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      New Insight into Abnormal Muscle Vasodilatory Responses in Aged Hypertensive Rats by in vivo Nuclear Magnetic Resonance Imaging of Perfusion

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          Objective: Increased peripheral arterial resistances and decreased maximum vasodilation are characteristic features of chronic hypertension. However, little data are available in the literature regarding the possible alterations in the temporal patterns of vasodilatory responses elicited by various stimuli. Design: This question was addressed by measuring skeletal muscle perfusion using nuclear magnetic resonance imaging combined with arterial spin labeling. Methods: Ninety-week-old male spontaneously hypertensive (SHR; n = 7) and normotensive Wistar Kyoto (WKY; n = 8) rats were studied, and calf muscle perfusion was measured at rest and during reactive hyperemia following total ischemia of 5 and 30 min duration. Results: Reactive hyperemia profiles differed according to duration of ischemia. In WKY rats, 5 min of ischemia induced a short peak of hyperemia lasting no more than 63 s, while 30 min of ischemia were followed by a prolonged hyperemic response of 261 s. In SHRs, after 5 min of ischemia, peak muscle arterial conductance was decreased to 0.5 ± 0.3 versus 0.9 ± 0.3 ml·min<sup>–1</sup>·100 g<sup>–1</sup>·mm Hg<sup>–1</sup> in the WKY rats (p < 0.05), as expected. After 30 min of ischemia, there was, in addition, a shortening of the hyperemic response duration. Time to post-ischemic half normalization of arterial conductance was 38 ± 24 s in the SHRs versus 149 ± 58 s in the WKY rats (p < 0.001). Conclusion: In vivo perfusion measurement not only confirmed the existence of a reduced maximum peripheral vasodilation in chronically hypertensive rats, it revealed a blunted hyperemic response after prolonged ischemia in the SHRs, which might be an important contributing factor to the increased sensitivity to ischemia in hypertension.

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          Most cited references 14

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          Perfusion imaging

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            Adaptive structural changes of the vascular walls in hypertension and their relation to the control of the peripheral resistance.

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              Determination of skeletal muscle perfusion using arterial spin labeling NMRI: validation by comparison with venous occlusion plethysmography.

               S Duteil,  C Wary,  P Carlier (2001)
              T(1)-based determination of perfusion was performed with the high temporal and spatial resolution that monitoring of exercise physiology requires. As no data were available on the validation of this approach in human muscles, T(1)-based NMRI of perfusion was compared to standard strain-gauge venous occlusion plethysmography performed simultaneously within a 4 T magnet. Two different situations were investigated in 21 healthy young volunteers: 1) a 5-min ischemia of the leg, or 2) a 2-3 min ischemic exercise consisting of a plantar flexion on an amagnetic ergometer. Leg perfusion was monitored over 5-15 min of the recovery phase, after the air-cuff arterial occlusion had been released. The interesting features of the sequence were the use of a saturation-recovery module for the introduction of a T(1) modulation and of single-shot spin echo for imaging. Spatial resolution was 1.7 x 2.0 mm and temporal resolution was 2 s. For data analysis, ROIs were traced on different muscles and perfusion was calculated from the differences in muscle signal intensity in successive images. To allow comparison with the global measurement of perfusion by plethysmography, the T(1)-based NMR measurements in exercising muscles were rescaled to the leg cross-section. The perfusion measurements obtained by plethysmography and NMRI were in close agreement with a correlation coefficient between 0.87 and 0.92. This indicates that pulsed arterial techniques provide determination of muscle perfusion not only with superior spatial and temporal resolution but also with exactitude.

                Author and article information

                J Vasc Res
                Journal of Vascular Research
                S. Karger AG
                February 2006
                16 February 2006
                : 43
                : 2
                : 149-156
                a NMR Laboratory, AFM-CEA, and bINSERM U582, Institute of Myology, IFR 14, Pitié-Salpêtrière University Hospital, Paris, France
                90944 J Vasc Res 2006;43:149–156
                © 2006 S. Karger AG, Basel

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                Page count
                Figures: 5, References: 35, Pages: 8
                Research Paper


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