Comparative accuracies of a finger blood pressure monitor and an oscillometric blood pressure monitor

A noninvasive blood pressure monitor (Finapres) that uses the methodology of Peaz to continuously display the arterial waveform from the finger has been introduced recently. The Finapres monitor overestimated systolic pressure by 5.8±11.9 mm Hg, while the Dinamap monitor underestimated systolic pressure by –6.9±9.2 mm Hg (P=0.003). Dinamap mean and diastolic pressure biases were less than 2 mm Hg, while the Finapres biases for these variables were significantly greater (7.7±10.0 and 8.2±9.8 mm Hg, respectively). There was no difference in systolic or mean pressure precision between the two devices (approximately 10 mm Hg), but the diastolic precision of the Dinamap unit was superior to that of the Finapres. While in most patients the Finapres monitor provided continuous blood pressure data equivalent to the data from the radial artery, marked bias (>15 mm Hg) was exhibited in 2 patients for all three pressure variables. Despite this bias, blood pressure changes were tracked closely in these 2 patients. We conclude that, in its current form, the Finapres monitor cannot be relied upon independently to accurately measure blood pressure in patients undergoing general anesthesia. Since the Dinamap monitor measures mean pressure reliably and accurately, we suggest that mean blood pressure values between the Finapres and Dinamap monitors be compared to guide one in interpreting Finapres data.Supported in part by a grant from Ohmeda Company, Boulder, CO.Presented in part at the annual meeting of the American Society of Anesthesiologists, New Orleans, October 1989.     

Noninvasive blood pressure monitoring from the supraorbital artery using an artificial neural network oscillometric algorithm

Objective. Our objective was to overcome the limitations of linear models of oscillometric blood pressure determination by using a nonlinear technique to model the relationship between the oscillometric envelope and systolic and diastolic blood pressures, and then to use that technique for near-continuous arterial pressure monitoring at the supraorbital artery.Methods. An adhesive pressure pad and transducer were used to collect oscillometric data from the supraorbital artery of 85 subjects. These data were then used to train an artificial neural network (ANN) to report diastolic or systolic pressure. Arterial pressure measurements defined by brachial artery auscultation were used as a reference. ANN results were compared with those obtained using a standard oscillometric algorithm that determined pressures based on fixed percentages of the maximum oscillometric amplitude.Results. The ANN produced better estimates of reference blood pressures than the standard oscillometric algorithm. Mean difference between target and actual output for the ANN was 0.50±5.73 mm Hg for systolic pressures, compared to the mean difference of the standard algorithm of 2.78±19.38 mm Hg. For diastolic pressures, the ANN had a mean difference of 0.04±4.70 mm Hg, while the mean difference of the standard algorithm was –0.34±9.75 mm Hg.Conclusions. The ANN produced a better model of the relationship between the oscillometric envelope and reference systolic and diastolic pressures than did the standard oscillometric algorithm. Noninvasive blood pressure measured from the supraorbital artery agreed with pressure measured by auscultation in the brachial artery, and may sometimes be more clinically useful than an arm cuff device.This research was supported, in part, by a grant from Baxter Healthcare Corporation (Santa Ana, CA), and Innerspace Medical (Irvine, CA). A grant of computer time from the Utah Supercomputer Institute, which is funded by the State of Utah and the IBM Corporation, is gratefully acknowledged.     

Comparison of Blood Pressure Measured by Oscillometry from the Supraorbital Artery and Invasively from the Radial Artery

In previous studies, oscillometric blood pressure measured from the supraorbital artery has been shown to agree quite well with pressure measured from the brachial artery in normal subjects. In this study, surgical patients whose conditions warranted the use of invasive blood pressure monitoring during the surgery were chosen. We compared systolic and diastolic blood pressure measured oscillometrically from the supraorbital artery with intraarterial blood pressures, measured invasively from the radial artery. A pressure bladder was attached to the forehead of each patient. The bladder was connected to a forehead blood pressure monitor. A catheter was inserted in a radial artery, and connected to a pressure monitor. Forehead blood pressure was measured every 5 min. Radial arterial pressure was averaged over the same period during which the forehead measurement was made. Blood pressures measured with the two methods were compared. For the systolic pressure, the difference between the two methods was –9.9 ± 17.9 mm Hg (mean ± SD). For diastolic pressure, the difference was –8.0 ± 10.9 mm Hg. There was a significant difference between the two methods in the patient population chosen in this study.     

