Positioning a pressure sensor of this type in the vascular system has been disclosed in connection with the control of heart pacemakers such as in U.S. Pat. No. 5,320,643 to Roline et al. or U.S. Pat. No. 5,271,395 issued to Whalstrand et al. for measurement of such parameters as respiration rate, minute ventilation, and changes in ventricular blood pressure.