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Critical Care (London, England) Sep 2016Volume infusions are one of the commonest clinical interventions in critically ill patients yet the relationship of volume to cardiac output is not well understood.... (Review)
Review
Volume infusions are one of the commonest clinical interventions in critically ill patients yet the relationship of volume to cardiac output is not well understood. Blood volume has a stressed and unstressed component but only the stressed component determines flow. It is usually about 30 % of total volume. Stressed volume is relatively constant under steady state conditions. It creates an elastic recoil pressure that is an important factor in the generation of blood flow. The heart creates circulatory flow by lowering the right atrial pressure and allowing the recoil pressure in veins and venules to drain blood back to the heart. The heart then puts the volume back into the systemic circulation so that stroke return equals stroke volume. The heart cannot pump out more volume than comes back. Changes in cardiac output without changes in stressed volume occur because of changes in arterial and venous resistances which redistribute blood volume and change pressure gradients throughout the vasculature. Stressed volume also can be increased by decreasing vascular capacitance, which means recruiting unstressed volume into stressed volume. This is the equivalent of an auto-transfusion. It is worth noting that during exercise in normal young males, cardiac output can increase five-fold with only small changes in stressed blood volume. The mechanical characteristics of the cardiac chambers and the circulation thus ultimately determine the relationship between volume and cardiac output and are the subject of this review.
Topics: Blood Circulation; Blood Pressure; Blood Volume; Cardiac Output; Humans; Stroke Volume
PubMed: 27613307
DOI: 10.1186/s13054-016-1438-7 -
Free Radical Biology & Medicine Sep 2016During exercise, oxygen and nutrient rich blood must be delivered to the active skeletal muscle, heart, skin, and brain through the complex and highly regulated... (Review)
Review
During exercise, oxygen and nutrient rich blood must be delivered to the active skeletal muscle, heart, skin, and brain through the complex and highly regulated integration of central and peripheral hemodynamic factors. Indeed, even minor alterations in blood flow to these organs have profound consequences on exercise capacity by modifying the development of fatigue. Therefore, the fine-tuning of blood flow is critical for optimal physical performance. At the level of the peripheral circulation, blood flow is regulated by a balance between the mechanisms responsible for vasodilation and vasoconstriction. Once thought of as toxic by-products of in vivo chemistry, free radicals are now recognized as important signaling molecules that exert potent vasoactive responses that are dependent upon the underlying balance between oxidation-reduction reactions or redox balance. Under normal healthy conditions with low levels of oxidative stress, free radicals promote vasodilation, which is attenuated with exogenous antioxidant administration. Conversely, with advancing age and disease where background oxidative stress is elevated, an exercise-induced increase in free radicals can further shift the redox balance to a pro-oxidant state, impairing vasodilation and attenuating blood flow. Under these conditions, exogenous antioxidants improve vasodilatory capacity and augment blood flow by restoring an "optimal" redox balance. Interestingly, while the active skeletal muscle, heart, skin, and brain all have unique functions during exercise, the mechanisms by which free radicals contribute to the regulation of blood flow is remarkably preserved across each of these varied target organs.
Topics: Blood Circulation; Cerebrovascular Circulation; Coronary Circulation; Exercise; Free Radicals; Humans; Muscle, Skeletal; Regional Blood Flow; Skin; Vasodilation
PubMed: 26876648
DOI: 10.1016/j.freeradbiomed.2016.01.017 -
Advances in Physiology Education Mar 2011The purpose of this brief review is to highlight key concepts about the neural control of the circulation that graduate and medical students should be expected to... (Review)
Review
The purpose of this brief review is to highlight key concepts about the neural control of the circulation that graduate and medical students should be expected to incorporate into their general knowledge of human physiology. The focus is largely on the sympathetic nerves, which have a dominant role in cardiovascular control due to their effects to increase cardiac rate and contractility, cause constriction of arteries and veins, cause release of adrenal catecholamines, and activate the renin-angiotensin-aldosterone system. These effects, as well as the control of sympathetic outflow by the vasomotor center in the medulla and the importance of sensory feedback in the form of peripheral reflexes, especially the baroreflexes, are discussed in the context of cardiovascular regulation.
