Effects of captopril on pulmonary haemodynamics

Systemic hemodynamics and pediatric lung disease: mechanistic links and therapeutic relevance

Chronic lung disease, also known as bronchopulmonary dysplasia, affects thousands of infants worldwide each year. The impact on resources is second only to bronchial asthma, with lung function affected well into adolescence. Diagnostic and therapeutic constructs have almost exclusively focused on pulmonary architecture (alveoli/airways) and pulmonary hypertension. Information on systemic hemodynamics indicates major artery thickness/stiffness, elevated systemic afterload, and/or primary left ventricular dysfunction may play a part in a subset of infants with severe neonatal-pediatric lung disease. Understanding the underlying principles with attendant effectors would aid in identifying the pathophysiological course where systemic afterload reduction with angiotensin-converting enzyme inhibitors could become the preferred treatment strategy over conventional pulmonary artery vasodilatation.NEW & NOTEWORTHY Extremely preterm infants are at a higher risk of developing severe bronchopulmonary dysplasia. In a subset of infants, diuretic and pulmonary vasodilator therapy is ineffective. Recent information points toward systemic hemodynamic disease (systemic arterial stiffness and left ventricular dysfunction) as a contributor via back-pressure changes. Mechanistic links include heightened renin angiotensin aldosterone system activity, inflammation, and oxygen toxicity. Angiotensin-converting enzyme inhibition may be operationally more suited compared with induced pulmonary artery vasodilatation.

Control of pulmonary vascular tone during exercise in health and pulmonary hypertension

Despite the importance of the pulmonary circulation as a determinant of exercise capacity in health and disease, studies into the regulation of pulmonary vascular tone in the healthy lung during exercise are scarce. This review describes the current knowledge of the role of various endogenous vasoactive mechanisms in the control of pulmonary vascular tone at rest and during exercise. Recent studies demonstrate an important role for endothelial factors (NO and endothelin) and neurohumoral factors (noradrenaline, acetylcholine). Moreover, there is evidence that natriuretic peptides, reactive oxygen species and phosphodiesterase activity can influence resting pulmonary vascular tone, but their role in the control of pulmonary vascular tone during exercise remains to be determined. K-channels are purported end-effectors in control of pulmonary vascular tone. However, K(ATP) channels do not contribute to regulation of pulmonary vascular tone, while the role of K(V) and K(Ca) channels at rest and during exercise remains to be determined. Pulmonary hypertension is associated with alterations in pulmonary vascular function and structure, resulting in blunted pulmonary vasodilatation during exercise and impaired exercise capacity. Although there is a paucity of studies pertaining to the regulation of pulmonary vascular tone during exercise in idiopathic pulmonary hypertension, the few studies that have been performed in models of pulmonary hypertension secondary to left ventricular dysfunction suggest altered control of pulmonary vascular tone during exercise. Since the increased pulmonary vascular tone during exercise limits exercise capacity, future studies are needed to investigate the vasomotor mechanisms that are responsible for the blunted exercise-induced pulmonary vasodilatation in pulmonary hypertension.

Angiotensin-converting enzyme inhibitor preserves p21 and endothelial nitric oxide synthase expression in monocrotaline-induced pulmonary arterial hypertension in rats

BACKGROUND

Pulmonary arterial hypertension (PAH) is associated with structural changes in the pulmonary vasculature characterized by the proliferation of cellular components of the vessels. ACE inhibitor (ACEI) may have beneficial effects in treating PAH, but its precise mechanism of action in the remodeling process is unclear. p21 is a cyclin-dependent kinase inhibitor that may have a protective role in this process by inhibiting cellular proliferation. Endothelial nitric oxide synthase (eNOS) has also been shown to be protective by its vasodilatory effect. Therefore, we investigated whether expression of p21 and eNOS was modulated by ACEI treatment in a rat model.

METHODS AND RESULTS

Monocrotaline (MCT) was administered to 2 groups of Sprague-Dawley rats fed a high-cholesterol diet, ie, one group received MCT concomitantly with enalapril treatment (MCT(+)/ACEI(+) rats), and the other group did not receive enalapril (MCT(+)/ACEI(-) rats). After 5 weeks, MRI showed right ventricular hypertrophy in MCT(+)/ACEI(-) rats. MCT(+)/ACEI(+) rats showed a preserved right ventricular morphology. Isolated pulmonary perfusion studies showed that ACEI significantly upregulated NO production, as measured by nitrite levels. Addition of N-methyl-D-glucamine dithiocarbamate-Fe solution, an NO-trapping agent, reversed the basal vasodilatory effect of ACEI in the pulmonary vasculature. Immunoblot analysis showed decreased p21 and eNOS expression in the lung in MCT(+)/ACEI(-) rats, whereas their expression was preserved with enalapril treatment.

CONCLUSIONS

ACEI suppresses the development of MCT-induced PAH in rats. The mechanism of action might involve the preservation of p21 and eNOS expression. Both p21 and endothelium-derived NO appear to have protective roles in the development of PAH.

Relationship between mixed venous oxygen saturation and cardiac index in patients with chronic congestive heart failure

The use of mixed venous oxygen saturation (SvO2) in patients with chronic congestive heart failure (CHF) has been advocated to analyze the action of therapy on cardiac index (CI). To evaluate the relationship between CI and SvO2, ten CHF patients (mean age 65 years) were studied before and one, two, three, four (T4), six, eight and 24 hours after oral administration of an angiotensin converting enzyme (ACE) inhibitor (perindopril, 4 mg). At T4, a 12 percent increase in CI (p less than 0.01) was associated with a 16 percent decrease in arteriovenous oxygen difference (p less than 0.01), a 13 percent increase in mixed venous oxygen pressure (PvO2) (p less than 0.01), and a 9 percent increase in SvO2 (p less than 0.05) with no significant change in arterial oxygen pressure. There was no correlation between CI and SvO2 (r = 0.22) and between CI and PvO2 (r = 0.23). Individual analyses were performed and patients were divided into two groups based on CI versus SvO2 r value; group 1, n = 6, r greater than 0.65 (0.65-0.90), group 2, n = 4, r less than 0.65 (0.14-0.20). The lack of correlation in group 2 was due to a drug-dependent increase in oxygen consumption (VO2) +18 percent vs -3 percent in group 1 (p less than 0.05) associated with a lack of increase in PvO2 +3 percent vs +14 percent in group 1 (p less than 0.05) despite a similar increase in oxygen availability +19 percent versus +16 percent. It was concluded that (1) a correlation between CI and SvO2 is not found in every patient with CHF; (2) the lack of correlation in four out of our ten patients was due to an associated and significant increase in CI and VO2 in group 2; (3) group 2 patients probably had an important oxygen debt before treatment; (4) SvO2 cannot be used instead of CI to determine the hemodynamic consequences of the use of cardiovascular drugs.

Captopril effects on pulmonary and systemic hemodynamics in chronic cor pulmonale

A placebo-controlled single-blind study on acute effects of captopril on hypoxic pulmonary hypertension was performed in 15 patients with severe chronic obstructive lung disease recovering from right heart failure. Ten patients received active drug (25 mg captopril orally), five patients received placebo and served as control subjects. Before drug administration, there was no difference in lung function data and pulmonary hemodynamics between patients in both groups. Captopril produced highly significant fall in systemic arterial pressure. No change in breathing frequency, minute ventilation, and pulmonary gas exchange was observed. There was no significant change in studied variables after placebo. The presented data suggest that captopril does not decrease pulmonary vascular resistance in patients with hypoxic pulmonary hypertension. A fall in pulmonary wedge pressure reflects a decrease in left ventricular afterload.