An innovative tomograph, which monitors the condition of the lungs in real time, is already being used by patients on artificial respiration in intensive care units (ICUs) at the Clinicas Hospital and the InCor Heart Institute in the city of Sao Paulo. The equipment helps the doctor to gauge and control the three basic variables used when air is injected into the lung by means of a mechanical ventilator: volume, pressure and flow. This control helps reduce the number of deaths in ICUs, because it makes it possible to visualize the organ’s reaction while it is receiving the air. “The lung has several lobes and, in some cases, one is sick and the other one is healthy. This means that, without this monitoring, there is an unequal distribution of the air inside the organ, which is extremely harmful,” explains Professor Marcelo Amato, who is responsible for the Experimental Pulmonology Laboratory at the University of Sao Paulo’s Medical School (FMUSP) and the coordinator of the research. “Besides being a waste of artificial respiration ,this poor air distribution causes an extra lesion, which literally begins to tear the lung.”
Given that the creation of equipment and devices in the bioengineering area applied to medicine requires not only knowledge of the mechanics of the materials used but also a deep understanding of the complex biological system that governs the human body, it took ten years of research to come up with the electrical impedance tomograph, a belt with 32 electrodes which, placed on the patient’s thorax and linked to a monitor, continually indicates the organ’s reactions via images obtained by the emission of high frequency, low intensity electric pulses. At present there is no commercial tomograph available for real-time lung monitoring. “There is another prototype that works along the same lines, which has been developed by researchers at a German university, the only difference being that they are still using 16 electrodes instead of 32,” says Amato says. The number of electrodes makes a difference in the clarity and visualization of the images.
“This means that they are about three to five years behind in relation to our equipment,” he explains. One of the plans of the Brazilian researchers is to increase the number of electrodes from 32 to 64 or 128, but only at a future date, because this modification will significantly increase the cost. The researcher estimates that it will take at least another two years to make the final adjustments needed to get the equipment to the point where it can be used by any ICU doctor, without a lot of prior instruction.
Since 2006, two of these tomographs have been in use at the Clinicas Hospital and another one at InCor. In one of the studies carried out, the device enabled doctors to detect problems that occur during lung transplant operations. “In unilateral lung transplant cases, we saw that the remaining lung demonstrates paradoxical behavior that obstructs the alveolar ventilation process, reducing ventilation efficiency and gas exchanges,” declares Amato. This discovery could have implications for surgical procedures to be adopted in the future. Perhaps a unilateral lung transplant may be more successful when accompanied by a total removal of the diseased lungs, instead of leaving one of the lungs inside the thorax. “In the same way as functional magnetic resonance made it possible to understand how the brain processes information, electric impedance tomography enables us to observe ventilation and pulmonary perfusion in real time, revealing previously unknown phenomena,” he explains.
It was during a visit to Professor Bruchard Lachmann’s laboratory at Erasmus University in the city of Rotterdam in Holland in 1997 that Amato came up with the idea of building a tomograph of this type. A student showed up at the laboratory with a prototype from the University of Sheffield, in England, which used the same principle of injecting electrical currents and measuring the voltages. “It was a very primitive prototype, which had never been used on patients or in artificial respiration experiments,” recalls Amato. “But when I saw the results of the experiments with baby pigs I realized this was exactly what I’d been looking for. A monitor that could see inside the lung and observe distinct, simultaneous phenomena in different pulmonary areas, during artificial respiration.”
The images were rather unclear and it was impossible to see them in real time, but it was a very exciting beginning for the researcher, who in the early 1990’s, when treating ICU leptospirosis patients with hemorrhaging lungs, noticed that the hemorrhage could be stanched by adjusting the pressure and the volume of air from the artificial respirator. “We noticed that the mortality rate among patients on artificial respiration could be halved if we managed to reduce the problems of heterogeneities and excessive stress within the lung, with special maneuvers and gentler ventilation treatment,” explains Amato, who at the time was an assistant physician in Pulmonology and was working at the Clinicas Hospital respiratory ICU. The technique, concerning pulmonary protection strategies, was the subject of an article in the New England Journal of Medicine in 1998. “The article has had more than a thousand citations and became a benchmark reference in the field,” explains the researcher. Based on the figures set out in this paper, which were confirmed by a study carried out in 2000 by a group of researchers from ARDSnet (Acute Respiratory Distress Syndrome Network) sponsored by the National Institutes of Health (NIH) of the United States, the volumes that were used up to then are no longer used. “It was common to put one liter of air in the lung every time the patient breathed, but nowadays this is unthinkable,” says the researcher.
