Efeitos da morte cerebral na microvasculatura pulmonar em um modelo experimental de doador de pulmão / Brain death effects on lung microvasculature in an experimental model of lung donor

RESUMO Objetivo A morte cerebral (MC) desencadeia alterações hemodinâmicas e inflamatórias importantes, comprometendo a viabilidade dos órgãos empregados em transplantes. Para compreender melhor as alterações microcirculatórias nos pulmões de doadores com MC, o presente estudo investigou a microcirculação pulmonar em um modelo de roedor com MC via microscopia intravital. Métodos Ratos Wistar machos foram anestesiados e ventilados mecanicamente. Eles foram submetidos a trepanação e a MC induzida por meio do aumento da pressão intracraniana. Os ratos do grupo Sham (SH), utilizado como controle, foram submetidos apenas à trepanação. Em ambos os grupos, foram monitorados o O2 expiratório e o CO2, e, após 3 horas, foi realizada a toracotomia e criada uma janela para observar a superfície pulmonar usando o sistema de microscopia intravital. As expressões pulmonares das moléculas de adesão intercelular (ICAM)-1 e da óxido nítrico-sintase endotelial (eNOS) foram avaliadas por imuno-histoquímica, e as citocinas foram medidas em amostras pulmonares. Resultados Três horas após os procedimentos cirúrgicos, a perfusão pulmonar foi de 73% no grupo SH. Por outro lado, os animais com MC apresentaram uma importante diminuição na perfusão do órgão para 28% (p = 0,036). O comprometimento microcirculatório pulmonar após a indução de MC foi associado a um aumento do número de leucócitos recrutados para o tecido pulmonar, além de uma redução na expressão de eNOS e um aumento na expressão de ICAM-1 nas células endoteliais do pulmão. Os ratos com MC apresentaram valores mais elevados de O2 expiratório e valores mais baixos de CO2 em comparação com os animais SH após 3 horas de monitorização. Conclusões Os dados apresentados demonstraram que a MC desencadeia uma importante hipoperfusão e inflamação nos pulmões, comprometendo a microcirculação pulmonar do doador.

ABSTRACT Objective Brain death (BD) triggers important hemodynamic and inflammatory alterations, compromising the viability of organs suitable for transplantation. To better understand the microcirculatory alterations in donor lungs caused by BD. The present study investigated the pulmonary microcirculation in a rodent model of BD via intravital microscopy. Methods Male Wistar rats were anaesthetized and mechanically ventilated. They were trepanned and BD was induced through the increase in intracranial pressure. As control group, sham-operated (SH) rats were trepanned only. In both groups, expiratory O2 and CO2 were monitored and after three hours, a thoracotomy was performed, and a window was created to observe the lung surface using an epi-fluorescence intravital microscopy. Lung expression of intercellular adhesion molecule (ICAM)-1 and endothelial nitric oxide synthase (eNOS) was evaluated by immunohistochemistry, and cytokines were measured in lung samples. Results Three hours after the surgical procedures, pulmonary perfusion was 73% in the SH group. On the other hand, BD animals showed an important decrease in organ perfusion to 28% (p = 0.036). Lung microcirculatory compromise after BD induction was associated with an augmentation of the number of leukocytes recruited to lung tissue, and with a reduction in eNOS expression and an increase in ICAM-1 expression on lung endothelial cells. BD rats showed higher values of expiratory O2 and lower values of CO2 in comparison with SH animals after three hours of monitoring. Conclusion Data presented showed that BD triggers an important hypoperfusion and inflammation in the lungs, compromising the donor pulmonary microcirculation.

SPECT and PET imaging of adrenomedullin receptors: a promising strategy for studying pulmonary vascular diseases.

Circulating adrenomedullin (AM) levels are elevated in several cardiovascular diseases, including pulmonary vascular diseases causing pulmonary hypertension. To date the perfusion agent 99mTc-albumin macroaggregates (MAA) is the only approved radiopharmaceutical used for imaging of pulmonary circulation. Unlike 99mTc-MAA, imaging the AM receptors involves a molecular process dependent on the density of the receptors and the affinity of specific radioligands. The AM receptors are abundantly distributed in lung capillaries and its integrity provides protection in the development of pulmonary vascular diseases. This review summarizes the development and characterization of radioligands for in vivo imaging of AM receptors as an early predictor of the onset of a pulmonary vascular disease.

