Regulation Of Tissue Oxygenation

This presentation describes various aspects of the regulation of tissue oxygenation, including the roles of the circulatory system, respiratory system, and blood, the carrier of oxygen within these components of the cardiorespiratory system. The respiratory system takes oxygen from the atmosphere and transports it by diffusion from the air in the alveoli to the blood flowing through the pulmonary capillaries. The cardiovascular system then moves the oxygenated blood from the heart to the microcirculation of the various organs by convection, where oxygen is released from hemoglobin in the red blood cells and moves to the parenchymal cells of each tissue by diffusion. Oxygen that has diffused into cells is then utilized in the mitochondria to produce adenosine triphosphate (ATP), the energy currency of all cells. The mitochondria are able to produce ATP until the oxygen tension or PO2 on the cell surface falls to a critical level of about 4–5 mm Hg. Thus, in order to meet the energetic needs of cells, it is important to maintain a continuous supply of oxygen to the mitochondria at or above the critical PO2 . In order to accomplish this desired outcome, the cardiorespiratory system, including the blood, must be capable of regulation to ensure survival of all tissues under a wide range of circumstances. The purpose of this presentation is to provide basic information about the operation and regulation of the cardiovascular and respiratory systems, as well as the properties of the blood and parenchymal cells, so that a fundamental understanding of the regulation of tissue oxygenation is achieved.

This presentation describes various aspects of the regulation of tissue oxygenation, including the roles of the circulatory system, respiratory system, and blood, the carrier of oxygen within these components of the cardiorespiratory system. The respiratory system takes oxygen from the atmosphere and transports it by diffusion from the air in the alveoli to the blood flowing through the pulmonary capillaries. The cardiovascular system then moves the oxygenated blood from the heart to the microcirculation of the various organs by convection, where oxygen is released from hemoglobin in the red blood cells and moves to the parenchymal cells of each tissue by diffusion. Oxygen that has diffused into cells is then utilized in the mitochondria to produce adenosine triphosphate (ATP), the energy currency of all cells. The mitochondria are able to produce ATP until the oxygen tension or PO in their vicinity falls to a critical level of about 1 mm Hg. Thus, in order to meet the energetic needs of cells, it is important to maintain a continuous supply of oxygen to the mitochondria at or above the critical PO. In order to accomplish this desired outcome, the cardiorespiratory system, including the blood, must be capable of regulation to ensure survival of all tissues under a wide range of circumstances. The purpose of this presentation is to provide basic information about the operation and regulation of the cardiovascular and respiratory systems, as well as the properties of the blood and parenchymal cells, so that a fundamental understanding of the regulation of tissue oxygenation is achieved. Table of Contents: Introduction / The Circulatory System and Oxygen Transport / The Respiratory System and Oxygen Transport / Oxygen Transport / Chemical Regulation of Respiration / Tissue Gas Transport / Oxygen Transport in Normal and Pathological Situations: Defects and Compensations / Matching Oxygen Supply to Oxygen Demand / Exercise and Hemorrhage / Measurement of Oxygen / Summary / References / Biography

The 30th scientific meeting of the International Society on Oxygen Transport to Tissue (ISOTT) was held at the Western Conference Centre, UMIST, Manchester, in August 2002. It was attended by some 96 delegates and accompanying persons and there were 128 presentations.

