Pulse oximeter signal at various blood flow conditions in an in vitro model.
Explore the source record for details and available documents.
Hematocrit↗
Biomedical subjects
L G Lindberg
Publications and source records attributed to L G Lindberg.
Pulse oximetry--clinical implications and recent technical developments.
The pulse oximeter has been shown to be a reliable monitor of arterial oxygen saturation and has therefore been recommended as mandatory monitoring for patients during anaesthesia and intensive care. In 1989 two review articles on pulse oximetry were published (1, 2) and two years ago Severinghaus and Kelleher summarized the literature between 1989 and October 1991 (3). Our aim is to focus the discussion on technical aspects and applications of pulse oximetry with special attention centered on recent developments. This review is consequently an update on pulse oximetry since the end of 1991, and the first on technically-based publications in the two last decades.
Animals↗
Presentation and evaluation of a new optical sensor for respiratory rate monitoring.
A new optical sensor for respiratory rate monitoring was simultaneously compared with an acoustic sensor and a transthoracic impedance plethysmograph during normoventilation in the respiratory rate range of 9-17 breaths per minute. The response characteristics of the optical sensor were then measured during simulation of central apnoea and tachypnoea. Visual observation was chosen as the reference method for monitoring the respiratory rate. The measurements were performed in ten healthy volunteers and the respiratory signals recorded on an analogue tape and strip-chart recorder and analysed off-line. The response characteristics of the fibre optic sensor corresponded well with those of the acoustic sensor and impedance plethysmograph. All three methods responded rapidly to an apnoeic event.
Adult↗
Accuracy of pulse oximetry at various haematocrits and during haemolysis in an in 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.
Hematocrit↗
Monitoring of respiratory and heart rates using a fibre-optic sensor.
A new method, which uses a fibre-optic probe to monitor respiratory and heart rates simultaneously, has been developed and evaluated. The results provide evidence that it is possible to monitor respiratory and heart rates using the reflection mode of photoplethysmography (PPG). The fibre-optic probe makes it possible to monitor from different sites on the patient, and the method is convenient to use. In addition, the probe is X-ray transparent, insensitive to electromagnetic interference (e.g. during MRI investigation) and may be made very light and small. Therefore the method is suitable for the observation of both adults and neonates, in hospitals as well as in other environments.
Adult↗
Photoplethysmograph from a laser source.
Explore the source record for details and available documents.
Blood Flow Velocity↗
The influence of changes in blood flow on the accuracy of pulse oximetry in humans.
Oxygen saturation (SpO2) was measured with a pulse oximeter in ten healthy, young men breathing air. A pulse oximeter probe was attached to the second toe and a laser Doppler probe to the first toe of the same foot for measurement of changes in peripheral blood flow. The pulse oximeter and laser Doppler readings were simultaneously compared when the foot was positioned 40 cm (position 1) above heart level, elevated 10 cm (position 2) above heart level and horizontally at heart level (position 3). Using this experimental human model, we achieved various blood flows. The AC and DC optical signals used for determination of oxygen saturation were recorded from the pulse oximeter and analysed. There was a significant increase (P less than 0.05) between position 1 and 3 in blood flow as measured by the laser Doppler flow meter. The corresponding pulse oximeter readings of haemoglobin saturation also increased significantly (P less than 0.05) comparing these two leg positions. Analysing the AC- and DC optical signals, the AC value of infrared light increased considerably, while the AC value of the red light decreased slightly. The DC values of red and infrared light did not change significantly. In summary, when blood flow was decreased, the ratio of red to infrared transmitted light was changed, resulting in a low SpO2 reading.
Adult↗
The accuracy of pulse oximetry at two haematocrit levels.
