Pulmonary artery reflection for differentially diagnosing primary pulmonary hypertension and chronic pulmonary thromboembolism

Pulmonary Hypertension Phenotype Can Be Identified in Heart Failure With Reduced Ejection Fraction Using Echocardiographic Assessment of Pulmonary Artery Pressure With Supportive Use of Pressure Reflection Variables

BACKGROUND

Pulmonary hypertension (PH) is frequent in patients with heart failure and reduced ejection fraction (HFrEF) with 2 different phenotypes: isolated postcapillary PH (IpcPH) and, with the worst prognosis, combined pre- and postcapillary PH (CpcPH). The aims of the present echocardiography study were to investigate (1) the ability to identify PH phenotype in patients with HFrEF using the newly adopted definition of PH (mean pulmonary artery pressure >20 mm Hg) and (2) the relationship between PH phenotype and right ventricular (RV) function.

METHODS

One hundred twenty-four patients with HFrEF consecutively referred for heart transplant or heart failure workup were included with echocardiography and right heart catheterization within 48 hours. We estimated systolic pulmonary artery pressure (sPAP_Doppler) and used a method to detect increased pulmonary vascular resistance (>3 Wood units) based on predefined thresholds of 3 pressure reflection (PRefl) variables (the acceleration time in the RV outflow tract [RVOT], the interval between peak RVOT and peak tricuspid regurgitant velocity, and the RV pressure augmentation following peak RVOT velocity).

RESULTS

Using receiver operator characteristic analysis in a derivation group (n = 62), we identified sPAP_Doppler ≥35 mm Hg as a cutoff that in a test group (n = 62) increased the likelihood of PH 6.6-fold. The presence of sPAP_Doppler >40 mm Hg and 2 or 3 positive PRefl variables increased the probability of CpcPH 6- to 8-fold. A 2-step approach with primarily assessment of sPAP_Doppler and the supportive use of PRefl variables in patients with mild/moderate PH (sPAP_Doppler 41-59 mm Hg) showed 76% observer agreement and a weighted kappa of 0.63. The steady-state (pulmonary vascular resistance) and pulsatile (compliance, elastance) vascular loading are increased in both IpcPH and CpcPH with a comparable degree of RV dysfunction.

CONCLUSIONS

The PH phenotype can be identified in HFrEF using standard echocardiographic assessment of pulmonary artery pressure with supportive use of PRefl variables in patients with mild to moderate PH.

A Comprehensive Assessment of Right Ventricular Function in Chronic Thromboembolic Pulmonary Hypertension

While chronic thromboembolic pulmonary hypertension (CTEPH) results from macroscopic and microscopic obstruction of the pulmonary vascular bed, the function of the right ventricle (RV) and increased RV afterload are the main determinants of its symptoms and prognosis. In this review, we assess RV function in patients diagnosed with CTEPH with a focus on the contributions of RV afterload and dysfunction to the pathogenesis of this disease. We will also discuss changes in RV function and geometry in response to treatment, including medical therapy, pulmonary endarterectomy, and balloon pulmonary angioplasty.

When right ventricular pressure meets volume: the impact of arrival time of reflected waves on right ventricle load in pulmonary arterial hypertension

Abstract

Right ventricular (RV) wall tension in pulmonary arterial hypertension (PAH) is determined not only by pressure, but also by RV volume. A larger volume at a given pressure generates more wall tension. Return of reflected waves early after the onset of contraction, when RV volume is larger, may augment RV load. We aimed to elucidate: (1) the distribution of arrival times of peak reflected waves in treatment‐naïve PAH patients; (2) the relationship between time of arrival of reflected waves and RV morphology; and (3) the effect of PAH treatment on the arrival time of reflected waves. Wave separation analysis was conducted in 68 treatment‐naïve PAH patients. In the treatment‐naïve condition, 54% of patients had mid‐systolic return of reflected waves (defined as 34–66% of systole). Despite similar pulmonary vascular resistance (PVR), patients with mid‐systolic return had more pronounced RV hypertrophy compared to those with late‐systolic or diastolic return (RV mass/body surface area; mid‐systolic return 54.6 ± 12.6 g m^–2, late‐systolic return 44.4 ± 10.1 g m^–2, diastolic return 42.8 ± 13.1 g m^–2). Out of 68 patients, 43 patients were further examined after initial treatment. At follow‐up, the stiffness of the proximal arteries, given as characteristic impedance, decreased from 0.12 to 0.08 mmHg s mL^–1. Wave speed was attenuated from 13.3 to 9.1 m s^–1, and the return of reflected waves was delayed from 64% to 71% of systole. In conclusion, reflected waves arrive at variable times in PAH. Early return of reflected waves was associated with more RV hypertrophy. PAH treatment not only decreased PVR, but also delayed the timing of reflected waves.

Key points

Right ventricular (RV) wall tension in pulmonary arterial hypertension (PAH) is determined not only by pressure, but also by RV volume. Larger volume at a given pressure causes larger RV wall tension.

Early return of reflected waves adds RV pressure in early systole, when RV volume is relatively large. Thus, early return of reflected waves may increase RV wall tension. Wave reflection can provide a description of RV load.

In PAH, reflected waves arrive back at variable times. In over half of PAH patients, the RV is exposed to mid‐systolic return of reflected waves. Mid‐systolic return of reflected waves is related to RV hypertrophy.

PAH treatment acts favourably on the RV not only by reducing resistance, but also by delaying the return of reflected waves.

Arrival timing of reflected waves is an important parameter for understanding the relationship between RV load and its function in PAH.

Limited value of pulse wave analysis in assessing arterial wave reflection and stiffness in the pulmonary artery

We explored the use of the augmentation index (AI) based on pulse wave analysis (PWA) in the pulmonary circulation as a measure of wave reflection and arterial stiffness in individuals with and without pulmonary arterial hypertension (PAH) and chronic thromboembolic pulmonary hypertension (CTEPH). Right heart catheterization was performed using a pressure and Doppler flow sensor-tipped catheter to obtain simultaneous pressure and flow velocity measurements in the pulmonary artery in 10 controls, 11 PAH patients, and 11 CTEPH patients. PWA was applied to the measured pressure, while wave intensity analysis (WIA) and wave separation analysis (WSA) were performed using both the pressure and velocity to determine the magnitudes and timings of reflected waves. Type C (AI < 0) pressure waveform dominated in controls and type A (AI > 12%) waveform dominated in PAH patients, while there was a mixture of types A, B, and C among CTEPH patients. AI was greater and the inflection time shorter in CTEPH compared to PAH patients. There was a poor correlation between AI and arterial wave speed as well as measures of wave reflection derived from WIA and WSA. The infection point did not match the timing of the backward compression wave in ~50% of the cases. In patients with type C waveforms, the inflection time correlated well to the timing of the late systolic forward decompression wave caused by ventricular relaxation. In conclusion quantifying pulmonary arterial wave reflection and stiffness using AI based on PWA may be inaccurate and should therefore be discouraged.

Changes in the Pulmonary Artery Wave Reflection in Dogs with Experimentally-Induced Acute Pulmonary Embolism and the Effect of Vasodilator

Simple Summary

Pulmonary hypertension (PH) remains a fatal disease, despite the advances in disease-specific therapies. This may be because the assessment of pulmonary hemodynamics in PH has not been established. Recently, several studies have reported that the pulmonary arterial wave reflection (PAWR) might influence the right ventricular afterload and could provide additional information regarding the severity and progression of PH. However, the pathophysiology of PAWR has some unclear points particularly in the case of acute pulmonary embolism (APE). The objective of this study was to investigate, for the first time, the characteristics of PAWR in a dog model of APE using dual-tipped sensor wire. From the result of the present study, after dogs developed PH by injections of dextran microsphere, PAWR was increased significantly along with the pulmonary vascular resistance (PVR) and reduced after vasodilator administration. In addition, PAWR was significantly correlated with PVR and right ventricular fractional area of change (FAC). These results indicating that PAWR may be useful as a new evaluation method in PH and may detect changes related to right ventricular afterload earlier than pulmonary artery pressure (PAP).

