Noninvasive Blood Pressure Device Research Articles

A simplified computer model of cardiovascular system with an arm branch.

Non-invasive pressure simulators that regenerate oscillometric waveforms promise an alternative to expensive clinical trials for validating oscillometric noninvasive blood pressure devices. However, existing simulators only provide oscillometric pressure in cuff and thus have a limited accuracy. It is promising to build a physical simulator that contains a synthetic arm with a built-in brachial artery and an affiliated hydraulic model of cardiovascular system. To guide the construction of this kind of simulator, this paper presents a computer model of cardiovascular system with a relatively simple structure, where the distribution of pressures and flows in aorta root and brachial artery can be simulated, and the produced waves are accordant with the physical data. This model can be used to provide the parameters and structure that will be needed to build the new simulator.

Accuracy of the CNAP monitor, a noninvasive continuous blood pressure device, in providing beat-to-beat blood pressure readings in the prone position

Study ObjectiveTo assess the accuracy of a noninvasive continuous arterial pressure (CNAP) monitor in patients who are positioned prone in the operating room. DesignProspective study. SettingOperating room at a children's hospital. Patients20 pediatric patients, aged 13.8 ± 2 years, and weight 63.7 ± 18.8 kg, scheduled for surgery in the prone position, and for which arterial catheter placement was planned. InterventionsMeasurements were recorded with an arterial line (AL) and a new noninvasive continuous blood pressure (BP) monitor. MeasurementsSystolic (SBP), diastolic (DBP), and mean arterial (MAP) pressure readings were captured from an arterial cannula and the CNAP device every minute during anesthesia. Main ResultsThe study cohort consisted of analysis of 4104 pairs of SBP, DBP, and MAP values, which showed an absolute difference between the AL and CNAP device readings of 7.9 ± 6.3 mmHg for SBP, 5.3 ± 4.3 mmHg for DBP, and 4.6 ± 3.9 mmHg for MAP. Bland-Altman analysis of MAP values showed a bias of 0.26 mmHg, with upper and lower limits of agreement of 12.18 mmHg and -11.67 mmHg, respectively. CNAP readings deviated from arterial values by ≤ 5 mmHg in 67% of MAP values, 59% of DBP values, and 43% of SBP readings. The difference was ≤ 10 mmHg for 94% of MAP readings, 90% of DBP values, and 73% of SBP readings. ConclusionsDuring prone positioning, the CNAP monitor provided clinically acceptable accuracy for MAP values, similar to those reported in adults in the supine position.

