The distribution of ventilation-perfusion ratios in the lungs of a dysmature foal.

This research investigates how the ventilation-perfusion rations in the lungs of a prematurely born foal change from 4 hours after birth to 11 days old, highlighting significant findings such as the lack of low ventilation-perfusion ratios when breathing air and a decrease in the right-to-left shunt when exposed to 100 per cent oxygen.

Study Objective and Method

• The study was aimed at examining the distribution of ventilation-perfusion (VA/Q) ratios in the lungs of a prematurely born foal.
• The researchers observed the foal at two key stages of development: 4 hours and 11 days after birth.
• To track these changes over time, the research team employed the use of the multiple inert gas elimination technique.

Key Findings

• The main discovery in this study was the lack of low VA/Q ratios in the foal when it was breathing air.
• The research suggests that the low oxygen partial pressure PaO2 in neonatal period is mainly caused by right-to-left shunt, a condition where blood bypasses the lungs.
• At 4 hours of age, the foal’s PaO2 was 5.48 kPa, and the right-to-left shunt accounted for 33.4% of the cardiac output.
• When the foal was 11 days old, the PaO2 increased to 9.76 kPa, and the right-to-left shunt represented 10.1% of the cardiac output.
• The researchers found that at both stages there was a significant point where ventilation was much greater than blood flow, but units with low VA/Q ratios were not present at either age.

Impact of Oxygen Administration

• The study found that oxygen breathing for 40 minutes did not increase the volume of the right-to-left shunt at either age.
• However, at eleven days of age, the right-to-left shunt volume decreased when the foal was exposed to 100 per cent oxygen.