Manipulation of central blood volume and implications for respiratory control function

Area of Science:

• Physiology
• Respiratory Control
• Cardiovascular Physiology

Background:

• The respiratory operating point balances controller and plant elements in respiratory control.
• The influence of central blood volume (CBV) on these elements and the operating point is not well understood.

Purpose of the Study:

• To investigate how manipulating CBV affects the controller and plant elements of the respiratory system.
• To determine the impact of CBV changes on the respiratory operating point.

Main Methods:

• Seventeen healthy males underwent water immersion (WI) and lower body negative pressure (LBNP) to alter CBV.
• Respiratory controller (Ve = S × (PetCO2 - B)) and plant (PetCO2 = A/Ve + C) characteristics were assessed.
• Changes in end-tidal PCO2 (PetCO2) and minute ventilation (Ve) were measured.

Main Results:

• CBV manipulation (WI/LBNP) altered PetCO2 but not Ve at the operating point, indicating a shift.
• Increased CBV (WI) shifted the controller's PetCO2 intercept (B) rightward; decreased CBV (LBNP) shifted it leftward (P < 0.05).
• The respiratory plant characteristics remained unchanged, while the controller element was modified.

Conclusions:

• Alterations in the respiratory operating point during CBV shifts are primarily driven by modifications to the controller element.
• The respiratory plant subsystem is not significantly affected by acute changes in CBV at the operating point.
• This study elucidates the role of the controller in respiratory adjustments to central blood volume fluctuations.