Indirect Blood Pressure Measurement Research Articles

Assessment of blood pressure in cats presented with urethral obstruction

AbstractObjective: To determine the arterial blood pressure at presentation in male cats with acute urethral obstruction, and to determine whether there was any correlation between these measurements and concurrent metabolic abnormalities.Design: Prospective, single cohort, observational study.Setting: Private, small animal, after‐hours emergency clinic.Animals: Twenty‐eight client‐owned male cats with acute urethral obstruction and no other known coexisting disease.Interventions: Indirect oscillometric blood pressure measurements obtained before blood sampling and treatment.Measurements and main results: Mean arterial blood pressure (MAP) measurements, physical examination parameters, serum blood urea nitrogen (BUN), creatinine, potassium, phosphorus, total calcium and magnesium concentration, venous pH, lead II electrocardiogram, and urine volume in bladder were evaluated. No cats were hypotensive at presentation; 71% (20/28) were normotensive (median MAP=100 mmHg, range 93–140 mmHg); and 29% (8/28) were hypertensive (median MAP=153 mmHg, range 145–176 mmHg). Compared with hypertensive cats, normotensive cats had significantly lower heart rates (P=0.0201) and lower calcium (P=0.0152). For all 28 cats, MAP correlated with serum potassium and total calcium (P=0.0033).Conclusions: Though potassium and total calcium were inversely and directly correlated respectively with blood pressure in cats with urethral obstruction, none of the cats were hypotensive on presentation. Normotension on admission does not support the absence of biochemical and physical abnormalities in obstructed cats.

Nonpulsatile and Noninvasive Transmittance and Reflectance Tissue-bed Oximetry

A new optical device was developed that measures blood pressure noninvasively, in small human subjects (neonates and premature infants) and small animals (Roeder RAR. Transducer for indirect measurement of blood pressure in small human subjects and animals, Purdue University, BME; 2003.: xi, 50 p.). The ability of this device to measure oxygen saturation enhances its value. The objective of this research was to add the ability to obtain SaO(2) from the same device and to obtain the calibration curve. Another objective was to determine which measurement method (transmittance or reflectance) is preferable. This new oximeter is unlike the conventional pulse oximeter in that it does not require a pulse, making it ideal for measuring oxygen saturation noninvasively in small human subjects with small amplitude pulses or without a pulse. A study was performed in 11 pigs, ranging in weight 20-27 kg. The pig tail was used as the measuring site for %SaO(2) measurements. Arterial blood samples were obtained from the femoral artery and oxygen saturation was measured with a blood-gas analyzer. A small blood-pressure cuff was used to render the optical path bloodless. A comparison of the transmittance and reflectance methods for measuring oxygen saturation was made. %SaO(2) measurements ranged from 4% to 100%. It was found that both the transmittance and reflectance methods can be used to measure %SaO(2) reliably in situations with or without a pulse.

Accuracy of an oscillometric blood pressure monitor during phenylephrine-induced hypertension in dogs

To examine the agreement between direct arterial blood pressure measurements obtained from 2 arteries and indirect blood pressure measurements obtained with an oscillometric blood pressure monitor (OBPM) during normotension and phenylephrine-induced hypertension in dogs. 16 male Beagles. In anesthetized dogs, arterial catheters were placed in the lingual and dorsal pedal arteries for measurement of arterial blood pressure. A blood pressure cuff was placed on either the dog's fore- or hind limb and connected to an OBPM. Systolic, diastolic, and mean arterial blood pressures (SAP, DAP, and MAP, respectively) were recorded from both arteries and the OBPM every 5 minutes for 30 minutes (baseline), during a 30-minute period in which dogs received a phenylephrine infusion IV to induce hypertension, and for 30 minutes after discontinuation of the infusion. Mean differences in blood pressure values and confidence intervals were calculated to compare the indirect and direct measurement techniques. In dogs, oscillometry underestimated SAP during normotension, and the difference between oscillometric and direct measurements increased during hypertension. Oscillometry underestimated DAP, but the difference between oscillometric and direct measurements decreased during hypertension. There was close agreement among techniques for MAP determinations. Biases between direct measurements and OPBM blood pressure values measured from dogs' forelimbs or hind limbs were not significantly different. In normotensive dogs, oscillometric measurements of MAP and SAP agreed more closely with direct arterial pressure measurements than oscillometric estimates of DAP. Oscillometric measurement of MAP was accurate during both normotension and hypertension in dogs.

