Principle of a noninvasive method of measuring Max(dP/dt) of the left ventricle: theory and experiments

Aortic acceleration as a noninvasive index of left ventricular contractility in the mouse

The maximum value of the first derivative of the invasively measured left ventricular (LV) pressure (+ dP/dtmax or P') is often used to quantify LV contractility, which in mice is limited to a single terminal study. Thus, determination of P' in mouse longitudinal/serial studies requires a group of mice at each desired time point resulting in "pseudo" serial measurements. Alternatively, a noninvasive surrogate for P' will allow for repeated measurements on the same group of mice, thereby minimizing physiological variability and requiring fewer animals. In this study we evaluated aortic acceleration and other parameters of aortic flow velocity as noninvasive indices of LV contractility in mice. We simultaneously measured LV pressure invasively with an intravascular pressure catheter and aortic flow velocity noninvasively with a pulsed Doppler probe in mice, at baseline and after the administration of the positive inotrope, dobutamine. Regression analysis of P' versus peak aortic velocity (vp), peak velocity squared/rise time (vp2/T), peak (+ dvp/dt or v'p) and mean (+ dvm/dt or v'm) aortic acceleration showed a high degree of association (P' versus: vp, r2 = 0.77; vp2/T, r2 = 0.86; v'p, r2 = 0.80; and v'm, r2 = 0.89). The results suggest that mean or peak aortic acceleration or the other parameters may be used as a noninvasive index of LV contractility.

Non-invasive radial pulse wave assessment for the evaluation of left ventricular systolic performance in heart failure

INTRODUCTION

Left ventricular (LV) developed pressure (dP/dt) is a classical index of myocardial contractility related to prognosis during heart failure. We sought to assess the reproducibility and feasibility of use of the maximal first derivative of the radial pulse, Rad dP/dt, as a peripheral criterion of ventricular contractility in patients with heart failure.

METHODS

We assessed 50 consecutive, patients with heart failure using aplanation tonometry to record the radial pulse wave and calculate Rad dP/dt. Echocardiography, Doppler flow and tissue Doppler imaging were used to record classical parameters of LV function: LV ejection fraction (LVEF), Tei index, dP/dt on mitral regurgitation (MR dP/dt) and peak systolic velocity (S'). Total systemic vascular resistance (TSVR) was calculated by use of the Doppler calculated cardiac output. Preload was assessed by the E/Ea ratio. Feasibility was tested in an ongoing prospective mortality study (n=310).

RESULTS

The Bland and Altman representation of repeated measurements of the Rad dP/dt showed good agreement. Feasibility was greater than 99% for a successful assessment on the right arm during the first attempt. The Rad dP/dt correlated with the LVEF, S' or Tei index as usual parameters of impaired contractility but not preload (E/Ea) or afterload (TSVR) parameters. MR dP/dt and Rad dP/dt were closely related (r=0.75, p<0.001). The ability of the arterial dP/dt to characterize LVEF was not modified by adjustment for arterial viscoelastic properties.

CONCLUSION

The maximal dP/dt of the radial pulse appears to be a valuable and reproducible peripheral criterion of LV systolic performance.

A noninvasive method of measuring wave intensity, a new hemodynamic index: application to the carotid artery in patients with mitral regurgitation before and after surgery

Wave intensity (WI) is a new hemodynamic index, which is defined as (dP/dt)(dU/dt) at any site of the circulation, where dP/dt and dU/dt are the time derivatives of blood pressure and velocity, respectively. Arterial WI in normal subjects has two positive sharp peaks. The first peak occurs during early systole when a forward-traveling compression wave is generated by the left ventricle. The magnitude of this peak increases markedly with an increase in cardiac contractility. The second peak, which occurs towards the end of systole, is caused by generation of a forward-traveling expansion wave by the ability of the left ventricle to actively stop aortic blood flow. The interval between the R wave of the ECG and the first peak of WI (R-1st peak interval) and the interval between the first and second peaks (1st-2nd interval) are approximately equal to the preejection period and left ventricular ejection time, respectively. Using a combined Doppler and echo-tracking system, we obtained carotid arterial WI noninvasively. We examined the characteristics of WI in 11 patients with mitral regurgitation (MR) before and after surgery, and 24 normal volunteers. In the MR group before surgery, the second peak was decreased and the (1st-2nd interval)/(R-R interval) ratio was reduced, compared with the normal group (140 +/- 130 vs 750 +/- 290mmHg m/s3. P < 0.0083; 20.7% +/- 3.4% vs 26.7% +/- 2.8%, P < 0.083). There were no significant differences in the first peak between the normal group and the MR group before and after surgery. The second peak in the MR group was increased significantly (P < 0.016 vs before surgery) to 1,150 +/- 830mmHg m/s3 in the early period after surgery (stage I), and to 1,090 +/- 580mmHgm/s3 in the late period after surgery (stage II). These values did not differ significantly from that of the normal group. At stage I, the (R-1st peak interval)/ (R-R interval) ratio was increased from 13.4% +/- 2.7% to 20.6% +/- 5.6% (P < 0.016 vs before surgery). At stage II, this ratio decreased to 16.2% +/- 2.8% (P < 0.016 vs stage I). but was still significantly higher than that before surgery. The (1st-2nd interval)/(R-R interval) ratio increased significantly after surgery (P < 0.016 vs before surgery) to values (27.0% +/- 4.5% at stage I and 28.9% +/- 2.6% at stage II) which did not differ significantly from that of the normal group. The recovery of the second peak after surgery suggests that the left ventricle had recovered the ability to actively stop aortic blood flow. Wave intensity is useful for analyzing changes in the working condition of the heart.

