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Effects of Transient Cerebral Hypoperfusion on Human Auditory Brainstem Responses

Adequate cerebral blood flow perfusion is crucial to maintaining brain function. The auditory brainstem response (ABR) has been demonstrated to be the most powerful diagnostic tool for assessing auditory function. This study aimed to determine the ABR under transient cerebral hypoperfusion caused by using oscillatory lower body negative pressure (OLBNP). As chronic cerebral hypoperfusion has been associated with the prolongation of the latency of ABR waves, we hypothesized that the fluctuation of cerebral blood flow perfusion also affects this latency. As prior data showing that cerebral autoregulation is not effectively engaged when pressure fluctuations are shorter than 30 sec periods (i.e., higher than 0.03 Hz), we used the sinusoidal pattern of an 18 sec period (0.056 Hz) of 0 ~ ‐ 40 mmHg OLBNP to induce transient cerebral hypoperfusion. Here, we measured ABR and cerebral blood flow velocity (MCAv) during 12 min of control and 12 min of OLBNP (40 cycle of 18‐sec periods) in 15 subjects (3 of whom were excluded from the analysis due to an insufficient number of data for ABR). Periodical changes in cerebrovascular variables were aligned relative to each 18 sec of OLBNP cycle onset and were subdivided into three phases (phase‐1: 0 ~ 6 sec, phase‐2: 6 ~ 12 sec, and phase‐3: 12 ~ 18 sec of OLBNP onset). For the ABR analysis, a total of 6800 individual sweeps were recorded for 12 min in the control and OLBNP conditions, and the recorded sweeps in the OLBNP condition were subdivided into three phases. We observed that OLBNP caused cyclic fluctuations of MCAv. One‐way repeated‐measures analysis of variance (ANOVA) and the post‐hoc comparison revealed that MCAv decreased significantly in phases‐1 and ‐2 compared to the control and phase‐3 (F(3, 33) = 16.54, p < 0.001). As for the ABR data, ANOVA and the post‐hoc comparison revealed that the latency of wave V of ABR at phase‐2 was delayed compared to phase‐1 (F(3, 33) = 3.70, p < 0.05). Moreover, the results showed that the inter‐individual difference in the variance over the phase conditions of the latency of wave V was significantly related to that of cerebral blood flow (r = 0.641, p < 0.05). Our data demonstrate that the fluctuation of cerebral blood flow perfusion could lead to the prolongation of the latency of ABR waves. This suggests that the transient cerebral hypoperfusion induced by an acute orthostatic blood shift to the lower body could impair auditory function.