Abstract

Pulmonary hypertension (PH) is a complex syndrome that has been frequently diagnosed in dogs and humans and can be detected by Doppler echocardiography and invasive catheterization. Recently, PAWR attracts much attention as a noninvasive approach for the early detection of PH. The present study aims to investigate the PAWR changes in acute pulmonary embolism (APE) and highlight the response of PAWR variables to vasodilator therapy in dogs. For this purpose, anesthesia and catheterization were performed in 6 Beagle dogs. After that, APE was experimentally conducted by Dextran microsphere administration, followed by vasodilator (Nitroprusside; 1μg/kg/min/IV) administration. The hemodynamics, echocardiography, PVR and PAWR variables were evaluated at the baseline, after APE and after administration of nitroprusside. The result showed a significant increase in PVR, PAP, tricuspid regurgitation (TR) as well as PAWR variables following APE induction compared with the baseline (p < 0.05). Vasodilation caused by administration of nitroprusside reduced the mean atrial pressure, PVR and PAWR parameters. There were a significant correlation and linear regression between PAWR indices and PVR as well as right ventricular function parameters. In conclusion, PAWR is not only correlated with PVR but also the right ventricular function parameter, which indicates that PAWR may be useful as a new evaluation method in PH, considering that PAWR can assess both right ventricular afterload and right ventricular function.

Arterial load and right ventricular-vascular coupling in pulmonary hypertension

Right ventricular (RV) functional adaptation to afterload determines outcome in pulmonary hypertension (PH). RV afterload is determined by the dynamic interaction between pulmonary vascular resistance (PVR), characteristic impedance (Z_c), and wave reflection. Pulmonary vascular impedance (PVZ) represents the most comprehensive measure of RV afterload; however, there is an unmet need for an easier bedside measurement of this complex variable. Although a recent study showed that Z_c and wave reflection can be estimated from RV pressure waveform analysis and cardiac output, this has not been validated. Estimations of Z_c and wave reflection coefficient (λ) were validated relative to conventional spectral analysis in an animal model. Z_c, λ, and the single-beat ratio of end-systolic to arterial elastance (E_es/E_a) to estimate RV-pulmonary arterial (PA) coupling were determined from right heart catheterization (RHC) data. The study included 30 pulmonary artery hypertension (PAH) and 40 heart failure with preserved ejection fraction (HFpEF) patients [20 combined pre- and postcapillary PH (Cpc-PH) and 20 isolated postcapillary PH, (Ipc-PH)]. Also included were 10 age- and sex-matched controls. There was good agreement with minimal bias between estimated and spectral analysis-derived Z_c and λ. Z_c in PAH and Cpc-PH groups exceeded that in the Ipc-PH group and controls. λ was increased in Ipc-PH (0.84 ± 0.02), Cpc-PH (0.87 ± 0.05), and PAH groups (0.85 ± 0.04) compared with controls (0.79 ± 0.03); all P values were <0.05. λ was the only afterload parameter associated with RV-PA coupling in PAH. In the PH-HFpEF group, RV-PA uncoupling was independent of RV afterload. Our findings indicate that Z_c and λ derived from an RV pressure curve can be used to improve estimation of RV afterload. λ is the only afterload measure associated with RV-PA uncoupling in PAH, whereas RV-PA uncoupling in PH-HFpEF appears to be independent of afterload consistent with an inherent abnormality of the RV myocardium.NEW & NOTEWORTHY Pulmonary vascular impedance (PVZ) represents the most comprehensive measure of right ventricle (RV) afterload; however, measurement of this variable is complex. We demonstrate that characteristic impedance (Z_c) and a wave reflection coefficient, λ, can be derived from RV pressure waveform analysis. In addition, RV dysfunction in left heart disease is independent of its afterload. The current study provides a platform for future studies to examine the pharmacotherapeutic effects and prognosis of different measures of RV afterload.

Right ventricular adaptation to pressure-overload: Differences between chronic thromboembolic pulmonary hypertension and idiopathic pulmonary arterial hypertension

BACKGROUND

Chronic thromboembolic pulmonary hypertension (CTEPH) and idiopathic pulmonary arterial hypertension (iPAH) are both associated with right ventricular (RV) failure and mortality. However, CTEPH patients are older, more often male and usually have more co-morbidities than iPAH patients, including a history of venous thromboembolism. Therefore, RV adaptation to pressure-overload in CTEPH may be different than in iPAH.

METHODS

We included all treatment-naive CTEPH and iPAH patients diagnosed in the Amsterdam UMC between 2000 and 2019 if cardiac magnetic resonance imaging (CMR) and a right heart catheterization were performed at time of diagnosis. Load-dependent RV volumes and mass were assessed with CMR. Load-independent RV contractility, afterload and diastolic stiffness in relation to afterload were obtained using single beat pressure-volume loop analysis. Differences in RV characteristics between CTEPH and iPAH were analyzed using multiple linear regression with interaction testing after correcting for confounders.

RESULTS

We included 235 patients in this study and performed pressure-volume loop analysis in 136 patients. In addition to being older and more often male, CTEPH patients had a lower pulmonary vascular resistance than iPAH patients at the time of diagnosis. After correcting for these confounders, CTEPH patients had a somewhat higher RV end-diastolic volume index (87 ± 27 ml vs 82 ± 25 ml; p < .01), and a lower RV relative wall thickness (0.6 ± 0,1 g/ml vs 0.7 ± 0,2 g/ml; p < .01). The correlation coefficient of RV diastolic stiffness to afterload was higher in CTEPH compared to iPAH (p < .05; independent of age and gender).

CONCLUSIONS

Despite differences in patient characteristics, disease etiology and physiology, RV functional parameters in CTEPH and iPAH are mostly similar. The right ventricle in CTEPH is marginally more dilated, stiffer and less hypertrophic than in iPAH.

Early return of reflected waves increases right ventricular wall stress in chronic thromboembolic pulmonary hypertension

Pulmonary vascular resistance (PVR) and compliance are comparable in proximal and distal chronic thromboembolic pulmonary hypertension (CTEPH). However, proximal CTEPH is associated with inferior right ventricular (RV) adaptation. Early wave reflection in proximal CTEPH may be responsible for altered RV function. The aims of the study are as follows: 1) to investigate whether reflected pressure returns sooner in proximal than in distal CTEPH and 2) to elucidate whether the timing of reflected pressure is related to RV dimensions, ejection fraction (RVEF), hypertrophy, and wall stress. Right heart catheterization and cardiac MRI were performed in 17 patients with proximal CTEPH and 17 patients with distal CTEPH. In addition to the determination of PVR, compliance, and characteristic impedance, wave separation analysis was performed to determine the magnitude and timing of the peak reflected pressure (as %systole). Findings were related to RV dimensions and time-resolved RV wall stress. Proximal CTEPH was characterized by higher RV volumes, mass, and wall stress, and lower RVEF. While PVR, compliance, and characteristic impedance were similar, proximal CTEPH was related to an earlier return of reflected pressure than distal CTEPH (proximal 53 ± 8% vs. distal 63 ± 15%, P < 0.05). The magnitude of the reflected pressure waves did not differ. RV volumes, RVEF, RV mass, and wall stress were all related to the timing of peak reflected pressure. Poor RV function in patients with proximal CTEPH is related to an early return of reflected pressure wave. PVR, compliance, and characteristic impedance do not explain the differences in RV function between proximal and distal CTEPH.NEW & NOTEWORTHY In chronic thromboembolic pulmonary hypertension (CTEPH), proximal localization of vessel obstructions is associated with poor right ventricular (RV) function compared with distal localization, though pulmonary vascular resistance, vascular compliance, characteristic impedance, and the magnitude of wave reflection are similar. In proximal CTEPH, the RV is exposed to an earlier return of the reflected wave. Early wave reflection may increase RV wall stress and compromise RV function.

