Near-infrared Spectroscopic Method for Assessing
the Tissue Oxygenation State of Living Lung
TOSHIO NORIYUKI, HIDEKI OHDAN, SHINKICHIRO YOSHIOKA, YOSHIHIRO MIYATA,
TOSHIMASA ASAHARA, and KIYOHIKO DOHI
Second Department of Surgery, Hiroshima University School of Medicine, 1-2-3 Kasumi, Minami-ku, Hiroshima, Japan
To quantify changes in tissue oxygenation of pathologic lungs, we applied a novel method using
near-infrared spectroscopy (NIRs). In in vitro experiments, we assayed the effect of photon scattering
on the absorption spectra of an in vitro system simulating structures of lung, which consists of test
tube containing air in hematocrit tubes and red blood cell suspension with various predetermined
hemoglobin concentrations. It was determined that photon scattering of the tissue containing air did
not affect the absorption in the NIR region. In in vivo experiments, we tested the applicability of the
NIRs technique in rat lungs under the following conditions: (1) hypoxic loading; (2) administration of
an inhibitor (NaCN) of the mitochondrial respiratory chain; (3) hemorrhagic shock. We found that:
(1) Changes in hemoglobin oxygenation state in the lung measured by NIRs depended on inspired
oxygen concentrations; (2) NaCN-induced reduction of cytochrome oxidase a,a3 in the lung was observed; and (3) Total hemoglobin levels in the lung decreased after bleeding. Changes in the hemoglobin oxygenation state and cytochrome oxidase redox state in the lung were determined using the
least-square-curve fitting for NIR absorption spectra. Our NIRs technique was capable of assessing
the hemoglobin oxygenation and cytochrome oxidase redox state in the lung. Noriyuki T, Ohdan H,
Yoshioka S, Miyata Y, Asahara T, Dohi K. Near-infrared spectroscopic method for assessing
AM J RESPIR CRIT CARE MED 1997;156:1656–1661.
the tissue oxygenation state of living lung.
In accordance with recent advances in lung surgery, there is an
increasing demand for a less-invasive method to assess the viability of lung tissue. In particular, monitoring of tissue hemodynamics and tissue oxygenation is considered to be important
in thoracic surgery with vascular reconstruction, especially lung
transplantation (1, 2). In general, optical measurements, including in vivo spectroscopy, have been used for monitoring
tissue hemodynamics and oxygenation in brain and liver (3, 4).
Near infrared (NIR) spectroscopy takes advantage of effective photon penetration to detect deep hemoglobin (Hb) in intact tissue (5). This method has been used to monitor regional
blood volume change, Hb oxygenation and the cytochrome
oxidase a.a3 (Cyt.aa3) redox state in organs, but has been applied only to solid organs, such as the brain, muscles, and liver
(6–9). In the present study, we examined whether NIR spectroscopy could be applied to the lung to monitor tissue viability.
This study was divided into two parts. First, we assayed the
effect of photon scattering on the absorption spectrum by in
vitro experiments using an in vitro system stimulating the
structures of lung. Because the lung contains air and therefore
differs from other organs that NIR spectroscopy had been applied. Second, for the in vivo experiments, we tested the appli(Received in original form January 29, 1997 and in revised form June 3, 1977)
Supported by the Japanese Ministry of Education, Grant-in-Aid for Scientific Research (B) No. 07457253.
Correspondence and requests for reprints should be addressed to Toshio Noriyuki,
M.D., Second Department of Surgery, Hiroshima University School of Medicine,
1-2-3 Kasumi, Minami-ku, Hiroshima, 734, Japan.
Am J Respir Crit Care Med Vol 156. pp 1656–1661, 1997
cability of NIR spectroscopic techniques in the rat lung under
various pathologic conditions (hypoxia, inhibited state of mitochondrial respiration and hemorrhagic shock). Hb oxygenation, total Hb volume, and the redox-state of Cyt.aa3 in the
lungs were evaluated with NIR spectroscopy under these conditions.
METHODS
In Vitro Experiment using In Vitro System Simulating
Structure of Lung
The in vitro system simulating the structures of the lung consisted of a
test tube containing red blood cells (RBCs) suspension and air in hematocrit tubes. Sealed hematocrit tubes containing air were closely
packed in the glass test tube (OD 10 mm, ID 8 mm) and the RBCs
suspension with and without milk (scattering material) was filled in a
gap among hematocrit tubes (Figure 1). Human RBCs were suspended in phosphate-buffered saline at various predetermined Hb
concentrations from 0.1 to 1.0 mM. The hematocrit tubes containing
air were intended to stimulate alveoli, and the RBCs suspension with
milk to simulate scattering biological pigments in the lung.
