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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 -
Minerva Anestesiologica Apr 2004Maintenance of adequate cardiac preload is of paramount importance in the treatment of patients undergoing major surgical surgery and in the critically ill setting. The... (Review)
Review
Maintenance of adequate cardiac preload is of paramount importance in the treatment of patients undergoing major surgical surgery and in the critically ill setting. The end point is to maintain the organ perfusion through volume replacement and therapy to optimize cardiac output, oxygen deliver. Various methods have been introduced into clinical practice to estimate cardiac preload. In the last 10 years the transpulmonary indicator dilution technique showed to be accurate as hemodynamic-volumetric monitoring. We briefly review the intra thoracic blood volume index as a preload index and the fluid responsiveness indexes, stroke volume variation and pulse pressure variation, available as novel parameters at the bed-side. The optimization of fluid balance and vasoactive drugs administration based on volumetric monitoring makes the transpulmonary indicator dilution technique a new option as an effective monitoring system where intravascular volume management is a primary objective.
Topics: Blood Volume; Catheterization, Peripheral; Hemodynamics; Humans; Monitoring, Intraoperative; Monitoring, Physiologic
PubMed: 15173701
DOI: No ID Found -
Critical Care (London, England) Oct 2016Oxygen delivery to cells is the basic prerequisite of life. Within the human body, an ingenious oxygen delivery system, comprising steps of convection and diffusion from... (Review)
Review
Oxygen delivery to cells is the basic prerequisite of life. Within the human body, an ingenious oxygen delivery system, comprising steps of convection and diffusion from the upper airways via the lungs and the cardiovascular system to the microvascular area, bridges the gap between oxygen in the outside airspace and the interstitial space around the cells. However, the complexity of this evolutionary development makes us prone to pathophysiological problems. While those problems related to respiration and macrohemodynamics have already been successfully addressed by modern medicine, the pathophysiology of the microcirculation is still often a closed book in daily practice. Nevertheless, here as well, profound physiological understanding is the only key to rational therapeutic decisions. The prime guarantor of tissue oxygenation is tissue blood flow. Therefore, on the premise of intact macrohemodynamics, the microcirculation has three major responsibilities: 1) providing access for oxygenated blood to the tissues and appropriate return of volume; 2) maintaining global tissue flood flow, even in the face of changes in central blood pressure; and 3) linking local blood flow to local metabolic needs. It is an intriguing concept of nature to do this mainly by local regulatory mechanisms, impacting primarily on flow resistance, be this via endothelial or direct smooth muscle actions. The final goal of microvascular blood flow per unit of time is to ensure the needed exchange of substances between tissue and blood compartments. The two principle means of accomplishing this are diffusion and filtration. While simple diffusion is the quantitatively most important form of capillary exchange activity for the respiratory gases, water flux across the blood-brain barrier is facilitated via preformed specialized channels, the aquaporines. Beyond that, the vascular barrier is practically nowhere completely tight for water, with paracellular filtration giving rise to generally low but permanent fluid flux outwards into the interstitial space at the microvascular high pressure segment. At the more leaky venular aspect, both filtration and diffusion allow for bidirectional passage of water, nutrients, and waste products. We are just beginning to appreciate that a major factor for maintaining tissue fluid homeostasis appears to be the integrity of the endothelial glycocalyx.
Topics: Animals; Blood Flow Velocity; Blood Volume; Blood-Brain Barrier; Glycocalyx; Hemodynamics; Humans; Microcirculation; Oxygen Consumption
PubMed: 27765054
DOI: 10.1186/s13054-016-1485-0 -
Journal of the American College of... May 2022A number of pathologic processes contribute to the elevation in cardiac filling pressures in heart failure (HF), including myocardial dysfunction and primary volume... (Review)
Review
A number of pathologic processes contribute to the elevation in cardiac filling pressures in heart failure (HF), including myocardial dysfunction and primary volume overload. In this review, we discuss the important role of the venous system and the concepts of stressed blood volume and unstressed blood volume. We review how regulation of venous tone modifies the distribution of blood between these 2 functional compartments, the physical distribution of blood between the pulmonary and systemic circulations, and how these relate to the hemodynamic abnormalities observed in HF. Finally, we review recently applied methods for estimating stressed blood volume and how they are being applied to the results of clinical studies to provide new insights into resting and exercise hemodynamics and therapeutics for HF.
