|Budget Amount *help
¥3,600,000 (Direct Cost: ¥3,600,000)
Fiscal Year 2002: ¥1,200,000 (Direct Cost: ¥1,200,000)
Fiscal Year 2001: ¥2,400,000 (Direct Cost: ¥2,400,000)
It has been demonstrated that water drinking caused a biphasic change in blood volume; an initial hemoconcentration followed by hemodilution in humans. This initial hemoconcentration was likely to be induced by a transient rise in blood pressure (BP). However, these mechanisms responsible for the rise in BP during water drinking remain unclear. To study the mechanism for the pressor response, blood density which reflected changes in blood volume, blood pressure (BP), heart rate (HR), muscle sympathetic nerve activity (MSNA) were continuously measured in humans, during drinking water of 500 ml or infusion of water of the same volume to the stomach through the gastric tube. Water drinking caused transient and significant increases in blood density, BP, HR and decrease in MSNA, however, gastric infusion caused no significant changes in BP, HR and MSNA. To further examine the effects of water temperature on the drinking induced changes in cardiovascular system, BP, HR and skin blood flow were continuously measured during drinking of 500 ml water at 5, 25, 37 or 50 ℃. Drinking of water at any temperature caused a transient increase in BP and HR immediately after drinking. An increase in BP, not HR, was changed according to water temperature, maximum at 5 ℃ and minimum at 37 ℃. Skin blood flow substantially increased during drinking, depending on water temperature, higher at 50 ℃ and lower at 5 ℃.
in conclusion, this rapid rise in BP might be caused through stimulations from the oropharyngeal region, swallowing act itself, swallowing-induced factors, and/or a feedforward mechanism by central descending signal from the higher brain centers. Further, BP and skin blood flow could be increased depending on water temperature, at least in part, through the possible involvement of thermoregulatory system.