We used NIR spectroscopy to observe the absorption spectra of
the in vitro system and the RBCs suspension in the glass test tube, and
analyzed changes in Hb concentration as described below.
A multichannel photodetector (MCPD-2000; Otuka Electrical Co.,
Osaka, Japan) with quartz optical fibers and a 300W halogen lamp
(Petite Ace 25; Sanyo Denki Co., Tokoyo, Japan), as a light source,
were used. MCPD-2000 was connected to a personal computer (PC9821 Xs; NEC, Tokyo, Japan). The tips of the optical fibers for NIR
spectroscopy were fixed on the test tube with attachment specially
made. As a reference spectrum, yogurt was used for scanning the in
vitro system and the RBCs suspension, and the light intensity was adjusted to bring the optical density to between 0.8 and 1.0. The re-
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Noriyuki, Ohdan, Yoshioka, et al.: NIR Spectroscopic Method for Lung
Figure 1. (A) Photograph of the in vitro system simulating structures of lung. (B) Schematic illustration of horizontal view of the in
vitro system.
flected light from the in vitro system was scanned within the range of
500 to 1,100 nm, and the sampling time of each scan was 200 msec.
The spectra in a series of 20 scans were averaged by the personal computer. The absorption spectra of scattering materials were transformed by applying the following equation to correct their flattened
shape attributed to the light path length distribution caused by photon
scattering:
corrected %abs ( λ ) = 1 ⁄ 7 { %abs ( λ ) ⋅ exp. [ 1.927 %abs ( λ ) ] +
%abs ( λ ) ⋅ exp. [ 0.827 %abs ( λ ) ] }
( 10, 11 )
where corrected %abs (l) and %abs (l) are corrected absorption and
actual absorption at a wavelength of l, respectively. The difference
between the corrected spectrum for Hb concentration of 0.1 mM and
that of another concentration was calculated. Multicomponent analysis of the difference in the spectra was performed in a wavelength
range of 700 to 1,000 nm with an equation following the Beer-Lambert law.
OD ( λ ) = L ( λ ) ⋅ { e 1 ( λ ) ⋅ ∆ [ oxy-Hb ] + e 2 ( λ ) ⋅
∆ [ deoxy-Hb ] + e 3 ( λ ) ⋅ ∆ [ water ] }
where OD (l), L (l), and e1–3 (l) are optical density, mean light path
length, and extinction coefficients, respectively, of each component at
a wavelength of l. Least-square curve fitting was used to calculate the
existential rate of the three components. The relationship of the predetermined RBC concentration and the absorption of total-Hb (a sum
of oxy-Hb and deoxy-Hb) measured by NIR spectroscopy was analyzed.
In Vivo Experiment using Rat Lung Under
Various Pathologic Conditions
All procedures involving rats were performed according to the guidelines of the National Institutes of Health “Guide for the Care and Use
of Laboratory Animals.”
Male Wister rats weighing 250 to 350 g (Charles River Japan,
Yokohama, Japan) were prepared with atropine (0.4 mg/kg, i.m.) and
anesthetized intraperitoneally with sodium pentobarbital (50 mg/kg)
and ketamine (40 mg/kg). After intubation with a 16 G polyvinyl tube
(Terumo Co., Tokyo, Japan), the rats were ventilated with a ventilator (SN-480-7; Shinano Co., Tokyo, Japan). The ventilator settings
were tidal volume, 10 mL/kg, respiratory frequency, 70 breaths/min,
positive end-expiratory pressure, 4 cm H2O. The carotid artery was
cannulated with a 3 Fr. polyethylene tube (Atom Co., Tokyo, Japan)
for blood pressure monitoring and blood sampling. Thoracostomy was
performed in the left 4th intercostal space, and the tips of the fiber
bundles for NIR spectroscopy were fixed at a position approximately
3 mm above the lung. Under these conditions, the following studies
were performed.
Figure 2. Absorption spectra of the RBC suspensions under various
hemoglobin (Hb) concentrations. (A) with milk (scattering material) (B) without milk.
