Physiology of the pulmonary circulation and the right heart

Review of Systemic Mock Circulation Loops for Evaluation of Implantable Cardiovascular Devices and Biological Tissues

CLINICAL IMPACT

On needs-based ex vivo monitoring of implantable devices or tissues/organs in cardiovascular simulators provides new insights and paves new paths for device prototypes. The insights gained could not only support the needs of patients, but also inform engineers, scientists and clinicians about undiscovered aspects of diseases (during routine monitoring). We analyze seminal and current work and highlight a variety of opportunities for developing preclinical tools that would improve strategies for future implantable devices. Holistically, mock circulation loop studies can bridge the gap between in vivo and in vitro approaches, as well as clinical and laboratory settings, in a mutually beneficial manner.

Assessment of Pulmonary Circulation of Critically Ill Patients Based on Critical Care Ultrasound

Pulmonary circulation is crucial in the human circulatory system, facilitating the oxygenation of blood as it moves from the right heart to the lungs and then to the left heart. However, during critical illness, pulmonary microcirculation can be vulnerable to both intrapulmonary and extrapulmonary injuries. To assess these potential injuries in critically ill patients, critical point-of-care ultrasound can be used to quantitatively and qualitatively evaluate the right atrium, right ventricle, pulmonary artery, lung, pulmonary vein, and left atrium along the direction of blood flow. This assessment is particularly valuable for common ICU diseases such as acute respiratory distress syndrome (ARDS), sepsis, pulmonary hypertension, and cardiogenic pulmonary edema. It has significant potential for diagnosing and treating these conditions in critical care medicine.

Left ventricular eccentricity index to assess precapillary pulmonary hypertension in dogs

INTRODUCTION

Interventricular septal flattening, frequently present in pulmonary hypertension (PH) can be quantified by the left ventricular eccentricity index (EI) measured at end-diastole (EId), end-systole (EIs) and at maximal septal flattening (EIm). In humans, EI correlates with invasive pulmonary arterial pressure. The aim of this study was to evaluate if EI correlates with parameters of right heart remodeling (RHR) and if EI is a quantitative marker of PH in dogs.

MATERIALS AND METHODS

Left ventricular eccentricity indices were retrospectively measured in four groups (no, mild, moderate and severe PH) with interpretable tricuspid and/or pulmonary regurgitation.

RESULTS

Ninety-seven dogs were included, with no (n = 29), mild (n = 13), moderate (n = 25) and severe (n = 30) PH. The intra- and inter-observer variability for EI measurements ranged from 2 % to 11 %. All EI were significantly elevated in severe compared to no, mild and moderate PH (P < 0.0005). In the moderate group, EIs and EIm were higher compared to the no PH group (P < 0.01). Tricuspid and pulmonary regurgitation pressure gradients and RHR parameters correlated with EId, EIs and EIm in all groups. Optimal cut-off values discriminating moderate and severe PH from no and mild PH were 1.24 (Sensitivity (Se) 60 %; Specificity (Sp) 90 %) for EId, 1.34 (Se 67 %; Sp 95 %) for EIs and 1.37 (Se 76 %; Sp 83 %) for EIm.

CONCLUSIONS

Left ventricular eccentricity indices are reproducible echocardiographic variables increasing with severity of PH. Dogs with moderate and severe PH can be discriminated from dogs with no or mild PH using EIs and EIm.

The Pulmonary Vasculature

The pulmonary circulation is a low-pressure, low-resistance circuit whose primary function is to deliver deoxygenated blood to, and oxygenated blood from, the pulmonary capillary bed enabling gas exchange. The distribution of pulmonary blood flow is regulated by several factors including effects of vascular branching structure, large-scale forces related to gravity, and finer scale factors related to local control. Hypoxic pulmonary vasoconstriction is one such important regulatory mechanism. In the face of local hypoxia, vascular smooth muscle constriction of precapillary arterioles increases local resistance by up to 250%. This has the effect of diverting blood toward better oxygenated regions of the lung and optimizing ventilation-perfusion matching. However, in the face of global hypoxia, the net effect is an increase in pulmonary arterial pressure and vascular resistance. Pulmonary vascular resistance describes the flow-resistive properties of the pulmonary circulation and arises from both precapillary and postcapillary resistances. The pulmonary circulation is also distensible in response to an increase in transmural pressure and this distention, in addition to recruitment, moderates pulmonary arterial pressure and vascular resistance. This article reviews the physiology of the pulmonary vasculature and briefly discusses how this physiology is altered by common circumstances.

Pulmonary Hypertension in Left Heart Diseases: Pathophysiology, Hemodynamic Assessment and Therapeutic Management

Pulmonary hypertension (PH) associated with left heart diseases (PH-LHD), also termed group 2 PH, represents the most common form of PH. It develops through the passive backward transmission of elevated left heart pressures in the setting of heart failure, either with preserved (HFpEF) or reduced (HFrEF) ejection fraction, which increases the pulsatile afterload of the right ventricle (RV) by reducing pulmonary artery (PA) compliance. In a subset of patients, progressive remodeling of the pulmonary circulation resulted in a pre-capillary phenotype of PH, with elevated pulmonary vascular resistance (PVR) further increasing the RV afterload, eventually leading to RV-PA uncoupling and RV failure. The primary therapeutic objective in PH-LHD is to reduce left-sided pressures through the appropriate use of diuretics and guideline-directed medical therapies for heart failure. When pulmonary vascular remodeling is established, targeted therapies aiming to reduce PVR are theoretically appealing. So far, such targeted therapies have mostly failed to show significant positive effects in patients with PH-LHD, in contrast to their proven efficacy in other forms of pre-capillary PH. Whether such therapies may benefit some specific subgroups of patients (HFrEF, HFpEF) with specific hemodynamic phenotypes (post- or pre-capillary PH) and various degrees of RV dysfunction still needs to be addressed.

