Ventral medullary extracellular fluid pH and blood flow during hypoxia

Nolan, William; Houck, P. C.; Thomas, Joerg; Davies, D. G.

doi:10.1152/ajpregu.1982.242.3.r195

Cited by 6 publications

(3 citation statements)

References 15 publications

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“…We also provide evidence suggesting that vascular responses are intact. Thus we propose this preparation may be suitable for studying the cerebrovasculature and its intimate relationship with central chemoreception (20).…”

Section: Discussionmentioning

confidence: 99%

Brain stem Po₂and pH of the working heart-brain stem preparation during vascular perfusion with aqueous medium

Wilson

Remmers

Paton

2001

American Journal of Physiology-Regulatory, Integrative and Comp

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The rat working heart-brain stem preparation (WHBP) is an in situ preparation having many of the advantages associated with in vitro preparations while retaining cardiovascular response functionality and an eupnoeic respiratory motor pattern. The preparation is perfused arterially with an aqueous medium having a much lower oxygen-carrying capacity than blood. To evaluate the efficacy of the artificial perfusion in providing adequate gas exchange within the brain stem, we used polarographic PO(2) and pH microelectrodes to determine the tissue PO(2) and pH of the medulla oblongata at various depths. When the perfusate was equilibrated with 5% CO(2) and 95% O(2), average tissue PO(2) was 294 Torr and no hypoxic areas were encountered. Tissue pH was remarkably uniform throughout the tissue, and on average was only 0.04 +/- 0.02 pH units more acidic than that of the perfusate. Increasing the PCO(2) of the perfusate increased tissue PO(2) and decreased arterial resistance. Decreasing perfusate PCO(2) (while keeping pH constant) decreased tissue PO(2) and reduced the respiratory activity. These results suggest that arterial PCO(2), independent of arterial pH, is an essential variable in determining both respiratory drive and cerebrovascular perfusion. We conclude that the medulla of the WHBP is oxygenated and within a physiological pH, which accounts for the eupneic pattern of respiratory motor activity it generates. Furthermore, this preparation may be a useful model for exploring mechanisms of central chemoreception as well as the dynamics of the cerebral vasculature responses following changes in blood gases.

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Section: Discussionmentioning

confidence: 99%

Brain stem Po₂and pH of the working heart-brain stem preparation during vascular perfusion with aqueous medium

Wilson

Remmers

Paton

2001

American Journal of Physiology-Regulatory, Integrative and Comp

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“…; Nolan et al . ); and (3) direct vascular mechanisms (see next paragraph). The relative contribution and importance of these processes remain unknown.…”

Section: Introductionmentioning

confidence: 99%

Integrative regulation of human brain blood flow

Willie

Tzeng

Fisher

et al. 2014

The Journal of Physiology

673

639

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Herein, we review mechanisms regulating cerebral blood flow (CBF), with specific focus on humans. We revisit important concepts from the older literature and describe the interaction of various mechanisms of cerebrovascular control. We amalgamate this broad scope of information into a brief review, rather than detailing any one mechanism or area of research. The relationship between regulatory mechanisms is emphasized, but the following three broad categories of control are explicated: (1) the effect of blood gases and neuronal metabolism on CBF; (2) buffering of CBF with changes in blood pressure, termed cerebral autoregulation; and (3) the role of the autonomic nervous system in CBF regulation. With respect to these control mechanisms, we provide evidence against several canonized paradigms of CBF control. Specifically, we corroborate the following four key theses: (1) that cerebral autoregulation does not maintain constant perfusion through a mean arterial pressure range of 60-150 mmHg; (2) that there is important stimulatory synergism and regulatory interdependence of arterial blood gases and blood pressure on CBF regulation; (3) that cerebral autoregulation and cerebrovascular sensitivity to changes in arterial blood gases are not modulated solely at the pial arterioles; and (4) that neurogenic control of the cerebral vasculature is an important player in autoregulatory function and, crucially, acts to buffer surges in perfusion pressure. Finally, we summarize the state of our knowledge with respect to these areas, outline important gaps in the literature and suggest avenues for future research. G -monomethyl-L-arginine; MAP, mean arterial pressure; MRI, magnetic resonance imaging; P aCO2 , arterial partial pressure of carbon dioxide; P aO2 , arterial partial pressure of oxygen; PET, positron emission tomography; SNS, sympathetic nervous system; VA, vertebral artery.Christopher Willie discovered physiology as an undergraduate student in the laboratory of Dr. Richard Wilson while working toward his Bachelors of Health Science degree at the University of Calgary. He met Dr Philip Ainslie at the same time and five years later began his PhD under Dr Ainslie's supervision. Mr. Willie's interests are studying human integrative physiology, with focus on cerebrovascular responses to changes in blood gases and blood pressure. To keep balanced, he enjoys rock, ice and alpine climbing around the world. In the future, Mr Willie plans to continue both his scientific and adventurous pursuits. Philip Ainslie is currently a Professor in the School of Health and Exercise Sciences at the University of British Columbia-Okanagan and holds a Canada Research Chair in Cerebrovascular Physiology. His main research focus attempts to examine the fundamental mechanisms that regulate human cerebral blood flow in health and in disease. He has a particular interest in how environmental stress -especially in the context of hypoxia, temperature, pressure and exercise -may impact on cerebral blood flow regulation.

