Pulse oximetry is an optical technique for the assessment of oxygen saturation in arterial blood and is based on the different light absorption spectra for oxygenated and deoxygenated hemoglobin and on two-wavelength photoplethysmographic (PPG) measurement of arterial blood volume increase during systole. The technique requires experimental calibration for the determination of the relationship between PPG-derived parameters and arterial oxygen saturation, and this calibration is a source of error in the method. We suggest a three-wavelength PPG technique for the measurement of arterial oxygen saturation that has no need for calibration if the three wavelengths are properly selected in the near-infrared region. The suggested technique can also be implemented for the assessment of venous oxygen saturation by measuring the decrease in transmission of light through a tissue after increasing its blood volume by venous occlusion. The oxygen saturation in venous blood is a parameter that is related to oxygen consumption in tissue and to tissue blood flow. The three-wavelength method has the potential to provide accurate oxygen saturation measurements in arterial and venous blood, but experimental validation of the theory is still required to confirm this claim.
Photoplethysmography (PPG) measures the cardiac-induced fluctuations and other changes in tissue blood volume by light transmission measurement. In the current study, light transmission was simultaneously measured in the two index fingers of healthy subjects, while the brachial artery in the left arm was occluded by a pressure cuff, so that no PPG signal appeared in the left finger. Correlated respiratory-induced changes in the PPG baseline in the right hand and in the light transmission in the left hand were found, indicating respiratory-induced blood volume changes in the finger distal to the occluded artery. The blood volume changes under the PPG probe distal to the occluded artery are interpreted as transition of blood volume from small arteries into big veins, mediated by the sympathetic nervous system.
Simultaneous measurements of the low frequency fluctuations of arterial blood pressure, heart rate, tissue blood content and tissue blood volume pulse were performed on 20 healthy male subjects. Arterial blood pressure was measured on the index finger by Finapres, simultaneously with photoplethysmography (PPG), which was measured on the other index finger. The changes in the PPG amplitude (AM), baseline (BL), and BV (defined by BV equals Const. - BL), are related to the changes in the tissue blood volume pulse (for AM) and the total tissue blood volume, (for BL and BV). The low frequency fluctuations of BV and AM were directly correlated, those of AM preceding those of BV by 4 - 13 heart beats. The low frequency fluctuations of SBP and DBP were inversely correlated to those of AM and BV. For most of the subjects P, which is the cardiac cycle period, was directly correlated with AM and BV. The interrelationship between the low frequency fluctuations in tissue blood volume, arterial blood pressure and heart period, provide us with a better understanding of the autonomic nervous control of the peripheral circulation.
Several parameters of the cardiovascular system such as heart rate, arterial blood pressure and blood flow fluctuate spontaneously due to the autonomic nervous system activity. In the current study, the low frequency fluctuations of the tissue blood volume and the blood volume pulse in the fingertips of healthy subjects were investigated using transmission photoplethysmography (PPG). The baseline of the PPG signal (BL) is inversely related to tissue blood volume so that the parameter BV, defined by: BV equals Const.-BL is directly related to the blood volume. The amplitude (AM) is directly related to the systolic blood volume increase. For most of the examinations BV and AM show positive correlation, which is expected since BV depends on the tissue blood volume and AM depends on the compliance of the blood vessels, both of which decrease during vasoconstriction, which is caused by higher activity of the sympathetic nervous system. The analysis of the PPG signal provides, therefore, a potential tool for study in the mechanism of the regulation of the microcirculation by the sympathetic nerves.
A sensor for measuring chest circumference by means of an optical fiber has been developed. The method is based on the measurement of light transmitted through a bent optical fiber, which is connected to an elastic band, wrapped around the chest, and whose radius of curvature changes due to the respiratory act. The amount of transmitted light is related to the radius of curvature of the fiber which depends on the chest circumference. The output of the respiratory sensor was checked qualitatively by changing the respiration depth. The changes in breathing effort were clearly demonstrated in the sensor output recording. The respiratory effort was also correlated with the heart rate, measured by photoplethysmography. Statistically significant correlation was found between the lungs' volume and the heart rate, but the correlation coefficient was not high. The magnitude of the breathing depth and the height of the corresponding respiratory changes of the heart cycle period were not correlated.