Topics: Blood Volume; Heart Failure; Hemodynamics; Humans
PubMed: 35512865
DOI: 10.1016/j.jacc.2022.02.050 -
Journal of Applied Physiology... Oct 2017Humans ascending to high altitude (HA) experience a reduction in arterial oxyhemoglobin saturation and, as a result, arterial O content ([Formula: see text]). As HA... (Review)
Review
Humans ascending to high altitude (HA) experience a reduction in arterial oxyhemoglobin saturation and, as a result, arterial O content ([Formula: see text]). As HA exposure extends, this reduction in [Formula: see text] is counteracted by an increase in arterial hemoglobin concentration. Initially, hemoconcentration is exclusively related to a reduction in plasma volume (PV), whereas after several weeks a progressive expansion in total red blood cell volume (RCV) contributes, although often to a modest extent. Since the decrease in PV is more rapid and usually more pronounced than the expansion in RCV, at least during the first weeks of exposure, a reduction in circulating blood volume is common at HA. Although the regulation of hematological responses to HA has been investigated for decades, it remains incompletely understood. This is not only related to the large number of mechanisms that could be involved and the complexity of their interplay but also to the difficulty of conducting comprehensive experiments in the often secluded HA environment. In this review, we present our understanding of the kinetics, the mechanisms and the physiological relevance of the HA-induced reduction in PV and expansion in RCV.
Topics: Acclimatization; Altitude; Blood Volume; Erythropoietin; Humans; Hypoxia; Oxygen; Oxyhemoglobins
PubMed: 28572493
DOI: 10.1152/japplphysiol.00118.2017 -
Investigative Radiology Sep 2022We propose a method of quantitatively measuring drug-induced microvascular volume changes, as well as drug-induced changes in blood oxygenation using calibrated blood... (Observational Study)
Observational Study
OBJECTIVES
We propose a method of quantitatively measuring drug-induced microvascular volume changes, as well as drug-induced changes in blood oxygenation using calibrated blood oxygen level-dependent magnetic resonance imaging (MRI). We postulate that for MRI signals there is a contribution to R2* relaxation rates from static susceptibility effects of the intravascular blood that scales with the blood volume/magnetic field and depends on the oxygenation state of the blood. These may be compared with the effects of an intravascular contrast agent. With 4 R2* measurements, microvascular blood volume (MBV) and tissue oxygenation changes can be quantified with the administration of a vasoactive drug.
MATERIALS AND METHODS
The protocol examined 12 healthy rats in a prospective observational study. R2* maps were acquired with and without infusion of adenosine, which increases microvascular blood flow, or dobutamine, which increases myocardial oxygen consumption. In addition, R2* maps were acquired after the intravenous administration of a monocrystalline iron oxide nanoparticle, with and without adenosine or dobutamine.
RESULTS
Total microvascular volume was shown to increase by 10.8% with adenosine and by 25.6% with dobutamine ( P < 0.05). When comparing endocardium versus epicardium, both adenosine and dobutamine demonstrated significant differences between endocardial and epicardial MBV changes ( P < 0.05). Total myocardial oxygenation saturation increased by 6.59% with adenosine and by 1.64% with dobutamine ( P = 0.27). The difference between epicardial and endocardial oxygenation changes were significant with each drug (adenosine P < 0.05, dobutamine P < 0.05).
CONCLUSIONS
Our results demonstrate the ability to quantify microvascular volume and oxygenation changes using calibrated blood oxygen level-dependent MRI, and we demonstrate different responses of adenosine and dobutamine. This method has clinical potential in examining microvascular disease in various disease states without the administration of radiopharmaceuticals or gadolinium-based contrast agents.
Topics: Adenosine; Animals; Blood Volume; Coronary Circulation; Dobutamine; Rats; Vasodilator Agents
PubMed: 35438656
DOI: 10.1097/RLI.0000000000000871 -
Minerva Anestesiologica Dec 2005Adequate restoration of intravascular volume remains an important therapeutic manoeuvre in managing the surgical, medical and the critically ill intensive care patient.... (Review)
Review
Adequate restoration of intravascular volume remains an important therapeutic manoeuvre in managing the surgical, medical and the critically ill intensive care patient. Definition of the ideal volume replacement strategy still remains one of the burning problems. The choice between colloid and crystalloid solutions continues to generate controversy. The highly controversial crystalloid/colloid dispute has been enlarged to a colloid/colloid debate because aside of the natural colloid albumin several non-protein (synthetic) colloids are available as plasma substitutes (e.g. dextrans, gelatins, hydroxyethyl starch [HES] solutions). Due to their varying physico-chemical properties, these solutions widely differ with regard to their pharmacokinetic and pharmacodynamic properties as well as to their hemodynamic efficacy and side-effects. HES is the most intensively studied plasma substitute. The different HES preparations are defined by concentration, molar substitution (MS), mean molecular weight (MW), and the C2/C6 ratio of substitution. Two new HES specification, a third-generation HES with a lower Mw and a lower MS (6% HES 130/0.4) than all other HES preparation and a first-generation HES prepared in a balanced solution, may be promising by improving the therapy of the hypovolemic patient. Albumin cannot be recommended for correction of hypovolemia because of ist extreme costs and because it can easily be replaced by other no-protein colloids. Dextrans should also not be used any more due to the negative effects on coagulation and its high anaphylactic potency. The historical crystalloid/colloid controversy has been focused primarily on outcome. There is increasing evidence that outcome (mortality) is not the correct measure when assessing the ideal volume replacement strategy. New concepts about critical care such as organ perfusion and organ function, the role of inflammation, immunological aspects, and wound healing may change this point of view. Volume replacement has been hitherto often based on art, dogma and personal beliefs. Further well-performed studies in this area will help more to shed new light on the ideal volume replacement strategy of the hypovolemic patient than more meta-analyses that are pooling old-to-very old studies to solve this problem.
