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Under Pressure

Sensor enables noninvasive monitoring of brain changes caused by trauma or pregnancy

087-088_Carreiras_222MARIANA COANin São Carlos and Ribeirão Preto, São Paulo State

It was just nine o’clock when Dr. Luiza da Silva Lopes, a neurosurgeon, sat down on a wooden bench and began the first of three operations she would perform that Friday morning, May 16, in a small room of the University of São Paulo (USP) Pediatric Neurosurgery Laboratory in the city of Ribeirão Preto, São Paulo State. With the scalpel in her right hand, she steadily made an incision of just over a centimeter along the scalp of an anesthetized mouse and withdrew the skin, muscles and fibrous membrane covering its skull bones. In less than five minutes the area was ready for Danilo Cardim, a biologist, to place a small sensor on top of the rodent’s skull. For the next 20 minutes, Cardim recorded the fluctuations in pressure inside the animal’s skull using a handheld device. It was developed by the group of which he is a part at the University of São Paulo in São Carlos. Improvements to the device are ongoing, and today there are five prototypes in operation, some of which are being used in experimental trials in humans.

A little later that morning, Dr. Lopes repeated the surgical procedure on two other mice, this time on pregnant mice, so Cardim could take new measurements. This data and other data collected in previous weeks would then be forwarded to Dr. Brenno Cabella, a medical physicist, for analysis using a number of sophisticated mathematical tools. The group’s goal is to see whether the pressure to which the brain is subjected inside the skull undergoes changes during pregnancy.

If their suspicion is confirmed and abnormal variations in pressure do occur, the trio, part of a team of nearly 40 people coordinated by a tireless researcher, Dr. Sérgio Mascarenhas, an 86-year-old physicist, will have achieved a further indicator that is on track to provide early identification of a health problem that kills women during pregnancy, preeclampsia. If identified early, the condition can be more successfully treated. Marked by an increase in blood pressure after the 22nd week of pregnancy, preeclampsia affects approximately 10% of the three million Brazilian women who become pregnant each year, and threatens the life of the mother as well as her fetus. It can trigger seizures in pregnant women and even lead to coma, while the fetus is in danger of running out of nutrients and oxygen by placental abruption or may be born prematurely. “This is a disease that weighs heavily on society: it is the biggest killer of children and pregnant women in the perinatal period,” says Dr. Geraldo Duarte, an obstetrician and head of the High Risk Service of the Ribeirão Preto School of Medicine’s Department of Obstetrics and Gynecology, and Mascarenhas’s collaborator on this project. “The science still owes a great deal in this area because we know little about the disease.”

016-023_Intracraniana_221-APending the outcome of the experiments with rodents, Dr. Duarte and Dr. Ricardo Cavalli, an obstetrician, plan to use the second and most recent version of the intracranial pressure sensor to begin monitoring pregnant women seen at USP’s Hospital das Clínicas in Ribeirão Preto. Totally noninvasive, the new version of the sensor has been developed and improved by Dr. Mascarenhas’s team at USP in São Carlos over the last four years, with funding from FAPESP and the Ministry of Health. Unlike the sensor used in the test with mice, this new version is designed to be used in humans without the need for surgical intervention, and in April 2014, was tested on a small group of patients in the neurocritical care unit of the Hospital de São João affiliated with the University of Porto in Portugal.

Made of a hard plastic material and a little bigger than a matchbox, the new version of the sensor is placed on the skin and hair of the patient while awake. During monitoring it remains attached by an elastic band similar to that worn by tennis players, which causes only a slight pressure on the skull and feels like a hat that’s a little too tight. The new version of the sensor works on a very simple principle. A pin resting on the skin fluctuates with the microscopic movements of the bones of the head, due to changes in intracranial pressure determined largely by the inflow of a greater volume of blood to the brain and its related structures with each beat of the heart. The displacement of the pin moves a lever to which deformation sensors (strain gauges) are attached, which transform the subtle movement into electrical signals transmitted to a device that amplifies and displays them in graph form on a monitor (see infographics). The current sensor is an important advance over the previous model, although the operating principle is the same: both measure fluctuations in cranial volume.

