Modeling of breath methane concentration profiles during exercise on an ergometer

Abstract

We develop a simple three compartment model based on mass balance equations which quantitatively describes the dynamics of breath methane concentration profiles during exercise on an ergometer. With the help of this model it is possible to estimate the endogenous production rate of methane in the large intestine by measuring breath gas concentrations of methane.

Figure 1

Spectrum of methane as measured by SRI-PTR-TOF-MS using ${\text{O}}_2^{+}$ primary ions.

Figure 2

Typical result of an ergometer session for one single volunteer. Average values: cardiac output (green), rest: ${\dot{Q}}_{\text{c}}$ = 5.41 [ℓ min⁻¹];75 W: ${\dot{Q}}_{\text{c}}$ = 11.07 [ℓ min⁻¹]; alveolar ventilation (red), rest: ${\dot{V}}_{\text{A}}$ = 10.69 [ℓ min⁻¹];75 W:${\dot{V}}_{\text{A}}$ = 33.12 [ℓ min⁻¹]; and exhaled end-tidal (nose sampling) methane levels (blue), rest: C_A = 31.08 [ppm]; 75 W: C_A = 11.92 [ppm], room air concentration of methane: 3.37 [ppm].

Figure 3

Three compartment model for methane: lung compartment with gas exchange, gut compartment with production of methane by enteric bacteria, and richly perfused tissue compartment containing the rest of the body including muscles (possible but small production and metabolic rate).

Figure 4

First panel: simulation of end-tidal methane concentration behavior during exercise conditions, see figure 2. Second panel: predicted methane concentrations in mixed venous blood ($C_{\overline{\text{v}}}$). Third panel: venous blood concentration returning from the gut (C_gut) and returning from the richly perfused tissue (C_rpt). Fourth panel: predicted profile of the fractional gut blood flow q_gut according to equation (11).