Back in Brazil after his trip to Holland, Amato got in touch with the University of Sheffield and managed to purchase the latest available prototype, which for all intents and purposes arrived here broken. It was at that point that he decided to begin to develop a device that could monitor the patient from his bedside. The first challenge was to succeed in producing an image from electrical currents circulating through the thorax. Whereas in the X-ray tomograph the detector captures linear emissions of X-rays, measured sequentially after changes of less than one degree in the angle of emission, in the case of the impedance tomograph the electrical current reaches the detector diffusely, with changes in the angle of emission at larger intervals. “A difficult problem, but not impossible to solve,” says Amato. At USP’s School of Engineering, Amato found one of his partners in the undertaking, Professor Raul González Lima, who started with the resolution of a mathematical problem. Subsequently, Professor Joyce Bevilaqua, from USP’s Institute of Mathematics and Statistics, also joined the group.
The tomograph gained some momentum when FAPESP gave its approval for this theme project in 2002. At that point development of the electronic part got underway with the help of the researcher Harki Tanaka, who was finishing his degree in Medicine at USP’s Medical School, more than two decades after graduating with a degree in electronic engineering from ITA (the Technological Institute of Aeronautics). “We met two to four times a week with several engineers, until we finally managed to put together a prototype,” Amato explains. This first prototype was very different from the current tomograph, being rather awkward, but it worked very well on a baby pig.
As there were still a number of areas in which the equipment needed improving, and one of these related to the medical area, in 2004 Amato presented the project to the Brazilian company Biomedical Dixtal, which initially became a partner without any government link. In 2007, almost during the final stage of the theme project, the Brazilian Innovation Agency – Research and Projects Financing (Finep) – approved a research project along the same lines, a partnership between the university, represented by the Medical School Foundation, and Dixtal, which had recently been taken over by Philips.
For the noise and electromagnetic interference from other ICU equipment not to compromise the accuracy of the voltage measurements of each electrode, the researchers developed an electrode belt in which the cables are completely encased. “Each cable has an internal electronic circuit to suppress the individual electromagnetic noise,” says Amato. The current cost of the components used in the tomograph is around R$10 to 15 thousand. “The equipment’s main advantage is that it doesn’t require any expensive hardware components.” Two patents have been filed for the device. One is on behalf of the physician and engineer Tanaka and concerns the electronic configurations. The other is on behalf of Dixtal, and covers the electrode belt configurations. “An agreement has been signed by the company and the Medical School Foundation regarding the transfer of royalties,” stresses Amato. “In other words, if the industrial sector decides to start selling the tomograph, we will get added research funds.”
Before the tomograph, Amato was in charge of other research in the artificial respiration field. One of the technologies that he developed and that has been adopted in medical practice is that of ventilation with pressure support and guaranteed volume (VAPSV), which is incorporated in the artificial ventilators made by Intermed, a company in the state of Sao Paulo that manufactures mechanical ventilation products for ICUs and the anesthetics area, as well as in three ventilation units produced by international companies. The technique consists of optimizing the flow supply to the patient’s lung when he or she wakes up from the anesthetic and begins to breathe. “With this technology, the ventilator notices the rate of the patient’s breathing and carries out calibration in order to work in harmony, adjusting the supply to the flow demand, while also ensuring that a minimum ventilation volume is maintained.”
1. New strategies in relation to artificial respiration: diagnosis and prevention of barotrauma/biotrauma by means of electrical impedance tomography (EIT) (nº 01/05303-4); Type Theme project; Coordinator Marcelo Britto Passos Amato – USP; Investment R$ 4,947,662.98 (FAPESP)
2. Clinical intelligence for tomography via electrical impedance; Type
ICTS – Companies Cooperation; Coordinator Marcelo Britto Passos Amato – USP; Investment R$898,600.00 (Finep)
AMATO, M. B. P. et al. Effect of a protective-ventilation strategy on mortality in the acute respiratory distress syndrome. The New England Journal of Medicine. v. 338, n. 6, p. 347-354. 5 Feb. 1998.
COSTA, E. L. V. et al. Real-time detection of pneumothorax using electrical impedance tomography. Critical Care Medicine. v. 36, n. 4, p. 1230-1238. Apr. 2008.