Contamination of the laryngoscope handle

This Invited Commentary accompanies the following original article: Howell V, Thoppil A, Young H, et al. Chlorhexidine to maintain cleanliness of laryngoscope handles. An audit and laboratory study. Eur J Anaesthesiol 2013; 30:216–221. In this issue of the European Journal of Anaesthesiology, Howell et al.1 address the problem of cross-contamination in the operating room associated with the use of non-disposable anaesthesia devices, particularly reusable laryngoscope handles. These authors need to be commended for attracting our attention to a very practical but largely overlooked issue and a simple means of improving patients’ security. The paper challenges our way of thinking in at least three directions. First, the widespread employment of single-use laryngoscope blades – mainly in relation to the risk of transmission of prions – may have reduced our vigilance towards the transmission risks associated with the laryngoscope handle despite the reality of this risk.2 Second, the possibility of severe clinical consequences of such transmission may have been considered as disputable. However, the October 2011 medical alert issued by the UK Medicine and Healthcare products Regulatory Agency (MHRA) proved the opposite. This alert indicates that ‘a patient death was caused by a failure to decontaminate a laryngoscope handle appropriately between each patient use.’ This led to cross-infection and subsequently septicaemia, confirming previous reports (http://www.mhra.gov.uk/home/groups/dtsbs/documents/medicaldevicealert/con129221.pdf.). Third, we trust our institutional decontamination protocols to prevent the possibility of such cross-contamination and delegate this task to the nurses. This again is misleading. Every anaesthesia department, in coordination with the local nosocomial infection prevention committee or the hospital hygiene department, should have a formal, written, updated procedure for decontamination of the laryngoscope handle between each patient use, in the operating room as well as in prehospital and intensive care settings. Such a protocol is not always available3 and, when present, its application depends on individual members of staff recalling the rules or the ‘repaint the fence’ process on a regular basis; it is known from human factors studies that this is not always reliable. Totally disposable laryngoscopes should be discussed in the light of their quality, cost and environmental impact. Improvements in this direction have been published as preliminary reports only,4 combining a disposable shell and a reusable light unit with a LED bubble and batteries. The cost of such a totally disposable one-piece external shell is in the range of the cost of a single-use metal blade. The problem highlighted for the laryngoscope handle is also of concern in relation to other non-disposable pieces of equipment in use in the operating theatre. The fibrescope has a unique place and is not used in every case. Moreover, special decontamination protocols as well as traceability are generally adopted after fibreoscopy. Conversely, less attention is paid to the cross-contamination hazard associated with screens and keyboards, the cuff of non-invasive blood pressure devices, pulse oximeter sensors and ECG cables, all of which are usually reusable.5 A recent survey of bacterial and mycological contaminants showed a 34% incidence of contamination of ECG wires, mainly for cables which had been in use for more than 6 months, possibly in relation to an increase in their surface porosity, allowing for more adhesion of germs.6,7 Finally, the good news in the study by Howell et al. is the immediate and long-lasting antimicrobial efficacy of chlorhexidine. The recommendation to use this agent routinely in addition to cleaning and autoclaving the handle if there is a risk of contamination with Clostridium difficile, and also at regular intervals, makes sense and should be adopted because it has proved to be efficient and cost-effective. Acknowledgements Assistance with the invited commentary: none declared. Financial support and sponsorship: none declared. Conflicts of interest: none declared. Comment from the Editor: this invited commentary was checked by the editors but was not sent for external peer review. PD is an associate editor of the European Journal of Anaesthesiology.

Accuracy of the CNAP™ monitor, a noninvasive continuous blood pressure device, in providing beat‐to‐beat blood pressure readings in pediatric patients weighing 20–40 kilograms

During perioperative care, the continuous measurement of blood pressure (BP) provides superior physiologic monitoring to intermittent techniques. However, such monitoring requires placement of an intraarterial catheter, which may be time-consuming or associated with adverse events and technical difficulty. A noninvasive, continuous BP monitoring device has been studied in the adult population. This study prospectively assesses its accuracy in pediatric patients, weighing 20-40 kg. The technology evaluated is the CNAP™ Monitor 500, developed by CNSystems AG (Graz, Austria). The study cohort included pediatric patients weighing between 20 and 40 kg, scheduled for surgery for which arterial line (AL) placement was planned. Systolic (sBP), diastolic (dBP), and mean arterial (MAP) blood pressure readings were captured from the AL and the CNAP™ device every minute during anesthetic care. The study cohort consisted of 20 patients (11 weighing between 30 and 40 kg and 9 weighing between 20 and 29.9 kg) with a mean age of 9.8 ± 3.4 years (range, 6-16 years) and weight of 29.8 ± 6.1 kg (range, 20.9-38.7 kg). There were a total of 1076 pairs each of sBP, dBP, and MAP values in the 20-29.9 kg group. The absolute difference between the sBP, dBP, and MAP was 9.8 ± 8.5, 6.8 ± 5.3, and 6.7 ± 6.2 mmHg, respectively. The correlation coefficient between the AL and the CNAP™ device was 0.48, 0.60, and 0.64 for the sBP, dBP, and MAP, respectively. The CNAP™ values (sBP, dBP, MAP) were ≤5 mmHg from the AL values in 38.6%, 48.5%, and 55.0% of the values, respectively. In the 30-40 kg group, there were a total of 2737 pairs of sBP, dBP, and MAP values. The absolute difference between the sBP, dBP, and MAP was 11.5 ± 9.3, 7.5 ± 5.3, and 7.9 ± 6.6 mmHg, respectively. The correlation coefficient between the arterial cannula and the CNAP™ device was 0.48, 0.45, and 0.51 for the sBP, dBP, and MAP, respectively. CNAP™ readings were ≤5 mmHg from the AL values (sBP, dBP, MAP) in 29.0%, 41.9%, and 40.5% of the values, respectively. Although some variation in its accuracy was noted, the CNAP™ device provides a noninvasive and continuous blood pressure reading which appears to be within clinically useful limits. It may be that modification of the finger cuffs is needed to improve its absolute accuracy as our clinical experience demonstrated that achieving an effective fit with the cuffs was at times difficult.

