Accuracy of four indirect methods of blood pressure measurement,with hemodynamic correlations

In 38 adults undergoing cardiac surgery, 4 indirect blood pressure techniques were compared with brachial arterial blood pressure at predetermined intervals before and after cardiopulmonary bypass. Indirect blood pressure measurement techniques included automated oscillometry, manual auscultation, visual onset of oscillation (flicker) and return-to-flow methods. Hemodynamic measurements or calculations included heart rate, cardiac index, stroke volume index, and systemic vascular resistance index. Indirect and intraarterial blood pressure values were compared by simple linear regression by patient and measurement period. Measurement errors (arterial minus indirect blood pressure) were calculated, and stepwise regression assessed the relationship between measurement error and heart rate, cardiac index, stroke volume index, and systemic vascular resistance index. Indirect to intraarterial blood pressure correlation coefficients varied over time, with the strongest correlations often occurring at the first and last measurement periods (preinduction and 60 minutes after cardiopulmonary bypass), particularly for systolic blood pressure. Within-patient correlations between indirect and arterial blood pressure varied widely—they were consistently high or low in some patients. In other patients, correlations were especially weak with a particular indirect blood pressure method for systolic, mean, or diastolic blood pressure; in some cases indirect blood pressure was inadequate for clinical diagnosis of acute blood pressure changes or trends. The mean correlations between indirect and direct blood pressure values were, for systolic blood pressure: 0.69 for oscillometry, 0.77 for auscultation, 0.73 for flicker, and 0.74 for return-to-flow; for mean blood pressure: 0.70 for oscillometry and 0.73 for auscultation; and for diastolic blood pressure: 0.73 for oscillometry and 0.69 for auscultation. The mean measurement errors (arterial minus indirect values) for the individual indirect blood pressure methods were, for systolic: 0 mm Hg for oscillometry, 9 mm Hg for auscultation, -5 mm Hg for flicker, 7 mm Hg for return-to-flow; for mean: -6 mm Hg for oscillometry, and -3 mm Hg for auscultation; and for diastolic: -9 mm Hg for oscillometry and -8 mm Hg for auscultation. Mean measurement error for systolic blood pressure was thus least with automated oscillometry and greatest with manual auscultation, while standard deviations ranging from 9 to 15 mm Hg confirmed the highly variable nature of single indirect blood pressure measurements. Except for oscillometric diastolic blood pressure, a combination of systemic hemodynamics (heart rate, stroke volume index, systemic vascular resistance index, and cardiac index) correlated with each indirect blood pressure measurement error, which suggests that particular numeric ranges of these variables minimize measurement error. This study demonstrates that striking variability occurs in the relationship between indirect and arterial blood pressure measurements, and that the systemic hemodynamic state influences accuracy of indirect blood pressure measurements. When the reproducibility of repeated indirect blood pressure measurements appears unsatisfactory or inconsistent with other clinical observations, clinicians may find that an alternative indirect blood pressure method is a better choice. Of the methods tested, no single indirect blood pressure technique showed precision superior to the others, but two methods yielded data only for systolic pressure. These findings lend support to intraarterial blood pressure measurement in conditions of hemodynamic variability, and suggest the theoretical benefits of continuous indirect blood pressure measurements. Annual meeting of the American Society of Anesthesiologists, New Orleans, LA, Oct 1984.     

Clinical comparison of automated auscultatory and oscillometric and catheter-transducer measurements of arterial pressure

