Effect of vehicle vibration on healthy term infants : method and infant car seat vibration quantification

Abstract

Even though infants are frequent vehicle travellers, little is known about the effect of vibrations on their comfort and health. Some studies have characterised the vibrational response of infant car seats, while others have focussed on the physiological responses of infants secured in infant car seats under varying operating conditions (stationary, vertically simulated or varying infant postures). The void identified in the current literature is - the relationship between in-vehicle multi-axis vibration input to a new-born infant seated in an infant car seat, and the resulting changes in posture and cardiorespiratory response of the infant. This study aims to form a basis for future studies seeking to investigate the effect of vehicle vibration on healthy, term infants by establishing a comprehensive method and investigating the multi-axis transmissibility of the infant car seat and subsequent vibration input that infants may experience during testing. The relationship between the responses of infants to vehicle vibration and the vibration frequencies, -magnitudes or -directions can be used to design infant car seats that not only provide protection in the event of a crash, but also promote the health of the infant under normal driving conditions. A comprehensive method was developed for an investigation into the effect of vehicle vibrations on new-born infants. Aspects addressed in this method include quantifying the vibration input to the infant, tracking the infant’s change in posture and measuring their cardiorespiratory response. As the proposed method relies on in-field testing, the road inputs and speed of the vehicle have been identified as aspects that may influence the vibration input to infants. The mission profile was selected such that it includes road inputs typically found during suburban driving. The vehicle speed was found to have a statistically significant (p < 0.05) influence on the vibrational response of the vehicle body, and based on available difference thresholds, will be perceptible by adult occupants. Whether these differences will result in different responses between infants remains to be investigated. The transmissibility of the infant car seat was determined over the selected mission profile. Although frequencies could be identified where the infant car seat amplified the vibration input to infants, the coherencies determined for the in-vehicle measurements made it challenging to interpret the transfer functions obtained. If the findings presented in this study are considered during investigations into the response of infants to vehicle vibration, a holistic approach will be followed which considers many of the aspects that may influence the observed responses. This should provide meaningful insight into the effect of vehicle vibration on the health of infants under normal driving conditions, as this effect has not been investigated before.