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Primerjava endotelijske funkcije in magnetno-resonancnih lastnosti žilne stene med bolniki s klasicno in dilatativno obliko ateroskleroze
Avtor: Jurij Štalc, Uroš Tominc
Mentor: doc. dr. Matije Kozak, doc. dr. Aleša Blinc
Izhodišce: Dilatativna ateroskleroza je redko obolenje arterij z anevrizmami. Patogeneza anevrizem ni popolnoma pojasnjena, vendar je znano, da gre za degenerativni ateroskleroticni proces, kateremu so verjetno pridruženi še drugi dejavniki (proteoliticni razkroj medcelicnine in odmiranje gladkih mišicnih celic žilne stene). Za nastanek te bolezni je verjetno pomembna okvara endotelija, kar je znano za klasicno obliko ateroskleroze. Sistemsko okvaro endotelija lahko ocenjujemo s standardiziranim testom žilne dilatacije. Spremembe v zgradbi anevrizmatsko spremenjene žilne stene lahko prikažemo z uporabo visoko locljivega magnetno-resonancnega slikanja (MRI). Namen: Z raziskavo smo želeli oceniti sistemsko funkcijo endotelija in s pomocjo MRI prikazati nekatere strukturne in morfološke znacilnosti žilne stene. Hipoteze: 1. Funkcija endotelija je pri preiskovancih s poplitealno anevrizmo drugacna kot pri preiskovancih s klasicno obliko ateroskleroze; 2. Magnetno-resonancni (MR) signal žilne stene je pri preiskovancu z anevrizmo v predelu anevrizme drugacen kot pri preiskovancu s klasicno obliko ateroskleroze v enakem žilnem segmentu; 3. MR signal žilne stene je pri preiskovancu z anevrizmo v predelu anevrizme drugacen kot v nerazširjenem delu žile v bližini razširitve; 4. Debelina žilne stene je pri preiskovancu z anevrizmo v razširjenem in nerazširjenem delu opazovanega žilnega segmenta enaka. Metode: V raziskavo smo vkljucili 12 moških z anevrizmo poplitealne arterije (starost 60,8 ± 12,4 let) (skupina A) in 9 moških (starosti 65,3 ± 9,8 let) s klasicno obliko ateroskleroze (skupina K). Sistemsko funkcijo endotelija smo ocenili s testom od endotelija odvisne in neodvisne vazodilatacije. Od endotelija odvisno in neodvisno vazodilatacijo smo izracunali iz premerov brahialne arterije, merjenih z ultrazvocnim aparatom. Meritve smo napravili v mirovanju, po aktivni hiperemiji in po odmerku gliceril trinitrata. Rezultate smo primerjali z uporabo Studentovega t-testa za neodvisne vzorce. Vsem preiskovancem smo napravili visoko locljive MRI slike precnega prereza noge na dveh standardnih mestih: na distalnem, ki je pri skupini K v višini špranje kolenskega sklepa, pri skupini A na najširšem delu anevrizme, ter na proksimalnem mestu, ki je bilo vsaj 6 cm proksimalneje od distalnega v skupini K oz. na nerazširjenem delu poplitealne arterije v skupini A. Podatke pridobljene iz slik (povprecna intenziteta signala in standardni odklon signala) smo med skupinama primerjali z Mann-Whitneyevim U-testom. Geometrijske lastnosti žilne stene smo primerjali s Studentovim t-testom. Podatke z obeh standardnih mest smo pri istem preiskovancu primerjali s parnim Wilcoxonovim testom. Rezultati: Primerjava od endotelija odvisne in neodvisne vazodilatacije med skupinama ni pokazala statisticno znacilnih razlik. Primerjava na mašcobo normirane povprecne intenzitete signala žilne stene (NIS) na obeh mestih ni pokazala statisticno znacilnih razlik niti znotraj skupine niti med skupinama. Našli pa smo razlike v normiranem standardnem odklonu intenzitete signala žilne stene (NSD), ki nam predstavlja merilo za homogenost signala žilne stene (proksimalno: skupina A mediana 0,081; skupina K mediana 0,132; p<0,05; distalno: skupina A mediana 0,085; skupina K mediana 0,111; p<0,05). Primerjava obeh mest žile pri istem preiskovancu ni znotraj obeh skupin pokazala statisticno znacilnih razlik niti za NIS niti za NSD. Na distalnem mestu smo v skupini A našli pomembno (p<0,05) zadebelitev (1,98 ± 0,82 mm) v primerjavi s proksimalnim mestom (1,35 ± 0,54 mm). Pri primerjavi debelin v skupini K nismo našli razlik. Zakljucek: Test od endotelija odvisne in neodvisne vazodilatacije je pokazal enako okvaro endotelija pri obeh skupinah. S tem testom nismo mogli ugotoviti za dilatativno aterosklerozo znacilnih sprememb v delovanju endotelija. Bolniku z anevrizmo se zaradi strukturnih sprememb v steni anevrizme MR signal žilne stene ne spremeni. NIS se med skupinama ni razlikoval, našli pa smo razlike v NSD, ki verjetno nastanejo zaradi drugacne porazdelitve struktur žilne stene. Na mestu anevrizme se žilna stena zadebeli, kar je verjetno posledica kompenzatornega odgovora na povecano tenzijo.