Arterial pressure measurements recorded from a radial artery catheter-transducer (RAC) system were compared with similar data obtained from an automated sphygmomanometer that uses both oscillometric (OSC) and auscultatory measurement techniques. Data were obtained from 50 patients during and immediately after surgery. The fundamental frequency of the RAC system was 23.7 ± 6.7 Hz (mean ± SD; range, 13 to 40 Hz), and the damping coefficient was 0.26 ± 0.06 (mean ± SD; range, 0.15 to 0.34). Linear regression analysis of RAC against OSC values (n = 385) revealed the following correlations: (1) systolic pressure: OSC = 0.92(RAC) + 3.5, r = 0.91; (2) diastolic pressure: OSC = 0.92(RAC) + 1.3, r = 0.76; and (3) mean pressure: OSC = 0.96(RAC) + 0.68, r = 0.84. There were significant differences between each pair of pressure values; mean percent differences (RAC pressure minus OSC pressure) were 4.5 ±0.3%, 5.5 ± 0.7%. and - 2.7 ± 0.5% for systolic, diastolic, and mean values, respectively. Manual and automated auscultatory measurements closely agreed, and both correlated well with OSC values for systolic and diastolic pressure. However, both manual and automated auscultatory, as well as OSC measurements, underestimated RAC systolic and overestimated RAC diastolic pressure.     

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.     

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.     

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.     

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.     

Does measurement of systolic blood pressure with a pulse oximeter correlate with conventional methods?

The pulse oximeter is commonly used in the operating room. We evaluated the use of a pulse oximeter to monitor systolic blood pressure in 20 healthy volunteers and 42 anesthetized patients. We compared the pulse oximeter method of measuring systolic blood pressure with the cuff methods using Korotkoff sounds and Doppler ultrasound as well as with direct pressure measurement through an intraarterial cannula. Systolic blood pressure values obtained by pulse oximeter correlated well with values obtained by other conventional methods. The best correlation was found with Doppler ultrasound (r = 0.996) and the worst with arterial cannulation (r = 0.880). We conclude that this method can be used intraoperatively to measure systolic blood pressure.     

A quantitative evaluation of the Hewlett-Packard 78354A noninvasive blood pressure meter

Oscillometrically determined brachial artery pressures were compared with simultaneous contralateral radial intraarterial pressures in 19 anesthetized adult cardiac surgical patients throughout their surgical procedures, interrupted only by nonpulsatile, low-pressure, low-flow cardiopulmonary bypass. Radial intraarterial pressure values ranged widely for systolic (55 to 207 torr), mean (43 to 141 torr), and diastolic (26 to 106 torr). Both error specification methods proposed by the Association for the Advancement of Medical Instrumentation were used and compared. As expected, error method 1 gave consistently lower mean errors, smaller error standard deviations, and higher correlation coefficients than did error method 2. The errors during time periods immediately before and after cardiopulmonary bypass were compared with those from more quiescent times. Higher mean errors, larger error standard deviations, and lower correlation and regression coefficients were found during those time periods surrounding cardiopulmonary bypass. In general, mean errors were lowest for systolic pressure, followed by mean and diastolic pressures in that order, whereas error standard deviations were smallest for mean pressure, followed by systolic and diastolic pressures. Correlation and regression coefficients were highest for systolic pressure, followed by mean and diastolic pressures. In summary, the oscillometric method provides convenient and reproducible estimates of radial intraarterial pressure during most clinical situations, typically with better accuracy than the auscultatory Korotkoff method. The accuracy and reproducibility are diminished during those periods immediately surrounding cardiopulmonary bypass, perhaps due to direct surgical manipulation of the heart with its attendant rapid changes in cardiac output and blood pressure.     

Peripheral vascular effects on auscultatory blood pressure measurement

Experiments were conducted to examine the accuracy of the conventional auscultatory method of blood pressure measurement. The influence of the physiologic state of the vascular system in the forearm distal to the site of Korotkoff sound recording and its impact on the precision of the measured blood pressure is discussed. The peripheral resistance in the arm distal to the cuff was changed noninvasively by heating and cooling effects and by induction of reactive hyperemia. All interventions were preceded by an investigation of their effect on central blood pressure to distinguish local effects from changes in central blood pressure. These interventions were sufficiently moderate to make their effect on central blood pressure, recorded in the other arm, statistically insignificant (i.e., changes in systolic [p<0.3] and diastolic [p<0.02]). Nevertheless, such alterations were found to modify the amplitude of the Korotkoff sound, which can manifest itself as an apparent change in arterial blood pressure that is readily discerned by the human ear. The increase in diastolic pressure for the cooling experiments was statistically significant (p<0.001). Moreover, both measured systolic (p<0.004) and diastolic (p<0.001) pressure decreases during the reactive hyperemia experiments were statistically significant. The findings demonstrate that alteration in vascular state generates perplexing changes in blood pressure, hence confirming experimental observations by earlier investigators as well as predictions by our model studies.Supported in part by NIH grants no. HL 10,330, HL 22,223, and HL 31,480.     

