Primary pulmonary hypertension: diagnosis, medical and surgical treatment

Primary pulmonary hypertension: 3D dynamic perfusion MRI for quantitative analysis of regional pulmonary perfusion

OBJECTIVE

The purpose of this study was to determine whether quantitative pulmonary perfusion parameters obtained from 3D dynamic contrast-enhanced MR perfusion data can be used to assess the severity of primary pulmonary hypertension (PPH) as indicated by pulmonary vascular resistance (PVR) and mean pulmonary artery pressure (MPAP).

CONCLUSION

Three-dimensional dynamic contrast-enhanced MRI has potential for assessment of disease severity as indicated by PVR and MPAP in patients with PPH.

Quantitative assessment of regional pulmonary perfusion in the entire lung using three-dimensional ultrafast dynamic contrast-enhanced magnetic resonance imaging: Preliminary experience in 40 subjects

PURPOSE

To assess regional differences in quantitative pulmonary perfusion parameters, i.e., pulmonary blood flow (PBF), mean transit time (MTT), and pulmonary blood volume (PBV) in the entire lung on a pixel-by-pixel basis in normal volunteers and pulmonary hypertension patients.

MATERIALS AND METHODS

Three-dimensional ultrafast dynamic contrast-enhanced MR imaging was performed in 15 normal volunteers and 25 patients with pulmonary hypertension. From the signal intensity-time course curves, PBF, MTT and PBV maps were generated using deconvolution analysis, indicator dilution theories, and the central volume principle, on a pixel-by-pixel basis. From pulmonary perfusion parameter maps of normal volunteers and pulmonary hypertension patients, regional PBF, MTT, and PBV were statistically evaluated.

RESULTS

Regional PBF, MTT, and PBV showed significant differences in the gravitational and isogravitational directions (P < 0.05). The quantitative pulmonary perfusion parameter maps demonstrated significant differences between normal volunteers and pulmonary hypertension patients (P < 0.05).

CONCLUSION

Three-dimensional ultrafast dynamic contrast-enhanced MR imaging is feasible for the assessment of regional quantitative pulmonary perfusion parameters in the entire lung on a pixel-by-pixel basis in normal volunteers and pulmonary hypertension patients.

Animal models of cardiac disease: potential usefulness for studying health effects of inhaled particles

Cardiac disease is one of the major causes of morbidity and mortality worldwide and is the leading cause of death in the United States. Epidemiologic studies have shown a close association between morbidity and mortality from cardiac disease, primarily in persons already affected, and with modest increases in levels of air pollution. At present, no mechanisms are known by which inhaled air pollutants interact with the heart to cause death. Thus, animal models of cardiac disease are needed to study possible interactions between inhaled pollutants and the heart and the resultant morbidity and mortality. Very little research in animals has been conducted in this area, and appropriate animal models must be carefully selected. The purpose of this review is to examine several potential animal models and to discuss their advantages and disadvantages in the study of cardiac disease and air pollution.

The pulmonary hypertensive fawn-hooded rat has a normal serotonin transporter coding sequence

The coding sequence of the serotonin transporter gene was compared in two strains of rat-the Wistar and the fawn-hooded rat (FHR). The FHR has an inherited platelet storage-pool deficiency and a widespread impairment of serotonin storage. It is also susceptible to systemic and pulmonary hypertension. The FHR provides a model to study the genetics in human systemic and pulmonary hypertension. We measured platelet function in these two strains by measuring incorporation of radiolabeled serotonin into a platelet suspension and found significant differences in serotonin uptake and release. The coding sequence for the serotonin transporter in the FHR has yet to be reported. No differences were found in the predicted amino acid sequence between these two strains of rat, either in the platelet or the lung samples or when compared with the published sequence of the brown rat. We conclude that differences in the primary structure of the serotonin transporter gene do not account for the altered serotonin storage in the FHR strain.

Patient selection, evaluation, and preoperative management for lung transplant candidates

The selection process to assess candidacy for transplant is based on medical and psychosocial criteria and surgical considerations. The degree of disease severity requiring transplantation for survival has become more apparent as the disparity in survival outcome widens between patients with and without transplant. The contraindications to transplant surgery have been modified over time. Candidate selection is considered in the context of the risks and benefits of the surgical procedure on a case by case basis. The wait for transplant has increased as the growth in the number of candidates for transplant exceeds available donors. As much as 30% of patients die on the UNOS waiting list.

