Aymen A. Awad

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.

What is the best site for measuring the effect of ventilation on the pulse oximeter waveform

The cardiac pulse is the predominant feature of the pulse oximeter (plethysmographic) waveform. Less obvious is the effect of ventilation on the waveform. There have been efforts to measure the effect of ventilation on the waveform to determine respiratory rate, tidal volume, and blood volume. We measured the relative strength of the effect of ventilation on the reflective plethysmographic waveform at three different sites: the finger, ear, and forehead. The plethysmographic waveforms from 18 patients undergoing positive pressure ventilation during surgery and 10 patients spontaneously breathing during renal dialysis were collected. The respiratory signal was isolated from the waveform using spectral analysis. It was found that the respiratory signal in the pulse oximeter waveform was more than 10 times stronger in the region of the head when compared with the finger. This was true with both controlled positive pressure ventilation and spontaneous breathing. A significant correlation was demonstrated between the estimated blood loss from surgical procedures and the impact of ventilation on ear plethysmographic data (rs = 0.624, P = 0.006).

The Use of Joint Time Frequency Analysis to Quantify the Effect of Ventilation on the Pulse Oximeter Waveform

Objective. In the process of determining oxygen saturation, the pulse oximeter functions as a photoelectric plethysmograph. By analyzing how the frequency spectrum of the pulse oximeter waveform changes over time, new clinically relevant features can be extracted. Methods. Thirty patients undergoing general anesthesia for abdominal surgery had their pulse oximeter, airway pressure and CO2 waveforms collected (50 Hz). The pulse oximeter waveform was analyzed with a short-time Fourier transform using a moving 4096 point Hann window of 82 seconds duration. The frequency signal created by positive pressure ventilation was extracted using a peak detection algorithm in the frequency range of ventilation (0.08–0.4 Hz = 5–24 breaths/minute). The respiratory rate derived in this manner was compared to the respiratory rate as determined by CO2 detection. Results. In total, 52 hours of telemetry data were analyzed. The respiratory rate measured from the pulse oximeter waveform was found to have a 0.89 linear correlation when compared to CO2 detection and airway pressure change. the bias was 0.03 breath/min, SD was 0.557 breath/min and the upper and lower limits of agreement were 1.145 and −1.083 breath/min respectively. The presence of motion artifact proved to be the primary cause of failure of this technique. Conclusion. Joint time frequency analysis of the pulse oximeter waveform can be used to determine the respiratory rate of ventilated patients and to quantify the impact of ventilation on the waveform. In addition, when applied to the pulse oximeter waveform new clinically relevant features were observed.

How Does the Plethysmogram Derived from the Pulse Oximeter Relate to Arterial Blood Pressure in Coronary Artery Bypass Graft Patients

Twenty patients scheduled for coronary artery bypass grafting had their ear and finger oximeter and radial artery blood pressure (Bpmeas) waveforms collected. The ear and finger pulse oximeter waveforms were analyzed to extract beat-to-beat amplitude and area and width measurements. The Bpmeas 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 Bpmeas for the first 10 patients. The ear pulse oximeter width (WidthEar) had the best correlation (r = 0.8). Linear regression was done between WidthEar and Bpmeas based on slope (b) and intercept (a) values, BP was calculated (Bpcalc) in the next 10 patients as:MATHwhere 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 WidthEar and Bpmeas 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.

Analysis of the ear pulse oximeter waveform

Objective: For years researchers have been attempting to understand the relationship between central hemodynamics and the resulting peripheral waveforms. This study is designed to further understanding of the relationship between ear pulse oximeter waveforms, finger pulse oximeter waveforms and cardiac output (CO). It is hoped that with appropriate analysis of the peripheral waveforms, clues can be gained to help to optimize cardiac performance. Methods.Part 1: Studying the effect of cold immersion test on plethysmographic waveforms. Part 2: Studying the correlation between ear and finger plethysmographic waveforms and (CO) during CABG surgery. The ear and finger plethysmographic waveforms were analyzed to determine amplitude, width, area, upstroke and downslope. The CO was measured using continuous PA catheter. Using multi-linear regression, ear plethysmographic waveforms, together with heart rate (HR), were used to determine the CO Agreement between the two methods of CO determination was assessed. Results.Part 1: On contralateral hand immersion, all finger plethysmographic waveforms were reduced, there was no significant change seen in ear plethysmographic waveforms, except an increase in ear plethysmographic width. Part 2: Phase1: Significant correlation detected between the ear plethysmographic width and other ear and finger plethysmographic waveforms. Phase 2: The ear plethysmographic width had a significant correlation with the HR and CO. The correlation of the other ear plethysmographic waveforms with CO and HR are summarized (Table 5). Multi-linear regression analysis was done and the best fit equation was found to be: CO = 8.084 − 14.248 × Ear width + 0.03 ×HR+ 92.322 × Ear down slope+0.027 × Ear Area Using Bland & Altman, the bias was (0.05 L) but the precision (2.46) is large to be clinically accepted. Conclusion. The ear is relatively immune to vasoconstrictive challenges which make ear plethysmographic waveforms a suitable monitor for central hemodynamic changes. The ear plethysmographic width has a good correlation with CO.

Oscillations in the plethysmographic waveform amplitude: phenomenon hides behind artifacts.

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Comparing the effect of arginine vasopressin on ear and finger photoplethysmography.

STUDY OBJECTIVE To test whether the relative insensitivity of craniofacial vessels to catecholamines differs in response to arginine vasopressin. DESIGN Prospective, observational human study. SETTING University hospital. PATIENTS 8 ASA physical status I and II women scheduled for elective myomectomy. INTERVENTIONS Patients underwent elective myomectomy surgery with intrauterine injection of arginine vasopressin. MEASUREMENTS Finger, ear, and forehead photoplethysmographs were monitored. Changes in the plethysmographic amplitudes were recorded before and after arginine vasopressin injection. MAIN RESULTS In all subjects, ear photoplethysmographic amplitude (but not oxygen saturation) decreased precipitously (62% +/- 10%; P < 0.001) after arginine vasopressin injection. In contrast, there was no significant decline in the finger signal (4.5% +/- 27%; P = 0.19). The forehead plethysmograph decreased in amplitude, but this finding did not achieve significance (33% +/- 18%; P = 0.18). CONCLUSION In contrast to prior observations during adrenergic activation, arginine vasopressin induced relatively greater vasoconstriction at the ear and forehead than at the finger. This finding has potential implications with respect to arginine vasopressins effect on blood flow and indicates that monitoring the ear plethysmographic signal may provide useful information during arginine vasopressin administration.

Silver rubber-hydrogel nanocomposite as pH-sensitive prepared by gamma radiation: Part I

Abstract Silver rubber-hydrogel nanocomposite based on silver/styrene butadiene rubber/polyvinylpyrrolidone/methacrylic acid (SBR/PVP/MAA)/Ag was prepared by gamma radiation-induced crosslinking. During the radiation crosslinking of SBR/PVP/MAA solution containing silver nitrate AgNO3 (0.01 mol), in situ reduction of Ag+ ions was performed under the radiolysis of water. The properties of sliver rubber-hydrogel nanocomposite were investigated by FT-IR, XRD, TEM, SEM, DSC and TGA techniques. Transmission electron microscope (TEM) reveals that AgNPs have uniform distribution and spherical shape with mean diameter in the range of 8–10 nm. Differential scanning calorimetry (DSC) results of the nanocomposite showed one phase suggesting the miscibility between rubber and hydrogel phases. The swelling measurement of the synthesized silver rubber-hydrogel nanocomposite in different pHs at room temperature was performed. The results showed that it has pH-sensitivity.