Pulmonary function tests in standing ponies: reproducibility and effect of vagal blockade.

This study investigates the reliability of pulmonary function measurements in standing ponies over time, and the impact of blocking the vagus nerve on these measurements. The research finds that while some measurements have small variability over time, others show larger fluctuations, especially over longer periods.

Study Design and Methodology

• The study involved taking measurements including arterial blood gas tensions, pulmonary mechanics, and lung volumes in 4 sedated ponies every hour for 6 hours, and in 5 ponies 4 times at 2-month intervals to assess the short- and long-term reproducibility of pulmonary function measurements.
• Variables studied included tidal volume (the amount of air in the lungs that gets replaced with each breath), minute ventilation (the total volume of air entering the lungs in a minute), respiratory rate, dynamic and quasistatic compliance (referring to the lung’s capacity to stretch and expand), functional residual capacity (the amount of air remained in the lungs after a normal expired breath), and total respiratory resistance (resistance to air flow in the airways).
• The effect of vagal blockade, a process that disrupts nerve signals to the lungs, was also studied in relation to these variables.

Key Findings

• Blood gas tensions showed small variability over both the short and long term. Total respiratory resistance and functional residual capacity also showed small variations over the short term, but noticeably bigger variations over the long term.
• Tidal volume, minute ventilation, respiratory rate, and dynamic and quasistatic compliance had larger variability over both the short and long term.
• When data from all ponies were combined a significant change did not occur in any of the variables over a 6-month period.
• Vagal blockade increased tidal volume while decreasing respiratory rate and total respiratory resistance. However, it did not affect arterial blood gas tensions, minute ventilation, dynamic compliance, quasistatic compliance, functional residual capacity, and lung and thoracic cage pressure-volume curves.
• With the intact vagus, total respiratory resistance decreased with increasing lung volume. However, after vagal blockade, the decrease in total respiratory resistance with lung volume was minimal.
• Dynamic compliance was found to be independent of the frequency in the range of 15 to 60 breaths per minute. This suggests that measurable inhomogeneity of peripheral time constants didn’t exist in the ponies under examination.