Hyperventilation enhances transcapillary diffusion of sodium fluorescein

Area of Science:

• Physiology
• Cardiovascular Physiology
• Microcirculation

Background:

• Voluntary hyperventilation (HV) is known to cause hemoconcentration.
• The precise mechanism of fluid shift during HV is not fully understood.
• Investigating transcapillary fluid dynamics during HV is crucial for understanding physiological responses.

Purpose of the Study:

• To test the hypothesis that HV increases transcapillary fluid shift into the interstitial compartment.
• To quantify changes in fluid distribution during controlled HV in healthy individuals.
• To explore the relationship between HV, hemoconcentration, and microvascular parameters.

Main Methods:

• Ten healthy male volunteers underwent 3 minutes of voluntary hyperventilation.
• Intravenous sodium fluorescein was used to assess transcapillary fluid movement via fluorescent light intensity (FLI).
• Hematocrit, serum proteins, skin temperature, and laser Doppler fluxmetry (LDF) were continuously monitored.

Main Results:

• HV significantly increased hematocrit and serum protein concentrations, indicating hemoconcentration.
• Interstitial FLI, a marker of transcapillary diffusion, was significantly higher during HV.
• No significant changes were observed in skin temperature or microvascular skin flux (LDF) during HV.

Conclusions:

• HV induces a significant transcapillary fluid shift into the interstitial space.
• The observed fluid shift occurs without alterations in microvascular skin flux.
• Findings suggest HV may increase capillary pressure or enhance capillary permeability for water and small solutes.