THE CEREBROVASCULAR TIME CONSTANT IN SEVERE TRAUMATIC BRAIN INJURY PATIENTS
The cerebrovascular time constant (τ), depends on cerebrovascular resistance and compliances of a network of pial arteries. This parameter characterizes the state of cerebral autoregulation. THE AIM OF THE STUDY was to assess the time constant of cerebral arterial bed in severe traumatic brain injury patients (TBI) with and without intracranial hematomas. We examined 110 polytrauma patients with severe TBI (mean 35±15 years, 61 men, 49 women). The first group included 52 patients without intracranial hematomas and the second group included 58 patients with epidural (7), subdural (48) and multiple (3) hematomas. Perfusion CT (PCT) was performed in 1-12 days after TBI in the first group and in 2-8 days after surgical evacuation of the hematoma in the second group. Arteriovenous amplitude of regional cerebral blood volume oscillation was calculated as the difference of arterial and venous blood volume in the “region of interest” of 1 cm2. Mean arterial pressure was measured and the flow rate of middle cerebral artery was recorded with transcranial dopplerography after PcT. Time constant was calculated by the formula of С. Avezaat (1984) modificated by М. Kasprowicz (2011) and M. Czosnyka(2012). RESULTS. The τ was shorter (p = 0.05) in both 1 and 2 group in comparison with normal date by M. Kasprowicz (2012). The time constant in the 2 group was shorter than in the 1 group, both on the side of the former hematoma (р=0.015), and on the contralateral side(p=0.047). The results indicate severe dysregulation of cerebral capillary blood flow in severe TBI which increases in the patients with traumatic intracranial hematomas.