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

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.

Influence of changes in ventricular systolic function and loading conditions on pulse contour analysis-derived femoral dP/dtmax

BACKGROUND

Femoral dP/dt_max (maximum rate of the arterial pressure increase during systole) measured by pulse contour analysis has been proposed as a surrogate of left ventricular (LV) dP/dt_max and as an estimator of LV systolic function. However, femoral dP/dt_max may be influenced by LV loading conditions. In this study, we evaluated the impact of variations of LV systolic function, preload and afterload on femoral dP/dt_max in critically ill patients with cardiovascular failure to ascertain its reliability as a marker of LV systolic function.

RESULTS

We performed a prospective observational study to evaluate changes in femoral dP/dt_max, thermodilution-derived variables (PiCCO2-Pulsion Medical Systems, Feldkirchen, Germany) and LV ejection fraction (LVEF) measured by transthoracic echocardiography during variations in dobutamine and norepinephrine doses and during volume expansion (VE) and passive leg raising (PLR). Correlations with arterial pulse and systolic pressure, effective arterial elastance, total arterial compliance and LVEF were also evaluated. In absolute values, femoral dP/dt_max deviated from baseline by 21% (201 ± 297 mmHg/s; p = 0.013) following variations in dobutamine dose (n = 17) and by 15% (177 ± 135 mmHg/s; p < 0.001) following norepinephrine dose changes (n = 29). Femoral dP/dt_max remained unchanged after VE and PLR (n = 24). Changes in femoral dP/dt_max were strongly correlated with changes in pulse pressure and systolic arterial pressure during dobutamine dose changes (R = 0.942 and 0.897, respectively), norepinephrine changes (R = 0.977 and 0.941, respectively) and VE or PLR (R = 0.924 and 0.897, respectively) (p < 0.05 in all cases). Changes in femoral dP/dt_max were correlated with changes in LVEF (R = 0.527) during dobutamine dose variations but also with effective arterial elastance and total arterial compliance in the norepinephrine group (R = 0.638 and R = - 0.689) (p < 0.05 in all cases).

CONCLUSIONS

Pulse contour analysis-derived femoral dP/dt_max was not only influenced by LV systolic function but also and prominently by LV afterload and arterial waveform characteristics in patients with acute cardiovascular failure. These results suggest that femoral dP/dt_max calculated by pulse contour analysis is an unreliable estimate of LV systolic function during changes in LV afterload and arterial load by norepinephrine and directly linked to arterial waveform determinants.

Associations of increased arterial stiffness with left ventricular ejection performance and right ventricular systolic pressure in mitral regurgitation before and after surgery: Wave intensity analysis

Background

The effect of increased arterial stiffness on mitral regurgitation (MR) is not clear. Using wave intensity (WI) analysis, which is useful for analyzing ventriculo-arterial interaction, we aimed to elucidate associations of increased arterial stiffness with left ventricular (LV) ejection performance and right ventricular systolic pressure (RVSP) in MR.

Methods and Results

We noninvasively measured carotid arterial WI and stiffness parameter (β) in 98 patients with non-ischemic chronic MR before and after surgery, and 98 age-and-gender matched healthy subjects by ultrasonography. WI is defined as WI = (dP/dt)(dU/dt) [P: blood pressure, U: velocity, t: time]. The peak value of WI (W₁) increases with LV peak dP/dt. The temporal WI index (Q-W₁)st, which is the standardized interval between the Q wave of the ECG and W₁, is a surrogate for preejection period. Ejection fraction (EF), left atrial volume index (LAVI), effective regurgitant orifice area (ERO), RVSP, and other echocardiographic data were also obtained. W₁ was enhanced in the MR group before surgery compared with the normal group (10.7 ± 5.7 vs 8.5 ± 3.6 × 10³ mmHg m/s³, p < 0.05). However, the results of two-way ANOVA showed this enhancement of W₁ was observed only in the subgroup of MR before surgery with lower arterial stiffness (β < 13, p< 0.0001). ERO, β and LAVI were predictor variables before surgery to determine RVSP. EF and (Q-W₁)st before surgery were predictor variables for EF after surgery.

Conclusions

In the MR group before surgery, increased arterial stiffness suppresses compensatory enhancement of W₁, and increases RVSP. Prolonged (Q-W₁)st has the potential for predicting low EF after surgery.

