Modeling Long-Term Facilitation of Respiration During Interval Exercise in Humans

Area of Science:

• Physiology
• Respiratory Control
• Exercise Science

Background:

• Long-term facilitation (LTF) of respiration is typically initiated by intermittent hypoxia and subsequent chemoreceptor stimulation.
• Comparable chemoreceptor stimulation can be achieved through combined exercise and carbon dioxide (CO2) inhalation, potentially leading to LTF.

Purpose of the Study:

• To investigate the possibility of inducing LTF through combined exercise and CO2 inhalation.
• To analyze the dynamic responses using mathematical models to differentiate neural and chemoreceptor-mediated CO2 effects on LTF.

Main Methods:

• Seven healthy subjects performed interval exercise with 3% inhaled CO2.
• Peripheral chemoreceptor sensitivity was estimated during light exercise (40 W) with air or 3% CO2.
• Mathematical models were applied to dynamic respiratory responses during and after 45% maximal oxygen uptake exercise.

Main Results:

• Peripheral chemoreceptor sensitivity approximately doubled resting levels during light exercise with 3% CO2.
• Ventilation increased significantly (17.0 ± 2.48 L/min, p < 0.001) during recovery after high-intensity exercise, consistent with LTF.
• Model fitting indicated that LTF augmentation followed second-order dynamics, suggesting neuronal plasticity.

Conclusions:

• Combined exercise and CO2 inhalation can induce significant LTF of respiration.
• The observed LTF exceeds that achieved with intermittent hypoxia alone.
• The underlying mechanism involves a balance between self-excitatory and self-inhibitory neuronal pools, indicating neuroplasticity.