Surgically induced unilateral pulmonary hypertension: time-related analysis of a new experimental model

Anomalous Origin of Left Pulmonary Artery From the Descending Aorta Diagnosed in an Athletic Adult

BACKGROUND

Anomalous origin of the left pulmonary artery from the aorta, also named hemitruncus arteriosus, is a rare congenital heart disease associated with high mortality. Patients are usually operated on in the first months of life to avoid irreversible damage caused by pulmonary arterial hypertension.

CASE SUMMARY

The authors present a challenging case of an athletic male patient with an anomalous left pulmonary artery originating from the descending aorta that was diagnosed when he was aged 27 years, with severe segmental pulmonary arterial hypertension in the left lung. Following multidisciplinary team meetings, conservative management was chosen.

DISCUSSION

Multimodality imaging plays a key role in both diagnosing and managing this birth defect and its potential complications.

TAKE-HOME MESSAGE

Management of this extremely rare congenital anomaly in the adult is yet to be fully understood and requires a multidisciplinary team in a tertiary center.

Anesthesia management in a patient with anomalous origin of left pulmonary artery from the descending aorta: A case report and literature review

Anomalous origin of the left pulmonary artery from the descending aorta is an extremely rare congenital malformation. There were merely four case reports of such malformation in previous literature, and all four cases underwent surgical repair in their first year of life. Actually, long-term pulmonary arterial hypertension and irreversible pulmonary vascular changes make anesthesia management quite a challenge, while anesthesia for managing these cases has not been discussed before. We present a 15-year-old boy undergoing corrective surgery and try to provide some tips on anesthesia management for this surgical procedure. Through optimal perioperative management, successful outcomes can be achieved for this malformation.

A pro-con debate: current controversies in PAH pathogenesis at the American Thoracic Society International Conference in 2017

The following review summarizes the pro-con debate about current controversies regarding the pathogenesis of pulmonary arterial hypertension (PAH) that took place at the American Thoracic Society Conference in May 2017. Leaders in the field of PAH research discussed the importance of the immune system, the role of hemodynamic stress and endothelial apoptosis, as well as bone morphogenetic protein receptor-2 signaling in PAH pathogenesis. Whereas this summary does not intend to resolve obvious conflicts in opinion, we hope that the presented arguments entice further discussions and draw a new generation of enthusiastic researchers into this vibrant field of science to bridge existing gaps for a better understanding and therapy of this fatal disease.

Challenges in the development of chronic pulmonary hypertension models in large animals

Pulmonary hypertension (PH) results in significant morbidity and mortality. Chronic PH animal models may advance the study of PH's mechanisms, evolution, and therapy. In this report, we describe the challenges and successes in developing three models of chronic PH in large animals: two models (one canine and one swine) utilized repeated infusions of ceramic microspheres into the pulmonary vascular bed, and the third model employed a surgical aorto-pulmonary shunt. In the canine model, seven dogs underwent microsphere infusions that resulted in progressive elevation of pulmonary arterial pressure over a few months. In this model, pulmonary endoarterial tissue was obtained for histology. In the aorto-pulmonary shunt swine model, 17 pigs developed systemic level pulmonary pressures after 2-3 months. In this model, pulmonary endoarterial tissue was sequentially obtained to assess for changes in gene and microRNA expression. In the swine microsphere infusion model, three pigs developed only a modest chronic increase in pulmonary arterial pressure, despite repeated infusions of microspheres (up to 40 in one animal). The main purpose of this model was for vasodilator testing, which was performed successfully immediately after acute microsphere infusions. Chronic PH in large animal models can be successfully created; however, a model's characteristics need to match the investigational goals.

A novel mouse model of high flow-induced pulmonary hypertension-surgically induced by right pulmonary artery ligation

BACKGROUND

This study sought to establish a new model of high-flow pulmonary hypertension (PH) in mice. This model may be useful for studies seeking to reduce the pulmonary vascular resistance and delay the development of PH caused by congenital heart disease.

