Transition from post-capillary pulmonary hypertension to combined pre- and post-capillary pulmonary hypertension in swine: a key role for endothelin

Challenging in pulmonary thromboembolism diagnosis in patients with disproportionate pulmonary hypertension and severe mitral stenosis: Report of two cases

Key Clinical Message

Before valvular interventions, echocardiography, especially the TEE or the ventilation/perfusion scan, should be performed to detect silent PTE and set a more accurate treatment and surgical plan.

Abstract

Pulmonary hypertension (PH) is a progressive and critical disease that can be caused by mitral stenosis (MS). Some of these patients present with disproportionate PH, which is an uncommon phenomenon and is considered a challenging diagnostic and treatment process. In these patients, other causes may also play a role in developing PH. This report presented two cases with disproportionate PH and severe MS who were scheduled for percutaneous mitral valvuloplasty (PMV). The pre-procedural echocardiography revealed systolic pulmonary artery pressure (sPAP) of 90 and 120 mmHg, mitral valve area of 0.80 and 0.55 cm2 by three-dimensional (3D) planimetry, and diastolic pressure gradient (DPG) of 13 and 18.8 mmHg, respectively. Furthermore, in the first patient, 3D transesophageal echocardiography (TEE) revealed multiple saddle-type organized thrombi in the proximal parts of the right and left pulmonary arteries, extending to the distal branches. In the second patient, 3D TEE revealed a large, relatively fresh, flow-limiting thrombosis in the proximal part of the right pulmonary artery. The diagnosis of pulmonary thromboembolism (PTE) in both patients was confirmed by CT angiography. In both patients, the valves were surgically repaired, while all thrombi were removed from the cardiac chambers and pulmonary vessels during surgery. In addition, patients underwent warfarin therapy orally. They were followed up 6 months after the intervention, and their clinical symptoms had improved significantly.

Clinical features do not identify risk of progression from isolated postcapillary pulmonary hypertension to combined pre- and postcapillary pulmonary hypertension

Pulmonary hypertension is a common sequelae of left heart failure and may present as isolated postcapillary pulmonary hypertension (Ipc-PH) or combined pre- and postcapillary pulmonary hypertension (Cpc-PH). Clinical features associated with progression from Ipc-PH to Cpc-PH have not yet been described. We extracted clinical data from patients who underwent right heart catheterizations (RHC) on two separate occasions. Ipc-PH was defined as mean pulmonary pressure >20 mmHg, pulmonary capillary wedge pressure >15 mmHg, and pulmonary vascular resistance (PVR) < 3 WU. Progression to Cpc-PH required an increase in PVR to ≥3 WU. We performed a retrospective cohort study with repeated assessments comparing subjects that progressed to Cpc-PH to subjects that remained with Ipc-PH. Of 153 patients with Ipc-PH at baseline who underwent a repeat RHC after a median of 0.7 years (IQR 0.2, 2.1), 33% (50/153) had developed Cpc-PH. In univariate analysis comparing the two groups at baseline, body mass index (BMI) and right atrial pressure were lower, while the prevalence of moderate or worse mitral regurgitation (MR) was higher among those who progressed. In age- and sex-adjusted multivariable analysis, only BMI (OR 0.94, 95% CI 0.90-0.99, p = 0.017, C = 0.655) and moderate or worse MR (OR 3.00, 95% CI 1.37-6.60, p = 0.006, C = 0.654) predicted progression, but with poor discriminatory power. This study suggests that clinical features alone cannot distinguish patients at risk for development of Cpc-PH and support the need for molecular and genetic studies to identify biomarkers of progression.