Topics: Autonomic Nervous System; Baroreflex; Blood Circulation; Humans; Receptors, Adrenergic; Sympathetic Nervous System
PubMed: 21385998
DOI: 10.1152/advan.00114.2010 -
Maturitas Sep 1990Ovarian steroids have effects on blood circulation involving the mechanisms which control blood flow and the changes that occur in the pathogenesis of atherosclerosis.... (Review)
Review
Ovarian steroids have effects on blood circulation involving the mechanisms which control blood flow and the changes that occur in the pathogenesis of atherosclerosis. Estrogens appear to protect women from cardiovascular disease through their effects on lipid metabolism as well as more direct effects on arterial walls which appear to inhibit atherosclerotic plaque formation. There is increasing evidence that estrogen replacement after menopause can markedly reduce female mortality due to vascular disease. Effects of hormone imbalance and deficiency on vasomotor control are clinically significant and hormone treatment appears to be effective in the management of a variety of conditions due to abnormal blood flow including vasomotor instability, migraine, vaginal dryness and, perhaps, some forms of angina. Most review articles have focused on the effects of ovarian steroids and lipid metabolism as well as the findings of recent epidemiologic studies. This is understandable as those investigations have proved so valuable in understanding the protective effects of estrogens. The present discussion, in contrast, focuses on the effects of ovarian steroids, estrogens in particular, on circulatory mechanisms. At the present time there is increasing interest in these studies. Findings thus far appear to contribute to understanding estrogen cardioprotection and also raise awareness of a variety of clinical conditions in which estrogen treatment could be indicated because of its effects on circulation.
Topics: Animals; Blood Circulation; Climacteric; Estrogen Replacement Therapy; Estrogens; Female; Humans; Menopause; Progestins; Vasomotor System
PubMed: 2215271
DOI: 10.1016/0378-5122(90)90008-t -
Scientific Reports Sep 2020Contemporary paradigm of peripheral and intracranial vascular hemodynamics considers physiologic blood flow to be laminar. Transition to turbulence is considered as a...
Contemporary paradigm of peripheral and intracranial vascular hemodynamics considers physiologic blood flow to be laminar. Transition to turbulence is considered as a driving factor for numerous diseases such as atherosclerosis, stenosis and aneurysm. Recently, turbulent flow patterns were detected in intracranial aneurysm at Reynolds number below 400 both in vitro and in silico. Blood flow is multiharmonic with considerable frequency spectra and its transition to turbulence cannot be characterized by the current transition theory of monoharmonic pulsatile flow. Thus, we decided to explore the origins of such long-standing assumption of physiologic blood flow laminarity. Here, we hypothesize that the inherited dynamics of blood flow in main arteries dictate the existence of turbulence in physiologic conditions. To illustrate our hypothesis, we have used methods and tools from chaos theory, hydrodynamic stability theory and fluid dynamics to explore the existence of turbulence in physiologic blood flow. Our investigation shows that blood flow, both as described by the Navier-Stokes equation and in vivo, exhibits three major characteristics of turbulence. Womersley's exact solution of the Navier-Stokes equation has been used with the flow waveforms from HaeMod database, to offer reproducible evidence for our findings, as well as evidence from Doppler ultrasound measurements from healthy volunteers who are some of the authors. We evidently show that physiologic blood flow is: (1) sensitive to initial conditions, (2) in global hydrodynamic instability and (3) undergoes kinetic energy cascade of non-Kolmogorov type. We propose a novel modification of the theory of vascular hemodynamics that calls for rethinking the hemodynamic-biologic links that govern physiologic and pathologic processes.
