Hao-Min Cheng

Quantification of the Calibration Error in the Transfer Function-Derived Central Aortic Blood Pressures

BACKGROUND The accuracy of the central aortic systolic (SBP-C) and pulse (PP-C) blood pressures estimated noninvasively by a generalized transfer function technique has been questioned. The purpose of the present study was to quantify precisely the impact of the input errors (differences between the oscillometric (SBP-O, DBP-O, PP-O) and invasive (SBP-B, DBP-B, PP-B) brachial systolic, diastolic, and pulse blood pressures) on the output errors (differences between the estimated and invasively measured SBP-C and PP-C). METHODS Invasive high-fidelity right brachial and central aortic pressure waveforms, and SBP-O, DBP-O, and PP-O (=SBP-O - DBP-O) were obtained simultaneously in 40 patients during cardiac catheterization. A generalized transfer function was applied on the individual brachial pressure waveform to derive predicted SBP-C and PP-C. RESULTS Observed input errors were -2.3 ± 5.8 mm Hg from SBP-O, 8.1 ± 5.3 mm Hg from DBP-O, and -10.4 ± 7.1 mm Hg from PP-O, respectively. The output errors were -2.2 ± 6.4 mm Hg and -10.3 ± 8.0 mm Hg for SBP-C and PP-C, respectively, when the brachial pressure waveforms were recalibrated using SBP-O and DBP-O. The outputs were determined by the inputs according to the Equation (1): SBP-C error = 0.97 × SBP-O error + 0.03 (r = 0.88, P < 0.01); and the Equation (2): PP-C error = 0.96 × PP-O error - 0.30 (r = 0.86, P < 0.01). CONCLUSIONS Noninvasive application of the generalized transfer function techniques produces estimates of SBP-C and PP-C with errors equivalent to those of the oscillometric blood pressure monitor in the estimation of SBP-B and PP-B. The output errors can be predicted from input errors of SBP-O and DBP-O.

Estimation of central systolic blood pressure using an oscillometric blood pressure monitor

Current noninvasive techniques for assessing central aortic pressure require the recording of an arterial pressure wave using a high-fidelity applanation tonometer. We therefore developed and validated a novel method to estimate the central aortic systolic pressure using an oscillometric blood pressure monitor alone. Invasive high-fidelity right brachial and central aortic pressure waves, and left-brachial pulse volume plethysmography from an oscillometric blood pressure monitor, were obtained at baseline and 3 min after administration of sublingual nitroglycerin in 100 patients during cardiac catheterization. In the initial 50 patients (Generation Group), Central systolic blood pressure was predicted by a multi-variate prediction model generated from the comprehensive analysis of the invasive brachial pressure wave, including brachial late-systolic shoulder pressure value and parameters related to wave reflection and arterial compliance. Another prediction model was similarly constructed from the noninvasively calibrated pulse volume plethysmography. Both models were validated in the subsequent 50 patients (Validation Group) with results: r=0.98 (P<0.001) and mean difference=0.5±4.5 (95% confidence interval −8.3 to 9.3) mm Hg for the invasive model, and r=0.93 (P<0.001) and mean difference=−0.1±7.6 (95% confidence interval −15.0 to 14.8) mm Hg for the noninvasive model. Thus, our results indicate that central aortic systolic blood pressure could be estimated by analysis of the noninvasive brachial pressure wave alone from an oscillometric blood pressure monitor.

Excessive wave reflections on admission predict post‐discharge events in patients hospitalized due to acute heart failure

The role of wave reflections in the pathogenesis of acute heart failure syndrome (AHFS) remains unclear. The present study investigated the long‐term prognostic values of the carotid augmentation index (cAI), carotid augmented pressure (cAP), amplitude of the reflected pressure wave from a decomposed carotid pressure wave (Pb), and carotid pulse pressure (PP) on admission in patients hospitalized due to AHFS.

Pulsatile hemodynamics and clinical outcomes in acute heart failure

BACKGROUND The role of pulsatile hemodynamics in the management of patients with acute heart failure syndrome (AHFS) remains to be elucidated. We investigated the changes of the pulsatile hemodynamics along the hospital course of AHFS in relation to short-term outcomes. METHODS A total of 80 AHFS patients (73.2 ± 14.1 years, 82.5% men) were enrolled and followed up for up to 6 months after discharge. Measures of the pulsatile hemodynamics including brachial and central systolic blood pressure (SBP) and pulse (PP) pressure, carotid-femoral pulse wave velocity (cf-PWV), carotid augmentation index (cAI and cAI(75)) and carotid augmented pressure (cAP) were obtained within 24 h of admission, before discharge, and 2 weeks after discharge. RESULTS During a follow-up of 174 ± 32 days (16-183 days), 29 patients experienced events including rehospitalization for heart failure, nonfatal myocardial infarction, nonfatal stroke, and mortality. Predischarge brachial and central PP, and cAP, and postdischarge brachial and central SBP and PP, cAP, and cf-PWV were significantly lower in patients without events than those with events. Predischarge central PP (hazard ratio per 1-s.d. and 95% confidence interval: 1.62 (1.12-2.34)) and cAP (1.47 (1.05-2.05)) predicted events independent of age and N-terminal pro-brain natriuretic peptide (NT-proBNP) levels. Similarly, postdischarge brachial and central SBP and PP, cAP, and cf-PWV were also significant independent predictors. CONCLUSION Suboptimal recovery of the perturbations of the pulsatile hemodynamics in patients hospitalized due to AHFS may relate to adverse short-term outcomes and warrant aggressive treatment.