Proteomics- and Metabolomics-Based Analysis of Metabolic Changes in a Swine Model of Pulmonary Hypertension

Pulmonary vein stenosis (PVS) causes a rare type of pulmonary hypertension (PH) by impacting the flow and pressure within the pulmonary vasculature, resulting in endothelial dysfunction and metabolic changes. A prudent line of treatment in this type of PH would be targeted therapy to relieve the pressure and reverse the flow-related changes. We used a swine model in order to mimic PH after PVS using pulmonary vein banding (PVB) of the lower lobes for 12 weeks to mimic the hemodynamic profile associated with PH and investigated the molecular alterations that provide an impetus for the development of PH. Our current study aimed to employ unbiased proteomic and metabolomic analyses on both the upper and lower lobes of the swine lung to identify regions with metabolic alterations. We detected changes in the upper lobes for the PVB animals mainly pertaining to fatty acid metabolism, reactive oxygen species (ROS) signaling and extracellular matrix (ECM) remodeling and small, albeit, significant changes in the lower lobes for purine metabolism.

Concomitant latent pulmonary vascular disease leads to impaired global cardiac performance in heart failure with preserved ejection fraction

AIMS

The REDUCE-LAP II trial demonstrated adverse outcomes after interatrial shunt device (IASD) placement in heart failure with preserved ejection fraction (HFpEF) attributed to latent pulmonary vascular disease (PVD). We hypothesized that exercise stress cardiovascular magnetic resonance (CMR) imaging could provide non-invasive characterization of cardiac and pulmonary physiology for improved patient selection.

METHODS AND RESULTS

The HFpEF-Stress trial prospectively enrolled 75 patients with exertional dyspnoea and diastolic dysfunction. Patients underwent rest and exercise stress right heart catheterization, echocardiography and CMR imaging. Pulmonary artery and capillary wedge pressures, cardiac index (CI) and pulmonary vascular resistance (PVR) were calculated. Latent PVD was defined as increased PVR ≥ 1.74 Wood units during exercise stress. CMR assessed long-axis strains (LAS) and filling volumes of all cardiac chambers. Right ventricular (RV) function was further quantified by stroke and peak flow volumes. Patients with latent PVD (n = 24) showed lower RV function (rest tricuspid annular plane systolic excursion, p = 0.010; stress RV LAS, p < 0.001) compared to patients without (n = 43). During exercise stress, RV stroke and peak flow volumes (p < 0.001) were reduced and led to impaired left atrial filling (p = 0.040) with a strong statistical trend to impaired ventricular (LV) filling (p = 0.098). This subsequently resulted in reduced LV-CI (p < 0.001) despite preserved LV systolic function (LV LAS p ≥ 0.255). The degree of RV dysfunction during exercise stress best predicted latent PVD (RV peak flow, area under the curve at rest 0.73 vs. stress 0.89, p = 0.004).

CONCLUSIONS

Latent PVD is a feature of HFpEF and is associated with impaired RV functional reserve, global diastolic filling and LV-CI. This can be quantified by CMR and used to identify patients likely to benefit from IASD implantation.

Combined pre- and post-capillary pulmonary hypertension in left heart disease

Patients with heart failure (HF) often have pulmonary hypertension (PH), which is mainly post-capillary; however, some of them also develop a pre-capillary component. The exact mechanisms leading to combined pre- and post-capillary PH are not yet clear, but the phenomenon seems to start from a passive transmission of increased pressure from the left heart to the lungs, and then continues with the remodeling of both the alveolar and vascular components through different pathways. More importantly, it is not yet clear which patients are predisposed to develop the disease. These patients have some characteristics similar to those with idiopathic pulmonary arterial hypertension (e.g., young age and frequent incidence in female gender), but they share cardiovascular risk factors with patients with HF (e.g., obesity and diabetes), with both reduced and preserved ejection fraction. Thanks to echocardiography parameters and newly introduced scores, more tools are available to distinguish between idiopathic pulmonary arterial hypertension and combined PH and to guide patients' management. It may be hypothesized to treat patients in whom the pre-capillary component is predominant with specific therapies such as those for idiopathic pulmonary arterial hypertension; however, no adequately powered trials of PH-specific treatment are available in combined PH. Early evidence of clinical benefit has been proven in some trials on phosphodiesterase type 5 inhibitors, while data on prostacyclin analogues, endothelin-1 receptor antagonists, and soluble guanylate cyclase stimulators are still controversial.

