Rapid decline and recovery of cerebral blood flow on return to upright posture

We examined cardiovascular and cerebrovascular regulation during standing. Nine women and nine men completed 10 min supine rest followed by 70 s standing. We also studied the effectiveness of the cardiopulmonary baroreflex (CPBR) during three levels of LBNP (-10,-20,-30mmHg). Mean flow velocity (MFVMCA)(MFVMCA) from the right middle cerebral artery (MCA, transcranial Doppler ultrasound), mean arterial pressure (MAP, Finapres), blood pressure at the level of the MCA (BPMCA)(BPMCA), and heart rate (HR) were monitored. An index of cerebrovascular resistance (CVRi)(CVRi) was calculated by CVRi=BPMCA/MFVMCACVRi=BPMCA/MFVMCA. Baseline values for MAP, MFVMCAMFVMCA, BPMCABPMCA, CVRiCVRi, and HR were not statistically different between men and women (P>0.1)(P>0.1). The ‘stand’ tests resulted in initial decreases in MAP (19.6–40.5%), MFVMCAMFVMCA (13.0–51.5%), BPMCABPMCA (54.6–81.0%), CVRiCVRi (49.3–73.1%) and an increase in HR (30.1–106.3%). A greater decrease in MFVMCAMFVMCA, as a percentage of baseline, was seen for men (P=0.007)(P=0.007). Men also showed a greater percentage change in MAP (P<0.004)(P<0.004) and BPMCABPMCA(P<0.04)(P<0.04). In the subjects studied for CPBR gain, the preliminary data revealed a negative correlation between reduction in MAP and CPBR gain (r=-0.648)(r=-0.648). Thus, it is possible the gender difference of smaller declines in MAP for women might have been related to relatively greater CPBR gains.