A pocket calculator program for non-invasive bedside assessment of cardiorespiratory function

A pocket calculator program has been written for the rapid bedside evaluation of cardiorespiratory function. The unique features of this program are that it makes use of recently available non-invasive techniques for measurement of arterial oxygen saturation and mixed venous P_CO2. This enables calculation of pulmonary venous admixture and mixed venous oxygen saturation without the need for central venous or pulmonary artery catheterization. If the ventilation and respired gas concentrations are also measured, cardiac output and alveolar ventilation can be expressed in litres per minute, and the dead space: tidal volume ratio calculated.     

Measurement of oxygen saturation in venous blood by dynamic near infrared spectroscopy

A method for the measurement of oxygen saturation in the venous blood, SvO2, based on optical measurements of light absorption in the infrared region is presented. The method consists of applying relatively low external pressure of 25 mm Hg on the forearm, thereby increasing the venous blood volume in the tissue, and comparing the light absorption before and after the external pressure application. SvO2 has been determined from light absorption measurements in two wavelengths, before and after the pressure application, using a formula derived for two adjacent wavelengths. The method has been applied to the hands and fingers of 17 healthy male subjects, using wavelengths of 767 and 811 nm. SaO2, the oxygen saturation for arterial blood, was also obtained from photoplethysmographic measurements in these two wavelengths (pulse oximetry) using the same formula. The mean (+/- SD) value of SaO2 was 94.5% (+/- 3.0). The mean value of SvO2 was 86.2% (+/- 4.1) for the finger and 80.0% (+/- 8.2) for the hand. These SvO2 values are reasonable for the finger and the hand where arterio-venous anastomoses exist. The method enables the measurement of SvO2 in the limbs, a parameter which is related to tissue blood flow and oxygen consumption.     

Near-infrared transmittance pulse oximetry with laser diodes

Pulse oximeters are widely used for noninvasive monitoring of oxygen saturation in arterial blood hemoglobin. We present a transmittance pulse oximetry system based on near-infrared (NIR) laser diodes (750 and 850 nm) for monitoring oxygen saturation of arterial blood hemoglobin. The pulse oximetry system is made up of the optical sensor, sensor electronics, and processing block. Also, we show experimental results obtained during the development of the whole NIR transmittance pulse oximetry system along with modifications in the sensor configuration, signal processing algorithm, and calibration procedure. Issues concerning wavelength selection and its implications for the improvement of the transmittance pulse oximetry technique are discussed. The results obtained demonstrate the proposed system's usefulness in monitoring a wide range of oxygen saturation levels.     

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。     

Coronary stent insertion into a 20-year-old Blalock-Taussig Shunt

A 21 year-old female with complex congenital heart disease presented with declining exercise tolerance, presyncope and increasing cyanosis despite regular venesection. Her double inlet left ventricle with rudimentary right ventricle, restrictive ventricular septal defect and pulmonary stenosis had been managed with a Classic Left Blalock-Taussig (B-T) Shunt aged 2 months and a Modified Right B-T Shunt at 4 years. Aortography revealed a patent but significantly narrowed Left B-T shunt with impaired blood flow and an aneurysmal pulmonary artery. Angioplasty and stenting of the shunt was undertaken and a 4.0 x 12mm coronary stent deployed. The patient's arterial oxygen saturation improved from 76% on pulse oximetry to 85% post procedure and she reported significantly improved exercise tolerance upon follow-up.     

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.     

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.     

Non-invasive diagnosis of early pulmonary disease in PECAM-deficient mice using infrared pulse oximetry

Pulse oximetry is a common tool for detecting reduced pulmonary function in human interstitial lung diseases. It has not previously been used in a mouse model of interstitial lung disease. Further, platelet endothelial cell adhesion molecule deficient mice rarely show symptoms until disease is advanced.Using blood oxygen saturation, different stages of disease could be identified in a non-invasive manner. These stages could be correlated to pathology. Collagen deposition, using Picrosirius Red, did correlate with blood oxygen saturation. These studies are the first to show the use of an infrared pulse oximetry system to analyze the progression of a fibrotic interstitial lung disease in a mouse model of the human diseases. Further, these studies show that an early alveolar damage/enlargement event precedes the fibrosis in this mouse model, a stage that represents the best targets for disease analysis and prevention. This stage does not have extensive collagen deposition. Most importantly, targeting this earliest stage of disease for therapeutic intervention may lead to novel treatment for human disease.     