Endothelial glycocalyx in hepatopulmonary syndrome: An indispensable player mediating vascular changes

Hepatopulmonary syndrome (HPS) is a serious pulmonary vascular complication that causes respiratory insufficiency in patients with chronic liver diseases. HPS is characterized by two central pathogenic features-intrapulmonary vascular dilatation (IPVD) and angiogenesis. Endothelial glycocalyx (eGCX) is a gel-like layer covering the luminal surface of blood vessels which is involved in a variety of physiological and pathophysiological processes including controlling vascular tone and angiogenesis. In terms of lung disorders, it has been well established that eGCX contributes to dysregulated vascular contraction and impaired blood-gas barrier and fluid clearance, and thus might underlie the pathogenesis of HPS. Additionally, pharmacological interventions targeting eGCX are dramatically on the rise. In this review, we aim to elucidate the potential role of eGCX in IPVD and angiogenesis and describe the possible degradation-reconstitution equilibrium of eGCX during HPS through a highlight of recent literature. These studies strongly underscore the therapeutic rationale in targeting eGCX for the treatment of HPS.

Exercise metabolomics in pulmonary arterial hypertension: Where pulmonary vascular metabolism meets exercise physiology

Pulmonary arterial hypertension is an incurable disease marked by dysregulated metabolism, both at the cellular level in the pulmonary vasculature, and at the whole-body level characterized by impaired exercise oxygen consumption. Though both altered pulmonary vascular metabolism and abnormal exercise physiology are key markers of disease severity and pulmonary arterial remodeling, their precise interactions are relatively unknown. Herein we review normal pulmonary vascular physiology and the current understanding of pulmonary vascular cell metabolism and cardiopulmonary response to exercise in Pulmonary arterial hypertension. We additionally introduce a newly developed international collaborative effort aimed at quantifying exercise-induced changes in pulmonary vascular metabolism, which will inform about underlying pathophysiology and clinical management. We support our investigative approach by presenting preliminary data and discuss potential future applications of our research platform.

The Right Ventricle in COVID-19

Infection with the novel severe acute respiratory coronavirus-2 (SARS-CoV2) results in COVID-19, a disease primarily affecting the respiratory system to provoke a spectrum of clinical manifestations, the most severe being acute respiratory distress syndrome (ARDS). A significant proportion of COVID-19 patients also develop various cardiac complications, among which dysfunction of the right ventricle (RV) appears particularly common, especially in severe forms of the disease, and which is associated with a dismal prognosis. Echocardiographic studies indeed reveal right ventricular dysfunction in up to 40% of patients, a proportion even greater when the RV is explored with strain imaging echocardiography. The pathophysiological mechanisms of RV dysfunction in COVID-19 include processes increasing the pulmonary vascular hydraulic load and others reducing RV contractility, which precipitate the acute uncoupling of the RV with the pulmonary circulation. Understanding these mechanisms provides the fundamental basis for the adequate therapeutic management of RV dysfunction, which incorporates protective mechanical ventilation, the prevention and treatment of pulmonary vasoconstriction and thrombotic complications, as well as the appropriate management of RV preload and contractility. This comprehensive review provides a detailed update of the evidence of RV dysfunction in COVID-19, its pathophysiological mechanisms, and its therapy.

The isobaric pulmonary arterial compliance in pulmonary hypertension

Pulmonary hypertension is associated with stiffening of pulmonary arteries which increases right ventricular pulsatile loading. High pulmonary artery wedge pressure (PAWP) in postcapillary pulmonary hypertension (Pc-PH) further decreases pulmonary arterial compliance (PAC) at a given pulmonary vascular resistance (PVR) compared with precapillary pulmonary hypertension, thus responsible for a higher total arterial load. In all other vascular beds, arterial compliance is considered as mainly determined by the distending pressure, due to non-linear stress-strain behaviour of arteries. We tested the applicability, advantages and drawbacks of two comparison methods of PAC depending on the level of mean pulmonary arterial pressure (mPAP; isobaric PAC) or PVR.

Right heart catheterisation data including PAC (stroke volume/pulse pressure) were obtained in 112 Pc-PH (of whom 61 had combined postcapillary and precapillary pulmonary hypertension) and 719 idiopathic pulmonary arterial hypertension (iPAH).

PAC could be compared over the same mPAP range (25–66 mmHg) in 792 (95.3%) out of 831 patients and over the same PVR range (3–10.7 WU) in only 520 (62.6%) out of 831 patients. The main assumption underlying comparisons at a given PVR was not verified as the PVR×PAC product (RC-time) was not constant but on the contrary more variable than mPAP. In the 788/831 (94.8%) patients studied over the same PAC range (0.62–6.5 mL·mmHg⁻¹), PVR and thus total arterial load tended to be higher in iPAH.

Our study favours comparing PAC at fixed mPAP level (isobaric PAC) rather than at fixed PVR. A reappraisal of the effects of PAWP on the pulsatile and total arterial load put on the right heart is needed, and this point deserves further studies.

