We used the velocity profile method with color Doppler imaging to estimate change in flow volume in the common carotid artery after a meal. Flow volume and resistive index of the common carotid artery, resistive index of the internal and external carotid arteries, maximum velocity and resistive index of the celiac artery, and sleepiness index were measured both before and after a meal. Total common carotid arterial flow volume had decreased 16.5 percent 30 minutes after the meal and returned to its initial volume 120 minutes after the meal; the sleepiness index increased 30 to 60 minutes after the meal. We assumed that increase in the resistance of the carotid artery accounted for the decrease in flow volume, and that the sleepiness index increased as a result. Although decrease in flow volume of the common carotid artery may cause sleepiness, no clear causal relationship between these two factors was found.