Besides heart rate and arterial blood pressure, several parameters of the cardiovascular system fluctuate spontaneously. In the current study, the fluctuations of tissue blood content and blood volume pulse were investigated using two parameters of the photoplethysmographic (PPG) signal: the parameter BV, defined by: BV=Const−BL where BL is the baseline of the PPG signal, and the amplitude (AM), which are related to the blood volume and to the systolic blood volume increase, respectively. The PPG measurements were performed on the fingertips of ten healthy male subjects for 5 to 10 min and the PPG signal was digitally analyzed. Both BV and AM show low frequency fluctuations, which, for 23 out of 26 examinations, were positively correlated, with a lag of BV relative to AM. In three examinations, however, the two parameters were inversely correlated. A lower correlation was found between each of these parameters and the PPG period, which is actually the cardiac period. The results show that several mechanisms are involved in the spontaneous periodic fluctuations in the vascoconstriction level, which are known to be mediated by the sympathetic nervous system. The digital PPG provides, therefore, a potential tool for evaluating the role of the sympathetic nerves in the regulation of the microcirculation.
A new type of intensity-modulated sensors based on a coated light guide is presented. These sensors operate preferentially in the regime of total internal reflection (TIR), rather than relying on violation of TIR as in conventional intensity-modulated sensors. Using a physical model of the new sensor structure, the output light intensity is computed as a function of the complex reflection and transmission coefficients at the substrate-film and film-ambient interfaces. Based on the theoretical results, an experimental setup has been constructed and evaluated for measurements on various liquids. The results confirm the predicted dependence of the output signal on the characteristics of the substrate-film-ambient system. Of particular importance is the novel feature that the output signal increases as the refractive index of the ambient medium increases, at certain incidence angles.
The temperature of uncovered skin does not provide useful information about the blood temperature and blood flow. The information obtained from the same measurement for thermally insulated skin is more significant. In the present study, noncontact measurement of the temperature of thermally insulated skin was performed, using a teflon cylinder with an infrared fiber which was applied on the skin of the hand. The fiber transmitted part of the infrared radiation emitted from the skin to an infrared radiometer. Preliminary results show that thermally insulated skin temperature can be obtained from measurements of the partial radiation transmitted through the thermal insulation device which was applied to the skin, and that this temperature is related to tissue blood flow more than uncovered skin temperature.
Several parameters of the cardiovascular system such as heart rate, arterial blood pressure and blood flow fluctuate spontaneously. These fluctuations are related to the autonomic nervous system activity. In particular the low frequency fluctuations are mediated by the sympathetic nervous system. In the cuttent study, the low frequency fluctuations of the tissue blood volume and the blood volume pulse in the fingertips of healthy subjects were investigated using photoplethysmography (PPG). The baseline of the PPG signal (BL) is inversely related to tissue blood volume so that the parameter BV, defined by: BV equals Const. minus BL is directly related to the blood volume. The amplitude (AM) is directly related to the systolic blood volume increase. For most of the examinations BV and AM show positive correlation but in some examinations the two parameters were inversely correlated. PPG measurements performed in near infrared radiation, showed better correlation between BV and AM than for red light PPG. The results show that several mechanisms are involved in the low frequency fluctuations in the tissue blood volume. The analysis of the PPG signal provides, therefore, a potential tool for studying the mechanism of the regulation of the microcirculation by the sympathetic nerves.