Results of a survey of blood pressure monitoring by intensivists in critically ill patients: A preliminary study

Maintenance of mean arterial pressure>65 mm Hg has been associated with improved clinical outcomes in many studies of critically ill patients. Current guidelines for the management of septic shock and guidelines for managing other critical illnesses suggest intra-arterial blood pressure measurement is preferred over automated oscillometric noninvasive blood pressure measurement. Despite these recommendations, anecdotal experience suggested that the use of noninvasive blood pressure measurement in our institution and others in preference to intra-arterial blood pressure measurement remained prevalent. We designed an online survey and sent it by e-mail. Intensive care units. A randomly selected group from the membership of the Society for Critical Care Medicine. None. Use of non-invasive and invasive blood pressure devices. Eight hundred eighty individuals received an invitation to complete the survey and 149 responded. We found that 71% (105 of 149) of intensivists estimated the correct cuff size rather than measuring arm circumference directly. In hypotensive patients, 73% of respondents (108 of 149) reported using noninvasive blood pressure measurement measurements for patient management. In patients on a vasopressor medication, 47% (70 of 149) of respondents reported using noninvasive blood pressure measurement for management. The use of noninvasive blood pressure measurement measurements in critically ill patients is common despite the paucity of evidence validating its accuracy in critically ill patients. Given this widespread use, accuracy and precision validation studies comparing noninvasive blood pressure measurement with intra-arterial blood pressure measurement in critically ill patients should be performed.

Evaluation of an indirect oscillometric blood pressure monitor in normotensive and hypotensive anesthetized dogs

To determine the accuracy and precision of an oscillometric noninvasive blood pressure device as a predictor of invasive direct blood pressure in healthy anesthetized hypotensive and normotensive dogs. Prospective observational study. University teaching hospital. Eight crossbred adult dogs. Anesthesia was induced with propofol and maintained with isoflurane. A catheter was placed in the dorsal pedal artery to record systolic, mean, and diastolic arterial blood pressures (aSAP, aMAP, and aDAP, respectively). The noninvasive blood pressure device cuff was placed around the contralateral front limb to record noninvasive systolic, mean, and diastolic blood pressure (nSAP, nMAP, and nDAP). Two states of blood pressure (BP) were studied: baseline state was established by keeping end-tidal isoflurane concentration at 1.2+/-0.1%. The hypotensive state was achieved by maintaining the same isoflurane concentration while withdrawing approximately 40% of the animal's blood volume until aMAP was stable at approximately 40 mm Hg. At the end of the study, blood was returned to the animal and it was allowed to recover from anesthesia. Agreement between the direct and indirect BP measurements was determined by the Bland-Altman method. The SAP and MAP but not DAP bias varied significantly between each BP state. Normotensive absolute biases (mean [SD]) for SAP, MAP, and DAP were -14.7 mm Hg (15.5 mm Hg), -16.4 mm Hg (12.1 mm Hg), and -14.1 mm Hg (15.8 mm Hg), respectively. Absolute biases during the hypotensive state for SAP, MAP, and DAP were -32 mm Hg (22.6 mm Hg), -24.2 mm Hg (19.5 mm Hg), and -16.8 mm Hg (17.2 mm Hg), respectively. The oscillometric device was not reliably predictive of intra-arterial BP during hypotension associated with acute hemorrhage.