Minimally invasive sensor (top) and noninvasive sensor (opposite): both use strain gauges

Minimally invasive sensor (top) and noninvasive sensor (opposite): both use strain gauges

The first sensor, used in experiments with animals (mice, rabbits and sheep) and also in initial tests with patients admitted to intensive care units, requires a cut in the scalp and implantation of the sensor on top of the skull. Dr. Mascarenhas began its design in 2007, and Gustavo Frigieri Vilela, a pharmacist who at the time was a PhD student of Dr. Mascarenhas in São Carlos, developed it further. Both were looking for a less aggressive and invasive form of monitoring intracranial pressure, one of the most important parameters that doctors analyze in people suffering head trauma and other problems of the central nervous system. Intracranial pressure values reveal whether the brain and its related structures are getting the proper amount of nutrients and oxygen, and whether toxins are being eliminated at the appropriate rate. They also are an indicator of how the central nervous system is reacting to abnormal conditions, such as injuries caused by head trauma, which in turn causes edema; changes in the blood supply occurring after a stroke, ischemia or bleeding; development of tumors and disorders in the circulation of cerebrospinal fluid, which bathes the brain and the spinal cord.

The most widely adopted method of intracranial pressure monitoring is considered somewhat invasive. A hole in the cranium must be opened into which the neurosurgeon inserts a sensor. The most superficial opening is near one of the membranes that surrounds and protects the brain. The deepest one penetrates about eight centimeters, which causes tiny lesions in the brain tissue and increases the risk of bleeding and infection. “On average, infections and bleeding occur in 3% of cases, which is an acceptable risk from a surgical point of view, but worsens the prognosis for a patient already in serious condition,” says Dr. Fernando Gomes Pinto, a neurosurgeon at USP’s Hospital das Clínicas in São Paulo. “Finding a way to measure intracranial pressure non-invasively could be of great benefit.”

Dr. Mascarenhas began to seek a less invasive way of monitoring intracranial pressure in 2006, in his words, “to be a nonconformist.” Shortly before that he had undergone major surgery to implant a valve in one of the chambers of the brain to drain excess fluid. Initially diagnosed as Parkinson’s disease, it caused him to have difficulty walking and memory problems, but his problem was something else: normal pressure hydrocephalus. Common in the elderly, the condition is caused by the buildup of cerebrospinal fluid in the chambers of the brain. A healthy adult produces half a liter, or about two glasses of fluid per day, a clear fluid that bathes the entire central nervous system and protects it, cushioning impacts and removing metabolites. With age, the cerebrospinal fluid re-absorption system may fail to function properly and fluid accumulates, pressing on the brain. This is similar to what is observed in infant hydrocephalus, which affects one in every 1,000 children and leads to skull deformation, because the skull bones have not yet consolidated.

From the present to the past: three generations of intracranial pressure monitors

EDUARDO CESARFrom the present to the past: three generations of intracranial pressure monitors EDUARDO CESAR

“About 300,000 valves have today been implanted in Brazil for this purpose,” says Dr. Mascarenhas. “The problem is that in 30% of the cases they become clogged and need to be replaced by surgical means.” What most disturbed him was the fact that one of the ways to assess the valve’s functioning from time to time required an intracranial pressure sensor to be implanted. “I could not accept that in the 21st century it was still necessary to make a hole in the head to measure intracranial pressure,” he recalls.

And so Dr. Mascarenhas decided to look for an alternative. From consulting with his engineering colleagues, he learned there were times when civil engineers made use of a small electrical device called a strain gauge to assess subtle deformations in structures such as concrete beams or the steel of a bridge or the columns of a building. In an initial test, Dr. Mascarenhas pasted a strain gauge to the top of a human skull borrowed from the Federal University of São Carlos (UFSCar) School of Medicine and inflated a birthday balloon inside. He coupled a device to measure blood pressure (manometer) to the balloon and compared the values ​​recorded on the manometer with those of the strain gauge (see Pesquisa FAPESP Issue No. 159). Although each device uses different units of measurement—the manometer measures in millimeters of mercury and the strain gauge in volts—the values showed the same behavior: growing in linear fashion with increasing pressure and likewise decreasing when the pressure was lower. It was a sign that the two tools measured the same phenomenon. But he had to convince doctors, which was not an easy task.

