Biomedical Engineering Reference
In-Depth Information
8.6.4 Measurement of steady-state H
2
S levels in blood and tissue
A major challenge to understanding the multiple roles that H
2
S plays in normal cel-
lular processes has been to accurately defi ne physiological vs pathological H
2
S levels
and the kinetics of H
2
S adjustments. Since any single-point H
2
S measurement is only
a snapshot of a dynamic steady state, the optimal method for this would be to use the
PHSS as an indwelling catheter. This approach is currently in development. An alter-
native method also in development places the PHSS in a fl ow-through micro cell to
sample
1 min sampling time. Integrating the H
2
S peak would
provide an accurate measure of the total free H
2
S in the sample. Although rodent
model blood H
2
S levels are often reported in the 40 to 100
µ
L volumes of blood in
M range as determined
with standard colorimetric assays which may refl ect the inclusion of other sulfi de
sources, we fi nd blood H
2
S levels much lower, typically less than 10
µ
µ
M at pH 7.3 and
37ºC (Kraus
et al.
, preliminary data).
8.7 CONCLUDING REMARKS AND FUTURE DIRECTIONS
The PHSS method of real-time H
2
S measurement allows for investigating the poten-
tially complex H
2
S kinetic responses of organs, tissues, cells, and mitochondria as
levels of O
2
and NO as well as metabolic state are adjusted within physiological limits.
Kinetic changes in H
2
S concentration continuously reported by the PHSS, which are
not seen with other H
2
S measurement techniques, suggest potentially complex interac-
tions of H
2
S production and consumption mechanisms. H
2
S may likely exist as a cellu-
lar pool of free and labile persulfi des able to rapidly respond to redox challenges with
production and consumption pathways that operate to maintain the pool. This possible
scenario reinforces the need for the PHSS as a valuable tool to provide a continual
report of H
2
S throughout the course of an experimental treatment or to accurately
determine H
2
S levels
in situ
.
The PHSS design is continually subject to change based on measurement needs. For
example, miniaturization will allow the PHSS to function as an indwelling catheter for
continuous
in-situ
measurement of H
2
S in blood and tissues. At the other end of the
spectrum, for continuous measurement of H
2
S at hydrothermal vent communities dur-
ing ocean fl oor investigations, the PHSS will need modifi cations to withstand pressure.
As our understanding of H
2
S biology and physiology expands, the demand for differ-
ent geometries and applications of the PHSS will increase.
8.8 ACKNOWLEDGMENTS
This research is supported in part by the American Heart Association grant-in-aid
0455296B and NIGMS grant 08-RGM073049A to DWK and WPI R&D research fund
for XZ.
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