The aim of this treatise is to summarize the current understanding of the mechanisms for blood flow control to skeletal muscle under resting conditions, how perfusion is elevated (exercise hyperemia) to meet the increased demand for oxygen and other substrates during exercise, mechanisms underlying the beneficial effects of regular physical activity on cardiovascular health, the regulation of transcapillary fluid filtration and protein flux across the microvascular exchange vessels, and the role of changes in the skeletal muscle circulation in pathologic states. Skeletal muscle is unique among organs in that its blood flow can change over a remarkably large range. Compared to blood flow at rest, muscle blood flow can increase by more than 20-fold on average during intense exercise, while perfusion of certain individual white muscles or portions of those muscles can increase by as much as 80-fold. This is compared to maximal increases of 4- to 6-fold in the coronary circulation during exercise. These increases in muscle perfusion are required to meet the enormous demands for oxygen and nutrients by the active muscles. Because of its large mass and the fact that skeletal muscles receive 25% of the cardiac output at rest, sympathetically mediated vasoconstriction in vessels supplying this tissue allows central hemodynamic variables (e.g., blood pressure) to be spared during stresses such as hypovolemic shock. Sympathetic vasoconstriction in skeletal muscle in such pathologic conditions also effectively shunts blood flow away from muscles to tissues that are more sensitive to reductions in their blood supply that might otherwise occur. Again, because of its large mass and percentage of cardiac output directed to skeletal muscle, alterations in blood vessel structure and function with chronic disease (e.g., hypertension) contribute significantly to the pathology of such disorders. Alterations in skeletal muscle vascular resistance and/or in the exchange properties of this vascular bed also modify transcapillary fluid filtration and solute movement across the microvascular barrier to influence muscle function and contribute to disease pathology. Finally, it is clear that exercise training induces an adaptive transformation to a protected phenotype in the vasculature supplying skeletal muscle and other tissues to promote overall cardiovascular health. Table of Contents: Introduction / Anatomy of Skeletal Muscle and Its Vascular Supply / Regulation of Vascular Tone in Skeletal Muscle / Exercise Hyperemia and Regulation of Tissue Oxygenation During Muscular Activity / Microvascular Fluid and Solute Exchange in Skeletal Muscle / Skeletal Muscle Circulation in Aging and Disease States: Protective Effects of Exercise / References

This e-book will review special features of the cerebral circulation and how they contribute to the physiology of the brain. It describes structural and functional properties of the cerebral circulation that are unique to the brain, an organ with high metabolic demands and the need for tight water and ion homeostasis. Autoregulation is pronounced in the brain, with myogenic, metabolic and neurogenic mechanisms contributing to maintain relatively constant blood flow during both increases and decreases in pressure. In addition, unlike peripheral organs where the majority of vascular resistance resides in small arteries and arterioles, large extracranial and intracranial arteries contribute significantly to vascular resistance in the brain. The prominent role of large arteries in cerebrovascular resistance helps maintain blood flow and protect downstream vessels during changes in perfusion pressure. The cerebral endothelium is also unique in that its barrier properties are in some way more like epithelium than endothelium in the periphery. The cerebral endothelium, known as the blood-brain barrier, has specialized tight junctions that do not allow ions to pass freely and has very low hydraulic conductivity and transcellular transport. This special configuration modifies Starling's forces in the brain microcirculation such that ions retained in the vascular lumen oppose water movement due to hydrostatic pressure. Tight water regulation is necessary in the brain because it has limited capacity for expansion within the skull. Increased intracranial pressure due to vasogenic edema can cause severe neurologic complications and death.

Angiogenesis is the growth of blood vessels from the existing vasculature. The field of angiogenesis has grown enormously in the past 30 years, with only 40 papers published in 1980 and nearly 6000 in 2010. Why has there been this explosive growth in angiogenesis research? Angiogenic therapies provide a potential to conquer cancer, heart diseases, and more than 70 of life's most threatening medical conditions. The lives of at least 1 billion people worldwide could be improved with angiogenic therapy, according to the Angiogenesis Foundation. In this little book, we provide a simple approach to understand the essential elements of the angiogenic process, we critique the most powerful angiogenesis assays that are used to discover proangiogenic and antiangiogenic substances, and we provide an in-depth physiological perspective on how angiogenesis is regulated in normal, healthy tissues of the human body. All tissues of the body require a continuous supply of oxygen to burn metabolic substrates that are needed for energy. Oxygen is conducted to these tissues by blood capillaries: more capillaries can improve tissue oxygenation and thus enhance energy production; fewer capillaries can lead to hypoxia and even anoxia in the tissues. This means that angiogenic therapies designed to control the growth and regression of blood capillaries can be used to improve the survival of poorly perfused tissues that are essential to the body (heart, brain, skeletal muscle, etc.) and to rid the body of unwanted tissues (tumors). Table of Contents: Overview of Angiogenesis / Angiogenesis Assays / Regulation: Metabolic Factors / Regulation: Mechanical Factors / Glossary / References / Author Biographies

A concise yet complete overview of the treatment of cardiovascular instability in the critically ill patient. The authors consider all aspects, ranging from basic physiology and pathophysiology to diagnostic tools and established and novel forms of therapy. The whole is rounded off with an integration of these principles into a series of clinically relevant scenarios.