Loss of lung microvascular endothelial Piezo2 expression impairs NO synthesis, induces EndMT, and is associated with pulmonary hypertension

Mechanical forces are translated into biochemical stimuli by mechanotransduction channels, such as the mechanically activated cation channel Piezo2. Lung Piezo2 expression has recently been shown to be restricted to endothelial cells. Hence, we aimed to investigate the role of Piezo2 in regulation of pulmonary vascular function and structure, as well as its contribution to development of pulmonary arterial hypertension (PAH). The expression of Piezo2 was significantly reduced in pulmonary microvascular endothelial cells (MVECs) from patients with PAH, in lung tissue from mice with a Bmpr2^+/R899X knock-in mutation commonly found in patients with pulmonary hypertension, and in lung tissue of monocrotaline (MCT) and sugen-hypoxia-induced PH (SuHx) PAH rat models, as well as from a swine model with pulmonary vein banding. In MVECs, Piezo2 expression was reduced in response to abnormal shear stress, hypoxia, and TGFβ stimulation. Functional studies in MVECs exposed to shear stress illustrated that siRNA-mediated Piezo2 knockdown impaired endothelial alignment, calcium influx, phosphorylation of AKT, and nitric oxide production. In addition, siPiezo2 reduced the expression of the endothelial marker PECAM-1 and increased the expression of vascular smooth muscle markers ACTA2, SM22a, and calponin. Thus, Piezo2 acts as a mechanotransduction channel in pulmonary MVECs, stimulating shear-induced production of nitric oxide and is essentially involved in preventing endothelial to mesenchymal transition. Its blunted expression in pulmonary hypertension could impair the vasodilator capacity and stimulate vascular remodeling, indicating that Piezo2 might be an interesting therapeutic target to attenuate progression of the disease.NEW & NOTEWORTHY The mechanosensory ion channel Piezo2 is exclusively expressed in lung microvascular endothelial cells (MVECs). Patient MVECs as well as animal models of pulmonary (arterial) hypertension showed lower expression of Piezo2 in the lung. Mechanistically, Piezo2 is required for calcium influx and NO production in response to shear stress, whereas stimuli known to induce endothelial to mesenchymal transition (EndMT) reduce Piezo2 expression in MVECs, and Piezo2 knockdown induces a gene and protein expression pattern consistent with EndMT.

Progress in Pulmonary Vein Stenosis: Lessons from Success in Treating Pulmonary Arterial Hypertension

Pulmonary vein stenosis (PVS) is a rare and poorly understood condition that can be classified as primary, acquired, status-post surgical repair of PVS, and/or associated with developmental lung disease. Immunohistochemical studies demonstrate that obstruction of the large (extrapulmonary) pulmonary veins is associated with the neointimal proliferation of myofibroblasts. This rare disorder is likely multifactorial with a spectrum of pathobiology. Treatments have been historically surgical, with an increasing repetitive interventional approach. Understanding the biology of these disorders is in its infancy; thus, medical management has lagged behind. Throughout medical history, an increased understanding of the underlying biology of a disorder has led to significant improvements in care and outcomes. One example is the treatment of pulmonary arterial hypertension (PAH). PAH shares several common themes with PVS. These include the spectrum of disease and biological alterations, such as vascular remodeling and vasoconstriction. Over the past two decades, an exponential increase in the understanding of the pathobiology of PAH has led to a dramatic increase in medical therapies that have changed the landscape of the disease. We believe that a similar approach to PVS can generate novel medical therapeutic targets that will markedly improve the outcome of these vulnerable patients.