Hypoxic load. FIO2 was changed by mixing pure nitrogen gas and
oxygen gas to create FIO2 of 1.0, 0.6, 0.2, 0.15, and 0.1, and the absorption spectra of four rat lungs were observed by NIR spectroscopy. The
difference between the spectrum of the lung was assessed for each
FIO2 value and for an FIO2 of 0.2. Through a multicomponent analysis
of those different spectra, the changes in concentration of oxy-, deoxyHb, and oxidized and reduced Cyt.aa3 were calculated. Whole blood
was simultaneously sampled from a 3 Fr. polyvinyl tube inserted into
the carotid artery, and SaO2, PaO2, PaCO2, and pH were measured with
a blood gas analyzer (ABL 510; Radiometer Trading Co., Copenhagen,
Denmark).
Administration of NaCN. Five rats received two doses of NaCN
(1 mg/kg) at an interval of 10 min to inhibit the mitochondrial respiratory chain under the condition of FIO2 1.0. Immediately prior to use,
NaCN was dissolved in saline at a concentration of 0.25 mg/ml. The
systemic blood pressure was monitored by an oscilloscope (DS-3300;
Fukuda Electrical Co., Tokyo, Japan) through a transducer. The spectra of the lung were continuously measured at 20-s intervals, and the
differences between the spectra of the lung prior to and following
NaCN administration were calculated. Using a multicomponent analysis of those different spectra, the changes in concentration of oxy-,
deoxy-Hb, and oxidized, and reduced Cyt.aa3 were quantified.
Hemorrhagic shock. To create a condition of hemorrhagic shock
for five rats, whole blood (5 ml/kg) was rapidly drawn twice at an interval of 10 min via the carotid artery under the condition of FIO2 1.0,
and systemic blood pressure was monitored. The spectra of the lung
were continuously measured at 30-s intervals, and the differences between the spectra of the lung prior to and following whole blood
drawing were calculated. Using a multicomponent analysis of those
difference spectra, the changes in concentration of oxy-, deoxy-Hb,
and oxidized, and reduced Cyt.aa3 were quantified.
In vivo NIR spectroscopy. For in vivo NIR spectrophotometric
measurement, the same method as the above mentioned in vitro experiment was used. The tips of the two optical fiber bundles were
fixed at a position approximately 3 mm above the lung. The reflected
light from the living lung was scanned within the range of 500 to 1,100
nm. The sampling time of each scan was 200 ms, and 20 serial scans
were averaged. The difference between the spectrum of the lung under the control condition and that under the manipulated condition in
each experiment was calculated. Within the range of 700 to 1,000 nm,
the difference in the spectrum was analyzed by a curve-fitting technique based on the least squares method using the standard spectra of
purified oxy-Hb, deoxy-Hb, oxidized Cyt.aa3, reduced Cyt.aa3 and water. The five components were fitted with the following equation:
OD ( λ ) = L ( λ ) ⋅ { e 1 ( λ ) ⋅ ∆ [ oxy-Hb ] + e 2 ( λ ) ⋅ ∆ [ deoxy-Hb ]
+ e 3 ( λ ) ⋅ ∆ [ oxidized Cyt.aa 3 ]
+ e 4 ( λ ) ⋅ ∆ [ reduced Cyt.aa 3 ]
+ e 5 ( λ ) ⋅ ∆ [ water ] }
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where OD (l), L (l), and e1–5 (l) are optical density, mean light path
length, and extinction coefficients, respectively, of each component at
a wavelength of l. The relative changes in each component were detected using this multicomponent analysis calculated on the basis of
singular value decomposition (12).
Statistical Analysis
All data are express as mean 6 SEM. Correlations between variables
in both the in vitro and in vivo experiments were assessed using linear
regression analysis. The statistical significance of differences in variables between control and manipulated conditions was assessed by
the paired t test. Significance was accepted for p values , 0.05.
RESULTS
In Vitro Experiment
Figures 2 and 3 show absorption spectra of the RBC suspension and the in vitro system with and without milk at various
Hb concentrations. In all spectra observed in this experiment,
the visible part below 600 nm was rough, caused by preventing
transmission over a longer path length due to increasing light
scattering. In contrast, the NIR part in the 700 to 1,100 nm
range was quite smooth and had a broad peak caused by oxyHb, which increased as the concentration of Hb increased in
the fluid. In this region, a peak caused by deoxy-Hb was invisible at 760 nm, because most RBC Hb was oxygenated in
room air.
