Intra-arterial Pressure Measurements Research Articles

Effects of Cryopreservation on the Viscoelastic Properties of Human Arteries

The purpose of this study was to use our newly developed mock circulation loop to determine the effects of cryopreservation on the common carotid artery (CCA) and the superficial femoral artery (SFA). Fourteen healthy arteries (7 CCA and 7 SFA) harvested from multiple organ donors between the ages of 18 and 35 years were tested before and after cryopreservation at -140 degrees C using dimethyl sulfoxide and the vapor phase of liquid nitrogen. Mean storage time was 4.2 months. The mock pulse rate was 60 beats/min and the following four systolic/diastolic pressures settings were used: 50/110, 80/140, 110/170, and 140/200 mm Hg. Simultaneous measurements of intra-arterial pressure and external arterial diameter were made using an intra-arterial pressure sensor and external piezoelectric sensors. Measured data were used to calculate pulsatility, volumetric compliance, stiffness, midwall radial arterial stress, Young's modulus, and the incremental modulus. After SFA cryopreservation, no significant changes were observed. Conversely, CCA cryopreservation led to a significant decrease in compliance and pulsatility and a significant increase in stiffness. Young's modulus, the incremental modulus, and midwall radial arterial stress did not change significantly. A clearcut decrease in hysteresis was observed after cryopreservation in the CCA. No evidence of structural changes was detected on light and scanning electron microscopy. Baseline findings in this study were consistent with classification of the CCA as an elastic artery and the SFA as a muscular artery. Cryopreservation had no effect on the viscoelastic properties of muscular arteries (SFA). Cryopreservation affected only values related to the cylindrical shape of the elastic arteries (CCA). It had no effect on values related to wall structure.

Intraarterial pressure measurements during angiographic evaluation of peripheral vascular disease: techniques, interpretation, applications, and limitations.

Many operative and percutaneous procedures are available for the treatment of occlusive disease involving the lower-extremity arterial system. Peripheral vascular disease involving the aorta and lower-extremity vessels usually is attributable to atherosclerosis. The lower-extremity arterial supply is divided segmentally into the inflow (aortoiliac) and outflow (femoropopliteal and tibioperoneal) vessels. Given the length of the lower-extremity vascular system, the propensity for multifocal disease, and the possibility of a nonvascular cause for a patient's symptoms, both localization of disease in arterial segments and determination of the hemodynamic impact of diseased sites are important for judicious treatment planning. This review focuses on the use of intraarterial pressure measurement as an adjunct to angiography and intravascular intervention in evaluating the significance of arterial occlusive disease in lower-extremity arteries.

Detection of sub-critical arterial stenoses by hyperaemic Doppler

This study assessed the potential of hyperaemic Doppler to detect sub-critical stenoses using a flowrig model. Pulsatile flow of a blood substitute was produced in a compliant circuit. A cadaver carotid artery, constricted by a silk suture produced a variable, focal stenosis. Forty-seven stenoses were created in five arteries. Pressure gradients and Doppler measurements were recorded simultaneously across each stenosis at low (200 ml/min) and high (400 ml/min) flow rates. The change in peak velocities between the arterial segment 2cm proximal to the stenosis (V1), and the stenotic jet (V2) were used to calculate three Doppler indices: (i) V2/V1 ratio, (ii) V2-V1 difference, (iii) a modified 'Bernoulli' value. A high flow pressure gradient of > or = 15% of the resting distal pressure (% delta P), represented a significant stenosis. There was improved correlation between Doppler indices and % delta P at high flow (r = 0.87 to 0.88) compared to low flow rates (r = 0.81 to 0.84). Optimum V2/V1 cut off values were determined by received operator characteristics (ROC) curve analysis. At low flow five sub-critical stenoses were not detected (sensitivity 82.8%) yet all but one of these lesions were identified at high flow (sensitivity of 96.6%). The V2-V1 and Bernoulli indices did not improve on the discriminant ability of the V2/V1 ratio. The V2/V1 ratio is sensitive to haemodynamic changes at enhanced flow rates across ideal arterial stenoses. The potential of hyperaemic Doppler to detect sub-critical lesions and so avoid intraarterial pressure measurements deserves further in vivo study.