The object of this study was to investigate the influence of haematocrit on the accuracy of pulse oximetry. Seven Swedish land race rabbits were studied. The oxygen saturation of haemoglobin was decreased step-wise using increasing fractions of nitrogen to the inspiratory gas. One pulse oximeter probe was attached on the front leg and another probe directly over the common carotid artery. The pulse oximeter readings (SpO2) were compared with simultaneous oxygen saturation analysis (SaO2) by a haemoximeter. The pulse oximeter measurements were performed at the haematocrit levels of approximately 40% and 11%, respectively. We found a good correlation between SpO2 and SaO2 in a wide range of the oxygen saturation, i.e. SaO2 26-100%. After haemodilution the correlation was improved in the range 86-100%, but not in the range 26-85%. No correlation between SpO2 and SaO2 was found when the sensor was attached directly over the artery during normal haematocrit levels. After haemodilution a better correlation was however obtained. These results indicate that the accuracy of pulse oximetry is dependent on the haematocrit level.
Animals↗
Nuclear DNA ploidy in mammary carcinomas; using nuclear size as co-parameter reveals more complex patterns.
Static DNA measurements using nuclear size as a co-parameter have been made on cell populations from 106 consecutive patients with proper imprints from fresh tumour tissues or fine-needle aspirates. When DNA content is plotted against the nuclear size of each individual cancer cell in a scatter diagram, different patterns are found. These patterns indicate the presence of subpopulations, which may be overlooked using conventional flow cytometric analysis or other techniques relying only on the nuclear DNA content. The presence of these subpopulations might, in addition, interfere with a correct definition and estimation of the percentage of S-phase cells.
Breast Neoplasms↗
Photoplethysmography. Part 1. Comparison with laser Doppler flowmetry.
Photoplethysmography (PPG) and laser Doppler flowmetry (LDF) were compared and evaluated. The comparison was accomplished considering differences in physical principles and geometrical and optical conditions. Changes in human skin perfusion were induced by cold and hot water provocation on limited areas of the finger and the forearm. The results showed that LDF and PPG, using red light at 630-660 nm and a commercial PPG probe, were in general equally sensitive in detecting a blood perfusion increase following a skin temperature elevation. However, we also found that PPG occasionally showed an inverse response to a skin temperature elevation, especially in finger skin. Furthermore, the study indicated that laser light is unsuitable as a light source in PPG using optical fibres of small diameter and with no fibre separation. It was also found that the physical dimensions of the probe (including the light source and photodetector) play an important role in determining the measuring volume and the quality of the signal.
Hot Temperature↗
Photoplethysmography. Part 2. Influence of light source wavelength.
When the microvascular blood perfusion in human skin is measured by photoplethysmography (PPG), infra-red light (800-960 nm) is normally used as the light source. The PPG signal, which consists of a pulsatile (AC) and a slowly fluctuating (DC) component, was studied at different optical wavelengths utilising optical fibres for guiding the light to and from the skin surface. Finger and forearm skin was examined and high and low skin blood perfusion was brought about by local water-induced temperature provocation. The analysis of the measurement results provided evidence that the use of shorter wavelengths in PPG (AC) for monitoring skin perfusion changes could be applicable. The use of different optical wavelengths also raises the possibility of recording perfusing changes at different depths in the superficial tissue. The sweat water content in stratum corneum of human skin will probably determine the total amount of reflected and backscattered radiation reaching the photodetector. This is important when the skin perfusion is changed by alterations in the environmental temperature conditions activating the sweat glands in tissue. Temperature-dependent optical characteristics of blood-free skin tissue may explain the limited ability of the DC component of PPG to monitor skin perfusion changes.
Hot Temperature↗
Basic studies of pulse oximetry in a rabbit model.
We have developed an animal model for the evaluation of pulse oximetry during severe hypoxaemia. Twelve rabbits were anaesthetized and mechanically ventilated via a tracheostomy tube. Increasing fractions of nitrogen were added to the gas mixture they inhaled to obtain severe hypoxaemia (saturation range 26%-100%). On 412 occasions, simultaneous pulse oximeter (SpO2) and invasive haemoximeter (SaO2) measurements were compared. The regression analysis of the data gave the equation: y = 0.7 x + 26.7, r = 0.90. In the SaO2 range less than or equal to 85%, the bias (mean value of SaO2-SpO2) was higher when compared with SaO2 greater than 85%. In an in vitro study the light absorption characteristics of rabbit haemoglobin (Hb) were compared to human Hb. The millimolar extinction coefficients of both reduced and oxygenated Hb from rabbits were found to be similar to human Hb. We consider the animal model (rabbit) suitable for studies of pulse oximetry during physiological and pathophysiological conditions.