A little over two centuries ago, medical schools taught that once the bone joints of the head consolidated, the skull became rigid and could not expand. The man who first proposed that idea was the Scottish anatomist Alexander Monro in 1783. Studying animals, patients and human cadavers, he and his student and collaborator, fellow Scot George Kellie, postulated, among other things, that the braincase that houses the brain, blood and cerebrospinal fluid could not expand in adults. This set of ideas, which became known as the Monro-Kellie doctrine, also stated that because it was not subject to deformation, any change in the volume of one of the components (blood, cerebrospinal fluid or brain tissue) would lead to a change in volume in one of the others, so that the total volume remained constant.

016-023_Intracraniana_221-BDr. Mascarenhas and his collaborators repeated the experiments with the balloon and the human skull and demonstrated that the Monro-Kellie doctrine needed to be revised. The sensor mounted with the strain gauge not only detected a subtle expansion of the skull (on the order of micrometers), proportional to the increase in internal pressure, but also recorded its retraction, also linear. “We showed that the material had no memory of the deformation, which would prevent use of the strain gauge in the sensor to monitor intracranial pressure,” said Dr. Mascarenhas during a long conversation on the morning of May 15 at the headquarters of the Institute of Advanced Studies (IEA), which he created and directs at USP in São Carlos.

Nearly four years of attempts were needed before a scientific journal agreed to publish the results. “Several publishers said the work was good, but defied an old and very solid medicine paradigm,” said Gustavo Vilela, a co-author of the article published in 2012 in Acta Neurochirurgica, during an interview at IEA’s headquarters.

While working to improve the sensor, Dr. Mascarenhas and Vilela were developing a portable monitor, also to be used outside operating rooms and ICUs. The current version of the monitor—the third ever produced—comes with all its electronic components embedded in the product. Weighing less than two kilos, it looks like a briefcase, about 30 cm in width, 30 cm in height and 15 cm deep. Its battery supports five hours of operation and its memory card, which can be replaced, has the capacity to store information for days of monitoring. In principle, it could be used by doctors or paramedics in an ambulance to assess the intracranial pressure of people involved in traffic accidents before reaching the hospital.

In addition to all the hardware, the new version of the monitor includes a program that converts the electrical signals generated by the skull’s pulsation into two graphs: the one displayed in a larger picture shows the evolution of pressure over a period of time ranging from 5 to 20 minutes, while the second, which appears in a smaller window, allows us to observe the shape (morphology) of the curve in a time interval of a few seconds. This graph is important because it tells the doctor how the brain is responding to injury. The researchers estimate that all the equipment (sensor and monitor) can be sold for about R$3,500, including taxes, or almost 15 times less than the invasive devices currently used to monitor intracranial pressure.

“The previous version had to be connected to a notebook and could not pass the radiation emission tests of the National Institute of Metrology, Quality, and Technology (Inmetro),” says Vilela. With five units now produced, the newest version of the monitor is ready to be submitted to Inmetro for quality and safety analyses. The researchers will have to await its approval before submitting it to the Brazilian Health Surveillance Agency (ANVISA) for analysis, whose approval is also necessary prior to clearance for sale of the equipment and its use in clinical practice. Even before passing these tests, however, the equipment can now be used for research.

“We intend to enter the university market to help develop a critical mass of users of the product,” says Vilela, a partner with Dr. Mascarenhas in Braincare, a company created in January 2014 to be the legal manufacturer of the device; a third party, Cluster Tech, also based in São Carlos, will be responsible for production. “We want to give the equipment to interested people and let them work things out because we do not have enough time or money to do all the tests,” says Dr. Mascarenhas. “Braincare does not want to be a manufacturer, but rather a company that develops ideas,” adds Vilela.