Quantifying the Influence of Wedge Pressure, Age, and Heart Rate on the Systolic Thresholds for Detection of Pulmonary Hypertension

Background The strong linear relation between mean (MPAP) and systolic (SPAP) pulmonary arterial pressure (eg, SPAP=1.62×MPAP) has been mainly reported in precapillary pulmonary hypertension. This study sought to quantify the influence of pulmonary arterial wedge pressure (PAWP), heart rate, and age on the MPAP-SPAP relation. Methods and Results An allometric equation relating invasive MPAP and SPAP was developed in 1135 patients with pulmonary arterial hypertension, advanced lung disease, chronic thromboembolic pulmonary hypertension, or left heart failure. The equation was validated in 60 885 patients from the United Network for Organ Sharing (UNOS) database referred for heart and/or lung transplant. The MPAP/SPAP longitudinal stability was assessed in pulmonary arterial hypertension with repeated right heart catheterization. The equation obtained was SPAP=1.39×MPAP×PAWP^-0.07×(60/heart rate)^0.12×age^0.08 (P<0.001). It was validated in the UNOS cohort (R²=0.93, P<0.001), regardless of the type of organ(s) patients were listed for (mean bias [-1.96 SD; 1.96 SD] was 0.94 [-8.00; 9.88] for heart, 1.34 [-7.81; 10.49] for lung and 0.25 [-16.74; 17.24] mm Hg for heart-lung recipients). Thresholds of SPAP for MPAP=25 and 20 mm Hg were lower in patients with higher PAWP (37.2 and 29.8 mm Hg) than in those with pulmonary arterial hypertension (40.1 and 32.0 mm Hg). In 186 patients with pulmonary arterial hypertension, the predicted MPAP/SPAP was stable over time (0.63±0.03 at baseline and follow-up catheterization, P=0.43). Conclusions This study quantifies the impact of PAWP, and to a lesser extent heart rate and age, on the MPAP-SPAP relation, supporting lower SPAP thresholds for pulmonary hypertension diagnosis in patients with higher PAWP for echocardiography-based epidemiological studies.

Pulmonary hemodynamics and wave reflections in adults with atrial septal defects

Using high-fidelity micromanometers and flow velocity sensors at right heart catheterization, we compared pulmonary hemodynamics and wave reflections in age-matched normal adults and those with atrial septal defects, separated into three subgroups based on levels of mean pulmonary artery pressure: low (<17 mmHg), intermediate (17–26 mmHg), high (>26 mmHg). We made baseline measurements in all groups and after intravenous sodium nitroprusside in the subgroups. All of the subgroups had higher than normal baseline pulmonary flows and corresponding power that did not differ among the subgroups. The pulmonary vascular resistance, input resistance, and characteristic impedance in the subgroups did not differ from normal. Aside from the elevated flow and power, the hemodynamics in the low subgroup did not differ from normal. The intermediate subgroup had significantly higher than normal right ventricular and pulmonary artery pressures, wave reflections, and shorter wave reflection time, which all reverted to normal after nitroprusside. The high subgroup had similar changes as the intermediate subgroup. Unlike that subgroup, however, the pressures, wave reflections, and reflection return time did not revert to normal after nitroprusside. Hence, elevated wave reflections, but not resistance or characteristic impedance, are the hallmark of pulmonary hypertension in adults with atrial septal defects. Our results demonstrate that detailed measurements of hemodynamics and assessment of responsiveness to vasodilators provide important information about the pulmonary circulation in atrial septal defect. Coupled with studies after defect closure, those results may be a better foundation than current ones for clinical decisions.

Endothelial Cell Mechano-Metabolomic Coupling to Disease States in the Lung Microvasculature

Lungs are the most vascular part of humans, accepting the totality of cardiac output in a volume much smaller than the body itself. Due to this cardiac output, the lung microvasculature is subject to mechanical forces including shear stress and cyclic stretch that vary with the cardiac and breathing cycle. Vessels are surrounded by extracellular matrix which dictates the stiffness which endothelial cells also sense and respond to. Shear stress, stiffness, and cyclic stretch are known to influence endothelial cell state. At high shear stress, endothelial cells exhibit cell quiescence marked by low inflammatory markers and high nitric oxide synthesis, whereas at low shear stress, endothelial cells are thought to "activate" into a pro-inflammatory state and have low nitric oxide. Shear stress' profound effect on vascular phenotype is most apparent in the arterial vasculature and in the pathophysiology of vascular inflammation. To conduct the flow of blood from the right heart, the lung microvasculature must be rigid yet compliant. It turns out that excessive substrate rigidity or stiffness is important in the development of pulmonary hypertension and chronic fibrosing lung diseases via excessive cell proliferation or the endothelial-mesenchymal transition. Recently, a new body of literature has evolved that couples mechanical sensing to endothelial phenotypic changes through metabolic signaling in clinically relevant contexts such as pulmonary hypertension, lung injury syndromes, as well as fibrosis, which is the focus of this review. Stretch, like flow, has profound effect on endothelial phenotype; metabolism studies due to stretch are in their infancy.

Proximal pressure reducing effect of wave reflection in the pulmonary circulation disappear in obstructive disease: insight from a rabbit model

Locating the site of increased resistance within the vascular tree in pulmonary arterial hypertension could assist in both patient diagnosis and tailoring treatment. Wave intensity analysis (WIA) is a wave analysis method that may be capable of localizing the major site of reflection within a vascular system. We investigated the contribution of WIA to the analysis of the pulmonary circulation in a rabbit model with animals subjected to variable occlusive pulmonary disease. Animals were embolized with different sized microspheres for 6 wk ( n = 10) or underwent pulmonary artery (PA) ligation for 6 wk ( n = 3). These animals were compared with a control group ( n = 6) and acutely embolized animals ( n = 4). WIA was performed and compared with impedance-based methods to analyze wave reflections. The control group showed a relatively high extent of reflected waves (15.7 ± 10.6%); reflections had a net effect of pressure reduction during systole, suggesting an open-end reflector. The pattern of wave reflection was not different in the group with partial PA ligation (12.4 ± 4.1%). In the chronically embolized group, wave reflection was not observed (3.6 ± 1.5%). In the acute embolization group, wave reflection was more prominent (37.3 ± 12.6%), with the appearance of a novel wave increasing pressure, suggesting the appearance of a closed-end reflector. Wave reflections of an open-end type are present in the normal rabbit pulmonary circulation. However, the pattern and nature of reflections vary according to the extent of pulmonary vascular occlusion.

NEW & NOTEWORTHY The study proposes an original framework of a complementary analysis of wave reflections in the time domain and in the frequency domain. The methodology was used in the pulmonary circulation with different forms of chronic obstructions. The results suggest that the pulmonary vascular tree generates a reflection pattern that could actually assist the heart during ejection, and chronic obstruction significantly modifies the pattern.

