Investigation of photoplethysmographic signals and blood oxygen saturation values on healthy volunteers during cuff-induced hypoperfusion using a multimode PPG/SpO2 sensor

Photoplethysmography (PPG) is a technique widely used to monitor volumetric blood changes induced by cardiac pulsations. Pulse oximetry uses the technique of PPG to estimate arterial oxygen saturation values (SpO?). In poorly perfused tissues, SpO? readings may be compromised due to the poor quality of the PPG signals. A multimode finger PPG probe that operates simultaneously in reflectance, transmittance and a combined mode called "transreflectance" was developed, in an effort to improve the quality of the PPG signals in states of hypoperfusion. Experiments on 20 volunteers were conducted to evaluate the performance of the multimode PPG sensor and compare the results with a commercial transmittance pulse oximeter. A brachial blood pressure cuff was used to induce artificial hypoperfusion. Results showed that the amplitude of the transreflectance AC PPG signals were significantly different (p < 0.05) than the AC PPG signals obtained from the other two conventional PPG sensors (reflectance and transmittance). At induced brachial pressures between 90 and 135 mmHg, the reflectance finger pulse oximeter failed 25 times (failure rate 42.2 %) to estimate SpO? values, whereas the transmittance pulse oximeter failed 8 times (failure rate 15.5 %). The transreflectance pulse oximeter failed only 3 times (failure rate 6.8 %) and the commercial pulse oximeter failed 17 times (failure rate 29.4 %).     

Accuracy of pulse oximetry at various haematocrits and during haemolysis in anin vitro model

In situations in which it may be impossible and/or unethical to evaluate pulse oximetry in humans, an in vitro model with circulating blood may be a necessity. The main objective was to develop such an in vitro model and, in this model, validate the pulse oximetry technique at various haematocrit levels. The pulsating character of arterial blood flow in a tubing system was simulated by using a specially constructed pressure-regulated roller pump. The tubing system was designed to minimise damage to red blood cells. The pulse oximeter readings (SpO₂) were compared with oxygen saturation analyses by a haemoximeter (SaO₂). The pulse oximetry readings were recorded at various haematocrit levels and during haemolysis in the SaO₂ range 60–100 per cent. At a haematocrit level of 41–44 per cent, there was no correlation between SaO₂ and SpO₂ readings. After diluting the blood with normal saline to a haematocrit of 10–11 per cent, a good correlation between SaO₂ and SpO₂ was found. Following haemolysis, the agreement between SaO₂ and SpO₂ was further improved. Using the developed in vitro model, the results indicate that the accuracy of a pulse oximeter may be dependent on the haematocrit level.     

Dynamic in vivo response characteristics of three oximeters: Hewlett-Packard 47201A, Biox III, and Nellcor N-100

Pulse oximeters (Biox III, Nellcor N-100) and a transmittance oximeter [Hewlett-Packard 47201A (HP)] were compared for SaO2 measurement and responsiveness during dynamic changes in arterial oxygen saturation and heart rate. Five sleep apnea syndrome patients were studied because they had large oscillations in SaO2 and heart rate in sleep. During sleep, each patient exhibited a series of rapid (18.0 +/- 8.3 s, mean +/- SD) oscillations in oxygen saturation (92.1 +/- 2.6% to 74.2 +/- 7.7%). Oxygen saturation measurements were sampled simultaneously from each oximeter by computer (at 2 Hz). Accuracy was assessed by comparing pulse and transmittance oxygen saturation measurements at the peak and trough of each apnea-related oscillation. Oximeter response was defined in terms of the "delay" or absolute time difference between the pulse oximeters and the transmittance oximeter for the determination of the peak and trough saturations. Linear regression analysis was used to establish accuracy and response relationships between pulse oximeter sensors (reusable ear, reusable digit, disposable digit, and disposable nasal sensors) and the transmittance oximeter sensor (reusable ear sensor). Pulse oximeter response delay was highly correlated with heart rate. Pulse oximeter SaO2 measurement and response characteristics varied considerably with sensor type (disposable, reusable) and sensor location (ear, nose, and digit). One must be aware of these differences in clinical and research application.     

Spectrophotometric monitoring of arterial oxygen saturation in the fingertip

A noninvasive oximeter that analyses the oxygen saturation of arterial blood in the fingertip is described. The light, after attenuating the infrared portion to avoid thermal injury, is applied to the fingertip through an optical transmitter made of glass fibres. The transmitted light is transferred to an optical reception system where a spectrophotometric determination of oxygen saturation is performed. The determination is performed by considering only the change in the attenuation of light caused by the inflow of arterial blood into the fingertip. The correlation between the oxygen saturation measured with the present instrument (y) and that with the blood-gas method (x), was y=0·907x+8·592 with a standard deviation and a correlation coefficient of 0·135% and 0·983, respectively. The reproducibility was assessed in a healthy subject by measuring the oxygen saturation repeatedly 60 times. The mean saturation was 95·82±0·675% (mean±standard deviation). The instrument has been useful in monitoring arterial oxygenation in patients with respiratory failure in our intensive-care unit. One of the disadvantages of the instrument is that the measurement is interrupted when the fingertip changes its position against the light beam.     