N-Carbamoylglutamate Supplementation on the Digestibility, Rumen Fermentation, Milk Quality, Antioxidant Parameters, and Metabolites of Jersey Cattle in High-Altitude Areas

This study aimed to assess the impact of the dietary supplementation of N-carbamoylglutamate (NCG) on nutrient digestibility, rumen fermentation, milk quality, oxidative stress, and metabolites in the plasma and feces of Jersey cattle under high altitude with the hypoxic condition. A total of 14 healthy lactating Jersey dairy cows with similar body conditions were selected and randomly divided into 2 groups. The control group (CON group, N = 6 replicates) was fed with a conventional complete diet, whereas the experimental group (NCG group, N = 8 replicates) received 20 g/d per head NCG supplementation. The experiment lasted for 60 days, the adaptation period was 12 days, and the formal experiment period was 48 days. Except that the NCG group showed an upward trend in dry matter intake (DMI) (p = 0.09) and the fermentation parameters, the molar proportion of butyric acid tended to decrease (p = 0.08); the two groups had no significant differences (p > 0.05) in nutrients digestibility, plasma immunity, and antioxidant ability. However, compared with the CON group, the milk fat rate and blood oxygen saturation of the NCG group showed an upward trend (p = 0.09). For indexes associated with altitude stress, the contents of thyroxine, transferrin, and endothelin both decreased significantly (p < 0.05) in the NCG group. Meanwhile, heat shock protein (p = 0.07) and aldosterone (p = 0.06) also showed a downward trend. A total of 114 different metabolites were identified from feces and plasma, 42 metabolites were derived from plasma that mainly included 5 kinds of Super Class, and 72 metabolites were derived from feces that mainly included 9 kinds of Super Class. The significantly increased plasma differential metabolites were 2,5-dihydroxybenzoate and salicyluric acid, and the significantly increased fecal differential metabolites were Butenafine (fold change > 2). Pathway analysis showed that after applying NCG as a feed additive, the changes of the Jersey dairy cows mainly focused on amino acid metabolism and lipid metabolism. These results indicated that adding NCG to the diet can prevent the hypoxic stress state of lactating Jersey cows in high-altitude areas and has a tendency to improve milk quality.

Animal models of pulmonary hypertension due to left heart disease

Pulmonary hypertension due to left heart disease (PH‐LHD) is regarded as the most prevalent form of pulmonary hypertension (PH). Indeed, PH is an independent risk factor and predicts adverse prognosis for patients with left heart disease (LHD). Clinically, there are no drugs or treatments that directly address PH‐LHD, and treatment of LHD alone will not also ameliorate PH. To target the underlying physiopathological alterations of PH‐LHD and to develop novel therapeutic approaches for this population, animal models that simulate the pathophysiology of PH‐LHD are required. There are several available models for PH‐LHD that have been successfully employed in rodents or large animals by artificially provoking an elevated pressure load on the left heart, which by transduction elicits an escalated pressure in pulmonary artery. In addition, metabolic derangement combined with aortic banding or vascular endothelial growth factor receptor antagonist is also currently applied to reproduce the phenotype of PH‐LHD. As of today, none of the animal models exactly recapitulates the condition of patients with PH‐LHD. Nevertheless, the selection of an appropriate animal model is essential in basic and translational studies of PH‐LHD. Therefore, this review will summarize the characteristics of each PH‐LHD animal model and discuss the advantages and limitations of the different models.

Numerical predictions of shear stress and cyclic stretch in pulmonary hypertension due to left heart failure

