Comparison of Changes in Systemic and Cerebral Hemodynamics in Two Variants of the Active Standing Test

Justification of methods for diagnosing disorders of systemic and cerebral hemodynamics in humans is an important task of fundamental medicine. The aim of this study was to compare changes in systemic hemodynamics and cerebral circulation in two modifications of the orthostatic test: during active transition to a standing position from a supine position or from a sitting position. In a group of 11 young volunteers of both sexes, blood pressure (BP), heart rate (HR) and stroke volume (SV) were continuously recorded, and changes in the concentration of oxyhemoglobin (OHb) and total hemoglobin (CHb) in the frontal cortex were assessed using infrared spectroscopy. In none of the tests, significant changes in mean BP occurred during verticalization, whereas changes in HR, SV, spectral power and phase synchronization of mean BP and HR oscillations in the low-frequency range (0.06-0.13 Hz) were observed. For most parameters, these changes were more pronounced in the “supine-standing” test than in the “sitting-standing” test. Along with that, an increase in the spectral power of low-frequency oscillations of CHb and OHb in small cerebral vessels, as well as the degree of synchronization of low-frequency oscillations of OHb and mean BP, which can reflect the processes of cerebral circulation control, were observed only in the “supine-standing” test. Thus, both variants of the active orthostatic test provide an assessment of systemic hemodynamics, whereas the “supine-standing” test is more appropriate for assessing cerebral circulation.