Purpose Cervical auscultation (CA) has been used to describe the stability of swallow-associated sounds of infant feeding. Initial discrete sounds (IDS), signals that predictably occur as the pressure in the pharynx increases with swallow, of low-risk preterm infants became more uniform with increasing postmenstrual age (PMA). This developmental progression is not present in infants with bronchopulmonary dysplasia. The purpose of this study is to identify the IDS signal of adult swallows and compare the stability of IDS signals of infants to that of adults. Additionally, we compared two acoustic detection devices for CA.
Methods We performed CA with a microphone and an accelerometer simultaneously fixed to the neck of healthy adults (n = 10). Each participant consumed a liquid, a pureed food (applesauce) and a solid (cookie). The variance index (VI), a measure of the stability of the IDS signal, was used to compare the IDS of adults to that of a group of suckle-feeding low-risk preterm infants (n = 12). Low risk was defined as no ongoing oxygen requirement, no BPD, no IVH ≥ Grade III, and no sepsis.
Results The microphone and accelerometer collected signals of similar duration. The signals collected by the microphone were vibratory and artificially amplified/attenuated according to the frequency response curve of the microphone. The signals collected by the accelerometer included additional inaudible signals, such as motion and pressure changes. The mean VI of adults swallowing liquid (29.9 ± 3.1 [SEM]), did not differ from preterm infants > 36 weeks PMA (37.8 ± 2.3) but was lower than the VI of infants < 36 weeks PMA (48.4 ± 1.9; p < .05).
Conclusion This is the first real-time comparison of microphones and accelerometers for CA. A microphone may be adequate for simple auditioning of cervical sounds. For more complex applications, an accelerometer should be considered. The stability of IDS signals of low-risk preterm infants approaches that of normal adults as the infants age, suggesting a link between the stability of IDS during early infant feeding and long-term neurologic development.