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.     

Mean blood pressure algorithms

Alternative methods of calculating average blood pressure are examined. It is suggested that the preferred method is calculation of the arithmetic mean if the average value itself is required. However, when blood pressure values arc used to calculate other results, only the instantaneous value is appropriate in all situations. Arithmetic mean blood pressure values may be used with arithmetic mean flow values to calculate resistance, but only if resistance is constant over the interval (laminar flow). To calculate ventricular stroke work, the root mean square averages must be used because in this instance the arithmetic average yields large errors. Most monitors do not use these methods consistently to derive average blood pressure values, thus, the displayed values differ from those obtained from the appropriate calculation. Computational convenience, truncation error in averaging, or true errors in measurement or understanding of the associated physiologic state may account for observed differences. The interpretation of maximum systolic and minimum diastolic pressures with each beat requires additional considerations. Common monitoring algorithms obscure clinically important details, particularly by distorting the relationship between respiratory variation and pulse pressure. Electrical Engineering Physiology     

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.     

Forehead pulse oximetry compared with finger pulse oximetry and arterial blood gas measurement

Usual monitoring sites for pulse oximetry involve the fingers, toes, ear lobe, and nasal septum. This study examined the performance of a forehead sensor compared with a finger sensor for the pulse oximeter and arterial blood gas (ABG) analysis. Ten healthy adult volunteers and 22 ventilator-dependent patients were studied. The arterial oxygen saturation detected by forehead pulse oximetry (SpO₂) correlated well with finger SpO₂ and arterial oxygen saturation (SaO₂) determined by arterial blood gas analysis in the healthy volunteers. Forehead SpO₂ in mechanically ventilated patients correlated well with finger SpO₂ and SaO₂ when heart rate detected by pulse oximeter differed less than 10% from apical heart rate. Factors that caused a difference in oximeter-detected heart rate and apical heart rate were extensive tissue edema, head movement, and difficulty securing good tape placement. This suggests that when signal strength is weak, causing poor pulse rate detection, there will also be problems associated with accurate SpO₂. The forehead pulse oximeter sensor works well on healthy, well-oxygenated volunteers. Difficulty was experienced when applying and using the sensor on critically ill patients. The reliability of the forehead pulse oximeter sensor has not been established at low saturations.     

Remote auscultatory patient monitoring during magnetic resonance imaging

A system for patient monitoring during magnetic resonance imaging (MRI) is described. The system is based on remote auscultation of heart sounds and respiratory sounds using specially developed pickup heads that are positioned on the precordium or at the nostrils and connected to microphones via polymer tubing. The microphones operate in a differential mode outside the strong magnetic field to reduce various sources of interference from the MRI equipment. After amplification, the signal is transmitted as infrared light to a small, battery-operated receiver and a headphone set. Thus, the patient can be simultaneously auscultated both inside and outside the shielded MRI room by infrared transmission through a metal mesh window. Bench tests of the system show that common mode acoustic noise is suppressed by approximately 30 dB in the frequency region of interest (100–1,000 Hz), and that polymer tubing having a diameter of approximately 2 mm can be used for efficient sound transmission. Recordings in situ show satisfactory detection of both heart sounds and respiratory sounds, although the signal is somewhat masked by noise during imaging. A clinical test incorporating 17 sedated or anesthetized patients was also performed. In all but four cases, the quality of the breath and heart sounds was regarded as acceptable or better.The authors are indebted to Dr Hans Selldén, St. Göran's Hospital, Stockholm, for his contributions to the clinical part of the study.This study was supported by the Swedish Board for Technical Development.     