A statistical model and simulator for cardiovascular pressure signals

Physiological signal simulators are often used to conduct validation studies of commercially available devices such as oscillometric non-invasive blood pressure (NIBP) monitors. Numerous assessment studies have been conducted using simulators to validate commercial NIBP monitors. While there are several simulators commercially available to evaluate oscillometric NIBP devices, currently there are no simulators designed to validate invasive pressure signal devices. A statistical model and simulator for invasive cardiovascular pressure signals such as arterial blood pressure and intracranial pressure are described. The model incorporates the effects of respiration on pressure signals and can be used to generate synthetic signals with time and frequency domain characteristics matching any desired subject population. Additionally, the way that noise and artefacts typically present in real pressure signals should be modelled is described. The proposed statistical model is a useful tool for validation of algorithms designed to process or analyse biomedical pressure signals to estimate parameters of clinical interest such as the cardiac frequency, heart rate variability, respiratory frequency, and pulse pressure variation in the presence of noise. The model can be used to simulate signals in order to validate commercial devices that process and analyse invasive pressure signals.

Ethanol-induced Coma after Therapeutic Ethanol Injection of a Hepatic Cyst

Ethanol-induced Coma after Therapeutic Ethanol Injection of a Hepatic Cyst

Automatic blood pressure measurement: the oscillometric waveform shape is a potential contributor to differences between oscillometric and auscultatory pressure measurements

To explore the differences between oscillometric and auscultatory measurements. From a simulator evaluation of a non-invasive blood pressure (NIBP) device regenerating 242 oscillometric blood pressure waveforms from 124 subjects, 10 waveforms were selected based on the differences between the NIBP (oscillometric) and auscultatory pressure measurements. Two waveforms were selected for each of five criteria: systolic over and underestimation; diastolic over and underestimation; and close agreement for both systolic and diastolic pressures. The 10 waveforms were presented to seven different devices and the oscillometric-auscultatory pressure differences were compared between devices and with the oscillometric waveform shapes. Consistent patterns of waveform-dependent over and underestimation of systolic and diastolic pressures were shown for all seven devices. The mean and standard deviation, for all devices, of oscillometric-auscultatory pressure differences were: for the systolic overestimated waveforms, 36 +/- 28/-6 +/- 3 and 23 +/- 2/-1 +/- 3 mmHg (systolic/diastolic differences); for systolic underestimated waveforms, -21 +/- 5/-4 +/- 3 and -11 +/- 4/-3 +/- 3 mmHg; for diastolic overestimated waveforms, 3 +/- 4/12 +/- 5 and 17 +/- 6/10 +/- 2 mmHg; for diastolic underestimated waveforms, 1 +/- 4/-22 +/- 4 and -9 +/- 6/-29 +/- 4 mmHg; and for the two waveforms with good agreement, 0 +/- 6/0 +/- 3 and -2 +/- 4/-4 +/- 3 mmHg. Waveforms for which devices showed good oscillometric and auscultatory agreement had smooth envelopes with clearly defined peaks, compared with the broader plateau and complex shapes of those waveforms for which devices over or underestimated pressures. By increasing the understanding of the characteristics and limitations of the oscillometric method and the effects of waveform shape on pressure measurements, simulator evaluation should lead to improvements in NIBP devices.

Effect of the shapes of the oscillometric pulse amplitude envelopes and their characteristic ratios on the differences between auscultatory and oscillometric blood pressure measurements