Monitoring arterial pressure

Monitoring arterial pressure is an important aspect of providing clinical care to the anaesthetized and critically ill patient. Because auto-regulation of major organ blood flow may be impaired in these patients, maintenance of an adequate organ perfusion pressure is essential, particularly to vital areas such as the brain, heart and kidneys. It is imperative that those patients experiencing or at risk of cardiovascular instability and inadequate organ perfusion are selected for direct continuous monitoring with beat-to-beat variation. Other patients still requiring routine cardiovascular monitoring may be adequately monitored with intermittent indirect blood pressure measurement. This article outlines the different types of arterial monitoring seen in the intensive care and operating theatre environment.

Evaluation of cuff-wrapping methods for the determination of ankle blood pressure

The ankle-brachial index, which is calculated by dividing ankle systolic blood pressure by brachial systolic blood pressure, is useful in diagnosing peripheral arterial disease. Consensus has not been reached, however, on a standard method for measuring ankle systolic blood pressure. This study evaluated two cuff-wrapping methods for measuring ankle systolic blood pressure, compared with intra-arterial pressure as a gold standard. Study participants were 24 consecutive adult patients who underwent surgery under general anesthesia at Kyoto Prefectural University Hospital in Japan between January and March 2002. Indirect ankle systolic blood pressure was measured in the posterior tibial artery using a Doppler device and two cuff-wrapping methods: spiral, and straight. Direct ankle systolic blood pressure was measured in the dorsalis pedis artery. Mean difference in ankle systolic blood pressure between indirect and direct measurements (indirect minus direct) was 1.4 mmHg [standard deviation of the difference (SDd), 17.6 mmHg] with the straight method and -1.4 mmHg (SDd, 22.2 mmHg) with the spiral method. The limit of agreements (mean difference +/-2 SDd) and intraclass correlation coefficient between two observers were -17.6 to 20.1 mmHg and 0.94, respectively, for the straight method and -39.4 to 40.0 mmHg and 0.78, respectively, for the spiral method. The straight method, the same cuff-wrapping method used for measuring brachial blood pressure, appears to represent a more suitable wrapping method because of better interobserver reproducibility. Accuracy and reproducibility of indirect ankle systolic blood pressure measurement, however, were not adequately improved by either of the wrapping methods.

Unique endothelial gene expression sensitivities to shear stress magnitude and spatial gradient

Indirect blood pressure measurements using high definition oscillometric (HDO) and Doppler devices were compared in 50 anaesthetised client-owned cats presented for various surgical procedures. Sites of cuff placement for Doppler were identified as forelimb and hindlimb and for HDO as forelimb and tail. Oscillometric and Doppler readings were obtained in 90.05% and 100% of attempts, respectively. Both devices enabled precise measurement of systolic arterial pressure (SAP), although the Doppler device gave higher precision. In the low pressure group (SAP < 100 mmHg; n = 30), 66.7% biases were within 10 mmHg of discrepancy, but in groups of normal (100 mmHg ≤ SAP ≤ 150 mmHg; n = 120) and high measurements (SAP > 150 mmHg; n = 62), 86.7% and 75.0% of discrepancy, respectively, were lower than 10 mmHg. Frequency of discrepancy at the range of 15 mmHg showed similar differences between pressure groups. There were significantly higher discrepancies when the cuff was positioned on the tail rather than on the leg. The SAP value obtained by HDO can be calculated from the Doppler measurement from SAP (HDO) = 0.8515 × SAP (Doppler) + 19.221 mmHg. Compared to Doppler, HDO overestimated low pressure and underestimated high pressure values.

Accuracy of Indirect Measurement of Blood Pressure in Neonatal Foals

The objectives of this study were to assess, in anesthetized neonatal foals, the accuracy of 2 automated indirect oscillometric monitors for measurement of mean arterial pressure (MAP), to determine the optimal site of cuff placement for MAP monitoring, and to determine the relationship between arterial blood pressure and cardiac output. Ten neonatal foals were anesthetized and instrumented with a catheter in the metatarsal artery for direct MAP monitoring and measurement of cardiac output by lithium dilution. Concurrent MAP measurements were obtained with Cardell and Dinamap oscillometric monitors with cuffs placed at 3 different sites (coccygeal, metatarsal, and median arteries). Blood pressure was manipulated by varying the depth of anesthesia and by administration of dobutamine or phenylephrine. A statistically significant (P = .025) interaction was found between the type of monitor and cuff placement site. With the Cardell monitor, placement of the cuff over the coccygeal artery resulted in a significantly lower bias than placement over the median or dorsal metatarsal artery (P < .0001 and P = .0149, respectively). No significant difference in bias was found with cuff placement site when using the Dinamap monitor. The correlation coefficient (r) between MAP and cardiac output was 0.47. Indirect oscillometry with a cuff placed over the coccygeal artery or dorsal metatarsal artery is an acceptable method for measuring MAP in foals. Blood pressure does not correlate well with cardiac output in anesthetized foals.