脉搏血氧饱和度检测中自适应滤波消除运动伪差的方法研究

目的研究脉搏血氧饱和度检测系统中运动伪差的消除方法,以提高脉搏血氧仪检测性能。方法通过脉搏血氧仪中的双光束构造噪声参考信号,利用最小均方自适应滤波法消除运动伪差干扰的影响。结果建立了脉搏血氧饱和度检测中消除运动伪差的计算方法,可成功地从运动伪差中提取正常光电容积脉搏波信号作为计算氧饱和度的依据。结论该计算方法简单,可用于实时处理,且测量结果可靠,为进一步抑制脉搏血氧仪噪声奠定了基础。     

In vitro performance test system for pulse oximeters

An in vitro system was developed capable of testing the accuracy and reproducibility of pulse oximeter readings. The pulse oximeter probe receives signals through a pulsating blood cuvette. The development of the design of the cuvette is described. Using the final design (or ‘model finger’), a comparison is made between readings from a Datex Satlite pulse oximeter (SpO₂) and saturation values obtained by use of a multiwavelength bench oximeter (SaO₂). Linear regression analysis of the data gives SpO₂=0·88 SaO₂+11·2 (r=0·979, p<0·001).     

Computer analysis system of blood oxygen saturation in an animal hypoxia model

An experimental animal hypoxia model has been developed. It consists of two sensors (an in vitro and in vivo model), an experimental device and a computer signal processing system. This method can easily be applied to determine and analyse blood oxygen saturation at various hypoxia levels. It can also be used to evaluate the accuracy of pulse oximetry over a wide range of oxyhemoglobin desaturation levels. The DC and AC components of recorded red and infra-red signals, the dual-wavelength ratio R₁₂ and the reading of a pulse oximeter (SpO₂) can be automatically calculated and displayed on a computer screen. Preliminary results of the animal hypoxia test indicate that the measurements made by the instrument correlate well with the oxygen saturation readings of the automatic blood gas analyser AVL945. The computer analysis system is suitable for repeated estimations in the animal model.     

Prevalence of hypoxemia in under-five children with pneumonia in an emergency pediatrics hospital in Sudan

Context:

Hypoxemia is a common and potentially lethal complication of acute respiratory infection in children under-five, particularly among those with severe disease.

Aims:

The aim of this study was to determine the prevalence of hypoxemia in under-five Sudanese children with pneumonia.

Settings and Design:

A cross-sectional study conducted in a pediatrics hospital in a developing country.

Subjects and Methods:

Data were collected using structured questionnaire and oxygen saturation was measured using a pulse oximeter. Hypoxemia was defined as arterial blood oxygen saturation <90%.

Results:

Of 150 studied patients, 86 (57.3%) were males and 46 (32%) were in the age group 2 to ≤12 months. Of the total number, 42.7% had hypoxemia (with pulse oximeter oxygen saturation <90%), out of them 36 (56.25%) were in the age group <2 months. Of the hypoxic patients, 30 (46.88%) had severe pneumonia, and 7 (10.94) had very severe pneumonia (P < 0.001).

Conclusions:

The prevalence of hypoxemia was 42.7% among the studied population. There was a significant association between the hypoxemia and small age group and very severe pneumonia. In limited resource settings pulse oximeter can be used to correctly identify hypoxemia in under-five children particularly among those diagnosed clinically as very severe pneumonia.     

心电同步在脉搏血氧测试中的应用

本文讨论了血氧饱和度测量中的一种新方法；心电信号的Ｒ波来同步脉表示皮信号，更好地从脉搏波信号中提取物征值。更进一步，根据Ｒ波对脉搏波中平均，提高信噪比，利用平均后的脉搏波计算血氧饱和度，经证明可得到更好的结果。     

Preoxygenation and pulse oximetry may delay detection of esophageal intubation

A case of delayed detection of esophageal intubation is described. Preoxygenation and pulse oximetry were used, and the first indication of tube misplacement was arterial desaturation indicated by the pulse oximeter. The combination of preoxygenation and pulse oximetry may contribute to delays in early detection of endotracheal tube misplacement for the following reasons: (1) preoxygenation results in a pulmonary reservoir of oxygen sufficient to maintain arterial hemoglobin saturation for an extended period of time; and (2) the maintenance of normal arterial saturations for an extended period after inadvertent esophageal tube placement may lead the practitioner to initially seek other causes of declining oxygen saturations. Although pulse oximetry is an acknowledged advance in patient monitoring, it must not be utilized as an early indication of correct endotracheal tube placement.     

