Dysphagia dietary guidelines and the rheology of nutritional feeds and barium test feeds

Dysphagia can lead to aspiration of oral feeds, thus causing pneumonia. Dysphagia is diagnosed by assessing the ability to swallow barium test feeds (BTF) of different viscosities. Dysphagia diet foods (DDF) are thickened as recommended by the National Dysphagia Diet (NDD) guidelines. To our knowledge, there are no published data evaluating if the viscosity of BTF or commercial DDF meet NDD guidelines.

A TA1000 rheometer (TA Instruments; New Castle, DE) measured dynamic viscosity of BTF and DDF using creep transformation under controlled stress. Thin DDF studied included Plus Energy Drink (Boost; Novartis/Nestle; Fremont, MI) and Instant Breakfast (Carnation; Wilkes-Barre, PA) and nectar- and honey-thick DDF from Hormel (Hormel Health Labs; Savannah, GA) and Novartis (Novartis/Nestle). The BTF studied were thin, nectar-, and honey-thick Polibar barium suspension or Varibar (E-Z-EM, Inc.; Lake Success, NY). We measured batch-to-batch variability in the viscosity of DDF, with and without shaking, and after 2 h at ambient temperature at a shear rate chosen to match natural swallowing.

We observed the following: (1) DDF: the viscosity of honey-thick DDF was consistent with NDD guidelines, but other products were not. All products had minimal change in viscosity over 2 h. Boost thin liquid had > 300% increase in viscosity after shaking. (2) BTF: thin barium had a viscosity consistent with NDD guidelines. The nectar- and honey-thick Polibar BTFs were thixotropic and had unacceptably high viscosity. Varibar BTFs were not thixotropic but were more viscous than the NDD guidelines.

There was a poor relationship between the viscosity of DDF and BTF. The viscosity of BFTs is much greater than the correspondingly named diet foods and the NDD guidelines. This can place patients at significant risk for oral aspiration.