Effect of Respiration on the Characteristic Ratios of Oscillometric Pulse Amplitude Envelope in Blood Pressure Measurement

Systolic and diastolic blood pressures (BPs) are important physiological parameters for disease diagnosis. Systolic and diastolic characteristic ratios derived from oscillometric pulse waveform have been widely used to estimate automated non-invasive BPs in oscillometric BP measurement devices. The oscillometric pulse waveform is easily influenced by respiration, which may cause variability to the characteristic ratios and subsequently BP measurement. This study quantitatively investigated how respiration patterns (i.e., normal breathing and deep breathing) affect the systolic and diastolic characteristic ratios. The study was performed with clinical data collected from 39 healthy subjects, and each subject conducted BP measurements during normal and deep breathings. Analytical results showed that the systolic characteristic ratio increased significantly from 0.52 ± 0.13 under normal breathing to 0.58 ± 0.14under deep breathing (p < 0.05), and the diastolic characteristic ratio was not significantly affected from 0.75 ± 0.12 under normal breathing to 0.76 ± 0.13 under deep breathing (p = 0.48). In conclusion, deep breathing significantly affected the systolic characteristic ratio, suggesting that automated oscillometric BP device which is validated under resting condition should be strictly used for measurements under resting condition

HOME MEASUREMENT OF BLOOD PRESSURE: PRESENT PROBLEMS AND PERSPECTIVE IMPROVEMENTS

The most frequently performed health test is the measurement of blood pressure. Popularity of home measurement increased substantially with the introduction of inexpensive automatic instruments to the market. Accurate measurement of blood pressure is important for diagnosis and management of hypertension. Inaccuracies of measurement with automatic oscillometric instruments are caused by wrong size cuff and by errors in algorithmic measurement. The authors developed several perspective improvements in the measurement of systolic pressure. An experimental system for acquisition and processing of arterial pressure pulses facilitated the development of these methods. More accurate measurement of the systolic pressure was achieved with a dual-cuff method. A new method of wrist-cuff pulse analysis facilitated estimation of hemodynamics. Estimation of hemodynamics simultaneously with measurement of blood pressure provides the physician with more complete picture of the type of hypertension and it facilitates better diagnosis and management. An inexpensive commercial instrument based on the methods developed by the authors could be used by the patient in home care

Assessment of model based (input) impedance, pulse wave velocity, and wave reflection in the Asklepios Cohort

Objectives : Arterial stiffness and wave reflection parameters assessed from both invasive and non-invasive pressure and flow readings are used as surrogates for ventricular and vascular load. They have been reported to predict adverse cardiovascular events, but clinical assessment is laborious and may limit widespread use. This study aims to investigate measures of arterial stiffness and central hemodynamics provided by arterial tonometry alone and in combination with aortic root flows derived by echocardiography against surrogates derived by a mathematical pressure and flow model in a healthy middle-aged cohort. Methods : Measurements of carotid artery tonometry and echocardiography were performed on 2226 ASKLEPIOS study participants and parameters of systemic hemodynamics, arterial stiffness and wave reflection based on pressure and flow were measured. In a second step, the analysis was repeated but echocardiography derived flows were substituted by flows provided by a novel mathematical model. This was followed by a quantitative method comparison. Results : All investigated parameters showed a significant association between the methods. Overall agreement was acceptable for all parameters (mean differences: -0.0102 (0.033 SD) mmHg*s/ml for characteristic impedance, 0.36 (4.21 SD) mmHg for forward pressure amplitude, 2.26 (3.51 SD) mmHg for backward pressure amplitude and 0.717 (1.25 SD) m/s for pulse wave velocity). Conclusion : The results indicate that the use of model-based surrogates in a healthy middle aged cohort is feasible and deserves further attention

Abnormal wave reflections and left ventricular hypertrophy late after coarctation of the aorta repair

Patients with repaired coarctation of the aorta are thought to have increased afterload due to abnormalities in vessel structure and function. We have developed a novel cardiovascular magnetic resonance protocol that allows assessment of central hemodynamics, including central aortic systolic blood pressure, resistance, total arterial compliance, pulse wave velocity, and wave reflections. The main study aims were to (1) characterize group differences in central aortic systolic blood pressure and peripheral systolic blood pressure, (2) comprehensively evaluate afterload (including wave reflections) in the 2 groups, and (3) identify possible biomarkers among covariates associated with elevated left ventricular mass (LVM). Fifty adult patients with repaired coarctation and 25 age- and sex-matched controls were recruited. Ascending aorta area and flow waveforms were obtained using a high temporal-resolution spiral phase-contrast cardiovascular magnetic resonance flow sequence. These data were used to derive central hemodynamics and to perform wave intensity analysis noninvasively. Covariates associated with LVM were assessed using multivariable linear regression analysis. There were no significant group differences (P≥0.1) in brachial systolic, mean, or diastolic BP. However central aortic systolic blood pressure was significantly higher in patients compared with controls (113 versus 107 mm Hg, P=0.002). Patients had reduced total arterial compliance, increased pulse wave velocity, and larger backward compression waves compared with controls. LVM index was significantly higher in patients than controls (72 versus 59 g/m(2), P<0.0005). The magnitude of the backward compression waves was independently associated with variation in LVM (P=0.01). Using a novel, noninvasive hemodynamic assessment, we have shown abnormal conduit vessel function after coarctation of the aorta repair, including abnormal wave reflections that are associated with elevated LVM

Quantitative Assessment of Blood Pressure Measurement Accuracy and Variability from Visual Auscultation Method by Observers without Receiving Medical Training