Figure 4 shows the relationship between the changes in total Hb measured by NIR spectroscopy and the predetermined
Hb concentration in each condition. In all conditions, there
were significant correlations: in vitro system with milk: y 5
20.10969 1 5.0752e-2 x, r 5 0.984, p , 0.05, in vitro system
without milk: y 5 20.16831 1 9.4931e-2 x, r 5 0.994, p , 0.05,
RBC suspension with milk: y 5 20.16324 1 0.10404 x, r 5
0.999, p , 0.05, RBC suspension without milk: y 5 20.19379 1
0.13059 x, r 5 0.998, p , 0.05).
In Vivo Experiment
Hypoxic load. Figure 5 shows the absorption spectra of rat
lung at different FIO2 values. In the NIR part, all spectra of lung
obtained from this experiment were stably reproducible. As
FIO2 decreased, a peak caused by deoxy-Hb at 760 nm became
prominent, and a broad peak at 750 to 950 nm caused by oxyHb became flat.
Figure 6A shows the relationship between the change in
SaO2 (DSaO2) measured by conventional blood gas analysis and
Figure 3. Absorption spectra of the in vitro system under various
Hb concentrations. (A) with milk (scattering material) (B) without
milk.
Figure 4. Linear correlations between the changes in total Hb
measured by NIR spectroscopy and predetermined Hb concentration in in vitro systems with and without milk (3/closed squares)
and in the RBC suspensions with and without milk (closed triangles/closed diamonds) [in vitro system with milk: y 5 20.10969 1
5.0752e-2 x (r 5 0.984, p , 0.05), in vitro system without milk:
y 5 20.16831 1 9.4931e-2 x (r 5 0.994, p , 0.05), RBC suspension with milk: y 5 20.16324 1 0.10404 x (r 5 0.999, p , 0.05),
RBC suspension without milk: y 5 20.19370 1 0.13059 x (r 5
0.998, p , 0.05)].
the changes in oxy-Hb in rat lungs measured by NIR spectroscopy. To determine the DSaO2, we subtracted SaO2 under each
FIO2 from SaO2 under FIO2 of 0.2. The changes in oxy-Hb correlated closely with DSaO2 (Y 5 0.280877 x 1 0.444212, r 5 0.92,
p , 0.001). Figure 6B shows the relationship between DSaO2
and the changes in oxidized and reduced Cyt.aa3 in rat lungs
measured by NIR spectroscopy. There was correlation between them (oxidized Cyt.aa3: Y 5 0.0534896 1 0.457061 x,
r 5 0.72, p , 0.01, reduced Cyt.aa3: Y 5 0.380488 2 0.0731549
x, r 5 20.72, p , 0.01).
Administration of NaCN. Systolic arterial blood pressure
fell from 108 6 4.90 mm Hg to 58.6 6 4.02 mm Hg immediately after the first administration of NaCN, and gradually recovered at a level of 74.6 6 3.73 mm Hg at 10 min after administration. The second administration caused a fall of systemic
blood pressure to 40.6 6 3.44 mm Hg.
Figure 7A shows the time course of the changes in oxidized
and reduced Cyt.aa3 after the point of intravenous administration of NaCN. The level of reduced Cyt.aa3 rose significantly
immediately after the NaCN administration, and rose still
more by repeating the administration. The level of oxidized
Figure 5. NIR spectra of rat lung under conditions of FIO2 0.1 to 1.0.
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Noriyuki, Ohdan, Yoshioka, et al.: NIR Spectroscopic Method for Lung
Figure 6. (A) Linear correlation between the changes in oxy-Hb in
rat lungs measured by NIR spectroscopy and the change in Sa O2
(DSaO2) measured by conventional blood gas analysis: Y 5
0.44212 1 0.280877 x (r 5 0.92, p , 0.001). (B) Linear correlations between the change in reduced (closed squares), oxidized
(closed diamonds) Cyt.aa3 measured by NIR spectroscopy and
DSaO2: [reduced Cyt.aa 3: Y 5 0.380488 2 0.0731549 x (r 5
20.72, p , 0.01), oxidized Cyt.aa3: Y 5 0.457011 1 0.0534896 x
(r 5 0.72, p , 0.01)].
Cyt.aa3 fell in response to the rising level of reduced Cyt.aa3.
These responses were related to the number of administrations.
These data show that the administration of NaCN caused a reduction of Cyt.aa3 in the mitochondria of the lung tissue. Figure 7B shows the time course of changes in oxy-Hb and deoxy-
Figure 7. (A) Changes in oxidized (closed squares) and reduced
(closed diamonds) Cyt.aa3 after intravenous administration of
NaCN. (B) Changes in oxy-Hb (closed squares) and deoxy-Hb
(closed diamonds) in lungs following administration of NaCN. Results are expressed as mean 6 SEM; error bars not shown appear
within the data point. (n 5 5) *, ** shows significance prior to and
following administration of NaCN (p , 0.05).