Continuous Noninvasive Determination of Pulsus Paradoxus: A Pilot Study

To evaluate two methods of continuous, noninvasive monitoring of pulsus paradoxus (PP). A single-subject, nonblind assessment was conducted of the ability of noninvasive monitoring techniques to measure experimentally induced PP. Variable degrees of PP were induced in a healthy adult breathing through a one-way valve to which a series of external airway resistances were added. Intra-arterial pressure (IAP), finger arterial blood pressure (FINAP), pulse oximeter pulse waveform, and chest wall motion were continuously recorded. For each resistance, PP was calculated from the IAP (PPIAP) and the FINAP (PPFINAP) recordings. PP was measured manually (PPmanual) in the opposite arm. The percentage pulse waveform decrease on inspiration (%PWDpleth) was derived from the oximeter pulse waveform. These measurements were compared with the PPIAP. Bias was assessed as the mean difference between PP measures. PPFINAP was highly correlated with PPIAP (r = 0.96; 95% CI 0.93 to 0.98; p < 0.0001). There was a weak correlation between PPmanual and PPIAP (r = 0.27; 95% CI -0.05 to 0.55; p = 0.0963). The %PWDpleth correlated with PPIAP (r = 0.59, 95% CI 0.32 to 0.78; p = 0.0002). Bias was -1.515 +/- 5.6 mm Hg between PPIAP and PPFINAP; and -4.508 +/- 23.4 mm Hg between PPIAP and PPmanual. An accurate and continuous PP can be measured noninvasively using a FINAP monitor. This method has much better agreement with IAP measurements than do manual measurements. The qualitative information provided by the oximeter pulse waveform is less accurate than that provided by the FINAP monitor, but is a potentially useful screening tool for detection of significant PP.

Assessment of stenoses in the aortoiliac tract by calculation of a vascular resistance change ratio before and after exercise

Intraarterial pressure measurement is the most reliable method to assess haemodynamically significant stenoses in the aortoiliac tract. We have tried to develop a simple and quick, non-invasive method to assess stenoses of this type. Prospective semi-blinded clinical study. It was postulated that a haemodynamically significant aortoiliac tract stenosis would result in a lesser degree of vascular resistance decrease after vasodilatation, compared to patients only suffering from femorodistal stenoses. We approximated vascular resistance by: (brachial pressure-ankle pressure)/femoral artery mean Doppler velocity. By dividing vascular resistance at rest by vascular resistance after exercise, we calculated the Resistance Change Ratio (RCR). In 34 patients (50 legs) with arterial stenoses, the pressure gradient over the aortoiliac segment was compared to the RCR. Legs were divided in three groups: group 1 consisted of 22 legs that showed a pressure gradient > 10 mmHg at rest; group 2 showed a pressure gradient > 10 mmHg after papaverine; group 3 showed a pressure gradient of 10 mmHg or less. The median RCR was: 0.74 (range: 0.23-4.04) for group 1, 0.71 (range: 0.36-1.80) for group 2 and 0.93 (range 0.36-2.06) for group 3. There was no significant difference between the groups (p = 0.19). The RCR could not be used to accurately detect stenoses in the aortoiliac.

Intra-arterial pressure measurement in neonates: dynamic response requirements

A computer simulation of a catheter manometer system was used to quantify measurement errors in neonatal blood pressure parameters. Accurate intra-arterial pressure recordings of 21 critically ill newborns were fed into this simulated system. The dynamic characteristics, natural frequency and damping coefficient, were varied from 2.5 to 60 Hz and from 0.1 to 1.4, respectively. As a result, errors in systolic, diastolic and pulse arterial pressure were obtained as a function of natural frequency and damping coefficient. Iso-error curves for 2%, 5% and 10% were constructed. Using these curves, the maximum inaccuracy of any neonatal catheter manometer system can be determined and used in the clinical setting.

Non-invasive aortoiliac assessment

To assess the accuracy of Duplex ultrasound in the assessment of aortoiliac disease. Prospective, semi-blind study. Vascular laboratory and radiology departments, University Hospital. Ninety-two patients underwent assessment of the aortoiliac segment by femoral pulse palpation, Duplex ultrasound and biplanar arteriography. Of these 184 aortoiliac segments, 68 were also assessed by intraarterial pressure measurements and 80 by magnetic resonance angiography (MRA). Femoral pulses were abnormal in all 32 occluded aortoiliac segments. Of 152 patent segments, femoral pulse palpation was misleading in 50 (33%). MRA detected all occlusions and had a sensitivity of 71% and specificity of 68% for stenoses, compared to arteriography. Colour flow Duplex misdiagnosed four occlusions as stenoses. Duplex had a sensitivity of 91% and specificity of 93% for stenoses when compared to arteriography. Two stenoses, detected by Duplex and confirmed by pressure gradients, were missed by arteriography. Pressure measurements remain the gold standard for aortoiliac examination, arteriography providing only morphological information. The limitations of femoral pulse palpation should be appreciated. Although MRA was faster, Duplex examination proved slightly more sensitive to stenoses. At present, colour Duplex provides the best non-invasive assessment of aortoiliac disease and could prevent unnecessary arteriograms.