Animals↗
Diagnosis of cystic hydatid disease: role of aspiration cytology.
Fine needle aspiration of mass lesions is reported in eleven patients in whom cystic hydatid disease (CHD) was not a differential diagnosis or whose serological results were negative. Aspiration was continued until no more fluid could be obtained. In five patients aspiration was done under ultrasound guidance. No sequelae were observed that could be attributed to aspiration per se. Aspirated fluid was stained with haematoxylin and eosin and giemsa or was passed through 5 micron polycarbonate filters which were then stained in the same way. The aspirated material and polycarbonate filters were also stained with trichrome which proved the best stain to demonstrate the acid-fast hooklets. Such filtration of the total volume of the aspirated material or that evacuated at operation is simple, quick, and accurate.
Adult↗
[Comparison of laser Doppler flowmetry and plethysmography].
Explore the source record for details and available documents.
Adult↗
A retrospective clinico-pathologic study of non-Hodgkin's lymphomas classified according to the nomenclatures of Lennert and of Rappaport.
The survival of 88 patients treated for non-Hodgkin's lymphoma 1972-73 have been reviewed. In 49 patients it was possible to do a re-classification of the lymphomas according to Rappaport's and Lennert's classifications. The main obstacle to the classification according to Lennert was inadequacy of the cyto-pathological material. The correlation between survival and pathology was studied and a comparison between the two classifications was made. Lennert's classification was found to have a good reproducibility and to be more accurate than Rappaport's in separating lymphomas with favourable prognosis from those with unfavourable.
Adult↗
A case of papillary-cystic epithelial neoplasm of the pancreas.
A 16-year-old girl presented with a left-sided abdominal mass. X-ray examination and computed tomography disclosed a well-defined tumor close to the tail of the pancreas, stretching the pancreatic branches from the splenic artery as demonstrated by arteriography. Ultrasonography suggested a partly cystic character. Cytologic fine-needle biopsy, histopathological and electron microscopical examination disclosed a cysto-papillary tumor, probably benign, and of an exocrine, ductular origin, and with pseudo-cystic areas similar to those found in adenoid cystic carcinoma of salivary glands. Immunohistochemistry did not demonstrate the presence of polypeptide hormones. The patient is without signs of tumor recurrence 18 months after operation.
Adolescent↗
Fine-needle-aspiration cytodiagnosis of recurrent malignant melanoma.
Sixty-four patients with melanoma (28 with clinical stage I disease and 36 with clinical stages II through IV disease) were fine-needle biopsied on suspicion of recurrent melanoma. Eighty-four biopsies were aspirated percutaneously and three at exploratory laparotomy. A tumor mass was present at 81 biopsies. The remaining biopsies were taken with the guidance of liver scan or fluoroscopy. In the patients with the diagnosis of recurrent malignant melanoma the cytodiagnosis was correct in 45 patients out of 47. One patient was diagnosed as breast cancer and one as malignant mesenchymal tumor. Of 40 biopsies considered normal, three were revised to be melanoma. No false-positive diagnosis was found. The frequency of false-negative diagnosis was 6%. Fine-needle-aspiration cytology is a suitable method to establish a correct diagnosis when there is a suspicion of recurrent disease during the follow-up of melanoma patients. The high diagnostic accuracy in patients with enlarged lymph nodes is excellent and makes the method preferable to diagnostic surgical excision biopsies.
Biopsy, Needle↗
The impact of cytological screening on the incidence of invasive cervical cancer.
A cytological screening program for the early detection and prevention of cervical cancer was started in the county of Malmöhus, southern Sweden in 1967. The incidence of invasive cervical cancer among women properly attending the screening program has been reduced over the 10 years to about one quarter of the incidence before the initiation of the program. Figures calculated from the whole female population, however, did not indicate a significant decrease in incidence. Adequate individual follow-up combined with computerized administrative programs and population registers seem to be necessary whenever the effects of a mass screening program are evaluated.
Adult↗