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“…For example, in conscious newborn lambs, before oral breathing was initiated, nasal obstruction for no longer than 15 min resulted in asphyxia and reduction in arterial pH that was more pronounced the younger was the animal (5). Administration of hypoxic mixture was associated with elevated tissue levels of lactic acid (6) and brain acidosis in adult rats (7). In contrast, brain stem extracellular acidosis without reduction in plasma pH was recorded during hypoxia in anesthetized, paralyzed, and artificially ventilated piglets (8).…”

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confidence: 99%

Respiratory Effects of Lactic Acid Injected into the Jugular Vein of Newborn Rabbits

Ducros

Trippenbach

1991

Pediatr Res

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ABSTRACT. To define respiratory effects of peripheral acidemia during early development, we injected lactic acid (LA) into the jugular vein of 3 2 1-to 7-d-old rabbit pups and four adult rabbits. The body weight of newborns varied between 67 +-1 7 g in 1-d-old and 119.8 -C 33.7 g in 7-dold animals versus 4 f 0.1 kg in adults. Animals were anesthetized with ketamine (30 mglkg) and urethane (0.6-1.2 g/kg), tracheotomized, and breathed spontaneously. Diaphragmatic electromyogram, tidal volume, esophageal pressure, and arterial pressure were recorded. In adult rabbits, a LA dose of 0.25 mM/kg elicited an increase in the rate of breathing with no change or a decrease in tidal volume (early response), followed by a deep and fast respiration (late response). The same LA dose had no effect or provoked only the late response in 1-and 2-d-old rabbits and led to the early and late responses in older newborns. The early response was abolished and the late response was diminished after vagotomy. Our results suggest that the early response is mediated by vagal afferents and the late response, although modified by vagal input, is of an extravagal origin. It is suggested that acidemia may be involved in the transient tachypnea syndrome in newborn infants. Possible contribution of vagal nonmyelinated endings in triggering the early response to LA is discussed.

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Ventral medullary extracellular fluid pH and blood flow during hypoxia

Cited by 6 publications

References 15 publications

Brain stem Po₂and pH of the working heart-brain stem preparation during vascular perfusion with aqueous medium

Brain stem Po₂and pH of the working heart-brain stem preparation during vascular perfusion with aqueous medium

Integrative regulation of human brain blood flow

Respiratory Effects of Lactic Acid Injected into the Jugular Vein of Newborn Rabbits

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Ventral medullary extracellular fluid pH and blood flow during hypoxia

Cited by 6 publications

References 15 publications

Brain stem Po2and pH of the working heart-brain stem preparation during vascular perfusion with aqueous medium

Brain stem Po2and pH of the working heart-brain stem preparation during vascular perfusion with aqueous medium

Integrative regulation of human brain blood flow

Respiratory Effects of Lactic Acid Injected into the Jugular Vein of Newborn Rabbits

Contact Info

Product

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Brain stem Po₂and pH of the working heart-brain stem preparation during vascular perfusion with aqueous medium

Brain stem Po₂and pH of the working heart-brain stem preparation during vascular perfusion with aqueous medium