反射式血氧饱和度监测仪的设计与应用

目的　设计反射式血氧饱和度监测仪并探讨其可行性及临床应用价值。方法　反射式血氧饱和度监测仪由转换器、驱动器、中央处理模块及液晶显示模块组成 ;由一分三光缆连接反射探头、核心后处理系统及数字显示系统组成 ;利用血液对光辐射吸收 (或反射 )强度成固定测量关系的原理 ,设计反射式血氧饱和度监测仪 ;通过测量 10只白兔在不同氧浓度下 ,以及 2 0例心外科大动脉瘤患者在不同温度下的血氧饱和度 (SaO2 )验证仪器效果。结果　反射式血氧饱和度监测仪的SaO2 与血气及临床一般的血氧饱和度仪监测的SaO2 无明显差异 (P >0 .0 5 )。结论　反射式血氧饱和度监测仪的设计是成功的 ,达到了临床应用要求     

Pulmonary function tests in home medical care

Home medical care for the aged has become important with the increasing population of elderly people in Japan. Home oxygen therapy (HOT) is a representative treatment for aged patients with chronic obstructive pulmonary diseases (COPD) or sequelae of pulmonary tuberculosis. In order to provide appropriate and safe home medical care, the pulmonary function tests need to be performed easily and simply at home. These tests include a pulse oximeter for arterial blood oxygen saturation monitoring in HOT, a peak flow meter or a handy-type spirometer for air way monitoring in asthmatic patients and a handy-type monitor for screening patients with sleep apnea syndrome (SAS). In using a pulse oximeter, the users need to keep in mind that the case is sometimes severe even though the oxygen saturation values are in the normal ranges, and also that, when oxygen saturation is low, high concentrated oxygen exposure sometimes deteriorates hypercapnia in patients with type II respiratory failure. A peak flow meter is not suitable for air way monitoring in patients with COPD or small air way diseases. The handy-type monitor for SAS needs to be improved not to interfere with the patient's natural sleep, and also to provide more simple analysis programs. Doctors should educate patients to go to hospital to see a doctor and to undergo close examinations whenever unexpected abnormal values are obtained. Equipment which can provide high quality test results with easier maneuver ability and analysis needs to be developed in the future.     

Monitoring pulse oximetry via radiotelemetry in freely-moving lambs

This study was aimed at validating the use of a custom-made wireless pulse oximeter in freely moving lambs, using radiotelemetry transmission. First, measurements obtained simultaneously using the new, wireless oximeter and a standard commercially-available pulse oximeter (Nonin 8500) were compared in five lambs during 5min episodes of normoxia, hypoxia and hyperoxia. Correlation between the two oximeters for both SpO(2) and heart rate was very good, regardless of oxygenation conditions. Secondly, the capabilities of our device were assessed during more than 45h of polysomnographic recordings in seven lambs. According to the plethysmographic pulse waveform, reliable SpO(2) values were obtained in more than 85% of recording time. Multiple decreases in SpO(2) were readily observed after spontaneous apneas in preterm lambs. It is concluded that our wireless pulse oximeter performs as reliably as a standard pulse oximeter for monitoring SpO(2) variations in lambs, and offers new perspectives for researchers interested in continuous monitoring of oxygenation throughout sleep stages and wakefulness.     

In vivo assessment and evaluation of lung tissue morphologic and physiological changes from non-contact endoscopic reflectance spectroscopy for improving lung cancer detection

We present a method for lung cancer detection exploiting reflectance spectra measured in vivo during endoscopic imaging of the lung. The measured reflectance spectra were analyzed using a specially developed light-transport model to obtain quantitative information about cancer-related, physiological, and morphologic changes in the superficial bronchial mucosa layers. The light-transport model allowed us to obtain the absorption coefficient (mua) and further to derive the micro-vascular blood volume fraction in tissue and the tissue blood oxygen saturation. The model also allowed us to obtain the scattering coefficient (mus) and the anisotropy coefficient (g) and further to derive the tissue scattering micro-particle volume fraction and size distribution. The specular component of the reflectance signal and the instrument response were accounted for during the analysis. The method was validated using 100 reflectance spectra measured in vivo in a noncontact fashion from 22 lung patients (50 normal tissue/benign lesion sites and 50 malignant lesion sites). The classification between normal tissue/benign lesions and malignant lesions was further investigated using the derived quantitative parameters and discriminant function analysis. The results demonstrated significant differences between the normal tissue/benign lesions and the malignant lesions in terms of tissue blood volume fraction, blood oxygen saturation, tissue scatterer volume fractions, and size distribution. The results also showed that the malignant lung lesions can be differentiated from normal tissue/benign lesions with both diagnostic sensitivity and specificity of better than 80%.     

