To test the validity of a relation between the pressure half time and the diastolic time interval, previously shown in a pulse duplication system, eight patients with prosthetic mitral valves and permanent pacemaker systems were studied. Recordings were made from the apex by continuous wave or pulsed Doppler echocardiography at heart rates between 75 and 150 beats/min. The pressure half time was found to be closely correlated with the diastolic time interval although there was individual variation and in three prostheses the pressure half time attained a plateau when the diastolic time interval was more than 300 ms. It is likely that the orifice area is the main controller of pressure half time where there is stenosis of the prosthesis, but that other factors such as ventricular or atrial compliance and the diastolic time interval may modify or obscure the effect of orifice area in normally functioning prosthetic valves.
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