The development of a new wholly domestic technology in healthcare takes a long time. It may take 10-15 years to complete all the procedures needed to analyze its safety and cost-effectiveness. And it is also a somewhat rare feat in Brazil. “Development is generally incremental; we have always been technology buyers, so the trade deficit in this area is negative at about R$10 billion,” says Paulo Henrique Antonino, general coordinator of healthcare equipment and materials for the Department of Science, Technology and Strategic Supplies of the Ministry of Health. “If everything the São Carlos group has demonstrated so far is confirmed, it will be a revolution,” he says. “We hope to have a product whose convenience enables it to be used on patients in the emergency care network.” Antonino believes that if this technology goes through all the stages of approval and is incorporated into medical practice, it can gain a share of the global market.

Advances to turn the prototype into a product are due, in large part, to the interaction between researchers from Braincare and Sapra Landauer, a radiological protection equipment company created by Dr. Mascarenhas in 1979 and managed by his two sons, Paul and Yvone, both physicists. “Sapra’s part is to help them get their feet on the ground,” says Dr. Yvone Mascarenhas during a conversation in May at Sapra’s headquarters, one two-story building 10 minutes away from the USP campus in São Carlos. “At the university, the tendency is always to try for improvements and not aim for commercialization,” he says. In his opinion, in order to improve a product you need to have some return, even financial, on what has already been done. “The market talks back to you,” he says. “In the case of this equipment, this is a market that is yet to be created, and we need to know what the market wants.”

The ability to monitor intracranial pressure noninvasively is something that has been a goal for a long time. “It is the dream of every neurosurgeon and neurologist,” says Esper Cavalheiro, a neuroscientist at the Federal University of São Paulo (Unifesp), which is closely watching the results of the São Carlos group. Cavalheiro, an epilepsy specialist, knows there are a number of situations in which chronically elevated intracranial pressure can lead to neuronal loss. “Direct methods of measuring intracranial pressure are invasive, and indirect ones, such as imaging, are only indicative and do not provide evidence that this increase is actually occurring,” he says. “It would be a huge help for anyone working with treating refractory epilepsy patients, who have increased intracranial pressure, especially those whose underlying disease is neurocysticercosis.”

Another group that could benefit from a noninvasive form of monitoring is children with hydrocephalus, a buildup of cerebrospinal fluid in the chambers (ventricles) of the brain, which in babies causes, among other things, deformation of the skull. “There are cases where there is doubt as to how well the valve implanted to reduce pressure in hydrocephalus is working,” says Dr. Sergio Cavalheiro, a pediatric neurosurgeon, also with Unifesp. Before the São Carlos group’s equipment is cleared for use in a clinical setting, Dr. Cavalheiro thinks it is necessary to show that the measured effects are due to expansion of the skull, not stretching of the skin. “If the measurement on top of the skin allows us to truly monitor intracranial pressure, it will be fantastic,” he says.

Dr. Felix Rígoli, a Uruguayan physician and the health technology and innovation coordinator for the Pan American Health Organization (PAHO) in Brazil, which also supports implementation of the project, sees this new technology as an opportunity to open a window into the unknown. “If intracranial pressure can be measured noninvasively, we will be able to monitor it continuously and attempt to discover what occurs in problems such as Alzheimer’s and even migraines,” he says. In such cases, there are ethical questions about the need for a surgical procedure to measure intracranial pressure. Dr. Rígoli thinks that a noninvasive way of monitoring would also provide information on normal intracranial pressure levels in healthy people, something that is still unknown. “The same may happen as occurred with blood pressure two centuries ago, when, finding a way to measure it outside the body led to a whole range of potential new applications, including disease prevention.”

With five prototypes of the new version of the equipment in use, the São Carlos and Ribeirão Preto researchers are now working to collect data on patients and attempting to demonstrate that their noninvasive monitoring device can measure the same phenomenon as the invasive one. In April 2014, Gustavo Vilela and Rodrigo Andrade, an engineer, spent a month in the city of Porto, Portugal, where they used the new equipment to monitor intracranial pressure in eight patients and compared their measurements with data obtained by invasive techniques. The 850 recorded hours are now being analyzed by Dr. Brenno Cabella back in Ribeirão Preto. The preliminary results, obtained earlier, which were presented at an international conference held in Singapore in November 2013, suggest that the two strategies measure the same thing. “In some cases, the correlation was very high,” Dr. Cabella says. But many more cases still need to be done, maybe a few hundred, so that the reproducibility of the measurements can be assessed.