Topics: Blood Volume; Colloids; Critical Care; Crystalloid Solutions; Fluid Therapy; Humans; Isotonic Solutions; Plasma Substitutes
PubMed: 16288182
DOI: No ID Found -
The Japanese Journal of Physiology 1990Dehydration due to hyperthermia induces both hyperosmolality and hypovolemia. Hyperosmolality reduces evaporative cooling, and alters the thermal responsiveness of the... (Review)
Review
Dehydration due to hyperthermia induces both hyperosmolality and hypovolemia. Hyperosmolality reduces evaporative cooling, and alters the thermal responsiveness of the hypothalamic center to changes in both the central and peripheral milieu. Hypovolemia also reduces the thermoregulatory response, but its effect is more variable. The potential sensor of hypovolemia is the CVP, which is influenced by redistribution of blood volume, changes in blood volume, and alterations in cardiac function. The control of CVP is related to the regulation of vascular compliance, stressed blood volume, and unstressed blood volume. Vascular compliance is also involved in the regulation of fluid shifts between the ISF and the intravascular fluid space, and buffers changes in the CVP. Regulation of fluid replacement after thermal dehydration can be considered both from the point of view of osmoregulation and volume regulation. In the rehydration process, control of plasma osmolality precedes blood volume regulation, which also suggests that changes in blood volume sensed as changes in the CVP are regulated within a narrow range by various mechanisms. These findings suggest a hierarchic structure for the homeostatic mechanisms related to thermoregulation, with higher priority being given to the maintenance of cardiac output and the cellular volume of the brain at the expense of peripheral circulation and cell volume.
Topics: Animals; Blood Volume; Body Fluids; Body Temperature Regulation; Central Venous Pressure; Dehydration; Hot Temperature; Humans; Thirst
PubMed: 2203923
DOI: 10.2170/jjphysiol.40.165 -
PloS One 2020In this study, the physiological values of volumes of plasma, cells, total blood and the F blood factors were identified in 24 adult tree shrews (Tupaia belangeri; 12...
In this study, the physiological values of volumes of plasma, cells, total blood and the F blood factors were identified in 24 adult tree shrews (Tupaia belangeri; 12 male and 12 female; average BW of 123.9±19.19 g). The two-compartment model method of Evans Blue dye was used to obtain the plasma volume and the venous hematocrit was measured by microhematocrit method. To establish the relationship between body weight (BW) and blood volume of tree shrews, We performed linear fitting for these two datasets. Results were analyzed according to gender and weight (<120g vs.>120g). Statistical significance was assessed using the unpaired student t test and one-way ANOVA. The average volumes per 100g body weight of plasma, red blood cell (RBC) and total blood were 5.42±0.543, 3.24±0.445, and 8.66±0.680ml respectively. The mean body hematocrit, cardiac hematocrit, jugular vein hematocrit, femoral vein hematocrit, and tail vein hematocrit was 37.43±4.096, 39.72±3.219, 43.04±4.717, 40.84±3.041, and 38.71±3.442% respectively. The F cardiac was 0.94±0.072, F jugular vein 0.88±0.118, F femoral vein 0.92±0.111, and the F tail vein 0.97±0.117. Blood volume (ml) was 85.89103×BW (kg). This is the first study to provide the parameters of plasma volume, cell volume, total blood volume and F factor and a baseline for future research on blood physiology of tree shrews.
Topics: Animals; Blood Volume; Body Weight; Cell Size; Female; Hematocrit; Male; Plasma Volume; Tupaiidae
PubMed: 32881864
DOI: 10.1371/journal.pone.0234835 -
Korean Journal of Anesthesiology Apr 2020Over 300 million surgical procedures are performed every year worldwide. Anesthesiologists play an important role in the perioperative process by assessing the overall... (Review)
Review
Over 300 million surgical procedures are performed every year worldwide. Anesthesiologists play an important role in the perioperative process by assessing the overall risk of surgery and aim to reduce the risk of complications. Perioperative hemodynamic and volume management can help to improve outcomes in perioperative patients. There has been ongoing discussion about goal-directed therapy. However, there is a consensus that fluid overload and severe fluid depletion in the perioperative period are harmful and can lead to adverse outcomes. This article provides an overview of how to evaluate the fluid responsiveness of patients, details which parameters could be used, and what limitations should be noted.
Topics: Blood Volume; Cardiac Output; Crystalloid Solutions; Fluid Therapy; Hemodynamics; Humans; Monitoring, Intraoperative; Perioperative Care
PubMed: 32106641
DOI: 10.4097/kja.20022