Analysis of Biphasic Right Ventricular Outflow Doppler Waveform in Patients with Pulmonary Hypertension

Pulmonary hypertension (PH) with pulmonary vascular disease (PVD) is a progressive and debilitating disease associated with increased pulmonary vascular resistance (PVR). Biphasic right ventricular outflow tract (RVOT) Doppler flow is frequently seen in severe PH patients with PVD. In association with hemodynamics, the precise analysis of biphasic RVOT Doppler flow (RVDF) has not been fully elucidated. Therefore, the purpose of the present study is to analyze the relation between the hemodynamics and indices of biphasic RVDF in PH patients with PVD.Seventy PH patients with biphasic RVDF were analyzed. All patients underwent transthoracic echocardiography and right heart catheterization. For the analysis of biphasic RVDF, the early waveform was determined as P₁ while the late waveform was determined as P₂. For each P₁ and P₂, the duration (D, seconds) and peak flow velocity (PFV, in m/second) were measured.P₁D and P₂PFV were significantly correlated with PVR (P₁D: r = -0.542, P < 0.0001, P₂PFV: r = -0.513, P < 0.0001). Therefore, we propose a novel RVDF formula for estimation of PVR, as follows. PVR = 26 - 77 × P₁D - 14 × P₂PFV. The PVR could be estimated by this proposed formula (r = 0.649, P < 0.0001), which is derived from one Doppler image only unlike previously used PVR prediction formula.P₁D and P₂PFV were associated with PVR. Moreover, this simple RVDF formula proposed herein can estimate PVR in PH patients with PVD.

Computer simulated modeling of healthy and diseased right ventricular and pulmonary circulation

We have previously developed a simulated cardiovascular physiology model for in-silico testing and validation of novel closed-loop controllers. To date, a detailed model of the right heart and pulmonary circulation was not needed, as previous controllers were not intended for use in patients with cardiac or pulmonary pathology. With new development of controllers for vasopressors, and looking forward, for combined vasopressor-fluid controllers, modeling of right-sided and pulmonary pathology is now relevant to further in-silico validation, so we aimed to expand our existing simulation platform to include these elements. Our hypothesis was that the completed platform could be tuned and stabilized such that the distributions of a randomized sample of simulated patients' baseline characteristics would be similar to reported population values. Our secondary outcomes were to further test the system in representing acute right heart failure and pulmonary artery hypertension. After development and tuning of the right-sided circulation, the model was validated against clinical data from multiple previously published articles. The model was considered 'tuned' when 100% of generated randomized patients converged to stability (steady, physiologically-plausible compartmental volumes, flows, and pressures) and 'valid' when the means for the model data in each health condition were contained within the standard deviations for the published data for the condition. A fully described right heart and pulmonary circulation model including non-linear pressure/volume relationships and pressure dependent flows was created over a 6-month span. The model was successfully tuned such that 100% of simulated patients converged into a steady state within 30 s. Simulation results in the healthy state for central venous volume (3350 ± 132 ml) pulmonary blood volume (405 ± 39 ml), pulmonary artery pressures (systolic 20.8 ± 4.1 mmHg and diastolic 9.4 ± 1.8 mmHg), left atrial pressure (4.6 ± 0.8 mmHg), PVR (1.0 ± 0.2 wood units), and CI (3.8 ± 0.5 l/min/m²) all met criteria for acceptance of the model, though the standard deviations of LAP and CI were somewhat narrower than published comparators. The simulation results for right ventricular infarction also fell within the published ranges: pulmonary blood volume (727 ± 102 ml), pulmonary arterial pressures (30 ± 4 mmHg systolic, 12 ± 2 mmHg diastolic), left atrial pressure (13 ± 2 mmHg), PVR (1.6 ± 0.3 wood units), and CI (2.0 ± 0.4 l/min/m²) all fell within one standard deviation of the reported population values and vice-versa. In the pulmonary hypertension model, pulmonary blood volume of 615 ± 90 ml, pulmonary arterial pressures of 80 ± 14 mmHg systolic, 36 ± 7 mmHg diastolic, and the left atrial pressure of 11 ± 2 mmHg all met criteria for acceptance. For CI, the simulated value of 2.8 ± 0.4 l/min/m² once again had a narrower spread than most of the published data, but fell inside of the SD of all published data, and the PVR value of 7.5 ± 1.6 wood units fell in the middle of the four published studies. The right-ventricular and pulmonary circulation simulation appears to be a reasonable approximation of the right-sided circulation for healthy physiology as well as the pathologic conditions tested.

Wave Intensity Analysis Provides Novel Insights Into Pulmonary Arterial Hypertension and Chronic Thromboembolic Pulmonary Hypertension

Background

In contrast to systemic hypertension, the significance of arterial waves in pulmonary hypertension (PH) is not well understood. We hypothesized that arterial wave energy and wave reflection are augmented in PH and that wave behavior differs between patients with pulmonary arterial hypertension (PAH) and chronic thromboembolic pulmonary hypertension (CTEPH).

Methods and Results

Right heart catheterization was performed using a pressure and Doppler flow sensor–tipped catheter to obtain simultaneous pressure and flow velocity measurements in the pulmonary artery. Wave intensity analysis was subsequently applied to the acquired data. Ten control participants, 11 patients with PAH, and 10 patients with CTEPH were studied. Wave speed and wave power were significantly greater in PH patients compared with controls, indicating increased arterial stiffness and right ventricular work, respectively. The ratio of wave power to mean right ventricular power was lower in PAH patients than CTEPH patients and controls. Wave reflection index in PH patients (PAH: ≈25%; CTEPH: ≈30%) was significantly greater compared with controls (≈4%), indicating downstream vascular impedance mismatch. Although wave speed was significantly correlated to disease severity, wave reflection indexes of patients with mildly and severely elevated pulmonary pressures were similar.

Conclusions

Wave reflection in the pulmonary artery increased in PH and was unrelated to severity, suggesting that vascular impedance mismatch occurs early in the development of pulmonary vascular disease. The lower wave power fraction in PAH compared with CTEPH indicates differences in the intrinsic and/or extrinsic ventricular load between the 2 diseases.

A review of wave mechanics in the pulmonary artery with an emphasis on wave intensity analysis

Mean pulmonary arterial pressure and pulmonary vascular resistance (PVR) remain the most common haemodynamic measures to evaluate the severity and prognosis of pulmonary hypertension. However, PVR only captures the non-oscillatory component of the right ventricular hydraulic load and neglects the dynamic compliance of the pulmonary arteries and the contribution of wave transmission. Wave intensity analysis offers an alternative way to assess the pulmonary vasculature in health and disease. Wave speed is a measure of arterial stiffness, and the magnitude and timing of wave reflection provide information on the degree of impedance mismatch between the proximal and distal circulation. Studies in the pulmonary artery have demonstrated distinct differences in arterial wave propagation between individuals with and without pulmonary vascular disease. Notably, greater wave speed and greater wave reflection are observed in patients with pulmonary hypertension and in animal models exposed to hypoxia. Studying wave propagation makes a valuable contribution to the assessment of the arterial system in pulmonary hypertension, and here, we briefly review the current state of knowledge of the methods used to evaluate arterial waves in the pulmonary artery.

Assessment of proximal pulmonary arterial stiffness using magnetic resonance imaging: effects of technique, age and exercise

Introduction

To compare the reproducibility of pulmonary pulse wave velocity (PWV) techniques, and the effects of age and exercise on these.

