Noninvasive blood pressure measurement in mice using pulsed Doppler ultrasound

Existing tail-cuff pressure devices for mice use tail flow sensors that measure only systolic and mean pressure. We developed a method to obtain systolic and diastolic pressure in mice using a pulsed Doppler flow velocity sensor and a tail-cuff and validated the method against pressure signals obtained simultaneously from a fluid-filled catheter. The tail-cuff was pressurized to suprasystolic levels to completely occlude the tail artery and then released gradually. The pressure at which the tail flow reappeared was recorded as systolic and the pressure at which the tail flow became continuous was recorded as diastolic. Regression analysis of tail-cuff pressures over catheter pressures obtained from healthy mice (n = 16) showed a high degree of association (r(sys) = 0.95, r(dia) = 0.94, both at p < 0.001). Bland-Altman analysis showed good agreement between the two methods, with a mean difference of -13 ( +/- 12 SD) mmHg and 3 ( +/- 10 SD) mmHg in the systolic (58 to 250 mmHg) and diastolic (48 to 178 mmHg) pressure measurements, respectively. Bland-Altman plots of tail-cuff blood pressures of a second group of mice (n = 20) showed good agreement between repeated measurements obtained on the same day, but had higher variability between measurements made on different days.     

Multivariate classification of systemic vascular resistance using photoplethysmography

Systemic vascular resistance (SVR) classification is useful for the diagnosis and prognosis of critical pathophysiological conditions, with the ability to identify patients with abnormally high or low SVR of immense clinical value. In this study, a supervised classifier, based on Bayes' rule, is employed to classify a heterogeneous group of intensive care unit patients (N = 48) as being below (SVR < 900 dyn s cm(-5)), within (900 ? SVR ? 1200 dyn s cm(-5)) or above (SVR > 1200 dyn s cm(-5)) the clinically accepted range for normal SVR. Features derived from the finger photoplethysmogram (PPG) waveform and other routine cardiovascular measurements (heart rate and mean arterial pressure) were used as inputs to the classifier. In the construction of the classifier model, two techniques were used to approximate the class conditional probability densities--a single Gaussian distribution model (also known as discriminant analysis) and a non-parametric model using the Parzen window kernel density estimation method. An exhaustive feature search was performed to select a feature subset that maximized the performance indicator, Cohen's kappa coefficient (κ). The Gaussian model with multiple features achieved the best overall kappa coefficient (κ = 0.57), although the results from the non-parametric model were comparable (κ = 0.51). The optimum subset in the Gaussian model consisted of PPG waveform variability features, including the low-frequency to high-frequency ratio (LF/HF) and the normalized mid-frequency power (MF(NU)), in addition to the PPG pulse wave features, such as pulse width, peak-to-notch time, reflection index, and notch time ratio. The classifier performed particularly well in discriminating low SVR, with a sensitivity of 85%, specificity of 86%, positive predictive value of 88% and a negative predictive value of 82%. The results highlight the feasibility of deploying a multivariate statistical approach of SVR classification in the clinical setting, simply using a non-invasive and easy-to-measure PPG waveform signal.     

Noninvasive assessment of coronary flow reserve with transthoracic signal-enhanced Doppler echocardiography.