Brachial blood pressure monitoring versus ankle monitoring during colonoscopy

OBJECTIVES: To compare ankle and brachial blood pressure monitoring before and during colonoscopy using automated noninvasive blood pressure (NIBP) monitors. METHODS: Forty-five consecutive patients who presented for outpatient colonoscopy had both ankle and brachial blood pressure monitoring with automated NIBP using an appropriately sized cuff for arm or leg size. Three baseline measurements were obtained, and then measurements were taken at 5-minute intervals during conscious sedation, with brachial blood pressure being the standard. RESULTS: The average of all of the ankle blood pressures was significantly higher for all systolic and mean arterial blood pressure readings. Diastolic blood pressure readings were higher at baseline, but not significantly different during the procedure. CONCLUSIONS: Ankle systolic and mean arterial blood pressures using automated NIBP monitoring for conscious sedation are significantly higher than brachial blood pressures. Ankle NIBP monitoring should only be used if brachial NIBP monitoring is not feasible, taking into consideration that ankle NIBP pressures are generally higher than brachial.     

Antegrade pulsatile arterial‐like flow in human limb veins at increased intravascular pressure

Aim:  The purpose was to study the effects of moderately to markedly increased local intravascular pressures on the flow characteristics in human limb veins. Methods:  The subject was either seated inside a pressure chamber with one arm slipped through a hole in the chamber door (n = 7) or positioned supine with a lower leg extended to the outside (n = 15). By increasing chamber pressure, transmural pressure in the vessels of the test limb was increased up to +150 mmHg for the arm and +240 mmHg for the leg. Venous flow profiles and arterial flow and vessel diameters were measured with ultrasonographic/Doppler techniques. The arm vessels were studied before and during blocking of the blood flow (BBF) through the hand. Results:  Antegrade, pulsatile, arterial‐like flow were observed at high distending pressures in the brachial and radial veins in all subjects and in ～50% of the subjects also in the cephalic vein and posterior tibial veins. In five of seven subjects, blood flow in the brachial vein remained pulsatile even during BBF. Conclusion:  That pulsatile flow was observed in all veins may suggest that moderately to markedly elevated intravascular pressures induce propagation of pulse waves from the arteries via the capillaries to the veins, and/or induce considerable arteriovenous shunting, by forcing open arteriovenous anastomoses.     