Methods

10 young healthy volunteers (YHV) and 20 older healthy volunteers (OHV) with no cardiac or lung condition were recruited. High temporal resolution phase contrast sequences were performed through the main pulmonary arteries (MPAs), right pulmonary arteries (RPAs) and left pulmonary arteries (LPAs), while high spatial resolution sequences were obtained through the MPA. YHV underwent 2 MRIs 6 months apart with the sequences repeated during exercise. OHV underwent an MRI scan with on-table repetition. PWV was calculated using the transit time (TT) and flow area techniques (QA). 3 methods for calculating QA PWV were compared.

Results

PWV did not differ between the two age groups (YHV 2.4±0.3/ms, OHV 2.9±0.2/ms, p=0.1). Using a high temporal resolution sequence through the RPA using the QA accounting for wave reflections yielded consistently better within-scan, interscan, intraobserver and interobserver reproducibility. Exercise did not result in a change in either TT PWV (mean (95% CI) of the differences: −0.42 (−1.2 to 0.4), p=0.24) or QA PWV (mean (95% CI) of the differences: 0.10 (−0.5 to 0.9), p=0.49) despite a significant rise in heart rate (65±2 to 87±3, p<0.0001), blood pressure (113/68 to 130/84, p<0.0001) and cardiac output (5.4±0.4 to 6.7±0.6 L/min, p=0.004).

Conclusions

QA PWV performed through the RPA using a high temporal resolution sequence accounting for wave reflections yields the most reproducible measurements of pulmonary PWV.

Pulmonary arterial compliance: How and why should we measure it?

The pulmonary circulation is a high-flow/low-pressure system, coupled with a flow generator chamber-the right ventricle-, which is relatively unable to tolerate increases in afterload. A right heart catheterization, using a fluid-filled, balloon-tipped Swan-Ganz catheter allows the measurement of all hemodynamic parameters characterizing the pulmonary circulation: the inflow pressure, an acceptable estimate the outflow pressure, and the pulmonary blood flow. However, the study of the pulmonary circulation as a continuous flow system is an oversimplification and a thorough evaluation of the pulmonary circulation requires a correct understanding of the load that the pulmonary vascular bed imposes on the right ventricle, which includes static and dynamic components. This is critical to assess the prognosis of patients with pulmonary hypertension or with heart failure. Pulmonary compliance is a measure of arterial distensibility and, either alone or in combination with pulmonary vascular resistance, gives clinicians the possibility of a good prognostic stratification of patients with heart failure or with pulmonary hypertension. The measurement of pulmonary arterial compliance should be included in the routine clinical evaluation of such patients.

The role of pulmonary arterial stiffness in COPD

COPD is the second most common cause of pulmonary hypertension, and is a common complication of severe COPD with significant implications for both quality of life and mortality. However, the use of a rigid diagnostic threshold of a mean pulmonary arterial pressure (mPAP) of ≥25mHg when considering the impact of the pulmonary vasculature on symptoms and disease is misleading. Even minimal exertion causes oxygen desaturation and elevations in mPAP, with right ventricular hypertrophy and dilatation present in patients with mild to moderate COPD with pressures below the threshold for diagnosis of pulmonary hypertension. This has significant implications, with right ventricular dysfunction associated with poorer exercise capability and increased mortality independent of pulmonary function tests.

The compliance of the pulmonary artery (PA) is a key component in decoupling the right ventricle from the pulmonary bed, allowing the right ventricle to work at maximum efficiency and protecting the microcirculation from large pressure gradients. PA stiffness increases with the severity of COPD, and correlates well with the presence of exercise induced pulmonary hypertension. A curvilinear relationship exists between PA distensibility and mPAP and pulmonary vascular resistance (PVR) with marked loss of distensibility before a rapid rise in mPAP and PVR occurs with resultant right ventricular failure. This combination of features suggests PA stiffness as a promising biomarker for early detection of pulmonary vascular disease, and to play a role in right ventricular failure in COPD. Early detection would open this up as a potential therapeutic target before end stage arterial remodelling occurs.

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Pulmonary hypertension is common in COPD.

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Right ventricular remodeling occurs at pressures below the diagnostic threshold of PH.

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Pulmonary arterial stiffening occurs early in the development of PH.

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Non-invasive measurement of pulmonary stiffness may serve as an early biomarker of PH.

Right ventricular wave reflection relate to clinical measures in pulmonary arterial hypertension

OBJECTIVES

When a forward running pressure wave from the right ventricle reaches the narrow vessels in the pulmonary circulation, it is reflected as a backward running wave. We aimed to relate changes in right ventricular waveform reflection (RVWR) to changes in clinical variables in pulmonary arterial hypertension (PAH) patients.

DESIGN

Twenty-one PAH patients with RV waveform recordings from two sequential catheterisations at least 6 months apart were included. Six-minute walked distance (6MWD) and brain natriuretic peptide (BNP) level were also available. RVWR was defined as 'the pressure from the inflection point on the upstroke RV pressure wave to RV peak pressure'. Direction of change in RVWR, 6MWD and BNP was classified as (+) if increased and (-) if decreased. Spearman correlations were used to analyse the relation between changes. Pearson's correlation coefficient was used to analyse relation between RVWR and pulmonary vascular resistance (PVR).

RESULTS

The correlation between change in RVWR and 6MWD was - 0.67 (p < 0.01) and between RVWR and BNP was - 0.53 (p < 0.05). Actual RVWR and PVR correlated both at first (0.56, p < 0.001) and at second right heart catheterisation (0.45, p < 0.001).

CONCLUSION

RVWR might have clinical implications indicating a change in clinical status and disease progression in patients with PAH.

Noninvasive pulmonary artery wave intensity analysis in pulmonary hypertension

Pulmonary wave reflections are a potential hemodynamic biomarker for pulmonary hypertension (PH) and can be analyzed using wave intensity analysis (WIA). In this study we used pulmonary vessel area and flow obtained using cardiac magnetic resonance (CMR) to implement WIA noninvasively. We hypothesized that this method could detect differences in reflections in PH patients compared with healthy controls and could also differentiate certain PH subtypes. Twenty patients with PH (35% CTEPH and 75% female) and 10 healthy controls (60% female) were recruited. Right and left pulmonary artery (LPA and RPA) flow and area curves were acquired using self-gated golden-angle, spiral, phase-contrast CMR with a 10.5-ms temporal resolution. These data were used to perform WIA on patients and controls. The presence of a proximal clot in CTEPH patients was determined from contemporaneous computed tomography/angiographic data. A backwards-traveling compression wave (BCW) was present in both LPA and RPA of all PH patients but was absent in all controls (P = 6e⁻⁸). The area under the BCW was associated with a sensitivity of 100% [95% confidence interval (CI) 63–100%] and specificity of 91% (95% CI 75–98%) for the presence of a clot in the proximal PAs of patients with CTEPH. In conclusion, WIA metrics were significantly different between patients and controls; in particular, the presence of an early BCW was specifically associated with PH. The magnitude of the area under the BCW showed discriminatory capacity for the presence of proximal PA clot in patients with CTEPH. We believe that these results demonstrate that WIA could be used in the noninvasive assessment of PH.

MRI model-based non-invasive differential diagnosis in pulmonary hypertension

Pulmonary hypertension(PH) is a disorder characterised by increased mean pulmonary arterial pressure. Currently, the diagnosis of PH relies upon measurements taken during invasive right heart catheterisation (RHC). This paper describes a process to derive diagnostic parameters using only non-invasive methods based upon MRI imaging alone. Simultaneous measurements of main pulmonary artery (MPA) anatomy and flow are interpreted by 0D and 1D mathematical models, in order to infer the physiological status of the pulmonary circulation. Results are reported for 35 subjects, 27 of whom were patients clinically investigated for PH and eight of whom were healthy volunteers. The patients were divided into 3 sub-groups according to the severity of the disease state, one of which represented a negative diagnosis (NoPH), depending on the results of the clinical investigation, which included RHC and complementary MR imaging. Diagnostic indices are derived from two independent mathematical models, one based on the 1D wave equation and one based on an RCR Windkessel model. Using the first model it is shown that there is an increase in the ratio of the power in the reflected wave to that in the incident wave (Wpb/Wptotal) according to the classification of the disease state. Similarly, the second model shows an increase in the distal resistance with the disease status. The results of this pilot study demonstrate that there are statistically significant differences in the parameters derived from the proposed models depending on disease status, and thus suggest the potential for development of a non-invasive, image-based diagnostic test for pulmonary hypertension.