MATERIALS AND METHODS

The right pulmonary artery was ligated via a right posterolateral thoracotomy. Pulmonary hemodynamics was evaluated by right heart catheterization immediately after ligation and at 2, 4, 8, and 12 wk postoperatively. The right ventricle (RV) and the left ventricle (LV) with septum (S) were weighed to calculate the RV/(LV + S) ratio as an index of right ventricular hypertrophy. Morphologic changes in the left lungs were analyzed, and percentages of muscularized pulmonary vessels were assessed by hematoxylin and eosin, elastica van Gieson and alpha-smooth muscle actin staining. All the study data were compared with data from a model of PH generated by hypoxic stimulation.

RESULTS

A pulmonary hypertensive state was successfully induced by 2 wk after surgery. However, the morphologic analysis demonstrated that pulmonary vascular muscularization, as evaluated using right ventricular systolic pressure and RV/(LV + S), was not significantly increased until 4 wk postoperatively. When mice from the new model and the hypoxic model were compared, no significant differences were observed in any of the evaluated indices.

CONCLUSIONS

High-flow PH can be induced within 4 wk after ligation of the right pulmonary artery, which is easily performed in mice. Such mice can be used as a model of high-flow PH.

Vascular histomolecular analysis by sequential endoarterial biopsy in a shunt model of pulmonary hypertension

The molecular mechanisms of pulmonary arterial hypertension (PAH) remain ill-defined. The aims of this study were to obtain sequential endoarterial biopsy samples in a surgical porcine model of PAH and assess changes in histology and mRNA expression during the disease progression. Differentially expressed genes were then analyzed as potential pharmacological targets. Four Yucatan micro-pigs underwent surgical anastomosis of the left pulmonary artery to the descending aorta. Endovascular samples were obtained with a biopsy catheter at baseline (before surgery) and from the left lung 7, 60, and 180 days after surgery. RNA was isolated from biopsy samples, amplified and analyzed. Dysregulated genes were linked to drugs with potential to treat or prevent PAH. With the development of PAH in our model, we identified changes in histology and in the expression of several genes with known or investigational inhibitors and several novel genes for PAH. Gene dysregulation displayed time-related variations during disease progression. Endoarterial biopsy provides a new method of assessing pulmonary vascular histology and gene expression in PAH. This analysis could identify novel applications for existing and new PAH drugs. The detection of stage- and disease-specific variation in gene expression could lead to individualized therapies.

The role of disturbed blood flow in the development of pulmonary arterial hypertension: lessons from preclinical animal models

Pulmonary arterial hypertension (PAH) is a progressive pulmonary vasoproliferative disorder characterized by the development of unique neointimal lesions, including concentric laminar intima fibrosis and plexiform lesions. Although the histomorphology of neointimal lesions is well described, the pathogenesis of PAH and neointimal development is largely unknown. After three decades of PAH pathobiology research the focus has shifted from vasoconstriction towards a mechanism of cancer-like angioproliferation. In this concept the role of disturbed blood flow is seen as an important trigger in the development of vascular remodeling. For instance, in PAH associated with congenital heart disease, increased pulmonary blood flow (i.e., systemic-to-pulmonary shunt) is an essential trigger for the occurrence of neointimal lesions and PAH development. Still, questions remain about the exact role of these blood flow characteristics in disease progression. PAH animal models are important for obtaining insight in new pathobiological processes and therapeutical targets. However, as for any preclinical model the pathophysiological mechanism and clinical course has to be comparable to the human disease that it mimics. This means that animal models mimicking human PAH ideally are characterized by: a hit recognized in human disease (e.g., altered pulmonary blood flow), specific vascular remodeling resembling human neointimal lesions, and disease progression that leads to right ventriclular dysfunction and death. A review that underlines the current knowledge of PAH due to disturbed flow is still lacking. In this review we will summarize the current knowledge obtained from PAH animal models associated with disturbed pulmonary blood flow and address questions for future treatment strategies for PAH.