Determination of Indirect Blood Pressure in the Companion Bird

Abstract The information gathered through arterial blood pressure measurement must be correctly interpreted for appropriate decisions to be made. Systolic blood pressure is the pressure exerted against the blood vessel wall during systole. Although direct arterial pressure measurement is ideal, it is not commonly used because of the need for specific technical skill, invasive nature of the procedure, and cost of equipment. All indirect blood pressure measurement techniques are based on detection of blood flow beneath an inflated cuff. Systolic blood pressure determination via ultrasonic Doppler flow detection (Doppler) has been found to correlate well with direct blood pressure measurements in ducks ( Anas platyrhynchos). Clinical techniques and applications for Doppler blood pressure monitoring will be discussed. Treatment of hypotension involves monitoring blood pressure, removal of the underlying cause, and volume support for hypovolemia. Hypertension has not yet been defined in the psittacine species. The routine use of blood pressure monitoring in the avian species can provide the clinician with a better knowledge base about intravascular volume status to avoid or minimize long-term complications of hypertension.

A comparison of CAT Doppler and oscillometric Memoprint machines for non-invasive blood pressure measurement in conscious cats

Indirect blood pressure measurements were compared in 28 conscious cats using Doppler and oscillometric blood pressure-measuring devices. Ten cats were used to compare Doppler measurements between two examiners and 18 cats were used to compare Doppler and oscillometric measurements. The Doppler machine obtained systolic and diastolic blood pressure readings in 100% and 51% of attempts, respectively. With the oscillometric machine, systolic and diastolic blood pressure readings were obtained in 52% of the attempts. With the Doppler, measures of mean systolic blood pressure between two examiners were positively correlated, but there was no correlation for diastolic blood pressure measures. When comparing the results obtained by Doppler and oscillometric machines there was no significant difference between mean systolic blood pressure readings, but the oscillometric machine produced significantly higher estimates of diastolic blood pressure. In both cases, the standard deviations for the oscillometric machine were considerably larger than those for the Doppler machine. The first reading of systolic blood pressure obtained with the Doppler machine was an excellent predictor of the mean of five readings, but this was not so for the oscillometric machine. It took less than 5 min to obtain five readings in 37.5% of cases with the Doppler machine but this was true for only 5% of cases with the oscillometric machine. Two cats with ophthalmological lesions consistent with systemic hypertension were identified. In these two patients, systolic blood pressure measurements were between 200 and 225 mmHg when measured by Doppler, and between 140 and 150 mmHg when measured by the oscillometric machine. This suggests that a lower reference range for normal systolic blood pressure values should be used for the oscillometric device.

