
Respiratory-induced fluctuations in heart rate—respiratory sinus arrhythmia—and similar fluctuations in arterial blood pressure have been intensively investigated, but in only a few studies the pattern of the change during inspiration and during expiration was investigated. Heart rate increases and systolic blood pressure decreases during inspiration [1,2,3] but there is strong variability in the relationship between heart rate or systolic blood pressure and the respiratory changes in chest circumference. The origin of these respiratory-induced fluctuations is not decisively known. Peripheral blood volume, as measured by light transmission through the tissue, has been shown to fluctuate at the respiratory rate [13,14,15,16,17,18], as it does with each heart beat, and so induces the photoplethysmographic (PPG) signal
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