In postcapillary and precapillary pulmonary hypertension patients, this study favours comparing pulmonary arterial compliance (PAC) at fixed mean pulmonary artery pressure level (isobaric PAC) rather than at fixed pulmonary vascular resistance levelhttps://bit.ly/3aTLYdS

Pulmonary vascular dysfunction among people aged over 65 years in the community in the Atherosclerosis Risk In Communities (ARIC) Study: A cross-sectional analysis

BACKGROUND

Heart failure (HF) risk is highest in late life, and impaired pulmonary vascular function is a risk factor for HF development. However, data regarding the contributors to and prognostic importance of pulmonary vascular dysfunction among HF-free elders in the community are limited and largely restricted to pulmonary hypertension. Our objective was to define the prevalence and correlates of abnormal pulmonary pressure, resistance, and compliance and their association with incident HF and HF phenotype (left ventricular [LV] ejection fraction [LVEF] ≥ or < 50%) independent of LV structure and function.

METHODS AND FINDINGS

We performed cross-sectional and time-to-event analyses in a prospective epidemiologic cohort study, the Atherosclerosis Risk in Communities study. This is an ongoing, observational study that recruited 15,792 persons aged 45-64 years between 1987 and 1989 (visit 1) from four representative communities in the United States: Minneapolis, Minnesota; Jackson, Mississippi; Hagerstown, Maryland; and Forsyth County, North Carolina. The current analysis included 2,810 individuals aged 66-90 years, free of HF, who underwent echocardiography at the fifth study visit (June 8, 2011, to August 28, 2013) and had measurable tricuspid regurgitation by spectral Doppler. Echocardiography-derived pulmonary artery systolic pressure (PASP), pulmonary vascular resistance (PVR), and pulmonary arterial compliance (PAC) were measured. The main outcome was incident HF after visit 5, and key secondary end points were incident HF with preserved LVEF (HFpEF) and incident HF with reduced LVEF (HFrEF). The mean ± SD age was 76 ± 5 years, 66% were female, and 21% were black. Mean values of PASP, PVR, and PAC were 28 ± 5 mm Hg, 1.7 ± 0.4 Wood unit, and 3.4 ± 1.0 mL/mm Hg, respectively, and were abnormal in 18%, 12%, and 14%, respectively, using limits defined from the 10th and 90th percentile limits in 253 low-risk participants free of cardiovascular disease or risk factors. Left heart dysfunction was associated with abnormal PASP and PAC, whereas a restrictive ventilatory deficit was associated with abnormalities of PASP, PVR, and PAC. PASP, PVR, and PAC were each predictive of incident HF or death (hazard ratio per SD 1.3 [95% CI 1.1-1.4], p < 0.001; 1.1 [1.0-1.2], p = 0.04; 1.2 [1.1-1.4], p = 0.001, respectively) independent of LV measures. Elevated pulmonary pressure was predictive of incident HFpEF (HFpEF: 2.4 [1.4-4.0, p = 0.001]) but not HFrEF (1.4 [0.8-2.5, p = 0.31]). Abnormal PAC predicted HFrEF (HFpEF: 2.0 [1.0-4.0, p = 0.05], HFrEF: 2.8 [1.4-5.5, p = 0.003]), whereas abnormal PVR was not predictive of either (HFpEF: 0.9 [0.4-2.0, p = 0.85], HFrEF: 0.7 [0.3-1.4, p = 0.30],). A greater number of abnormal pulmonary vascular measures was associated with greater risk of incident HF. Major limitations include the use of echo Doppler to estimate pulmonary hemodynamic measures, which may lead to misclassification; inclusions bias related to detectable tricuspid regurgitation, which may limit generalizability of our findings; and survivor bias related to the cohort age, which may result in underestimation of the described associations.

CONCLUSIONS

In this study, we observed abnormalities of PASP, PVR, and PAC in 12%-18% of elders in the community. Higher PASP and lower PAC were independently predictive of incident HF. Abnormally high PASP predicted incident HFpEF but not HFrEF. These findings suggest that impairments in pulmonary vascular function may precede clinical HF and that a comprehensive pulmonary hemodynamic evaluation may identify pulmonary vascular phenotypes that differentially predict HF phenotypes.

Development and Validation of a Life-Sized Mock Circulatory Loop of the Human Circulation for Fluid-Mechanical Studies

Mock circulatory loops (MCLs) are usually developed for assessment of ventricular assist devices and consist of abstracted anatomical structures represented by connecting tubing pipes and controllable actuators which could mimic oscillating flow processes. However, with increasing use of short-term peripheral mechanical support (extracorporeal life support [ECLS]) and the upcoming evidence of even counteracting flow processes between the failing native circulation and ECLS, MCLs incorporating the peripheral vascular system and preserved anatomical structures are becoming more important for systematic assessment of these processes. For reproducible and standardized fluid-mechanical studies using magnetic resonance imaging, Doppler ultrasound, and computational fluid dynamics measurements, we developed a MCL of the human circulation. Silicon-based life-sized dummies of the human aorta and vena cava (vascular module) were driven by paracorporeal pneumatic assist devices. The vascular module is placed in a housing with all arterial branches merging into peripheral resistance and compliances modules, and blood-mimicking fluid returns to the heart module through the venous dummy. Compliance and resistance chambers provide for an adequate simulation of the capillary system. Extracorporeal life support cannulation can be performed in the femoral and subclavian arteries and in the femoral and jugular veins. After adjusting vessel diameters using variable Hoffmann clamps, physiologic flow rates were achieved in the supraaortic branches, the renal and mesenteric arteries, and the limb arteries with physiologic blood pressure and cardiac output (4 L/min). This MCL provides a virtually physiologic platform beyond conventional abstracted MCLs for simulation of flow interactions between the human circulation and external circulation generated by ECLS.