Oscillometric noninvasive blood pressure (NIBP) devices determine pressure by analysing the oscillometric waveform using empirical algorithms. Many algorithms analyse the waveform by calculating the systolic and diastolic characteristic ratios, which are the amplitudes of the oscillometric pulses in the cuff at, respectively, the systolic and diastolic pressures, divided by the peak pulse amplitude. A database of oscillometric waveforms was used to study the influences of the characteristic ratios on the differences between auscultatory and oscillometric measurements. Two hundred and forty-three oscillometric waveforms and simultaneous auscultatory blood pressures were recorded from 124 patients at cuff deflation rates of 2-3 mmHg/s. A simulator regenerated the waveforms, which were presented to two NIBP devices, the Omron HEM-907 [OMRON Europe B.V. (OMCE), Hoofddorp, The Netherlands] and the GE ProCare 400 (GE Healthcare, Tampa, Florida, USA). For each waveform, the paired systolic and paired diastolic pressure differences between device measurements and auscultatory reference pressures were calculated. The systolic and diastolic characteristic ratios, corresponding to the reference auscultatory pressures of each oscillometric waveform stored in the simulator, were calculated. The paired differences between NIBP measured and auscultatory reference pressures were compared with the characteristic ratios. The mean and standard deviations of the systolic and diastolic characteristic ratios were 0.49 (0.11) and 0.72 (0.12), respectively. The systolic pressures recorded by both devices were lower (negative paired pressure difference) than the corresponding auscultatory pressures at low systolic characteristic ratios, but higher than the corresponding auscultatory pressures at high systolic pressures. Conversely, the differences between the paired diastolic pressure differences were higher at low diastolic characteristic ratios, compared with those at high diastolic characteristic ratios. The paired systolic pressure differences were within +/-5 mmHg for those waveforms with systolic characteristic ratios between 0.4 and 0.7 for the Omron and between 0.3 and 0.5 for the ProCare. The paired diastolic pressure differences were within +/-5 mmHg for those waveforms with diastolic characteristic ratios between 0.4 and 0.6 for the Omron and between 0.5 and 0.8 for the ProCare. The systolic and diastolic paired oscillometric-auscultatory pressure differences varied with their corresponding characteristic ratios. Good agreement (within 5 mmHg) between the oscillometric and auscultatory pressures occurred for oscillometric pulse amplitude envelopes with specific ranges of characteristic ratios, but the ranges were different for the two devices. Further work is required to classify the different envelope shapes, comparing them with patient conditions, to determine if a clearer understanding of the different waveform shapes would improve the accuracy of oscillometric measurements.

Can a simulator that regenerates physiological waveforms evaluate oscillometric non-invasive blood pressure devices?

A simulator has been developed that enables previously recorded clinical oscillometric waveforms to be regenerated for testing oscillometric non-invasive blood pressure measurement devices. Two non-invasive blood pressure devices were evaluated using the simulator with its database of 243 waveforms, to assess the value of a simulator for such evaluations. Two oscillometric non-invasive blood pressure devices, both of which had previously been validated against auscultatory references, were selected. The Omron HEM-907 (Omron, Hoofddorp, The Netherlands) measures the pressure during linear cuff deflation and the GE ProCare 400 (GE Healthcare, Tampa, Florida, USA) measures during step deflation. Each non-invasive blood pressure device was attached to the simulator and pressures were recorded from all 243 waveforms. The differences between the systolic and diastolic pressures measured by each non-invasive blood pressure device and the auscultatory references for each waveform were calculated. These were assessed with the European and American validation standards and with the British Hypertension Society protocol. The paired pressure differences (non-invasive blood pressure device minus auscultatory reference) for each device complied partly, but not fully, with the standards or protocol. The means (+/-standard deviation) of the paired systolic and diastolic pressures differences for the Omron were -2.4 mmHg (+/-5.9 mmHg) and -8.9 mmHg (+/-6.5 mmHg), and for the ProCare were -6.5 mmHg (+/-10.4 mmHg) and -2.9 mmHg (+/-7.0 mmHg), respectively. The pressures recorded by the Omron device met the standards for systolic pressures but failed for diastolic pressures and conversely for the ProCare. This represents the first evaluation of non-invasive blood pressure devices with a simulator that generates previously recorded clinical oscillometric waveforms. It allowed data from over 100 study participants to be used. Both devices had been previously clinically validated, but their evaluation using the simulator with its regenerated waveforms only partly met the required criteria. Although the results did not fully match previous clinical validations, these initial results give encouragement that a simulator with sufficient stored waveforms might be able to replace the difficult and expensive clinical evaluation of non-invasive blood pressure devices that has prevented many devices from being fully evaluated.

Automated non-invasive blood pressure devices: are they suitable for use?

