Friedrich C. Blumberg

Impaired cardiac autonomic control relates to disease severity in pulmonary hypertension

Pulmonary arterial hypertension (PAH) results in chronic right heart failure, which is associated with an increase in sympathetic tone. This may adversely affect cardiac autonomic control. We investigated the changes in cardiac autonomic nervous activity in relation to disease severity in patients with PAH. In 48 patients with PAH (median World Health Organization class III, pulmonary artery pressure 52±14 mmHg, pulmonary vascular resistance 1,202±718 dyn·s·cm−5, cardiac index 2.0±0.8 L·min−1·m−2) and 41 controls, cardiac autonomic nervous activity was evaluated by measurement of heart rate variability (HRV) and baroreflex sensitivity. All patients underwent cardiopulmonary exercise testing (peak oxygen uptake 13.2±5.1 mL·kg−1·min−1, minute ventilation/carbon dioxide production slope 47±16). In patients with PAH, spectral power of HRV was reduced in the high-frequency (239±64 versus 563±167 ms2), low-frequency (245±58 versus 599±219 ms2) and very low-frequency bands (510±149 versus 1106±598 ms2; all p<0.05). Baroreflex sensitivity was also blunted (5.8±0.6 versus 13.9±1.2 ms·mmHg−1; p<0.01). The reduction in high-frequency (r = 0.3, p = 0.04) and low-frequency (r = 0.33, p = 0.02) spectral power and baroreflex sensitivity (r = 0.46, p<0.01) was related to the reduction in peak oxygen uptake. Patients with PAH have a marked alteration in cardiac autonomic control that is related to exercise capacity and may, therefore, serve as an additional marker of disease severity.

Differential expression of cardiac ANP and BNP in a rabbit model of progressive left ventricular dysfunction

OBJECTIVE Activation of atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) is considered a hallmark of myocardial remodeling. To determine magnitude and relative proportion of activation during the progression to heart failure, we assessed ANP and BNP gene expression in atrial and left ventricular (LV) tissue in a newly developed model of progressive rapid ventricular pacing-induced heart failure in rabbits. METHODS Six animals underwent progressive pacing with incremental rates (330 beats per min (bpm) to 380 bpm over 30 days), resulting in congestive heart failure (CHF). Five animals underwent pacing at 330 bpm for 10 days only (early LV dysfunction, ELVD) and five additional animals served as control group (CTRL). RESULTS ELVD was characterized by decreased mean arterial pressure (P=0.05 vs. CTRL) as well as significantly impaired LV function (LV fractional shortening (FS) P<0.01 vs. CTRL) and dilatation (P<0.01 vs. CTRL). CHF was characterized by further decreased mean arterial pressure (P<0.01 vs. ELVD), further impaired LV function (FS P<0.03 vs. ELVD) and dilatation (P<0.01 vs. CTRL). In control animals, significant ANP expression was observed only in atrial tissue (P<0.02 vs. BNP) while BNP expression was ubiquitous but marginal (LV P<0.05 vs. ANP). In ELVD, activation of ANP (atria and LV P<0.05 vs. CTRL) and BNP (atria P<0.05 vs. CTRL, LV n.s.) was observed. In CHF, LV-BNP increased further markedly (P<0.01 vs. CTRL, P<0.05 vs. ELVD) while atrial ANP and BNP expression as well as LV ANP expression remained unchanged (all P=n.s. vs. ELVD). CONCLUSION The current studies demonstrate differential activation of atrial and LV ANP and BNP under normal conditions and during the progression to heart failure and provide a molecular basis for the superiority of BNP as marker of LV dysfunction and CHF.

Impact of right ventricular reserve on exercise capacity and survival in patients with pulmonary hypertension.

Pulmonary hypertension is a clinical syndrome characterized by a progressive increase in pulmonary vascular resistance leading to right ventricular failure and death. Pulmonary arterial hypertension (PAH) and chronic thromboembolic pulmonary hypertension (CTEPH) are key subgroups of this disorder with comparable clinical and pathological findings. Resting pulmonary haemodynamics correlate only moderately with functional parameters and do not predict prognosis in these patients sufficiently accurately. We therefore correlated exercise haemodynamics with peak oxygen uptake (peakVO2) and determined their prognostic significance.