This study aimed to quantify blood pressure (BP) measurement accuracy and variability with determinations from visualizing Korotkoff sound waveform. Thirty video clips of BP recordings from the educational training database of the British Hypertension Society were converted to Korotkoff sound waveforms. Ten observers without receiving medical training were asked to determine systolic and diastolic BPs (SBP and DBP) from the randomly arranged video clips and Korotkoff sound waveforms using two measurement methods: a) traditional manual auscultatory method of listening for Korotkoff sounds; and b) visual auscultation method by visualising the Korotkoff sound waveform, which was repeated three times on different days, making a total of 6 BP measurements from each observer on each BP recording. The measurement variability was calculated from the standard deviation of the three repeats, and the measurement error was calculated against the reference answers. Statistical analysis showed that, in comparison with the traditional manual auscultatory method, visual auscultation method significantly reduced overall measurement variability from 2.2 to 1.1 mmHg for SBP and from 1.9 to 0.9 mmHg for DBP (both p<0.001). It also showed that BP measurement errors were significant for both techniques (all p<0.01, except DBP from the traditional method). Although significant, the overall mean measurement errors were small, which were -1.5 and -1.2 mmHg for SBP, and -0.7 and 2.6 mmHg for DBP, respectively from the traditional manual auscultatory and visual auscultation methods. In conclusion, the visual auscultation method had the ability to achieve an acceptable degree of BP measurement accuracy, with smaller measurement variability in comparison with the traditional manual auscultatory method

Optimizing the Electrocardiogram and Pressure Monitoring

journal articleBiomedical Informatic

Methods of Blood Pressure Measurement in the ICU*

OBJECTIVE:: Minimal clinical research has investigated the significance of different blood pressure monitoring techniques in the ICU and whether systolic vs. mean blood pressures should be targeted in therapeutic protocols and in defining clinical study cohorts. The objectives of this study are to compare real-world invasive arterial blood pressure with noninvasive blood pressure, and to determine if differences between the two techniques have clinical implications. DESIGN:: We conducted a retrospective study comparing invasive arterial blood pressure and noninvasive blood pressure measurements using a large ICU database. We performed pairwise comparison between concurrent measures of invasive arterial blood pressure and noninvasive blood pressure. We studied the association of systolic and mean invasive arterial blood pressure and noninvasive blood pressure with acute kidney injury, and with ICU mortality. SETTING:: Adult intensive care units at a tertiary care hospital. PATIENTS:: Adult patients admitted to intensive care units between 2001 and 2007. INTERVENTIONS:: None. MEASUREMENTS AND MAIN RESULTS:: Pairwise analysis of 27,022 simultaneously measured invasive arterial blood pressure/noninvasive blood pressure pairs indicated that noninvasive blood pressure overestimated systolic invasive arterial blood pressure during hypotension. Analysis of acute kidney injury and ICU mortality involved 1,633 and 4,957 patients, respectively. Our results indicated that hypotensive systolic noninvasive blood pressure readings were associated with a higher acute kidney injury prevalence (p = 0.008) and ICU mortality (p < 0.001) than systolic invasive arterial blood pressure in the same range (≤70 mm Hg). Noninvasive blood pressure and invasive arterial blood pressure mean arterial pressures showed better agreement; acute kidney injury prevalence (p = 0.28) and ICU mortality (p = 0.76) associated with hypotensive mean arterial pressure readings (≤60 mm Hg) were independent of measurement technique. CONCLUSIONS:: Clinically significant discrepancies exist between invasive and noninvasive systolic blood pressure measurements during hypotension. Mean blood pressure from both techniques may be interpreted in a consistent manner in assessing patients' prognosis. Our results suggest that mean rather than systolic blood pressure is the pre ferred metric in the ICU to guide therapy.National Institute of Biomedical Imaging and Bioengineering (U.S.) (Grant R01EB001659

Comparison Between Invasive and Noninvasive Methods to Estimate Subendocardial Oxygen Supply and Demand Imbalance

Background Estimation of the balance between subendocardial oxygen supply and demand could be a useful parameter to assess the risk of myocardial ischemia. Evaluation of the subendocardial viability ratio (SEVR, also known as Buckberg index) by invasive recording of left ventricular and aortic pressure curves represents a valid method to estimate the degree of myocardial perfusion relative to left ventricular workload. However, routine clinical use of this parameter requires its noninvasive estimation and the demonstration of its reliability. Methods and Results Arterial applanation tonometry allows a noninvasive estimation of SEVR as the ratio of the areas directly beneath the central aortic pressure curves obtained during diastole (myocardial oxygen supply) and during systole (myocardial oxygen demand). However, this "traditional" method does not account for the intra-ventricular diastolic pressure and proper allocation to systole and diastole of left ventricular isometric contraction and relaxation, respectively, resulting in an overestimation of the SEVR values. These issues are considered in the novel method for SEVR assessment tested in this study. SEVR values estimated with carotid tonometry by "traditional" and "new" method were compared with those evaluated invasively by cardiac catheterization. The "traditional" method provided significantly higher SEVR values than the reference invasive SEVR: average of differences +/- SD= 44 +/- 11% (limits of agreement: 23% - 65%). The noninvasive "new" method showed a much better agreement with the invasive determination of SEVR: average of differences +/- SD= 0 +/- 8% (limits of agreement: -15% to 16%). Conclusions Carotid applanation tonometry provides valid noninvasive SEVR values only when all the main factors determining myocardial supply and demand flow are considered