Session S72.4

Changes in Heart Rate and Tissue Blood Volume Induced by Inspiration and Expiration

D Dayan, A Babchenko, M Nitzan*

Jerusalem College of Technology
Jerusalem, Israel

Respiration induces fluctuations in heart rate and arterial blood pressure, originating from direct mechanical effect of thoracic pressure changes on the blood vessels or from changes in vagal or sympathetic tone, which can be either direct or induced by baroreceptor activity. In order to study the relationship between cardiovascular hemodynamics and temporal changes during respiration, we used photoplethysmographic (PPG) signal, which reflects the cardiac-induced increase in the tissue blood volume during systole, simultaneously with novel depth-of-breath sensor. The principle of the latter is based on the dependence of light transmission through bent optic-fiber on its radius of curvature. The optic-fiber sensor was connected to an elastic chest belt which increased its radius of curvature during inspiration, resulting in higher light transmission through the optic-fiber. A PPG device, composed of infrared light-emitting-diode and photodetector were attached to the index fingers of 15 healthy persons, and the PPG signal was recorded during deep breathing (6 inspirations per min) simultaneously with the output of the optic-fiber sensor.
In most examinations the tissue blood volume (which is inversely related to the PPG baseline) in the finger increased during inspiration. Since inspiration is associated with lower thoracic pressure, the effect cannot be explained by direct mechanical effect on the veins and is therefore related to changes in vagal or sympathetic tone. The increase of heart rate during inspiration is generally attributed to decrease in vagal activity, while our results which show inspiration-induced vasodilatation indicate either decrease in sympathetic activity or increase in sympathetic-induced vasodilatation. In few examinations tissue blood volume decreased during inspiration probably indicating sympathetic-induced vasoconstriction.

(Abstract Control Number: 190)