Pulse oximetry and finger blood pressure measurement during open-heart surgery

Pulse oximeter arterial hemoglobin oxygen saturation (SpO₂) and finger arterial pressure (FINAP) were continuously monitored before, during, and after cardiopulmonary bypass in 15 male patients. SpO₂ was monitored simultaneously with two pulse oximeters, a Nellcor N-100 and an Ohmeda Biox III. The readings obtained from the two pulse oximeters were compared with arterial blood measurements obtained using a CO-oximeter. FINAP was monitored by a prototype device (Finapres) based on the Peaz volume-clamp method. FINAP was correlated with intraarterial pressure (IAP). Both pulse oximeters functioned well before cardiopulmonary bypass. The correlations with CO-oximeter values were 0.927 for the N-100 and 0.921 for the Biox III. Immediately after the onset of cardiopulmonary bypass, the N-100 pulse oximeter stopped displaying values. The Biox III pulse oximeter continued to display values during the cardiopulmonary bypass period; the correlation with CO-oximeter values was 0.813. After cardiopulmonary bypass, the N-100 began displaying values in 2 to 10 minutes. After cardiopulmonary bypass the correlation with CO-oximeter values was 0.792 for the N-100 and 0.828 for the Biox III pulse oximeter. The Finapres finger blood pressure device functioned well in 13 of 15 patients before cardiopulmonary bypass. The mean bias ± precision of FINAP-IAP for mean pressure was 8.3±10.2 mm Hg (SD) and the correlation coefficient was 0.814. During cardiopulmonary bypass, the Finapres device functioned well in 10 of 15 patients. The mean bias precision of FINAP-IAP, for mean pressure in these 10 patients was 6.6±8.7 mm Hg and the correlation coefficient was 0.902. Immediately after cardiopulmonary bypass, the Finapres functioned well in 11 of 15 patients. The mean bias ± precision of FINAP-IAP for mean pressure was 8.6±14.1 mm Hg and the correlation coefficient was 0.533. This study documented that devices for continuous noninvasive monitoring can usually function well under the extreme conditions seen during open-heart surgery. Pulse oximeters may find a place in the monitoring of patients during open-heart surgery, although they cannot totally replace the invasive techniques. Under the conditions of diminished pulsatile peripheral blood flow we observed some differences between the two pulse oximeters.     

Use of A Neonatal Blood Pressure Cuff to Monitor Blood Pressure In The Adult Finger – Comparison With A Standard Adult Arm Cuff

Background. There are few suitable methods for monitoring blood pressure continously (or intermittently) for research in adult stroke patients, who are ill but do not justify invasive intensive care monitoring. Method. We tested a neonatal arm blood pressure in adults by placing it on the forefinger (finger cuff). We compared the repeatability of the finger cuff with blood pressure measured by a standard adult arm cuff using the oscillometric technique in 168 ambulatory outpatients attending a cerebrovascular disease clinic. Results. The mean difference between sequential mean blood pressure readings with the finger cuff was 0.55 mm Hg (95% confidence interval (CI) –14.36 to 15.47 mm Hg), and for the arm cuff was 3.31 mm Hg (95% CI –23.33 to 16.71 mm Hg). Measurements made with the arm cuff were shown to affect subsequent arm cuff readings made within a few minutes of the first. The mean difference between the finger cuff and arm cuff mean blood pressure readings was 0.03 mm Hg (95% CI –26.07 to 26.14 mm Hg) and agreement was better when the blood pressure was measured with the finger cuff first rather than the arm cuff. However, although there was no difference in the mean blood pressure recordings both systolic and diastolic blood pressure measurements differed systematically between arm and finger cuff. Conclusion. The reproducibility of sequential blood pressure measurements made with the finger cuff was better than with the arm cuff. The performance of the finger cuff compared with that of the arm cuff was sufficiently good to encourage use of the finger cuff in research involving automatic intermittent monitoring to observe sequential blood pressures over time in stroke patients. However, measurements of systolic and diastolic pressure were not the same with the two cuffs and further work on calibration of the finger cuff would be useful.     

Auscultatory mean blood pressure

This study examined the relationship between direct mean arterial blood pressure and cuff pressure for the maximum acoustic index calculated from the Korotkoff sounds in the dog. The acoustic index was computed by summing the squares of amplitudes in each Korotkoff sound complex, thereby providing a measure of acoustic energy content. Mean arterial pressure was compared with cuff pressure for the maximum acoustic index. Ten mongrel dogs were fitted with appropriately sized blood-pressure cuffs containing a microphone mounted inside the bladder and positioned over the brachial artery. The Korotkoff sounds, cuff pressure, and direct arterial pressure were recorded over a range of mean arterial pressures (23 to 155 mm Hg), achieved by manipulating the depth of anesthesia with halothane. It was found that cuff pressure at the maximum acoustic index overestimated mean arterial blood pressure by a mean of 14% (range, -8 to + 30%). Supported by grant HL31089 from the National Heart, Lung, and Blood Institute and sponsored in part by the Kendall Company, Barrington, IL.     

