Chest
Volume 91, Issue 3, March 1987, Pages 333-337
Journal home page for Chest

Validity of Ear Oximetry in Clinical Exercise Testing

https://doi.org/10.1378/chest.91.3.333Get rights and content

Because of suspicion that the ear oximeter might measure the oxyhemoglobin saturation of arterial blood inaccurately during heavy exercise, we made concurrent ear oximetric and blood measurements on 14 consecutive patients with arterial catheters during clinical exercise tests. After correcting for carboxyhemoglobin, the estimated and measured values for the oxyhemoglobin saturation of the blood agreed well, as did resting ear and blood values; however, during heavy exercise, ear oximetric values were falsely elevated in two patients with interstitial pulmonary disease and were falsely depressed in five patients with cardiovascular limitation to exercise. In another patient, ear oximetric values declined during heavy exercise despite mild hyperoxia, suggesting hypoperfusion of the ear. Considering the clinical and physiologic importance of oxyhemoglobin saturation, ear oximetric values during heavy exercise should be cautiously interpreted.

Section snippets

MATERIAL AND METHODS

This analysis includes 14 patients, all recently referred to our laboratory for clinical exercise testing, in whom we obtained concurrent data from both a brachial arterial catheter and an ear oximeter (Biox IIA). Prior to exercise, each patient was interviewed, examined by a physician, and received a chest roentgenogram, resting test of respiratory function, and resting 12-lead electrocardiogram. Informed consent was obtained.

After rubbing the external ear briskly for 15 to 20 seconds with an

RESULTS

During rest and unloaded cycling, the 28 simultaneous ear oximetric and blood oximetric values for oxyhemoglobin saturation were not significantly different (96.6±0.28 percent vs 96.5±0.37 percent; t = 0.333; p>0.5); however, comparison of the blood and ear oximetric values obtained during the highest tolerated work rates revealed striking discrepancies in some patients. We divided the patients into three groups, based on the pattern of late-exercise ear oximetric response (Table 1). Group A

DISCUSSION

We obtained good agreement between the estimated and measured blood oxyhemoglobin saturation. This occurred despite the relatively high concentration of carboxyhemoglobin found in many of our patients. When the blood oximetric measures are properly corrected for the hemoglobin unavailable for oxygenation because of carbon monoxide, the direct blood estimates and measures of oxyhemoglobin saturation show no systematic differences. Previous studies have identified the importance of

ACKNOWLEDGMENT

We thank Dr. Stan Siu and Ms. Concepcion Enriquez for professional and technical assistance and Ms. Barbara Young for preparation of the manuscript.

References (0)

Cited by (0)

Manuscript received June 23; revision accepted September 6.

Estimation of oxyhemoglobin saturation by measurement of arterial oxygen pressure and pH with use of the Severinghaus15 equation has been determined to be, in general, less accurate than direct blood oxygen saturation measurement. Nevertheless, comparison of the estimated (by Radiometer blood gas analyzer) and measured (by IL CO-oximeter) oxygen saturation of available hemoglobin in the 64 samples of arterial blood showed a mean difference of only 0.4 percent. The differences at measured saturation of carboxyhemoglobin of 5.0 to 7.1, 4.0 to 4.9, 3.0 to 3.9, 2.0 to 2.9, 1.0 to 1.9, and 0.0 to 0.9 percent were 0.4, 0.5, 0.5, 0.5, 0.5, and 0 percent, respectively. This comparison, with a correlation coefficient of 0.95, confirms the accuracy of the direct measurement of oxygen saturation of available hemoglobin in these patients' arterial blood. In contrast, there was a mean difference of 2.3 percent when the comparison between estimated and measured oxyhemoglobin saturation was made without correcting for carboxyhemoglobin.

View full text