Therapeutic Research

Abstract

The differences in the middle cerebral artery blood flow velocity（MCA_V）and systemic arterial blood pressure（BP）between 10 healthy young males and 10 healthy young females were examined at rest and during 6 min of cycle exercise at an intensity of 100W for males and 50W for females. The systolic, diastolic, and mean MCA_V were continuously measured using a transcranial Doppler ultrasound velocimeter. The systolic, diastolic, and mean BP were also recorded by sphygmomanometry. The mean MCA_V（MCA_Vm）for both males and females was significantly（each p＜0.05）increased by 18.7％ and 17.3％, respectively, from rest to exercise. The mean values of MCA_Vm at rest and during exercise for females were significantly（p＜0.05）greater than the corresponding values for males（rest 63.5±14.7 vs. 48.6±11.6 cm sec−1, exercise 72.8±11.7 vs. 57.5±14.6 cm sec−1）. In contrast, the mean BP（MBP）was significantly（p＜0.05）less in females than in males during exercise, whereas the MBP at rest was not significantly different between the two groups. Furthermore, to clarify the females’ greater MCA_Vm in terms of physiological significance, we simulated the volumetric blood flow through the MCA and its potential for oxygen delivery to the downstream tissues by applying the physiological data available from the literature and from the experiments. The greater blood flow in the MCA in females compensates for the relatively lower arterial oxygen content, which is transported as oxyhemoglobin contained in a smaller number of red blood cells, to give a similar oxygen transport to that in males. These results suggest that the females’ greater MCA_Vm, compensating for the lower arterial oxygen content, plays an important role in efficiently transporting oxygen through the bloodstream to tissues at a similar level to that of males.