Decreased time constant of the pulmonary circulation in chronic thromboembolic pulmonary hypertension

This study analyzed the relationship between pulmonary vascular resistance (PVR) and pulmonary arterial compliance (Ca) in patients with idiopathic pulmonary arterial hypertension (IPAH) and proximal chronic thromboembolic pulmonary hypertension (CTEPH). It has recently been shown that the time constant of the pulmonary circulation (RC time constant), or PVR × Ca, remains unaltered in various forms and severities of pulmonary hypertension, with the exception of left heart failure. We reasoned that increased wave reflection in proximal CTEPH would be another cause of the decreased RC time constant. We conducted a retrospective analysis of invasive pulmonary hemodynamic measurements in IPAH (n = 78), proximal CTEPH (n = 91) before (pre) and after (post) pulmonary endarterectomy (PEA), and distal CTEPH (n = 53). Proximal CTEPH was defined by a postoperative mean pulmonary artery pressure (PAP) of ≤25 mmHg. Outcome measures were the RC time constant, PVR, Ca, and relationship between systolic and mean PAPs. The RC time constant for pre-PEA CTEPH was 0.49 ± 0.11 s compared with post-PEA-CTEPH (0.37 ± 0.11 s, P < 0.0001), IPAH (0.63 ± 0.14 s, P < 0.001), and distal CTEPH (0.55 ± 0.12 s, P < 0.05). A shorter RC time constant was associated with a disproportionate decrease in systolic PAP with respect to mean PAP. We concluded that the pulmonary RC time constant is decreased in proximal CTEPH compared with IPAH, pre- and post-PEA, which may be explained by increased wave reflection but also, importantly, by persistent structural changes after the removal of proximal obstructions. A reduced RC time constant in CTEPH is in accord with a wider pulse pressure and hence greater right ventricular work for a given mean PAP.

Proximal pulmonary arterial obstruction decreases the time constant of the pulmonary circulation and increases right ventricular afterload

The time constant of the pulmonary circulation, or product of pulmonary vascular resistance (PVR) and compliance (Ca), called the RC-time, has been reported to remain constant over a wide range of pressures, etiologies of pulmonary hypertension, and treatments. We wondered if increased wave reflection on proximal pulmonary vascular obstruction, like in operable chronic thromboembolic pulmonary hypertension, might also decrease the RC-time and thereby increase pulse pressure and right ventricular afterload. Pulmonary hypertension of variable severity was induced either by proximal obstruction (pulmonary arterial ensnarement) or distal obstruction (microembolism) eight anesthetized dogs. Pulmonary arterial pressures (Ppa) were measured with high-fidelity micromanometer-tipped catheters, and pulmonary flow with transonic technology. Pulmonary ensnarement increased mean Ppa, PVR, and characteristic impedance, decreased Ca and the RC-time (from 0.46 ± 0.07 to 0.30 ± 0.03 s), and increased the oscillatory component of hydraulic load (Wosc/Wtot) from 25 ± 2 to 29 ± 2%. Pulmonary microembolism increased mean Ppa and PVR, with no significant change in Ca and characteristic impedance, increased RC-time from 0.53 ± 0.09 to 0.74 ± 0.05 s, and decreased Wosc/Wtot from 26 ± 2 to 13 ± 2%. Pulse pressure increased more after pulmonary ensnarement than after microembolism. Concomitant measurements with fluid-filled catheters showed the same functional differences between the two types of pulmonary hypertension, with, however, an underestimation of Wosc. We conclude that pulmonary hypertension caused by proximal vs. distal obstruction is associated with a decreased RC-time and increased pulsatile component of right ventricular hydraulic load.

Mechanics and Function of the Pulmonary Vasculature: Implications for Pulmonary Vascular Disease and Right Ventricular Function

The relationship between cardiac function and the afterload against which the heart muscle must work to circulate blood throughout the pulmonary circulation is defined by a complex interaction between many coupled system parameters. These parameters range broadly and incorporate system effects originating primarily from three distinct locations: input power from the heart, hydraulic impedance from the large conduit pulmonary arteries, and hydraulic resistance from the more distal microcirculation. These organ systems are not independent, but rather, form a coupled system in which a change to any individual parameter affects all other system parameters. The result is a highly nonlinear system which requires not only detailed study of each specific component and the effect of disease on their specific function, but also requires study of the interconnected relationship between the microcirculation, the conduit arteries, and the heart in response to age and disease. Here, we investigate systems-level changes associated with pulmonary hypertensive disease progression in an effort to better understand this coupled relationship.

Pulmonary vascular wall stiffness: An important contributor to the increased right ventricular afterload with pulmonary hypertension

Pulmonary hypertension (PH) is associated with structural and mechanical changes in the pulmonary vascular bed that increase right ventricular (RV) afterload. These changes, characterized by narrowing and stiffening, occur in both proximal and distal pulmonary arteries (PAs). An important consequence of arterial narrowing is increased pulmonary vascular resistance (PVR). Arterial stiffening, which can occur in both the proximal and distal pulmonary arteries, is an important index of disease progression and is a significant contributor to increased RV afterload in PH. In particular, arterial narrowing and stiffening increase the RV afterload by increasing steady and oscillatory RV work, respectively. Here we review the current state of knowledge of the causes and consequences of pulmonary arterial stiffening in PH and its impact on RV function. We review direct and indirect techniques for measuring proximal and distal pulmonary arterial stiffness, measures of arterial stiffness including elastic modulus, incremental elastic modulus, stiffness coefficient β and others, the changes in cellular function and the extracellular matrix proteins that contribute to pulmonary arterial stiffening, the consequences of PA stiffening for RV function and the clinical implications of pulmonary vascular stiffening for PH progression. Future investigation of the relationship between PA stiffening and RV dysfunction may facilitate new therapies aimed at improving RV function and thus ultimately reducing mortality in PH.

Are pulmonary artery pulsatility indexes able to differentiate chronic pulmonary thromboembolism from pulmonary arterial hypertension? An echocardiographic and catheterization study

The differentiation between chronic pulmonary thromboembolic hypertension (CTEPH) and pulmonary arterial hypertension (PAH) remains a clinical challenge. The aim of our study was to evaluate the usefulness of both echocardiographically and invasively derived pulmonary artery pulsatility indexes in the etiologic differentiation of patients with CTEPH and PAH. We retrospectively analyzed the results of echocardiographic and invasive hemodynamic examinations in 125 patients with either CTEPH (n = 62) or PAH (n = 63). Invasive data were obtained in 52 patients with CTEPH and 43 PAH patients. Using echocardiography, pulmonary artery systolic (PASP), diastolic (PADP) and mean (PAMP) pressures were estimated from velocities of tricuspid regurgitation and pulmonary regurgitation, respectively. Pulse pressure (PP) was calculated as the difference between PASP and PADP. To obtain pulmonary artery pulsatility indexes, we normalized PP by PASP (PP/PASP), by PAMP (PP/PAMP) and by PADP (PP/PADP). Pulsatility indexes assessed by echocardiography did not differ between CTEPH and PAH patients except for PP/PAMP [PP/PAMP (1.82 ± 0.33 vs. 1.40 ± 0.3, p < 0.001)]. Invasively derived pulsatility indexes were significantly higher in subjects with CTEPH (0.60 ± 0.08 vs. 0.53 ± 0.09 for PP/PASP; 0.98 ± 0.21 vs. 0.81 ± 0.21 for PP/PAMP; 1.58 ± 0.52 vs. 1.21 ± 0.41 for PP/PADP; all p < 0.001). The areas under the receiver-operating characteristic curves analysis showed that no cutoff value allowed discriminating between CTEPH and PAH by using echocardiographically or invasively derived pulsatility indices. Invasively derived pulmonary artery pulsatility indexes as well as echocardiographically determined PP/PAMP indexes are higher in CTEPH compared to PAH. However, due to the important overlap no optimal threshold values of these parameters can be given to allow satisfactory discrimination of the two diseases in clinical practice.

