Spontaneous oscillations of arterial blood pressure, cerebral and peripheral blood flow in healthy and comatose subjects

Slow and rhythmic spontaneous oscillations of cerebral and peripheral blood flow occur within frequencies of 0.5-3 min(-1) (0.008-0.05 Hz, B-waves) an d 3-9 min(-1) (0.05-0.15 Hz, M-waves). The generators and pathways of such oscillations are not fully understood. We compared the coefficient of varia nce (CoV), which serves as an indicator for the amplitude of oscillations a nd is calculated as the percent standard deviation of oscillations within a particular frequency band from the mean, to study the impairment of genera tors or pathways of such oscillations in normal subjects and comatose patie nts in a controlled fashion. With local ethic committee approval, data were collected from 19 healthy volunteers and nine comatose patients suffering from severe traumatic brain injury (n = 3), severe subarachnoid hemorrhage (n = 3), and intracerebral hemorrhage (n = 3). Cerebral blood flow velociti es were measured by transcranial Doppler ultrasound (TCD), peripheral vasom otion by finger tip laser Doppler flowmetry (LDF), and ABP by either non-in vasive continuous blood pressure recordings (Finapres method) in control su bjects, or by direct radial artery recordings in comatose patients. Each re cording session lasted similar to 20-30 min. Data were stored in the TCD de vice for offline analysis of CoV. For CoV in the cerebral B-wave frequency range there was no difference between coma patients and controls, however t here was a highly significant reduction in the amplitude of peripheral B-wa ve LDF and ABP vasomotion (3.8 +/- 2.1 vs. 28.2 +/- 16.1 for LDF, p < 0.001 ; and 1.2 +/- 0.7 vs. 4.6 +/- 2.8 for ABP, p < 0.007) This observation was confirmed for spontaneous cerebral and peripheral oscillations in the M-wav e frequency range. The CoV reduction in peripheral LDF and ABP oscillations suggest a severe impairment of the proposed sympathetic pathway in comatos e patients. The preservation of central TCD oscillations argues in favor of different pathways and/or generators of cerebral and peripheral B- and M-w aves.