Why take detours when you can  walk the direct path?

How a model from the 1960s hel­ped us revo­lu­tio­ni­ze con­ven­tio­nal car­dio­vas­cu­lar diagnostics. 

Mea­su­ring arte­ries directly

The Mis­si­on

The dia­gno­stic short­co­ming of tra­di­tio­nal and inac­cu­ra­te arte­ri­al dia­gno­stics  inspi­red and ulti­m­ate­ly dro­ve us to invent some­thing bet­ter. We left well-trod­den paths and deve­lo­ped a com­ple­te­ly new and ground­brea­kin­gly dif­fe­rent mea­su­re­ment method — with the poten­ti­al to revo­lu­tio­ni­ze con­ven­tio­nal car­dio­vas­cu­lar diagnostics.

Pre­sent “old school” car­dio­vas­cu­lar dia­gno­stics looks like that: Lack­ing pre­cis­i­on in the mea­su­red values, thus also lack­ing relia­bi­li­ty. Logi­cal­ly, the data obtai­ned are then of very limi­t­ed use for the ear­ly detec­tion and pre­ven­ti­on of car­dio­vas­cu­lar diseases.

This serious defi­ci­en­cy of tra­di­tio­nal car­dio­vas­cu­lar dia­gno­stics based on makes­hift para­me­ters pro­vi­ded the impe­tus for our mis­si­on — the deve­lo­p­ment of a com­ple­te­ly novel mea­su­re­ment method with pre­vious­ly unknown depth of precision.

The revo­lu­tio­na­ry idea behind it: An indi­vi­dua­li­zed simu­la­ti­on model pro­vi­ding insight into the actu­al arte­ri­al tree pro­per­ties of any human being — wit­hout any inter­ven­ti­on in the body, but nevert­hel­ess ‘direct­ly’.

The ori­gi­nal model by Abra­ham Noor­der­graaf and Nico­laas Westerhof


The start­ing point of all the fol­lo­wing steps towards the deve­lo­p­ment of a new mea­su­re­ment method within vas­cu­lar dia­gno­stics was working with a model. More pre­cis­e­ly, we had to deci­de on a spe­ci­fic and alre­a­dy exis­ting simu­la­ti­on model. The most important cri­ter­ion: It had to be sui­ta­ble as the basis for a modi­fied arte­ri­al tree model that could be appli­ed to any human. Amidst the ple­tho­ra of models based on an ana­lo­gy bet­ween the elec­tri­cal cir­cuit and the blood cir­cuit, our choice fell on the model by Abra­ham Noor­der­graaf and Nico­laas Wes­ter­hof, published as ear­ly as 1969 at the Uni­ver­si­ty of Penn­syl­va­nia. The strength of this par­ti­cu­lar model lies, among other things, in the fact that it is well docu­men­ted and quite relata­ble — thus, it for­med the ide­al basis for fur­ther developments.

Cru­cial corrections

The ori­gi­nal model had been labo­rious­ly wired by hand and had seve­ral sim­pli­fi­ca­ti­ons in terms of repro­du­cing the human arte­ri­al tree. In par­ti­cu­lar, indi­vi­du­al arte­ri­al seg­ments (wind­kes­sel ele­ments) had been lum­ped tog­e­ther into lar­ger units. In our simu­la­ti­ons, we dis­co­ver­ed that this led to a dis­tor­ted repro­duc­tion of the actu­al flow pro­per­ties in the arte­ries. We, the­r­e­fo­re, resol­ved the­se sim­pli­fi­ca­ti­ons in the vir­tu­al model repli­ca with the aid of spe­cial soft­ware and thus achie­ved a signi­fi­cant­ly more refi­ned, com­plex, and thus rea­li­stic repre­sen­ta­ti­on of the arte­ri­al system.

The ori­gin of the arte­ri­al avatar


For illus­tra­ti­ve pur­po­ses, we were able to repro­du­ce typi­cal pul­se cur­ve shapes in the vir­tu­al artery model, for exam­p­le by simu­la­ting ves­sels set to ’nar­row’ or ‘wide’. Next, we defi­ned a total of eight sys­tem para­me­ters. They are used to repro­du­ce almost all pul­se wave­forms occur­ring in real people’s lives. The­se para­me­ters are both based on a reasonable simu­la­ti­on time and a high simu­la­ti­on qua­li­ty. Moreo­ver, the­se para­me­ters ulti­m­ate­ly descri­be the actu­al arte­ri­al cir­cu­la­ti­on pro­per­ties, making them indis­pensable. Hence, they are also of high inte­rest for cli­ni­cal application.

The final step was to deve­lop a com­pu­ta­tio­nal rule that adjus­ted our eight model para­me­ters so that we ended up with the image of the arte­ri­al cir­cu­la­to­ry sys­tem of a real per­son. As a result, the data ‘out­put’ looks like this: The opti­mi­zed model para­me­ter set as well as the achie­ved simu­la­ti­on qua­li­ty can be unmist­aka­b­ly read off in per­cen­ta­ges via the soft­ware. In ‘bad­ly’ simu­la­ted cases the qua­li­ty rea­ches an accu­ra­cy of 97%, often 99.5%, but also 99.9%. At 100%, the­re would be a per­fect match bet­ween simu­la­ti­on and reality.

From hand-wired model to soft­ware simu­la­ted ver­si­on: model refi­ne­ment leads to rea­li­stic pul­se wave­forms.

The trans­for­ma­ti­on of the ori­gi­nal Wes­ter­hof model to the refi­ned arte­ri­al avatar

The Model in operation

When the mea­su­re­ment of a pati­ent with VASCASSIST is com­ple­ted after ten to fif­teen minu­tes, the ‘moment of truth has come after the fina­liza­ti­on of three cal­cu­la­ti­on stages of the under­ly­ing algorithm:

The patient’s vas­cu­lar data, inclu­ding the spe­ci­fic phy­si­cal wall pro­per­ties, can now be read at a glan­ce based on the arte­ri­al tree model crea­ted during cal­cu­la­ti­on: With such depth of detail and the­r­e­fo­re at the same dia­gno­stic level as if loo­king direct­ly into the arte­ries. Using con­nec­ted soft­ware, the recor­ded pul­se waves can then be trans­fer­red to a desk­top or note­book and visua­li­zed, rea­dy to be ana­ly­zed in detail. Even the ear­liest vas­cu­lar chan­ges are detec­ta­ble — in many cases, serious com­pli­ca­ti­ons can thus be avo­ided through ide­al­ly rapid inter­ven­ti­ons. Many car­dio­vas­cu­lar dise­a­ses are reve­a­led during the soft­ware-sup­port­ed visua­liza­ti­on by striking devia­ti­ons from the ’nor­mal’, i.e. healt­hy, pul­se cur­ve shape.

From model indi­vi­dua­liza­ti­on to dif­fe­rent pul­se waveforms

Sam­ple cal­cu­la­ti­on of a 65 year old’s arte­ri­al model