[9] Chetta A, Harris ML, Lyall RA, Rafferty GF, Polkey MI, O[11] FDA, Department of Health and Human Services. A PrimerDesign of an MR Airway Pressure Device Team Members Jon Cappel - Communicator Kevin Johnson - BSAC Laura Sheehan - Leader Noelle Simatic - BWIG Client Dr. Haughton – UW Hospital Department of Radiology Advisor Professor Mitch Tyler – UW Department of Biomedical Engineering December 7, 2005Table of Contents Item Page Number(s) Abstract 3 1 Introduction 3 1.1 Problem Statement 3 1.2 Medical Background 3 1.2.1 Headache Syndromes 3 1.2.2 Chiari I Malformation 3-4 1.2.3 Valsalva Maneuvers 4-5 1.2.4 Airway and Pressure Monitors 5-6 1.2.5 Ventilation Systems 6 1.2.6 MR Background 6-7 1.3 Client and Design Requirements 7 2 Preliminary Design 7 2.1 Mouthpieces 7-9 2.2 Valves 9-11 2.3 Transducers 11-13 2.4 Device Sanitation 13 3 Constructing and Calibrating the Prototype 14 3.1 Redesign of the Balloon Valve 14-15 3.2 Parts and Vendors 15-16 3.3 Constructed Design 16 3.4 Device Calibration 16-17 4 Testing 17 4.1 Preliminary Testing 17-18 4.2 Testing in MR 18-20 5 Future Work 20 5.1 Design Modifications 20-21 5.2 Additional Testing 21 5.2.1 Phantom Test 21 5.2.2 Simulated Patient Protocol 21 5.3 Clinical Trials 21-22 6 References 22 Appendix A: Circuit Diagram 23 Appendix B: Product Design Specification 24-25 2Abstract An airway pressure device was designed for use in an MR imager. This device will assist our client in studying CSF flow during Valsalva maneuvers performed by children with Chiari I malformation. Current research suggests that CSF flow decreases during Valsalva maneuvers in these patients. The final product consists of a rigid mouthpiece, pressure transducer, and compressed air operated valve system. 1 Introduction Our client, Dr. Haughton, is a Radiologist at the UW Hospital interested in monitoring the airway pressure of patients during MR imaging. 1.1 Problem Statement Dr. Haughton is currently studying cerebrospinal fluid (CSF) flow during Valsalva maneuvers performed by children with Chiari I malformations. Current research suggests that CSF flow decreases during Valsalva maneuvers in these patients. The airway pressure device would help monitor the exhalation force exerted by each child during a Valsalva maneuver in the MR suite. Knowing the pressure exerted by each patient in the study would be extremely beneficial for data analysis and accuracy. 1.2 Medical Background To provide a solid understanding of our client’s research and design requirements, background information was obtained on headache syndromes, Chiari I malformations, Valsalva maneuvers, airway monitors, ventilation systems, and MR imaging systems. 1.2.1 Headache Syndromes Cough or Valsalva-induced headaches are a type of Indomethacin-responsive headache syndromes [1]. A Valsalva-induced headache is specifically defined as, “transient severe head pain that occurs when coughing, sneezing, weight-lifting, bending, straining at stool, or stooping [1].” The etiology of most indomethacin-responsive headaches is unknown, and patients with Valsalva-induced headaches often have abnormal neurological signs. For this reason, MR imaging is often used to look for abnormalities in the patient’s cervical-medullary junction. A variety of abnormalities have been found in these patients, but Chiari I malformation is the most common. Researchers hypothesize that transient increases in intracranial pressure (ICP) cause these headaches, and indomethacin is effective in treating these headaches because it decreases ICP. Patients with Chiari I have elevated ICP. In addition, performing a Valsalva maneuver increases ICP. The result of combining these two circumstances is severe headaches. Additional studies will help better understand the pathology of these headaches and may lead to improved treatments. 1.2.2 Chiari I Malformation The congenital cerebellar malformation known as Chiari I was discovered in 1890 by Dr. Hans Chiari, a German pathologist. In a normal person, the brainstem sits in a funnel-like cavity just above the spinal cord. However, in a person with Chiari I malformation the posterior fossa is not formed properly. This causes the downward displacement of the brainstem into the funnel-like cavity which causes pressure on this part of the brain and spinal cord. Obstruction of the cerebral spinal fluid through this area is common in Chiari patients, as the tonsils of the 3cerebellum are often stuffed down into the funnel-like cavity. The Figures 1 and 2 demonstrate the differences between the location of the cerebellum in a normal person and in a person with the Chiari I malformation. Figures 1 and 2: Diagrams of a Normal Cerebellum and a Cerebellum of a patient with Chiari I Malformation respectively [2] Although the exact cause of this type of cerebellar malformation is unknown, it is suggested that it occurs during early embryonic development of the brainstem and spinal cord. It is estimated that 1 child out of every 1000 births has this type of congenital anomaly although most people do not develop symptoms until adolescence or adulthood [3]. Symptoms of Chiari I malformation include headache, dysphasia, pain, hoarseness in voice, numbness, visual disturbance, ataxia, and syncope in extreme cases [2]. Patients are most commonly diagnosed with Chiari I malformations through the use of MR imaging. Current research suggests that the pain experienced by Chiari I patients is often accentuated by physical exertion, Valsalva maneuvers (sneezing, coughing or straining), head dependency, and sudden changes in posture [4]. In particular, Valsalva maneuvers seem to produce sudden changes in spinal venous volume and pressure [5]. 1.2.3 Valsalva Maneuvers A Valsalva maneuver is an expiratory effort against a closed glottis. The purpose of a Valsalva maneuver is to increase air pressure in the lungs, in order to help a person exert physical effort or force things out of the body. During this maneuver, the abdominal muscles tighten up and press upward against the diaphragm causing it to bulge upward which compresses the chest cavity. Certain chest muscles also tighten to bring the rib cage down, which compresses the chest cavity even
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