Effects of the supine and prone position on diaphragm thickness in healthy term infants

Abstract

Background-The physiological basis underlying the decline in the incidence of sudden infant death syndrome (SIDS) associated with changing the sleep position from prone to supine remains unknown. Aims-To evaluate diaphragm thickness (t di ) and shortening in healthy term infants in the prone and supine positions in order to determine whether changes in body position would aVect diaphragm resting length and the degree of diaphragm shortening during inspiration. Methods-In 16 healthy term infants, diaphragm thickness at the level of the zone of apposition on the right side was measured using ultrasonography. Heart rate (HR), breathing frequency (f), and transcutaneous oxyhaemoglobin saturation (SaO 2 ) were recorded simultaneously during diaphragm imaging with the infants in the supine and prone positions during quiet sleep. Results-At end expiratory (EEV) and at end inspiratory lung volumes (EIV), t di increased significantly in the prone position. The change in t di during tidal breathing was also greater when the infant was prone. SaO 2 , HR, and f were not significantly diVerent at EEV and at EIV in both positions. Conclusion-In healthy term infants, placed in the prone position, the diaphragm is significantly thicker and, therefore, shorter, both at EEV and EIV. Diaphragm shortening during tidal breathing is greater when the infant is prone. In the prone position, the decreased diaphragm resting length would impair diaphragm strength, and the additional diaphragm shortening during tidal breathing represents added work performed by the diaphragm. This may compromise an infant's capacity to respond to stressful situations when placed in the prone position and may contribute to the association of SIDS with prone position.

Diaphragm dimensions of the healthy term infant

“…The noninvasive feature of ultrasonography makes it well suited for the study of neonatal diaphragm (12,19,20). Our findings that 1) t di at end-expiration is positively associated with BW and BL and 2) calculated diaphragm strength is independent of length and weight are similar to what we previously found in adults.…”

Effect of posture on oxygenation and respiratory muscle strength in convalescent infants

“…22 The postulated effect of the prone posture on diaphragmatic function in healthy term neonates 20 is not supported by either our findings of a higher PIMAX in the supine compared with the prone posture or postural differences in diaphragm configuration recently described in healthy term neonates. 10 Using ultrasonographic examination, Relian et al 10 showed that the diaphragm was significantly thicker at end expiratory volume in the prone than in the supine posture. In addition, the prone posture was associated with greater diaphragm thickening during inspiration.…”

“…9 Changes in posture by alterations in respiratory system mechanics or lung volume could affect diaphragm function by influencing the resting length of the diaphragm or the degree to which it shortened during inspiration. 10 We therefore hypothesised that any posture related changes in oxygenation in convalescent infants could be explained by alterations in respiratory muscle strength. The aims of two consecutive studies were to test that hypothesis.…”

Sudden infant death syndrome and perinatal risk factors

“…The hypothesis that prone position overburdens the diaphragm was investigated by Rehan et al within a study that included 16 healthy children [18]. This study showed that in this position the diaphragm is much thinner and shorter at the endings of inspiratory and expiratory lung volume.…”