130 Section PHYSIOLOGICAL ANTHROPOLOGY COMPARISON OF CEREBROVASCULAR AND CARDIOVASOCULAR RESPONSES TO DYNAMIC ORTHOSTATIC STRESS USING SINUSOIDAL LOWER-BODY NEGATIVE PRESSURE Ishibashi Keita1 , Oyama Fuyuki1 Yasukouchi Akira2 1 , Yoshida Hisao1 , Higuchi Shigekazu2 Graduate School of Engineering, Chiba University, Chiba, Japan 2Faculty of Design, Kyushu University, Fukuoka, Japan In the evolution of human bipedalism, gravity is one of the essential environmental factors to which humans had to adapt. <...> The high metabolic demand of the human brain necessitates the upward delivery of a large proportion of the cardiac output (CO), and the relatively large length of human legs causes blood pooling in the legs along with orthostatic stress. <...> The ability of cerebral vasculature to maintain relatively steady blood fl ow in the face of changing mean arterial pressure (MAP), termed cerebral autoregulation (CA), is critical to adapt to gravity. <...> Although CA is an integral component of the systemic circulation system, little is known about the relationship between cardiovascular regulation and dynamic CA in response to transient changes in MAP, such as during changes in posture. <...> We examined the cerebrovascular and cardiovascular responses to dynamic orthostatic stress using sinusoidal lower-body negative pressure (SLBNP), which can simulate orthostatic blood shifts. <...> We measured the middle cerebral arterial blood fl ow velocity (MCAv) and cerebral blood oxygenation (OxyHb), MAP and CO in 13 adult male subjects. <...> Two different periodic changes (18- and 90-sec of 0 to −40 mmHg) of SLBNP were provided. <...> The transfer function of gain to MAP (that is, vascular conductance during the 90-sec period) was signifi cantly larger than that of the 18-sec period in all parameters (MCAv, OxyHb, and CO), but the conductance ratio between 90-sec and 18-sec was signifi cantly larger in CO compared to MCAv. <...> These results suggest that the systemic regulatory system including CA could be responsive to the slow fl uctuations of MAP and that CA is relatively stable over a wide range of MAP fl uctuations in frequency. <...> The unique characteristic of CA could also include the ability to maintain relatively steady blood fl ow in the face of changing frequencies of MAP fl uctuation. <...> Key words: cerebral <...>