Susceptibility to high-altitude pulmonary edema is associated with increased pulmonary arterial stiffness during exercise

High-altitude pulmonary edema (HAPE), a reversible form of capillary leak, is a common consequence of rapid ascension to high altitude and a major cause of death related to high-altitude exposure. Individuals with a prior history of HAPE are more susceptible to future episodes, but the underlying risk factors remain uncertain. Previous studies have shown that HAPE-susceptible subjects have an exaggerated pulmonary vasoreactivity to acute hypoxia, but incomplete data are available regarding their vascular response to exercise. To examine this, seven HAPE-susceptible subjects and nine control subjects (HAPE-resistant) were studied at rest and during incremental exercise at sea level and at 3,810 m altitude. Studies were conducted in both normoxic (inspired Po₂ = 148 Torr) and hypoxic (inspired Po₂ = 91 Torr) conditions at each location. Here, we report an expanded analysis of previously published data, including a distensible vessel model that showed that HAPE-susceptible subjects had significantly reduced small distal artery distensibility at sea level compared with HAPE-resistant control subjects [0.011 ± 0.001 vs. 0.021 ± 0.002 mmHg^-1; P < 0.001). Moreover, HAPE-susceptible subjects demonstrated constant distensibility over all conditions, suggesting that distal arteries are maximally distended at rest. Consistent with having increased distal artery stiffness, HAPE-susceptible subjects had greater increases in pulmonary artery pulse pressure with exercise, which suggests increased proximal artery stiffness. In summary, HAPE-susceptible subjects have exercise-induced increases in proximal artery stiffness and baseline increases in distal artery stiffness, suggesting increased pulsatile load on the right ventricle.NEW & NOTEWORTHY In comparison to subjects who appear resistant to high-altitude pulmonary edema, those previously symptomatic show greater increases in large and small artery stiffness in response to exercise. These differences in arterial stiffness may be a risk factor for the development of high-altitude pulmonary edema or evidence that consequences of high-altitude pulmonary edema are long-lasting after return to sea level.

The prognostic value of pulmonary artery compliance in cardiogenic shock

The aim of this study was to evaluate the pathophysiological role and the prognostic significance of pulmonary artery compliance (C_PA), a measure of right ventricular pulsatile afterload, in cardiogenic shock. We retrospectively included 91 consecutive patients with cardiogenic shock due to primary left ventricular failure, monitored with a pulmonary artery catheter within the first 24 h. C_PA was calculated as the ratio of stroke volume to pulmonary artery pulse pressure, and we determined whether C_PA predicted mortality and whether it performed better than other pulmonary hemodynamic variables. The overall in-hospital mortality in our cohort was 27%. Survivors and nonsurvivors had comparable left ventricular ejection fraction, systolic, diastolic and mean pulmonary artery pressure, transpulmonary gradient, diastolic pressure gradient, and pulmonary vascular resistance at 24 h. In contrast, C_PA was the only pulmonary artery variable significantly associated with mortality in univariate and multivariate analyses. Mortality increased from 4.5% at the highest quartile of C_PA (3.6–6.5 mL/mmHg) to 43.5% at the lowest quartile (0.7–1.7 mL/mmHg). In 64 patients with a PAC inserted immediately upon admission, we calculated the trend of C_PA between admission and 24 h. This trend was positive in survivors (+0.8 ± 1.3 ml/mmHg) but negative in nonsurvivors (−0.1 ± 1.0 mL/mmHg). The lower C_PA in nonsurvivors was associated with more severe right ventricular systolic dysfunction. In conclusion, a reduced compliance of the pulmonary artery promotes right ventricular dysfunction and is independently associated with mortality in cardiogenic shock. Future studies should evaluate the impact on pulmonary arterial compliance and right ventricular afterload of therapies used in cardiogenic shock.

The Role of Echocardiography in Neonates and Pediatric Patients on Extracorporeal Membrane Oxygenation

Indications for extracorporeal membrane oxygenation (ECMO) and extracorporeal cardiopulmonary resuscitation (ECPR) are expanding, and echocardiography is a tool of utmost importance to assess safety, effectiveness and readiness for circuit initiation and separation. Echocardiography is key to anticipating complications and improving outcomes. Understanding the patient's as well as the ECMO circuit's anatomy and physiology is crucial prior to any ECMO echocardiographic evaluation. It is also vital to acknowledge that the utility of echocardiography in ECMO patients is not limited to the evaluation of cardiac function, and that clinical decisions should not be made exclusively upon echocardiographic findings. Though echocardiography has specific indications and applications, it also has limitations, characterized as: prior to and during cannulation, throughout the ECMO run, upon separation and after separation from the circuit. The use of specific and consistent echocardiographic protocols for patients on ECMO is recommended.

Attenuation of human hypoxic pulmonary vasoconstriction by acetazolamide and methazolamide

RATIONALE

Acetazolamide, a carbonic anhydrase inhibitor used for preventing altitude illness attenuates hypoxic pulmonary vasoconstriction (HPV) while improving oxygenation. Methazolamide, an analog of acetazolamide, is more lipophilic, has a longer half-life, and activates a major antioxidant transcription factor. However, its influence on the hypoxic pulmonary response in humans is unknown.

