Respiratory mechanics and breathing pattern in the neonatal foal.

The research article focuses on understanding the breathing patterns, muscle activation patterns, and aspects of lung volumes in neonatal foals. The study debunks the existing hypothesis that foals keep their end-expiratory lung volume higher than the relaxation volume due to a highly compliant chest wall, emphasizing instead that the foal’s chest wall is significantly rigid.

Research Methodology and Measurements

• The study was carried out on healthy, term neonatal foals which were 2 and 7 days old. The researches aimed to understand the lung volumes, breathing pattern and activation pattern of respiratory muscles in these foals.
• Breathing pattern was measured in awake, unsedated foals during moments of quiet breathing in different positions, namely standing and in a lateral position.
• The researchers looked at the end-expiratory lung volume (EEV) – the volume of air left in the lungs after a passive exhalation, and the relaxation volume of the respiratory system (Vrx) – being the volume at which the pressure inside the lungs equals to the pressure outside.

Key Findings

• The usual breathing pattern of a neonatal foal was identified as being characterized by a monophasic inspiratory and expiratory flow pattern, meaning it had one phase of increasing and one phase of decreasing flow for both inspiration and expiration.
• Both the act of inhaling and exhaling were active, with the onset of Edi (Electrical activity of the diaphragm) activity seen before the start of the inspiratory flow. Meanwhile, phasic abdominal muscle activity was noticeable throughout most of the expiration period.
• The study found no evidence to support the existing hypothesis that a normal, term neonatal foal actively maintains an end-respiratory lung volume greater than the relaxation volume of their respiratory system because of a highly compliant chest wall.
• The lung volume and lung compliance values, when normalized, were similar to those observed in neonates from other species. However, the chest wall compliance, when normalized, was notably lower. This implies that the foal’s chest wall is not highly flexible or compliant but is rather rigid.

Conclusions

• The researchers concluded that the chest wall of a term neonatal foal is adequately rigid to avert a low relaxation volume. This characteristic likely saves the foal from having to use a breathing strategy that maintains an end-expiratory lung volume higher than the lung’s relaxation volume.