Transcutaneous oxygen and carbon dioxide tensions compared to arterial blood gases in normals

BACKGROUND: Most hyperbaric medicine centers do not monitor arterial oxygen (P(aO(2))) and carbon dioxide (P(aCO(2))) tensions during hyperbaric oxygen, but many can transcutaneously monitor oxygen (P(tcO(2))) and carbon dioxide (P(tcCO(2))). METHODS: We compared P(tcO(2)) and P(tcCO(2)) measurements to simultaneous P(aO(2)) and P(aCO(2)) measurements in 10 healthy volunteers to determine if P(tcO(2)) and P(tcCO(2)) measurements are surrogates for P(aO(2)) and P(aCO(2)) in the hyperbaric environment. We took blood samples via arterial catheter and took P(tcO(2)) and P(tcCO(2)) chest measurements while the subjects were compressed in a monoplace hyperbaric chamber at pressures between 0.85 atmospheres absolute (atm abs) (our local atmospheric pressure, at altitude 1,300 m) and 3.0 atm abs, while the subjects breathed air, then oxygen. RESULTS: The P(tcO(2)) correlated with P(aO(2)) (r(2) = 0.99). Under all the conditions, the P(tcO(2)) values were lower than P(aO(2)) values by approximately 10%. The P(tcCO(2)) was 2-6 mm Hg higher than the P(aCO(2)), but the correlation was low (r(2) = 0.21). CONCLUSIONS: The P(tcO(2)) in normal humans may be used to estimate the P(aO(2)). The P(tcCO(2)) may not be an adequate reflection of the P(aCO(2)). It is unknown if P(tcO(2)) and P(tcCO(2)) measurements in critically ill patients can replace P(aO(2)) and P(aCO(2)) measurements.     

Accuracy of oscillometric blood pressure measurement according to the relation between cuff size and upper-arm circumference in critically ill patients

OBJECTIVE: To evaluate the accuracy of oscillometric blood pressure measurement according to the relation between cuff size and upper-arm circumference in critically ill patients. DESIGN: Prospective data collection. SETTING: Emergency department in a 2,000-bed inner city hospital. PATIENTS: Thirty-eight patients categorized into three groups according to their upper-arm circumference (group I: 18-25 cm; group II: 25.1-33 cm; and group III: 33.1-47.5 cm) were enrolled in the study protocol. INTERVENTIONS: In each patient, all three cuff sizes (Hewlett-Packard Cuff 40401 B, C, and D) were used to perform an oscillometric blood pressure measurement at least within 3 mins until ten to 20 measurements for each cuff size were achieved. Invasive mean arterial blood pressure measurement was done by cannulation of the contralateral radial artery with direct transduction of the systemic arterial pressure waveform. The corresponding invasive blood pressure value was obtained at the end of each oscillometric measurement. MEASUREMENT AND MAIN RESULTS: Overall, 1,494 pairs of simultaneous oscillometric and invasive blood pressure measurements were collected in 38 patients (group I, n = 5; group II, n = 23; and group III, n = 10) over a total time of 72.3 hrs. Mean arterial blood pressure ranged from 35 to 165 mm Hg. The overall discrepancy between oscillometric and invasive blood pressure measurement was -6.7+/-9.7 mm Hg (p<.0001), if the recommended cuff size according to the upper-arm circumference was used (539 measurements). Of all the blood pressure measurements, 26.4% (n = 395) had a discrepancy of > or =10 mm Hg and 34.2% (n = 512) exhibited a discrepancy of > or =20 mm Hg. No differences between invasive and noninvasive blood pressure measurements were noted in patients either with or without inotropic support (-6.6 + 7.2 vs. -8.6 + 6.8 mm Hg; not significant). CONCLUSION: The oscillometric blood pressure measurement significantly underestimates arterial blood pressure and exhibits a high number of measurements out of the clinically acceptable range. The relation between cuff size and upper-arm circumference contributes substantially to the inaccuracy of the oscillometric blood pressure measurement. Therefore, oscillometric blood pressure measurement does not achieve adequate accuracy in critically ill patients.     