OBJECTIVE

To determine if a clinically relevant dosing of methazolamide improves oxygenation, attenuates HPV and augments plasma antioxidant capacity in men exposed to hypoxia when compared to an established dosing of acetazolamide known to suppress HPV.

METHODS

In this double-blind, placebo-controlled, cross-over trial, eleven participants were randomized to treatments with methazolamide (100mg b.i.d.) and acetazolamide (250mg t.i.d.) for two days prior to 60 minutes of hypoxia (F_IO₂≈0.12).

MEASUREMENTS

Pulmonary artery systolic pressure (PASP), alveolar ventilation (V̇_A), blood gases and markers of redox status were measured. Pulmonary vascular sensitivity to hypoxia was determined by indexing PASP to alveolar PO₂.

RESULTS

Acetazolamide caused greater metabolic acidosis compared with methazolamide, but the augmented V̇_A and improved oxygenation with hypoxia were similar. The rise in PASP with hypoxia was lower with methazolamide (9.0 ± 0.9 mmHg) and acetazolamide (8.0 ± 0.7 mmHg) compared with placebo (14.1 ± 1.3 mmHg; P < 0.05). The pulmonary vascular sensitivity to hypoxia (ΔPASP/ΔP_AO₂) was reduced equally by both drugs. Only acetazolamide improved the non-enzymatic plasma antioxidant capacity.

CONCLUSIONS

Although acetazolamide only had plasma antioxidant properties, methazolamide led to similar improvements in oxygenation and reduction in HPV at a dose causing less metabolic acidosis than acetazolamide in humans.

Safety of right heart catheterization for pulmonary hypertension in very elderly patients

Right heart catheterization (RHC) is the reference test in diagnosing pulmonary hypertension (PH). The increasing age of patients at the time of diagnosis raises the issue of the morbidity of this invasive test in elderly individuals. We hypothesized that the morbidity associated with RHC would be increased in elderly patients and highlight differences in hemodynamic characteristics compared to younger patients. A retrospective study was conducted in a regional referral center for PH. Data for all consecutive RHCs performed during the study period were analyzed. Over a five-year period, 1060 RHCs were performed. Of the patients, 228 (21.5%) were aged ≥75 years and 832 (78.5%) were aged <75 years. Duration of the procedure and site of puncture did not differ according to age group (all P > 0.05). Nine procedures (0.9%) led to complications: three (1.3%) in patients aged >75 years and six (0.7%) in younger patients aged (P = 0.5). Eight were local vascular injuries, directly related to a femoral vein puncture (P < 0.001). Pulmonary arterial pressure and cardiac output were lower in patients aged >75 years than in younger patients (P = 0.001). RHC may be performed regardless of patient age. The rate of RHC complications is not increased in individuals aged >75 years. As most complications were related to femoral vein puncture, this route should be avoided whenever possible.

[Pathophysiology of right ventricular hemodynamics]

The right ventricle (RV) plays a key role in the maintenance of an adequate cardiac output whatever the demand, and thus contributes to the optimization of the ventilation/perfusion ratio. The RV has a thin wall and it buffers the physiological increases in systemic venous return without causing a deleterious rise in right atrial pressure (RAP). The RV is coupled to the pulmonary circulation which is a low pressure, low resistance, high compliance system. In the healthy subject at rest, the contribution of the RV to right heart systolic function is surpassed by the contribution of both left ventricular contraction and the respiratory pump. RV systolic function plays a contributory role during exercise and in patients with pulmonary hypertension. The RV compensates better for volume overload than for pressure overload and is more capable of sustaining chronic increases in load than acute ones. An impaired RV-pulmonary artery coupling leads to a major mismatch between RV function and arterial load ("afterload mismatch") and is associated progressively with a low cardiac output and a high RAP. Right ventricular dysfunction is involved in the pathophysiology of both cardiovascular and pulmonary diseases, and may partly explain the deleterious haemodynamic consequences of mechanical ventilation.

The prognostic value of the relationship between right atrial and pulmonary capillary wedge pressure in diverse cardiovascular conditions

BACKGROUND

Physical examination of jugular venous pressure is used to estimate right atrial (RA) pressure and infer left-sided filling pressure to assist volume management. Previous studies in advanced heart failure patients showed about 75% concordance between RA and pulmonary capillary wedge (PCW) pressures. We sought to determine the relationship between mean RA and mean PCW pressure and assess the clinical significance in a broad population of patients undergoing invasive right heart catheterization (RHC).

METHODS

We examined 4135 RHC cases at a single academic medical center from February 2007 to December 2014, analyzing baseline variables, hemodynamic data, and in-hospital mortality.

RESULTS

The overall Pearson correlation for mean RA and PCW pressures was 0.68 with 70% concordance between dichotomized pressures (RA ≥10 and PCW ≥22 mmHg). Results were similar in subgroups with heart failure (r=0.67, 72%), STEMI/NSTEMI (r=0.60, 69%), unstable angina (r=0.78, 69%), stable/no angina (r=0.72, 67%), and valvular disease (r=0.61, 72%; Chi-square P=.15). Mean RA pressure was independently associated with in-hospital mortality in multivariate analysis (OR 1.12 [95% CI 1.081-1.157] per 1 mmHg increase, P<.001). The RA/PCW ratio was not independently associated with in-hospital mortality. Mean RA pressure was also weakly associated with worse renal function (rho=-0.16, P<.001).