Isolated post-capillary pulmonary hypertension (Ipc-PH) occurs due to left heart failure, which contributes to 1 out of every 9 deaths in the United States. In some patients, through unknown mechanisms, Ipc-PH transitions to combined pre-/post-capillary PH (Cpc-PH) and is associated with a dramatic increase in mortality. Altered mechanical forces and subsequent biological signaling in the pulmonary vascular bed likely contribute to the transition from Ipc-PH to Cpc-PH. However, even in a healthy pulmonary circulation, the mechanical forces in the smallest vessels (the arterioles, capillary bed, and venules) have not been quantitatively defined. This study is the first to examine this question via a computational fluid dynamics model of the human pulmonary arteries, arterioles, venules, and veins. Using this model, we predict temporal and spatial dynamics of cyclic stretch and wall shear stress with healthy and diseased hemodynamics. In the normotensive case for large vessels, numerical simulations show that large arteries have higher pressure and flow than large veins, as well as more pronounced changes in area throughout the cardiac cycle. In the microvasculature, shear stress increases and cyclic stretch decreases as vessel radius decreases. When we impose an increase in left atrial pressure to simulate Ipc-PH, shear stress decreases and cyclic stretch increases as compared to the healthy case. Overall, this model predicts pressure, flow, shear stress, and cyclic stretch that providing a way to analyze and investigate hypotheses related to disease progression in the pulmonary circulation.

Pulmonary Hypertension in the Context of Heart Failure With Preserved Ejection Fraction

Heart failure with preserved ejection fraction (HFpEF) is the most common form of heart failure and frequently is associated with pulmonary hypertension (PH). HFpEF associated with PH may be difficult to distinguish from precapillary forms of PH, although this distinction is crucial because therapeutic pathways are divergent for the two conditions. A comprehensive and systematic approach using history, clinical examination, and noninvasive and invasive evaluation with and without provocative testing may be necessary for accurate diagnosis and phenotyping. After diagnosis, HFpEF associated with PH can be subdivided into isolated postcapillary pulmonary hypertension (IpcPH) and combined postcapillary and precapillary pulmonary hypertension (CpcPH) based on the presence or absence of elevated pulmonary vascular resistance. CpcPH portends a worse prognosis than IpcPH. Despite its association with reduced functional capacity and quality of life, heart failure hospitalizations, and higher mortality, therapeutic options focused on PH for HFpEF associated with PH remain limited. In this review, we aim to provide an updated overview on clinical definitions and hemodynamically characterized phenotypes of PH, pathophysiologic features, therapeutic strategies, and ongoing challenges in this patient population.

Impaired pulmonary vasomotor control in exercising swine with multiple comorbidities

Pulmonary hypertension is common in heart failure with preserved ejection fraction (HFpEF). Here, we tested the hypothesis that comorbidities [diabetes mellitus (DM, streptozotocin), hypercholesterolemia (HC, high-fat diet) and chronic kidney disease (CKD, renal microembolization)] directly impair pulmonary vasomotor control in a DM + HC + CKD swine model. 6 months after induction of DM + HC + CKD, pulmonary arterial pressure was similar in chronically instrumented female DM + HC + CKD (n = 19) and Healthy swine (n = 18). However, cardiac output was lower both at rest and during exercise, implying an elevated pulmonary vascular resistance (PVR) in DM + HC + CKD swine (153 ± 10 vs. 122 ± 9 mmHg∙L^-1∙min∙kg). Phosphodiesterase 5 inhibition and endothelin receptor antagonism decreased PVR in DM + HC + CKD (- 12 ± 12 and - 22 ± 7 mmHg∙L^-1∙min∙kg) but not in Healthy swine (- 1 ± 12 and 2 ± 14 mmHg∙L^-1∙min∙kg), indicating increased vasoconstrictor influences of phosphodiesterase 5 and endothelin. Inhibition of nitric oxide synthase produced pulmonary vasoconstriction that was similar in Healthy and DM + HC + CKD swine, but unmasked a pulmonary vasodilator effect of endothelin receptor antagonism in Healthy (- 56 ± 26 mmHg∙L^-1∙min∙kg), whereas it failed to significantly decrease PVR in DM + HC + CKD, indicating loss of nitric oxide mediated inhibition of endothelin in DM + HC + CKD. Scavenging of reactive oxygen species (ROS) had no effect on PVR in either Healthy or DM + HC + CKD swine. Cardiovascular magnetic resonance imaging, under anesthesia, showed no right ventricular changes. Finally, despite an increased contribution of endogenous nitric oxide to vasomotor tone regulation in the systemic vasculature, systemic vascular resistance at rest was higher in DM + HC + CKD compared to Healthy swine (824 ± 41 vs. 698 ± 35 mmHg∙L^-1∙min∙kg). ROS scavenging induced systemic vasodilation in DM + HC + CKD, but not Healthy swine. In conclusion, common comorbidities directly alter pulmonary vascular control, by enhanced PDE5 and endothelin-mediated vasoconstrictor influences, well before overt left ventricular backward failure or pulmonary hypertension develop.

