Evaluation of Spontaneous Swallow Frequency in Healthy People and Those With, or at Risk of Developing, Dysphagia: A Review

Dysphagia is a common and frequently undetected complication of many neurological disorders and of sarcopoenia in ageing persons. Spontaneous swallowing frequency (SSF) has been mooted as a possible tool to classify dysphagia risk. We conducted a review of the literature to describe SSF in both the healthy population and in disease-specific populations, in order to consider its utility as a screening tool to identify dysphagia. We searched Medline, Embase, Cochrane Database of Systematic Reviews and Cochrane Central Register of Controlled Trials databases. Metadata were extracted, collated and analysed to give quantitative insight. Three hundred and twelve articles were retrieved, with 19 meeting inclusion and quality criteria. Heterogeneity between studies was high (I(2) = 99%). Mean SSF in healthy younger sub-groups was 0.98/min [CI: 0.67; 1.42]. In the Parkinson’s sub-group, mean SSF was 0.59/min [0.40; 0.87]. Mean SSF in healthy older, higher risk and dysphagic populations were similar (0.21/min [0.09; 0.52], 0.26/min [0.10; 0.72] and 0.30/min [0.16; 0.54], respectively). SSF is a novel, non-invasive clinical variable which warrants further exploration as to its potential to identify persons at risk of dysphagia. Larger, well-conducted studies are needed to develop objective, standardised methods for detecting SSF, and develop normative values in healthy populations.