Relation between blood flow and tissue blood oxygenation in human fingertip skin.

BACKGROUND: Tissue blood flow (BF) is thought to be involved in the regulation of tissue blood oxygenation (StO2). The purpose of the present study was to show the relation between BF and StO2 by measuring them simultaneously under different conditions. METHODS: Twenty-one healthy subjects (age 21-30years) participated in this study. We measured BF and StO2 in a small area of skin (fingertip, palm, forearm) simultaneously using a laser Doppler flowmeter and a tissue oxygenation monitor. Three measurements were made at rest while performing mental arithmetic and during constriction of the ipsilateral upper arm. RESULTS: At rest, BF and StO2 were higher in the fingertip than in the palm or forearm (p<0.01). Performing mental arithmetic produced significant decreases in BF, oxygenated hemoglobin, and StO2 in the fingertip (p<0.05). Constriction of the ipsilateral upper arm produced significant decreases in BF and StO2 (p<0.05) and an increase in oxygenated hemoglobin (p<0.05). Both procedures produced significant increases in deoxygenated hemoglobin (p<0.05), which was in antiphase to the decrease in StO2. CONCLUSIONS: BF decrease produced a significantly decreased StO2 in fingertip skin. The results show that simultaneous measurement of BF and StO2 is beneficial for showing the close relation between them.

Effects of sample hardness on human chewing force: a model study using silicone rubber.

This study aims to clarify the effects of sample hardness on chewing force of humans. Silicone rubber was chosen as a food model, and three silicone rubber samples of varying hardness were chewed between the upper and lower incisors or molars in a natural way. Chewing force, contact area between a specimen and teeth, and pressure applied into the specimen were dynamically measured with a multiple-point sheet sensor. The multiple-point measurement revealed that a harder sample evoked higher peak force, longer duration, higher impulse, and higher active pressure values, whereas the chewing cycle and time to peak were not affected by sample hardness. The contact area between the sample and teeth decreased for the harder sample during incisor chewing. The peak force and force-related parameters, contact area, time to peak and bite force duration showed higher values for molar bites than for incisor bites, while the chewing cycle was similar in both cases. The measurement with the sheet sensor system clearly indicated that sample hardness modified chewing force of humans. We hypothesise that the effect of sample hardness is mainly mediated by mechanoreceptors in the periodontal ligament.

Involvement of trigeminal spinal nucleus in parasympathetic reflex vasodilatation in cat lower lip.

We examined whether the trigeminal spinal nucleus (Vsp) forms part of the central mechanism by which electrical stimulation of the central cut end of the lingual nerve (LN) evokes parasympathetic reflex vasodilatation in the lower lip in artificially ventilated, cervically vagosympathectomized cats deeply anesthetized with alpha-chloralose and urethane. For this purpose, we made microinjections within the brain stem to produce nonselective, reversible local anesthesia (lidocaine) or soma-selective, irreversible neurotoxic damage (kainic acid). Local anesthesia of Vsp by microinjection of lidocaine (2%; 1 microl/site) reversibly and significantly reduced the ipsilateral-LN-evoked parasympathetic reflex vasodilatation. Unilateral microinjection of kainic acid (10 mM/site; 1 microl) into Vsp ipsilateral to the stimulated LN led to an irreversible reduction in the reflex vasodilatation but had no effect on the vasodilatation elicited by stimulation of the contralateral LN. Such microinjection of kainic acid into Vsp had no effect on the vasodilatation evoked by electrical stimulation of the ipsilateral inferior salivatory nucleus. Electrical stimulation of Vsp elicited a blood flow increase in the lower lip in an intensity- and frequency-dependent manner, regardless of whether systemic arterial blood pressure rose or fell. Hexamethonium (1.0 mg/kg iv) significantly reduced the vasodilator responses elicited by electrical stimulation of the central cut end of LN or of Vsp, each to a similar degree. After hexamethonium, both vasodilator responses showed time-dependent recovery. These results strongly suggest that Vsp is an important bulbar relay for LN-evoked parasympathetic reflex vasodilatation in the cat lower lip.