Ear Oximeter Research Articles

Effect of isocapnic hypoxia on systolic time intervals in conscious man.

The effects of progressive isocapnic hypoxia on the systolic time intervals were studied in 10 healthy human subjects. We induced hypoxia by a rebreathing method and monitored the arterial oxygen saturation continuously and non-invasively by means of an ear oximeter. Arterial oxygen saturation (SaO2) was allowed to fall to a level of 75 per cent and was then held constant for five minutes. As SaO2 fell, heart rate increased linearly, with a mean increase of 0.83 beats/min per one per cent fall in SaO2. The pre-ejection phase index decreased from a mean of 127.2 ms at full oxygen saturation to 120.1 ms at steady-state hypoxia levels, while the ratio of the pre-ejection phase to left ventricular ejection time decreased from a mean of 0.330 to 0.301. The left ventricular ejection time index increased from 417.4 ms to 429.3 ms, while no statistically significant difference was found in the length of electromechanical systole.

Clinical and physiological manifestations of bronchiolitis and pneumonia. Outcome of respiratory syncytial virus.

The physiological abnormalities and clinical correlates of 32 infants consecutively hospitalized with lower respiratory tract disease from respiratory syncytial virus (RSV) were studied in an attempt to characterized the infant most at risk for the acute and long-term complications of RSV infection. Arterial oxygen saturation (Sao2) determinations were obtained daily by means of an ear oximeter. On admission all infants were hypoxemic with a mean Sao2 of 87% (range, 74% to 95%). The mean of the lowest Soa2 recorded during their hospitalization was 85.5% (range, 53% to 96%). The hypoxemia improved little during hospitalization but showed improvement three to seven weeks later. The severity of the hypoxemia correlated significantly with the duration of viral shedding, occurrence of apnea, respiratory rate, age, and percentage of immature neutrophils. Clinical severity did not correlate with the degree of hypoxemia.

Accuracy sensitivity to carboxyhemoglobin, and speed of response of the Hewlett-Packard 47201A ear oximeter.

We have shown that the Hewlett-Packard 47201A ear oximeter measures arterial O2 saturation within 95 per cent confidence limits of +/- 4 per cent when arterial blood saturation is more than 65 per cent, but at lower saturations the oximeter consistently provides a reading that is too low. The oximeter is sensitive to carboxyhemoglobin, progressively overestimating arterial saturation as carboxyhemoglobin concentration increases from 0 to 18 per cent. The time response is exponential, with a normal time constant of 3 sec, but this is halved in the fast mode or operation.

Accuracy, Sensitivity to Carboxyhaemo-Globin, and Speed of Response of the Hewlett Packard 47201A Ear Oximeter

Accuracy, Sensitivity to Carboxyhaemo-Globin, and Speed of Response of the Hewlett Packard 47201A Ear Oximeter

Ventilatory and waking responses to hypoxia in sleeping dogs

We examined waking and ventilatory responses to acute hypoxia in four dogs during natural sleep. Progressive hypoxia was induced by a rebreathing technique in which alveolar CO2 pressure (PACO2) was held at the eucapnic level. Arterial O2 saturation (SaO2) was measured with an ear oximeter, and sleep stage was determined by electroencephalographic and behavioral criteria. Arousal from eucapnic hypoxia occurred at a SaO2 of 87.5 +/- 2.6% (mean +/- SE) during slow-wave sleep (SWS), and at a SaO2 of 70.5 +/- 3.4% during rapid-eye-movement (REM) sleep (P less than 0.005). The irregular pattern of breathing typical of REM sleep persisted during hypoxia. However linear regression analysis of breath-by-breath instantaneous minute volume of ventilation (VI) against SaO2 revealed regression coefficients in REM sleep that were similar to those found in SWS and wakefulness. This finding contrasts with earlier observations of a decreased response of VI to CO2 during REM sleep. The results indicate that although waking responses to hypoxia are delayed in REM sleep, ventilatory responses remain intact and therefore may be of importance in maintaining adequate ventilation during this stage of sleep.

Calibration of a new ear oximeter in humans during exposure to centrifugation.

An optoelectronic ear oximeter (Hewlett-Packard, model 47201A) was evaluated as a noninvasive method for determining arterial oxygen saturation (SaO2) in human subjects during exposure to various levels of accelerative forces. This physiological calibration involved exposing five subjects, while breathing air and wearing the ear oximeter for 60 s to each of three levels of accelerative forces (3, 5, and 7 G); arterial blood samples were withdrawn concurrently. SaO2 was calculated indirectly from the oxygen tensions (PaO2) measured from the sampled arterial blood with a blood gas analyzer and corrected for pH and base excess. These data were compared, as were similar data taken from the same subjects breathing three different hypoxic gas mixtures while resitng at earth's gravity (1 G). Regression analyses of these data for both experimental groups (a, G exposure, or b, hypoxic exposure), comparing the ear-oximeter SaO2 with the calculated SaO2, showed the ear oximeter to be accurate with correlation coefficients of 0.95 and 0.98, respectively.