Several methods have been developed for the qualitative and quantitative measurement of breathing effort. The most useful kind of breathing pattern monitor includes devices for recording chest and abdomen dimension changes, such as impedance plethysmography and respiratory induction plethysmography. These devices can measure the tidal volume in relative terms, and even measure it in absolute terms after suitable calibration. In this study a novel method for measuring chest circumference based on an optical fiber is presented. The sensor is based on the measurement of light transmitted through a bent optical fiber, which is connected to an elastic band, wrapped around the chest, and whose radius of curvature changes due to the respiratory act. The amount of transmitted light is related to the radius of curvature of the fiber which depends on the chest circumference. The output of the respiratory sensor was checked qualitatively by changing the respiration rate and depth. The changes in breathing effort were clearly demonstrated in the sensor output recording. The respiratory effort was also correlated with the heart rate, measured by photoplethysmography. Statistically significant correlation was found between the lungs' volume and the heart rate, but the correlation coefficient was not high.
The variability in heart rate is related to the activity of the autonomic nervous system, which influences the heart rate either directly or via the peripheral circulation. In this study direct measurement of peripheral circulation parameters and their variability was obtained by means of photoplethysmography which provides assessment of the blood volume in the tissue and its increase during systole by measuring the light absorption in the tissue. Both blood volume and systolic blood volume increase showed oscillations in very low frequency, about 0.02 Hz and in relative high frequency, about 0.3 Hz, which is related to respiration. In comparison to the variability of the heart rate the high frequency oscillation has lower amplitude but the low frequency oscillation is much higher.
The temperature increase of thermally insulated skin provides useful information about its blood flow and the blood temperature. The measurement of skin temperature by a contact thermometer, such as a thermistor, is not accurate, because it depends on the pressure exerted on the skin by the thermometer. In order to have reproducible measurement of the skin temperature, noncontact temperature measurement is preferable. Suitable insulation is achieved by using a cylinder of lowthermal-conductivity material, covered by polyethylene layers, which is applied on the skin. The polyethylene layers permit partial transmission of the infrared radiation through it. Preliminary results show that both the transient and the steady-state temperature increase can be obtained from measurements of radiation transmitted through the thermal insulation that was applied to the skin, and that the steady-state temperature increase is more closely related to tissue blood flow than the uncovered-skin temperature is.
The temperature of uncovered skin does not provide useful information about the blood temperature and blood flow. The information obtained from the same measurement for thermally insulated skin is more significant. In order to measure the temperature of thermally insulated skin, a teflon cylinder, covered by polyethylene layers, was applied on the skin of the hand. The polyethylene layers permit partial transmission of the infrared radiation through it. Preliminary results show that underskin temperature can be obtained from measurements of radiation transmitted through the thermal insulation which was applied to the skin, and that underskin temperature is related to tissue blood flow more than uncovered skin temperature.
A device for the recording of the photoplethysmographic (PPG) signal, which filters the dc value without distorting the pulse shape, was developed. PPG measurements were performed on the finger of the left hand while the right hand exerted a static muscle stress. The amplitude and the period of the PPG signal decreased when the other hand was raised to above heart level, and when it exerted a handgrip stress. These effects are associated with increased activity of the sympathetic nervous system.
A photoplethysmography (PPG) device, which filters the dc signal without distorting the pulse shape, was developed. Measurements were performed on the finger, for hand at heart level, below and above it. The PPG signal was highest above heart level, and lowest below heart level. It seems that the compliance and the resistance of the blood vessels influence the PPG curve.
Measurement of uncovered skin surface temperature by measuring the infrared radiation emitted from the skin does not provide useful information about the blood temperature and blood flow. The information obtained from the same measurement for thermally insulated skin is more significant. The skin is insulated by a special device, which permits partial transmission of the infrared radiation through it. Preliminary results show that skin blood flow and under-skin temperature can be assessed from measurements of radiation transmitted through the thermal insulation which was applied to the skin.
We present a new type of intensity-modulated sensor based on a coated lightguide. Using a physical model of the coated lightguide the output light intensity was computed as a function of the reflection and transmission complex coefficients at the substrate-film and film-ambient interface. Based on these theoretical results an experimental setup for measuring various parameters of a liquid was constructed. The results demonstrate the dependence of the output signals on the characteristics of the substrate-film-ambient system. In particular the output signal increases for some incidence angles as the refractive index of the ambient medium increases.
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