Peripheral vascular surgery with magnetic resonance angiography as the sole preoperative imaging modality

Purpose: Magnetic resonance angiography (MRA) is a developing technique that provides arteriograms without the risks associated with iodinated contrast and arterial puncture or the expense of hospitalization. Prior reports have demonstrated the accuracy of peripheral vessel MRA for evaluation of the aorta through pedal vessels. This study sought to determine whether vascular reconstructions could be planned and accomplished on the basis of MRA alone.Methods: Eighty consecutive candidates for bypass with ischemic rest pain or tissue loss were studied with preoperative outpatient MRA of the juxtarenal aorta through the foot. Confirmation of MRA findings was provided by intraoperative intraarterial pressure measurements for proximal vessels and postbypass arteriography for the runoff. Life-table analysis of graft patency and limb salvage was performed.Results: Two patients could not tolerate MRA and required contrast arteriography, but all others underwent reconstructive procedures on the basis of MRA alone (11 aortobifemoral, 67 infrainguinal). Intraoperative findings regarding suitability of inflow and outflow vessels confirmed the accuracy of the MRAs in every case. MRA indicated that none of the patients undergoing infrainguinal bypass had significant inflow occlusive disease, and this was confirmed at operation with pressure measurements of inflow vessels that were always within 10 mm Hg (peak systolic) of systemic pressure. The results of intraoperative completion arteriography and preoperative MRAs were identical for all but two patients who had minor discrepancies. All aortobifemoral reconstructions remained patent, and all limbs remained intact. The infrainguinal reconstructions had an 84% limb salvage rate and 78% primary graft patency rate at 21 months. Comparison of charges for patients undergoing preoperative MRA versus contrast angiography showed a cost savings of $1288 for each patient treated with preoperative MRA alone.Conclusions: MRA is a noninvasive, cost-effective outpatient imaging technique that, if properly performed and interpreted, is sufficient for planning peripheral bypass procedures. Its use may supplant contrast arteriography in many patients.

Blood pressure-lowering effect of an orally active vasopressin V1 receptor antagonist in mineralocorticoid hypertension in the rat.

We studied the contribution of vasopressin to the maintenance of high blood pressure in deoxycorticosterone acetate (DOCA)-salt hypertension in the rat using the nonpeptide orally effective vasopressin V1 receptor antagonist OPC-21268. Binding kinetic studies demonstrated that oral OPC-21268 (30 mg/kg) acted as a competitive antagonist at the vasopressin V1 receptor in DOCA-salt and salt control rats. Basal mean intra-arterial blood pressure was 140 +/- 4 mm Hg (n = 12) in DOCA-salt rats compared with 111 +/- 2 mm Hg in salt control rats (n = 18). Acute oral OPC-21268 (30 mg/kg) significantly (P < .01) reduced mean intra-arterial pressure in DOCA-salt hypertension, with an average maximal decrease of 24 +/- 3 mm Hg occurring at 2.5 +/- 0.7 hours after dosing. Systolic blood pressure (tail-cuff) in DOCA-salt rats was 178 +/- 2 mm Hg. Chronic oral OPC-21268 (30 mg/kg) twice daily for 7 days significantly (P < .01) reduced systolic blood pressure in DOCA-salt hypertension, with an average maximal decrease of 27 +/- 5 mm Hg. The antihypertensive effect was reversed 5 days after treatment with OPC-21268 was stopped. In water control rats basal systolic pressure (120 +/- 1 mm Hg, n = 20) was unchanged by chronic oral OPC-21268 (30 mg/kg twice daily for 7 days), and this was confirmed by direct measurement of mean intra-arterial pressure. After chronic oral OPC-21268 (30 mg/kg twice daily for 7 days) hepatic V1 receptor binding was significantly reduced for up to 10 hours (P < .05).(ABSTRACT TRUNCATED AT 250 WORDS)

In vivo determination of human arterial compliance: preliminary investigation of a new technique.

