The pulse oximetry is a non-invasive method to monitor the oxygen saturation and is clinically used for many years. However this technology has some limitations. In case of the presence of dysfunctional hemoglobin derivatives as carboxyhemoglobin (COHb) or methemoglobin (MetHb) the readings of the pulse oximeter are distorted. This erroneous diagnosis of the patient’s status can result in a life threatening situation. This paper will describe a sensor system for noninvasive determination of carboxy- and methemoglobin.
This paper will describe a novel multi-wavelength photometric method to measure carboxyhemoglobin (COHb) and methemoglobin (MetHb) concentration non-invasively.
COHb and MetHb are so called dysfunctional hemoglobin derivatives and they are not able to carry oxygen. Standard pulse oximeters are only able to measure two derivatives, namely oxyhemoglobin (O2Hb) and deoxyhemoglobin (HHb) but the presence of other derivatives in the blood may distort the readings. The paper presents a new approach of a noninvasive sensor system to measure COHb and MetHb and the validation in vivo and in vitro.
The paper will describe the novel multi-wavelength photometric device OxyTrue Hb® which is capable to measure the hemoglobin (Hb) and methemoglobin (MetHb) concentration non-invasively. Clinic trails in blood donation centers and during the dialysis are done to prove and demonstrate the performance of the system. The results are compared to the gold standard, the BGA measurement.
During the perioperative period, which includes the period before surgery and after surgery (postoperative), it is essential to measure diagnostic parameters such as: blood oxygen saturation; hemoglobin (Hb) concentration; and pulse rate. The Hb concentration in human blood is an important parameter to evaluate the physiological condition of an individual, as Hb is the oxygen carrying component of red blood cells. By determining the Hb concentration, it is possible, for example, to observe intraoperative or postoperative bleeding, and use this information as a trigger for autologous/ allogenic blood transfusions. In blood donation center it is also an essential parameter for the decision regarding the acceptance of the donor.
Hemoglobin (Hb) is an important component of red blood cells. The primary function of Hb is the transport of oxygen
from the lungs to the tissue and carbon dioxide back to the lungs. The Hb concentration in human blood is an important
parameter in evaluating the physiological status of an individual and an essential parameter in every blood count.
Invasive methods are used to measure the Hb concentration, whereby blood is taken from the patient and subsequently
analyzed. Apart from the discomfort of drawing blood samples, an added disadvantage of this method is the delay
between the blood collection and its analysis, which does not allow real time patient monitoring in critical situations. A
non-invasive method allows pain free continuous on-line patient monitoring with minimum risk of infection and
facilitates real time data monitoring allowing immediate clinical reaction to the measured data.
Simulations of light propagation in biological tissues are a useful method in detector development for tissue
spectroscopy. In practice most attention is paid to the adequate description of tissue structures and the ray trace
procedure. The surrounding light source geometry, such as output window, reflector and casing is neglected. Instead, the
description of the light source is usually reduced to incident beam paths. This also applies to detectors and further
surrounding tissue connected sensor geometry. This paper discusses the influence of a complex and realistic description
of the light source and detector geometry with the ray tracing software ASAP (Breault Research Organization).
Additionally simulations include the light distribution curve in respect to light propagation through the tissue model. It
was observed that the implementation of the geometric elements of the light source and the detector have direct influence
on the propagation paths, average photon penetration depth, average photon path length and detected photon energy. The results show the importance of the inclusion of realistic geometric structures for various light source, tissue and sensor
scenarios, especially for reflectance measurements. In reality the tissue surrounding sensor geometry has a substantial
impact on surface and subsurface reflectance and transmittance due to the fact that a certain amount of photons are
prevented from leaving the tissue model. Further improvement allows a determination of optimal materials and geometry
for the light source and sensors to increase the number of light-tissue-interactions by the incident photons.
Currently, invasive methods are used to measure the hemoglobin concentration and the most hemoglobin-derivatives, whereby blood is taken from the patient and subsequently analyzed. The noninvasive method presented here allows pain free continuous on-line patient monitoring with minimum risk of infection and facilitates real time data monitoring allowing immediate clinical reaction to the measured data. Visible and near infrared (VIS-NIR) spectroscopy in combination with photo-plethysmography (PPG) is used for a detection of human tissue properties and the measurement of hemoglobin concentration in whole blood and hemoglobin derivatives. The absorption, scattering and the anisotropy of blood and tissue is a function of the irradiated wavelengths. This fact is used to calculate the optical absorbability characteristic of blood and tissue which is yielding information about blood components like hemoglobin-concentration (cHb), carboxyhemoglobin (COHb) and arterial oxygen saturation (SaO2). The ratio between the PPG peak to peak pulse amplitudes for each wavelength is used in combination with a dynamic spectrum extraction. The prediction of the bloodand tissue-parameters is based on a Principal Component Regression (PCR) method. The non-invasive sensor system is calibrated with a lab based artificial blood circulatory system and with data from clinical studies.
Based on the human circulatory system, an artificial blood circulatory system was developed to allow the controlled
variation of the following blood parameters: total hemoglobin concentration (ctHb), oxyhemoglobin (O2Hb)
methemoglobin (MetHb) and carboxyhemoglobin (COHb). The optical properties of the blood were observed by online
spectrometer measurements. The purpose of this was to observe and quantify the absorption, transmission and scattering
properties of human whole blood in the wavelength range of 400 to 1700 nm. All the non-invasive measurements of the
whole blood transmission-spectra were compared with sample results obtained by a Blood Gas Analyzer (BGA) to
validate the results. For all measurements, donor erythrocyte concentrates were used. The concentration of hemoglobin
was changed by adding fixed amounts of blood plasma to the erythrocyte concentrate. Oxygen saturation and COHb
were adjusted by a continuous flow of N2, N2-CO and compressed air through a hollow fibre membrane oxygenator.
