Movements of thoracic and abdominal compartments during ventilation at rest and during exercise.

This study examines the relationship between the movements of the chest and abdomen in thoroughbred horses during exercise, specifically while running, and how these movements contribute to tidal volume – the normal amount of air displaced between normal inhalation and exhalation. The research found that an increase in chest and abdomen diameter during exercise does not significantly contribute to the tidal volume, suggesting that lengthening of the thoracoabdominal segment might be the primary factor determining it.

Study Methods and Observations

• The researchers conducted simultaneous measurements of chest (Ch) and abdominal (Ab) circumferences along with respiratory airflow in thoroughbred horses to test their hypothesis that the chest’s circumferential expansion contributes minimally to tidal volume in a running thoroughbred.
• At rest, during a walk and trot, the flow, chest, and abdominal signals were observed to be in phase. This basically meant that the expansion and contraction patterns of chest and abdomen were synchronized with the airflow.
• During canter and gallop however, changes in chest and abdomen were out of phase with each other indicating that they expanded and contracted at different times instead of simultaneously. In addition, both chest and abdomen were found to be out of phase with the airflow as well.

Findings

• During exercise, small changes in chest and abdominal circumferences were observed and these changes did not increase even when tidal volume increased.
• In contrast, an increase in ventilation at rest, facilitated by lobeline administration, resulted in a significant increase in tidal volume. Large excursions of the chest were always synchronized with the airflow.
• Furthermore, an increase in chest circumference was seen in 3 horses, which indicates that chest stiffness per se does not prevent expansion of the chest circumference.

Conclusions

• Based on the findings, the researchers concluded that during running, neither an increase in chest nor abdominal expansion significantly contributed to tidal volume.
• The main determinant of tidal volume may instead be the elongation of the thoraco-abdominal segment. This suggests that the lengthening of the body segment connecting the chest and the abdomen during exercise could have a more substantial role in regulating tidal volume than earlier assumed.