Heart rate response to isocapnic hypoxia in conscious man.

We studied the effect of acute progressive hypoxia on heart rate in conscious healthy subjects. The PCO2 was held constant (+/- 1.5 mmHg) midway between the resting end-tidal and mixed-venous levels. Hypoxia was induced by having the subject rebreathe from a small bag so that the PO2 fell at a rate related to the subject's oxygen consumption. Arterial oxygen saturation (Sao2) was measured continuously during the procedure with an ear oximeter. We found that heart rate (HR) was best fitted to an inverse linear relation to arterial oxygen saturation and a power relation to PO2. The range of deltaHR/deltaSao2 was 0.62-1.46 beats/min per 1% fall in Sao2 (mean +/- SE = 0.98 +/- 0.06). There was no relationship between heart rate and ventilatory responses to hypoxia.

Arterial chemoreceptors, ventilation and heart rate in man.

1. Transient changes of heart rate (HR) and ventilation were recorded following step changes in alveolar gas composition in three healthy subjects. From a steady state of normo- or slightly hypercapnic hypoxia (PA,CO2 38-46 torr, PA,O2 50-60 torr) arterial chemoreceptor stimulation was transiently relieved by breathing a CO2-free mixture for two breaths, either pur O2 (causing a fall in PA,CO2 and a rise in PA,O2; O2 test) or a low O2 mixture (causing a fall in PA,CO2 without any change in PA, O2; CO2 test). For both test types ventilation was either allowed to change freely ('free-breathing' tests) or was consciously maintained at the pre-test level by the subjects ('controlled-breathing tests). The circulatory delay from the lungs to the ear was measured with a sensitive ear oximeter. 2. In all 'free-breathing' tests ventilation decreased significantly after a mean latency of 5.2 sec; the average lung-ear circulation time was 4.9 sec. HR increased slightly above pre-test levels in eighty-one of one hundred and four tests of all types, the changes being significant after a latency identical to that of the ventilatory changes. Except in the 'controlled-breathing' CO2 tests this early tachycardia was followed by a decrease in HR within the following 5-6 sec. 3. These findings indicate that the primary effect of withdrawal of arterial chemoreceptor stimulation in conscious man as in the anesthetized animal is tachycardia. The secondary development of bradycardia in 'free-breathing' CO2 tests is probably due to the operation of a lung reflex sensing changes in ventilation. The absence of bradycardia in 'controlled-breathing' CO2 tests and its presence in 'controlled-breathing' O2 tests, finally, suggest that relief of systemic hypoxia causes a slowing of the heart not due to lung reflexes but to some other mechanism which operates with a latency nearly twice as long as the arterial chemoreflex.

COMPARISON OF NON-INVASIVE METHODS OF ESTIMATING OXYGENATION IN INFANTS: TCO2 EAR OXIMETRY

Two non-invasive methods of estimating arterial oxygenation in newborn infants were compared: ear oximetry (Hewlett-Packard 47201A) and transcutaneous oximetry(TCO2) (Roche 5301). 33 infants ranging in weight from 870 to 4000 gm, age from 6 hours to 28 days were studied. In one group of 15 infants, TCO2 was compared with simultaneously determined PaO2 sampled from a temporal or umbilical artery. These values were highly correlated (r=.75, p<.001, Syx=15.5). In a group of 18 infants SaO2, PaO2, and saturation by ear oximetry were determined simultaneously. Correlation between these values was also high (r=.84,p<.001, Syx=8.2). Deviation of non-invasively determined values for oxygenation vs values obtained by direct arterial sampling did not depend on systolic pressure, pH, or length of time the sensor was applied to the subject. Similar results were found in a group of 6 infants where both non-invasive methods were used together. While the ear oximeter gives more precise data and exhibits a less “damped” signal than TCO2, it is more difficult to maintain contact between sensor and subject for long periods of time and is therefore less practical in its present form for use in neonates. Both methods are accurate and practical, and are clinically useful in (1)unstable patients during the onset or recovery from illness, and (2) patients with apnea who lack an umbilical artery catheter.