Echocardiography Can Identify Patients With Increased Pulmonary Vascular Resistance by Assessing Pressure Reflection in the Pulmonary Circulation

Background—

Pulmonary hypertension is a frequent finding in patients with cardiopulmonary disorders. It is important to recognize pulmonary hypertension due to increased pulmonary vascular resistance (PVR), as this affects treatment and prognosis. Patients with increased PVR have an increased pulmonary pressure reflection. We hypothesized that pressure reflection can be described by echocardiography and that variables related to pressure reflection can identify patients with increased PVR.

Methods and Results—

The study comprised 98 patients investigated within 24 hours of right heart catheterization and 20 control subjects. The pressure reflection variables were obtained by pulsed Doppler in the pulmonary artery and continuous Doppler of tricuspid regurgitation. We selected 3 variables related to pressure reflection: the interval from valve opening to peak velocity in the pulmonary artery (AcT, ms), the interval between pulmonary artery peak velocity and peak tricuspid velocity (tPV-PP, ms), and the right ventricular pressure increase after peak velocity in the pulmonary artery (augmented pressure, AP, mm Hg). The correlation between simultaneous catheter- and echocardiography-determined AP was strong (n=19, R =0.83). The AcT, tPV-PP, and AP in patients with a PVR of >3 Woods units (n=71) was (mean±SD) 77±16 ms, 119±36 ms, and 22±12 mm Hg, respectively, and differed from patients with a PVR of ≤3 Woods units (n=27, P <0.0001), 111±32 ms, 39±54 ms, and 3±4 mm Hg, and from controls, 153±32 ms, −19±45 ms, and 0 mm Hg, respectively ( P <0.0001). The AcT, tPV-PP, and AP values were not correlated with capillary wedge pressure ( R =0.08–0.16). The areas under the receiver operator characteristic curve (95%CI) for AcT, tPV-PP, and AP were 0.87 (0.82 to 0.95), 0.94 (0.89 to 0.99), and 0.98 (0.95 to 1.0), respectively.

Conclusions—

In this study, we describe a novel echocardiography method for assessing pressure reflection in the pulmonary circulation. This method can be used to identify patients with pulmonary hypertension due to increased PVR.

Quantitative assessment of pulmonary vascular resistance and reactivity in children with pulmonary hypertension due to congenital heart disease using a noninvasive method: new Doppler-derived indexes

We assessed the usefulness of transthoracic Doppler-derived indexes obtained in the proximal pulmonary artery (PA) branch for estimating pulmonary vascular resistance (PVR) in 45 children with congenital heart disease (CHD) and 23 normal control subjects. The acceleration time, inflection time (InT), deceleration index, and peak velocity, which were measured from the systolic PA flow velocity curve obtained at the sites of the main PA, and right and left PA, were compared with the PVR in patients with CHD. In addition, changes in either Doppler-derived indexes or PVR during 100% oxygen administration were compared in 22 patients showing a baseline PVR >or=4.6 U/m(2) (high PVR). The heart-rate-corrected InT (InTc) values obtained in the left PA in the high PVR group were significantly lower than those in the main PA (4.7 +/- 1.5 vs. 7.5 +/- 3.0; p < 0.001). The InTc obtained from the left PA separated patients with high and low PVR (4.7 +/- 1.4 vs. 9.9 +/- 2.4; p < 0.001) and no significant differences in InTc were found between the low PVR and the control groups. An increase in InTc to >6 during 100% oxygen administration for the high PVR group indicated good PA reactivity with a sensitivity of 93%, specificity of 100%, and agreement of 95% (kappa = 0.83). Moreover, this InTc index correlated inversely with PVR (r = -0.80). In conclusion, our method can noninvasively separate high and low PVR and assess the PA reactivity for high PVR in children with CHD.

Alterations of pressure waveforms along the coronary arteries and the effect of microcirculatory vasodilation

OBJECTIVES

We sought to investigate the differences of pressure waveforms at a distal point of an epicardial coronary artery comparatively to the ostium and to assess the effect of microcirculatory vasodilation on them.

BACKGROUND

Pressure waveforms in the systematic circulation and their alterations along the aorta due to wave reflections from the periphery have been extensively studied. However, similar data regarding intracoronary pressure waveforms and the effects of coronary microcirculation on them are limited.

METHODS

In 18 patients who underwent diagnostic coronary angiogram or percutaneous coronary intervention in the left circumflex or the right coronary artery, we studied pressure waveforms recorded by a high-fidelity pressure wire, which was advanced to the ostium and to a distal site of the free of significant lesions left anterior descending coronary artery. Pressure recording was performed both at rest and at hyperemia induced by intravenous infusion of adenosine. Analysis of pressure waveforms at the frequency domain was performed with Fast Fourier Transform.

RESULTS

At baseline conditions, distal pressure waveforms were characterized by higher pulsatility, higher presystolic wave and higher amplitude of the 11th to the 15th harmonics. Hyperemia increased the pulsatility, compressed the notch and decreased the amplitude of higher than the 10th harmonics of distal waveforms.

CONCLUSIONS

This study identifies differences of pressure waveforms between proximal and distal sites of free of significant lesions coronary arteries, which are affected by the status of coronary microcirculation and may therefore facilitate assessment of microvascular disease.

Echocardiography in Chronic Thromboembolic Pulmonary Hypertension

Chronic thromboembolic pulmonary hypertension (CTEPH) is a significant complication of venous thromboembolism and is caused by incomplete resolution of pulmonary emboli. The persistent chronic pulmonary hypertension leads to right-ventricle pressure overload. As a result, there is often significant functional and morphological alteration of both the right and the left ventricle. Transthoracic echocardiography, which allows for the estimation of pulmonary arterial pressures, not only plays an important role in the diagnosis of pulmonary hypertension but also provides insights in the pathophysiology of CTEPH. This article reviews the echocardiographic techniques and findings in CTEPH patients.

Quantification of right ventricular afterload in patients with and without pulmonary hypertension

Right ventricular (RV) afterload is commonly defined as pulmonary vascular resistance, but this does not reflect the afterload to pulsatile flow. The purpose of this study was to quantify RV afterload more completely in patients with and without pulmonary hypertension (PH) using a three-element windkessel model. The model consists of peripheral resistance (R), pulmonary arterial compliance (C), and characteristic impedance (Z). Using pulmonary artery pressure from right-heart catheterization and pulmonary artery flow from MRI velocity quantification, we estimated the windkessel parameters in patients with chronic thromboembolic PH (CTEPH; n = 10) and idiopathic pulmonary arterial hypertension (IPAH; n = 9). Patients suspected of PH but in whom PH was not found served as controls (NONPH; n = 10). R and Z were significantly lower and C significantly higher in the NONPH group than in both the CTEPH and IPAH groups (P < 0.001). R and Z were significantly lower in the CTEPH group than in the IPAH group (P < 0.05). The parameters R and C of all patients obeyed the relationship C = 0.75/R (R(2) = 0.77), equivalent to a similar RC time in all patients. Mean pulmonary artery pressure P and C fitted well to C = 69.7/P (i.e., similar pressure dependence in all patients). Our results show that differences in RV afterload among groups with different forms of PH can be quantified with a windkessel model. Furthermore, the data suggest that the RC time and the elastic properties of the large pulmonary arteries remain unchanged in PH.

