Cerebral Blood Flow Pulse Is Influenced By Ascending Aortic Flow During Acute Hypotension

Abstract

PURPOSE: Recently, it has been suggested that cardiac function is one of important physiological factors to determine cerebral blood flow (CBF). However, dynamic relationship between cardiac outflow and CBF is still unknown. The purpose of the present study was to assess the dynamic relationship between arterial blood pressure (BP) or ascending aortic blood flow and CBF. METHODS: Six male healhy subjects participated (age, height, and weight; 33±6 yrs, 173±3 cm, and 72±8 kg) in the present study. Continuous beat-by-beat arterial BP was recorded from a finger using the Penaz method. Ascending aortic blood flow velocity (Ao-BFV) and middle cerebral artery blood flow velocity (MCA-BFV) were continuously measured using supra-sternum and transcranial Doppler ultrasound. After 10 min of resting condition, bilateral thigh cuffs were rapidly inflated to 200 mmHg and maintained for 2 min. Then both cuffs were rapidly deflated, and data were subsequently collected for 1 min. The same measurements were performed in the supine and 45-degree semi- Fowler’s positions. Pearson’s correlation coefficients were calculated to identify the relationship between relative change of BP or Ao-BFV and those of MCA-BFV among individuals. RESULTS: Correlation coefficient of mean BP and mean MCA-BFV was much larger than that of mean Ao-BFV and mean MCA-BFV in both the supine and semi-Fowler’s positions (R=0.615 vs. 0.009 and 0.353 vs. -0.753). In contrast, the correlation coefficient of pulse BP and pulse MCA-BFV was much smaller than that of pulse Ao-BFV and pulse MCA-BFV in the supine position (R=-0.068 vs 0.659), while it was comparable in the semi-Fowler’s position (R=0.555 vs 0.435). CONCLUSIONS: Dynamic change in mean CBF are likely to be only influenced by mean BP. However, dynamic change in pulse CBF seems to be more influenced by that of pulse ascending aortic blood flow rather than pulse BP especially in the supine position.