We assess the data quality of calculated tissue oxygen saturation (SO2) and haemoglobin concentrations
recorded on muscle during an incremental cycling protocol in healthy volunteers. The protocol
was repeated three times at the same day and a fourth time at a different day to estimate the reproducibility
of the method. A novel broad-band, spatially resolved spectrometer (SRS) system was employed
which allowed us to compare SRS-based oxygenation parameters with modified Lambert-Beer
(MLB) data. We found that the inter-subject variation in SO2 (standard deviation about 6 %) is considerably
larger than the reproducibility (about 1.5 %) both for same day and different day tests. When
changes in SO2 during the cycling test were considered the reproducibility is better than 1 %. Time
courses of SRS-based haemoglobin parameters are different from MLB-data with higher reproducibility
for SRS. The magnitudes of the haemoglobin changes were found to be considerably larger for
the SRS method. Furthermore, the broad band approach was tested against a four-wavelength analysis
with the differences found to be negligible.
We used spatially resolved near-infrared spectroscopy (SRS-NIRS) to assess calf and thigh muscle
oxygenation during running on a motor-driven treadmill. Two protocols were used: An incremental
speed protocol (velocity = 6 - 12 km/h, ▵v = 2 km/h) was performed in 3 minute stages, while a
pacing paradigm modulated step frequency alternatively (2.3 Hz [SLow]; 3.3 Hz [SHigh]) during a
constant velocity for 2 minutes each. A SRS-NIRS broadband system (600 - 1000 nm) was used to
measure total haemoglobin concentration and oxygen saturation (SO2). An accelerometer was placed
on the hip joints to measure limb acceleration through the experiment. The data showed that the calf
(SO2 58 to 42%) desaturated to a significantly lower level than the thigh (61 to 54%). During the
pacing protocol, SO2 was significantly different between the SLow vs. SHigh trials. Additionally,
physiological data as measured by spirometry were different between the SLow vs. SHigh pacing trials
(VO2 (2563± 586 vs. 2503 ± 605 mL/min). Significant differences in VO2 at the same workload
(speed) indicate alterations in mechanical efficiency. These data suggest that SRS broadband NIRS
can be used to discern small changes in muscle oxygenation, making this device useful for metabolic
exercise studies in addition to spirometry and movement monitoring by accelerometers.
Near-infrared spectroscopy is used to quantify the subcutaneous adipose tissue thickness (ATT) over five muscle groups (vastus medialis, vastus lateralis, gastrocnemius, ventral forearm and biceps brachii muscle) of healthy volunteers (n=20). The optical lipid signal (OLS) was obtained from the second derivative of broad band attenuation spectra and the lipid absorption peak (=930 nm). Ultrasound and MR imaging as well as mechanical calliper readings were taken as reference methods. The data show that the OLS is a good predictor for ATT (<16 mm) with absolute and relative errors of <0.8 mm and <24%, respectively. The optical method compares favourably with calliper reading. The finding of a non-linear relationship of optical signal vs. ultrasound is explained by a theoretical two-layer model based on the diffusion approximation for the transport of photons. The crosstalk between the OLS and tissue hemoglobin concentration changes during an incremental cycling exercise was found to be small, indicating the robustness of OLS. Furthermore, the effect of ATT on spatially-resolved spectroscopy measurements is shown to decrease the calculated muscle hemoglobin concentration and to increase oxygen saturation.
Neurological impairments following cardio-pulmonary bypass (CPB) during open heart surgery can result from
microembolism and ischaemia. Here we present results from monitoring cerebral haemodynamics during CPB with near
infrared spatially resolved broadband spectroscopy. In particular, the study has the objective (a) to monitor oxy- and
deoxy-hemoglobin concentrations (oxy-Hb, deoxy-Hb) and their changes as well as oxygen saturation during CPB
surgery and (b) to develop and test algorithms for the calculation of these parameters from broad band spectroscopy. For
this purpose a detection system was developed based on an especially designed lens imaging spectrograph with
optimised sensitivity of recorded reflectance spectra for wavelengths between 600 and 1000 nm. The high f/#-number of
1:1.2 of the system results in about a factor of 10 higher light throughput combined with a lower astigmatism and
crosstalk between channels when compared with a commercial mirror spectrometers (f/# = 1:4). For both hemispheres
two independent channels each with three source-detector distances (&rgr; = 25 . 35 mm) were used resulting in six spectra.
The broad band approach allows to investigate the influence of the wavelength range on the calculated haemoglobin
concentrations and their changes and oxygen saturation when the attenuation A(&lgr;) and its slope &Dgr;A(&lgr;)/&Dgr;&rgr; are evaluated. Furthermore, the different depth sensitivities of these measurement parameters are estimated from Monte Carlo
simulations and exploited for an optimization of the cerebral signals. It is demonstrated that the system does record
cerebral oxygenation parameters during CPB in infants. In particular, the correlation of haemoglobin concentrations with blood supply (flow, pressure) by the heart-lung machine and the significant decreases in oxygen saturation during cardiac arrest is discussed.
