Chapter-1 / Physiological Foundations - WHNLive Public Library

1. Physiological foundations. ~ la~), if the condition that d ~ A (d =P rtlcle dlam t r) i fulfilled. The Doppler frequencyhift Af of the wave scattered back bytho moved particle is proportional to the transmlt~erfrequency f o and the particle velocity v,proJ ted onto the transmission or receiverdire tion:2v .Af = fo • , With c = speed of soundc-vThe velocity range of the blood corpusclesrelevant for the microcirculation lies between5 and 0.5 mm/s. Using an ultrasound instrumentdesigned in our Institute for this task,anUS frequency of 7.5 mHz is applied. The valueof Af is therefore only a few Hz. (By comparison,with the laser Doppler flowmeter, workingwith light, the value of ~f is 1-2 kHz.)The speed orientation of the blood corpusclesin the area of small vessels is completely isotropic,so a "Doppler frequency spectrum of theblood velocities of < 5 mm/s occurs symmetricallywith the transmission frequency, by contrastto the asymmetric Doppler spectrum ofthe flowing blood in larger vessels.Our apparatus uses the impulse Doppler process.Firstly it enables a critical intensity notto be crossed despite high impulse energies and,secondly, a selection in depth is possible.The electronic processing of the back-scatteredsignal with subsequent Fourier analysis makespossible the assessment of a narrow range ofvelocity. With the developed multi-elementtransducer, analysable signals up to penetrationdepths of almost 2.5 cm can be gained.An exact interpretation of the results is difficultand requires great experience, as themeasured value, the amplitude of which isdetermin¢ by the amount of moving scatterersand the Doppler frequency by the velocity, doesnot allow us to distinguish between the disturbingblood corpuscles and other moving tissueparts. It is particularly necessary in this methodto distinguish the required measurement signalfrom those signals which occur due to tissuemovement in the pulse rhythm. It should bestated here, however, that even these tissuemovements represent an indirect measure oftissue circulation. This method will not be ableto claim to be a reliable, abSOlute measurementprocess. It should, however, be sufficient fora qualitative relative measurement. Thus itcould help in the recognition of the selectivevascular occlusion in the cancer tissue near theurface in cancer multi tep therapy, as well as inthe recognition of the elimination of peripheralcirculatory di orders by means of therapeuticA frequently used way to assess the bloodmicrocirculation in tissue which can be at anydepth beneath the body surface, is the 133Xeclearance method. The 133Xe isotope of theheavy inert rare gas is almost ideally suited foruse in humans due to its short half-life of 5.27days and its 'Y-radiation energy of 81 keY, aswell as its relative frequency of 27 % [70].Depending on the aim envisaged, the radioactiveisotope is added to the circulation, eitherin gas form via the lungs, or dissolved in physiologicalsodium chloride solution via the vascularsystem, usually on the arterial side. The clearance,normally measured with highly accurateand directionally sensitive 'Y-scintillation countersin the target area, correlates with the tissueblood flow, hence, with the microcirculation[72].In the view of Reference (70] and the fact thatthe author set up the laboratory for nuclearmedicine of the Medical Academy of Dresdenin 1964, and from the knowledge of the work(72] from the year 1967, it was obvious thatthe 133Xe clearance method should be used totest whether it is possible to ameliorate anexisting placentar insufficiency (disturbed fetomaterno-placentalrelationship) by means of theoxygen multistep therapy. The impulse for experimentsalong these lines resulted from adiscussion with Kyank. Several gynecologicalstudy groups followed from this stimulus, andwe learned of positive results [73].Further areas of application of the 133Xe clearancemethod, which has been ready for use inour Institute for some time, are the assessmentand the combat of peripheral circulatory disorders[71, 72, 74], the recognition of the timepoint of of the microcirculation inhibition orthe triggering ofhemostasis in the cancer multisteptherapy [22, 23, 76, 77] and in the determinationof the local cerebral flood flow [7578, 79].The lasting improvement in health status afterthe end of the 02MT procedure (after end of02 application) was discovered in 1977 bmeasurement of the resting P02-art [3] thenproven and scrutinized. In 1982 th jointmeasurement of the resting P0 2 - ven(d terminationof 11) [6] was added. Since th n thestrength and the urprising duration of ththerapy effect have al 0 be n prov d b murement of the resting O2 uptak [37] of thparamet rs of lung function, ph i al p rformancecapacity [61] and pti al r a ti n tim[63]. Studi with d t rmin ti n f r ting 0production, bioI i al ag nd mi r ir ul i n