Normal fluctuation of physiologic cardiovascular variables during anesthesia and the phenomenon of “smoothing”

With the advent of automated anesthesia record keeping devices, concern has arisen that “abnormal” values will appear in the record and possibly lead to medicolegal compromise. A retrospective review of automated records from a series of anesthesia cases was undertaken to determine if abnormal values do occur, how frequent they are, and whether they cause problems. A total of 14,826 (4,942 each) noninvasive heart rate, systolic, and diastolic blood pressure readings from 118 case printouts generated by a Diatek Arkive Patient Information Management System (63 cases) or a Data-scope Datatrac record keeper (55 cases) were recorded. The study sample covered a broad range of surgical operations, anesthetic procedures, and patient ages and medical histories. During these 118 anesthetics, the majority of readings of all three variables fell within normal ranges (defined for this study as 80 to 180 and 50 to 110 mm Hg for systolic and diastolic blood pressures, respectively, and 60 to 140 beats/min for heart rate). During the anesthetics, 3.6% of the systolic pressure readings, 13.25% of the diastolic readings, and 4.25% of the heart rate readings were recorded outside these ranges. No serious intraoperative or postoperative anesthesia complications were associated with these out-of-range readings, nor would they be expected in a sample of this size, since serious anesthetic complications are rare. This preliminary observation of one person's experience may help address the concern associated with allowing high and low blood pressure and heart rate readings to be automatically recorded “unsmoothed.” In medicolegal situations, it should also begin to demonstrate that such fluctuations are neither uncommon nor abnormal, and that a true record of these readings should be neither a cause for concern nor an opportunity for medicolegal exploitation.     

Use of a radial artery compression device for noninvasive, near-continuous blood pressure monitoring in the ED

This study's goal was to test a novel device using continuous partial radial artery compression for mean arterial pressure (MAP) measurement. A prospective, nonblind, convenience-sample trial at a level I center (annual ED census 70,000) enrolled 15 adults with indwelling radial arterial catheters and accessible contralateral radial pulse. Subjects had MAPs measured simultaneously by test device (TEST assessments), oscillometric brachial artery cuff (OSC), and arterial line (ART). There was no difference between the three groups' MAP means (P = .98). R(2) values for ART/OSC and ART/TEST were 0.96 and 0.95, respectively (P <.001). TEST and OSC MAP readings were equally likely (P = 0.66) to be within 5 mm Hg of ART in both the overall set of 307 MAPs and in the subset of 120 cases in which ART MAPs were below 80 (P = .47). The TEST device performed at least as well as oscillometric assessment, offering advantages of noninvasive, near-continuous data.     

Evaluation of two adaptive sodium nitroprusside control algorithms

Computer control of sodium nitroprusside infusion may be safer and provide better control of arterial blood pressure than is achieved with manual control. In a series of test maneuvers in 20 mongrel dogs, the performance of two adaptive control algorithms(controllers) was compared and their safety tested. The controllers were set to infuse sodium nitroprusside to decrease mean arterial pressure and maintain it 20 to 30 mm Hg below the control pressure. Then, sequentially, the right atrium was paced to simulate a supraventricular tachydysrhythmia, the right ventricle was intermittently paced to simulate ventricular extrasystoles, large tidal volumes were given to simulate a respiratory-therapy maneuver, the catheter was clamped to simulate clotting, an air bubble was introduced, and the infused sodium nitroprusside concentrations were either doubled or halved. Next, 500 ml of blood was drawn. Then, in sequence, positive end-expiratory pressure was applied, the right atrium was paced, and large tidal volume breaths were given to cause the blood pressure to fluctuate. When the controllers were turned on, mean arterial pressure reached the set point and remained within 5 mm Hg of the target pressure after 8.6±0.9 minutes (mean ± SEM). The controllers properly handled the differences in sodium nitroprusside sensitivity and the catastrophic challenges presented in the experiments. When the animals were not being disturbed, stability was maintained and the blood pressure was kept well within 5 mm Hg of the desired pressure. The controllers rejected all invalid pressure signals during testing. During the challenges imposed by dysrhythmias, respiratory therapy, hypovolemia, and blood transfusion, the controllers returned the pressure to the desired value in less than 10 minutes. Under our test conditions, differences in behavior between the two controllers were not significant.     

