John Amoore

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

Objective To explore the differences between oscillometric and auscultatory measurements. Method 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. Results 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. Conclusion 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.

Oscillometric sphygmomanometers: a critical appraisal of current technology.

AimBlood pressure (BP), a key vital sign, monitors general health. Oscillometric devices are increasingly used for measurement, although their accuracy continues to be critically debated. A functional block diagram is used to review the components that affect accuracy. MethodsA block diagram is presented covering the components from cuff to algorithm. The oscillometric waveform is described, considering factors that can alter its shape. Methods used to assess accuracy, including the potential use of simulators, are described. Results and discussionThe block diagram focuses attention on cuff, amplifier, signal processing and algorithm. The importance of correct cuff size is emphasized. Accuracy can be affected by the extraction of the oscillometric pulses and the interpolation to compensate for higher deflation rates. Modern electronic amplifiers are assumed to be stable and do not drift, an assumption largely untested. Crucial to accuracy is the algorithm, but there is no standard algorithm and limited theoretical basis, leading to significant measurement errors in groups of patients, even by approved devices. The causes are not well understood, but differences in oscillometric waveform shape between patient groups have been observed and may explain auscultatory–oscillometric differences. The ability of theoretical models to explain the effects of arterial stiffness on BP measurements is discussed. Validation remains statistical though steps have been taken to improve it. ConclusionThe indirect nature of BP measurement poses particularly problems for ensuring accuracy. Critical assessment has done much to improve standards, but a solid theoretical understanding of the technique has not been formulated and further work is required.

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

IntroductionOscillometric 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. MethodsTwo 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. ResultsThe 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. Discussion and conclusionThe 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.

Validation of oscillometric noninvasive blood pressure measurement devices using simulators

Oscillometric noninvasive blood pressure devices measure blood pressure using an indirect method and proprietary algorithms and hence require validation in clinical trials. Clinical trials are, however, expensive and give contradictory results, and validated devices are not accurate in all patient groups. Simulators that regenerate oscillometric waveforms promise an alternative to clinical trials provided they include sufficient physiological and pathological oscillometric waveforms. Simulators should also improve the understanding of the oscillometric method.

Do SpaceLabs ambulatory non-invasive blood pressure recorders measure blood pressure consistently over several years use?

ObjectiveTo assess the measurement consistency of SpaceLabs ambulatory recorders (Spacelabs, Washington, USA) that are in regular use. MethodsA total of 14 SpaceLabs 90207 and one 90217 ambulatory recorders were tested for measurement consistency using the Dynatech CuffLink (Dynatech, Nevada, USA), a commercially available non-invasive blood pressure (NIBP) simulator. The NIBP recorders were tested at a range of pressures with 20 repeated determinations at a simulated 120/80 mmHg and five repeated determinations at simulated pressures of 80/50, 100/80, 150/100, 200/165 and 250/195 mmHg. Tests were carried out in 1998, 2002 and late 2003 or early 2004. ConclusionsAll 15 SpaceLabs recorders measured consistently over the 6 years with 89.5% of the differences in average pressures, recorded by any particular device at each recorded pressure, less than 2 mmHg between successive test episodes. The maximum difference was 4.5 mmHg and 60.1% of the differences were less than 1 mmHg. The measurements for all devices were within the tolerances specified by the supplier for the device when tested with the simulator. Maintenance records also show that most devices required breakdown maintenance less than once every 3 years. The results show that the SpaceLabs devices maintain measurement consistency in the demanding conditions of ambulatory pressure recording over several years.

Oscillometric Noninvasive Blood Pressure Measurement Devices and Simulators

Unless users of oscillometric noninvasive blood pressure simulators understand both the indirect nature of the oscillometric method and its empirical implementation, they can misunderstand the performances of both noninvasive blood pressure devices and simulators. The article describes the variation in the oscillometric pulses with cuff pressure, leading to an overview of the characteristics, limitations, and applications of simulators. The differences between pressures recorded by noninvasive blood pressure devices and simulator settings are explained, emphasizing that unless the simulator uses physiologic oscillometric envelopes, the differences do not necessarily imply lack of calibration of noninvasive blood pressure device or simulator. Simulator functional specifications are described, advocating that simulators include physiologic oscillometric envelopes and pulse waveforms.

The Role of Clinical Engineers in Hospitals

The appropriate deployment of technology contributes to the improvement in the quality of healthcare, the containment of cost, and to increased access to services. The traditional role of the clinical engineer repairing and maintaining devices has evolved to now include the equally important role of supporting and optimizing the use of healthcare technology. This chapter is an overview of the activities undertaken by clinical engineers. These activities are grouped under two headings: supporting and advancing care, and healthcare technology management. Clinical engineering activity within hospitals should be balanced to include both the management of the healthcare technology itself and also the support for the clinicians who use the technology in clinical practice. The supporting and advancing care and healthcare technology management roles can be considered the pillars of any clinical engineering service. However, it is important to recognize and acknowledge at all times that these roles are complementary and are tightly integrated in practice. With knowledge of the engineering, physics, and system science underpinning electro-medical devices and systems, and experience gained in working collaboratively in the clinical environment, clinical engineers play an important role in ensuring positive outcomes for patients arising from the use of technology and reducing negative ones.

Need for re-validation of automated blood pressure devices for use in unstable conditions

The current validation of non-invasive blood pressure (NIBP) device is performed under resting condition. However, NIBPs are often used without giving much consideration about the measurement conditions. This study aimed to provide scientific data on the use of BP devices in unstable conditions. BP measurements were performed on 20 healthy subjects under both resting and regular deep breathing conditions. During the measurement the oscillometric cuff pressure waveforms were recorded digitally. They were then regenerated by a specially designed BP simulator and presented to two clinically validated hospital grade automatic NIBP devices to obtain automated BPs. Automated BPs obtained from the two conditions were finally compared between the two devices. Under resting condition, there was no significant diference in both automated SBP and DBP between the two devices. However, under regular deep breathing condition, significant SBP and DBP diferences were observed between the two devices (both P<;O.OJ; mean±SD: 118.8±10.6 vs 115.1±11.6 mmHg for SBP; 68.5±8.6 vs 65.3±8.9 mmHg for DBP). For the effect of deep breathing on BP measurement, significant SBP decrease was observed only from device 2 (P<;0.05, with a mean diference±SD of 3.8±6.2 mmHg), indicating inconsistent measurements between the two devices under unstable conditions. Our results provide scientific evidence that automated BP devices can be used only under the condition for which the validation was performed.

Health Technology Management

The complete range of electromedical devices and systems bought by a hospital constitutes a valuable financial asset with capital and revenue resourcing requirements. Their selection, procurement, upkeep, and life cycle needs to be carefully managed to ensure they are cost effective, up to date, and continue to support the corporate objectives of the hospital. Managing healthcare technology and the risks involved should be governed by a strategic, organization-wide policy that informs and guides those who use and manage the technology. The term healthcare technology management (HTM) describes the scientific and technical support of electromedical devices and clinical information technologies, and financial stewardship. In this chapter the HTM program is described as well as how clinical engineers manage the medical devices, ensure they are maintained in a satisfactory condition, and are kept available for use. This includes a discussion of how to develop device-specific equipment support plans and how to deal with the challenges of assigning often limited resources to execute these plans. The importance of delivering a health technology management program within a quality cycle is emphasised.