KEYWORDS: Tissues, Tissue optics, Monte Carlo methods, Near infrared spectroscopy, Ultrasonography, Signal attenuation, Absorption, Scattering, Spectroscopy, Oxygen
The measurement of skeletal muscle oxygenation by NIRS methods is obstructed by the subcutaneous adipose tissue
which might vary between < 1 mm to more than 12 mm in thickness. A new algorithm is developed to minimize the
large scattering effect of this lipid layer on the calculation of muscle haemoglobin / myoglobin concentrations. First, we
demonstrate by comparison with ultrasound imaging that the optical lipid signal peaking at 930 nm is a good predictor of
the adipose tissue thickness (ATT). Second, the algorithm is based on measurements of the wavelength dependence of
the slope &Dgr;A/&Dgr;&rgr; of attenuation A with respect to source detector distance &rgr; and Monte Carlo simulations which estimate
the muscle absorption coefficient based on this slope and the additional information of the ATT. Third, we illustrate the
influence of the wavelength dependent transport scattering coefficient of the new algorithm by using the solution of the
diffusion equation for a two-layered turbid medium. This method is tested on experimental data measured on the vastus
lateralis muscle of volunteers during an incremental cycling exercise under normal and hypoxic conditions
(corresponding to 0, 2000 and 4000 m altitude). The experimental setup uses broad band detection between 700 and
1000 nm at six source-detector distances. We demonstrate that the description of the experimental data as judged by the
residual spectrum is significantly improved and the calculated changes in oxygen saturation are markedly different when
the ATT correction is included.
Near-infrared spectroscopy (NIRS) is widely applied for applications monitoring skeletal muscle oxygenation. However,
this method is obstructed by the subcutaneous adipose tissue thickness (ATT) which might vary between < 1 mm to
more than 12 mm. Though diffuse optical imaging can be applied to measure ATT, the objective here is to get this
measure from spectroscopic data of a single source-detector distance. For the measurement of the optical lipid signal we
used a broad band spatially resolved system (SRS), which is based on measurements of the wavelength dependence of
the attenuation A for source detector distances &rgr; between 29 mm and 39 mm. Ultrasound images served as an anatomical
reference of the lipid layer. The measurements were taken on 5 different muscle groups of 20 healthy volunteers, each
for left and right limbs, e.g. vastus medialis, vastus lateralis and gastrocnemius muscle on the leg and ventral forearm
muscles and biceps brachii muscle on the arm. Different analysis strategies were tested for the best calculation of ATT.
There is a good non-linear correlation between optical lipid signal and ultrasound data, with an overall error in ATT
prediction of about 0.5 mm. This finding is supported experimentally by additional MRI measurements as well as a
multi-layer Monte Carlo (MC) model. Based on this data of the ATT thickness, a newly developed algorithm which
exploits the wavelength dependence of the slope in attenuation with respect to source-detector distance and MC
simulation for these parameters as a function of absorption and scattering coefficients delivers a considerably better fit of
reflectance spectra when fitting haemoglobin concentrations. Implications for the monitoring of muscle oxygen
saturation are discussed.
We designed a system incorporating the independent measurement of blood flow and oxygenation of haemoglobin. This is based on laser-Doppler spectroscopy with NIR wavelengths which gives a measure for changes in blood flow or tissue perfusion as well as reflectance spectroscopy in the VIS wavelength range for the calculation of the oxygenated and deoxygenated haemoglobin components. The co-registration of these parameters allows the neurovascular coupling of brain to be investigated. This is demonstrated by recording functional activity of the rat brain during electrical forepaw stimulation.
Near-infrared spectroscopy (NIRS) is used for the non-invasive measurement of muscle oxygenation during an incremental cycle test in healthy volunteers. A broad band spatially resolved system is used that allows the reliability of current algorithms to be inspected with the main emphasis on tissue oxygen saturation (SO2) and oxygenated and deoxygenated haemoglobin concentrations. Physiological conditions were modulated by changing oxygen supply from normal (21 % O2 in inspired air) to conditions corresponding to 2000 and 4000 m altitude above sea level (15.4 and 11.9 % O2). Under these hypoxic conditions the decrease in SO2 with increased exercise power is highly correlated with the oxygen content of the inspired air. There is a clear correlation with physiological parameters (heart rate, pulse oxymetry, blood gas, lactate, spirometric data). Skin oxygenation parameters are compared to those of muscle.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.