CONCLUSION

In patients undergoing right catheterization for diverse indications, the mean RA and PCW pressures correlated moderately well, but there was discordance in a sizable minority, in whom assessment of left-sided filling pressures using estimated jugular venous pressure may be misleading. Elevated right atrial pressure is a marker for in-hospital mortality.

Clinical characteristics and survival of systemic sclerosis patients with pulmonary hypertension and elevated wedge pressure: Observations from the PHAROS cohort

BACKGROUND AND OBJECTIVE

Systemic sclerosis (SSc) is a complex autoimmune disease commonly associated with pulmonary hypertension (PH). When associated with elevated pulmonary artery wedge pressure (PAWP), pulmonary artery pressure (PAP) is either in-proportion (post-capillary PH) or higher than expected (combined PH) relative to the increased PAWP.

METHODS

Patients from the PHAROS registry (a prospective observational cohort of SSc-PH patients) who had mean PAP ≥ 25 and PAWP > 15 on right heart catheterization were stratified based on diastolic pressure gradient (DPG). Kaplan-Meier analysis was performed to compare survival and PH-related hospitalization. Baseline factors were compared between patients dying and those who survived using Cox regression analysis.

RESULTS

A total of 59 patients were included, of whom 21 (36%) patients were classified as combined PH and 38 (64%) had post-capillary PH. No baseline characteristics were significantly different between the two groups. There were no differences in survival or PH-related hospitalization between the groups. The only baseline factor independently associated with death was lower 6-min walk distance (6MWD) (hazard ratio (HR): 1.33 per 25 m decrease, 95% CI: 1.11-1.59, P = 0.002). PH-specific medications were started during follow-up in significantly more patients in the combined PH group compared with the post-capillary group (86% vs 50%, P = 0.01).

CONCLUSION

Outcomes were similar between SSc patients with post-capillary PH and combined pre- and post-capillary PH. 6MWD at baseline can predict risk for death in SSc patients with PH and an elevated PAWP. More patients with combined PH were started on PH-specific medications, and the clinical benefit of treating this subgroup specifically in SSc patients needs further exploration.

Pulmonary hypertension due to left heart disease

Pulmonary hypertension due to left heart disease, also known as group 2 pulmonary hypertension according to the European Society of Cardiology/European Respiratory Society classification, is the most common cause of pulmonary hypertension. In patients with left heart disease, the development of pulmonary hypertension favours right heart dysfunction, which has a major impact on disease severity and outcome. Over the past few years, this condition has been considered more frequently. However, epidemiological studies of group 2 pulmonary hypertension are less exhaustive than studies of other causes of pulmonary hypertension. In group 2 patients, pulmonary hypertension may be caused by an isolated increase in left-sided filling pressures or by a combination of this condition with increased pulmonary vascular resistance, with an abnormally high pressure gradient between arteries and pulmonary veins. A better understanding of the conditions underlying pulmonary hypertension is of key importance to establish a comprehensive diagnosis, leading to an adapted treatment to reduce heart failure morbidity and mortality. In this review, epidemiology, mechanisms and diagnostic approaches are reviewed; then, treatment options and future approaches are considered.

Review: Hemodynamic Characteristics and Outcomes of Sickle Cell Disease Associated Pulmonary Hypertension

Pulmonary hypertension (PH) is a leading cause of morbidity and early mortality in adults with sickle cell disease (SCD). However, the prevalence, hemodynamic profile and prognosis of SCD-PH remain controversial and need frequent updates. Pulmonary hypertension determined by right heart catheterization (RHC) occurs in 6% to 10% of adults with SCD. Hemodynamically, SCD-PH may be pre-capillary or post-capillary in nature. The exact etiology is unknown and often multifactorial; hence a thorough diagnostic evaluation following established PH guidelines is essential to determine disease prevalence, etiology and outcomes. Data on the efficacy and safety of pulmonary arterial hypertension (PAH) therapy are limited in SCD; clinical trials in these patients are urgently needed. This review provides an overview of RHC-determined hemodynamic characteristics, current management modality and outcomes; we also highlight recent advances and unmet research needs in SCD-PH.

Hemodynamic evidence of vascular remodeling in combined post- and precapillary pulmonary hypertension

Although commonly encountered, patients with combined postcapillary and precapillary pulmonary hypertension (Cpc-PH) have poorly understood pulmonary vascular properties. The product of pulmonary vascular resistance and compliance, resistance-compliance (RC) time, is a measure of pulmonary vascular physiology. While RC time is lower in postcapillary PH than in precapillary PH, the RC time in Cpc-PH and the effect of pulmonary wedge pressure (PWP) on RC time are unknown. We tested the hypothesis that Cpc-PH has an RC time that resembles that in pulmonary arterial hypertension (PAH) more than that in isolated postcapillary PH (Ipc-PH). We analyzed the hemodynamics of 282 consecutive patients with PH referred for right heart catheterization (RHC) with a fluid challenge from 2004 to 2013 (cohort A) and 4,382 patients who underwent RHC between 1998 and 2014 for validation (cohort B). Baseline RC time in Cpc-PH was higher than that in Ipc-PH and lower than that in PAH in both cohorts (P < 0.001). In cohort A, RC time decreased after fluid challenge in patients with Ipc-PH but not in those with PAH or Cpc-PH (P < 0.001). In cohort B, the inverse relationship of pulmonary vascular compliance and resistance, as well as that of RC time and PWP, in Cpc-PH was similar to that in PAH and distinct from that in Ipc-PH. Our findings demonstrate that patients with Cpc-PH have pulmonary vascular physiology that resembles that of patients with PAH more than that of Ipc-PH patients. Further study is warranted to identify determinants of vascular remodeling and assess therapeutic response in this subset of PH.

sGC-cGMP-PKG pathway stimulation protects the healthy but not the failing right ventricle of rats against ischemia and reperfusion injury

BACKGROUND

To investigate whether modulation of the sGC-cGMP-PKG pathway protects against ischemia and reperfusion injury in the healthy and the failing right ventricle (RV).