Measurement of blood pressure by a trained observer using a mercury sphygmomanometer is accepted as the gold standard, but there has been an increase in the use of automated devices employing the oscillometric technique. Not all such devices have been clinically validated, and some do not carry an appropriate CE mark. This survey aimed to assess the state of the European Union market for automated non-invasive blood pressure devices in terms of information provided by companies relating to compliance, validation and intended use. A total of 116 companies were identified as being potentially active (i.e. manufacturer, supplier, agent or distributor). Of these, 110 that could be contacted were asked to provide details of their company and their non-invasive blood pressure products via a questionnaire. Eighty-six companies were found to be actively involved in the supply of 158 different models of automated non-invasive blood pressure device. These included 54 devices for use on the arm and 62 for use on the wrist (total 116 in our main categories), and 42 others (ambulatory monitors, patient monitors, defibrillators or finger devices). We received responses for 61% (71/116) of the main category arm and wrist devices and 80% (57/71) of these provided claims for CE marking. Of the CE marked devices for which we received a response, 41% (12/29) of arm devices and 39% (11/28) of wrist devices claimed some form of clinical validation, or evidence was found subsequent to the survey. Of these claims, 65% (15/23) related to an earlier, or similar, product and 48% (11/23) were based on published studies. Inconsistencies were found between claims for diagnostic suitability and claims for clinical validation. A majority of models available on the European Union market were not validated by clinical trial to one of the recognized protocols.

Physostigmine for the Acute Treatment of Restless Legs Syndrome

We present a case report of an acute episode of restless legs syndrome that interfered with the performance of a diagnostic imaging procedure of the cervical spine. The patient had a 19-yr history of restless leg syndrome with periodic limb movements during sleep. Treatment with additional sedation and opioids did not alleviate the leg movements. IV administration of 1 mg of physostigmine eradicated all extraneous leg motion.

Oscillometric blood pressure measurement: the methodology, some observations, and suggestions.

Most noninvasive blood pressure (NIBP) devices use the oscillometric method. Published studies of oscillometric methodology introduced varied algorithmic approaches for determination of systolic (SBP), diastolic (DBP), and mean arterial (MAP) blood pressures. While there is a general agreement about MAP determination, controversy exists about the determination of SBP and DBP Accuracy of oscillometric devices has been questioned and validation studies have revealed problems. Several validation protocols have been developed but they are expensive and time consuming to conduct and they have their own limitations. Instruments for bench testing of NIBP devices are useful for some device functions, but they cannot perform dynamic accuracy tests. The issue of accuracy is becoming very important as health care professionals increasingly rely on electronic NIBP devices. The authors developed a compact system for acquisition of NIBP waveforms. Some representative oscillometric waveforms are introduced here to demonstrate the oscillometric method and its shortcomings. A finger photoplethysmograph (PPG) was used to demonstrate a potential improvement of SBP determination. The concept and significance of an oscillometric blood pressure waveform database is introduced and its applications are discussed.

Low-cost oscillometric non-invasive blood pressure monitors: device repeatability and device differences

Automated non-invasive blood pressure measuring devices based on the oscillometric technique are used widely for self-measurement and are often used in clinics in place of the manual, auscultatory method. Oscillometry was originally developed for monitoring purposes and there are questions over its suitability for making diagnostic measurements. This study measured the differences between automated devices, in the absence of physiological variability. We studied 19 low-cost, automated, non-invasive blood pressure devices, using a repeatable artificial arm simulator, and measured the within-device repeatability and between-device differences. We found that the devices were repeatable (mean within-device difference 1 mmHg), but between-device differences were 4.4 mmHg (systolic pressure) and 3.6 mmHg (diastolic pressure), for normal and high-normal blood pressures. Individual devices are sufficiently repeatable for clinical trend use, but differences between devices are sufficiently large that they may be misinterpreted as clinically significant.