Topics: Blood Circulation; Blood Vessels; Hemodynamics; Humans; Hydrodynamics; Models, Biological; Nonlinear Dynamics; Pulsatile Flow
PubMed: 32968087
DOI: 10.1038/s41598-020-72309-8 -
Mutation Research. Reviews in Mutation... 2016Exposure to therapeutic doses of ionizing radiation is associated with damage to the heart and coronary arteries. However, only recently have studies with high-quality... (Meta-Analysis)
Meta-Analysis Review
Exposure to therapeutic doses of ionizing radiation is associated with damage to the heart and coronary arteries. However, only recently have studies with high-quality individual dosimetry data allowed this risk to be quantified while also adjusting for concomitant chemotherapy, and medical and lifestyle risk factors. At lower levels of exposure the evidence is less clear. In this article I review radiation-associated risks of circulatory disease in groups treated with radiotherapy for malignant and non-malignant disease, and in occupationally- or environmentally-exposed groups receiving rather lower levels of radiation dose, also for medical diagnostic purposes. Results of a meta-analysis suggest that excess relative risks per unit dose for various types of heart disease do not exhibit statistically significant (p>0.2) heterogeneity between studies. Although there are no marked discrepancies between risks derived from the high-dose therapeutic and medical diagnostic studies and from the moderate/low dose occupational and environmental studies, at least for ischemic heart disease and stroke there are indications of larger risks per unit dose for lower dose rate and fractionated exposures. Risks for stroke and other types of circulatory disease are significantly more variable (p<0.0001), possibly resulting from confounding and effect-modification by well known (but unobserved) risk factors. Adjustment for any of mean dose, dose fractionation or age at exposure results in the residual heterogeneity for cerebrovascular disease becoming non-significant. The review provides strong evidence in support of a causal association between both low and high dose radiation exposure and most types of circulatory disease.
Topics: Blood Circulation; Cardiovascular Diseases; Environmental Exposure; Humans; Occupational Exposure; Radiation Dosage; Radiation, Ionizing
PubMed: 27919337
DOI: 10.1016/j.mrrev.2016.07.008 -
Journal of Traditional Chinese Medicine... Dec 2020To investigate the efficacy of Chinese medicines on Qi stagnation and blood stasis in rats with myocardial ischemia.
OBJECTIVE
To investigate the efficacy of Chinese medicines on Qi stagnation and blood stasis in rats with myocardial ischemia.
METHODS
Fifty male Wistar rats were randomly divided into five groups (n = 10) as follows: (a) sham operation (Sham), (b) myocardial ischemia (Model), (c) treatment that regulates Qi (Qi), (d) treatment that promotes blood circulation (Blood), (e) treatment that both regulates Qi and promotes blood circulation (QB). The rat model was established via activities restriction for 6 h followed by tail clamp stimulation for 5 mins every day for 7 d and occlusion left coronary anterior descending artery. Afterwards rats were treated with medicines that regulate Qi and/or promote blood circulation via gavage for 14 d. Behavioral parameters were evaluated using open field and elevated plus-maze tests. The tongue color and sublingual vein were visually examined. Blood flow perfusion of tongue and auricle were detected using PIM Ⅱ. The mesenteric microcirculation was examined via capillaroscopy, and hemodynamics was assessed using a polygraph system. Serum homocysteine (Hcy), creatine kinase isoenzyme (CKMB) levels and endothelin-1 (ET-1) were measured. Hematoxylin and eosin staining and transmission electron microscopy were employed to detect the myocardial morphology and ultrastructure, respectively.
RESULTS
Compared with findings in Sham group, rats in model group had coarse hair, dark mucosa of the lips and claw, low activity, and increased anxiety. Compared with findings in Model group, rats in the three treatment groups exhibited a lighter tongue color without an extended and varicose sublingual vein. There were significant increases of auricle blood flow perfusion in the Qi group and tongue bottom blood flow perfusion in the QB group. Compared with findings in Model rats, rats in Blood group exhibited improved mesenteric microcirculation associated with increased mesenteric blood flow and a larger arteriole diameter. Moreover, compared with findings in Model rats, Qi and QB rats exhibited increased left ventricular ± dp/dtmax, decreased serum CKMB, Hcy, ET-1 levels, and reduced myocardial ultrastructural damage.
CONCLUSION
Myocardial ischemia damage was suppressed by Traditional Chinese Medicines that regulate Qi and promote blood circulation.