Accuracy of Indirect Measurement of Blood Pressure in Neonatal Foals

Accuracy of Indirect Measurement of Blood Pressure in Neonatal Foals

ASSESSMENT OF BLOOD PRESSURE IN CATS PRESENTED WITH URETHRAL OBSTRUCTION

Introduction: The biochemical consequence of acute obstructive uropathy can alter the hemodynamic profile. The objectives of this study were to determine the arterial blood pressure at presentation of male cats with acute urethral obstruction and to correlate these measurements with concurrent metabolic abnormalities.Study Design: Prospective research study in a private small animal after‐hours emergency clinic. The subjects were client owned male cats presented with acute urethral obstruction and no other known concurrent disease.Measurements: Indirect oscillometric blood pressure measurements of urethral obstructed male cats were obtained at admission prior to blood sampling and treatment. Data recorded and studied: mean arterial blood pressure (MAP), physical examination parameters, serum blood urea nitrogen (BUN), creatinine, potassium, phosphorus, total calcium and magnesium concentration, venous pH, electrocardiogram lead II, and urine volume in bladder.Results: Twenty‐eight cats were included in the study. Using normal values for MAP in cats, the results fell into 2 groups: normotensive (MAP 90–140 mmHg) and hypertensive (MAP&gt;140 mmHg). Seventy‐one percent (20/28) were considered normotensive (mean 113±14.6 mmHg). Twenty‐nine percent (8/28) were considered hypertensive (mean 154±9.8 mmHg). In the normotensive group, the mean body temperature was 37.6±1.5°C, the mean heart rate was 179±42.2/min, and 64% (9/20) had an abnormal cardiac rhythm. In the hypertensive group, the mean body temperature was 38.3±0.6°C, the mean heart rate was 219±18.0/min, and all had normal cardiac rhythm. In the normotensive group, the serum biochemical abnormalities were more severe. Sixty percent of the normotensive casts (12/20) were azotemic (BUN&gt;34 mg/dl) with a mean of 114±95.2; 58% (11/19) were hypercreatinemic (&gt;2.2 mg/dl) with a mean of 8.9±7.9, and 55% (11/20) were hyperkalemic (&gt;4.2 mEq/L) (mean 6.2±7.9). Within the hypertensive cats group, 50% (4/8) were mildly azotemic (BUN – mean 49±24.4 mg/dl); 50% (4/8) were hypercreatinemic (mean 2.9±1.95 mg/dl), and only 1/8 was hyperkalemic (mean 3.9±0.6 mEq/L). The volume of urine in the bladder at the time of presentation did not seem to be significantly different between the 2 groups (94.7±57.1 ml in the normotensive group vs. 83.8±26.7 ml in the hypertensive group).Conclusions: The results suggest that cats with acute urethral obstruction and a normal mean arterial pressure at presentation were more likely to have severe azotemia, hypercreatinemia and hyperkalemia.

Using photoplethysmographic signal for increasing the accuracy of indirect blood pressure measurement

Using photoplethysmographic signal for increasing the accuracy of indirect blood pressure measurement

Both body and arm position significantly influence blood pressure measurement

The position of both the body and the arm during indirect blood pressure (BP) measurement is often neglected. The aim of the present study was to test the influence of the position of the patient on BP readings: (1) sitting with the arms supported precisely at the right atrium level and (2) supine: (a) with the arms precisely at the right atrium level and (b) with the arms on the examination bed. In a first group of 57 hypertensive patients, two sessions of BP and heart rate (HR) measurements were performed in two positions: sitting and supine with the arms supported precisely at right atrium level in both positions. BP was measured simultaneously at both arms, with a Hawksley Random Zero sphygmomanometer at the right arm, and with an automated oscillometric device (Bosomat) at the left arm. BP and HR readings obtained in the two positions were then compared. In a second group of 25 normo- and hypertensive persons, two sessions of BP and HR readings were performed in supine with the arms in two different arm positions: (a) the arm placed precisely at right atrium level and (b) the other arm on the examination bed. The measurements were performed at both arms with two automated devices (Bosomat). The readings taken in the two positions were compared. Both systolic BP (SBP; by 9.5 +/- 9.0 (standard deviation, s.d.); right arm) and diastolic BP (DBP; by 4.8 +/- 6.0 mmHg; right arm) were significantly higher in the supine than in the sitting position. When the two different arm positions (body continously supine) were compared in the second part of the study, significantly higher SBP (by 4.6 +/- 6.1 mmHg) and DBP (by 3.9 +/- 2.8 mmHg) were obtained when the arm of the patient was placed on the bed (below the right atrium level), than when the arm was placed at the level of the right atrium. BP readings in sitting and supine positions are not the same. When according to guidelines the arm of the patient is meticulously placed at the right atrium level in both positions, the difference is even greater than when the arm rests on the desk or on the arm support of the chair. Moreover, in the supine position small but significant differences in BP are measured between arm on a 5 cm-high pillow and arm on the bed. In every study reporting BP values, the position of both the body and especially the arm should be precisely mentioned.

Indirect arterial blood pressure measurement in nonsedated Irish wolfhounds: reference values for the breed.

Arterial blood pressure measurements were obtained from 158 healthy Irish wolfhounds using the oscillometric technique to establish reference values for the breed. In contrast to other sight hounds, Irish wolfhounds have low arterial blood pressure. Mean systolic pressure for the group was 116.0 mm Hg. Mean diastolic pressure was 69.2 mm Hg, and the mean value for mean arterial pressure was 87.8 mm Hg. Blood pressure measurements were higher in older wolfhounds than in young dogs. There was no difference between systolic and mean arterial blood pressures in lateral recumbency compared to standing position. However, diastolic pressure was slightly lower when standing. Calm dogs had lower pressure than anxious wolfhounds. There was a significant interaction between the effects of age, gender, and mood on systolic, diastolic, and mean arterial blood pressure values.

