Central Cardiovascular Control

The most prominent function of the central nervous system is the control of motor functions by rapidly transmitted impulses through efferent cranial and spinal peripheral nerves. Besides electrically transmitted neural impulses, humoral mechanisms with more sustained actions are exercised by the brain and spinal cord to regulate body homeostasis. Thus, the brain may be regarded as an "endocrine gland" discharging neurohormones (peptides) either into the general circulation (neurohypophyseal hormones) or into the hypothalamo-adenohypophyseal portal circulation (releasing and inhibiting hormones). The brain, therefore, which is protected by the blood-brain barrier from disturbing and potentially noxious exogenous and endogenous agents circulating in the blood, has to have certain neurohemal regions beyond this barrier, such as the neural lobe and the median eminence (infundibulum), where neurohor mones have free access to the blood stream. To regulate somatic and autonomic functions in the best possible way, the central nervous system is highly dependent on feedback signals conveyed through somatic and visceral afferent nerves as well as on peripheral humoral signals such as peripheral hormones and other circulating substances that are under homeostatic regulation, e. g. , peptides, arnines, electrolytes, and other biologically active agents. In this chapter, the role of the blood-brain barrier in the regulation of these sub stances will be discussed with special emphasis on the access through the blood-brain barrier to cardiovascular centers. 2 The Blood-Brain Barrier 2.

This new analysis of reflex and hormonal control of the human cardiovascular system developed from questions raised in Human Circulation: During Physical Stress (Rowell, 1986) and from recent findings. The goal is to help students, physiologists and clinicians understand the control of pressure, vascular volume, and blood flow by examining the cardiovascular system during orthostasis and exercise, two stresses that most affect these variables. A discussion of the passive physical properties of the vascular system provides a basis for explaining how vascular control is modified by mechanical, neural, and humoral factors. Interactive effects of the vasculature on cardiac performance are emphasized; they reveal the importance of autonomic control, supplemented by muscle pumping, in maintaining adequate ventricular filling pressure. The author's detailed analysis of how total oxygen consumption is restricted focuses on limitations in cardiac pumping ability, oxygen diffusion from lungs to blood and from blood to active muscle, oxidative metabolism and neural control of organ blood flow. An unsolved mystery is the nature of the signals that govern the cardiovascular responses to exercise. This is discussed in a new and critical synthesis of ideas and evidence concerning the "error signals" that are sensed and then corrected by activation of the autonomic nervous system during exercise.

The most prominent function of the central nervous system is the control of motor functions by rapidly transmitted impulses through efferent cranial and spinal peripheral nerves. Besides electrically transmitted neural impulses, humoral mechanisms with more sustained actions are exercised by the brain and spinal cord to regulate body homeostasis. Thus, the brain may be regarded as an "endocrine gland" discharging neurohormones (peptides) either into the general circulation (neurohypophyseal hormones) or into the hypothalamo-adenohypophyseal portal circulation (releasing and inhibiting hormones). The brain, therefore, which is protected by the blood-brain barrier from disturbing and potentially noxious exogenous and endogenous agents circulating in the blood, has to have certain neurohemal regions beyond this barrier, such as the neural lobe and the median eminence (infundibulum), where neurohor mones have free access to the blood stream. To regulate somatic and autonomic functions in the best possible way, the central nervous system is highly dependent on feedback signals conveyed through somatic and visceral afferent nerves as well as on peripheral humoral signals such as peripheral hormones and other circulating substances that are under homeostatic regulation, e. g. , peptides, arnines, electrolytes, and other biologically active agents. In this chapter, the role of the blood-brain barrier in the regulation of these sub stances will be discussed with special emphasis on the access through the blood-brain barrier to cardiovascular centers. 2 The Blood-Brain Barrier 2.

This book presents the proceedings of a satellite symposium of the XXVllth International Congress of IUPS held in Berlin, July 12-15, 1977 the latest of a series of meetings dealing with the organization of the autonomic nervous system, especially its central nervous control (Warsaw 1971, Tokyo 1974, Heidelberg 1976). This was an occasion for the discussion of the rapidly increasing experience of laboratories and research groups in a number of countries. Interest is growing in the organization of the sympathetic and parasympathetic nerve supplies, and there is much new material derived largely from single unit re cordings within both central and peripheral nervous structures. It has long been known that various rhythms originating in central ner vous structures, including the respiratory rhythm, are reflected in autonomic outflows. Moreover, the autonomic responses themselves rarely appear in isolation, and are usually seen as part of patterns of change involving a number of organs and systems. These facts alone imply com plex interactions within the central nervous system, which indicate that studies of relationships between the relevant inputs, intrinsic central nervous activity and autonomic outputs constitute a special branch of neurophysiology which needs to be developed in order to gain insights into the forms of central nervous organization which are in volved.

Research centering on blood flow in the heart continues to hold an important position, especially since a better understanding of the subject may help reduce the incidence of coronary arterial disease and heart attacks. This book summarizes recent advances in the field; it is the product of fruitful cooperation among international scientists who met in Japan in May, 1990 to discuss the regulation of coronary blood flow.

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.