Incremental prognostic value of cardiopulmonary exercise testing and resting haemodynamics in pulmonary arterial hypertension

BACKGROUND Pulmonary arterial hypertension (PAH) is a fatal disease despite recent treatment advances. Individual risk stratification is important. Exercise capacity and invasive haemodynamic data are both relevant, but data on the combined prognostic power are lacking. METHODS 226 consecutive patients with idiopathic or familial PAH were included at seven specialised tertiary centres. All patients underwent right heart catheterization and cardiopulmonary exercise testing (CPET). RESULTS During follow-up (1508 ± 1070 days) 72 patients died and 30 underwent transplantation. On multivariate analysis percentage of predicted peak oxygen uptake (%predicted peak VO2 [risk ratio 0.95]), pulmonary vascular resistance (PVR [1.105,]) and increase in heart rate during exercise (ΔHR [0.974]) were independent prognostic predictors (all p<0.0001). Peak VO2 allowed for risk stratification with a survival of 100, 92.9, 87.4 and 69.6% at 1 year and 97.7, 63.2, 41 and 23% at 5 years for the 4th, 3rd, 2nd and 1st quartiles, respectively. Dichotomizing by median peak VO2 and intra-group median PVR showed a worse 1-year survival for patients with low peak VO2/higher PVR compared to patients with low peak VO2/low PVR, high peak VO2/high PVR and high peak VO2/low PVR (65 vs. 93, 93, 100%, p<0.001). At 10 years survival was different for all 4 subgroups (19 vs. 25 vs. 48 vs. 75%, adjusted p<0.05). CONCLUSIONS Peak VO2, PVR and ΔHR independently predict prognosis in patients with PAH. Low peak VO2, high PVR and low ΔHR refer to poor prognosis. Combined use of peak VO2 and PVR provides accurate risk stratification underlining the complementary prognostic information from cardiopulmonary exercise testing and resting invasive haemodynamic data.

Improvement of bleomycin-induced pulmonary hypertension and pulmonary fibrosis by the endothelin receptor antagonist Bosentan

RATIONALE There is evidence that endothelin plays a key role in the development of pulmonary hypertension (PH) in pulmonary fibrosis (PF). However, the functional consequence of the unselective endothelin receptor antagonist Bosentan in PH and PF has not yet been studied. Therefore, we investigated the effects of Bosentan on the development of PH in the model of Bleomycin-induced PF in rats. METHODS Adult male Wistar rats were randomly assigned to the following groups: untreated animals (controls), Bleomycin-induced PF (Bleomycin) and Bleomycin-induced PF treated with Bosentan (Bleomycin+Bosentan). Exercise capacity was evaluated by treadmill exercise testing. PH was assessed by right ventricular systolic pressure (RVSP) and right ventricular hypertrophy. For quantification of PF the hydroxyproline content in lung tissue (HPC) was measured. RESULTS Compared to controls, animals with Bleomycin-induced PF showed a significant reduction in exercise capacity (44% vs. 100%), significantly higher RVSP (65 mmHg vs. 23 mmHg), significantly more right ventricular hypertrophy (0.55 vs. 0.24) and significantly higher HPC (60.5 vs. 14.8). Bosentan treatment in animals with Bleomycin-induced PF resulted in significantly greater exercise capacity (98% vs. 44%) and a trend towards lower RVSP (52 mmHg vs. 65 mmHg), significantly less right ventricular hypertrophy (0.34 vs. 0.55) and significantly lower HPC (16.7 vs. 60.5) compared to untreated Bleomycin-induced PF. CONCLUSION Application of Bosentan in Bleomycin rats resulted in significantly higher exercise capacity as a result of improvements in PH and PF.