OBJECTIVES: The feasibility of noninvasive assessment of coronary flow reserve (CFR) in the distal left anterior descending artery (LAD) with echocardiography-enhanced transthoracic pulsed wave Doppler guided by high-resolution transthoracic color Doppler (TTCD) was investigated. The results were compared with the degree of coronary diameter stenosis obtained during cardiac catheterization. BACKGROUND: Assessment of CFR has proven to be useful in the selection of patients undergoing invasive treatment of coronary artery disease and in estimating their prognosis. However, CFR could only be determined invasively in everyday practice during catheterization procedures. Recent development of high-resolution TTCD allows transthoracic visualization of distal LAD and supra-apical intramyocardial perforator branches and noninvasive measurement of CFR with pulsed wave Doppler technique. METHODS: CFR was determined by measuring the ratio of pulsed wave Doppler time velocity integral during adenosine-induced hyperemia (140 microgram/kg/min intravenously) to baseline value. If the baseline Doppler signal of LAD flow was insufficient, an echocardiography (echo) enhancer (Levovist) was used. Forty-five patients were examined by TTCD (7-MHz B-mode, 5-MHz color Doppler, and 3.5-MHz pulsed wave Doppler) after coronary angiography had been performed. Group 1 consisted of 15 patients without heart disease, group 2 of 15 patients with 50% to 85% isolated LAD diameter stenosis, and group 3 of 15 patients with >85% LAD diameter stenosis. RESULTS: Peripheral LAD coronary flow at baseline condition was assessed in 40 (88%) patients with TTCD. CFR could be quantified in 36 (80%) of the 45 patients: in 18 patients without echo enhancer, and in 18 patients with echo-enhancing agent. CFR could not be assessed in 9 (20%) patients. CFR in the various groups was as follows: group 1, 3. 13 +/- 0.57; group 2, 2.23 +/- 0.20 (vs group 1: P <.01); and group 3, 1.64 +/- 0.30 (vs group 2: P <.02). CONCLUSION: CFR in the LAD can be determined in 80% of patients with pulsed wave Doppler guided by high-resolution TTCD combined with intravenously administered echo-enhancing agent.     

Noninvasive measurement of cardiac output by continuous-wave Doppler echocardiography: initial experience and review of the literature

Doppler echocardiographic measurement of the velocity of blood flow in the ascending aorta is a noninvasive method for determining cardiac output in the critically ill patient. Fifty-four patients in the medical intensive care unit (35 men and 19 women, age range 41 to 91 years) in whom a Swan-Ganz catheter had been inserted underwent measurement of cardiac output with use of a commercially available continuous-wave Doppler echocardiographic instrument. The aortic root diameter was measured by A-mode echocardiography. An additional 26 patients (17 men and 9 women, age range 20 to 83 years) who had undergone an open-heart surgical procedure and had hemodynamic monitoring in the postoperative period also underwent Doppler measurement of cardiac output. In these patients, the aortic root diameter was measured directly intraoperatively. Cardiac output was also determined by thermodilution in both groups. An adequate A-mode study was possible in 83% of the medical patients but only 27% of the surgical patients. Doppler signals were adequate in 84% of the medical patients and 92% of the surgical patients. The correlation between thermodilution and Doppler-derived cardiac output was good in both the medical (r = 0.94, SEE = 0.78, P less than 0.001) and the surgical (r = 0.85, SEE = 0.78, P less than 0.001) group. Doppler echocardiography is a promising noninvasive method for determining cardiac output in critically ill patients.     

Noninvasive assessment of great cardiac vein flow by Doppler echocardiography: a validation study.

The objectives of this study were (1) to compare great cardiac vein (GCV) flow velocity detected by pulsed Doppler echocardiography (PDE) with Doppler guide wire (DGW) in the experimental setting and (2) to clarify whether transthoracic Doppler echocardiography (TTDE) can detect GCV flow in humans. Using opened-chest dogs, we detected GCV flow by PDE under the guidance of color flow Doppler mapping. GCV flow velocity was recorded by PDE and DGW, simultaneously. In 23 volunteers, GCV flow velocity was measured by TTDE. In the experimental setting, the prominent systolic flow wave of the GCV was obtained in PDE and DGW. There were good agreements between PDE and DGW for the measurements of GCV flow velocity (peak velocity: r = 0.98, y = 1.12chi-5.9; time velocity integral: r = 0.97, y = 1.10chi-0.71). In the human subjects, clear envelopes of GCV flow velocity were obtained in 21 (91%) of 23 subjects with the use of TTDE.     

Noninvasive cerebrospinal fluid shunt flow measurement by Doppler ultrasound using ultrasonically excited bubbles: a feasibility study.

