The prediction of saliva swallowing frequency in humans from estimates of salivary flow rate and the volume of saliva swallowed

Saliva swallowing frequency is an important factor in models of oral clearance. It varies widely among individuals, and the basis for that variation has not been established. This study evaluated the use of unstimulated flow rate and the volume of saliva swallowed as predictors of swallowing frequency in 128 first-year dental students. A microphone was placed over the larynx, and swallowing activity was recorded for 30 min between 3–6:00 p.m.. The average interval between swallows was determined, and individuals retained saliva in the mouth for a period equal to that time. Retained saliva was spat out, and volume was determined gravimetrically. Four replicate tubes were collected. Flow rate was determined as sample volume over average swallow time. A subset of 10 individuals was measured on two further occasions 2–3 months apart. An independent estimate of flow rate was taken on the second occasion. Repeat-measures analysis of variance and intraclass correlations were used to estimate the reproducibility of replicate volumes, and of measurements taken on different occasions. Associations between swallowing interval, saliva volume, and flow rate were evaluated by multiple regression. Replicate volumes were highly reproducible, as were measurements of volumes, swallow times, and flow rates on different occasions. Saliva volume and flow rate jointly accounted for 99% of variance in swallowing intervals. Swallowing intervals were shortest for individuals who combined high flow rates with small saliva volumes; current models suggest that their oral clearance might be most efficient. Swallowing intervals were longest for individuals with low flow rates and large volumes; their oral clearance might be the least efficient.