Hyperbaric Oxygen Treatment -
Analysis Of Oxygen Transport To Tissues
The scientific paper presented below is a first result of a joint research started by a team of scientists working in three different disciplines - Applied Mathematics, Physical Chemistry and Physics. Analyzing oxygen transport to ischemic / hypoxic tissues during hyperbaric oxygen treatment, the process is explained beyond the molecular diffusion transport mechanism.
The research itself was motivated by a sad event with fortunate outcome. A full account of the story you can find in the testimonial of Prof. Eugene Levich. Below are brief facts about the research team members
Dr. Eugene Levich. Professor of Theoretical Physics and Professor of Engineering at CYNY. Resigned in 1991 to establish a private businesses while continuing his research activities. Among areas of Prof. Levich's scientific activities are Turbulence in Fluids snf Plasma, Phase transitions, Geophysical Phenomena, Astrophysics and Cosmology, Optical storage for computers and other complex systems. Recently Prof. Levich has focused in biophysics, working in the team with Dr. Alex Babchin and Prof. Gregory Sivashinsky in the research guided by Dr. Y. Melamed and described here.
Dr. Alex Babchin is a Distinguished Scientist (retired) of The Alberta Research Council, Canada. The areas of Dr. Babchin's expertise include Colloids, Surfaces, Porous Media, Physiochemical Hydrodynamics and Osmotic Phenomena. Dr. Babchin currently resides in Tel Aviv, Israel and is involved in HBOT research.
Dr. Gregory Sivashinsky is the Bauer-Neumann Professor in Theoretical Mechanics and Applied Mathematics at Tel Aviv University, Israel. His area of expertise covers various aspects of fluid mechanics including hydrodynamic instabilities, reactive flows and transport in porous media. Currently Dr. Sivashinsky is involved in the HBOT research.
Dr. Yehuda Melamed, M.D. the Founder and Director of Elisha & Rambam Hospitals Hyperbaric & Diving Medical Center of Haifa, Israel has guided this research. The work in the project has been assisted by the UK and internationally recognized authority in the field of Hyperbaric Oxygen Therapy, Prof. Philip James M.D. of Wolfson Hyperbaric Medicine Unit, University of Dundee, Ninewells Hospital and Medical School, Dundee, Scotland.
Featured article. Pages 1, 2, 3.
The Physics And Physiology Of Oxygen: An Interdisciplinary Approach To Explain Oxygen Transport To Ishemic / Hypoxic Tissue In Hyperbaric Oxygen Treatment
A. Babchin1, E. Levich1, Y. Melamed2, G. Sivashinsky1
1Tel Aviv University, Tel Aviv 69978, Israel, 2Hyperbaric Medical Center, Elisha and Rambam Hospitals, Haifa, 34636, Israel
ABSTRACT
Hyperbaric oxygen (HBO) treatment defines the medical procedure when the patient inhales pure oxygen at elevated pressure conditions. Many diseases and all injuries are associated with a lack of oxygen in tissues, known as hypoxia. HBO provides an effective method for fast oxygen delivery in medical practice. The exact mechanism of the oxygen transport under HBO conditions is not fully identified. The objective of this article is to extend the colloid and surface science basis for the oxygen transport in HBO conditions beyond the molecular diffusion transport mechanism. At a pressure in the hyperbaric chamber of two atmospheres, the partial pressure of oxygen in the blood plasma increases 10 times. The sharp increase of oxygen concentration in the blood plasma creates a considerable concentration gradient between the oxygen dissolved in the plasma and in the tissue. The concentration gradient of oxygen as a nonelectrolyte solute causes an osmotic flow of blood plasma with dissolved oxygen. In other words, the molecular diffusion transport of oxygen is supplemented by the convective diffusion raised due to the osmotic flow, accelerating the oxygen delivery from blood to tissue. A non steady state equation for nonelectrolyte osmosis is solved asymptotically. The solution clearly demonstrates two modes of osmotic flow: normal osmosis, directed from lower to higher solute concentrations, and anomalous osmosis, directed from higher to lower solute concentrations. The fast delivery of oxygen from blood to tissue is explained on the basis of the strong molecular interaction between the oxygen and the tissue, causing an influx of oxygen into the tissue by convective diffusion in the anomalous osmosis process. The transport of the second gas, nitrogen, dissolved in the blood plasma, is also taken into the consideration. As the patient does not inhale nitrogen during HBO treatment, but exhales it along with oxygen and carbon dioxide, the concentration of nitrogen in blood plasma drops and the nitrogen concentration gradient becomes directed from blood to tissue. On the assumption of weak interaction between the inert nitrogen and the human tissue, normal osmosis for the nitrogen transport takes place. Thus, the directions of anomalous osmotic flow caused by the oxygen concentration gradient coincide with the directions of normal osmotic flow, caused by the nitrogen concentration gradient. This leads to the conclusion that the presence of nitrogen in the human body promotes the oxygen delivery under HBO conditions, rendering the overall success of the hyperbaric oxygen treatment procedure.