A pocket calculator program for noninvasive assessment of cardiorespiratory function

A pocket calculator program is described which facilitates rapid evaluation of pulmonary function at rest and during exercise. It embodies the Fick Principle applied to carbon dioxide; mixed venous carbon dioxide tension is measured by rebreathing, obviating the need for central venous or pulmonary artery catheterisation. The program is in two parts, Gas Phase and Blood Phase, which may be used separately. The variables calculated include tidal volume, CO2 production, oxygen consumption, respiratory quotient, alveolar ventilation and dead space: tidal volume ratio (Gas Phase); bicarbonate concentration, base excess, veno-arterial CO2 content difference, cardiac output, mixed venous oxygen saturation and pulmonary venous admixture (Blood Phase). Use of the program enables these variables to be calculated rapidly and accurately. Accuracy is improved by the application of equations which correct for alveolar-to-blood tension differences, effects of differing hemoglobin concentrations, arterial oxygen saturations and acid-base abnormalities; these calculations are otherwise very lengthy, time consuming and prone to error. The program allows simple noninvasive measurements to be applied to patients with a wide variety of metabolic, cardiac and pulmonary abnormalities in rest and exercise.     

Recirculation in double lumen catheter veno-venous extracorporeal membrane oxygenation measured by an ultrasound dilution technique

Recirculation is a limiting factor for oxygen delivery in double lumen catheter veno-venous extracorporeal membrane oxygenation (DLVV-ECMO). This study compares three different methods for the determination of the recirculation fraction during double lumen catheter veno-venous ECMO at ECMO flow rates of 150, 125, 100, 75, and 50 ml/kg.min in nine lambs: (1) an ultrasound dilution method, in which the change in ultrasound velocity in blood after injection of a saline bolus as a marker is used for determination of recirculation; (2) an SvO2 method using real mixed venous blood oxygen saturation, the gold standard, for determination of recirculation fraction; and (3) the CVL method, in which oxygen saturation of a blood sample of the inferior vena cava is considered to represent mixed venous oxygen saturation. In all methods, the recirculation fraction increased with increasing ECMO flow rate. The correlation coefficient between the ultrasound dilution method and the SvO2 method was 0.68 (p < 0.01); mean difference was -2.4% (p = 0.6). Correlation coefficient between the ultrasound dilution method and the CVL method was 0.48 (p < 0.01); mean difference was -18.1% (p < 0.01). The correlation coefficient between the SvO2 method and the CVL method was 0.51 (p < 0.01); mean difference was -15.7% (p < 0.01). The ultrasound dilution method is a useful method for measurement of the recirculation fraction in DLVV-ECMO and is easier to use than the other methods.     

无线传输在脉搏血氧饱和度无创监测中的应用

随着光电子技术的快速发展,基于光电检测原理的血氧饱和度在线测量方法得到了广泛研究。本文对传统双波长透射式血氧饱和度测量方法进行了改进,并在系统中应用了无线数字信号传输和数据小波处理方法。经实验验证,基于以上原理提出的脉搏血氧饱和度检测方法和无线数字信号传输方法,有效地消除了非血氧成分与其他干扰因素对测量结果的影响,并且突破了测量的空间限制。     

自适应脉搏氧系统设计与实现

介绍一种自适应脉搏氧测量系统,使用模拟开关切换反馈电阻阻值,粗调系统增益;通过前级反馈调节MCU的DA输出,改变恒流驱动大小,微调系统增益。在两种机制协调下,实现系统增益精确控制,实现信号的宽范围测量,满足在低灌注指数下对弱脉搏的信号采集,并实现脉率、灌注指数、血氧饱和度的精确计算。     

Algorithms for automated oximetry along the retinal vascular tree from dual-wavelength fundus images

We present an automated method to perform accurate, rapid, and objective measurement of the blood oxygen saturation over each segment of the retinal vascular hierarchy from dual-wavelength fundus images. Its speed and automation (2 s per entire image versus 20 s per segment for manual methods) enables detailed level-by-level measurements over wider areas. An automated tracing algorithm is used to estimate vessel centerlines, thickness, directions, and locations of landmarks such as bifurcations and crossover points. The hierarchical structure of the vascular network is recovered from the trace fragments and landmarks by a novel algorithm. Optical densities (OD) are measured from vascular segments using the minimum reflected intensities inside and outside the vessel. The OD ratio (ODR=OD600/OD570) bears an inverse relationship to systemic HbO2 saturation (SO2). The sensitivity for detecting saturation change when breathing air versus pure oxygen was calculated from the measurements made on six subjects and was found to be 0.0226 ODR units, which is in good agreement with previous manual measurements by the dual-wavelength technique, indicating the validity of the automation. A fully automated system for retinal vessel oximetry would prove useful to achieve early assessments of risk for progression of disease conditions associated with oxygen utilization.     