Algorithm to identify components of arterial blood pressure signals during use of an intra-aortic balloon pump

Existing bedside cardiovascular monitors often inaccurately measure arterial blood pressure during intra-aortic balloon pump (IABP) assist. We have developed an algorithm that correctly identifies features of arterial pressure waveforms in the presence of IABP. The algorithm is adaptive, functions in real-time, and uses information from the electrocardiographic (ECG) and arterial blood pressure signals to extract features and numeric values from the arterial blood pressure waveform. In its current form, it requires reliable ECG beat detection and was not intended to operate under conditions of extremely poor balloon timing. The algorithm was evaluated by an expert (P.F-C.) on a limited data set, which consisted of 12 1-minute epochs of data recorded from 6 intensive care unit patients. A criterion for selection of patients was that the ECG beat detector could detect ECG beats correctly from the waveforms. The overall sensitivity and positive predictivity for beat detection were 94.04% and 100%, respectively. For feature identification, the overall sensitivity was greater than 89%, positive predictivity was 100%, and the false-positive rate was 0%. The performance measures may be biased by the criteria for patient selection. This approach to identifying waveform features during IABP improves the accuracy of measurements. The utility of using 2 sources of information to improve measurement accuracy has been demonstrated and should be applicable to other physiologic signal-processing applications.     

Oxygen uptake and mean blood pressure as indicators of induced hyperthermia

This dog study was designed to identify which of two measurements (oxygen consumption, mean blood pressure) tracked the onset of hyperthermia as reflected by rectal temperature. The animals were anesthetized, paralyzed, and mechanically ventilated. Hyperthermia was induced with 2,4-dinitrophenol (5 mg/kg) injected intravenously in 5 dogs. It was found that the best and earliest predictor of approaching hyperthermia was the increase in oxygen consumption, which increased 10% in 1.72 min. Mean blood pressure was an insensitive indicator of approaching hyperthermia. Rectal temperature, not surprisingly, was found to be a late and undependable early indicator of developing hyperthermia, requiring about 15 minutes to exhibit a definite increase. It is concluded that among these indicators, monitoring oxygen consumption (ml/min) is the most reliable way to identify a metabolic change such as incipient hyperthermia.     

Optimal sites for forehead oscillometric blood pressure monitoring

Objective. Blood pressure is usually measured noninvasively with a cuff on the arm or the leg. Circumstances exist, however, when an alternative site for blood pressure measurement is desirable. This study is designed to identify a location on the forehead where blood pressure can be reliably measured noninvasively.Methods. We mapped the superficial temporal artery and/or the supraorbital artery in 65 volunteers and found a rectangular area where an adhesive pressure pad could be placed over each artery. Oscillometric signals were recorded from four different locations over the forehead in 19 of the 65 volunteers to compare the amplitude of the signal and mean blood pressure between locations.Results. The course of the supraorbital artery is quite consistent. It passed through a 2.5-×1-cm rectangular area on the forehead in all volunteers in which it was mapped. The medial border of the rectangle is 0.5-cm medial and 1-cm above the medial corner of the left eyebrow. The course of the superficial temporal artery differed remarkably from person to person. We could not find an area of reasonable size to cover the artery in all volunteers. Mean blood pressures were the same in all forehead locations. The signal was the weakest on the center of the forehead and strongest directly over the superficial temporal artery.Conclusions. Our results show that the supraorbital artery, an end-artery of the internal carotid artery, which emerges through the supraorbital foramen and crosses the forehead near the center, is the preferred site to monitor blood pressure noninvasively on the forehead with an adhesive pressure bladder.This study was supported, in part, by Innerspace Medical Inc., Irvine, CA, and by NASA's Rocky Mountain Space Grant Consortium. This study was presented, in part, at the 1994 Annual Meeting of the American Society of Anesthesiologists, San Francisco, October 15–19, 1994.     

