Perfluorocarbon emulsions are emulsions containing either bubbles or droplets which have perfluorocarbons inside them. Some of them are commonly used in medicine as ultrasound contrast agents, and others have been studied for use as oxygen therapeutics.
The most common use of perfluorocarbon emulsions is as ultrasound contrast agents. In this application, microscopic bubbles containing perfluorocarbon gas are injected intravenously and flow through the bloodstream. [1] An ultrasound machine then sends soundwaves through a tissue of interest, and the bubbles reflect the soundwaves to a greater extent than the surrounding tissues, thereby giving the blood greater contrast on ultrasound viewers. This can allow greater visibility of the structure of an organ of interest, or a better indication of the level of blood perfusion or blood volume in an area of interest. [2] The bubbles persist in the blood stream with half-lives of minutes before the perfluorocarbon molecules leave the bubbles and enter the surrounding fluids, before eventually passing through the lungs where they are exhaled. [3] [4] [5] [6] [7] Notable ultrasound contrast agents include DEFINITYⓇ and OptisonTM which are FDA approved, SONAZOIDⓇ which is approved in Japan, and EchoGen which was formerly approved in Europe but never marketed. [8] [9] [10] [11] [12]
Other perfluorocarbon emulsions have been tested as oxygen therapeutics. When perfluorocarbons are exposed to high concentrations of oxygen, large amounts of oxygen dissolve into the perfluorocarbons. If the perfluorocarbon/oxygen solution is then exposed to a low oxygen environment, then oxygen diffuses out of the solution. [13] Three different approaches sought to utilize this characteristic to improve oxygen delivery to tissue.
Early perfluorocarbon emulsions for oxygen delivery were developed as blood substitutes. They used large-molecule perfluorocarbons with boiling points higher than body temperature which were formed into liquid emulsion droplets. The emulsions were injected intravenously and circulated through the bloodstream, and the droplets picked up oxygen when passing through the lungs and offloaded oxygen when passing through the capillaries in other tissues. [13] The primary form of excretion of the perfluorocarbon was through the reticulo-endothelial system - the droplets would remain in the bloodstream until they were recognized by the immune system, would be taken up by phagocytes, and broken down thereby releasing the perfluorocarbon molecules which eventually pass through the lungs and be exhaled. [14] These high boiling point perfluorocarbons typically had half-lives measured in hours or days. [13] [15] Relatively large doses were required and the and could have side effects including pneumonia. [13] Despite these challenges, Fluosol-DA was approved by the FDA and was marketed as a blood substitute in the United States from 1989 through 1994 when it was withdrawn from the market due to poor sales. [16] Perftoran was approved in the Soviet Union in 1994 and remained in limited use in Russia at least as late as 2019. [17]
The second approach to oxygen delivery tested a perfluorocarbon emulsion not as a blood substitute, but rather as a cerebrospinal fluid (CSF) substitute. In order to increase oxygen delivery to the brains of patients that had reduced blood flow due to acute ischemic stroke, artificial CSF mixed with pre-oxygenated perfluorocarbon emulsion was continuously added into the skull by a ventricular catheter while CSF was continuously removed by a lumbar catheter. Animal studies in cats with acute ischemic stroke showed very strong results, so a clinical trial in four humans was conducted. All four patients survived for 30 days to 2 years before dying of other causes. Enrollment in the trial was slow however, which caused the funding for the project to be cut. [18]