Inadvertent Attachment of a Blood Pressure Device to a Needleless IV “Y-site”: Surprising, Fatal Connections

Noninvasive blood pressure devices are commonplace and necessary in most emergency departments, but did you know that they have the potential to cause serious harm or even death to patients with intravenous access? It seems almost impossible, yet there have been 3 reports of this type of incident to the Food and Drug Administration (FDA) MedWatch program and to the Institute for Safe Medication Practices (ISMP) in the past 18 months!1

Oscillometric blood pressure devices and simulators: measurements of repeatability and differences between models

Primary objective: To measure the repeatability and pressure pulse envelope of simulators used for testing oscillometric non-invasive blood pressure (NIBP) devices; to study the effect of different envelopes on NIBP devices, and to measure the difference between NIBP devices due to different oscillometric algorithms.Methods: Three different models of NIBP simulator and 18 different patient monitors with NIBP function were studied. We developed a pressure measurement system (accuracy 0.048?mmHg) to measure the repeatability of simulators. The effect of changing the envelope was measured by using three simulators with one NIBP device. Differences between 18 NIBP devices were measured using one simulator at seven blood pressure settings.Main outcomes and results: Simulators generate repeatable pressure pulse envelopes (?<?0.2?mmHg) but the magnitude and shape depends on the model of simulator. Oscillometric NIBP devices are highly repeatable (?<?2?mmHg) when presented with a repeatable pressure pulse envelope, but different devices employ different algorithms and give different results. For a simulated standard blood pressure setting of 120/80?mmHg, estimates of systolic pressure ranged from 112.6 to 126.6?mmHg (sd of 3.0?mmHg), and diastolic pressure ranged from 74.8 to 86.9?mmHg (sd of 3.5?mmHg).Conclusions: Simulators and NIBP devices are sufficently repeatable for clinical use, but further systematic clinical studies are required to better characterize the pressure pulse envelope for different patient groups.

Factitious Arterial Blood Pressure Measurements from Automated Oscillotonometer

Automated, noninvasive blood pressure devices facilitate repeated blood pressure measurements in anesthetized patients. The authors report the recording of multiple factitious measurements of blood pressure in a small infant by using one of these devices.

HEART RATE VARIABILITY ANALYSIS

S109 Heart rate variability (HRV), as measured by changes in RR intervals, traditionally has been used to quantify autonomic tone and the relative contributions of the sympathetic and parasympathetic nervous systems. Decreases in HRV have been reported to be associated with disease states such as diabetes and myocardial dysfunction, and acute changes have been associated with severe ischemia and impending death. Acute changes in HRV are also associated with the administration of anesthetic agents since these agents may affect automaticity and conduction [1]. As presently determined, HRV simply assesses the overall RR interval. However, the SA node and AV node receive different innervation [2]. We sought to determine if, during a process designed to activate vagal reflexive (baroreceptor) mechanisms, alterations in atrial/atrioventricular conduction - as opposed to sinoatrial automaticity alone - may contribute to HRV. Methods: Five healthy volunteers (28-35 years old) were monitored with an automated noninvasive blood pressure device and an EKG which sampled at 250 Hz during a baseline period and then during an infusion of phenylephrine which was titrated to provide a 20% increase in mean arterial pressure (average rate 0.8 [micro sign]g/kg/min). The beat-to-beat PR and RR intervals then were determined during 60-sec artifact-free intervals in each subject. Results: The data indicate that, in addition to previously documented changes in the automaticity of the SA node, RR variability is also influenced by changes in atrial/atrioventricular conduction. As shown in Figure 1 and Figure 2, beat-to-beat percent change of PR (top) was less than that of RR (bottom), but nonetheless substantial.Figure 1Figure 2Conclusion: Time and frequency domain analyses of HRV as assessed by RR interval changes have traditionally been used to assess autonomic tone. We have shown that changes in autonomic outflow dynamically affect intra-atrial/AV nodal conduction as well as SA automaticity, suggesting that perhaps both PR and RR variability should be analyzed to gain a more complete assessment of autonomic tone and of the effects of disease states, anesthetic agents, and therapies on cardiac function.

MONITORING THE PERIPHERAL VASCULAR SYSTEM

SUMMARY The invasive technique of arterial cannulation for blood pressure measurement is justifiable by the high yield of information with minimal risk to the patient. It also facilitates the collection of arterial blood samples for blood gas analysis, electrolyte measurement, and other studies. Recent, more sophisticated noninvasive blood pressure devices may reduce the need for direct invasive measurements; automated, noninvasive blood pressure devices now are used routinely intraoperatively.