M. Kozàkovà

Early impairment of coronary flow reserve and increase in minimum coronary resistance in borderline hypertensive patients.

Objective To evaluate relations between coronary flow velocity and myocardial oxygen demand at rest, as well as coronary vasodilator capacity and flow reserve, in asymptomatic subjects with borderline hypertension as compared to normotensive controls and patients with sustained high blood pressure (HBP) and without left ventricular hypertrophy (LVH). Subjects and methods Forty-two asymptomatic males were studied: 13 healthy normotensive volunteers; 12 subjects with borderline HBP and 17 asymptomatic subjects with sustained systemic hypertension. Coronary flow velocity in left anterior descending artery and coronary flow reserve were assessed by transesophageal echodoppler at baseline and during intravenous adenosine infusion. Left ventricular mass, peak systolic wall stress (PSWS; Pa), and midwall fractional shortening (MFS; %) were obtained from M-mode images of the left ventricle in transthoracic long-axis view and in transesophageal transgastric view. Results Coronary flow velocity at baseline was not significantly different in the three groups, despite significantly higher rate-pressure product (RPP) in the hypertensive groups as compared with controls. Only in control subjects, was resting coronary flow velocity significantly correlated with RPP (y = 4279 + 200x, r = + 0.58, P < 0.05) and PSWS (y = 17.2 + 5.1x, r = + 0.62, P < 0.05). Coronary reserve was 3.5 ± 0.65 in controls and significantly lower (P < 0.05) in borderline hypertensive (2.87 ± 0.46) and in sustained hypertensive subjects (2.66 ± 0.56). Minimum coronary resistance was significantly increased in both hypertensive groups (1.30 ± 0.29 and 1.39 ± 0.48 mmHg/s per cm) as compared to normotensive controls (0.93 ± 0.20 mmHg/s per cm, P < 0.01). Conclusions In asymptomatic subjects with borderline hypertension and without LVH, a significant reduction in coronary flow reserve is already detectable and appears almost entirely related to an impaired coronary vasodilator capacity rather than to an increased myocardial oxygen demand.

The first order absolute moment in contour tracking

A procedure to outline contours automatically in temporal sequences of cardiovascular images is presented. The contour determined on the n/sup th/ frame of the sequence is used as the starting contour to determine the contour on the (n+1)/sup th/ frame. When given a starting contour standard edge detectors can efficiently locate only ideal discontinuities with step shape. First and second Gaussian derivatives, computed at points p/sub i/ of the starting contour, directly provide amplitude and direction of the vectors which join p/sub i/ to the respective points of the final contour. Conversely, if the discontinuity does not show an ideal profile with step shape, the computation of the Gaussian derivatives must be carried out at all points between the starting and the final contour. In the paper, a property of the first order absolute moment is exploited to develop a robust and efficient iterative procedure which can be used to locate discontinuities that do not show an ideal step profile.

LARGE ARTERY FUNCTION AND VENTRICULAR ARTERIAL COUPLING FOLLOWING CARDIOVASCULAR UNLOADING RELATED TO PROLONGED BED REST IN YOUNG HEALTHY SUBJECTS: PP.31.218

Background: prolonged head-down tilt bed rest (HDTBR) is followed by a decrease in circulating volume possibly affecting large artery structure and function. Aim of the study was to investigate common carotid artery (CCA) remodelling and ventricular-arterial (VA) coupling after HDTBR. Methods: ten healthy male volunteers (age 23 ± 2) were studied before and after a 35-day HDTBR. Ultrasound (Esaote MyLab30) was used to estimate LV volumes, transmitral and aortic flow velocity (FV), CCA diameter and FV, high resolution IMT (Q-IMT). Applanation tonometry (PulsePen, DiaTecne), was used to explore large artery dynamics and wave reflection (WR). Carotid-femoral pulse wave velocity (PWV) was also estimated (Complior, Alam). Results: no changes were observed for central BP vs baseline, while LV volumes and stroke volume significantly decreased and HR increased (from 58 ± 2 to 73 ± 6, p < 0.05). Myocardial performance index (MPI), a Doppler derived index of global LV function [isovolumic contraction time+isovolumic relaxation time)/LV ejection time], increased after HDTBR (0.71 ± 0.12 vs 0.52 ± 0.06, p < 0.005), as well as arterial elastance (Ea = end systolic pressure/stroke volume) and LV elastance [Elv = end systolic pressure (ESP)/end systolic volume (ESV)] (for Ea: 1.08 ± 0.198 vs 1.31 ± 0.21, p = 0.01; for Elv 1.478 ± 0.32 vs 1.765 ± 0.42, p = 0.04), with unchanged Ea/Elv (0.74 ± 0.09 vs 0.76 ± 0.1). PWV, CCA diameter, systolic FV and QIMT did not change, while diastolic and mean FV significantly increased (p < 0.05: FVd from 25 ± 4 to 29 ± 4 cm/s, FVm from 42 ± 8 to 52 ± 11 cm/s). Pulsatility index [PI = (peak systolic velocity-diastolic velocity)/Mean velocity] decreased from 2.3 ± 0.3 to 1.9 ± 0.2, p < 0.02). Applanation tonometry showed no significant changes for Augmentation Index (AIx) and time to WR, while PPI (Pulse Pressure Index: PP/MBP) decreased from 0.55 ± 0.14 to 0.45 ± 0.09, p < 0.05). Conclusions: after prolonged HDTBR, a reduction in LV pump function is observed with unchanged VA coupling. No significant changes are found in intrinsic arterial stiffness, CCA remodelling and WR, while changes in arterial dynamics indicate a reduction in the pulsatile component and an increase in the steady component of BP, possibly associated with reduced circulating volume and increased peripheral vasodilation.