Transient ventilatory and heart rate responses to moderate nonabrupt pseudorandom exercise

Area of Science:

• Exercise Physiology
• Human Physiology
• Respiratory Physiology

Background:

• Understanding the rapid physiological responses to exercise is crucial for interpreting exercise tests and training.
• The dynamics of ventilatory control during complex exercise stimuli are not fully elucidated.
• Previous research suggests both humoral and non-humoral mechanisms influence exercise ventilation.

Purpose of the Study:

• To investigate the dynamic ventilatory response to a complex, non-anticipatory exercise challenge in humans.
• To characterize the timing and magnitude of the initial ventilatory response (phase 1 hyperpnea) during exercise.
• To explore the relationship between phase 1 hyperpnea and other physiological variables like end-tidal gases and heart rate.

Main Methods:

• Six healthy volunteers performed a dynamic exercise challenge using a chair ergometer with a pseudorandom binary sequence (fPRBS) torque.
• Breath-by-breath ventilation, end-tidal CO2 and O2, and heart rate were continuously monitored.
• Cross-covariant analysis was used to estimate the impulse response of ventilation to the exercise stimulus.

Main Results:

• A distinct phase 1 hyperpnea was observed within the same breath as exercise onset, preceding hypocapnia.
• Phase 1 hyperpnea accounted for approximately 26% of the total ventilatory response.
• A delayed phase 2 hyperpnea, associated with slower dynamics and followed by hypercapnia, was also identified.
• Heart rate exhibited an abrupt increase during phase 1, peaking near the transition to phase 2.

Conclusions:

• The findings support a non-humoral mechanism for the phase 1 exercise hyperpnea.
• The complex exercise stimulus effectively elicited distinct fast (phase 1) and slow (phase 2) ventilatory responses.
• The results provide insights into the rapid neural control of ventilation during dynamic exercise.