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Flowmeters designed to measure the rate and the volume of blood flow through a particular organ (e.g., liver, brain, heart) or vessel of the circulatory system. Most blood flowmeters measure blood flow transcutaneously in all vessels except those blocked by bone or air (i.e., outside the skull or thorax). Some instruments have probes that are placed directly on a blood vessel during surgical procedures; other probes are threaded through a catheter to measure blood flow from inside a blood vessel. Dedicated electronic blood flowmeters are available using a variety of techniques, including electromagnetic, ultrasound, and laser devices; some external instruments using ultrasonic and near infrared spectography can perform non-invasive blood flow measurements inside the cranium (i.e., transcranial flowmeters). Blood flowmeters are intended for applications such as the assessment of air embolism, atherosclerosis, varicose veins, and venous thrombosis; they are also used to measure blood flow after coronary artery bypass, organ transplant, and other vascular reconstructive surgery.
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