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W C Chiu

Publications and source records attributed to W C Chiu.

21 records · Page 2Linked to original sources

[Validity of estimating left ventricular relaxation and filling dynamics by Doppler trans-mitral flow].

To evaluate the validity of estimating left ventricular (LV) diastolic function using the Doppler transmitral flow profile, the relationship of transmitral flow to LV relaxation and LV filling dynamics was observed. A total of 54 subjects, including patients with ischemic heart disease, idiopathic cardiomyopathy, and normal persons were examined. LV filling dynamics were assessed in 20 of them who had no regional wall motion abnormality or irregular LV geometry. Peak velocity of rapid filling (R) and acceleration of rapid filling (AR) at the mitral annular level were measured as indices of transmitral flow during the rapid filling period. LV relaxation was evaluated according to the time constant of LV isovolumic pressure decline (T) using the method of Weiss et al. The correlation coefficient between R and T was -0.27 and that between AR and T was -0.16, indicating lack of correlations. The v-wave of pulmonary wedge pressure (PWPv) was measured as an index for left atrial driving pressure during the rapid LV filling period. Multiple regression analyses of R or AR as dependent variables and T and PWPv as independent variables revealed significant correlations (r = 0.66 and r = 0.59). The peak transit rate (PTR = R/TVI) and atrial transit fraction (ATF = TVIa/TVI) were determined from the time integral of the transmitral flow velocity (TVI = time velocity integral during diastole, TVIa = time velocity integral during the atrial contraction phase). Also, the peak filling rate (PFR) during the rapid filling and atrial filling fraction (AFF) were determined by left ventriculography.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

Regional asynchrony of segmental contraction may explain the "oxygen consumption paradox" in stunned myocardium.

Despite apparently depressed function, stunned myocardium maintains oxygen consumption and has the capacity to increase contractility with inotropic stimulation. We hypothesized that during stunning, O2 demand is maintained because regional segment work is performed, but is asynchronous with global left ventricular contraction, and that inotropic stimulation would restore regional work and synchrony. Thirteen open-chest anesthetized dogs were subjected to three left anterior descending (LAD) coronary artery occlusions (10 min) and reperfusions (15 min) to produce regional myocardial stunning. Segment shortening and force development were measured independently and simultaneously in the LAD (experimental) region and circumflex (control) regions. Regional myocardial work was calculated as the integrated product of instantaneous force and shortening, during two periods: 1) over the entire cardiac cycle (Positive Work), and 2) limited to the systolic portion of the cardiac cycle (Systolic Work). Regional myocardial O2 consumption (MVO2) was calculated from regional blood flow (radiolabeled microspheres) and O2 saturation data (microspectrophotometry). Occlusion of the LAD produced a delay in onset of segment shortening in the ischemic region, but not in regional force development. A time delay of 67-81 ms persisted through the three stages of occlusions and reperfusions. Systolic regional work was depressed to a greater extent (924 +/- 182 to 149 +/- 118 g*mm*min-1) than total positive regional work (1437 +/- 337 to 857 +/- 174 g*mm*min-1). Regional subepicardial MVO2 in the stunned region was not different than in the control region (7.3 +/- 1.5 vs. 6.9 +/- 1.4 ml O2*min-1*100 g-1). Local infusion of isoproterenol reversed the delay in regional shortening from 73 +/- 7 to 21 +/- 8 ms, thereby augmenting systolic work (298%) more than positive work (60%), without a significant increase in MVO2 (7.3 +/- 1.5 to 10.5 +/- 3.2 ml O2*min-1*100 g-1). It is concluded that myocardial stunning decreases regional systolic work due to regional mechanical asynchrony, while MVO2 is used supported total positive work which was not significantly reduced. Isoproterenol restores regional work by restoring synchrony, without greatly affecting regional MVO2.

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