Different methemoglobin concentrations were adjusted by using natrium nitrite. The blood temperature was kept
constant at 37 °C via a tube heating mechanism, with a separate circulation of water passing through the membrane
Oxygenator. The Temperature and pressure of the system were automatically controlled and monitored. The model was
also used to test new non-invasive measurement systems, and for this reason special cuvettes were designed to imitate
human tissue and generate plethysmographical signals. In the future, the blood circulatory system has the potential to be
used for testing, validating and also to calibrate newly developed optical prototype devices. It can also be used to further
investigate blood components of interest.
NIR-spectroscopy and Photoplethysmography (PPG) is used for a measurement of blood components. The absorptioncoefficient
of blood differs at different wavelengths. This fact is used to calculate the optical absorbability characteristics
of blood which is yielding information about blood components like hemoglobin (Hb), carboxyhemoglobin (CoHb) and
arterial oxygen saturation (SpO2). The measured PPG time signals and the ratio between the peak to peak pulse
amplitudes are used for a measurement of these parameters. Hemoglobin is the main component of red blood cells. The
primary function of Hb is the transport of oxygen from the lungs to the tissue and carbon dioxide back to the lungs. The
Hb concentration in human blood is an important parameter in evaluating the physiological status of an individual and an
essential parameter in every blood count. Currently, invasive methods are used to measure the Hb concentration,
whereby blood is taken from the patient and subsequently analyzed. Apart from the discomfort of drawing blood
samples, an added disadvantage of this method is the delay between the blood collection and its analysis, which does not
allow real time patient monitoring in critical situations. A noninvasive method allows pain free continuous on-line
patient monitoring with minimum risk of infection and facilitates real time data monitoring allowing immediate clinical
reaction to the measured data.
KEYWORDS: Wavelets, Heart, Continuous wavelet transforms, Signal detection, Control systems, Measurement devices, Digital signal processing, Analytical research, Blood, In vivo imaging
Photo-plethysmography (PPG) is frequently used in research on microcirculation of blood. It is a non-invasive procedure
and takes minimal time to be carried out. Usually PPG time series are analyzed by conventional linear methods, mainly
Fourier analysis. These methods may not be optimal for the investigation of nonlinear effects of the hearth circulation
system like vasomotion, autoregulation, thermoregulation, breathing, heartbeat and vessels. The wavelet analysis of the
PPG time series is a specific, sensitive nonlinear method for the in vivo identification of hearth circulation patterns and
human health status. This nonlinear analysis of PPG signals provides additional information which cannot be detected
using conventional approaches. The wavelet analysis has been used to study healthy subjects and to characterize the
health status of patients with a functional cutaneous microangiopathy which was associated with diabetic neuropathy.
The non-invasive in vivo method is based on the radiation of monochromatic light through an area of skin on the finger.
A Photometrical Measurement Device (PMD) has been developed. The PMD is suitable for non-invasive continuous online
monitoring of one or more biologic constituent values and blood circulation patterns.
NIR-spectroscopy and Photoplethysmography (PPG) and is used for a measurement of blood components. The fact that
the absorption-coefficients μa and scattering-coefficients μs for blood differ at difference wavelengths has been exploited
and is used for calculation of the optical absorbability characteristics of human blood yielding information on blood
components like hemoglobin and oxygen saturation. The measured PPG time signals and the ratio between the peak to
peak pulse amplitudes are used for a measurement of these parameters. A newly developed PMD device has been
introduced. The non-invasive in-vivo multi-spectral method is based on the radiation of monochromatic light, emitted by
laser diodes, through an area of skin on the finger. Deferrals between the proportions of hemoglobin and plasma in the
intravasal volume should be detected photo-electrically by signal-analytic evaluation of the signals. The computed
nonlinear coefficients are used for the measurement and calculation of the relative hemoglobin concentration change.
Results with this photometric method to measure changes in the hemoglobin concentration were demonstrated during
measurements with a hemodynamic model and healthy subjects. The PMD is suitable for non-invasive continuous online
monitoring of one or more biologic constituent values. The objective of this development is to reduce the
dependence on measurement techniques which require that a sample of blood be withdrawn from the patient for in-vitro
analysis. Any invasive method used on the patient to obtain blood is accompanied by problems of inconvenience, stress,
and discomfort. The patient is also exposed to the normal risks of infection associated with such invasive methods.
The development of this photometric device is based on the realisation of a photoplethysmography measurement device developed for the German Space Agency DLR. It is well known in biomedical engineering that pulsatile changes of blood volume in tissue can be observed by measuring the transmission or the reflection of light. The non-invasive multi-spectral method described here is based on the radiation of monochromatic light, emitted by laser diodes in the range of 600 nm to 1400 nm, through an area of skin on the finger. After interaction with the tissue the transmitted light is detected non-invasively by photo-diodes. The method makes use of the intensity fluctuations caused by the pulse wave. The ratio between the peak to peak pulse amplitudes measured at different wavelengths and its dependence on the optical absorbability characteristics of human blood yields information on the blood composition. Deferrals between the proportions of haemoglobin and water in the intravasal volume should be detected photo-electrically by signal-analytic evaluation of the signals. The computed coefficients are used for the measurement and calculation of the arterial oxygenic saturation (SaO2) and the relative haemoglobin concentration change. Results of clinical measurements are presented for a de-oxygenation study with ICG-bolus injection (indocyanine green).
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