Objective: This study tested two related hypotheses: (1) brain blood flow is reduced during postmenopausal hot flashes, and (2) the magnitude of this reduction in brain blood flow is greater during hot flashes when blood pressure is reduced.
Methods: Eleven healthy, normotensive postmenopausal women rested in a temperature-controlled laboratory (∼ 25°C) for approximately 120 minutes while waiting for a hot flash to occur. The onset of a hot flash was objectively identified by an abrupt increase in sternal sweat rate (capacitance hygrometry). Middle cerebral artery blood velocity (MCAv; transcranial Doppler) and mean arterial pressure (Finometer) were measured continuously. Each hot flash was divided into eight equal segments, and the segment with the largest reduction in MCAv and mean arterial pressure was identified for each hot flash.
Results: During experimental sessions, 25 hot flashes occurred (lasting a mean [SD] of 6.2 [2.8] min, with a mean frequency of 3  hot flashes per participant). Seventy-six percent of hot flashes were accompanied by a clear reduction (>5%) in brain blood flow. For all hot flashes, the mean maximal decrease in MCAv was 12% (9%) (7  cm s−1). This value did not correlate with corresponding changes in mean arterial pressure (R = 0.36).
Conclusions: These findings demonstrate that hot flashes are often accompanied by clear reductions in brain blood flow that do not correspond with short-term reductions in mean arterial blood pressure.