Trans-abdominal monitoring of fetal arterial blood oxygenation using pulse oximetry

Pulse oximetry (oxygen saturation monitoring) has markedly improved medical care in many fields, including anesthesiology, intensive care, and newborn intensive care. In obstetrics, fetal heart rate monitoring remains the standard for intrapartum assessment of fetal well being. Fetal oxygen saturation monitoring is a new technique currently under development. It is potentially superior to electronic fetal heart rate monitoring (cardiotocography) because it allows direct assessment of both the fetal oxygen status and fetal tissue perfusion. Here we present the analysis for determining the most optimal wavelength selection for pulse oximetry. The wavelengths we chose as the most optimal are the first in the range of 670-720 nm and the second in the range of 825-925 nm. Further, we discuss the possible systematic errors during our measurements and their contribution to the obtained saturation results. We present feasibility studies for fetal pulse oximetry, monitored noninvasively through the maternal abdomen. Our preliminary experiments show that the fetal pulse can be discriminated from the maternal pulse and thus, in principle, the fetal arterial oxygen saturation can be obtained. We present the methodology for obtaining these data, and discuss the dependence of our measurements on the fetal position with respect to the optode assembly.     

Influence of normothermic cardiopulmonary bypass on body oxygen metabolism during lung transplantation

Studies have demonstrated that cardiopulmonary bypass (CPB) adversely affects pulmonary circulation, which is involved in metabolism in the lung, and that pulmonary circulation after CPB can restore the prostaglandin E2 (PGE2) level mainly standing for levels of key vasostimulators augmented during CPB, which may influence systemic tissue perfusion and body oxygen metabolism. However, in lung transplantation (Lx), pulmonary circulation is restored to the graft, which might induce another CPB reaction. We prospectively examined the influence of CPB on body oxygen metabolism in Lx. Left Lx was successfully performed on 10 dogs (group-on: with normothermic CPB without cardiac arrest, group-off: without CPB; n = 5 vs. 5). At 30 minutes after graft perfusion, the right pulmonary artery and bronchus were clamped. Body weight, donor-to-recipient body weight ratio, and clinical parameters were comparable between the two groups, except for the hematocrit level during CPB. At 90 minutes after graft perfusion, mixed venous oxygen saturation (SvO2) was lower (p < 0.01) and O2 extraction rate (p < 0.01), PGE2 (p = 0.025), and arterial blood ketone body ratio (KBR) (p < 0.01) were higher in group-on than in group-off, whereas these parameters were comparable before graft perfusion between the two groups. O2 consumption and acetic acid were higher in group-on than in group-off, whereas O2 delivery and 3-hydroxy propioic acid were comparable between the groups. In conclusion, Lx during CPB may induce a new inflammatory reaction and influence body oxygen metabolism, contrary to the restoration of pulmonary circulation after CPB.     

Spectral oximetry assessed with high-speed ultra-high-resolution optical coherence tomography

We use Fourier domain optical coherence tomography (OCT) data to assess retinal blood oxygen saturation. Three-dimensional disk-centered retinal tissue volumes were assessed in 17 normal healthy subjects. After removing DC and low-frequency a-scan components, an OCT fundus image was created by integrating total reflectance into a single reflectance value. Thirty fringe patterns were sampled; 10 each from the edge of an artery, adjacent tissue, and the edge of a vein, respectively. A-scans were recalculated, zeroing the DC term in the power spectrum, and used for analysis. Optical density ratios (ODRs) were calculated as ODR(Art)=ln(Tissue(855)Art(855))ln(Tissue(805)Art(805)) and ODR(Vein)=ln(Tissue(855)Vein(855))ln(Tissue(805)Vein(805)) with Tissue, Art, and Vein representing total a-scan reflectance at the 805- or 855-nm centered bandwidth. Arterial and venous ODRs were compared by the Wilcoxon signed rank test. Arterial ODRs were significantly greater than venous ODRs (1.007+/-2.611 and -1.434+/-4.310, respectively; p=0.0217) (mean+/-standard deviation). A difference between arterial and venous blood saturation was detected. This suggests that retinal oximetry may possibly be added as a metabolic measurement in structural imaging devices.     

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.