Because normal cerebrospinal fluid (CSF) has almost no natural Doppler scatterers, patency testing of ventriculoperitoneal cerebrospinal fluid shunts (small silastic tubing with lumen diameter of approximately 1 mm draining excessive CSF from the brain) cannot be performed by Doppler ultrasound. We have developed a low-frequency bubble excitation system that generates microbubble scatterers in both distilled water and CSF. Doppler ultrasound can then be used for flow measurement in a ventriculoperitoneal shunt. By using low duty-cycle (approximately 10%), low-frequency (approximately 30 kHz), and low-amplitude (approximately 30 kPa) ultrasound, a population of microbubbles can be maintained for sufficiently long times (>10 min) for Doppler ultrasound measurement, although bubble initiation is inconsistent. The minimum pressure needed for bubble maintenance was found to decrease with increasing burst length and duty cycle. It has been possible to detect the presence of CSF shunt flow down to a mean flow rate of 3 mL/h (mean velocity approximately 0.6 mm/s). The bubble maintenance scheme developed satisfies the safety parameters specified by the American Institute of Ultrasound in Medicine (AIUM) and the US Food and Drug Administration (FDA). Results from both in vitro and in vivo (externalized shunts) experiments indicate the feasibility of this scheme for determining realistic CSF shunt flows, though some practical problems remain before the technique will be ready for clinical use.     

Noninvasive assessment of right atrial pressure using Doppler tissue imaging.

Right atrial pressure (RAP) reflects volume and pressure hemodynamics of right cardiac chambers. Previous attempts for noninvasive assessment of RAP include 2-dimensional and Doppler correlates of RAP, which require the presence of optimal subcostal views that may not be always feasible. In this study we utilized Doppler tissue imaging of the tricuspid annulus in the apical 4-chamber view, for noninvasive assessment of RAP. An inverse relationship was demonstrated between mean RAP and the interval between the end of the systolic annular motion to the onset of the early diastolic filling wave (right ventricular regional isovolumic relaxation time).     

Demonstration of coronary artery flow using transthoracic Doppler echocardiography.

Transthoracic Doppler echocardiography is emerging as a promising method for evaluating coronary artery disease. After a period of training, detection and measurement of distal left anterior descending coronary artery flow with transthoracic Doppler echocardiography is feasible in more than 90% of the patients. Using transthoracic Doppler echocardiography with a high-frequency transducer and special setting of low Nyquist limits, pathologic coronary flow dynamics can be demonstrated. Measurement of coronary flow reserve may impact diagnosis or clinical treatment in those: (1) with anginal chest pain and angiographically normal coronary arteries; (2) with intermediate-grade coronary obstruction where the physiologic significance is in doubt; and (3) who have had an attempt at revascularization and the effectiveness of the therapy is uncertain.     

Noninvasive optimization of left ventricular filling using esophageal Doppler

OBJECTIVE: To confirm whether the descending aortic blood flow velocity waveform variable of flow time corrected for heart rate, measured using an esophageal Doppler transducer, can be used for noninvasive optimization of left ventricular (LV) filling. SETTING: ICU and operating theater. SUBJECTS: Forty-three mechanistically ventilated patients in the ICU or undergoing cardiothoracic surgery in whom a pulmonary arterial catheter was in situ. INTERVENTIONS: LV preload was a) increased from hypovolemic states (pulmonary arterial occlusion pressure [PAOP] less than 8 mm Hg) by fluid challenge, b) decreased from normovolemic states (PAOP 10 to 15 mm Hg) by either iv nitrates or intravascular fluid loss, and c) decreased from heart failure or fluid overload states (PAOP greater than 20 mm Hg) by iv nitrates. No other maneuver was performed concurrently. MEASUREMENTS AND MAIN RESULTS: Descending aortic blood flow was measured by an esophageal Doppler transducer. Corrected flow time was calculated by dividing systolic flow time by the square root of the cycle time. PAOP and corrected flow time increased after fluid challenges in hypovolemic states, and decreased when LV preload was decreased from normovolemic states. However, when preload was decreased from overload states, PAOP always decreased, but the corrected flow time usually increased before any subsequent decrease. The greatest value of corrected flow time corresponded with the maximal stroke volume seen. CONCLUSIONS: Esophageal Doppler measurement of aortic blood flow can be used for rapid, noninvasive optimization of LV filling in mechanically ventilated patients.     