Measurement Accuracy of a Stand-Alone Oscillometric Central Blood Pressure Monitor: A Validation Report for Microlife WatchBP Office Central

BACKGROUND The superiority of prognostic value of blood pressure (BP) measured at central aorta (CBP) over conventional brachial BP measured by cuff-based BP monitors has reignited the development of new noninvasive techniques for estimating CBP. The present study validated the accuracy of CBP measured by a newly developed stand-alone CBP monitor. METHODS The CBP monitor provided readings of brachial systolic BP (SBP), brachial diastolic BP (DBP), central SBP, and central pulse pressure (PP). Brachial PP and central DBP were calculated from the relevant readings. The accuracy of the brachial and central SBP, PP, and DBP was validated against the simultaneously recorded invasively measured central aortic SBP, PP, and DBP, according to the invasive standard requirements for the noninvasive brachial BP monitors from the Association for the Advancement of Medical Instrumentation (AAMI) in 85 subjects (255 measurements; age range, 30-93 years). RESULTS The mean differences of cuff BP with reference to the invasively measured central SBP, PP, and DBP were -2.6 ± 9.0, -8.6 ± 11.2, and 6.1 ± 7.0 mm Hg, respectively, with the former two being obviously underestimated at high CBP and overestimated at low CBP. In contrast, the corresponding differences for the central SBP, PP, and DBP measured by the CBP monitor were -0.6 ± 5.5, -0.4 ± 7.0, and -0.2 ± 6.5 mm Hg, respectively, without obvious systematic bias. The distribution of measurement errors for central SBP, PP, and DBP surpassed the AAMI criteria. CONCLUSION Central SBP, PP, and DBP can be measured accurately by a stand-alone automatic BP monitor.

Estimation of central aortic systolic pressure from the second systolic peak of the peripheral upper limb pulse depends on central aortic pressure waveform morphology

Background: Direct identification of second systolic peaks of peripheral upper limb pulses (pSBP2) has been used to represent central systolic blood pressure (cSBP), but its accuracy at low SBP was questioned. Objectives: We investigated the relationship of pSBP2 with characteristics of central pressure waveforms. Methods: High-fidelity central aortic and right brachial pressure waveforms were simultaneously recorded using a custom-made dual pressure sensor catheter in 78 patients (65.9 ± 12.9 years) during catheterization for 285 measurements. Results: Overall agreement between cSBP and pSBP2 was good (mean difference −0.9 ± 4.8, r = 0.98), with a systematic bias at low SBP. We examined agreements of different waveform types according to the relationship of the second systolic peak of aortic pressure waveforms (cSBP2) to cSBP. Of type A (positive late systolic augmentation) and type B (zero augmentation) aortic pressure waveforms, in which cSBP = cSBP2, agreement between pSBP2 and cSBP was excellent (mean difference −0.4 ± 4.1, r = 0.99). There were 40 type C aortic pressure waveforms (negative augmentation; cSBP > cSBP2) with cSBP 107.2 ± 13.9 mmHg. Their cSBP2, compared with cSBP, showed closer agreement (mean difference −0.6 ± 3.2 vs. −4.0 ± 7.2 mmHg) and better correlation (r = 0.97 vs. 0.85, P = 0.03) with pSBP2. Conclusion: pSBP2 can be used with type A and B aortic pressure waveforms for estimation of cSBP. However, it should not be used with type C aortic pressure waveforms, typically at low SBP, because pSBP2 is closer to cSBP2 than cSBP. This explains why pSBP2 underestimates cSBP at low SBP.

Usefulness of systolic time intervals in the identification of abnormal ventriculo-arterial coupling in stable heart failure patients*

The ratio of effective arterial elastance (Ea) to ventricular end‐systolic elastance (Ees) indicates the status of ventriculo‐arterial coupling.

Measurement of central aortic pulse pressure: noninvasive brachial cuff-based estimation by a transfer function vs. a novel pulse wave analysis method.