METHODS

Hearts from male Wistar rats with a healthy RV (n=39) or a hypertrophic and failing RV induced by pulmonary trunk banding (n=57) were isolated and perfused in a pressure-controlled modified Langendorff setup. The isolated hearts were randomized to control, ischemic preconditioning (IPC, 2×5min of global ischemia), a phosphodiesterase-5 (PDE5) inhibitor vardenafil (66nM) alone and in combination with a cGMP-dependent protein kinase (PKG) blocker KT 5823 (1μM). Failing hearts were exposed to the same protocols and to soluble guanylate cyclase stimulation/activation, and phosphodiesterase 9 inhibition. All interventions were followed by 40min of global ischemia and 120min of reperfusion. The effects on the RV were evaluated by measurement of the infarct size/area-at-risk ratio (IS/AAR).

RESULTS

In healthy hearts, IPC and pharmacological preconditioning with vardenafil reduced RV infarct size. PKG blockade by KT-5823 did not alter infarct size per se but abolished the cardioprotective effect of vardenafil. In the hypertrophic and failing hearts, none of the conditioning strategies altered RV infarct size.

CONCLUSION

PDE-5 inhibition by vardenafil protects the healthy right ventricle against ischemia and reperfusion injury by a PKG dependent mechanism. Neither ischemic preconditioning nor pharmacologic stimulation of the sGC-cGMP-PKG pathway induces cardioprotection in the hypertrophic and failing RV.

Determinants of 6-minute walk distance in patients with idiopathic pulmonary fibrosis undergoing lung transplant evaluation

Little is known about the physiologic determinants of 6-minute walk distance in idiopathic pulmonary fibrosis. We investigated the demographic, pulmonary function, echocardiographic, and hemodynamic determinants of 6-minute walk distance in patients with idiopathic pulmonary fibrosis evaluated for lung transplantation. We performed a cross-sectional analysis of 130 patients with idiopathic pulmonary fibrosis who completed a lung transplantation evaluation at the Hospital of the University of Pennsylvania between 2005 and 2010. Multivariable linear regression analysis was used to generate an explanatory model for 6-minute walk distance. After adjustment for age, sex, race, height, and weight, the presence of right ventricular dilation was associated with a decrease of 50.9 m (95% confidence interval [CI], 8.4-93.3) in 6-minute walk distance ([Formula: see text]). For each 200-mL reduction in forced vital capacity, the walk distance decreased by 15.0 m (95% CI, 9.0-21.1; [Formula: see text]). For every increase of 1 Wood unit in pulmonary vascular resistance, the walk distance decreased by 17.3 m (95% CI, 5.1-29.5; [Formula: see text]). Six-minute walk distance in idiopathic pulmonary fibrosis depends in part on circulatory impairment and the degree of restrictive lung disease. Future trials that target right ventricular morphology, pulmonary vascular resistance, and forced vital capacity may potentially improve exercise capacity in patients with idiopathic pulmonary fibrosis.

Management of pulmonary hypertension and right heart failure in the intensive care unit

Management of acute right ventricular failure, both with and without coexisting pulmonary hypertension, is a common challenge encountered in the intensive care setting. Both right ventricular dysfunction and pulmonary hypertension portend a poor prognosis, regardless of the underlying cause and are associated with significant morbidity and mortality. The right ventricle is embryologically distinct from the left ventricle and has unique morphologic and functional properties. Management of right ventricular failure and pulmonary hypertension in the intensive care setting requires tailored hemodynamic management, pharmacotherapy, and often mechanical circulatory support. Unfortunately, our understanding of the management of right ventricular failure lags behind that of the left ventricle. In this review, we will explore the underlying pathophysiology of the failing right ventricle and pulmonary vasculature in patients with and without pulmonary hypertension and discuss management strategies based on evidence-based studies as well as our current understanding of the underlying physiology.

Chronic Pulmonary Complications of Sickle Cell Disease

Sickle cell disease (SCD), the most common genetic hemolytic anemia worldwide, affects 250,000 births annually. In the United States, SCD affects approximately 100,000 individuals, most of African descent. Hemoglobin S (HbS) results from a glutamate-to-valine mutation of the sixth codon of the β-hemoglobin allele; the homozygous genotype (HbSS) is associated with the most prevalent and severe form of the disease. Other SCD genotypes include HbSC, composed of one HbS allele and one HbC (glutamate-to-lysine mutation) allele; and HbS-β-thalassemia(0) or HbS-β-thalassemia(+), composed of one HbS allele and one β-thalassemia allele with absent or reduced β-chain production, respectively. Despite advances in care, median survival remains in the fifth decade, due in large part to chronic complications of the disease. Chronic pulmonary complications in SCD are major contributors to this early mortality. Although our understanding of these conditions has improved much over the past 10 to 15 years, there remains no specific treatment for pulmonary complications of SCD. It is unclear whether conventional treatment regimens directed at non-SCD populations have equivalent efficacy in patients with SCD. This represents a critical research need. In this review, the authors review the state-of-the-art understanding of the following pulmonary complications of SCD: (1) pulmonary hypertension; (2) venous thromboembolic disease; (3) sleep-disordered breathing; (4) asthma and recurrent wheezing; and (5) pulmonary function abnormalities. This review highlights the advances as well as the knowledge gaps in this field to update clinicians and other health care providers and to garner research interest from the medical community.