Hyperoxic vasoconstriction of human pulmonary arteries: a novel insight into acute ventricular septal defects

Objectives. Acute rises in pulmonary artery pressures following postinfarction ventricular septal defects present a challenge. We hypothesised that the abnormally high oxygen content exposure to the pulmonary arteries may be a factor. We investigated the contractile responses of human pulmonary arteries to changes in oxygen tension. Methods. Isometric tension was measured in large and medium sized pulmonary artery rings obtained from lung resections for patients with bronchial carcinoma (n = 30). Fresh rings were mounted in organ baths bubbled under basal conditions with hyperoxic or normoxic gas mixes and the gas tensions varied during the experiment. We studied whether voltage-gated calcium channels and nitric oxide signalling had any role in responses to oxygen changes. Results. Hypoxia caused a net mean relaxation of 18.1% ± 15.5 (P < 0.005) from hyperoxia. Subsequent hyperoxia caused a contraction of 19.2% ± 13.5 (P < 0.005). Arteries maintained in normoxia responded to hyperoxia with a mean constriction of 14.8% ± 3.9 (P < 0.005). Nifedipine inhibited the vasoconstrictive response (P < 0.05) whilst L-NAME had no effect on any hypoxic vasodilatory response. Conclusions. We demonstrate that hyperoxia leads to vasoconstriction in human pulmonary arteries. The mechanism appears to be dependent on voltage-gated calcium channels. Hyperoxic vasoconstriction may contribute to acute rises in pulmonary artery pressures.

Therapeutic effect of eNOS-transfected endothelial progenitor cells on hemodynamic pulmonary arterial hypertension

Hemodynamic pulmonary arterial hypertension (HPAH) is a common symptom in congenital heart disease (CHD) patients with a left-to-right shunt. Endothelial NO synthase (eNOS) and endothelial-like progenitor cells result in significant improvement of right ventricular systolic pressure in established pulmonary arterial hypertension (PAH) models. We hypothesized that bone marrow (BM)-derived endothelial progenitor cells (EPCs) and eNOS would prevent HPAH in a newly established rat model. The heNOS gene was cloned into a PSUCMV vector, and a high-titer adenovirus was generated. Mononuclear cells (MNCs) from rat BM were differentiated into EPCs by treatment with various cytokines, and a high purity of EPCs (>70%) was confirmed using the markers DiI ac-LDL, UEA-1, vWF and Flk-1. An ideal rat HPAH model was successfully established based on right lung lobectomy, and was confirmed by pressure measurement and histological staining. heNOS was successfully transfected into EPCs, which were then transplanted into HPAH rats. Two weeks after transplantation, the systolic pulmonary arterial blood pressure (sPAP) was significantly reduced by heNOS-EPCs treatment and by transplantation of control EPCs. The high number of muscular pulmonary arteries and the thickness of the muscular coat characteristic of HPAH rats were clearly reversed or even restored to normal levels following transplantation of EPCs, particularly eNOS-EPCs. These findings indicate a critical role of eNOS in HPAH treatment and suggest that eNOS-transfected EPCs may provide an effective strategy for HPAH treatment in CHD patients.

Patent Ductus Arteriosus and Respiratory Outcome in Premature Infants

A persistent ductus arteriosus is a common event in preterm infants. The systemic-to-pulmonary shunting that occurs as the pulmonary vascular resistance decreases after birth can have significant cardiovascular and respiratory consequences. Acute pulmonary effects include pulmonary edema and hemorrhage, worsened lung mechanics and deterioration in gas exchange with hypoxemia and hypercapnia. The increased pulmonary blood flow can also produce damage to the capillary endothelium and trigger an inflammatory cascade. This, plus the need for longer and more aggressive mechanical ventilation, can explain the association between patent ductus arteriosus and an increased risk for bronchopulmonary dysplasia in extremely premature infants.