冠状动脉造影正常伴心前区疼痛患者冠状动脉微血管功能的无创性超声多普勒评估

目的　经胸多普勒超声心动图 (TTDE)与冠状动脉内多普勒 (ICD)相对照 ,分析TTDE探测冠状动脉造影正常者左前降支 (LAD)远端血流的准确性 ;分析冠状动脉造影正常者冠状动脉微血管功能的变化。方法　利用TTDE探测 3 5例冠状动脉造影正常者LAD远端的基础状态及经静脉注入腺苷后的最大血流速度 ,计算冠状动脉血流速度储备 (CFVR)、冠状动脉阻力 (CVR )和最小冠状动脉阻力指数 (CVRI)。分析比较 2 0例心前区疼痛患者 (A组 )和 15例正常人 (B组 )上述冠状动脉血流参数测值。结果　 3 5例冠状动脉造影正常者TTDE所探测的基础状态血流速度 (APVb)、最大充血反应状态血流速度 (APVh)和CFVR与ICD的探测结果密切相关 (r分别为 0 .79,0 .83 ,0 .85 )。A组与B组APVb、APVh和CVR的差异均无显著性意义 (P >0 .0 5 ) ,但A组CFVR低于B组 ,而CVRI高于B组 (均P <0 .0 5 )。结论　TTDE是一项可行、可信的无创性探测CFVR的方法。冠状动脉造影正常伴心前区疼痛患者存在冠状动脉微循环功能障碍。     

Noninvasive assessment of wall-shear rate and vascular elasticity using combined ARFI/SWEI/spectral Doppler imaging system

The progression of atherosclerotic disease is a complex process believed to be a function of the localized mechanical properties and hemodynamic loading associated with the arterial wall. It is hypothesized that measurements of cardiovascular stiffness and wall-shear rate (WSR) may provide important information regarding vascular remodeling, endothelial function and the growth of soft lipid-filled plaques that could help a clinician better predict the occurrence of clinical events such as stroke. Two novel ARFI based imaging techniques, combined on-axis/off-axis ARFI/Spectral Doppler Imaging (SAD-SWEI) and Gated 2D ARFI/Spectral Doppler Imaging (SAD-Gated), were developed to form co-registered depictions of B-mode echogenicity, ARFI displacements, ARF-excited transverse wave velocity estimates and estimates ofwall-shear rate throughout the cardiac cycle. Implemented on a commercial ultrasound scanner, the developed techniques were evaluated in tissue-mimicking and steady-state flow phantoms and compared with conventional techniques, other published study results and theoretical values. Initial in vivo feasibility of the method is demonstrated with results obtained from scanning the carotid arteries of five healthy volunteers. Cyclic variations over the cardiac cycle were observed in on-axis displacements, off-axis transverse-wave velocities and wall-shear rates.     

Noninvasive study of left ventricular function and systemic haemodynamics during dipyridamole echocardiography stress test

Summary. Left ventricular function and systemic haemodynamics were noninvasively assessed during cardiac stress testing with dipyridamole (0–84 mg kg^-1 i.v.) in 10 subjects (44–61 years) with normal coronary arteries (group 1), and in 14 patients (46–77 years) with coronary artery disease either without (group 2, n= 6) or with (group 3, n= 8) echocardiographic evidence for myocardial ischaemia during test. Left ventricular wall motion and dimensions, and aortic root pressure and flow were obtained by Doppler echocardiography combined with an externally traced subclavian artery pulse calibrated with brachial artery pressures. Peripheral arterial resistance, total arterial compliance, and aortic characteristic impedance were estimated from aortic root pressure and flow, by use of a three-element windkessel model of the systemic circulation. Left ventricular ejection fraction improved from baseline to peak stress in group 1 (mean ± SD: 62 ± 6% vs. 65 ± 6%, P= 0–05), whereas it was not significantly changed in group 2 (58 ± 10% vs. 56 ± 6%) and decreased in group 3 (53 ± 10% vs. 43 ± 10%, P<0–05). Otherwise, the haemodynamic response was similar in the three groups: heart rate and cardiac index increased by at least 30% and 37%, respectively, whereas stroke index and arterial pressures were maintained at or slightly above baseline. Peripheral resistance decreased by at least 22%, and total arterial compliance and aortic characteristic impedance were not significantly altered during test. The worsening of wall motion abnormality at peak stress in group 3 was not significantly related to the change in systemic haemodynamics. Thus, dipyridamole acted predominantly on the arterioles without significantly influencing the large systemic arteries. Myocardial ischaemia during test impaired regional and global left ventricular function, but did not influence the systemic haemodynamic response.     