Vascular remodeling and growth factor gene expression in the rat lung during hypoxia

Recent studies suggest that the vasoactive peptides endothelin-1 and -3 and the mitogens VEGF and PDGF-A and -B could be involved in the pathogenesis of hypoxic pulmonary hypertension. We were interested to investigate whether these peptides could also be involved in the vascular remodeling occurring during chronic hypoxia (10% oxygen; 1 and 3 weeks) in the rat. Hypoxia increased significantly systolic right ventricular pressure and typical morphological signs of vascular remodeling were found. This was accompanied by increased ET-1 and the ET-3 mRNA expression after acute (6 h; P < 0.05) and chronic hypoxia of 1 (P < 0.05) and 3 weeks (P < 0.05). In contrast, we found no effects of hypoxia on the gene expression of VEGF and PDGF-A and -B in the lung. Our findings indicate that ET-3 in addition to ET-1 could be involved in the process of hypoxia-induced vascular remodeling, whereas it appears less likely that the mitogens VEGF and PDGF-A and -B are essentially involved in the pathogenesis of hypoxic pulmonary hypertension.

Increased pulmonary prostacyclin synthesis in rats with chronic hypoxic pulmonary hypertension

OBJECTIVE The regulation of pulmonary prostacyclin synthesis is not completely understood. We tested the hypothesis that prostacyclin production is predominantly stimulated by hemodynamic factors, such as increased shear-stress, and is thus increased in rats with chronic hypoxic pulmonary hypertension. METHODS To this end, we determined pulmonary prostacyclin synthase (PGIS) gene expression, circulating levels of the stable prostacyclin metabolite 6-keto prostaglandin F(1alpha) (6-keto-PGF(1alpha)), pulmonary endothelin (ET)-1 gene expression, and ET-1 plasma levels in rats exposed to 4 weeks of hypoxia (10% O(2)) in the presence or absence of either the nitric oxide (NO) donor molsidomine (MD, 15 mg/kg/day) or the ET-A receptor antagonist LU135252 (LU, 50 mg/kg/day). RESULTS Right ventricular systolic pressure (RVSP), the cross-sectional medial vascular wall area of pulmonary arteries, and ET-1 production increased significantly during hypoxia. PGIS mRNA levels increased 1.7-fold, and 6-keto-PGF(1alpha) plasma levels rose from 8.2+/-0.8 to 12.2+/-2.2 ng/ml during hypoxia (each P<0.05 vs. normoxic controls). MD and LU reduced RVSP and pulmonary vascular remodeling similarly (each P<0.05 vs. hypoxia), but only MD inhibited pulmonary ET-1 formation (P<0.05 vs. hypoxia). Nevertheless, both drugs attenuated the increase in PGIS gene expression and plasma 6-keto-PGF(1alpha) levels (each P<0.05 vs. hypoxia). CONCLUSION Our data suggest that prostacyclin production in hypertensive rat lungs is predominantly increased by hemodynamic factors while hypoxia, NO and ET-1 per are less important stimuli, and that this increase may serve as a compensatory mechanism to partially negate the hypoxia-induced elevation in pulmonary vascular tone.

Effects of simvastatin on pulmonary fibrosis, pulmonary hypertension and exercise capacity in bleomycin-treated rats

Pulmonary fibrosis is often complicated by pulmonary hypertension. Statins reduce fibroblast activity in vitro and pulmonary hypertension in vivo. We investigated whether Simvastatin exerts beneficial effects on pulmonary fibrosis and pulmonary hypertension in Bleomycin‐treated rats in vivo.