The many faces and outcomes of pulmonary vein stenosis in early childhood

Pulmonary vein stenosis is a rare and poorly understood condition causing obstruction of the large pulmonary veins and of blood flow from the lungs to the left atrium. This results in elevated pulmonary venous pressure and pulmonary edema, pulmonary hypertension, potentially cardiac failure, and death. Clinical signs of the disease include failure to thrive, increasingly severe dyspnea, hemoptysis, respiratory difficulty, recurrent respiratory tract infections/pneumonia, cyanosis, and subcostal retractions. On chest radiograph, the most frequent finding is increased interstitial, ground-glass and/or reticular opacity. Transthoracic echocardiography with pulsed Doppler delineates the stenosis, magnetic resonance imaging and multislice computerized tomography are used for further evaluation. Interventional cardiac catherization, surgical techniques, and medical therapies have been used with varying success as treatment options.

The neurohormonal basis of pulmonary hypertension in heart failure with preserved ejection fraction

AIMS

Pulmonary hypertension (PH) represents an important phenotype among the broader spectrum of patients with heart failure with preserved ejection fraction (HFpEF), but its mechanistic basis remains unclear. We hypothesized that activation of endothelin and adrenomedullin, two counterregulatory pathways important in the pathophysiology of PH, would be greater in HFpEF patients with worsening PH, and would correlate with the severity of haemodynamic derangements and limitations in aerobic capacity and cardiopulmonary reserve.

METHODS AND RESULTS

Plasma levels of C-terminal pro-endothelin-1 (CT-proET-1) and mid-regional pro-adrenomedullin (MR-proADM), central haemodynamics, echocardiography, and oxygen consumption (VO2) were measured at rest and during exercise in subjects with invasively-verified HFpEF (n = 38) and controls free of HF (n = 20) as part of a prospective study. Plasma levels of CT-proET-1 and MR-proADM were highly correlated with one another (r = 0.89, P < 0.0001), and compared to controls, subjects with HFpEF displayed higher levels of each neurohormone at rest and during exercise. C-terminal pro-endothelin-1 and MR-proADM levels were strongly correlated with mean pulmonary artery (PA) pressure (r = 0.73 and 0.65, both P < 0.0001) and pulmonary capillary wedge pressure (r = 0.67 and r = 0.62, both P < 0.0001) and inversely correlated with PA compliance (r = -0.52 and -0.43, both P < 0.001). As compared to controls, subjects with HFpEF displayed right ventricular (RV) reserve limitation, evidenced by less increases in RV s' and e' tissue velocities, during exercise. Baseline CT-proET-1 and MR-proADM levels were correlated with worse RV diastolic reserve (ΔRV e', r = -0.59 and -0.67, both P < 0.001), reduced cardiac output responses to exercise (r = -0.59 and -0.61, both P < 0.0001), and more severely impaired peak VO2 (r = -0.60 and -0.67, both P < 0.0001).

CONCLUSION

Subjects with HFpEF display activation of the endothelin and adrenomedullin neurohormonal pathways, the magnitude of which is associated with pulmonary haemodynamic derangements, limitations in RV functional reserve, reduced cardiac output, and more profoundly impaired exercise capacity in HFpEF. Further study is required to evaluate for causal relationships and determine if therapies targeting these counterregulatory pathways can improve outcomes in patients with the HFpEF-PH phenotype.