Hb in the lungs after administration of NaCN. The level of
oxy-Hb transiently fell immediately after the first NaCN administration, and gradually rose over the initial level. The same
response was observed after the second administration. The
level of deoxy-Hb remained constant during the observation
period.
Hemorrhagic shock. Systolic arterial blood pressure fell
from 99.6 6 5.13 mm Hg to 68.2 6 6.17 mm Hg immediately
after the first blood drawing, and gradually recovered to a
level of 83.4 6 2.73 mm Hg until 10 min after the blood drawing. The second blood drawing caused a fall of systemic blood
pressure to 43.6 6 3.40 mm Hg.
Figure 8 shows the time course of changes in total Hb (oxyHb 1 deoxy-Hb) and reduced Cyt.aa3 in rat lungs after phlebotomy. The level of total Hb fell significantly immediately
after the first blood drawing and gradually recovered to the
initial level at 10 min after the blood drawing. The second
blood drawing resulted in an irreversible fall of total Hb. The
level of reduced Cyt.aa3 rose significantly immediately after
the first blood drawing and rose still more by the second blood
drawing.
DISCUSSION
It is important to evaluate the hemodynamics and the tissue
viability of the lung for thoracic surgery, especially for lung
transplantation and operations with vascular reconstruction
(1, 2). To quantify changes in tissue oxygenation of pathologic
lungs, we applied a novel method using NIR spectroscopy.
The parameters measured by NIR spectroscopy (changes in
Hb oxygenation and Cyt.aa3 redox state) should be useful
markers for evaluating pulmonary function and lung tissue viability, because Cyt.aa3 is the terminal member of the mitochondrial respiratory chain and its redox state changes in response to oxygen availability at the cellular level (13). NIR
spectroscopy was first introduced by Jobsis, and has been applied in a number of clinical and physiologic situations (5). It is
based on the fact that the absorption intensity of NIR light
depends on the level of Hb oxygenation, the redox state of
Cyt.aa3, and biological content. In the visible part of the spectrum, below 700 nm, the intense absorption bands of hemoglobin (Hb) and increasing light scattering phenomena prevent
Figure 8. Changes in total Hb (closed squares) and reduced Cyt.aa3
(closed diamonds) in rat lungs after blood drawing. Results are expressed as mean 6 SEM; error bars not shown appear within the
data point. (n 5 5) *, ** shows significance prior to and following
whole blood drawing (p , 0.05).
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transmission over longer pathlengths. However, in the 700 nm
to 1,300 nm range of NIR, a significant amount of radiation can
be effectively transmitted through biological materials over
longer distances (5). Absorption by hemoglobin shows an original change within the NIR region depending on oxygenation
conditions. In the NIR range, deoxy-Hb has an absorption peak
at 760 nm, but oxy-Hb does not (14). Cyt.aa3 has a weak absorption band within the NIR region. When Cyt.aa3 is oxidized, the weak absorption band is in the 780 to 870 nm region
with a broad maximum from 820 to 840 nm, and when Cyt.aa3
is reduced, this band disappears (15). NIR spectroscopy takes
advantage of changes in the absorption of substances and has
been used to monitor regional blood volume change, Hb oxygenation and Cyt.aa3 redox state in organs (6–9).
To calculate changes in oxy-Hb, deoxy-Hb, and oxidized
and reduced Cyt.aa3 through analysis of the NIR spectra, the
following two methods have been used: the three to six separate wavelengths method, which solves simultaneous equations at wavelengths (16–18), and the continuous wavelength
method, which involves a curve-fitting technique based on the
least-squares method using the spectra of purified standards at
wavelength increments of 2 nm between 700 and 1,000 nm (19,
20). In comparison with the former method, the latter has the
advantage of compensating for individual variations in background absorption through calculation of differences in the
spectra (11, 21, 22). This method could be applied to various
organs that may have peculiar pigments. Considering this advantage, we chose the continuous wavelength NIR spectroscopy
for the in vivo assessment of lung tissue oxygenation.