Effects of high PEEP and fluid administration on systemic circulation, pulmonary microcirculation, and alveoli in a canine model.

This study aimed to determine the response of systemic circulation, pulmonary microcirculation, and alveoli to high positive end-expiratory pressure (PEEP) in a canine model. This study was conducted in nine mixed-breed dogs on mechanical ventilation under anesthesia. The PEEP was initially set at 5 cmH2O (PEEP5), the PEEP was then increased to 25 cmH2O (PEEP25), and then saline was used for fluid loading. Data were obtained at the following time points: PEEP5; PEEP25 prefluid loading; and PEEP25 postfluid loading. The images of subpleural lung microcirculation were assessed by sidestream dark-field microscopy, and the hemodynamic data were collected from pulse contour waveform-derived measurements. Compared with PEEP5, the lung microvascular flow index (MFI, 2.3 ± 0.8 versus 0.9 ± 0.8, P = 0.001), lung perfused vessel density (PVD, 4.2 ± 2 versus 1.5 ± 1.8, P = 0.004), lung proportion of perfused vessel (PPV, 93 ± 14 versus 40 ± 4, P = 0.003), cardiac output (2.5 ± 0.6 versus 1.4 ± 0.5, P = 0.001), and mean blood pressure (116 ± 24 versus 91 ± 31, P = 0.012) were significantly lower at PEEP25 prefluid loading. After fluid loading, there were no significant differences in cardiac output or mean arterial pressure between the PEEP5 and PEEP25 postfluid loading levels. However, the lung microcirculatory MFI, PVD, and PPV at PEEP25 postfluid loading remain lower than at PEEP5. A significant increase in septal thickness was found at PEEP25 postfluid loading relative to septal thickness at PEEP25 prefluid loading (25.98 ± 5.31 versus 40.76 ± 7.9, P = 0.001). Under high PEEP, systemic circulation was restored after fluid loading, but lung microcirculation was not. Moreover, the septal thickness of alveoli significantly increased after fluid loading.NEW & NOTEWORTHY An excessively high positive end-expiratory pressure (PEEP) can impair the systemic circulation and alveolar microcirculation. In the high-PEEP condition, fluid loading restored the systemic circulation but did not affect the impaired lung microcirculation. The septal thickness of the alveoli significantly increased after fluid loading in the high-PEEP condition.

Increased pulmonary arteriolar tone associated with lung oxidative stress and nitric oxide in a mouse model of Alzheimer's disease.

Vascular dysfunction and decreased cerebral blood flow are linked to Alzheimer's disease (AD). Loss of endothelial nitric oxide (NO) and oxidative stress in human cerebrovascular endothelium increase expression of amyloid precursor protein (APP) and enhance production of the Aß peptide, suggesting that loss of endothelial NO contributes to AD pathology. We hypothesize that decreased systemic NO bioavailability in AD may also impact lung microcirculation and induce pulmonary endothelial dysfunction. The acute effect of NO synthase (NOS) inhibition on pulmonary arteriolar tone was assessed in a transgenic mouse model (TgAD) of AD (C57BL/6-Tg(Thy1-APPSwDutIowa)BWevn/Mmjax) and age-matched wild-type controls (C57BL/6J). Arteriolar diameters were measured before and after the administration of the NOS inhibitor, L-NAME Lung superoxide formation (DHE) and formation of nitrotyrosine (3-NT) were assessed as indicators of oxidative stress, inducible NOS (iNOS) and tumor necrosis factor alpha (TNF-α) expression as indicators of inflammation. Administration of L-NAME caused either significant pulmonary arteriolar constriction or no change from baseline tone in wild-type (WT) mice, and significant arteriolar dilation in TgAD mice. DHE, 3-NT, TNF-α, and iNOS expression were higher in TgAD lung tissue, compared to WT mice. These data suggest L-NAME could induce increased pulmonary arteriolar tone in WT mice from loss of bioavailable NO In contrast, NOS inhibition with L-NAME had a vasodilator effect in TgAD mice, potentially caused by decreased reactive nitrogen species formation, while significant oxidative stress and inflammation were present. We conclude that AD may increase pulmonary microvascular tone as a result of loss of bioavailable NO and increased oxidative stress. Our findings suggest that AD may have systemic microvascular implications beyond central neural control mechanisms.