Tissue hypoxia distal to a Peñaz finger blood pressure cuff

The Peñaz finger method to measure blood pressure uses a finger cuff in which the pressure level fluctuates in the vicinity of the mean arterial pressure level and thereby interferes with the circulation of blood to and from the fingertip. We measured capillary blood gases and saturation of hemoglobin in the finger during Peñaz finger blood pressure (PFBP) monitoring to assess the degree to which it impairs circulation in the fingertip. Within 2.5 minutes after initiating PFBP monitoring, capillary oxygen tension (Po₂) had decreased significantly, from about 71 mm Hg to between 49 and 58 mm Hg for up to 50 minutes. These changes were quite different from those occurring when an occlusive tourniquet was applied around the finger. Within 10 minutes of tourniquet application, acidosis (pH 7.25), hypercapnia (carbon dioxide tension, 59.0 mm Hg), and hypoxemia (Po₂, 29 mm Hg) resulted. Within 30 seconds of releasing the PFBP cuff, capillary blood gas values were back to normal. Interspersing 30-second rest periods every 5 minutes during 35 minutes of PFBP monitoring actually decreased capillary oxygen values compared with monitoring without such rest periods. A finger pulse oximeter distal to the PFBP cuff showed desaturation from an average of 97% to 93.7%, with much variability. However, desaturation was statistically significant within 1 minute of application of the PFBP cuff. Within 1 minute the finger volume increased an average of 0.05 ml. After 1 minute the volumes varied widely and, on the average, returned to normal despite continued PFBP monitoring.     

Comparative effects of cuff size and tightness of fit on accuracy of blood pressure measurements

To determine the effect of snugness of cuff wrap on the accuracy of blood pressure (BP) measurements, we performed two studies on 6 healthy volunteers. In both studies, control values were obtained from the right upper arm with cuffs of appropriate size and snug fit. Study 1 had two phases. In the first, cuffs of appropriate size were wrapped snugly around the upper left arm of seated subjects. The effects of two other degrees of cuff snugness on the measurement of BP were evaluated by placing a filled 250-mL intravenous fluid bag between the cuff and arm over the triceps, measuring BP, then draining the same bag of half its contents and then all of its contents without rewrapping the cuff (loose, very loose fit), each time measuring BP. The second phase of study 1 was identical in procedure, except that the cuffs used on the left arm were one size too small. In study 2, the experimental cuffs were placed just above the right ankle. To alter the signal-to-noise ratio, BP was raised or lowered: the standing position elevated mean BP by an average of 90 mm Hg, and elevation of the legs decreased mean BP by an average of 43 mm Hg. In study 1, we found that appropriately sized cuffs, whether wrapped tightly or loosely, gave correct BP readings. Cuffs snugly wrapped, but too small for the subject, gave high BP readings, on the average by approximately 10 mm Hg. Loose wrapping of small cuffs gave variable results in individual subjects that exaggerated systolic BP from 2 to 80 mm Hg. In study 2, elevating the legs or standing decreased or increased BP consistently. Loose wrapping of appropriately sized cuffs around the ankles of the subjects had no additional significant effect on BP.     

