Venous anatomy and pathophysiology
Helane S Fronek in The Fundamentals of Phlebology: Venous Disease for Clinicians, 2007
Reflux of the deep veins can be verified by using spectral and color Doppler, relying on various maneuvers to observe flow in response to valve closure/function. These may include the use of distal or proximal manual vein compression, Valsalva, or a rapid cuff inflation device. Force imposed through the vein creates a pressure gradient causing normal one-way valves to close. Extensive research has established that normal valve function in all veins (excluding the common femoral vein) results in retrograde flow of no greater than 0.5 s. Retrograde flow in the common femoral vein should be no greater than 1.5 s. The extent of reflux necessary to produce clinical symptoms is yet to be discovered. Reflux may be seen on grayscale as the movement of echogenic aggregates of blood cells in the retrograde direction, or with color flow.
Arteriovenous Shunts for Hemodialysis
Waldemar L. Olszewski in CRC Handbook of Microsurgery, 2019
The method includes anastomosing of the radial artery with the median cubital vein, destroying the vein valves within the peripheral part of the cephalic vein, and ligation and transection above the shunt of both the cephalic vein and the median vein (Figure 3). In this way, arterial blood is forced to flow backward within the vein, causing an immediate marked dilatation of the main venous trunk below the shunt. In a few weeks after the operation, significantly widened veins can be seen along the whole surface of the forearm. Transection of both veins above the shunt prevents excessive outflow of arterial blood bypassing the more distal veins. Destroying the vein valves facilitates free backward flow of arterial blood in the vein and prevents formation of venous aneurysms. Moreover, in case of thrombosis, the ligated venous ends facilitate removal of the thrombus from the shunt.
Complications of open repair of femoral and popliteal aneurysms
Sachinder Singh Hans, Mark F. Conrad in Vascular and Endovascular Complications, 2021
In cases of early graft failure, the bypass should be inspected for technical error, which could include a proximal or distal anastomotic complication, or a twisting or kinking of the graft. The inflow artery should be evaluated for adequate flow and to ensure that there are no proximal hemodynamically significant lesions that would be affecting it, along with assessment of the outflow artery, as low flow and poor runoff may be etiologies of early graft thrombosis. The anastomoses should be examined for technical defects. The bypass conduit should also be examined for twist, kinks, or sites of possible compression thoughout its course. In the case of vein conduit, the vein should be examined for any abnormal segment or retained valves. The patient should also be anticoagulated, and a hypercoagulable state or thrombogenic conduit should be considered. Thrombectomy may be performed by gently passing a balloon catheter, and possibly also locally instilling a thrombolytic such as tissue plasminogen activating factor. Once flow is restored in the graft, the graft, as well as the arteries proximal and distal to it, may be further interrogated with digital subtraction angiography (using multiple projections if no obvious defect is found) or duplex ultrasound. If the conduit is believed to be the factor leading to failure, if the original graft was prosthetic, and there is satisfactory quality vein, consider redoing the bypass with vein. If original bypass was with vein which is now felt to be of poor quality, consider redoing bypass with better quality vein if available or with a prosthetic conduit.
Current methods and new approaches to assess aqueous humor dynamics
Published in Expert Review of Ophthalmology, 2021
Carol B. Toris, Meghal Gagrani, Deepta Ghate
Two invasive methods to measure EVP involve cannulating the episcleral veins to get a direct measurement of EVP or cannulating the anterior chamber to change the IOP to get an indirect measurement of EVP. Cannulating the episcleral vein is technically challenging because of the small diameter (50–100 microns) and low fluid volume (less than 4.3 mm/sec) of the episcleral veins [122]. Once cannulated, the EVP is measured by a pressure transducer. The measurement can be affected by the direction in which cannula is placed relative to the flow. EVP is likely overestimated if the cannula is oriented against the flow [123]. An even more sensitive method is a servo-null micropipette system utilizing a tiny micropipette tip with an internal diameter of 2–4 microns to cannulate the episcleral veins [6,124]. The micropipette is filled with a fluid of a different electrical resistance than serum which is attached to a piezoelectric valve connected to an air pressure source. A difference between the pressure in the pipette and the pressure in the vein causes the fluid to move either into or out of the pipette. The valve pressure is adjusted accordingly until the fluid returns to its null position. This endpoint is considered equivalent to the pressure within the vein.
Modelling and simulation of fluid flow through stenosis and aneurysm blood vessel: a computational hemodynamic analysis
Published in Computer Methods in Biomechanics and Biomedical Engineering, 2023
J. V. Ramana Reddy, Hojin Ha, S. Sundar
Blood vessels play an important role in the circulatory system; These are in the form of tubes that carry blood between the heart and all parts of the body. The blood vessel size varies enormously; in the case of arteries, it varies from 1 mm to 8 µm while 1 mm to 20 µm for veins. An artery carries oxidized blood away from the heart, whereas a vein is the blood vessel that collects and transports blood toward the heart. The general appearance of the arteries is rounded lumen, while veins are irregular and often collapse. As compared to arteries, veins are thin-walled vessels with a large and irregular lumen. The diseases of arteries, veins, and lymph vessels alert to blood flow disorders that affect circulation, thus resulting in disturbance in organ function. An aneurysm is a pathological condition. It weakens the blood vessel wall due to the bulging area in that area, resulting in an abnormal widening or ballooning more significant than 50% of the standard diameter. The arteries are mostly exposed to an aneurysm rather than a vein among the several blood vessels.
Unfavorable outcomes in microsurgery: possibilities for improvement
Published in Journal of Plastic Surgery and Hand Surgery, 2019
Paolo Cariati, Almudena Cabello Serrano, Fernando Monsalve Iglesias, Maria Roman Ramos, Jose Fernandez Solis, Ildefonso Martinez Lara
It is important to emphasize that only 8 of the 65 (12.3%) oncological patients received RT before reconstructive surgery in our series. Specifically, five patients from Group 1 and 3 patients from Group 2 had previously been treated with ablative surgery and postoperative radiotherapy. Hence, the quality and quantity of the vessels was acceptable in most cases. In Group 1, the facial artery was used in 86.7% of cases (n = 46), followed by the cranial thyroid artery (11.3%; n = 6), and external carotid artery (1.8%; n = 1). All arterial anastomoses were end to end. Regarding the veins, the facial vein was the most used followed by the external jugular vein. We tried to use two veins whenever possible. Also, all venous anastomoses were end to end. In Group 2, the facial artery was also the artery most frequently used (77.7%; n = 14) followed by the external carotid artery (22.2%; n = 4). No arterial anastomoses were performed with the cranial thyroid artery in this group. The external carotid artery was used after an intraoperative spasm of the facial artery in two cases and in the salvage surgery of a fibula flap 12 h after primary reconstructive surgery. In only one case was the first choice. The facial vein was the one most commonly used, followed by the external jugular vein. All arterial and venous anastomoses were end-to-end also in this group.