Effect of position on the mechanical interaction between the rib cage and abdomen in preterm infants

Abstract

To determine the influence of body position on chest wall and pulmonary function, we studied the ventilatory, pulmonary mechanics, and thoracoabdominal motion profiles in 20 preterm infants recovering from respiratory disease who were positioned in both the supine and prone position. Thoracoabdominal motion was assessed from measurements of relative rib cage and abdominal movement and the calculated phase angle (an index of thoracoabdominal synchrony) of the rib and abdomen Lissajous figures. The ventilatory and pulmonary function profiles were assessed from simultaneous measurements of transpulmonary pressure, airflow, and tidal volume. The infants were studied in quiet sleep, and the order of positioning was randomized across patients. The results demonstrated no significant difference in ventilatory and pulmonary function measurements as a function of position. In contrast, there was a significant reduction (-49%) in the phase angle of the Lissajous figures and an increase (+66%) in rib cage motion in prone compared with the supine position. In addition, the degree of improvement in phase angle in the prone position was correlated to the severity of asynchrony in the supine position. We speculate that the improvement in thoracoabdominal synchrony in the prone position is related to alterations of chest wall mechanics and respiratory muscle tone mediated by a posturally related shift in the area of apposition of the diaphragm to the anterior inner rib cage wall and increase in passive tension of the muscles of the rib cage. This study suggests that the mechanical advantage associated with prone positioning may confer a useful alternative breathing pattern to the preterm infant in whom elevated respiratory work loads and respiratory musculoskeletal immaturity may predispose to respiratory failure.

Changes in lung volume and ventilation following transition from invasive to noninvasive respiratory support and prone positioning in preterm infants

“…Placing the infant in prone position did not change tidal volume but did result in a significant reduction in respiratory rate compared to supine position. As TcPCO 2 remained stable this suggests more efficient breathing, probably caused by a reduction in thoraco-abdominal asynchrony (7).…”

“…Many infants on noninvasive support are placed in the prone position as previous studies have demonstrated that this reduces thoraco-abdominal asynchrony, improves oxygenation and increases functional residual capacity (5,7,24). Our study also shows an increase in EELV when switching from supine to prone position but adds important information on its regional distributions.…”

“…To make these transitions successful, infants should be able to maintain an optimal EELV and normal ventilation during nCPAP. Placing infants in prone position might facilitate this transition to nCPAP as this posture seems to increase EELV and improve respiratory mechanics (5)(6)(7)(8).…”

Response of oxygen saturation in preterm infants receiving rib cage stabilization with an elastic band in two body positions: a randomized clinical trial

“…and support of the rib cage with the elastic band. Previous studies only investigated the correlation between postural positioning and thoracoabdominal synchrony, describing enhancements in diaphragm function, oxygen saturation, and oxygen partial pressure, as well as reductions in heart rate and gastroesophageal reflux episodes 3,5,[12][13][14] .…”

“…In the supine position, however, the zone of apposition decreases, demanding greater respiratory work with thoracoabdominal distortions 13 . Thus, our study showed that, when the chest band is worn in the supine position, the rib cage stabilizes and makes breathing easier for small amplitudes with mobile phrenic center, stable ribs, and fixed lower back, which creates a stronger contraction of the diaphragm, causing greater alveolar distensibility 23 , generating greater saturation with lower respiratory rate values.…”