The effect of cuff pressure deflation rate on accuracy in indirect measurement of blood pressure with the auscultatory method

The importance of cuff deflation rate in the auscultatory method of measuring blood pressure was investigated using a computer-based model. To determine the relationship between the cuff deflation rate and the measurement error, two cuff deflation protocols were used, one based on heart rate (mm Hg per heartbeat), the other on a constant rate (mm Hg per second). The different deflation protocols and rates were tested using a constant blood pressure of 120/80 mm Hg and heart rates ranging from 40 to 120 beats/min. It was confirmed that a cuff deflation rate that is time based will introduce larger errors at low heart rates. Using heart rate as a basis for cuff deflation rate yields a constant error that is independent of heart rate. The currently used standard of 3 mm Hg/s could result in a maximum error of 2.5 mm Hg in both systolic and diastolic pressures at a heart rate of 72 beats/min. The maximum systolic and diastolic errors increase to more than 4 mm Hg at 40 beats/min. A deflation rate of 2 mm Hg/beat, however, yields a maximum error of 2 mm Hg for both systolic and diastolic pressures, independent of heart rate. A cuff deflation rate based on heart rate is recommended to help minimize changes in measurement error when measuring blood pressure if a wide range of heart rates will be encountered.Supported by grants from IVAC, San Diego, CA, and Physio Control, Redmond, WA.     

Clinical evaluation of the oscillometric blood pressure monitor in adults and children based on the 1992 AAMI SP-10 standards

Objective and Methods. A noninvasive blood pressure monitor (model BP8800MS, Colin Medical Instruments Corp., San Antonio, TX) that uses the oscillometric principle was evaluated against the manual auscultatory method in 85 adults and 85 children following the requirements of the 1992 AAMI SP-10 standard. This was the first evaluation study of the electronic sphygmomanometers according to the new AAMI standards.Results. In adult subjects, the mean difference and standard deviation of the differences between the oscillometric and auscultatory methods were 2.81 ± 5.35 mm Hg (mean ± SD) for systolic and 0.04 ± 4.90 mm Hg for diastolic; in children, they were 3.18 ± 5.96 mm Hg for systolic and –0.82 ± 5.24 mm Hg for diastolic. Excellent correlation between the oscillometric and auscultatory methods, particularly the diastolic pressure, is due to usage of the Phase V Korotkoff's sounds for auscultatory detection of the diastolic pressure, increased accuracy of the two observers' measurements, and proper selection of cuff sizes depending on the mid-arm circumference. Five different-sized cuffs were used in this study. The cuff-width-to-midarm circumference ratio was adjusted to be 0.4 or larger to minimize the measurement error associated with mismatch of cuff-size/arm-size relationship. The distribution of errors associated with each cuff was nearly the same.Conclusions. The 1992 AAMI SP-10 standards offer a thorough evaluation of the oscillometric sphygmomanometer by enforcing more stringent criteria on (1) agreement between two observers, (2) wide spectrum of blood pressure from hypertensive (above 180 mm Hg) to hypotensive, and (3) data analysis. The oscillometric blood pressure monitor evaluated in this study meets the specifications of the new AAMI SP-10 standards and can offer an accurate, automatic, and noninvasive measure of both systolic and diastolic blood pressure in adults and children. It can safely replace the manual or automatic auscultatory system in various clinical settings.This study was supported in part by a grant in aide from Nippon Colin (Komaki, Japan) and Colin Medical Instruments (San Antonio, TX). The authors acknowledge Dr. James Pool and Ms. Charlyne Allston-Wright of the Department of Medicine, Baylor College of Medicine, for providing hypertensive subjects. Technical assistance by Ms. Julie Glueck of the Department of Surgery, Baylor College of Medicine, is also acknowledged.     