The pulmonary vasodilator properties of potassium channel opening drugs

1. This article reviews the effects of potassium channel opening drugs (KCOs) on blood vessels of the pulmonary circulation. KCOs are effective pulmonary vasodilators in vitro (isolated arteries and perfused lungs) and in vivo in a variety of animal species. They prevent or reverse pulmonary vasoconstriction/contraction induced by a range of vasoconstrictor spasmogens or by alveolar hypoxia. 2. The pulmonary vasorelaxant effects of the KCO drugs are blocked by glibenclamide, do not depend on the endothelium, are dependent on the vasoconstrictor spasmogen used to contract the preparations and are enhanced in preparations taken from pulmonary hypertensive rats. 3. Selectivity for pulmonary compared with systemic vessels is seen in vessels from pulmonary hypertensive rats but not in the absence of pulmonary hypertension. 4. The pulmonary vasodilatation that is induced by (a) endothelium derived hyperpolarising factor, (b) endothelin, (c) increased pulmonary blood flow or (d) prolonged, severe hypoxia is probably due to potassium efflux through the same population of potassium channels as those on which the KCOs act. 5. Acute hypoxic pulmonary vasoconstriction, and also the depolarisation seen in arteries from chronically hypoxic rats, each involve inhibition of potassium efflux through glibenclamide-insensitive potassium channels. 6. It is suggested that the KCOs warrant investigation as possible therapeutic agents in the treatment of pulmonary hypertension.

Effects of two K+ channel openers, aprikalim and pinacidil, on hypoxic pulmonary vasoconstriction

This study investigated the effects of two K+ channel openers, aprikalim and pinacidil, on hypoxic pulmonary vasoconstriction induced in isolated rat lung perfused at constant flow. In order to evaluate the mechanism of the hypoxic vasoconstriction we also studied the effects of an inhibitor of the endothelium-derived relaxing factor (EDRF), NG-nitro-L-arginine methyl ester (100 microM), an inhibitor of the guanylate cyclase, methylene blue (30 microM), two K+ channel blockers, glibenclamide (1 microM) and tetraethylammonium (20 mM). In normoxia, NG-nitro-L-arginine methyl ester, methylene blue, glibenclamide or tetraethylammonium did not enhance significantly the baseline perfusion pressure, suggesting that neither EDRF nor K+ channels are involved in the modulation of the low basal pulmonary vascular tone. In hypoxia, aprikalim and pinacidil (0.03-3 microM) induced a concentration-dependent decrease of pulmonary pressure, exhibiting their spasmolytic effects in acute hypoxia. The hypoxic pressure response was significantly increased by NG-nitro-L-arginine methyl ester, methylene blue and tetraethylammonium, but not by glibenclamide suggesting that EDRF and K+ channels other than ATP-sensitive K+ channels are involved in the modulation of the hypoxic pressure response. The spasmolytic effects of aprikalim and pinacidil (1 microM) were not modified by NG-nitro-L-arginine methyl ester, but were partially reduced by tetraethylammonium and completely abolished by glibenclamide, suggesting that these effects are mainly but not exclusively mediated through ATP-sensitive K+ channel opening.

Mechanisms and pathology of monocrotaline pulmonary toxicity

Monocrotaline (MCT) is an 11-membered macrocyclic pyrrolizidine alkaloid (PA) that causes a pulmonary vascular syndrome in rats characterized by proliferative pulmonary vasculitis, pulmonary hypertension, and cor pulmonale. Current hypotheses of the pathogenesis of MCT-induced pneumotoxicity suggest that MCT is activated to a reactive metabolite(s) in the liver and is then transported by red blood cells (RBCs) to the lung, where it initiates endothelial injury. While several lines of evidence support the requirement of hepatic metabolism for pneumotoxicity, the mechanism and relative importance of RBC transport remain undetermined. The endothelial injury does not appear to be acute cell death but rather a delayed functional alteration that leads to disease of the pulmonary arterial walls by unknown mechanisms. The selectivity of MCT for the lung, as opposed to that of other primarily hepatotoxic PAs, appears likely to be a consequence of the differences in hepatic metabolism and blood kinetics of MCT. A likely candidate for a reactive metabolite of MCT is the dehydrogenation product monocrotaline pyrrole (MCTP). Secondary or phase II metabolism of MCT through glutathione (GSH) conjugation has been characterized recently and appears to represent a detoxification pathway. The role of inflammation in the progression of MCT-induced pulmonary vascular disease is uncertain. Both perivascular inflammation and platelet activation have been proposed as processes contributing to the response of the vascular media. This review presents the experimental evidence supporting these hypotheses and outlines additional questions that arise from them.