Topics: Animals; Blood Circulation; Drugs, Chinese Herbal; Heart Ventricles; Male; Myocardial Ischemia; Qi; Rats; Rats, Wistar
PubMed: 33258349
DOI: 10.19852/j.cnki.jtcm.2020.06.009 -
Critical Care (London, England) Oct 2012Hemodynamic monitoring is used to identify deviations from hemodynamic goals and to assess responses to therapy. To accomplish these goals one must understand how the... (Review)
Review
Hemodynamic monitoring is used to identify deviations from hemodynamic goals and to assess responses to therapy. To accomplish these goals one must understand how the circulation is regulated. In this review I begin with an historical review of the work of Arthur Guyton and his conceptual understanding of the circulation and then present an approach by which Guyton's concepts can be applied at the bedside. Guyton argued that cardiac output and central venous pressure are determined by the interaction of two functions: cardiac function, which is determined by cardiac performance; and a return function, which is determined by the return of blood to the heart. This means that changes in cardiac output are dependent upon changes of one of these two functions or of both. I start with an approach based on the approximation that blood pressure is determined by the product of cardiac output and systemic vascular resistance and that cardiac output is determined by cardiac function and venous return. A fall in blood pressure with no change in or a rise in cardiac output indicates that a decrease in vascular resistance is the dominant factor. If the fall in blood pressure is due to a fall in cardiac output then the role of a change in the return function and cardiac function can be separated by the patterns of changes in central venous pressure and cardiac output. Measurement of cardiac output is a central component to this approach but until recently it was not easy to obtain and was estimated from surrogates. However, there are now a number of non-invasive devices that can give measures of cardiac output and permit the use of physiological principles to more rapidly appreciate the primary pathophysiology behind hemodynamic abnormalities and to provide directed therapy.
Topics: Blood Circulation; Blood Pressure; Cardiac Output; Hemodynamics; Humans; Monitoring, Physiologic; Positive-Pressure Respiration; Shock
PubMed: 23106914
DOI: 10.1186/cc11395 -
Canadian Journal of Physiology and... Jul 2020Over the past 66 years, our knowledge of the role of the endothelium in the regulation of cardiovascular function and dysfunction has advanced from the assumption that... (Review)
Review
Over the past 66 years, our knowledge of the role of the endothelium in the regulation of cardiovascular function and dysfunction has advanced from the assumption that it is a single layer of cells that serves as a barrier between the blood stream and vascular smooth muscle to an understanding of its role as an essential endocrine-like organ. In terms of historical contributions, we pay particular credit to (1) the Canadian scientist Dr. Rudolf Altschul who, based on pathological changes in the appearance of the endothelium, advanced the argument in 1954 that "one is only as old as one's endothelium" and (2) the American scientist Dr. Robert Furchgott, a 1998 Nobel Prize winner in Physiology or Medicine, who identified the importance of the endothelium in the regulation of blood flow. This review provides a brief history of how our knowledge of endothelial function has advanced and now recognize that the endothelium produces a plethora of signaling molecules possessing paracrine, autocrine, and, arguably, systemic hormone functions. In addition, the endothelium is a therapeutic target for the anti-diabetic drugs metformin, glucagon-like peptide I (GLP-1) receptor agonists, and inhibitors of the sodium-glucose cotransporter 2 (SGLT2) that offset the vascular disease associated with diabetes.
Topics: Blood Circulation; Diabetic Angiopathies; Endothelium, Vascular; History, 20th Century; Humans; Hypoglycemic Agents; Muscle, Smooth, Vascular; Physiology; Vasoconstriction; Vasodilation
PubMed: 32150686
DOI: 10.1139/cjpp-2019-0677 -
Journal of the Royal Society of Medicine Dec 2007Even though Lazarus phenomenon is rare, it is probably under reported. There is no doubt that Lazarus phenomenon is a reality but so far the scientific explanations have... (Review)
Review
Even though Lazarus phenomenon is rare, it is probably under reported. There is no doubt that Lazarus phenomenon is a reality but so far the scientific explanations have been inadequate. So far the only plausible explanation at least in some cases is auto-PEEP and impaired venous return. In patients with PEA or asystole, dynamic hyperinflation should considered as a cause and a short period of apnoea (30-60 seconds) should be tried before stopping resuscitation. Since ROSC occurred within 10 minutes in most cases, patients should be passively monitored for at least 10 minutes after the cessation of CPR before confirming death.
Topics: Blood Circulation; Cardiopulmonary Resuscitation; Heart Arrest; Humans; Recovery of Function; Time Factors
PubMed: 18065707
DOI: 10.1177/0141076807100012013