Volume of a swallow: role of orifice size and viscosity

Following approval by an Institutional Review Board and a pilot study with adults, children aged 24 months to 71 months were encouraged to drink from a 28 fl oz flexible, plastic bottle with either a small diameter orifice (7 mm) or large diameter orifice (28 mm). The bottles contained either a low viscosity, an intermediate viscosity, or a higher viscosity liquid. Approximately 24 children evaluated each orifice/viscosity combination. The results, expressed as ml/swallow/kg body weight, showed that reducing orifice diameter reduced the volume of a swallow for the low viscosity liquid but did not appear to affect swallow volume for the intermediate or higher viscosity liquids. Additionally, swallow volume was found to be inversely related to viscosity of the test liquid.