J. Biomedical Science and Engineering, 2011, 4, 529-534 doi:10.4236/jbise.2011.48068 Published Online August 2011 (http://www.SciRP.org/journal/jbise/ JBiSE ). Published Online August 2011 in SciRes. http://www.scirp.org/journal/JBiSE Pattern of respiratory-induced changes in fingertip blood volume measured by light transmission Meir Nitzan 1 , Daniel Dayan 1 , Eran Shalom 1 , Yuval Slovik 2 , Alan Murray 3 1 Department of Applied Physics/Medical Engineering, Jerusalem College of Technology, Jerusalem, Israel; 2 Department of Otorhinolaringology, Head and Neck Surgery, Soroka University Medical Center, Beer Sheva, Israel; 3 Department of Medical Physics Freeman Hospital, Newcastle, UK. Email: nitzan@jct.ac.il Received 16 May 2011; revised 13 June 2011; accepted 5 July 2011. 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. Keywords: Light Absorption; Deep Breathing; Sympathetic Nervous system; Tissue Blood Volume 1. INTRODUCTION Respiratory-induced fluctuations in heart rate—respira- tory sinus arrhythmia—and similar fluctuations in arte- rial 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 dur- ing inspiration [1-3] 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. They have been attributed to fluctua- tions in central autonomic activity caused by spontane- ous oscillations in respiratory center activity or by respi- ratory-induced mechanical effects on the aortic baro- receptors and the pulmonary stretch receptors [2-4]. The direct mechanical effect of respiratory-induced thoracic pressure changes on arterial blood pressure and on cen- tral veins may also be significant [5-7]. Respiratory-induced fluctuations have also been found in the peripheral circulatory system. Deep inspiration reduces skin blood flow, measured by skin temperature [8,9] and by laser Doppler flowmetry [9-12], and this reduction has been attributed to higher sympathetic ac- tivity. Peripheral blood volume, as measured by light transmission through the tissue, has been shown to fluc- tuate at the respiratory rate [13-18], as it does with each heart beat, and so induces the photoplethysmographic (PPG) signal. Two possible mechanisms have been suggested for the origin of tissue blood fluctuations with respiration: mechanical influence of the negative thoracic pressure during inspiration on the arteries and veins in the thorax [14-17] and respiratory changes in sympathetic activity [15-18]. The effect of respiration on sympathetic activity has been demonstrated by several studies [19-21], which showed higher muscle sympathetic nerve activity