Contribution of tissue lipid to long xenon residence times in muscle

Abstract

Experiments demonstrate that the mean residence time of an inert gas in tissue is longer than that predicted by a single-compartment model of gas exchange. Also the relative dispersion (RD, the standard deviation of residence times divided by the mean) is 1 according to this model, but RDs in real tissues are closer to 2, suggesting that a multiple-compartment model might be more accurate. The residence time of a gas is proportional to its solubility in the tissue. Although the noble gases in particular are 10 times more soluble in lipid than in nonlipid tissues, models of gas exchange generally do not incorporate measurements of the lipid in tissue, which may lead to error in the predicted gas residence times. Could a multiple-compartment model that accounts for the lipid in tissue more accurately predict the mean and RD of gas residence times? In this study, we determined the mean and RD of Xe residence times in intact and surgically isolated muscles in a canine model. We then determined the lipid content and the perfusion heterogeneity in each tissue, and we used these measurements with a multiple-compartment model of gas exchange to predict the longest physiologically plausible Xe residence times. Even so, we found the observed Xe mean residence times to be twice as long as those predicted by the model. However, the predicted RDs were considerably larger than the observed RDs. We conclude that lipid alone cannot account for the residence times of Xe in tissue and that a multiple-compartment model is not an accurate representation of inert gas exchange in tissue.

Extracting non-Gaussian governing laws from data on mean exit time

“…Firstly, we take the simulated data from 1 Au =− as the observations on MET ob U by difference scheme provided by Eq. (24). The data set has 2J points on escaping interval ( 1,1)…”

“…Lévy motion is a non-Gaussian process with heavy-tailed distribution and has been widely used in modeling various systems with heavy-tailed fluctuations [16][17][18] . Mean exit time, also called as mean residence time or mean first passage time, is a significant deterministic quantity and has been observed or measured in many systems such as fluid, industrial, chemical and physiological systems [19][20][21][22][23][24][25][26] . For instance, the mean residence time of a fluid particle can be measured by "pulse experiment 22 ", which consists of introducing a pulse of tracer in the inlet to the domain, while measuring continuously the tracer concentration at a given point.…”

“…The mean residence time of a fluid in water storage tanks and wastewater lagoons is often measured by Lagrangian simulation of particles injected into the domain 23 . Novotny et al 24 determined the mean residence time of Xenon in intact and surgically isolated muscles by recording the time-dependent background radioactivity with a detector positioned midway between the two detectors over the tissues. Nasserzadeh et al 25 have clearly demonstrated that residence times of gas particles in large incinerator plants can be measured by a pseudo-random binary signal tracer technique successfully and economically.…”

Quantifying model uncertainty in dynamical systems driven by non-Gaussian Lévy stable noise with observations on mean exit time or escape probability

“…Mean residence time has been observed or measured in chemical, industrial and physiological systems [13,24]. For example, the mean residence time for Xe in intact and surgically isolated muscles can be measured [25]. It is found that the mean residence time of Xe is longer than that predicted by a single-compartment model of gas exchange, and this leads to the understanding that a multiple-compartment model might be more accurate according to larger relative dispersion (the standard deviation of residence time divided by the mean).…”