Indirect oscillometric and direct blood pressure measurements in anesthetized and conscious neonatal foals

AbstractObjective:To investigate the agreement between indirect oscillometric and direct blood pressure measurement in the equine neonate.Design:Prospective observational study.Setting:University Veterinary Teaching Hospital.Animals:Ten crossbred foals of 30–46 hours of age.Interventions:Six animals (Group 1) were anesthetized. Four animals (Group 2) were restrained on a mat. All animals were instrumented with a catheter in the greater metatarsal artery and an oscillometric blood pressure cuff over the coccygeal artery. Blood pressure was varied with dobutamine, phenylephrine, nitroprusside, and increased depth of anesthesia (Group 1) or dopamine (Group 2).Measurements and main results:Simultaneous direct and indirect blood pressure measurements were obtained from the greater metatarsal artery and the coccygeal artery, respectively. There was good agreement between the 2 methods for mean and diastolic blood pressures in both groups, but not for systolic pressure. The agreement was best in mean blood pressure of anesthetized foals (mean bias –1.07; limits of agreement – 9.39, 7.25 mmHg).Conclusions:Indirect oscillometry appears to be an acceptable method for measuring mean arterial blood pressure in both anesthetized and conscious neonatal foals, and may be a valid method of monitoring critically ill foals.

Model-based synthetic fuzzy logic controller for indirect blood pressure measurement

In this paper, a new measurement system for the noninvasive monitoring of the continuous blood pressure waveform in the radial artery is presented. The proposed system comprises a model-based fuzzy logic controller, an arterial tonometer and a micro syringe device. The flexible diaphragm tonometer registers the continuous blood pressure waveform. To obtain accurate measurement without distortion, the tonometer's mean chamber pressure must be kept equal to the mean arterial pressure (MAP), the so-called optimal coupling condition, such that the arterial vessel has the maximum compliance. Since the MAP cannot be measured directly, to keep the optimal coupling condition becomes a tracking control problem with unknown desired trajectory. To solve this dilemma, a model-based fuzzy logic controller is designed to compensate the change of MAP by applying a counter pressure on the tonometer chamber through the micro syringe device. The proposed controller consists of a model-based predictor and a synthetic fuzzy logic controller (SFLC). The model-based predictor estimates the MAPs changing tendency based on the identified arterial pressure-volume model.

Indirect arterial blood pressure measurement at the wrist using a pad-type square cuff and volume-oscillometric method.

Using theoretical and experimental approaches, we examined whether blood pressure at the wrist can be accurately measured by a volume-oscillometric method using a small pad-type square cuff placed above the radial artery (RA). Nuclear magnetic resonance imaging of the wrist allowed us to determine the geometry of two-dimensional (2-D) finite-element models. Finite-element method (FEM) analysis predicted that the pressure transmission ratio (calculated tissue pressure over externally applied pressure; square cuff to RA) was 98.8% for a cuff with a bladder sidelength 0.25 times the wrist diameter placed on the skin surface between the tendons of the brachioradialis muscle (Ta) and the flexor capri radialis muscle (Tb) and over the site (L) at which RA crosses the most protuberant spot on the volar aspect of the distal end of the radius. In addition, FEM analysis using a 3-D finite-element model (constructed by extending the 2-D finite-element model at site L in the longitudinal direction) showed that for all square cuffs with bladder sidelengths greater than or equal to 0.25 times the wrist diameter, the external pressure was transmitted almost completely to RA beneath the cuff center. Moreover, when the bladder sidelength was 0.44 times the wrist diameter, but not 0.29 times the wrist diameter, the mean blood pressure measured at site L in human subjects was similar to that measured at the upper arm. Taken together, the theoretical and the experimental results suggest that (i) blood pressure at the wrist can be measured accurately using a pad-type square cuff placed on the skin surface between Ta and Tb at site L, and (ii) the minimum bladder sidelength for accurate readings is somewhere between one-third and one-half of the wrist diameter.

Direct vs. indirect blood pressure measurement at peak anaerobic exercise.

