Intracranial Blood Flow Assist Device: Validation and Optimization using a Mathematical Model
By Limor Batino M.sc student
A cerebral blood flow assist device was developed to ensure blood and oxygen supply to the brain in cases of increased intracranial pressure that compromises blood flow.
The brain has high metabolic demands. Tissue integrity and functionality depend on regular blood supply. Compromised cerebral blood flow (CBF) may have irreversible detrimental effects on brain tissue including neurological damage and eventual death. Traumatic brain injury, edema and stroke are common clinical scenarios leading to elevated intracranial pressure (ICP). Increased ICP reduces brain perfusion pressure by counteracting the arterial pressure within cerebral vessels, eventually decreasing cerebral blood flow. Today’s therapy strategies for reduced CBF focus on ICP reduction and mean arterial pressure augmentation. Those therapies are systemic therapies that alter the entire hemodynamic or respiratory status of the patient.
A novel CBF assist device, the intracranial balloon pump, offers a local approach for CBF augmentation. The device consist of a balloon catheter driven by a computer-controlled pump. The inflatable balloon is inserted into one of the brain ventricles and pulsates in synchrony with cardiac cycle. Inflating in diastole and deflating in systole, the balloon augments blood flow in the brain.
To support the device development process theoretically, we developed a mathematical model of intracranial hydro/hemodynamics. We used an electrical lumped parameters model technique in which the hemodynamic system is equivalent to an electrical circuit. The model included three components, blood, cerebrospinal fluid and brain tissue and was embedded with the unique characteristics of the intracranial environment. The rigid cranium enclosing the brain creates a distinctive environment, greatly affects the hydro/hemodynamic system by introducing an external pressure to the system, the ICP. Using the model, we were able to reproduce the physiological behavior of the system as well as the pathological behavior of elevated ICP and reduced CBF. We tested the device operating principle with the model and searched for an optimal inflation and deflation timing along the cardiac cycle. We found that improper timing activation of the balloon might be harmful while proper activation is very efficient, achieving up to 20% improvement of blood flow in high ICP level of 30 mmHg.           

IntraCranial Blood Flow Assist Device: Validation of a Novel Concept using Animal Models
By Tal Or, M.Sc student
Cerebral pathologies such as brain edema, traumatic brain injury (TBI), hydrocephalus and stroke, can result in elevated intracranial pressure (ICP).  An abnormal increase in ICP reduces cerebral perfusion pressure (CPP) by counteracting the arterial pressure within cerebral vessels, eventually decreasing cerebral blood flow (CBF). Diminished CBF can lead to cerebral ischemia or hypoxia followed by neurologic damage and death. Therefore, improvement of cerebral perfusion is a key target for patients undergoing neurocritical care. Most therapies today which help to reduce ICP or improve CBF are aggressive and alter the entire hemodynamic or respiratory status of the patient, inducing a deleterious effect on heart, lungs and renal system. These therapies include mannitol, vasopressors, hyperventilation and hyper-osmolar therapy.
                In this work, we present a novel concept to augment CBF: an intracranial balloon pump (ICBP). The device is based on an inflatable balloon that is placed in the cerebral ventricle and pulsates in synchrony with the cardiac cycle. During diastole the balloon is inflated, “squeezing” blood out of the cerebral veins and creating a space in the skull occupied by the balloon. At the beginning of systole, the balloon is deflated, resulting in an ICP drop due to reduced intracranial volume. This sudden decrease in ICP allows the arteries to grow in diameter, thereby reducing both backpressure and resistance to flow. This, in turn, generates larger CBF. 

   A computer controlled prototype was designed and constructed. The device was tested and verified. The ICBP development and implementation was guided and optimized using a theoretical model which assessed the alterations in cerebral hemodynamics. The ICBP was tested in 8 swine experiments. We studied the ICBP efficacy at baseline and with graded ICP elevation. Results show consistently instantaneous modification of the ICP waveform and significant CBF augmentation during ICBP activation. No significant changes in systemic physiological hemodynamic parameters (e.g. heart rate, arterial blood pressure) were observed during ICBP activation. PCO2 and pH levels were kept within the normal range as well. In conclusion, both theoretical and experimental studies demonstrated that the device can increase CBF in all ranges of ICP. 
 
        Thesis was done under the supervision of Prof. Ofer Barnea1 and Dr. Omer Doron2,
1. Department of Biomedical Engineering, Tel-Aviv University, Tel-Aviv, Israel
2. Department of Neurosurgery, Hadassah University Medical Center, Jerusalem, Israel

העבודות נעשו בהנחיית פרופ' עופר ברנע , המחלקה להנדסה ביו-רפואית, אוניברסיטת תל-אביב