A prototype device for standardized calibration of pulse oximeters

OBJECTIVE

To develop and test a method for standardized calibration of pulse oximeters.

METHODS

A novel pulse oximeter calibration technique capable of simulating the behavior of real patients is discussed. It is based on an artificial finger with a variable spectral-resolved light attenuator in conjunction with an extensive clinical database of time-resolved optical transmission spectra of patients fingers in the wavelength range 600-1000 nm. The arterial oxygen saturation of the patients at the time of recording was derived by analyzing a corresponding blood sample with a CO-oximeter. These spectra are used to compute the modulation of the light attenuator which is attached to the artificial finger. This calibration method was tested by arbitrarily playing back recorded spectra to pulse oximeters and comparing their display to the value they displayed when the spectra were recorded.

RESULTS

We were able to demonstrate that the calibrator could generate physiological signals which are accepted by a pulse oximeter. We also present some experience of playing back recorded patient spectra. The mean difference between the original reading of the pulse oximeters and the display when attached to the calibrator is 1.2 saturation points (displayed oxygen saturation SpO2) with a standard deviation of 1.9 saturation points.

CONCLUSIONS

The tests have shown the capabilities of a spectral light modulator for use as a possible calibration standard for pulse oximeters. If some improvements of the current prototype can be achieved we conclude from the experience with the device that this novel concept for the calibration of pulse oximeters is feasible and that it could become an important tool for assessing the performance of pulse oximeters.

A prototype device for standardized calibration of pulse oximeters II

OBJECTIVE

There is no commonly accepted in vivo calibration method for pulse oximeters available up to now. On the basis of a prototype device for the calibration of pulse oximeters which was introduced recently, a second approach based on the same concept was tackled in order to design a reliable method for standardized calibration of pulse oximeters.

METHODS

An extensive clinical database of time-resolved optical transmission spectra of patient fingers is used to simulate the behavior of patients. A device which is capable of playing back these spectroscopic data to pulse oximeters, and a database where the oxygen status measured with the reference method (Co-Oximetry) is stored, are the main parts of the concept. The playback device has an artificial finger as interface to the pulse oximeters and serves to collect light from the pulse oximeter for analysis and to playback simulated light to the pulse oximeter. The light intensity emitted by two LEDs which illuminates the pulse oximeter detector is controlled via a computer in such a way that it is the same as if the pulse oximeter light had passed the finger. The pulse oximeter display during the data playback can thus be compared to the true SaO2 of the patient. The device is tested with 4 pulse oximeters based on 100 patient spectra.

RESULTS

For the four pulse oximeters used in this investigation, an Agilent Technologies CMS monitor (formerly Hewlett-Packard), an Ivy 2000 with Masimo Set technology and Nellcor N-3000 and N-395, there is good correlation between SPO2 and SaO2, and mean and standard deviation of in vivo SpO2-SaO2 and playback SpO2-SaO2 are in good agreement. For two instruments, Nellcor N3000 and Agilent CMS Monitor, a quantitative comparison between the in vivo and in vitro SpO, results was derived. A mean of the deviation playback vs. in vivo SpO2 is less than 0.5% SpO2. The error limits are comparable with the calibration error of the conventional calibration routine. The device is also capable of data playback even in situations with rapid desaturation changes, as displayed in Figure 2. For the other tested pulse oximeters the results are comparable.

CONCLUSIONS

Compared to the first prototype the current version is simpler and less expensive in production. Many of previously existing problems are solved and the applicability to a large variety of pulse oximeters and sensors is given. The novel concept for the calibration of pulse oximeters is a tool for assessing the performance of pulse oximeters.

Neonatal sucking as a clinical assessment tool: preliminary findings

The sucking patterns of 42 healthy full-term and 44 preterm infants whose gestational age at birth was 30.9 +/- 2.1 weeks were compared using the Kron Nutritive Sucking Apparatus for a 5-minute period. The measured pressures were used to calculate six characteristics of the sucking response: maximum pressure generated, amount of nutrient consumed per suck, number of sucks per episode, the duration or width of each suck, the length of time between sucks, and the length of time between sucking episodes. The maximum pressure of the term infant (100.3 +/- 35) was higher, p less than .05, than the maximum pressure of the preterm infant (84 +/- 33). Term infants also consumed more formula per suck (45.3 +/- 20.3 vs. 37.6 +/- 15.9, p less than .05). In addition, they had more sucks/episode (13.6 +/- 8.7 vs. 7.7 +/- 4.1, p less than .001) and maintained the pressure longer for a wider suck width (0.49 +/- 0.1 vs. 0.45 +/- 0.08, p less than .05). Sucking profiles of the preterm infant are significantly different from the full-term infant. These sucking profiles can be developed as a clinically useful tool for nursing practice.

Diagnostic value of knee extension torque tracings in suspected anterior cruciate ligament tears

The purpose of this study was to determine the diagnostic accuracy of knee extensor muscle torque tracings in patients suspected of having damage to the anterior cruciate ligament of the knee joint. The knee extensor torque tracings of 30 patients suspected of having anterior instability of the knee joint were reviewed independently for abnormalities believed to be associated with anterior cruciate ligament damage. These results were compared blindly with an arthroscopic evaluation. The diagnostic accuracy of the torque tracing approach was determined by calculating the prevalence, sensitivity, specificity, and positive and negative predictive values. The sensitivity and specificity were calculated to be 25.0% and 85.7%, respectively. These results suggest that the curve patterns examined in this article have poor diagnostic accuracy and are of little benefit as a clinical diagnostic aid.