Accuracy of ambulatory blood pressure determination: a comparative study.

This study was designed to discriminate, according to their accuracy, between three ambulatory pressurometers (Diasys 200R, Novacor; P IV, Del Mar Avionics; SpaceLab 90202, SpaceLab). The evaluation was performed against invasive arterial reference measurements. Accuracy was assessed by calculating the error on pressure (EOP) as the difference between invasive and non-invasive measurement of arterial blood pressure. For the systolic values, accuracy (mean of EOP differences) and uncertainty (SD of these differences) were -0.9 +/- 9.7, -4.3 +/- 10.1 and -16.7 +/- 10.1 mmHg for, respectively, Diasys, PIV and SpaceLab. For diastolic values, they were, respectively, 5.9 +/- 6.7, 6.8 +/- 8.5 and 9.1 +/- 6.6 mmHg. EOP was then separated in two different types of errors: (i) the error of dispersion appreciated by the index of homogeneity calculated by a Lehmann analysis and leading to a statistical classification (ii) the error due to the drift of EOP with the reference value, this last error being easier to correct. Two different behaviours were observed for the EOP: (i) the drift of EOP of systolic values was significantly larger for the oscillometric (SpaceLab) than for the auscultatory (Diasys and P IV) method, with no difference between Diasys and P IV (ii) the homogeneity index was not statistically different among these three devices. These data suggest that, in case the correction of the drift of EOP is carried out, there is no statistical significant difference in accuracy between these three pressurometers. However, in our experimental conditions, the two ambulatory pressurometers recording the Korotkoff sounds have a better accuracy than the one using the oscillometric approach.

Accuracy of pulse oximetry during moderate exercise: a comparative study.

This study was designed to discriminate, according to their accuracy, between eight pulse oximeters (PO) using a realistic evaluation performed by means of a moderate exercise to provide artefacts and thus represent a typical clinical situation. Accuracy was assessed by calculating error on saturation (EOS) as the difference between simultaneous measurement of non-invasive (SpO2) and invasive functional (SfO2) arterial blood oxygen saturation. An index of homogeneity of EOS (InH), calculated using a Lehmann analysis, was chosen as a representative of error dispersion, leading to a statistical classification; the influence on error introduced by the drift of EOS with SfO2 was thus eliminated. We obtained a clear-cut separation of the eight PO (Datex Satlite (DA), Kontron 7840 (KO), Nellcor 200 (NE), Novametrix 505 (NO), Ohmeda 3700 (OH), PPG-Hellige (PP), Physiocontrol 1600 (PH), and Radiometer Oxi (RA] into two statistically different subgroups by comparing their InH standard deviation (SD). There is a highly statistically significant difference between the accuracy measured for the high precision subgroup with an InH SD ranging from +/- 1.6 to +/- 1.9% SaO2 (DA, PH, and RA), and that measured for the low precision subgroup whose InH SD ranges from +/- 2.8 to +/- 5.0% SaO2 (NE, OH, NO, KO, PP). These results suggest that, in our clinical conditions, there is a wide range of inhomogeneity of error from one PO to another. The error introduced by the drift of EOS with SfO2 should be considered separately.