Validation and Demonstration of an Isolated Acoustic Recording Technique to Estimate Spontaneous Swallow Frequency

Spontaneous swallowing is considered a reflexive, pharyngeal clearance mechanism. Reductions in spontaneous swallow frequency may be a sensitive index for dysphagia and related morbidities. This study evaluated an acoustic recording technique as a measure to estimate spontaneous swallow frequency. Initially, a multichannel physiologic (surface electromyography, swallow apnea, cervical auscultation) recording technique was validated and subsequently compared to an isolated acoustic (microphone) recording technique on a sample of younger (25 ± 2.8 years) and older (68 ± 5.3 years) healthy adult participants. Sensitivity (94 %), specificity (99 %), and classification accuracy (98 %) were high for swallow identification from the multichannel physiologic recording technique. Interjudge reliability was high (k = 0.94, 95 % CI = 0.92–0.96). No significant differences in spontaneous swallow frequency were observed between the multichannel physiologic recordings and the acoustic recordings (0.85 vs. 0.81 swallows per minute). Furthermore, these two techniques were highly correlated (r = 0.95). Interjudge reliability for swallow identification via acoustic recordings was high (k = 0.96, 95 % CI = 0.94–0.99). Preliminary evaluation of the temporal stability of spontaneous swallow frequency measured from acoustic recordings indicated that time samples as short as 5 min produce viable results. Age differences were identified in spontaneous swallow frequency rates, with older participants swallowing less frequently than younger participants (0.47 vs. 1.02 swallows per minute). Collectively, these results indicate that an isolated acoustic recording technique is a valid approach to estimate spontaneous swallow frequency.