ANP gene expression in rat hearts during hypoxia

Abstract It is unclear whether the increase in plasma atrial natriuretic peptide (ANP) concentration during hypoxia is due to direct, hypoxia-induced upregulation of ANP secretion in the heart, or to pressure overload of the right ventricle (RV) following hypoxia-induced pulmonary hypertension. To test the hypothesis that hypoxia leads to an early upregulation of the ANP gene, we examined the influence of acute and prolonged inspiratory hypoxia (6 h, 1 or 3 weeks) on the expression of ANP messenger ribonucleic acid (mRNA) in rat heart and compared the results with the expression of the ANP gene after acute pressure overload induced by experimental coarctation of the main pulmonary artery. As a molecular marker for hypertrophy we determined the ratio of α- and β-myosin gene expression. Hypoxia increased systolic RV pressure from 20.0 ± 1.6 mmHg to 27.8 ± 1.6 mmHg (P < 0.01) and 41.6 ± 2.1 mmHg (P < 0.05) after 1 and 3 weeks hypoxia respectively. The ANP plasma concentration did not change significantly after 6 h or 1 week: 232 ± 21 pg/ml (control), 246 ± 25 pg/ml (6 h), 268 ± 25 pg/ml (1 week), but increased significantly after 3 weeks hypoxia (446.8 ± 99.56 pg/ml; P < 0.05). ANP mRNA levels in different regions of the heart did not change after 6 h or 1 week hypoxia. After 3 weeks hypoxia ANP mRNA had increased 2.7-fold in the RV (P < 0.05), 4.2-fold in the left ventricle (LV, P < 0.05), 3.5-fold in the septum (S, P < 0.05) and about 1.4-fold in the right (n.s.) and left atrium (n.s.). Relative ventricular masses increased significantly only for the RV (190%, P < 0.05) during hypoxia. The β/α-myosin mRNA ratio did not change after 6 h hypoxia but, contrary to ANP gene expression, increased after just 1 week (6.1-fold in RV, 7.8-fold in LV, 6-fold in S; P < 0.05) and was more pronounced in the RV after 3 weeks (9.4-fold in RV, 7.6-fold in LV, 9.1-fold in S; P < 0.05). The increase in the β/α-myosin mRNA ratio in the LV contrasts with a lack of increase in relative ventricular mass. Acute pressure overload in the RV after pulmonary arterial banding significantly increased ANP-mRNA and the β/α-myosin mRNA ratio after 1 day in the RV. In the LV ANP mRNA was unchanged. The delayed upregulation of the ANP gene suggests that hypoxia per se is not a significant stimulus for ANP gene expression in the heart and that hypoxia-induced ANP-gene expression in the heart is regulated predominantly by the increase in RV afterload due to hypoxia-induced increased pulmonary pressure. The upregulation of ANP and β-myosin mRNA in the LV during chronic hypoxia has yet to be elucidated.

Effects of chronic hypoxia on renal PDGF-A, PDGF-B, and VEGF gene expression in rats.

Background: There is evidence from in vitro studies to suggest that the genes of platelet-derived growth factor (PDGF), and vascular endothelial growth factor (VEGF) are, like the erythropoietin gene, regulated by oxygen tension. Hypoxia-induced stimulation of, for example, PDGF or VEGF might be involved in the pathogenesis of acute or chronic renal failure and in renal ‘inflammatory’ diseases (glomerulonephritis, vasculitis, allograft rejection). Methods: Male Wistar rats were exposed to chronic normobaric hypoxia (10% O2, 90% N2) for 4 weeks. Additional groups of rats were treated with the endothelin receptor antagonist LU13525 and the NO donor molsidomine. Renal mRNA levels of PDGF-A, PDGF-B, and VEGF were semiquantitated using RNase protection assays. Results: Renal gene expression of PDGF-A and PDGF-B was neither affected by 2 or 4 weeks of hypoxia nor by concomitant treatment with LU135252 or molsidomine. Chronic hypoxia did also not change VEGF gene expression; however, concomitant treatment with LU135252 increased all VEGF subtypes (188, 164, 120). Conclusions: The findings of the present study suggest that renal PDGF and VEGF gene expression in vivo during chronic hypoxia for 2 and 4 weeks is not sensitive to tissue hypoxia in contrast to cell culture experiments. During chronic hypoxia with concomitant blockade of endothelin receptors, all VEGF subtypes were increased, suggesting an inhibitory action of endothelins with regard to renal VEGF gene expression.