In order to apply NIR spectroscopy to living lungs, it is necessary to take into account the effect of photon scattering
caused by air in alveoli and the effect of changing tissue density on the absorption spectra of the lung due to changing volume caused by respiration. First, we demonstrated in in vitro
experiments that the presence of air did not intensify photon
scattering in the NIR region, and the Hb level in scattering
materials with air was correctly measured by NIR spectroscopy
(Figure 4). Next, to determine the changing density of lung tissue due to respiration, we measured the in vivo lung absorption
spectra under shortening sampling time (200 msec) and increasing sampling frequency (20 scans) and averaged the spectra obtained by these scans. In vivo experiments demonstrated
that reproducible spectra were obtained from living lung tissue under this special measurement condition (Figure 5). These
findings support the applicability of NIR spectroscopy to in vivo
lungs.
Our NIR spectroscopic method for monitoring living tissues has three steps in the process of evaluating changes in biologic components affected by oxygenation. The first step is to
scan an actual absorption spectrum of living tissue. The second step is correcting the flattening of this spectrum. With regard to the application of continuous wavelength NIR spectroscopy of biologic tissues, the flattening of the absorption
spectra due to photon scattering should be taken into account,
because of the light path length distribution and the mean
light path length changes as a function of absorption. In this
study, therefore, the flattening of the absorption spectra was
corrected by applying an equation that incorporated that relationship between e · C (e is the extinction coefficient, C is the
concentration of the absorber) and the actual absorption in
scattering materials. In prior reports, a similar method has been
used, and its usefulness has been proven (10, 11). The last step
is a multicomponent least-square curve fitting using of standard spectra for analyzing the corrected spectrum. In the multicomponent curve-fitting, it is necessary to select appropriate
standard components which have characteristic absorption
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spectra in the NIR region. It is well known that oxy-, deoxyHb, and oxidized and reduced Cyt.aa3 should be included in
the standard component (5, 23, 24). In addition to these, we
chose water as another standard component for the multicomponent analysis because lung edema due to increasing water
content in the tissues occurs in various pathologic conditions.
In this study, therefore, the above five components were fitted, and relative changes in the components were quantified.
The validity of all analyses in this study was confirmed by regression analysis (r . 0.9).
To estimate the validity of quantifying Hb oxygenation and
Cyt.aa3 redox state in living lungs using of our NIR spectroscopic technique, we performed NIR spectrophotometric measurements in rat lungs under various pathologic conditions
such as hypoxia, inhibited state of mitochondrial respiration,
and hemorrhagic shock. In the experiment during hypoxia, it
was shown that oxy- and deoxy-Hb levels in the lungs measured by NIRs changed reasonably, and the oxy-Hb level correlated closely with SaO2 levels measured simultaneously. In
the experiment under an inhibited state of mitochondrial respiration, cyanide-induced Cyt.aa3 redox state response (shifting to reduction state) could be observed in rat lungs in realtime using NIRs. An interesting change in the oxy-Hb level in
the lungs was observed, i.e., a transient fall immediately after
NaCN administration and a gradual rising over the initial level
(25). The transient decrease of arterial blood pressure may
have been responsible for the initial fall of the oxy-Hb level,
and the later rise may have been caused by the reduced oxygen consumption at the cellular level in lung tissues affected
by the inhibition of mitochondrial respiration. And then, the
rise of total Hb (oxy-Hb plus deoxy-Hb) may have been caused
by cardiac failure induced by cyanide. In the experiment during hemorrhagic shock, a falling total Hb level and the shifting
of the Cyt.aa3 redox state to the reduction state in lung tissues
could be observed using NIR spectroscopy. These results demonstrate that NIR spectroscopy can quantify the Hb oxygenation and the redox state of Cyt.aa3 in living lungs.
There are limitations related to the use of in vivo NIR spectroscopy in living tissues. In our system, only relative changes
in each biologic component can be obtained, because a calibration factor has not been established. In our study, general
anesthesia and thoracotomy were performed in experimental
animals, and NIR spectroscopy was conducted directly above
the lung. However, other investigators have demonstrated
that NIR spectroscopy can be employed for noninvasive measurement of cerebral blood volume in human infants and children (26, 27). Considering the good transparency of biologic
tissues to NIR light, some technical improvements, such as the
use of a more powerful light source and more efficient optical
probes, may facilitate noninvasive clinical NIR monitoring of
lungs in the future.
In conclusion, our NIR spectroscopic technique is able to
assess quantitatively tissue oxygenation at both the vascular
and cellular levels in living lung tissues through monitoring of
Hb oxygenation and the Cyt.aa3 redox state, and should be
useful to assess the viability of lung tissue. Further studies are
necessary to clarify the usefulness of NIR spectroscopy in the
clinical setting.
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