BACKGROUND The prognostic value of central aortic pulse pressure (PP-C) may have been underestimated due to its measurement inaccuracy. We aimed to investigate the accuracy of noninvasive brachial cuff-based estimation of PP-C by a generalized transfer function (GTF) or a novel pulse wave analysis (PWA) approach to directly estimate PP-C. METHODS Invasive high-fidelity right brachial and central aortic pressure tracings, and left brachial pulse volume plethysmography (PVP) waveforms from an oscillometric blood pressure (BP) monitor were all digitized simultaneously in 40 patients during cardiac catheterization. An aortic-to-brachial GTF and a PWA multivariate prediction model using the PVP waveforms calibrated to brachial cuff systolic BP (SBP) and diastolic BP(DBP) were constructed. Accuracy of the two methods was examined in another 100 patients against invasively measured PP-C. RESULTS The error of cuff PP in estimating PP-C was 1.8 ± 12.4 mm Hg. Application of the GTF on noninvasively calibrated PVP waveforms produced reconstructed aortic pressure waves and PP-C estimates with errors of -3.4 ± 11.6 mm Hg (PP-C = reconstructed aortic SBP - aortic DBP) and -2.3 ± 11.4 mm Hg (PP-C = reconstructed aortic SBP - cuff DBP), respectively. The observed systematic errors were proportional to the magnitudes of PP-C. In contrast, the error of the PWA prediction model was 3.0 ± 7.1 mm Hg without obvious proportional systematic error. CONCLUSIONS Large random and systematic errors are introduced into the PP-C estimates when PP-C is calculated as the difference between the estimated central SBP and central or cuff DBP. The accuracy can be improved substantially with the novel PWA approach.

Comparative Effectiveness of Blood Pressure-lowering Drugs in Patients who have Already Suffered From Stroke: Traditional and Bayesian Network Meta-analysis of Randomized Trials

AbstractHypertension is the most important risk factor for stroke and stroke recurrence. However, the preferred blood pressure (BP)-lowering drug class for patients who have suffered from a stroke has yet to be determined.To investigate the relative effects of BP-lowering therapies [angiotensin-converting enzyme inhibitor (ACEI), angiotensin receptor blockers (ARB), &bgr; blockers, calcium channel blockers (CCBs), diuretics, and combinations of these drugs] in patients with a prior stroke history, we performed a systematic review and meta-analysis using both traditional frequentist and Bayesian random-effects models and meta-regression of randomized controlled trials (RCTs) on the outcomes of recurrent stroke, coronary heart disease (CHD), and any major adverse cardiac and cerebrovascular events (MACCE). Trials were identified from searches of published hypertension guidelines, electronic databases, and previous systematic reviews.Fifteen RCTs composed of 39,329 participants with previous stroke were identified. Compared with the placebo, only ACEI along with diuretics significantly reduced recurrent stroke events [odds ratio (OR) = 0.54, 95% credibility interval (95% CI) 0.33–0.90]. On the basis of the distribution of posterior probabilities, the treatment ranking consistently identified ACEI along with diuretics as the preferred BP-lowering strategy for the reduction of recurrent stroke and CHD (31% and 35%, respectively). For preventing MACCE, diuretics appeared to be the preferred agent for stroke survivors (34%). Moreover, the meta-regression analysis failed to demonstrate a statistical significance between BP reduction and all outcomes (P = 0.1618 for total stroke, 0.4933 for CHD, and 0.2411 for MACCE).Evidence from RCTs supports the use of diuretics-based treatment, especially when combined with ACEI, for the secondary prevention of recurrent stroke and any vascular events in patients who have suffered from stroke.

Diagnostic performance of a stand-alone central blood pressure monitor: application of central blood pressure in the diagnosis of high blood pressure

BACKGROUND Oscillometric central blood pressure (CBP) monitors have emerged as a new technology for blood pressure (BP) measurements. With a newly proposed diagnostic threshold for CBP, we investigated the diagnostic performance of a novel CBP monitor. METHODS We recruited a consecutive series of 138 subjects (aged 30-93 years) without previous use of antihypertensive agents for simultaneous invasive and noninvasive measurements of BP in a catheterization laboratory. With the cutoff (CBP ≥130/90 mm Hg) for high blood pressure (HBP), the sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of the novel CBP monitor were calculated with reference to the measured CBP. In comparison, the diagnostic performance of the conventional cuff BP was also evaluated. RESULTS The noninvasive CBP for detecting HBP in a sample with a prevalence of 52% showed a sensitivity of 93% (95% confidence interval (CI) = 91-95), specificity of 95% (95% CI = 94-97), PPV of 96% (95% CI = 94-97), and NPV of 93% (95% CI = 90-95). In contrast, with cuff BP and the traditional HBP criterion (cuff BP ≥140/90 mm Hg), the sensitivity, specificity, PPV, and NPV were 49% (95% CI = 44-53), 94% (95% CI = 92-96), 90% (95% CI = 86-93), and 63% (95% CI 59-66), respectively. CONCLUSIONS A stand-alone oscillometric CBP monitor may provide CBP values with acceptable diagnostic accuracy. However, with reference to invasively measured CBP, cuff BP had low sensitivity and NPV, which could render possible management inaccessible to a considerable proportion of HBP patients, who may be identifiable through noninvasive CBP measurements from the CBP monitor.