Pressure-flow relations across the normal mitral valve.

The stenotic mitral valve area is a major determinant of the atrioventricular pressure-flow relation, and mean atrioventricular pressure gradient is proportionate to the square of mean flow rate. In the absence of obstruction, this relation is linear. The effect of the normal mitral valve area on this pressure-flow relation has not been previously examined. Pulsed Doppler studies of transmitral flow were performed simultaneously with thermodilution cardiac outputs in 25 patients in sinus rhythm and with no valvular disease. Mean flow rate was determined as thermodilution stroke volume/diastolic filling period measured by Doppler. Several instantaneous pressure gradients were estimated from multiple velocity measurements using the modified Bernoulli equation and were plotted against time. Mean pressure gradient was estimated by dividing the area under the pressure-time curve by the diastolic filling period. Average and standard deviation of mean flow rate and pressure gradient was 223 +/- 70 ml/s and 1.4 +/- 0.8 mm Hg, respectively. There was an excellent linear correlation between these 2 parameters (r = 0.91, SEE = 30 ml/s). This confirms the linear relation of mean pressure gradient to mean flow rate in the absence of obstruction. The excellent correlation, obtained without considerations of individual variations of valve area, suggests that this relation is independent of valve area, under normal physiologic conditions.

Range ambiguity in pulsed Doppler ultrasound: the ambiguity clarified?

Pulsed Doppler ultrasound (PW) can be used to determine the location of frequency shifts within the cardiac chambers or great vessels. However, it is possible to record similar frequency shifts at sample volume locations distal to their original site; this is referred to as range ambiguity (RA). Eleven patients were studied with combined Doppler and two-dimensional echocardiography (2-D) to determine the circumstances in which RA occurs. Mapping of various flow patterns with PW was performed in each of four 2-D views beginning at 2 cm distances from the transducer and at subsequent 1-cm intervals until the maximal range of the PW was achieved. Range ambiguity was demonstrated only in the four-chamber view in patients with enlarged cardiac chambers or if an abnormal flow pattern was present. The site of origin of the ambiguous signals was dependent on the pulse repetition frequency (PRF) employed. Range ambiguity occurs more often when a relatively high PRF is used. Range ambiguity may be used for mapping of abnormal flow beyond the range of PW or for recording of high velocities at sample volumes far from the transducer without frequency aliasing.

The therapeutic implications of diastolic time changes in systemic hypertension.

Twenty-five patients with chronic systemic hypertension were studied. Systolic time intervals and diastolic time were determined at baseline and after 12 weeks of therapy with nadolol, with or without bendroflumethiazide (treatment phase I), then after 12 weeks of therapy with hydralazine, bendroflumethiazide, or both (treatment phase II). Systolic, diastolic, and mean blood pressures were equally controlled after either treatment regimen. Heart rate was significantly slower after treatment phase I compared to baseline or after treatment phase II (p less than 0.001). Systolic time per minute was significantly shorter and diastolic time per beat and per minute were significantly longer after treatment phase I compared to baseline or after treatment phase II (p less than 0.001). Double and triple products decreased after either mode of therapy; however, these parameters were significantly lower after treatment phase I compared to treatment phase II (p less than 0.01). These changes in systolic and diastolic time and double and triple products may be of clinical significance during therapy of chronic systemic hypertension and may help explain the regression of left ventricular hypertrophy in patients with hypertension treated with sympathetic blocking agents.