Correlation between Spectral Density of Intracranial B-Waves and Velocity of Cerebral Blood Flow Autoregulation

V.B. Semenyutin, V.A. Aliev, A.V. Kozlov

Polenov Research Neurosurgical Institute, Saint Petersburg, Russia

 

A cuff test is known to be the main method of quantitative evaluation of autoregulation disorders of cerebral blood flow. At the same time the last years are characterized by a growth of interest in studying autoregulation of cerebral blood flow (ARCBF) by means of analysis of spontaneous oscillations of linear blood flow velocity (LBFV) in arteries of the brain base. They are registered with the help of transcranial Doppler (TCD) in the absence of external factors, effecting systemic and cerebral hemodynamics.

A peculiar attention should be paid to periodic intracranial oscillations within the range of 0.008-0.035 Hz or the so-called B-waves, which were discovered in the spectrum of intracranial pressure (Lundberg N., 1960). However, later on it was found out, that they originate in the spectrum of LBFV. An exact cause of their appearance is not clear up to the end. The most probable supposition is that B-waves reflect a state of regulatory mechanisms of the cerebral circulation system at the expense of smooth-muscle cells of cerebral vessels (adequacy of vasodilation and vasoconstriction processes) or stem rhythm drivers, which change cerebral blood flow with certain periodicity by effecting the activity of vasomotor neurons.

Literature contains no data on quantitative characteristics of intracranial B-waves of LBFV, watched in normal states and pathology, which results in disorders of ARCBF.

The goal of the present study was to estimates spectral density of intracranial B-waves on the basis of TCD-monitoring of LBFV in patients with intracranial aneurysms and a different degree of ARCBF disorders.

Materials and Methods. There were 25 patients with intracranial aneurysms, aged 25-60. A state severity in a hemorrhagic period corresponded to the II-III degree (Hunt-Hess scale) in 19 cases. A compensated state (no vasospasm and intracranial hypertension) was watched in 15 patients in a remote period of hemorrhage. A control group was represented by 15 healthy volunteers, aged 25-56.

Multi Dop X (DWL, Germany) was used for bilateral TCD-monitoring of LBFV in middle cerebral arteries. ARCBF velocity (RoR) in cases with intracranial aneurysms was estimated by means of a cuff test according to a standard method. It was done before anesthesia induction. B-waves of LBFV were estimated on the basis of spectral analysis within the range of 0.008-0.035 Hz. A standard algorithm and Statistica 6.0 for Windows were used (Time Series and Prognostication module, an interval of 280 sec).

Results. Spectral density of intracranial B-waves of LBFV did not exceed 1000 (cm/s)2/Hz in both middle cerebral arteries of healthy volunteers and was equal to 216±35 (cm/s)2/Hz (left) and 227±45 (cm/s)2/Hz (right). Mean values of LBFV were as follows: 53.8±4.4 cm/s (left) and 49.7±4.2 cm/s (right).

The analysis of results was carried out with taking into account a side of aneurysm localization. As for aneurysms of anterior communicating and basilar arteries, a localization side corresponded to a region, from which aneurysm was contrasted, and, as a rule, to a hemisphere with the most marked changes, caused by subarachnoid hemorrhage.

As for patients, examined in a remote period of hemorrhage, spectral density of B-waves of LBFV on the side of aneurysm localization and the opposite side was 538±70 (cm/s)2/Hz and 505±53 (cm/s)2/Hz respectively. Indices of LBFV and RoR were as follows: 60.1±14.1 cm/s and 59.1±9.8 cm/s; 21.1±0.4 %/s and 20.9±0.4 %/s respectively. It demonstrated absence of ARCBF disorders. There was no reliable difference in spectral density of intracranial B-waves, watched in this group of patients and healthy volunteers (p>0.05).

Patients, examined in a hemorrhagic period of the disease, had the following indices of spectral density of LBFV on the side of aneurysm localization and the opposite side: 6502±2480 (cm/s)2/Hz and 3387±954 (cm/s)2/Hz respectively. LBFV and RoR were as follows: 111.8±26.6 cm/s and 74.7±7.9 cm/s; 13.7±1.4 %/s and 14.9±1.1 %/ respectively. It was indicative of ARCBF disorders. Indices of spectral density were reliably higher, than identical values in healthy volunteers and patients in a remote period of hemorrhage (p<0.05). Besides, spectral density of B-waves of LBFV of patients in a hemorrhagic period of the disease was reliably higher on the side of aneurysm localization (p<0.05).

Conclusion. Indices of spectral density of intracranial B-waves of LBFV can be used for quantitative estimation of ARCBF. When spectral density of intracranial B-waves of LBFV in initial segments of basilar arteries exceeds 1000 (cm/s)2/Hz, it is likely to be a diagnostic criterion of ARCBF disorders.