To obtain more detailed information about the dynamic mechanical properties of human arteries in vivo, using a new technique based on intravascular ultrasound. (IVUS). Arterial compliance was measured in the common and/or external iliac arteries of 6 patients using an IVUS device, concurrently obtained intraarterial pressure measurements, and a video motion analysis system. Compliance decreased with increasing vessel diameter and mean arterial pressure. Pre- and postangioplasty measurements were obtained in 2 patients but did not demonstrate a consistent change in compliance following angioplasty. We conclude that IVUS provides an accurate means for in vivo determination of human arterial compliance, the practical value of which needs to be established.

Duplex ultrasound in patients with suspected aorto-iliac occlusive disease

Duplex ultrasound scanning was used to localise and classify aorto-iliac occlusive disease. The study included 76 consecutive examinations of 73 patients with signs suggestive of proximal occlusive disease either by history or from traditional non-invasive laboratory investigation. Duplex ultrasound scanning indicated the presence of significant proximal occlusive disease in 70/101 limbs with suspected aorto-iliac disease. In total, 383/393 proximal arterial segments were assessed. A complete evaluation of the aorto-iliac region was possible in 91% of the patients. Duplex scanning was superior to oscillometric amplitude measurements and to CW Doppler examination, especially in patients with concomitant disease of the proximal superficial and deep femoral arteries. Duplex classification of stenoses correlated well with angiographic results obtained in 60 limbs with exact agreement in 194/211 (92%) arterial segments. Three of the patients with disparity between ultrasonography and angiography were investigated with intraarterial pressure measurements demonstrating that these lesions were underestimated by angiography. We conclude that Duplex ultrasound is feasible and accurate in detecting and grading lesions in the aorto-iliac region. This method provides important clinically useful haemodynamic information non-invasively in patients with suspected aorto-iliac occlusive disease.

How can the assessment of the hemodynamic significance of aortoiliac arterial stenosis by duplex scanning be improved? A comparative study with intraarterial pressure measurement

Purpose: The current diagnostic criteria used to assess the severity of stenoses in the aortoiliac arteries by duplex scanning are mainly based on information related to changes in cross-sectional area and are flow independent. Consequently, duplex scanning fails to detect approximately one quarter of hemodynamically significant aortoiliac lesions compared with intraarterial pressure measurements. The aim of this study is to improve the assessment of the hemodynamic significance of aortoiliac lesions by duplex scanning.Methods: A prospective study in 60 patients was performed in which duplex scanning at rest was compared with intraarterial pressure measurements before and after the administration of papaverine. A simplified Bernoulli equation was used to calculate pressure gradients across stenoses (ΔPBern). Two flow-related parameters, the increase in peak systolic velocity (ΔPSV) across the stenosis and the end-diastolic velocity at the site of the stenosis, were also measured and compared with intraarterial pressure measurements.Results: ΔPBern and ΔPSV showed a sensitivity and specificity of 81% and 88%, respectively, for the detection of hemodynamically significant lesions at rest. However, ΔPBern could often not give an accurate calculation of the pressure gradient. Receiver operator characteristic analysis showed that a cut-off level for ΔPSV in the range of 1.4 to 1.5 m/s was best able to detect significant lesions at rest. The end-diastolic velocity parameter had a limited diagnostic value.Conclusion: Although useful in clinical decision making, ΔPBern often could not give an accurate calculation of the pressure gradient. ΔPSV is a simple and practical spectral analysis parameter to differentiate between significant and insignificant stenoses. This parameter also has the potential to detect hemodynamically less critical lesions if duplex scanning is performed under conditions of increased flow. Further evaluation is needed.

Pseudohypertension and the measurement of blood pressure.

Riva-Rocci Korotkoff (RRK) blood pressure measurements may overestimate the intra-arterial pressure (IAP) in individual patients. To study pseudohypertension, defined as an overestimation larger than 10 mm Hg, we compared RRK and IAP measurements in 76 patients. These patients were considered to be at risk for pseudohypertension because of high age, hypertension, or vascular disease. RRK measurements underestimated simultaneously measured systolic IAP values by 6.0 +/- 6.5 (mean +/- SD) mm Hg, whereas simultaneous diastolic RRK readings overestimated the IAP by 1.9 +/- 5.6 mm Hg. Diastolic overestimation increased slightly with age. Vascular rigidity, as measured by counterpressure plethysmography, did not correlate with these errors. Systolic and diastolic pseudohypertension was observed in two and five patients, respectively. Pseudohypertension was only present in the group in which IAP was measured in the aorta. However, the number of patients with systolic and diastolic pseudohypertension could be increased to three and seven by using the average intra-arterial systolic and diastolic pressure during an RRK measurement or to six and 11 by using the IAP during a control period just before an RRK measurement rather than the IAP at the moment of appearance or disappearance of the Korotkoff sounds. The widely diverging prevalence of pseudohypertension described in the literature might be explained because of such different comparison techniques.