CLINICAL TRIAL REGISTRATION

NCT01418248; https://clinicaltrials.gov/ct2/results? term=NCT01418248&Search=Search.

Heart‑lung crosstalk in pulmonary arterial hypertension following myocardial infarction (Review)

Left heart disease is the main cause of clinical pulmonary arterial hypertension (PAH). Common types of left heart disease that result in PAH include heart failure, left ventricular systolic dysfunction, left ventricular diastolic dysfunction and valvular disease. It is currently believed that mechanical pressure caused by high pulmonary venous pressure is the main cause of myocardial infarction (MI) in individuals with ischemic cardiomyopathy and left ventricular systolic dysfunction. In the presence of decreased cardiac function, vascular remodeling of pulmonary vessels in response to long-term stimulation by high pressure in turn leads to exacerbation of PAH. However, the underlying pathological mechanisms remain unclear. Elucidating the association between the development of MI and PAH may lead to a better understanding of potential risk factors and better disease treatment. In this article, the pathophysiological effects of multiple systems in individuals with MI and PAH were reviewed in order to provide a general perspective on various potential interactions between cardiomyocytes and pulmonary vascular cells.

Experimental models of cardiac physiology and pathology

Experimental models of cardiac disease play a key role in understanding the pathophysiology of the disease and developing new therapies. The features of the experimental models should reflect the clinical phenotype, which can have a wide spectrum of underlying mechanisms. We review characteristics of commonly used experimental models of cardiac physiology and pathophysiology in all translational steps including in vitro, small animal, and large animal models. Understanding their characteristics and relevance to clinical disease is the key for successful translation to effective therapies.

Intervening with the Nitric Oxide Pathway to Alleviate Pulmonary Hypertension in Pulmonary Vein Stenosis

Pulmonary hypertension (PH) as a result of pulmonary vein stenosis (PVS) is extremely difficult to treat. The ideal therapy should not target the high-pressure/low-flow (HP/LF) vasculature that drains into stenotic veins, but only the high-pressure/high-flow (HP/HF) vasculature draining into unaffected pulmonary veins, reducing vascular resistance and pressure without risk of pulmonary oedema. We aimed to assess the activity of the nitric oxide (NO) pathway in PVS during the development of PH, and investigate whether interventions in the NO pathway differentially affect vasodilation in the HP/HF vs. HP/LF territories. Swine underwent pulmonary vein banding (PVB; n = 7) or sham surgery (n = 6) and were chronically instrumented to assess progression of PH. Pulmonary sensitivity to exogenous NO (sodium nitroprusside, SNP) and the contribution of endogenous NO were assessed bi-weekly. The pulmonary vasodilator response to phosphodiesterase-5 (PDE5) inhibition was assessed 12 weeks after PVB or sham surgery. After sacrifice, 12 weeks post-surgery, interventions in the NO pathway on pulmonary small arteries isolated from HP/LF and HP/HF territories were further investigated. There were no differences in the in vivo pulmonary vasodilator response to SNP and the pulmonary vasoconstrictor response to endothelial nitric oxide synthase (eNOS) inhibition up to 8 weeks after PVB as compared to the sham group. However, at 10 and 12 weeks post-PVB, the in vivo pulmonary vasodilation in response to SNP was larger in the PVB group. Similarly, the vasoconstriction to eNOS inhibition was larger in the PVB group, particularly during exercise, while pulmonary vasodilation in response to PDE5 inhibition was larger in the PVB group both at rest and during exercise. In isolated pulmonary small arteries, sensitivity to NO donor SNP was similar in PVB vs. sham groups irrespective of HP/LF and HP/HF, while sensitivity to the PDE5 inhibitor sildenafil was lower in PVB HP/HF and sensitivity to bradykinin was lower in PVB HP/LF. In conclusion, both NO availability and sensitivity were increased in the PVB group. The increased nitric oxide sensitivity was not the result of a decreased PDE5 activity, as PDE5 activity was even increased. Some vasodilators differentially effect HP/HF vs. HP/LF vasculature.