着衣测量血压对结果的影响

目的探讨血压计袖带缠绕上肢时隔一层衣物对血压测量结果的影响。方法用2种方法分别测量同一组研究对象的右上肢肱动脉血压，2种方法测得的血压值采用配对t检验的方法进行统计学分析。结果2种方法测得的收缩压和舒张压值在统计学上差异均有显著性，隔一层厚度〈0．5cm衣物测得的收缩压和舒张压值均显著高于标准方法测得的血压值（P〈0．01）。收缩压的平均差值为1．54mmHg，舒张压的平均差值为1．01mmHg。结论医护人员在为无血压异常病史的患者测量血压时，可以隔一层厚度〈0．5cm的衣袖缠绕袖带进行测量，这样对血压测量的结果不会有显著影响。对处于高血压或低血压临界值的患者，在测量血压时，一定要按标准方法操作。     

四种血糖测定方法的比较

目的了解四种血糖测定方法结果的差异及影响因素。方法分别用己糖激酶法（HK）、氧化酶法（GOD—POD）法和手工比色法测定53例患者血清葡萄糖浓度,同时用血糖监测仪测定患者毛细血管血葡萄糖浓度,然后对四组测定结果进行配对资料t检验处理及相关性分析。结果血糖正常时,HK法比GOD—POD法结果平均高0．13mmol／L（2．5％）,比手工比色法结果平均高0．49mmol／L（9．4％）,比血糖监测仪结果平均高0．30mmol／L（5．7％）,分别对HK法与GOD-POD法、GOD-POD法与手工比色法、HK法与血糖监测仪进行相关分析,相关系数1分别为0．99、0．94和0．68;高血糖时,HK法比GOD-POD法结果平均高0．20mmol／L（1．7％）,比手工比色法结果平均高1．84mmol／L（15．7％）,比血糖监测仪结果平均高1．5mmol／L（12．9％）,其相关系数吖分别为0．99、0．95和0．85。结论血糖正常时,HK法与GOD-POD法、手工比色法、血糖监测仪所测结果均有显著性差异,P值分别为〈0．01、〈0．01及〈0．05;高血糖时,HK法与GOD-POD法、手工比色法及血糖监测仪所测结果均有显著性差异,P值均〈0．01。相关性分析表明,HK法与GOD—POD法呈高度直线正相关,GOD-POD法与手工比色法相关性良好,而HK法与血糖监测仪相关性较差。     

Noninvasive continuous blood pressure measurement: A clinical evaluation of the Cortronic APM 770

The Cortronic APM 770 (Cortronic, Ronkonkoma, NY) is a commercial device that claims to measure blood pressure noninvasively and continuously with the use of a standard blood pressure cuff. The aim of our study was to assess the performance of the continuous-mode blood pressure readings of the Cortronic during anesthesia and surgery. We recorded blood pressure in 5 patients bilaterally. An intraarterial pressure (IAP) curve was recorded from 1 arm and the Cortronic pressure curve (CPC) was recorded from the other. For statistical analysis the period between 2 Cortronic recalibrations was defined as the intercalibration interval. The duration of these intervals ranged from 20 to 0.5 minutes. Four paired samples were drawn from each interval. The first sample in an interval represented the recalibration blood pressure; the other samples represented the continuous blood pressure. A total of 1,232 samples were taken, of which 308 were recalibration. The median of the differences and the 2.5th and 97.5th percentile limits of agreement were determined. Their respective values for diastolic and systolic recalibration measurements were 5, –17, and 34 mm Hg, and 6, –12, and 38 mm Hg. Their values for continuous measurements were 4, –23.5, and 32 mm Hg, and 6, –30, and 70 mm Hg. Changes in CPC were evaluated against changes in the corresponding IAP by plotting them in 4-quadrant graphs. In these graphs the Spearman rank correlations were betweenr=–0.17 andr=0.01. We observed opposite CPC and IAP trends on 24 occasions during this study. We performed a simple simulation study to better understand the measurement method of the Cortronic. The study showed a positive relationship between pulsation volume and CPC amplitude, and between pulsation rate and CPC amplitude. We conclude that during anesthesia and surgery continuous-mode blood pressure readings of the Cortronic are unreliable, and suggest that the phenomenon of the two pressures' moving in opposite directions is inherent to the measurement principles of the device.