The present study compared the direct intra-arterial method with the indirect conventional sphygmomanometer during all-out anaerobic exercise, in young healthy subjects. Systolic and diastolic blood pressures were measured by intraarterial means and by auscultation. Fourteen young healthy males (23+/-2 yrs) were measured at rest and during all-out anaerobic exercise. Comparisons were made with simultaneously determined intra-arterial catheter and auscultation measurements. The data suggest that indirect systolic pressure is highly correlated with the direct method at rest (r = 0.684), with mean of 107+/-7 and 101+/-6 mmHg, respectively, and during all-out anaerobic exercise (r = 0.87), with mean of 197+/-11 and 191+/-9 mmHg, respectively. Indirect diastolic blood pressure correlates well with intra-arterial at rest (r = 0.62), with mean of 84+/-11 and 77+/-9 mmHg, respectively. However, during all-out anaerobic exercise, the correlation coefficient between the direct and the indirect methods was low (r = 0.36), with mean of 101+/-12 and 103+/-9 mmHg, respectively. These results suggest that when utilizing an all-out anaerobic exercise, the indirect method is not valid for assessment of diastolic pressure. In addition, although the anaerobic test is a dynamic type of exercise, its blood pressure responses for both direct and indirect methods were similar to those seen during isometric exercise.

Interand Intraindividual Variation in Doppler Ultrasonic Indirect Blood Pressure Measurements in Healthy Cats

This study was undertaken to evaluate reference ranges for systolic blood pressure (SBP) in cats under conditions mimicking a clinical setting. SBP was measured in 50 healthy adult cats of various ages (range, 1.5–16 years) and body weights (range, 2.2–6.1 kg) by Doppler ultrasonic sphygmomanometry. A cuff width of 2.5 cm was used, placed on the left antebrachium, and this represented a mean cuff width of 35% limb circumference (range, 31–42%). The mean (6SD) SBP in the 50 cats was 162 ± 19 mm Hg (range 124–210), with only 1 cat having a SBP ≤ 200 mm Hg. No significant difference (P &gt; .05) in SBP was found between male and female cats, and no significant correlation was found between SBP and age (rs= 0.075) or body weight (rs= 0.007). Further studies in some of these cats indicated that allowing a period of 10 minutes for acclimatization to the environment where SBP was recorded resulted in a significant decrease in SBP from 176 ± 17 to 157 ± 21 mm Hg (n = 7) and that use of a 3.3‐cm‐width cuff resulted in a significant decrease in measured SBP from 168 ± 13 to 164 ± 13 mm Hg (n = 10). Reproducibility of SBP measurements was evaluated in 7 cats by assessing SBP 7 times at intervals of ≤24 hours over a 10‐day period. These 7 cats had a low intraindividual coefficient of variation of SBP measurements (CV ≥ 7.9%) although 2 of the 7 cats had SBP values .200 mm Hg on at least 1 occasion.

The relative accuracy of sequential same-arm and simultaneous opposite-arm measurements for the intra-arterial validation of blood pressure monitors

To compare the results of simultaneous opposite-arm and sequential same-arm intra-arterial validation of automated blood pressure monitors. Intra-arterial blood pressure measurements were compared with blood pressure measurements obtained using conventional sphygmomanometry and two automated blood pressure monitors (the Dinamap XL and the SpaceLabs Scout) using a methodology based on the protocol published by the Association for the Advancement of Medical Instrumentation (AAMI) for the intra-arterial validation of automated monitors. Thirteen women with radial arterial lines were recruited from the obstetric intensive care unit at Groote Schuur Hospital, Cape Town. For each woman, intra-arterial blood pressure measurements were compared with those obtained by mercury sphygmomanometry and by using the two automated blood pressure monitors with both a sequential same-arm protocol and a simultaneous opposite-arm protocol. The mean and SD of the differences was calculated for each protocol and the results were compared using Student s t test. The differences between the 'means of the differences' for these two protocols never differed by more than 2 mmHg. For individuals the differences between data obtained using the two methodologies were up to 32 mmHg for mercury sphygmomanometry and 18 mmHg for the automated monitors. The differences between the SD of the differences were all less than 3 mmHg except for that of systolic blood pressure obtained by mercury sphygmomanometry, which was 7 mmHg The results of this study show that a sequential same-arm and a simultaneous opposite-arm comparison of intra-arterial and indirect blood pressure measurements yield similar results.