Right ventricular oxygen delivery as a determinant of right ventricular functional reserve during exercise in juvenile swine with chronic pulmonary hypertension

Assessing right ventricular (RV) functional reserve is important for determining clinical status and prognosis in patients with pulmonary hypertension (PH). In this study, we aimed to establish RV oxygen (O₂) delivery as a determinant for RV functional reserve during exercise in swine with chronic PH. Chronic PH was induced by pulmonary vein banding (PVB), with sham operation serving as control. RV function and RV O₂ delivery were measured over time in chronically instrumented swine, up to 12 wk after PVB at rest and during exercise. At rest, RV afterload (pulmonary artery pressure and arterial elastance) and contractility (E_es and dP/dt_max) were higher in PH compared with control with preserved cardiac index and RV O₂ delivery. However, RV functional reserve, as measured by the exercise-induced relative change (Δ) in cardiac index, dP/dt_max, and end-systolic elastance (E_es), was decreased in PH, and RV pulmonary arterial coupling was lower both at rest and during exercise in PH. Furthermore, the increase in RV O₂ delivery was attenuated in PH during exercise principally due to a lower systolic coronary blood flow in combination with an attenuated increase in aorta pressure while arterial O₂ content was not significantly altered in PH. Moreover, RV O₂ delivery reserve correlated with RV functional reserve, Δcardiac index (r² = 0.85), ΔdP/dt_max (r² = 0.49), and ΔE_es (r² = 0.70), all P < 0.05. The inability to sufficiently increase RV O₂ supply to meet the increased O₂ demand during exercise is principally due to the reduced RV perfusion relative to healthy control values and likely contributes to impaired RV contractile function and thereby to the limited exercise capacity that is commonly observed in patients with PH.NEW & NOTEWORTHY Impaired right ventricular (RV) O₂ delivery reserve is associated with reduced RV functional reserve during exercise in a swine model of pulmonary hypertension (PH) induced by pulmonary vein banding. Our data suggest that RV function and exercise capacity might be improved by improving RV O₂ delivery.

Changes in the nitric oxide pathway of the pulmonary vasculature after exposure to hypoxia in swine model of neonatal pulmonary vascular disease

Neonatal pulmonary vascular disease (PVD) is increasingly recognized as a disease that complicates the cardiopulmonary adaptations after birth and predisposes to long-term cardiopulmonary disease. There is growing evidence that PVD is associated with disruptions in the nitric oxide (NO)-cGMP-phosphodiesterase 5 (PDE5) pathway. Examination of the functionality of different parts of this pathway is required for better understanding of the pathogenesis of neonatal PVD. For this purpose, the role of the NO-cGMP-PDE5 pathway in regulation of pulmonary vascular function was investigated in vivo, both at rest and during exercise, and in isolated pulmonary small arteries in vitro, in a neonatal swine model with hypoxia-induced PVD. Endothelium-dependent vasodilatation was impaired in piglets with hypoxia-induced PVD both in vivo at rest and in vitro. Moreover, the responsiveness to the NO-donor SNP was reduced in hypoxia-exposed piglets in vivo, while the relaxation to SNP and 8-bromo-cyclicGMP in vitro were unaltered. Finally, PDE5 inhibition-induced pulmonary vasodilatation was impaired in hypoxia-exposed piglets both in vitro and in vivo at rest. During exercise, however, the pulmonary vasodilator effect of PDE5 inhibition was significantly larger in hypoxia-exposed as compared to normoxia-exposed piglets. In conclusion, the impaired endothelium-dependent vasodilatation in piglets with hypoxia-induced PVD was accompanied by reduced responsiveness to NO, potentially caused by altered sensitivity and/or activity of soluble guanylyl cyclase (sGC), resulting in an impaired cGMP production. Our findings in a newborn animal model for neonatal PVD suggests that sGC stimulators/activators may be a novel treatment strategy to alleviate neonatal PVD.