Distribution of ventilation in pregnant Shetland ponies measured by Electrical Impedance Tomography.

This research investigated how pregnancy influences lung ventilation in Shetland pony mares, using Electrical Impedance Tomography (EIT). Findings suggest that late pregnancy can hinder the respiratory function in the most ventral lung sections of the animal.

Objective and Method

• The study aimed to assess the impact of pregnancy on the distribution of ventilation in pregnant Shetland ponies. This was done by using Electrical Impedance Tomography (EIT) to examine the ventral to dorsal (V/D) and left to right (L/R) ventilation distribution ratios, as well as the centration in specific areas of interest within the mare’s chest.
• Electrical impedance tomography (EIT) is an advanced, non-invasive technique that provides real-time, regional lung ventilation data, representing the impedance changes related to the volume changes in the thorax and enabling the research team to observe how ventilation works in different regions of the pony’s lungs.

Research Setup

• Six pregnant Shetland pony mares were repeatedly analyzed using EIT, starting from at least four weeks before giving birth (antepartum) up until three weeks after delivery (postpartum).
• The ponies were conscious and standing during the examination, providing a realistic measure of their normal breathing mechanics.

Findings

• The research found that there was a significant decrease in the V/D ventilation distribution ratio as the mares’ gestation progressed, decreasing from 0.74 ± 0.09 at 28 days before birth (AP28), to 0.68 ± 0.10 three days before birth (AP3).
• Notably, there was a significant increase in the V/D ratio to 0.96 ± 0.08 seven days after birth (PP7), indicating a recovery of the ventilation distribution after parturition.
• However, the left to right (L/R) distribution of ventilation did not show any significant difference before or after birth. This suggests that the changes are primarily observed in the front-to-back axis (ventral to dorsal) in these ponies.
• The most ventral areas of the lungs (dependent regions) had less ventilation during the late stages of pregnancy (days AP28 and AP3) compared to after giving birth (PP7), indicating that late pregnancy might affect the ability of these regions to function effectively.

Significance and Implications

• This study provided valuable insights into how late-stage pregnancy affects the pulmonary function in Shetland ponies, highlighting an area of lung physiology that might be compromised during gestation.
• Besides, this research demonstrated that EIT is a feasible method for repeated measures of ventilation distribution in conscious, standing ponies—which could be impactful for future veterinary investigations into equine respiratory health.