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 pathophysiology of pulmonary hypertension in left heart disease

Pulmonary hypertension (PH) is characterized by elevated pulmonary arterial pressure leading to right-sided heart failure and can arise from a wide range of etiologies. The most common cause of PH, termed Group 2 PH, is left-sided heart failure and is commonly known as pulmonary hypertension with left heart disease (PH-LHD). Importantly, while sharing many clinical features with pulmonary arterial hypertension (PAH), PH-LHD differs significantly at the cellular and physiological levels. These fundamental pathophysiological differences largely account for the poor response to PAH therapies experienced by PH-LHD patients. The relatively high prevalence of this disease, coupled with its unique features compared with PAH, signal the importance of an in-depth understanding of the mechanistic details of PH-LHD. The present review will focus on the current state of knowledge regarding the pathomechanisms of PH-LHD, highlighting work carried out both in human trials and in preclinical animal models. Adaptive processes at the alveolocapillary barrier and in the pulmonary circulation, including alterations in alveolar fluid transport, endothelial junctional integrity, and vasoactive mediator secretion will be discussed in detail, highlighting the aspects that impact the response to, and development of, novel therapeutics.

The resistance-compliance product of the pulmonary circulation varies in health and pulmonary vascular disease

Pulmonary vascular resistance (PVR) is traditionally used to describe pulmonary hemodynamic characteristics. However, it does not take into account pulmonary artery compliance (Ca) or pulsatile flow. The product of PVR and Ca is known as RC time. Previous studies assert that the PVR-Ca relationship is fixed and RC time is constant between health and disease states. We hypothesized that RC time was not constant in health and pulmonary vascular disease. Right heart catheterizations performed in Papworth Hospital over a 6 year period were analyzed. Subjects were divided into those with normal pulmonary hemodynamics (NPH group; n = 156) and pulmonary arterial hypertension (PAH group; n = 717). RC time and the right ventricle (RV) oscillatory power fraction were calculated. RC time for the NPH group (0.47 ± 0.13 sec) is significantly lower than the PAH group (0.56 ± 0.16 sec; P < 0.0001). The RV oscillatory power fraction is lower in the NPH group (P < 0.0001). RC time correlates inversely with the RV oscillatory power fraction in each group. We conclude, there is an inverse relationship between PVR and Ca, however, this relationship is not always fixed. Consequently, RC time is significantly lower in health compared to disease with elevated pulmonary artery pressures. PAH leads to a decrease in cardiac efficiency.

Sympathetic nervous system activation and β-adrenoceptor blockade in right heart failure

Right heart failure may develop from pulmonary arterial hypertension or various forms of congenital heart disease. Right ventricular adaptation to the increased afterload is the most important prognostic factor in pulmonary hypertension and congenital heart disease, which share important pathophysiological mechanisms, despite having different aetiologies. There is substantial evidence of increased sympathetic nervous system activation in right heart failure related to both pulmonary hypertension and congenital heart disease. It is unknown to which degree this activation is an adaptive response, a maladaptive response, or if it mainly reflects disease progression. Several experimental studies and clinical trials have been conducted to answer these questions. Here, we review the existing knowledge on sympathetic nervous system activation and the effects of β-adrenoceptor blockade in experimental and clinical right heart failure. This review identifies important gaps in our understanding of the right ventricle and discusses the potential of β-blockers in the treatment of right heart failure.

A novel in vivo approach to assess radial and axial distensibility of large and intermediate pulmonary artery branches

Pulmonary arteries (PAs) distend to accommodate increases in cardiac output. PA distensibility protects the right ventricle (RV) from excessive increases in pressure. Loss of PA distensibility plays a critical role in the fatal progression of pulmonary arterial hypertension (PAH) toward RV failure. However, it is unclear how PA distensibility is distributed across the generations of PA branches, mainly because of the lack of appropriate in vivo methods to measure distensibility of vessels other than the large, conduit PAs. In this study, we propose a novel approach to assess the distensibility of individual PA branches. The metric of PA distensibility we used is the slope of the stretch ratio-pressure relationship. To measure distensibility, we combined invasive measurements of mean PA pressure with angiographic imaging of the PA network of six healthy female dogs. Stacks of 2D images of the PAs, obtained from either contrast enhanced magnetic resonance angiography (CE-MRA) or computed tomography digital subtraction angiography (CT-DSA), were used to reconstruct 3D surface models of the PA network, from the first bifurcation down to the sixth generation of branches. For each branch of the PA, we calculated radial and longitudinal stretch between baseline and a pressurized state obtained via acute embolization of the pulmonary vasculature. Our results indicated that large and intermediate PA branches have a radial distensibility consistently close to 2%/mmHg. Our axial distensibility data, albeit affected by larger variability, suggested that the PAs distal to the first generation may not significantly elongate in vivo, presumably due to spatial constraints. Results from both angiographic techniques were comparable to data from established phase-contrast (PC) magnetic resonance imaging (MRI) and ex vivo mechanical tests, which can only be used in the first branch generation. Our novel method can be used to characterize PA distensibility in PAH patients undergoing clinical right heart catheterization (RHC) in combination with MRI.