Pulse oximetry: a new way of determining the heart rate in chicken embryos

 With pulse oximetry it is possible to record the pulse-synchronic variation of the oxygen saturation due to variable blood flow during systole and diastole. In the present study on chicken embryos, the pulse rate based on oximetry was compared with the heart rate recorded by means of ECG. We conclude that the pulse curve detected by means of pulse oximetry can be used to determine the heart rate in chicken embryos between day 12 and day 20 of incubation. Received: 8 April 1997 / Received after revision: 20 June 1997 / Accepted: 26 June 1997     

Multiple-scattering effects in transmission oximetry

To develop an algorithm for the spectrophotometric determination of the oxygen saturation in blood, a model for the transmission of light in a scattering and absorbing medium is developed, taking into account effects of multiple scattering. The computed results obtained by a Monte Carlo simulating program agreed well with those found by experiment. The results were compared with those obtained by the commonly used algorithm of transmission oximetry (based on Lambert-Beer's law) and it was found that the calibration curves obtained by this method were strongly dependent on the haematocrit and thickness of the sample. These curves were less reliable the lower the saturation of oxygen.     

Effect of supplemental nocturnal oxygen on gas exchange in patients with severe obstructive lung disease

We studied the effect of supplemental nocturnal oxygen on blood gases in 15 patients with severe but stable chronic obstructive lung disease (ratio of forced expired volume in one second to forced vital capacity, 37.2 +/- 1.8 [mean +/- S.E.] per cent of predicted; arterial oxygen tension, 50.7 +/- 1.4 mm Hg; and arterial carbon dioxide tension [PCO2], 53.1 +/- 1.5 mm Hg). Sleep variables and measures of gas exchange were determined on two consecutive nights; on the first night the subjects breathed supplemental oxygen, and on the second they breathed room air. Transcutaneous PCO2 was measured with an infrared sensor, and arterial oxygen saturation with an ear oximeter. Breathing of supplemental oxygen sufficient to keep oxygen saturation at or above 90 per cent was associated with only small increases (less than 6 mm Hg) in PCO2 throughout sleep, as compared with values while subjects were breathing room air. The increase in PCO2 occurred early in the night and was not progressive. Only three patients, who were found to have obstructive sleep apnea in addition to obstructive lung disease, had larger increases in PCO2 during sleep and reported morning headaches. We conclude that nocturnal oxygen does not induce clinically important increases in PCO2 during sleep in patients with stable obstructive lung disease and therefore can safely be used to prevent the dangerous consequences of hypoxia.     

Oxygen saturation determined using a novel wavelet ratio surface

A wavelet-based method is presented for oxygen saturation measurement using photoplethysmogram signals from a standard pulse oximeter device. The transform moduli of both red and infrared signals are used to derive a novel wavelet ratio surface. Projection of the pulse component onto this surface allows optimal derivation of oxygen saturation.     

Contactless Multiple Wavelength Photoplethysmographic Imaging: A First Step Toward “SpO<Subscript>2</Subscript> Camera” Technology

We describe a route toward contactless imaging of arterial oxygen saturation (SpO₂) distribution within tissue, based upon detection of a two-dimensional matrix of spatially resolved optical plethysmographic signals at different wavelengths. As a first step toward SpO₂-imaging we built a monochrome CMOS-camera with apochromatic lens and 3λ-LED-ringlight (λ₁ = 660 nm, λ₂ = 810 nm, λ₃ = 940 nm; 100 LEDs λ⁻¹). We acquired movies at three wavelengths while simultaneously recording ECG and respiration for seven volunteers. We repeated this experiment for one volunteer at increased frame rate, additionally recording the pulse wave of a pulse oximeter. Movies were processed by dividing each image frame into discrete Regions of Interest (ROIs), averaging 10 × 10 raw pixels each. For each ROI, pulsatile variation over time was assigned to a matrix of ROI-pixel time traces with individual Fourier spectra. Photoplethysmograms correlated well with respiration reference traces at three wavelengths. Increased frame rates revealed weaker pulsations (main frequency components 0.95 and 1.9 Hz) superimposed upon respiration-correlated photoplethysmograms, which were heartbeat-related at three wavelengths. We acquired spatially resolved heartbeat-related photoplethysmograms at multiple wavelengths using a remote camera. This feasibility study shows potential for non-contact 2-D imaging reflection-mode pulse oximetry. Clinical devices, however, require further development.