Study On Orthostatic Tolerance Monitoring System And Its Application

Orthostatic tolerance test (OTT) is a practical technique. Its diagnostic value to syncope cases has already been widely accepted by scholars both at home and abroad. It is generally accepted that this technique can provide direct diagnostic reference for vasovagal syncope (VVS). It is well known that the diagnosis of VVS is a very difficult clinical problem. Despite thorough examination of cardiovascular and nervous system, including traumatic electrical physiologic inspection, the causes of over half of the cases are unable to identify. In the past, only speculated diagnoses of VVS can be obtained by excluding other causes through case history inquiry. However, the diagnosis has many disadvantages such as complicated steps, time consuming, not to mention that most of the examination method has no specificity value to the diagnosis of VVS.OTT is the reflexive regulation of autonomic nerve activity induced bythe sudden shift from supine position to head up tilt position. It has been reported by many studies that the hypotension-bradycardia symptom induced by the test is almost the identical reproduction of the natural seizure of VVS. 甌he syncopal signal symptom and physical sign of the induced and spontaneous VVS are similar in that both have the onset of nausea, cold sweat, pale complexion, the disappearance of posture tension, decrease of hearing acuity, lags in response, blurring in eyesight, sleepiness etc at the beginning. (2)The onset time and duration of blood pressure and heart rate changes are also similar for the induced syncope and spontaneous syncope. (3) Catecholamine concentrations in peripheral blood before and during the seizure of syncope are also the same for the induced and spontaneous VVS. Therefore, the American heart Association and the American Association for Heart Diseases established a special committee in 1996 to review the diagnosis of VVS with OTT in literature and concluded that OTT was a reliable diagnostic criterion for WS, it can be regarded as the " gold standard ". And is the only diagnostic technique so far.For many years, the process of OTT is as flows: the test subjects rest in supine position on the diagnostic bed for 10-20 minutes, change the subjects to active standing quickly, then measure the heart rate (HR) and blood pressure (BP) , observe their clinical manifestation, finally the autonomic nerve reaction of the VVS patient is evaluated. In recent years, the clinical people have changed OTT diagnostic bed to tilt table. The tilt angle and velocity can be controlled automatically to put the subject to the desired tilt angle (generally 60 degrees to 80 degrees), and at the same time observe the response of the subject dynamically with cardiogram and electricalsphygmomanometer. Thus the subjective impact of the inspector was decreased and the passive strain of the subject was reduced. This makes the OTT more objective and reliable. During the process of OTT inspection, however, the tilt velocity of the tilt table is not stable and the monitoring of physiological index is not synchronous with the motion of the electrical driven tilt table. Moreover, the tilt table with high rotation speed required in aerospace medicine has not been realized yet. Therefore, we have made useful attempts in our laboratory in recent years and have developed an orthostatic tolerance monitoring system. The purposes are: Stable the rotation speed of the tilt table and the tilt angle; Synchronize the physiological index monitoring and the tilt table operation by computerized control; Increase the rotation speed of the tilt table. The rotation speed of the present system is 45 degrees per second with the maximum rotation speed of 90 degrees per second. Then the normal reference of OTT and its diagnostic value to air syncope were established by using the orthostatic tolerance monitoring system. The autonomic nerve function of syncopal pilot under orthostatic stress was evaluated and the methodology to simulate the push pull maneuver (PPM) with tilt table was founded. The main conten...