Biventricular Support With the Jarvik 2000 Ventricular Assist Device in a Calf Model of Pulmonary Hypertension

The Jarvik 2000 ventricular assist device (VAD) is clinically efficacious for treating end-stage left ventricular failure. Because simultaneous right ventricular support is also occasionally necessary, we developed a biventricular Jarvik 2000 technique and tested it in a calf model. One VAD was implanted in the left ventricle with outflow-graft anastomosis to the descending aorta. The other VAD was implanted in the right ventricle with outflow-graft anastomosis to the pulmonary artery. Throughout the 30 day study, hemodynamic values were continuously monitored. On day 30, both pumps were evaluated at different speeds, under various hemodynamic conditions. By gradually occluding the pulmonary artery proximally or distally, we simulated varying degrees of high pulmonary vascular resistance, right ventricular hypertension, global heart failure, or ventricular fibrillation. The two VADs maintained biventricular support even during pulmonary artery occlusion and ventricular fibrillation, yielding a cardiac output of 3-11 L/min, left ventricular end-diastolic pressure of 11-24 mm Hg, and central venous pressure of 9-25 mm Hg. End-organ function was unimpaired, and no major adverse events occurred. The dual VADs offered safe, effective biventricular assistance in the calf. Additional studies are needed to assess the effects of lowered pulse pressure upon the pulmonary circulation and to develop a single pump speed controller.

Myocardial and pulmonary effects of aqueous oxygen with acute hypoxia

BACKGROUND

The purpose of this paper was to evaluate myocardial and pulmonary effects of aqueous oxygen (AO) delivered directly into the pulmonary circulation in acute hypoxia.

METHODS

Six calves (2 months old, 68.0 +/- 2.2 kg) after general anesthesia, mechanical ventilation, and median sternotomy underwent total right heart bypass using fixed flow with continuous pressure and blood gas measurements in carotid and femoral arteries, left atrium, the coronary sinus and PA. Measurements of systemic and PA pressures and O2 saturations; myocardial O2 atrioventricular (AV) differences; and O2 extraction were made. After base line measurements, hypoxic ventilation reducing the mean arterial PO2 from 277 +/- 102 mm Hg to 47 +/- 4 mm Hg (p < 0.0005) was maintained for 30 minutes. Without changes in the hypoxic ventilation (mean arterial PO2 = 49 +/- 11 mm Hg) 3 ml/min of hyperbaric aqueous oxygen (AO = oxygen diluted in saline solution) was administered into the PA for 30 minutes. Pulmonary blood flow was maintained during the entire experiment (3.7 +/- 0.3 L/min).

RESULTS

Hypoxic ventilation significantly raised (p < 0.05) the systolic (30 +/- 7 vs 21 +/- 4 mm Hg), diastolic (20 +/- 6 vs 12 +/- 3 mm Hg), and mean (23 +/- 7 vs 15 +/- 3 mm Hg) PA pressure; PA/systemic pressure ratio for systolic (0.37 +/- 0.08 vs 0.25 +/- 0.06) and mean (0.56 +/- 0.19 vs 0.29 +/- 0.11) pressures; and pulmonary vascular resistance (PVR) (5.63 +/- 1.06 vs 3.53 +/- 0.75 U). Aqueous oxygen (AO) infusion significantly reduced (p < 0.05) the values obtained with hypoxic ventilation; systolic (23 +/- 5 vs 30 +/- 7 mm Hg), diastolic (11 +/- 4 vs 20 +/- 6 mm Hg), and mean (14 +/- 3 vs 23 +/- 7 mm Hg) PA pressure; PA/systemic pressure ratio for systolic (0.25 +/- 0.05 vs 0.37 +/- 0.08) and mean pressures (0.29 +/- 0.12 vs 0.56 +/- 0.19); and PVR (3.41 +/- 1.01 vs 5.63 +/- 1.06 U). AO infusion in the pulmonary circulation did not influence the myocardial O2 atrioventricular (AV) difference or the O2 extraction.

CONCLUSIONS

Infusion of hyperbaric AO solution into the PA can completely reverse the negative effects of acute hypoxia on the pulmonary circulation without affecting the myocardial metabolism.