Estimation of central aortic pressure by SphygmoCor requires intra-arterial peripheral pressures

Central arterial pressure, measured close to the heart, may be of more patho-physiological importance than conventional non-invasive cuff blood pressure. The technique of applanation tonometry using SphygmoCor has been proposed as a non-invasive method of estimating central pressure. This relies on mathematically derived generalized transfer functions, which have been previously validated using invasive peripheral pressure measurements. We compared simultaneous estimates of central aortic pressure using this technique with those measured directly during the routine diagnostic cardiac catheterization of 30 subjects (age range 27-84 years), half of whom were aged 65 years or more. This was done by applanating the left radial artery and recording the non-invasive brachial cuff blood pressure to generate a central aortic pressure estimate, using the SphygmoCor radial transfer function. The comparative results were analysed using Bland-Altman plots of mean difference. SphygmoCor, on average, underestimated systolic central arterial pressure by 13.3 mmHg and overestimated diastolic pressure by 11.5 mmHg. The results were similar in patients aged under and above 65 years. Furthermore, non-invasively measured brachial pressures were seen to give an overall closer estimate of the central arterial pressure than the SphygmoCor system. The transfer function has been validated from invasively measured arterial pressures and the current use by the system of non-invasive measures may explain the discrepancies. However, age, drugs and arterial disease would also be expected to play a role.     

Arterial pressure measurements using infrared photosensors: comparison with CW Doppler

We evaluated the accuracy of modern infrared photosensors (IPs) from a photoplethysmography (PPG) machine as flow detector in determining the systolic arterial pressures and ankle/brachial indices (ABIs) in comparison to the traditional continuous wave Doppler (Doppler) method. Pressures were obtained by placing an appropriate pneumatic cuff above the elbow and ankle. The Doppler probe was placed at brachial artery, posterior tibial artery and dorsalis pedis artery, and the IP was placed on the pad of the index finger and great toe. The two techniques were compared in 181 limbs in our non‐invasive vascular laboratory, 133 limbs with normal and 48 limbs with abnormal ABIs. The accuracy of absolute ankle pressure measurements was also compared by both methods. We found that IPs from PPG machine have a good correlation (linear regression r=0·96 for normal and r=0·95 for abnormal ankle pressures) with the Doppler method. There was no significant difference (P≤0·0001) in the ABIs calculated by two methods in either normal or abnormal subjects. The PPG method was easier, quicker and automated as compared with the cumbersome Doppler method. While PPG method does not differentiate between occlusive disease of posterior tibial and anterior tibial/dorsalis pedis arteries, it is better suited for non‐compliant patients and is superior to Doppler method in advanced occlusive arterial disease. We recommend that it be used on a routine basis.     

Evaluation in animals of a system to estimate tracheal pressure from the endotracheal tube cuff

Objective. Flow through an endotracheal tube (ETT) causes a pressure loss across the tube. This loss results in a difference between pressure measured at the airway and pressure measured in the trachea. This difference can lead to errors when calculating pulmonary mechanics and when setting ventilators. We have tested a method of estimating tracheal pressure from the pressure in the ETT cuff.Methods. Pressure transducers were placed in the proximal ETT connector, in the trachea, and in the ETT cuff (through the inflation port). Instantaneous periods of zero flow, detected with a flow meter, were used to calculate the slope and offset of the line relating cuff pressure to tracheal pressure. The system was tested on the bench using a ventilator and lung simulator and in 2 dogs and 5 pigs. Tests were performed at various cuff pressures, trachea diameters, ETT sizes, respiratory rates, tidal volumes, and airway obstructions. Results. In bench tests, our estimate of tracheal pressure was within –4.0±2.6% of the actual tracheal pressure (mean = standard deviation [SD]). In animal tests, our estimation of tracheal pressure was within –0.6±5%. In all bench test measurements and in 40 of 42 animal measurements, the error was less than 1 cm H₂O.Conclusions. The cuff estimation technique gives real-time, continuous, noninvasive tracheal pressure measurements in intubated animals with cuffed ETTs.