Blood pressure tracking systems and their application to biofeedback

Two automatic electronic systems for tracking diastolic or systolic blood pressure (BP) and their use in biofeedback experiments are described. Both systems are based on the use of an arm cuff and the recording of Korotkoff sounds with a microphone. An electronic control system receives input from the microphone and provides output to several solenoid valves that control compressed airflow to the cuff. For one of the tracking systems we devised, the cuff is alternately inflated for 45 sec and deflated for 45 sec. During inflation, small increments and decrements in cuff pressure, based on the occurrence of Korotkoff sounds, are used to track BP. The other tracking system is slower but provides more continuous measurements: The cuff is alternately inflated to approximately the BP level for 5 sec and then deflated for 5 sec. During each inflation, the number of Korotkoff sounds is recorded by the system and according to this number, the amount of inflation on the next trial is automatically adjusted so that the cuff pressure follows BP. Both systems have been used successfully in biofeedback applications.