PATTERNS OF HYPOXEMIA IN INFANTS WITH RESPIRATORY SYNCYTIAL VIRUS(RSV) BRONCHIOLITIS AND PNEUMONIA, MEASURED BY EAR OXIMETRY

The degree and duration of hypoxemia in babies with RSV has not been studied. We used an ear oximeter to measure dally the arterial satuation(% Sat)on 32 infants consecutively admitted with RSV bronchiolitis and pneumonia; median age 2 months. Oximetry readings compared to simultaneous arterial gases gave a correlation coefficient of 0.95, and 0.7 compared to capillary gases. On admission these infants' mean % Sat was 86%(pO2=53 mm Hg), range 75-95%(pO2 41-75). The lowest mean value was not until day 3 and was 85%(pO2 51) with a range of 53-96%(pO2 28-87). The severity of hypoxemia fluctuated in any given day and was prolonged. At discharge the mean % Sat=90%(pO2 60) range 83-98% (pO2 47-113); only 3 infants had values >93%(or >pO2 66). Mean % Sat of 9 infants 3-7 weeks after discharge was 96%(pO2 87), range 93-98%(pO2 66-113). Clinical detection of hypoxemia was difficult. Marked hypoxemia existed without cyanosis. However, severity of hypoxemia correlated with cyanosis, respiratory rate, younger age and % bands. No correlation existed with total WBC, PMNs, nor clinical severity judged by retraction and lethargy. Thus, RSV hypoxemia may be severe, prolonged, and clinically occult. Ear oximetry is a valuable and non-invasive technic in the management of infants with RSV lower respiratory tract disease.

Noninvasive Measurement of Cardiac Function during Exercise, Using Resaturation Curves

The resaturation curve, a noninvasive indicator-dilution test using an ear oximeter to detect rates of change in arterial oxygen saturation during breathing of various concentrations of oxygen, was used to assess cardiac performance in normal subjects and in 108 patients with cardiac valvular disease. Measurements made during exercise included the time constant of resaturation (tau) and beat-to-beat changes in arterial oxygen saturation (the left heart clearance fraction). At maximum rates of voluntary work, patients had a significantly reduced clearance fraction and longer tau than normal subjects. Clearance fraction and tau improved in patients after aortic valve replacement; deterioration occurred in tau and clearance fraction over time in patients treated medically, as compared to normal subjects who showed little change during a ten-year period. Clearance fraction and tau correlated with hemodynamic data obtained during cardiac catheterization. The resaturation curve provides an objective measure of cardiac impairment that can be readily repeated during follow-up of patients with heart disease.

A dual control system for assisting respiration.

A dual control system for assisting respiration was developed. The following features were included: (i) ventilation is controlled by the metabolic rate from continuously measured CO2 output, (ii) physiologic dead space approximated as a linear function of tidal volume is used to estimate alveolar ventilation, and (iii) oxygen concentration in the inspired gas is regulated by the arterial oxygen saturation continuously measured with an ear oximeter.

Use of an ear oximeter to assess lung function.

Values of arterial oxygen saturation were estimated using an ear oximeter while subjects breathed a mixture of 15% oxygen in nitrogen. Results obtained from patients with lung disease were clearly separated from results obtained from normal subjects, and the lowereing of saturation was related to the clinical severity of the disease. Patients with low oximeter readings with 15% oxygen also had low levels of arterial oxygen tension during exercise.

Influence of breathing pattern on oxygen exchange during hypoxia and exercise.

During hypoxia, arterial oxygen saturation (SaO2) measured by ear oximeter shows cyclic fluctuations which are related to the pattern and rate of breathing. Continuous recordings of SaO2 may be corrected for distortion, due to circulatory transport, to yield approximate values for pulmonary end-capillary saturation (Sc'O2). This permits calculation of the corresponding end-capillary PO2 (Pc'O2). We have used this technique to study the effect of spontaneous and imposed breathing patterns on mean Pc'O2, amplitude of Pc'O2 (delta Pc'O2) and minute ventilation (VE). The studies were conducted during mild hypoxia, at rest and exercise. The amplitude of delta Pc'O2 is inversely related to breathing frequency. When frequency is constant, patterns with with prolonged expiration or end-expiratory pauses produce large delta Pc'O2 and greater VE. This effect is reversed with prolonged inspiration or end-inspiratory pauses. Spontaneous breathing patterns produced smaller delta Pc'O2, with lower VE than imposed patterns. These findings are compatible with animal studies which suggest the magnitude of PaO2 fluctuations produced by the breathing pattern may act as a feedback stimulus to ventilation. The breathing patterns, which are spontaneously chosen, produce the minimum delta Pc'O2 and VE.

Ear oximeter calibration using alveolar Po 2 measurements.

An indirect method of calibrating an ear oximeter using alveolar Po2measurements has been tested in 10 normal subjects. An oximeter calibration curve was constructed for each individual subject by comparing the output of an ear oximeter with arterial oxygen saturation calculated from alveolar Po2and PCO2during 10 to 20 seconds of hypoxia produced by breathing low oxygen mixtures in the supine position. Hypoxia is terminated by having the subject breathe oxygen, and it is assumed that arterial saturation reaches 100% and that discrepancies between end-expired and arterial gas tensions due to ventilation-perfusion imbalance, impaired diffusion, and right-to-left shunts are negligible under the conditions of calibration. The accuracy of the indirect calibration method was tested by comparing it with direct calibration using arterial blood samples. It is concluded that the indirect calibration method gives a reasonably accurate measure of arterial oxygen saturation in the range of 25–100%.

