Assessment of changes in arterial compliance by photoplethysmography

Many medications have constrictive or dilatory influences on blood vessels; they can influence either big or small vessels, but the available non-invasive methods for the assessment of blood flow or blood vessels compliance are not appropriate for microcirculation. We have previously used photoplethysmography (PPG) for the measurement of light absorption changes in the tissue, for the assessment of blood volume changes in the tissue and in the current study the PPG signal is used for the evaluation of changes in several hemodynamic parameters during epiduraI anesthesia. The sympathetic block which accompanies epidural anesthetic treatment results in pain relief since the sympathetic nerve fibers mediate the pain sense. The sympathetic nervous system is also associated with active constriction of the blood vessels, so that after the sympathetic block the arterioles are dilated.