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Juerg Feldmann

Fortiori Design LLC
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 #1 
I  got a very nice mail  with a  great  critical  question  on tHb  and trend in blood flow. The basic    question or  positive critic  was, whether   there are  real scientific  papers  , who would back up  our   idea, that tHb  changes  can track  blood flow  for example  from upper body  to lower body  as we  claim  is happening   with  non-involved muscles. . This is  an absolutely  justified  and  good question, as it sounds  nearly too good  to be true  that a small equipment like that  would allow  an incredible feedback on   exchange of  blood  volume  and as  such as well on energy supply.

Now  here   one  study  we may look at  in this  discussion.

Multi-site and multi-depth near-infrared spectroscopy in a model of simulated (central) hypovolemia: lower body negative pressure.

Bartels SA1, Bezemer R, de Vries FJ, Milstein DM, Lima A, Cherpanath TG, van den Meiracker AH, van Bommel J, Heger M, Karemaker JM, Ince C.

Author information

  • 1Department of Intensive Care, Erasmus Medical Center, University Medical Center, Rotterdam, The Netherlands. s.bartels@erasmusmc.nl

Abstract

PURPOSE:

To test the hypothesis that the sensitivity of near-infrared spectroscopy (NIRS) in reflecting the degree of (compensated) hypovolemia would be affected by the application site and probing depth. We simultaneously applied multi-site (thenar and forearm) and multi-depth (15-2.5 and 25-2.5 mm probe distance) NIRS in a model of simulated hypovolemia: lower body negative pressure (LBNP).

METHODS:

The study group comprised 24 healthy male volunteers who were subjected to an LBNP protocol in which a baseline period of 30 min was followed by a step-wise manipulation of negative pressure in the following steps: 0, -20, -40, -60, -80 and -100 mmHg. Stroke volume and heart rate were measured using volume-clamp finger plethysmography. Two multi-depth NIRS devices were used to measure tissue oxygen saturation (StO2) and tissue hemoglobin index (THI) continuously in the thenar and the forearm. To monitor the shift of blood volume towards the lower extremities, calf THI was measured by single-depth NIRS.

RESULTS:

The main findings were that the application of LBNP resulted in a significant reduction in stroke volume which was accompanied by a reduction in forearm StO2 and THI.

CONCLUSIONS:

NIRS can be used to detect changes in StO2 and THI consequent upon central hypovolemia. Forearm NIRS measurements reflect hypovolemia more sensitively than thenar NIRS measurements. The sensitivity of these NIRS measurements does not depend on NIRS probing depth. The LBNP-induced shift in blood volume is reflected by a decreased THI in the forearm and an increased THI in the calf.

 

 This is  another reaosn  why we like to have SmO2  and tHb  wqhen assessing ,as they  complement each other in  many ways. Using just SmO2  (or in fact HHb  and O2Hb ) without  at least looking at tHb trends can sometimes give  some  wrong conclusions.

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