Ventilatory inhomogeneity determined from multiple-breath washouts during sustained microgravity on Spacelab SLS-1

Area of Science:

• Physiology
• Space Medicine
• Respiratory Physiology

Background:

• Ventilatory inhomogeneity, the uneven distribution of ventilation within the lungs, is a key factor in respiratory function.
• Understanding how microgravity affects ventilatory patterns is crucial for long-duration spaceflight and astronaut health.

Purpose of the Study:

• To investigate the impact of short-term microgravity exposure on ventilatory inhomogeneity in healthy humans.
• To compare ventilatory inhomogeneity in microgravity versus normal gravity (1 G) and different body postures.

Main Methods:

• Multiple-breath nitrogen washouts (MBNW) were performed on four subjects before, during, and after 9 days in microgravity.
• Subjects underwent MBNW at two different tidal volumes (700 ml and 1,250 ml).
• Six indexes of ventilatory inhomogeneity were calculated, including distribution of specific ventilation (SV) and dead space measurements.

Main Results:

• Significant ventilatory inhomogeneity was observed in the standing position under normal gravity.
• Microgravity exposure did not lead to significant changes in the measured indexes of ventilatory inhomogeneity compared to standing 1 G.
• Transitioning from standing to supine posture in 1 G significantly increased ventilatory inhomogeneity, indicating posture-dependent effects.

Conclusions:

• The primary determinants of ventilatory inhomogeneity during tidal breathing in the upright posture are not gravitational in origin.
• Short-term microgravity exposure does not significantly alter ventilatory inhomogeneity in healthy humans.
• Posture plays a more significant role in ventilatory inhomogeneity than short-term microgravity exposure.