Webinar 'Photonics in Healthcare'
Thursday 28 January
15:00 - 17:00
Terence H. Risby
Johns Hopkins University, Baltimore, USA
Title: A real time in vivo assessment of human homeostasis?
The concept that blood, urine, and other body fluids and tissues can be collected and analyzed to yield information to monitor human homeostasis is the foundation of modern medicine. However, the use of breath as a collectable sample has not received comparable clinical use.
The ability to exchange oxygen for carbon dioxide is essential for many life forms. In animals, this gas exchange occurs at the alveolar-blood capillary membrane in the respiratory tract. Oxygen and carbon dioxide are passively transported from blood to breath or vice versa and the diffusion of these gases is governed by their concentration gradients across the alveolar-capillary junction. Any additional molecule present in the blood or in the inspiratory air will also pass into the breath or blood respectively. The only requirement for this transport is that molecules must exhibit significant vapor pressures. The molecular profile of breath will be the product of the composition of the inspiratory air and the volatile molecules that are present in the blood. The bulk matrix of breath is a mixture of nitrogen, oxygen, carbon dioxide, water vapor and the inert gases. The remainder of breath (<100ppm) is a mixture of as many as 500 different compounds. These molecules have both endogenous and exogenous origins. Normal and abnormal physiological processes are the source for endogenous molecules. The sources of exogenous molecules are inspiratory air, ingested foods and beverages, and any exogenous molecule that has entered the body by other routes (such as dermal absorption).
Breath tests fall into two basic categories: tests that quantify molecules in breath after administration of a drug or substrate; and tests that quantify molecules in breath without any prior administration of a drug or substrate. The first group of tests is based upon the detection of a metabolite of the drug or substrate. The second group of breath tests is based upon the detection of molecules that are produced endogenously as a result of normal or abnormal physiologies. The common requirement for most breath tests is that breath should be collected under carefully controlled conditions that include careful monitoring of the ventilation of the subject.
There are two directions for future studies in clinical breath analysis: profiling molecules in breath, and development of real-time breath monitors for specific molecules. Breath profiling or breath fingerprinting can be considered to be a subfield of human metabalomics, which is a popular new area of research. The development of real-time breath monitors is an area of research currently receiving active interest. Monitors based upon mid-infrared technologies using multipass absorption cells and quantum cascade lasers are exciting possibilities.
Although clinical breath analysis is currently in its infancy it offers unique capabilities to the field of clinical chemistry. This presentation will review “Photonics: A real time in vivo assessment of human homeostasis” and will also discuss good laboratory practices related to breath collection.
Dr. Risby is Professor Emeritus of Environmental Health Sciences at the Bloomberg School of Public Health of the Johns Hopkins University. Dr. Risby’s interests in breath biomarkers of exposure assessment, tissue injury, disease progression, and therapy began more than thirty-five years ago when he conducted a pilot study to analyze breath intra-operatively during human liver transplantation. This study enabled reperfusion injury to be measured independently from ischemic damage. The Johns Hopkins breath analysis laboratory in collaboration with clinical colleagues has published numerous publications. Dr. Risby was a founding member for the International Association for Breath Research (IABR) and the new Journal of Breath Research (JBR). He is currently associate editor of the journal BIOMARKERS and formerly associate editor the Journal of Breath Research. Dr. Risby has brought his expertise in chromatography and spectroscopy to bear on applications relevant to research on a variety of diseases including liver diseases and finding unique markers in breath that relate to the functional status of the disease. The research program of Dr. Risby’s laboratory has been supported with funds from the federal government. The current focus of Risby’s research is the use of breath biomarkers in clinical molecular epidemiological studies.
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