Noninvasive estimation of left ventricular Max(dP/dt) from aortic flow acceleration and pulse wave velocity

The Doppler method of obtaining left ventricular Max(dP/dt) proposed recently was based on the measurement of mitral regurgitation velocity. Since Max(dP/dt) is an isovolumic phase index, its use in cases of mitral regurgitation may be open to argument. However, we had proposed a noninvasive method of estimating left ventricular Max(dP/dt) based on different principles. In our method, Max(dP/dt) had been given by Max(dP/dt) = (rho)cMax (du/dt), where rho is the blood density, c is the pulse wave velocity, and u is the flow velocity in the aorta. We had derived the above equation theoretically, and confirmed its validity by animal experiments. In our previous study, we also applied our method in the clinical setting. The aortic flow velocity was measured by Doppler echocardiography, and the pulse wave velocity by mechanocardiography or Doppler echocardiography. (Rho)cMax(du/dt) obtained noninvasively was compared with Max(dP/dt) measured with a catheter-tip micromanometer. We found an excellent correlation between (rho)cMax(du/dt) and Max(dp/dt), and concluded that (rho)Max(du/dt) is useful in assessing noninvasively the contractile state of the left ventricle. Here, we summarize our method, review previous results, and report new results of the clinical application of our method.

Measurement of left ventricular dp/dt by simultaneous Doppler echocardiography and cardiac catheterization

Left ventricular dp/dt is a useful isovolumic index for evaluating acute directional changes in myocardial contractility. To test the hypothesis that Doppler echocardiography can measure left ventricular dp/dt by using the mitral regurgitation velocity curve, 14 patients with at least a mild degree of mitral regurgitation (four with coronary artery disease, four with valvular heart disease, four with dilated cardiomyopathy, one with carcinoid, and one with mitral valve prosthesis) were studied by continuous-wave Doppler echocardiography. Simultaneously, left ventricular pressure was measured with a manometer-tipped catheter to generate actual dp/dt. Curves of left ventricular pressure and mitral regurgitant Doppler-derived velocities of three cardiac cycles were digitized at 1-msec intervals. The rate of Doppler-derived velocity increase was converted to a rate of pressure increase by using the modified Bernoulli equation. Mean dp/dt during various time intervals of the mitral regurgitation velocity envelope (1 to 2 m/sec, 2 to 3 m/sec, and 1 to 3 m/sec) corresponding to left ventricular-left atrial pressure differences of 12, 20, and 32 mm Hg, respectively, were calculated. Doppler-derived left ventricular dp/dt (y) correlated with catheter-derived left ventricular dp/dt (x) as follows: at the 1 to 2 m/sec interval, y (mm Hg/sec) = 0.84x + 137, r = 0.91, SEE = 90; at the 2 to 3 m/sec interval, y = 1.1x - 89, r = 0.96, SEE = 80; and at the 1 to 3 m/sec interval, y = 1.1x + 23, r = 0.98, SEE = 50.(ABSTRACT TRUNCATED AT 250 WORDS)

What stops the flow of blood from the heart?

The determinants of aortic pressure and flow are generally studied using impedance methods, the results of which indicate that reflected waves are important, particularly during aortic flow deceleration. An alternative analysis of measured aortic pressure and velocity, using the method of characteristics to calculate the energy flux per unit area of the waves, suggests a different conclusion. We suggest that aortic deceleration is caused by a discrete expansion wave propagating from the left ventricle, and that energy thus recovered by the ventricle may be coupled to early filling of the ventricle.