A third approach to oxygen delivery is to move perfluorocarbon molecules into positions where they can enhance the flow of oxygen through the lower parts of the oxygen cascade. While it is difficult to observe the positioning of the perfluorocarbon molecules directly, molecules positioned in the right places between red blood cells and mitochondria may reduce resistance to oxygen flow. [19] [20] In cases where the oxygen tension at the mitochondria are very low, this would expose nearby red blood cells to lower oxygen tensions and cause them to offload more oxygen as described by the oxygen–hemoglobin dissociation curve. The most notable example is dodecafluoropentane emulsion (DDFPe, formerly EchoGen, now NanO2). The drug is injected intravenously then the perfluorocarbon molecules then spread widely before eventually passing through the lungs whey they are evaporated and exhaled. [21] [5] The drug showed very strong results in animal studies of acute ischemic stroke, heart attack and other indications. [22] [23] [24] [25] The drug was tested in a Phase Ib/II clinical trial in 24 patients who had reduced blood flow to the brain due to acute ischemic stroke, where it was intended to increase oxygen delivery to the brain to keep the tissue alive until blood flow could be normalized. The high dose group of patients in the clinical trial had improved functional independence compared to placebo, though the number of patients tested was small and there were confounding factors including differences in stroke severity, so larger clinical trials are needed to confirm the effect. [26] Another perfluorocarbon, perfluorooctyl bromide, has been shown in animal studies to collect in tumor tissue and increase oxygenation of those tumors, potentially by improving the flow of oxygen from red blood cells. [27]
Perfluorocarbon(s) | Boiling Point (°C) | Bubble or Droplet | Scientific Name of Perfluorocarbon | Trade Names of Emulsion | Company | Primary Uses | Status |
---|---|---|---|---|---|---|---|
C3F8 | -36.7 | Bubble | Octafluoropropane, or perflutren | DEFINITYⓇ, Luminity, OptisonTM | Lantheus Medical Imaging, GE Healthcare | Ultrasound Contrast Agents | Approved in the US and Europe [8] [28] [9] [29] |
C4F10 | -1.9 | Bubble | Perfluorobutane | SONAZOIDⓇ | Daiichi Sankyo | Ultrasound Contrast Agent | Approved in Japan, [10] available in Korea, Norway, Taiwan, and China [30] |
C5F12 | 29 | Bubble and/or Droplet | Dodecafluoropentane Emulsion, DDFPe | NanO2TM, NVX-108, NVX-208, EchoGen | NuvOx Pharma, Sonus Pharmaceuticals | Oxygen Therapeutic - Oxygen Flow Enhancer, or Ultrasound Contrast Agent | Phase Ib/II complete in acute ischemic stroke [26] [11] [12] |
C8Cl2F16 | 115 | Droplet | Perfluorodichlorooctane | Oxyfluor | HemaGen | Oxygen Therapeutic - Blood Substitute | Discontinued during Phase II trial [31] |
C8BrF17 | 142 | Bubble (when mixed with nitrogen gas), or Droplet | Perfluorooctyl bromide | Imagent | Alliance Pharmaceuticals | Ultrasound contrast agent, contrast for MRI and CT, and Oxygen Therapeutic - Oxygen Flow Enhancer | Discontinued clinical development, continuing pre-clinical development [32] [27] |
C8BrF17, and C10F21Br | 142, 185 | Droplet | Perfluorooctyl bromide and perfluorodecylbromide | OxygentTM | Alliance Pharmaceuticals | Oxygen Therapeutic - Blood Substitute | Discontinued [33] |
C10H2F18 | 64.3 | Droplet | Bis-perfluorobutylethelene | oxygenated fluorocarbon nutrient emulsion (OFNE) | Integra Life Sciences | Oxygen Therapeutic - CSF Substitute | Discontinued [18] |
C10F18, and C9F21N | 142 | Droplet | Perfluorodecalin and Perfluorotripropylamine | Fluosol, Fluosol-DA | Green Cross Corporation | Oxygen Therapeutic - Blood Substitute | Discontinued [34] |
C10F20 | 148.5 | Droplet | Perfluorodecene | ABL-101, Oxycyte | Aurum Biosciences, Tenax Therapeutics, Oxygen Biotherapeutics | Oxygen Therapeutic - Blood Substitute | Phase I clinical trial in acute ischemic stroke [35] |
C22F41N | 172 | Droplet | Perftoran | Perftoran, or VIDAPHOR | FluorO2 | Oxygen Therapeutic - Blood Substitute | Approved in Russia [34] |
Priapism is a condition in which a penis remains erect for hours in the absence of stimulation or after stimulation has ended. There are three types: ischemic (low-flow), nonischemic (high-flow), and recurrent ischemic (intermittent). Most cases are ischemic. Ischemic priapism is generally painful while nonischemic priapism is not. In ischemic priapism, most of the penis is hard; however, the glans penis is not. In nonischemic priapism, the entire penis is only somewhat hard. Very rarely, clitoral priapism occurs in women.