Validation of Doppler measurement of pressure gradients across peripheral model arterial stenosis

Hemodynamic assessment of aortoiliac occlusive disease is necessary for successful arterial reconstruction of the legs. Various methods have been proposed, and the "pull through" intraarterial pressure measurement method is accepted as the best standard. The pressure readings, however, seemed to depend on the intraluminal position of the catheter. To explain these observations and make a comparison between the Doppler method and the pull through method, we have studied centerline velocity changes at the stenosis throat by Doppler ultrasonography, and axial and lateral pressure gradients by use of pressure transducers mounted 10 mm and 40 mm downstream of short (4 mm) axisymmetric sharp-edged model stenoses having cross-sectional reduced areas of 64%, 84%, 91%, and 96%. Axial manometric pressures measured 10 mm beyond the throat of 84% stenosis were more than twice as high as the lateral pressures. No significant difference was observed between axial and lateral pressures measured 40 mm downstream from the throat. This pressure distribution has important clinical relevance. Mean and peak pressure gradients for both the Doppler method and manometric measurements were compared. Measurements with Doppler method and manometric measurements indicated that mean pressure gradients (r = 0.98; SEE = +/- 2.4 mm Hg) correlate better than peak pressure gradients (r = 0.90; SEE = +/- 16.5 mm Hg). Doppler gradients were higher than manometer gradients. Overestimation was 13% for mean pressure gradients and ranged from 10% to 150% for peak pressure gradients. Explanation for the difference between mean Doppler and catheter gradient may be the pressure recovery occurring in the relaminarized poststenotic regions.

Validation of Doppler measurement of pressure gradients across peripheral model arterial stenosis

Hemodynamic assessment of aortoiliac occlusive disease is necessary for successful arterial reconstruction of the legs. Various methods have been proposed, and the “pull through” intraarterial pressure measurement method is accepted as the best standard. The pressure readings, however, seemed to depend on the intraluminal position of the catheter. To explain these observations and make a comparison between the Doppler method and the pull through method, we have studied centerline velocity changes at the stenosis throat by Doppler ultrasonography, and axial and lateral pressure gradients by use of pressure transducers mounted 10 mm and 40 mm downstream of short (4 mm) axisymmetric sharp-edged model stenoses having cross-sectional reduced areas of 64%, 84%, 91%, and 96%. Axial manometric pressures measured 10 mm beyond the throat of 84% stenosis were more than twice as high as the lateral pressures. No significant difference was observed between axial and lateral pressures measured 40 mm downstream from the throat. This pressure distribution has important clinical relevance. Mean and peak pressure gradients for both the Doppler method and manometric measurements were compared. Measurements with Doppler method and manometric measurements indicated that mean pressure gradients (r = 0.98; SEE = ± 2.4 mm Hg) correlate better than peak pressure gradients (r = 0.90; SEE = ± 16.5 mm Hg). Doppler gradients were higher than manometer gradients. Overestimation was 13% for mean pressure gradients and ranged from 10% to 150% for peak pressure gradients. Explanation for the difference between mean Doppler and catheter gradient may be the pressure recovery occurring in the relaminarized poststenotic regions.

When to stop resuscitation--the significance of cuff blood pressure.

Fifteen consecutive patients who had been resuscitated from cardiac arrest and transferred immediately to an Intensive Care Unit were studied. Measurements of intraarterial pressure, cardiac output and systemic vascular resistance demonstrate that 'cuff' blood pressure may not always be related to intraarterial pressure or cardiac output and cannot be used for diagnostic, therapeutic, or prognostic purposes. Following resuscitation, a palpable pulse was present in each of these patients, but did not correlate with adequacy of cardiac output. Too often we hear during a cardiac arrest the question 'Does the patient have an output?', when we should really be asking 'Does the patient have a pulse?'. The palpation of a pulse is a simple and important indication of spontaneous cardiac activity. However cardiac output must be measured and it's adequacy cannot be inferred from this basic clinical measurement.