[Abstract / English version]
Primerjava endotelijske funkcije in magnetno-resonancnih lastnosti žilne stene med bolniki s klasicno in dilatativno obliko ateroskleroze
Author: Jurij Štalc, Uroš Tominc
Mentor: doc. dr. Matije Kozak, doc. dr. Aleša Blinc
Background: Dilatative atherosclerosis is a rare form of degenerative process manifested by arterial aneurysms. The pathogenesis of aneurysm formation is not completely understood, however, involvement of proteolytic degradation of intracellular matrix and smooth muscle cell necrosis are important. It is believed that endothelial dysfunction is involved in dilatative and occlusive atherosclerosis. As a surrogate for estimation of systemic endothelial dysfunction a standardized endothelium-dependent vasodilatation test can be used. Alteration of arterial wall in aneurysm due to smooth muscle cell necrosis and/or matrix degeneration/degradation can be visualized and estimated by high-resolution magnetic resonance imaging (MRI). Aim: The aim of our study was to measure endothelial dysfunction and to identify some structural and morphological characteristics of dilatative atherosclerosis by MRI. Hypotheses: 1. Endothelial function of patients with aneurysms assessed by endothelium-dependent vasodilatation test is more impaired than in patients with classic atherosclerosis. 2. MR signal from the vessel wall of popliteal aneurysm differs from that of atherosclerotic vessel wall; 3. MR signal from the vessel wall of popliteal aneurysm differs in comparison to the signal from nearby non-dilated site. 4. Thickness of the vessel wall at the dilated (aneurysmal) site equals to the thickness of non-dilated site of the same vessel. Methods: We included 12 male patients with popliteal artery aneurysm (age 60,8 ± 12,4 years) (group A) and 9 male patients (age 65,3 ± 9,8 years) with classic atherosclerosis (group K). Endothelial function was estimated by endothelium-dependent vasodilatation test. The endothelium-dependent and endothelium-independent dilatations were calculated using the diameters of the brachial artery measured by high-resolution ultrasound at rest, after reactive hyperemia and after sublingual glyceril trinitrat application. The results were compared using Students t-test. In all patients a high-resolution cross-section MRI through two standardized locations was made. The distal location was knee-joint fissure in group K or the widest section of the aneurysm in the group A. The proximal location was at least 6 cm proximally to the distal one in the group K or a non-dilated section of artery in the group A. The data taken from MR images (average intensity of the signal, standard deviation of the signal and geometrical characteristics of the vessel wall) was then statistically compared between the two groups using Mann-Whitney U test. We have also compared the data from both standardized locations of the same patient with Wilcoxon matched pairs test. Results: The comparisons of endothelium-dependent and endothelium-independent dilatation between groups showed no significant difference. The comparisons of normalized average vessel wall signal intensity (NIS) also showed no significant difference at both locations. However, we found that normalized standard deviation of the vessel wall MR signal (NSD) (a measure for homogeneity of the signal from vessel wall) was significantly different between groups in proximal (group A median 0,081; group K median 0,132; p<0,05) as it was at the distal location (group A median 0,085; group K median 0,111; p<0,05). Comparing NIS of proximal and distal location of the vessel for every patient showed no significant difference neither in group A nor in group K. Comparing NSD of proximal and distal location for every patient also showed no significant difference neither in group A nor in group K. Comparing the proximal and distal vessel wall thickness we found significant thickening of the vessel wall in group A (1,98 ± 0,82 mm at aneurysm site; 1,35 ± 0,54 mm at non-dilated site; p<0,05) and no thickening in group K. Conclusions: Endothelium-dependent vasodilatation test was impaired in both groups equally. By using this test, we could not detect aneurysm specific characteristics of endothelial dysfunction. Changes in vessel wall structure due to aneurysm in the same patient did not result in changes of its MR signal. NIS did not differ between both groups probably because the constituents of the vessel wall were the same; however the NSD was different probably due to different distribution of the vessel wall constituents. We found significant thickening of aneurysmal wall probably due to compensatory proliferation / hypertrophy.