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Gas bubbles are taken under control

November 14, 2003

The system developed by the Moscow scientists with the financial assistance of the Russian Foundation for Basic Research and the Foundation for Assistance to Small Innovative Enterprises will instantly allow to detect and measure gas micro-bubbles being formed in blood inside the pump oxygenator. A small device which looks like some kind of a bracelet on the arterial line of the pump oxygenator and is connected to the computer will be recording all bubbles, searching for potentially dangerous ones and will ensure the timely opportunity to get rid of them.

A patient on the operating table is exposed to numerous risks, especially if the operation is so complex, that extracorporeal circulation is required. One of the dangers is a risk of embolism by a gas bubble, which may occur in the process of blood circulation in the pump oxygenator. It is not always clear why the gas bubbles originate, but they do almost in all the cases. The smaller ones, less than 10 microns in diameter are not particularly dangerous, as they quite rapidly dissolve by themselves. As for bigger bubbles, they may plug in a vessel like a cork, thus disrupting normal blood circulation and causing very bad problems for the organism.

In order to avoid such consequences, it is necessary to trace all the bubbles formed in a pump oxygenator, detect the biggest ones as the most dangerous and get rid of them. The matter is that it has only been possible so far to apply a qualitative approach to this problem, but the scientists have not had any clue to solving it at the quantitative level - to detect gas bubbles in blood and to determine their number and size. In other words, the scientists were unable to distribute the bubbles by size.

However, this problem can soon be solved due to the effort of the scientists from the Moscow research-and-production company 'BIOSS'. They developed a special system of detecting micro-bubbles on the arterial line of the pump oxygenator to perform extracorporeal circulation.

It consists of several parts. The core of the device is an electronic unit with the ultrasonic detector, which reminds a bracelet, but is very intelligent. Its action is based on the Doppler effect - the fact that the frequency of oscillation or the radiation wave length is changing when re-echoed from a moving object. Omitting technical details, the essence is that the generator creates a continuous ultrasonic wave, it is reflected from the bubbles and the detector, in its turn, catches the echoed signal.

Then an analog-to-digital converter 'translates' the assisted signal into the computer language, making the signal digital and then it is further transmitted to the data processing, storage and display unit. This way it is possible to display at any time a bar chart at the PC screen, showing how many gas bubbles are moving in blood flow inside the pump oxygenator and to evaluate their sizes.

So far, there has been built only one test copy of this remarkable device. The developers are currently testing it on a special calibration test bench. The device was especially developed and built for the purpose of creating gas bubbles of the predetermined size in the liquid imitating blood. First, it was necessary to calibrate the system, and the scientists did not have the standard. They had to develop it separately.

The system successfully underwent the first tests both at the test bench and at the real pump oxygenator. "Our system has demonstrated all the capabilities we expected to get", said Tengiz Mosidze, the project manager and leading engineer. It quickly records gas bubbles ranging from 10 to 400 microns in diameter and accurately determines their sizes. We still need to perform medical tests. Currently, we are developing the algorithm of the computer program which will allow to analyze the situation and evaluate the probability of embolism. And for the future project we have plans to develop a system capable not only to detect dangerous bubbles in blood, but also to remove them automatically."

Informnauka (Informscience) Agency