Abstract
We measured respiratory muscle electromyograms (EMG), inspiratory (I) and expiratory (E) airflow patterns and functional residual capacity (FRC) in six ponies at rest, during treadmill walking at 1.8 mph-5, 10, and 15% grades, and during 2, 4, and 6% CO 2 inhalation. There were several similarities in the responses to exercise and CO 2 inhalation. The shapes of the I and E flow patterns were not changed appreciably from the respective control patterns during either condition. Mean diaphragm EMG increased from control ( P < 0.05) at 1.8 mph- 10 and 15% grades, and during 4 and 6% CO 2 inhalation. However, mean transversus abdominis EMG did not change significantly from control ( P > 0.10) during either condition. Exercise did not have an effect ( P > 0.05) on FRC, and there was only a slight ( P < 0.05) increase in FRC (100 ml or 2%) during 6% CO 2 inhalation. Based on the fact that we did not find major differences between exercise and CO 2 inhalation in mean diaphragm and transversus abdominis EMG, I and E flow patterns, and FRC we conclude that factor(s) other than the ventilatory stimulus and the non-ventilatory functions of the respiratory muscles are important determinants of the pony's respiratory muscle recruitment pattern under these conditions.
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