Low systemic vascular resistance state in patients undergoing cardiopulmonary bypass.

OBJECTIVE: To determine the prevalence, hemodynamic characteristics, and risk factors for the low systemic vascular resistance (SVR) state in patients who have undergone cardiopulmonary bypass. DESIGN: Prospective cohort study. SETTING: The intensive care unit of a tertiary care hospital. PATIENTS: Seventy-nine consecutive patients who underwent coronary artery bypass graft, mitral valve, or aortic valve procedures. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: Low SVR was defined as an indexed systemic vascular resistance (SVRi) of <1800 dyne x sec/cm5 x m2 at two consecutive times postoperatively. SVRi, cardiac index, mean arterial pressure, temperature, and central venous pressure were recorded before bypass and at 0, 1, 2, 4, 8, and 16 hrs after bypass. We recorded age, gender, urgency of operation, use of angiotensin-converting enzyme inhibitors and calcium channel blockers, ejection fraction, pump time, cross-clamp time, use of antifibrinolytics, type of oxygenator, amrinone use, postoperative biochemical and hematologic values, medication use, fluid balance, intensive care unit admission duration, and hospital admission duration. We assessed the role of diabetes mellitus, current smoking, and systemic hypertension. The incidence of the low-SVR state was 35 of 79 patients during a 3-month period (44%). At 8 hrs postoperatively, the SVRi in low-SVR and non-low-SVR patients was 1594+/-50 (SEM) and 2103+/-56 (SEM) dyne x sec/cm5 x m2, respectively (p < .001). In low-SVR patients, there was an initial and sustained increase in cardiac index and central venous pressure that preceded the decrease in mean arterial pressure. The decrease in mean arterial pressure was maximal at 8 hrs postoperatively. Patients with low SVR were more likely to have longer cross-clamp times, to be male, and to have lower postoperative platelet counts (p < .05 for all). Low-SVR patients were less likely to require dobutamine in the first 4 hrs postoperatively. CONCLUSIONS: Low SVR, a probable manifestation of systemic inflammatory response syndrome, is common in patients after cardiopulmonary bypass. These patients may respond better to a vasopressor to restore vascular tone than to volume loading to further increase cardiac index.     

Hemodynamic assessment of critically ill patients using echocardiography Doppler

PURPOSE OF REVIEW: The evaluation of hemodynamic status in critically ill patients is a leading recommended indication of transesophageal echocardiography in the intensive care unit. Advantages and diagnostic yield of transesophageal echocardiography in this setting are particularly relevant when considering limitations and questioned prognostic impact of pulmonary artery catheterization. RECENT FINDINGS: Recent clinical studies have been performed to validate and assess the value of transesophageal echocardiography in determining cardiac output, cardiac preload dependence, right ventricular function, and left ventricular filling pressure. In addition, diagnostic capacity and therapeutic impact of transesophageal echocardiography have been widely reported in various intensive care unit settings. SUMMARY: Transesophageal echocardiography appears well suited for the determination of cardiac index and to track its variations after therapeutic interventions. Although repeated measurements of left ventricular end-diastolic dimension allows to accurately track preload variations, a single determination is not reliable to predict fluid responsiveness in intensive care unit patients. Identification of preload dependence in hemodynamically unstable patients currently tends to rely mainly on dynamic parameters that use cardiopulmonary interactions under mechanical ventilation. Transesophageal echocardiography also allows to adequately assess right ventricular function and left ventricular filling pressure using combined Doppler modalities. Adequate education and training of intensivists and anesthesiologists is crucial to further develop the use of transesophageal echocardiography in the intensive care unit setting. Despite the absence of randomized controlled studies documenting transesophageal echocardiography benefits on patient outcome, present evidence and experience strongly recommend a larger use of echocardiography Doppler for a comprehensive functional hemodynamic assessment of critically ill patients with circulatory failure.     