“At this stage, the research is in the transition from technical refinement and animal research into clinical evaluation with patients,” says Dr. Celeste Dias, the coordinator of the neurocritical care unit of the Hospital de São João in Porto. “My biggest contribution begins here: to collaborate in the clinical research,” says Dr. Dias. She was introduced to the work of the São Carlos researchers in 2010 at an international conference, and she put them in touch with the team of Marek Czosnyka of the University of Cambridge in England; Czosnyka is a renowned expert on intracranial pressure analysis and has collaborated with Dr. Dias. In October Danilo Cardim will go to Cambridge to work on his PhD with Czosnyka’s group. Cardim, who evaluated intracranial pressure variations in epileptic mice for his master’s degree, will take with him two prototypes of the non-invasive equipment; while there he will monitor the intracranial pressure of patients who have suffered brain trauma or stroke and compare the results with records of the invasive technique.

Besides trauma, stroke and hydrocephalus, problems that are known to require a determination of intracranial pressure, the researchers intend to extend this parameter to other health problems in which nothing is known about intracranial pressure behavior, such as preeclampsia.

In São Carlos and Ribeirão Preto, Doctors Cavalli and Duarte and Mascarenhas’s team hope that the noninvasive monitoring will provide some signal that serves as an early indicator of the risk of developing preeclampsia. There are commercially available tests today that measure the level of two blood compounds. But they only test whether a woman will develop this form of hypertension typical of pregnancy at a maximum of three weeks before her blood pressure starts to rise and symptoms appear such as headaches, dizziness and mental confusion. “It is extremely difficult to find a predictor that works well and earlier,” says Dr. Cavalli, who returned in March from a research internship at Harvard University, where he investigated the effectiveness of these blood markers. “We want to find an indicator that lets us know early in a pregnancy who has a higher risk of developing the problem,” he says.

In early May 2014, Dr. Cavalli conducted a pilot study with volunteers to assess the applicability of the noninvasive sensor. In just one afternoon, the researchers monitored the intracranial pressure of eight pregnant women. “We saw that it is very simple and fast,” he says.

“If we can make an earlier diagnosis, we can triage patients at risk of developing preeclampsia and also follow the progress of the treatment,” says Dr. Duarte, who  plans to conduct a clinical trial in the near future with the noninvasive monitor; he will track changes in the intracranial pressure of pregnant women throughout their pregnancies and compare the results with those of blood marker tests.

Although there is no data in the scientific literature linking preeclampsia with changes in intracranial pressure, Dr. Duarte says there is evidence that this may occur. “We may not find any link, but we may find something that no one has as yet discovered,” he says. “If it works, it may be possible to help reduce the rate of perinatal and maternal mortality.”

1. Development of a minimally invasive device for monitoring intracranial pressure (No. 08/53436-2); Grant mechanism Innovative Research in Small Businesses Program (PIPE); Principal investigator Sergio Mascarenhas Oliveira (Sapra/S.A.); Investment R$ 221,430.90 (FAPESP).
2. Registration and marketing of a minimally invasive device for monitoring intracranial pressure (No. 11/51080-9); Grant mechanism Innovative Research in Small Businesses Program (PIPE); Principal investigator Sergio Mascarenhas Oliveira (Sapra/S.A.); Investment R$165,647.77 (FAPESP).
3. Development of a noninvasive sensor, hardware and software for monitoring intracranial pressure in patients with hydrocephalus and stroke (No. 12/50129-7); Grant mechanism Innovative Research in Small Businesses Program (PIPE); Principal investigator Gustavo Henrique Frigieri Vilela (Sapra/S.A.); Investment R$219,948.02 (FAPESP).

Scientific article
MASCARENHAS, S. et al. The new ICP minimally invasive method shows that the Monro-Kellie doctrine is not valid. Acta Neurochirurgica. 2012.