AN EAR OXIMETER USING D-C. OPERATIONAL AMPLIFIERS

An ear oximeter was constructed with d-c. operational amplifiers and a conventional two-channel earpiece. The amplifiers are required to provide the necessary signal level for continuous computation of the current ratio, corresponding to an estimate of percentage oxygen saturation.Calibration was effected by analysis of 69 arterial blood samples from 23 patients, the values ranging from 60 to 99% oxygen saturation. With the assumption of a linear relationship between recorder currents (or ratio of two currents, one in each color channel), a regression equation for a straight line was calculated, the points having a standard deviation of ± 3.9% from the regression line. Simple inspection, however, revealed a curvature in the arrangement of calibration points. Cornwall, Marshall, and Boyes assert that this is due to an error in the oximeter equation and propose that an equation in the form of a power function be substituted. The experimental data were recalculated to show that the calibration points fit a power curve best when the exponent is equal to two.

A theoretical analysis of some errors in oximetry.

Oximeters, photoelectric instruments for the rapid estimation of blood oxygen saturation, are based on the principles of bichromatic photometry. The need for relative simplicity in design and operation of these instruments, particularly of ear oximeters, requires that assumptions be made which are only partially met in practice. The present paper is concerned with an analysis of errors arising from these assumptions. Suggestions to improve the accuracy of the measurement are presented.

Nomograms for correction of blood Po2, Pco2, pH, and base excess for time and temperature.

Nomograms for correction of blood Po2, Pco2, pH, and base excess for time and temperature.

Use of the Ear Oximeter for Assay of Pulmonary Disability

SUMMARY An oximetric method for assessing pulmonary impairment has been devised. The decrease in arterial oxygen saturation, measured by an ear oximeter, and the work performed by stepping up and down on an 8-inch step 30 times per minute not to exceed five minutes are correlated. An index of disability is calculated as follows: DI = Decrease % arterial O2 saturation after exercise Total foot pounds work done × 10 5 Fifteen normal subjects had scores ranging from +14 to −20 (median= −1) and 14 patients with pulmonary diseases not expected to interfere with pulmonary function had scores ranging from +142 to −12 (median=+9). Thirty-six of the 51 patients with diseases expected to interfere with function and who were receiving therapy had scores from −24 to −1112 (median= −126). The remaining 15 had scores in the range of the normal subjects. Had these 51 patients not been receiving treatment, the number of patients responding to the test would probably have been nearer 100 per cent. Studies in another 16 patients showed that changes in arterial blood saturation by oximetry agreed well with changes obtained by arterial blood gas analysis. The correlation coefficient r=0.944. The method is easy, simple, rapid and causes little or no anxiety in the subject tested. The testing equipment can be easily set up in a plant dispensary or in a field location.

Estimation of mitral regurgitation by injection of dye into the left ventricle with simultaneous left atrial sampling: A clinical study of sixty confirmed cases

The degree of mitral régurgitation has been estimated during 123 transthoracic left heart catheterizations by injection of T-1824 into the left ventricle with continuous simultaneous left atrial sampling through a cuvette oximeter. The ratio of the left atrial regurgitant curve area to the forward flow curve area inscribed by an ear oximeter has been used as an index of the severity of regurgitation. A ratio of 0.20 or less indicated minimal, 0.20 to 0.50 moderate, and greater than 0.50 severe mitral insufficiency. A direct estimate of regurgitation was obtained in 60 cases, 55 at operation and 5 at postmortem examination. There was satisfactory agreement between this direct estimate and the predicted degree of mitral insufficiency. There was no case in which the dye method failed to indicate mitral insufficiency when it was found at operation, but there were 3 “false positive” results in which minimal or moderate insufficiency by dye test was not confirmed at thoracotomy. To examine the problem of incomplete left atrial mixing of dye or nonrepresentative sampling, two dye injections were made into the left ventricle. Sampling was made from the same site in the left atrium in 22 patients and from two different sites in the left atrium in another group of 23 patients. Comparison of the ratios of regurgitant to forward flow curve areas did not indicate that serious misinterpretation would result from incomplete left atrial mixing. The method was helpful in assessing the cfficacy of open annuloplasty for the treatment of mitral insufficiency. Postoperative studies of dye injection provided objective evidence of the reduction or recurrence of regurgitation. The method permitted combining the estimate of regurgitation with an estimate of stenosis by measurement of the transmitral valvular gradient during one procedure.