Additional hemodynamic measurements with an esophageal Doppler monitor: a preliminary report of compliance, force, kinetic energy, and afterload in the clinical setting

The esophageal Doppler monitor (EDM) is a minimally-invasive hemodynamic device which evaluates both cardiac output (CO), and fluid status, by estimating stroke volume (SV) and calculating heart rate (HR). The measurement of these parameters is based upon a continuous and accurate approximation of distal thoracic aortic blood flow. Furthermore, the peak velocity (PV) and mean acceleration (MA), of aortic blood flow at this anatomic location, are also determined by the EDM. The purpose of this preliminary report is to examine additional clinical hemodynamic calculations of: compliance (C), kinetic energy (KE), force (F), and afterload (TSVR(i)). These data were derived using both velocity-based measurements, provided by the EDM, as well as other contemporaneous physiologic parameters. Data were obtained from anesthetized patients undergoing surgery or who were in a critical care unit. A graphical inspection of these measurements is presented and discussed with respect to each patient's clinical situation. When normalized to each of their initial values, F and KE both consistently demonstrated more discriminative power than either PV or MA. The EDM offers additional applications for hemodynamic monitoring. Further research regarding the accuracy, utility, and limitations of these parameters is therefore indicated.

Development and application of a logistic-based systolic model for hemodynamic measurements using the esophageal Doppler monitor

The esophageal Doppler monitor (EDM) is a clinically useful device for minimally invasive assessment of cardiac output, preload, afterload, and contractility. An empirical model, based upon the logistic function, has been developed. Use of this model illustrates how the EDM could estimate the net effect of aortic and non-aortic contributions to inertia, resistance, and elastance within real time. This is based on an assumed mechanical impedance conceptually resembling that of a series arrangement of a spring, mass, and dashpot. In addition, when used with an invasive radial arterial catheter, the EDM may also estimate aortic pulse wave velocity, as well as aortic characteristic impedance, and characteristic volume. Approximations of left ventricular stroke work and stroke power can also be made. Furthermore, the effects of inertia, resistance, and elastance, on mean blood pressure during systole, can be quantified. These additional parameters could offer insight for clinicians, as well as researchers, and may be beneficial in further examining and utilizing clinical hemodynamics with the EDM. These additional measurements also underscore the need to integrate the EDM with existing and future monitoring equipment.

Radial pressure waveform dP/dt max is a poor indicator of left ventricular systolic function

BACKGROUND

The first derivative of left ventricular (LV) pressure over time (dP/dt max) is a marker of LV systolic function that can be assessed during cardiac catheterization and echocardiography. Radial artery dP/dt max has been proposed as a possible marker of LV systolic function and we sought to test this hypothesis.

MATERIALS AND METHODS

We compared simultaneously recorded radial dP/dt max (by high-fidelity tonometry) with LV dP/dt max (by high-fidelity catheter and echocardiography parameters analogous to LV dP/dt max). In study 1, beat-to-beat radial dP/dt max and LV dP/dt max were recorded at rest and during supine exercise in 12 males (aged 61 +/- 12 years) undergoing cardiac catheterization. In study 2, 2D-echocardiography and radial dP/dt max were recorded in 54 patients (separate to study 1; 39 men; aged 64 +/- 10 years) at baseline and peak dobutamine-induced stress. Three basal septum measures were taken as being analogous to LV dP/dt max: 1. Peak systolic strain rate; 2. Strain rate (SR-dP/dt max) during isovolumic contraction (IVCT) and; 3. Tissue velocity during IVCT.

RESULTS

In study 1 there was a significant difference between resting LV dP/dt max (1461 +/- 383 mmHg s(-1)) and radial dP/dt max (1182 +/- 319 mmHg s(-1); P < 0.001), and a poor, but statistically significant, correlation between the variables (R(2) = 0.006; P < 0.05). Similar results were observed during exercise. In study 2 there were weak (R(2) = -0.12; P = 0.01) to non-significant associations between radial dP/dt max and all echocardiographic measures analogous to LV dP/dt max at rest or peak stress.

CONCLUSION

Radial pressure waveform dP/dt max is not a reliable marker of LV systolic function.