Modeling Intercapillary Distance as a Regulator of Tissue Denitrogenation Rate

Removing nitrogen gas from body tissue by breathing 100% oxygen (denitrogenation) before exposure to a low-pressure environment reduces risk of decompression sickness (DCS) caused by nitrogen bubble formation. This is a priority in activities that include DCS risk such as unpressurized flight or astronaut extravehicular activity. Tissue denitrogenation is determined by perfusion, so modeling intercapillary distance (ICD) as a perfusion characteristic could be exploited to predict denitrogenation efficiency.

Five inert gas exchange models were developed that combine a cylindrical conceptualization of tissue surrounding a single capillary (Krogh model) in which denitrogenation can occur, with estimates of ICD from 10-50 µm used to represent capillary density. Rate of nitrogen washout (dPN2 · dt-1) was estimated using ICD and initial tissue nitrogen pressure as predictor variables. Regressions were performed to compare model output to fractional washout volumes obtained using Behnke's whole-body washout functions as a benchmark.

Mean denitrogenation fractions generated by these mixed-venous models correlated strongly with fractional Behnke washout curves (Pearson's r = 1). Emergent tissue nitrogen washout half-time rates ranged from 5.5-90 min. Differences in lean and adipose tissue ICD and nitrogen solubility impact tissue nitrogen concentration but not pressure.

The use of a "leaky nitrogen reservoir" multicylinder ICD perfusion model offers a theoretical framework on which to base denitrogenation rates within and across tissue types. This modeling approach may permit the development of improved perfusion-enhancing denitrogenation strategies and DCS risk models. Dart T, Mock J, Beer J. Modeling intercapillary distance as a regulator of tissue denitrogenation rate. Aerosp Med Hum Perform. 2026; 97(3):137-144.