Anaesthesia management for pulmonary endarterectomy

PURPOSE OF REVIEW

Options for the surgical treatment of chronic thromboembolic pulmonary hypertension are either lung transplantation or pulmonary endarterectomy. Pulmonary endarterectomy is considered permanently curative and the treatment of choice. The procedure dramatically improves functional status and provides an excellent immediate and long-term survival, much better than transplantation. Pulmonary endarterectomy, until recently performed in only a few highly specialized centres, is now spreading worldwide with good results. This review will focus on the understanding of the pathophysiology of the disease and on recent advances in assessment and treatment strategies.

RECENT FINDINGS

Recent data reinforce the thromboembolic nature of chronic thromboembolic pulmonary hypertension, and have shown that the disorder is more common than was thought and remains underdiagnosed. There has recently been a remarkable surge in the understanding of the mechanisms involved in the pathogenesis of pulmonary hypertension. Advances in diagnosis, surgical techniques, preoperative treatment, and perioperative management have improved the prognosis of this debilitating disease. New information about pretreatment and medical treatment with prostanoids and endothelin receptor antagonists is now available.

SUMMARY

Pulmonary endarterectomy can be successfully performed in selected centres using a multidisciplinary approach involving the specialities of surgery, pulmonary medicine, cardiology, radiology, anaesthesiology and critical care medicine. The largest risk factor remains the degree of operability related to a high pulmonary vascular resistance caused by permanent changes in the pulmonary vascular bed. Early operation is now recommended to prevent these irreversible changes. Further investigations are warranted to establish the role of new drugs in surgical patients with chronic thromboembolic pulmonary hypertension.

Echocardiography in pulmonary vascular disease

The assessment of pulmonary artery pressure, right ventricular function, right ventricular filling pressure, and tricuspid regurgitation provides invaluable information in the care of patients with pulmonary vascular disease. Echocardiography provides a rapid, noninvasive, portable, and accurate method to evaluate these parameters and also provides information on left ventricular and valvular function. Echocardiography has therefore become one of the most commonly performed diagnostic studies in patients with pulmonary vascular disease, and the technique's applications in this area are likely to grow. This article presents an overview of the current uses of echocardiography in pulmonary vascular disease and pulmonary hypertension.

Feasibility of Routine Pulmonary Arterial Impedance Measurements in Pulmonary Hypertension

OBJECTIVES

Right ventricular (RV) afterload is best described by a pulmonary arterial impedance (PVZ) spectrum, which integrates pulmonary vascular resistance (PVR), elastance, and wave reflection. We evaluated the feasibility of PVZ determinations in patients with pulmonary arterial hypertension (PAH) during routine right heart catheterization and Doppler echocardiography.

DESIGN

Prospective study.

SETTING

Academic hospital.

PATIENTS

Twenty-two patients with PAH.

INTERVENTIONS

Right heart catheterization with a fluid-filled Swan-Ganz catheter, Doppler echocardiography, and administration of inhaled nitric oxide (NO) [10 to 20 ppm; 17 patients], maximum tolerated dose of IV epoprostenol (average, 8.5 ng/kg/min; 5 patients), and IV dobutamine (8 micro g/kg/min; 8 patients).

MEASUREMENTS AND RESULTS

PVZ was calculated from the spectral analysis of synchronized pulmonary artery pressure (Ppa) and flow waves. The mean (+/- SE) Ppa was 63 +/- 3 mm Hg, and the mean PVR was 16 +/- 2 Wood units. The PVZ spectrum was markedly shifted to higher than normal pressures and frequencies, with a mean 0-Hz impedance (Z(0)) of 1,506 +/- 138 dyne. s. cm(-5), and a mean characteristic impedance (Zc) of 124 +/- 11 dyne. s. cm(-5), which are in keeping with data from previous studies. Inhaled NO levels decreased Ppa, PVR, Z(0), and Zc without a change in cardiac output. Epoprostenol administration did not affect Ppa, increased cardiac output, and decreased Z(0) and Zc. Dobutamine administration increased cardiac output and Ppa, and decreased PVR and Z(0), without changing Zc.

CONCLUSIONS

The determination of PVZ to quantify RV afterload is feasible during routine right heart catheterization and Doppler echocardiography. The measurement is sensitive to pharmacologic interventions.

First-pass scintigraphy with 99mTc macroaggregated albumin: a method for evaluating pulmonary arterial flow pulsatility

OBJECTIVES

The aim of this work was to develop and describe a non-invasive scintigraphic technique to detect flow pulsatility in peripheral pulmonary arteries.

METHODS

Ten normal volunteers were submitted to a first-pass scintigraphy using Tc macroaggregated albumin (Tc-MAA). A time-activity curve was generated for the right lung lateral third. Activity was shown to be restricted to the arterial compartment of the lungs, since there was no detectable progression of the radiopharmaceutical to the systemic circulation. Consequently, the rise in lung activity was attributed to the arterial inflow and the first derivative of the time-activity curve was assumed to represent pulmonary arterial flow.

RESULTS

Pulmonary flow curves showed two main positive peaks in six volunteers, followed by a third small peak in three others. Flow was predominant during systole, with an important reduction in magnitude before the diastolic peak, leading to a negative count variation in eight subjects. This pattern is comparable to that described in central pulmonary vessels by different methods.

CONCLUSIONS

First-pass scintigraphy with Tc-MAA was able to detect flow pulsatility in pulmonary arteries. These results need to be confirmed in a larger number of individuals, and, if shown to be reproducible, may increase our understanding of lung flow physiology, and of its modifications in the presence of cardiopulmonary diseases.

Reflection in the arterial system and the risk of coronary heart disease

BACKGROUND

Although it was reported that the augmentation index and inflection time are closely related to reflection in the arterial system and large artery function, it is not known whether these indices of the ascending aortic pressure waveform increase the risk of coronary heart disease (CHD). The purpose of this study was to evaluate whether the aortic reflection of the ascending aortic pressure waveform is related to an increased risk of CHD.

METHODS

We enrolled 190 men and women who had chest pain, normal contractions, no local asynergy, and no history of myocardial infarction. We measured the ascending aortic pressure using a fluid-filled system. The inflection time was defined as the time interval from initiation of a systolic pressure waveform to the inflection point. We investigated the association between the inflection time and augmentation index of the ascending aorta and the risk of CHD.

RESULTS

Both the inflection time and augmentation index were associated with an increased risk of CHD. The crude prevalence rates of CHD were 66.0% for the shortest quartile and 10.6% for the longest quartile of the inflection time, and 17.0% for the lowest quartile and 40.4% for the highest quartile of the augmentation index. The multiple-adjusted odds ratio of CHD was 30.8 (95% confidence interval [CI] 7.43-128.05) for the shortest quartile of the inflection time compared with the longest quartile and was 3.82 (95% CI 1.26-11.59) for the highest quartile of the augmentation index compared with the lowest quartile.

CONCLUSIONS

The augmentation index and inflection time were associated with an increased risk of CHD.