How does the plethysmogram derived from the pulse oximeter relate to arterial blood pressure in coronary artery bypass graft patients?

UNLABELLED: Twenty patients scheduled for coronary artery bypass grafting had their ear and finger oximeter and radial artery blood pressure (Bp(meas)) waveforms collected. The ear and finger pulse oximeter waveforms were analyzed to extract beat-to-beat amplitude and area and width measurements. The Bp(meas) waveforms were analyzed to measured systolic blood pressure (BP), mean BP, and pulse pressure. The correlation coefficient was determined between the derived waveforms from the pulse oximeter and Bp(meas) for the first 10 patients. The ear pulse oximeter width (Width(Ear)) had the best correlation (r = 0.8). Linear regression was done between Width(Ear) and Bp(meas) based on slope (b) and intercept (a) values, BP was calculated (Bp(calc)) in the next 10 patients as: [equation: see text] where i = systolic BP, mean BP, and pulse pressure. The initial bias was too large to be clinically useful. To improve clinical applicability a period of calibration was introduced in which the first 50 readings of Width(Ear) and Bp(meas) for each patient were used to calculate the intercept. After calibration the systolic BP, mean BP and pulse pressure bias values were -2.6, -1.88 and -1.28 mm Hg, and the precision values were 15.9 10.09, and 9.94 mm Hg, respectively. The present attempt to develop a clinically useful method of noninvasive BP measuring was partly successful with the requirement of a calibration period. IMPLICATIONS: Statistical comparison was made between measured blood pressure (BP) from arterial line and calculated BP derived from ear pulse oximeter waveform in 10 patients undergoing coronary artery bypass graft surgery. Using 62,077 paired readings, the mean difference for systolic BP, mean BP, and pulse pressure between the 2 methods was -2.6, -1.88, and -1.28 mm Hg, respectively.

Different responses of ear and finger pulse oximeter wave form to cold pressor test.

The cold pressor test is often used to assess vasoconstrictive responses because it simulates the vasoconstrictive challenges commonly encountered in the clinical setting. With IRB approval, 12 healthy volunteers, aged 25--50 yr, underwent baseline plethysmographic monitoring on the finger and ear. The contralateral hand was immersed in ice water for 30 s to elicit a systemic vasoconstrictive response while the recordings were continued. The changes in plethysmographic amplitude for the first 30 s of ice water immersion (period of maximum response) of the finger and ear were compared. The data indicate a significant disparity between the finger and the ear signals in response to the cold stimulus. The average finger plethysmographic amplitude measurement decreased by 48% +/- 19%. In contrast, no significant change was seen in the ear plethysmographic amplitude measurement, which decreased by 2% +/- 10%. We conclude that the ear is relatively immune to the vasoconstrictive effects. These findings suggest that the comparison of the ear and finger pulse oximeter wave forms might be used as a real-time monitor of sympathetic tone and that the ear plethysmography may be a suitable monitor of the systemic circulation.

Arterial-pulse oximetry loops: a new method of monitoring vascular tone.

OBJECTIVE: We report the off-line calculation of the vascular compliance of the finger and suggest the continuous on-line use of this methodology as an aid to monitoring the peripheral vascular resistance. This method consists of the simultaneous analysis of the waveform signals from the pulse oximeter monitors and the arterial pressure as indicators of "volume" and pressure respectively to continuously calculate the vascular "compliance" (volume change per unit pressure change). This should be seen as a "relative compliance" as the pulse plethysmograph signal is not calibrated. This new methodology allows for continuous monitoring of peripheral vascular compliance as a beat-to-beat indicator of peripheral vascular resistance. The vaso-constrictors, phenylephrine and ephedrine, were shown to decrease the compliance as predicted. METHODS: The arterial pressure and pulse oximeter waveforms were obtained during routine anesthetic care. The waveforms were collected with a computer data-acquisition system and then analyzed "off-line" as an indirect indicator of total vascular tone. Demographic and clinical information including drug administration were recorded. RESULTS: A case report is presented using this new form of analysis. Vascular compliance changes induced by phenylephrine and ephedrine were studied. A dose response curve of peripheral vascular compliance to phenylephrine was generated from these data. CONCLUSIONS: By plotting the pulse oximeter waveforms versus the arterial waveforms, multiple volume versus pressure (relative compliance) loops were obtained. Analysis of these loops may assist in the monitoring of vascular compliance.

The detection of peripheral venous pulsation using the pulse oximeter as a plethysmograph.

The pulse oximeter can serve as a sensitive photoelectric plethysmograph in the operating room. It was noted in several cases that the plethysmographic waveform showed a high degree of variability during diastole. Three patients are described with discrete diastolic peaks on the plethysmograph. Further investigation revealed that these diastolic peaks appear to correlate with peripheral venous pulsation, which seems to have a central venous origin. Evidence is presented that the plethysmographic detection of the venous-pulse may be useful in estimating the changing volume status of the patient.