Cardiogenic oscillation phase relationships during single-breath tests performed in microgravity

Area of Science:

• Physiology
• Aerospace Medicine
• Respiratory System Dynamics

Background:

• Cardiogenic oscillations are measurable in lung gas washout studies.
• Understanding lung function in microgravity is crucial for astronaut health.

Purpose of the Study:

• To investigate phase relationships of cardiogenic oscillations during single-breath washouts in normal gravity (1 G) and microgravity (microG).
• To determine how microgravity affects airway closure and ventilation-perfusion (VA/Q) distributions.

Main Methods:

• Single-breath washouts (SBW) using helium, sulfurhexafluoride, oxygen, and argon bolus were performed in 1 G and microG.
• Cross-correlation analysis of gas signals identified phase differences, expressing them as angles.
• Phase relationships between inspired gases and resident gases, including CO2, were analyzed.

Main Results:

• Phase relationships between inspired gases (He) and resident gas (N2) showed no significant change between 1 G and microG.
• Airway closure patterns remained consistent, suggesting closure occurs in lung regions with high specific ventilation near residual volume.
• Carbon dioxide (CO2) phase relationships with helium (He) reversed in microG, indicating association of high ventilation areas with high VA/Q ratios.

Conclusions:

• Microgravity alters the distribution of ventilation and perfusion, leading to a wider range of VA/Q ratios.
• The observed changes in VA/Q distribution in microgravity may reconcile previous findings of an unaltered overall VA/Q range despite more homogeneous ventilation and perfusion.