LONG-TERM REGISTRATION OF CUTANEOUS MICROCIRCULATION DURING GENERAL-ANESTHESIA

under the provision that the active control of the microcirculatory pe rfusion is eliminated. Using this approach, we have been able to detec t a highly stable The temporal dynamics of the systemic arterial press ure can be monitored noninvasively from the skin of the earlobe or for ehead by photoplethysmography blood pressure rhythm in the range of 0. 15 Hz during psychophysical relaxation or sleep. The aim of the presen t study was to investigate the occurrence and behavior of blood pressu re rhythms below 0.2 Hz during general anesthesia. In 30 patients (ASA groups I-II) undergoing basic surgical procedures, photoplethysmograp hic recordings from the earlobe were made during the whole time of ane sthesia. The recorded signals were divided into segments of 200 s of d uration, the temporal structure of which was analyzed by fast Fourier transform. Different characteristic patterns of rhythmical behavior we re detected: (1) absence of activity below 0.2 Hz ('low-frequency rang e'); (2) slow sinusoidal rhythmicity below 0.05 Hz; (3) 'chaotic' beha vior, i.e. multiple incoherent fluctuations without stationary periods or amplitudes; (4) short-term rhythmical activity at about 0.15 Hz, a nd (5) long-term rhythmical activity at about 0.15 Hz. In patients suf ficiently sedated to eliminate low-frequency activity, rhythmicity cou ld sometimes be triggered by certain surgical stimuli, the response to which was suppressed by injection of opioids. The data presented stro ngly suggest that rhythmical perfusion patterns of the cutaneous micro circulation could serve as an indicator for the depth of anesthesia.