L’associazione fra dilatazione arteriosa e incremento dello spessore medio-intimale in una

5. Conclusioni

I principali risultati ottenuti in questo studio utilizzando metodiche ultrasonore innovative confermano l’importante ruolo dei fattori emodinamici nel determinismo del rimodellamento arterioso associato all’età. In una popolazione di soggetti normali senza fattori di rischio cardiovascolare, predittore indipendente del rimodellamento arterioso, oltre all’età, sono risultati la pressione arteriosa diastolica e la taglia corporea. I parametri metabolici (LDL colesterolo, HDL colesterolo, trigliceridi) seppur abbiano dimostrato correlazioni significative in analisi di regressione lineare non si sono confermati, nel modello di analisi multivariata comprendente i fattori emodinamici, determinanti indipendenti dell’ aumento dello spessore medio-intimale.

Inoltre, età e pressione arteriosa sembrano essere responsabili di un incremento del diametro arterioso che a sua volta si associa ad una riduzione della velocità di flusso e di conseguenza dello shear effettivo misurato (e non calcolato) in prossimità delle pareti del vaso. Parallelamente è stato confermato un aumento della rigidità arteriosa associata all’età.

Tutto questo è in accordo con l’ipotesi basata su studi sperimentali, che l’interazione fra forze emodinamiche e alterazioni strutturali di parete età-correlate, in primis la variazione qualitativa e quantitativa delle principali proteine costituenti la matrice extracellulare quali collagene ed elastina, comporti dapprima una dilatazione arteriosa cui si associa una riduzione del WSR ed un aumento dello spessore medio-intimale. Come si evince dalla letteratura sperimentale, la riduzione del WSR potrebbe essere uno dei meccanismi implicati nel determinismo dell’ispessimento medio-intimale, in quanto in grado di promuovere la proliferazione e la migrazione delle cellule muscolari lisce ed il fenotipo delle cellule endoteliali [45,24].

L’associazione fra dilatazione arteriosa e incremento dello spessore medio-intimale in una

popolazione di soggetti sani senza fattori di rischio cardiovascolare, potrebbe essere interpretata

alla luce della teoria della “mutual adaptation”, secondo cui variazioni emodinamiche sarebbero

in grado di modulare il diametro arterioso della carotide comune e di indurre, in una logica di

adattamento reciproco, cambiamenti dello spessore medio intimale allo scopo di mantenere o

ripristinare i livelli fisiologici di shear stress e di stress tensivo in prossimità della parete del

vaso. In quest’ottica l’ispessimento medio-intimale potrebbe essere considerato entro certi limiti

in soggetti senza fattori di rischio cardiovascolare, una risposta fisiologica della parete vasale

alle variazioni delle forze emodinamiche ed al processo di invecchiamento vascolare, e non un

marker precoce di aterosclerosi.

confrontare le correlazioni che le variabili emodinamiche hanno presentato nelle due popolazioni, nel gruppo di soggetti aterosclerotici lo studio è stato indirizzato essenzialmente alla misurazione del Wall Shear Rate e alla raccolta di dati. Peraltro, come atteso, i valori di WSR sono risultati significativamente ridotti rispetto ai soggetti normali.

In questa tesi è stata presentata l’esperienza preliminare ottenuta con nuova metodica Multigate

Doppler a doppio fascio ultrasonoro. Essa offre la possibilità di indagare diversi distretti arteriosi

studiando il profilo di velocità di flusso e la geometria vascolare e di ottenere misurazioni di

WSR in tempo reale. Inoltre, la migliore riproducibilità presentata dalla metodica e la maggiore

accuratezza nelle determinazione dell’angolo Doppler possono avere implicazioni cliniche

significative in vari ambiti quali la misura del flusso volumetrico e la stima dell’entità della

stenosi arteriosa.

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