Examination was made of the effects of gum hardness on cerebral blood flow (CBF), oxygen uptake (VO2), heart rate (HR) and blood pressure during gum-chewing. Ten healthy male and female volunteers chewed 6 g of each of five gums differing in hardness (I, soft gum 6.4×103 poise ; II, regular gum 2.0×104 poise ; III, semi-hard gum 5.7×104 poise ; N, hard gum 7.7×104 poise ; V, super hard gum 1.4×105 poise) for ten minutes chewing 60 times per minute. Right common carotid blood flow volume (rCCBFV) for 30 to 60 second interval, blood pressure for 2 min interval and continuous measurements of right tympanic membrane temperature (rTty), right skin temperature on muscle of mastication (rTskin), VO2 and HR were measured during rest for 10 min, chewing and recovery.
The following results were obtained:
1) rCCBFV increased significantly from 6 to 15% the resting level onset of chewing and continued during gum-chewing. Increased rCCBFV returned quickly to resting level on cessation of mastication. rCCBFV increased most during the mastication of semi-(III) and hard gum (IV), and was least when chewing soft (I), regular (II) and super-hard gum (V). The response of rCCBFV to gum-chewing depended on change of common carotid blood velocity (r=0.629, p<0.001).
2) Changes in rTty and rTskin depended on gum hardness. Significant temporary decrease in rTty onset of chewing was observed for soft (I), regular (II) and semihard gum (III), but not for hard (N) and super-hard gum (V). Gradual increase in rTty was noted starting at 5 min after the onset of mastication for all gums examined. Peak levels of rTty could be seen at about 5 min after cessations of mastication. Magnitude of increase in rTty after gum-chewing depended on gum hardness. The hardest gum (V) coused the greatest increase in rTty. rTskin increased significantly at the onset of mastication, and peaked immediately following cessation of gum-chewing.
3) The response of VO2, HR and systolic and diastolic blood pressure during gumchewing depended on gum hardness. VO2 quickly decreased to less than the resting level immediately after cessation of gum-chewing. Slight increase in HR and blood pressure persisted throughout the recovery period.
The present results suggest that gum-chewing increases cerebral blood flow due to change in rCCBFV and rTty, which is indication of change in internal carotid arterial blood flow. Moderate hardness of food may possibly lead to greater increase in CBF during mastication than soft and/or very hard food.