INTRODUCTION
Osmotic phenomenas relevance for the oxygen transport in Hyperbaric Oxygen treatment was clearly emphasized by Hills [1]. The intent of this article is to quantify this effect for a non-steady state problem and express results using a convensional colloids and surfaces science approach. As this paper is interdisciplinary the necessary information for understanding of hyperbaric oxygen treatment is provided in the Introduction, which will be followed by the solution for the osmotic problem and discussion of its biophysical application.
The administration of oxygen is not generally viewed as a treatment although it is obvious that many diseases and all injuries are associated with a lack of oxygen in tissues known as hypoxia. There is also good evidence that a restriction of oxygen availability in the tissues may inhibit or even prevent recovery and this applies to tissues as diverse as bone and brain. The role of oxygen in metabolism is beyond question [2], but research has now shown that oxygen is also critical to the regulation of at least 30 genes [3].
The body normally responds to hypoxia, for example that induced by exercise, by increasing the volume of blood flow through the tissue but this may not be possible when, for example, an artery is blocked or when an increase in tissue water compresses the capillaries of the microcirculation. In the latter condition it is necessary to increase the gradient for oxygen transport to tissue by raising the inspired partial pressure of the gas. This is a function of the percentage of oxygen respired and the ambient atmospheric pressure.
The range of atmospheric pressures inhabited by Man varies from 800mmHg at the Dead Sea in Israel, to 475mmHg in La Paz in Bolivia. It has been shown that patients with lung disease benefit from visiting the Dead Sea [4] and it is common knowledge that patients heal more slowly at high altitudes [5]. Sea level pressure is normally 760mm, but weather systems change sea level pressure by more than 10% and, as this determines the inspired partial pressure of oxygen, it too will have amodest influence on recovery from disease and injury.
The maximum oxygen tension possible when breathing air at 760mmHg is less than 160mmHg (21%) because of the presence of water vapor and mixing with the exhaled carbon dioxide. However, there is a second reason for a reduced tension; areas of the lung which are ventilated may not receive the optimum blood flow. This is known as the ventilation-perfusion mismatch. The normal dissolved oxygen tension at sea level of about 100mmHg is, nevertheless, capable of ensuring that the four sites for oxygen binding on the hemoglobin molecule are occupied resulting in about 19 ml of oxygen per 100 ml of blood being transported. Because this parameter can be easily measured so-called hemoglobin saturation has become a clinical endpoint. However the oxygen must be dissociated from hemoglobin to be available for transport from blood to the tissues and it is the level of oxygen available to tissue that is critical [6].
Although the bulk of oxygen is transported by hemoglobin, the sole determinant of the transport of oxygen to the tissues is the concentration of oxygen dissolved in plasma. Because of the poor solubility of oxygen in plasma, which is close to the value for sea water, only 0.35 ml of oxygen is transported in a solution per 100 ml of blood. This value, however, can be increased linearly by increasing both the inspired oxygen percentage and the ambient pressure. Breathing 100% at three times atmospheric pressure (three atmospheres absolute, 3 ATA) sufficient oxygen is transported in the solution to meet the resting needs of the body and hemoglobin oxygen transported is not required [7].
To allow the pressure surrounding a patient to be increased an enclosure, known as a hyperbaric chamber, is needed, hence the term hyperbaric oxygen treatment [8]. There is wealth of clinical evidence demonstrating that hyperbaric oxygen treatment can improve recovery in a wide variety of conditions but the physical effects of an abrupt change of ambient pressure have not been fully explored. The first effect of an increase in the dissolved oxygen content of blood is an increase in the concentration gradient for the transport of oxygen into tissues. Oxygen will dissolve in the cells of the capillary wall and then transfer via the interstitial fluid dissolving through the cell membrane to finally reach the internal mitochondria.
This is by far the most important mechanism for oxygen transport. However the volume of interstitial fluid is often increased in pathological conditions and it is important to rate limit the loss of fluid from blood into tissues. This is dependent on capillary permeability and an increased oxygen tension reduces cardiac output and blood flow. So, paradoxically, breathing oxygen under increased partial pressure of oxygen can simultaneously reduce blood flow whilst increasing the concentration gradient for the transport of oxygen to tissues.
This mechanism is of unique importance in those conditions where hypoxia is due to microcirculatory closure due to an increase in the tissue water content. Another mechanism which requires experimental validation relates to osmotic forces created by the abrupt change of gas concentrations in plasma. Osmotic pressure causes convective diffusion transport in addition to the molecular transport of oxygen.
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