The hemodynamic effects of adenosine infusion after experimental right heart infarct in young swine

Lung Circulation

The circulation of the lung is unique both in volume and function. For example, it is the only organ with two circulations: the pulmonary circulation, the main function of which is gas exchange, and the bronchial circulation, a systemic vascular supply that provides oxygenated blood to the walls of the conducting airways, pulmonary arteries and veins. The pulmonary circulation accommodates the entire cardiac output, maintaining high blood flow at low intravascular arterial pressure. As compared with the systemic circulation, pulmonary arteries have thinner walls with much less vascular smooth muscle and a relative lack of basal tone. Factors controlling pulmonary blood flow include vascular structure, gravity, mechanical effects of breathing, and the influence of neural and humoral factors. Pulmonary vascular tone is also altered by hypoxia, which causes pulmonary vasoconstriction. If the hypoxic stimulus persists for a prolonged period, contraction is accompanied by remodeling of the vasculature, resulting in pulmonary hypertension. In addition, genetic and environmental factors can also confer susceptibility to development of pulmonary hypertension. Under normal conditions, the endothelium forms a tight barrier, actively regulating interstitial fluid homeostasis. Infection and inflammation compromise normal barrier homeostasis, resulting in increased permeability and edema formation. This article focuses on reviewing the basics of the lung circulation (pulmonary and bronchial), normal development and transition at birth and vasoregulation. Mechanisms contributing to pathological conditions in the pulmonary circulation, in particular when barrier function is disrupted and during development of pulmonary hypertension, will also be discussed.

Pulmonary blood flow and its distribution in highly trained endurance athletes and healthy control subjects

Pulmonary blood flow (PBF) is an important determinant of endurance sports performance, yet studies investigating adaptations of the pulmonary circulation in athletes are scarce. In the present study, we investigated PBF, its distribution, and heterogeneity at baseline and during intravenous systemic adenosine infusion in 10 highly trained male endurance athletes and 10 untrained but fit healthy controls, using positron emission tomography and [15O]water at rest and during adenosine infusion at supine body posture. Our results indicate that PBF at rest and during adenosine stimulation was similar in both groups (213 ± 55 and 563 ± 138 ml·100 ml−1·min−1 in athletes and 206 ± 83 and 473 ± 212 ml·100 ml−1·min−1 in controls, respectively). Although the PBF response to adenosine was thus unchanged in athletes, overall PBF heterogeneity was reduced from rest to adenosine infusion (from 84 ± 18 to 70 ± 19%, P < 0.05), while remaining unchanged in healthy controls (77 ± 16 to 85 ± 33%, P = 0.4). Additionally, there was a marked gravitational influence on general PBF distribution so that clear dorsal dominance was observed both at rest and during adenosine infusion, but training status did not have an effect on this distribution. Regional blood flow heterogeneity was markedly lower in the high-perfusion dorsal areas, both at rest and during adenosine, in all subjects, but flow heterogeneity in dorsal area tended to further decrease in response to adenosine in athletes. In conclusion, reduced blood flow heterogeneity in response to adenosine in endurance athletes may be a reflection of capillary reserve, which is more extensively recruitable in athletes than in matched healthy control subjects.

Ação da adenosina na circulação pulmonar de pacientes com hipertensão pulmonar primária

INTRODUÇÃO: A adenosina é um nucleosídeo com potente ação vasodilatadora. Apesar de seus efeitos sobre o território arterial pulmonar ser conhecido, seu efeito sobre o território capilar/venoso ainda não foi descrito. OBJETIVO: Estudar o comportamento das resistências arterial e venosa da circulação pulmonar de pacientes com hipertensão pulmonar primária antes e depois da administração de adenosina. MÉTODO: Foram estudados sete pacientes com hipertensão pulmonar primária que apresentaram resposta positiva durante o teste agudo com adenosina. Resistência arterial e resistência venosa foram determinadas pela estimativa da pressão capilar pulmonar realizada através da análise da curva de decaimento da pressão arterial pulmonar, antes e depois da administração da adenosina. RESULTADOS: Após a administração da adenosina, houve um aumento do índice cardíaco (1,71 ± 0,23 para 2,72 ± 0,74 L.min-1.m-2) com concomitante diminuição da resistência vascular pulmonar (2.924 ± 1.060 para 1.975 ± 764 dina.s.cm-5.m-2), sem variações significativas da pressão arterial pulmonar média (75,6 ± 16,8 para 78,1 ± 18,8 mmHg), da pressão de oclusão da artéria pulmonar (15,3 ± 1,5 para 15,4 ± 1,9 mmHg) e da pressão capilar pulmonar (43,8 ± 5,8 para 44,5 ± 4,9 mmHg). A proporção entre a resistência arterial e a resistência vascular pulmonar total também apresentou variação não significativa (50 ± 15 para 49 ± 17%). Estes achados sugerem que a adenosina teve ação não somente sobre o território arterial mas também sobre o território capilar/venoso. CONCLUSÃO: Os autores concluem que o mecanismo de ação da adenosina não é restrito ao território arterial da circulação pulmonar e que este tipo de análise, através da determinação da pressão capilar pulmonar, pode ser útil no estudo das diversas drogas que agem sobre a circulação pulmonar.