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Medical ultrasound refers to diagnostic techniques using ultrasound, as well as therapeutic applications of ultrasound. In diagnosis, it is used to create an image of internal body structures such as tendons, muscles, joints, blood vessels, and internal organs, to measure some characteristics or to generate an informative audible sound. The usage of ultrasound to produce visual images for medicine is called medical ultrasonography or simply sonography. The practice of examining pregnant women using ultrasound is called obstetric ultrasonography, and was an early development of clinical ultrasonography.
Cerebral edema is excess accumulation of fluid (edema) in the intracellular or extracellular spaces of the brain. This typically causes impaired nerve function, increased pressure within the skull, and can eventually lead to direct compression of brain tissue and blood vessels. Symptoms vary based on the location and extent of edema and generally include headaches, nausea, vomiting, seizures, drowsiness, visual disturbances, dizziness, and in severe cases, coma and death.
A blood substitute is a substance used to mimic and fulfill some functions of biological blood. It aims to provide an alternative to blood transfusion, which is transferring blood or blood-based products from one person into another. Thus far, there are no well-accepted oxygen-carrying blood substitutes, which is the typical objective of a red blood cell transfusion; however, there are widely available non-blood volume expanders for cases where only volume restoration is required. These are helping doctors and surgeons avoid the risks of disease transmission and immune suppression, address the chronic blood donor shortage, and address the concerns of Jehovah's Witnesses and others who have religious objections to receiving transfused blood.
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Blood doping is a form of doping in which the number of red blood cells in the bloodstream is boosted in order to enhance athletic performance. Because such blood cells carry oxygen from the lungs to the muscles, a higher concentration in the blood can improve an athlete's aerobic capacity (VO2 max) and endurance. Blood doping can be achieved by making the body produce more red blood cells itself using drugs, giving blood transfusions either from another person or back to the same individual, or by using blood substitutes.
Cerebral infarction is the pathologic process that results in an area of necrotic tissue in the brain. It is caused by disrupted blood supply (ischemia) and restricted oxygen supply (hypoxia), most commonly due to thromboembolism, and manifests clinically as ischemic stroke. In response to ischemia, the brain degenerates by the process of liquefactive necrosis.
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Crocetin is a natural apocarotenoid dicarboxylic acid that is found in the crocus flower together with its glycoside, crocin, and Gardenia jasminoides fruits. It forms brick red crystals with a melting point of 285°C.
Animal models of ischemic stroke are procedures inducing cerebral ischemia. The aim is the study of basic processes or potential therapeutic interventions in this disease, and the extension of the pathophysiological knowledge on and/or the improvement of medical treatment of human ischemic stroke. Ischemic stroke has a complex pathophysiology involving the interplay of many different cells and tissues such as neurons, glia, endothelium, and the immune system. These events cannot be mimicked satisfactorily in vitro yet. Thus a large portion of stroke research is conducted on animals.
Perfluoro tert-butylcyclohexane is a perfluorinated chemical compound. It is a component of the experimental therapeutic oxygen carrier called Oxycyte.
Perfusion is the passage of fluid through the lymphatic system or blood vessels to an organ or a tissue. The practice of perfusion scanning is the process by which this perfusion can be observed, recorded and quantified. The term perfusion scanning encompasses a wide range of medical imaging modalities.
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Cerebral blood volume is the blood volume in a given amount of brain tissue.
A specific branch of contrast-enhanced ultrasound, acoustic angiography is a minimally invasive and non-ionizing medical imaging technique used to visualize vasculature. Acoustic angiography was first developed by the Dayton Laboratory at North Carolina State University and provides a safe, portable, and inexpensive alternative to the most common methods of angiography such as Magnetic Resonance Angiography and Computed Tomography Angiography. Although ultrasound does not traditionally exhibit the high resolution of MRI or CT, high-frequency ultrasound (HFU) achieves relatively high resolution by sacrificing some penetration depth. HFU typically uses waves between 20 and 100 MHz and achieves resolution of 16-80μm at depths of 3-12mm. Although HFU has exhibited adequate resolution to monitor things like tumor growth in the skin layers, on its own it lacks the depth and contrast necessary for imaging blood vessels. Acoustic angiography overcomes the weaknesses of HFU by combining contrast-enhanced ultrasound with the use of a dual-element ultrasound transducer to achieve high resolution visualization of blood vessels at relatively deep penetration levels.
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