Comparative Aspects of the Regulation of Cutaneous and Cerebral Microcirculation During Acute Blood Loss

Objective. Using laser Doppler flowmetry (LDF) and wavelet-analysis of microvascular blood flow oscillations to determine the features of regulation of cutaneous and cerebral microhemocirculation at early stages of acute fixed volume blood loss.

Materials and methods.Experiments were carried out on 31 male outbred rats weighing 300 g to 400 g. The animals were anesthetized by intraperitoneal injection of pentobarbital (45 mg/kg). The tail artery was catheterized for invasive measurement of mean blood pressure (BP) and blood withdrawal. The LDF method (ЛАКК-02 device, LAZMA, Russia) was used to record microvascular blood flow simultaneously in the right ear and the pial vessels of the left parietal region. An acute fixed-volume hemorrhage model was used. The target blood loss volume was 30% of the total blood volume (TBV). Within 10 minutes after the end of hemorrhage (posthemorrhagic period), the blood pressure and the LDF-gram were recorded. The following LDF-gram parameters were analyzed: the mean value of IP; the maximum amplitude of blood flow oscillations (Amax) and the corresponding frequency (Fmax) in the frequency band 0.01—0.4 Hz. Statistical processing of the data was performed using Statistica 7.0.

Results. At baseline, the values of IP, Аmax and Fmax in the brain were higher than in the skin. At posthemorrhagic period, BP decreased, on average, from 105 to 41 mm Hg. Against this background, IP in the skin decreased by 65%, while in the brain it reduced only by 17%, as compared with the baseline values (P0,0001). In the same time these organs were characterized by a unidirectional dynamics of patterns of fluxmotion. In both investigated organs, Amax increased sharply, and Fmax decreased. In posthemorrhagic period, fluxmotion not only «slowed down», but was also synchronized in a relatively narrow frequency band: for the skin Fmax was about 0.04 Hz (at the border of the endothelial and neurogenic band), for the brain about 0.09 Hz (neurogenic range).

Conclusion. Acute blood loss at a volume of 30% of TBV is accompanied by the unidirectional dynamics of changes in the amplitude and frequency characteristics of cutaneous and cerebral blood flow oscillations: an increase in the amplitude, slowing down and synchronization of the fluxmotion in a narrow frequency band. The results of present study and literature data allow assuming that during hypotension, the mechanisms for reducing the dominant fluxmotion pattern frequency are associated with a decrease in pressure on the vessel walls, while an increase in amplitude is associated with the activation of the sympathoadrenal system.

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