A rapid, accurate, noninvasive technique for diagnosing critical and subcritical stenoses in aortoiliac arteries

Accurate hemodynamic evaluation of the aortoiliac system for the purpose of determining the need for an inflow procedure currently requires invasive pressure measurements. This study was undertaken to evaluate a noninvasive technique with the aortofemoral transfer function. Twenty-eight human aortoiliac segments were studied with intraarterial pressure measurements, with and without papaverine injection, and by calculation of the Doppler-derived mean power frequency index obtained by digital signal processing of aortic and femoral spectra. The procedure is menu driven and can be performed by any duplex ultrasound technologist. This technique involves recording 20 aortic and 20 femoral Doppler signals, requiring less than 1 minute of data acquisition time. Intraarterial pressure measurements were used to classify arteries into the three following groups: (1) normal arteries, (2) arteries with subcritical stenoses, and (3) arteries with critical stenoses. The mean power frequency index of group 1 arteries (n = 7) was 0.63 ± 0.04, of group 2 arteries (n = 6) was 0.46 ± 0.02, and of group 3 arteries (n = 15) was 0.21 ± 0.05. These mean power frequency index values were significantly different by analysis of variance (ANOVA) (p < 0.0001). Each group could be differentiated from the other groups with a sensitivity of 0.83 to 1.00, a specificity of 1.00, and an accuracy of 0.92 to 1.00 compared to intraarterial pressure measurements, including papaverine testing. Measurement of the mean power frequency index is a rapid, noninvasive technique that diagnoses and quantifies aortoiliac stenoses with an accuracy similar to intraarterial pressure measurements.

A rapid, accurate, noninvasive technique for diagnosing critical and subcritical stenoses in aortoiliac arteries

Accurate hemodynamic evaluation of the aortoiliac system for the purpose of determining the need for an inflow procedure currently requires invasive pressure measurements. This study was undertaken to evaluate a noninvasive technique with the aortofemoral transfer function. Twenty-eight human aortoiliac segments were studied with intraarterial pressure measurements, with and without papaverine injection, and by calculation of the Doppler-derived mean power frequency index obtained by digital signal processing of aortic and femoral spectra. The procedure is menu driven and can be performed by any duplex ultrasound technologist. This technique involves recording 20 aortic and 20 femoral Doppler signals, requiring less than 1 minute of data acquisition time. Intraarterial pressure measurements were used to classify arteries into the three following groups: (1) normal arteries, (2) arteries with subcritical stenoses, and (3) arteries with critical stenoses. The mean power frequency index of group 1 arteries (n = 7) was 0.63 +/- 0.04, of group 2 arteries (n = 6) was 0.46 +/- 0.02, and of group 3 arteries (n = 15) was 0.21 +/- 0.05. These mean power frequency index values were significantly different by analysis of variance (ANOVA) (p less than 0.0001). Each group could be differentiated from the other groups with a sensitivity of 0.83 to 1.00, a specificity of 1.00, and an accuracy of 0.92 to 1.00 compared to intraarterial pressure measurements, including papaverine testing. Measurement of the mean power frequency index is a rapid, noninvasive technique that diagnoses and quantifies aortoiliac stenoses with an accuracy similar to intraarterial pressure measurements.

Blood pressure measurement during transport A comparison of direct and oscillotonometric readings in critically ill patients

This study assessed the accuracy of oscillotonometric blood pressure measurement in critically ill patients during transfer. Direct intra-arterial pressure measurements were taken in 44 transported patients as a 'gold standard' and compared with readings from four portable automatic oscillotonometers--the Dinamap 8100, Lifestat 100, Propaq 102 and Takeda UA711. All under-read systolic pressure (by 13%, 21%, 19% and 13% respectively) and over-read diastolic pressure (by 15%, 5%, 27% and 15% respectively) in comparison to direct pressure measurement. The limits of agreement for 95% of comparisons were broad. The systematic difference between direct and oscillotonometric measurements and the variability between and within patients show that direct oscillotonometric measurements are not interchangeable in these patients. Portable automatic oscillotonometers should not be substituted for direct monitoring in such circumstances.

Accurate measurement of intraarterial pressure through radial artery catheters in neonates

A technique is described for accurate measurement of intraarterial pressure through radial artery catheters in neonates. The technique, which can be used for short-term monitoring, uses cannulation of the radial artery with a 24-gauge Teflon catheter, connected by a Luer-Lok fitting to a three-way stopcock and a high-fidelity tip transducer. In vitro studies showed that the system is linear and the frequency response is flat (+/- 3 dB) up to 50 Hz. The technique permits gathering of high-quality pressure data and can be used in the area of neonatal clinical research for short-term monitoring. It needs to be developed further before routine application in clinical practice can be recommended.