The Natural Swallow: Factors Affecting Subject Choice of Bolus Volume and Pharyngeal Swallow Parameters in a Self-selected Swallow.

Predetermined volumes are used extensively throughout clinical assessment of swallowing physiology, but bolus volumes selected by an individual in their natural swallow can vary greatly from those used in structured assessment. This study aims to identify factors influencing self-selected volume and how the mechanics of self-selected volume swallows differ from predetermined volume swallows. We used pharyngeal high-resolution manometry (HRM) with simultaneous videofluoroscopy to measure swallowing pressures in the velopharynx, hypopharynx, and upper esophageal sphincter (UES). Data were collected from 95 healthy adults during thin liquid swallows of 10 mL and a self-selected comfortable volume. An intraclass correlation coefficient (ICC) was calculated to analyze within-subject self-selected volume reliability. Linear mixed effects regression models were used to examine the association of subject characteristics with self-selected swallow volume and of self-selected volumes on pharyngeal swallowing pressures and timing events. Mean self-selected volume was 16.66 ± 7.70 mL. Increased age (p = 0.002), male sex (p = 0.021), and increased pharyngeal hold area (p = 0.007) were significantly associated with increase in self-selected bolus volume. There was good reliability between subjects' individual swallow volumes (ICC = 0.80). Velopharyngeal maximum pressure and pressure integral, tongue base duration and maximum pressure, UES pre- and post-swallow maximum pressure, and overall pharyngeal contractile integral decreased significantly with self-selected boluses. Understanding a patient's natural swallow volume, and how their natural swallow functions, will be important for designing clinical evaluations that place stress on the patient's natural swallowing mechanics in order to assess for areas of dysfunction.