Noninvasive assessment of myocardial ischemia in the left ventricular inferior regions by coronary flow reserve measurement using transthoracic doppler echocardiography

OBJECTIVE: The purpose of this study was to evaluate the potential of noninvasive measurement of coronary flow reserve (CFR) by transthoracic Doppler echocardiography (TTDE) for the assessment of myocardial ischemia in the left ventricular (LV) inferior regions. BACKGROUND: Although coronary flow assessment by TTDE has been determined for the assessment of perfusion abnormality in the LV anterior regions, the usefulness of this method has not been well investigated in the LV inferior regions. METHODS: We studied 50 patients (43 men; mean age 60 +/- 9 years) with suggested coronary artery disease. CFR in the posterodescending coronary artery (PDA) was calculated as a ratio of hyperemic to basal peak (peak CFR) and mean (mean CFR) flow velocities in the PDA, which were measured by TTDE. CFR values were compared with the results of exercise 201-thallium single photon emission computed tomography. RESULTS: CFR was successfully measured in 43 of 50 patients (86%). Mean and peak CFR < 2 were shown in 10 of 12 patients with abnormal perfusion in the LV inferior regions, whereas CFR > or = 2 were shown in 30 of 31 patients with normal perfusion. Thus, CFR < 2 in the PDA by TTDE had a sensitivity of 83% and a specificity of 97% for the assessment of perfusion abnormality in the LV inferior regions by 201-thallium single photon emission computed tomography. CONCLUSIONS: CFR in the PDA measured by TTDE provides data equivalent to those obtained by 201-thallium single photon emission computed tomography for myocardial ischemia in the LV inferior regions.     

多普勒超声心动描记术检测胎儿机械性QT间期

目的 探讨多普勒超声心动描记术在测量胎儿机械性QT间期中的应用价值。 方法 对胎儿心脏无异常的早孕期、中孕期和晚孕期孕妇各100名行胎儿多普勒超声心动描记术检查。记录左心室流入道及流出道血流频谱,测量机械性QT间期,即自二尖瓣舒张期A峰结束至下一个舒张期E峰开始的时间,同时测量胎儿心率。 结果 胎儿机械性QT间期和心率呈正态分布,早孕、中孕和晚孕组胎儿机械性QT间期均值的95%可信区间分别为225.25~231.21 ms、241.21~248.79 ms和253.23~259.45 ms;不同孕期组间胎儿机械性QT间期和心率的差异均有统计学意义(P均<0.01);胎儿机械性QT间期与孕周呈正相关(r=0.499,P<0.01),胎儿心率与孕周呈负相关(r=-0.628,P<0.01)。 结论 应用多普勒超声心动描记术检测胎儿机械性QT间期简便易行,图像清晰且重复性好,可为临床诊断胎儿心律失常提供重要依据。     

Nicotinamide increases systemic vascular resistance in ovine endotoxemia

OBJECTIVE: The nuclear enzyme Poly(ADP-Ribose)-Polymerase (PARP) has been hypothesized as playing a major role in various forms of inflammation. PARP activation is induced by DNA strand breakage and can result in intracellular energy depletion and, ultimately, cell death. Further, it is thought to influence cardiovascular function and organ failure in endotoxemia. Here, we investigated the effect of the PARP inhibitor nicotinamide on cardiovascular and liver function in healthy and chronically endotoxemic sheep. DESIGN: Prospective controlled trial. SETTING: University research laboratory. Subjects: 12 female adult sheep. INTERVENTIONS: Six healthy sheep, instrumented for chronic study, received nicotinamide intravenously as a bolus of 40 mg/kg followed by a continuous infusion of 10 mg.kg(-1).h(-1); six animals received the vehicle. One hour after bolus application, a continuous infusion of endotoxin ( Salmonella typhosa, 10 ng.kg(-1).min(-1)) was started. Hemodynamic parameters were determined before and during endotoxemia. MEASUREMENTS AND RESULTS: Treatment with nicotinamide resulted in a significantly higher systemic vascular resistance index and lower cardiac index in endotoxemic animals, but not in controls. It also attenuated endotoxin-induced increase in gamma-glutamyl transferase. CONCLUSIONS: The PARP inhibitor nicotinamide attenuates impairment of cardiovascular function during endotoxemia. In addition, PARP activation may be involved in endotoxin-induced liver injury.