Pulmonary hemodynamics following acute atelectasis

Ammonia exposure by intratracheal instillation causes severe and deteriorating lung injury and vascular effects in mice

OBJECTIVE

Ammonia (NH₃) is a corrosive alkaline gas that can cause life-threatening injuries by inhalation. The aim was to establish a disease model for NH₃-induced injuries similar to acute lung injury (ALI) described in exposed humans and investigate the progression of lung damage, respiratory dysfunction and evaluate biomarkers for ALI and inflammation over time.

METHODS

Female BALB/c mice were exposed to an NH₃ dose of 91.0 mg/kg·bw using intratracheal instillation and the pathological changes were followed for up to 7 days.

RESULTS

NH₃ instillation resulted in the loss of body weight along with a significant increase in pro-inflammatory mediators in both bronchoalveolar lavage fluid (e.g. IL-1β, IL-6, KC, MMP-9, SP-D) and blood (e.g. IL-6, Fibrinogen, PAI-1, PF4/CXCL4, SP-D), neutrophilic lung inflammation, alveolar damage, increased peripheral airway resistance and methacholine-induced airway hyperresponsiveness compared to controls at 20 h. On day 7 after exposure, deteriorating pathological changes such as increased macrophage lung infiltration, heart weights, lung hemorrhages and coagulation abnormalities (elevated plasma levels of PAI-1, fibrinogen, endothelin and thrombomodulin) were observed but no increase in lung collagen. Some of the analyzed blood biomarkers (e.g. RAGE, IL-1β) were unaffected despite severe ALI and may not be significant for NH₃-induced damages.

CONCLUSIONS

NH₃ induces severe acute lung injuries that deteriorate over time and biomarkers in lungs and blood that are similar to those found in humans. Therefore, this model has potential use for developing diagnostic tools for NH₃-induced ALI and for finding new therapeutic treatments, since no specific antidote has been identified yet.

Pulmonary Hypertension in Left Heart Disease

Pulmonary hypertension is common in left heart disease and is related most commonly to passive back transmission of elevated left atrial pressures. Some patients, however, may develop pulmonary vascular remodeling superimposed on their left-sided heart disease. This review provides a contemporary appraisal of existing criteria to diagnose a precapillary component to pulmonary hypertension in left heart disease as well as discusses etiologies, management issues, and future directions.

Association between right-sided cardiac function and ultrasound-based pulmonary congestion on acutely decompensated heart failure: findings from a pooled analysis of four cohort studies

BACKGROUND

Right ventricular (RV) dysfunction and RV-pulmonary artery (PA) uncoupling are associated with the development of pulmonary congestion during exercise. However, there is limited information regarding the association between these right-sided cardiac parameters and pulmonary congestion in acutely decompensated heart failure (HF).

METHODS

We performed an individual patient meta-analysis from four cohort studies of hospitalized patients with HF who had available lung ultrasound (B-lines) data on admission and/or at discharge. RV function was assessed by tricuspid annular plane systolic excursion (TAPSE), RV-PA coupling was defined as the ratio of TAPSE to PA systolic pressure (PASP).

RESULTS

Admission and discharge cohort included 319 patients (75.8 ± 10.1 years, 46% women) and 221 patients (77.9 ± 9.0 years, 47% women), respectively. Overall, higher TAPSE was associated with higher ejection fraction, lower PASP, b-type natriuretic peptide and B-line counts. By multivariable analysis, worse RV function or RV-PA coupling was associated with higher B-line counts on admission and at discharge, and with a less reduction in B-line counts from admission to discharge. Higher B-line counts at discharge were associated with a higher risk of the composite of all-cause mortality and/or HF re-hospitalization [adjusted-HR 1.13 (1.09-1.16), p < 0.001]. Furthermore, the absolute risk increase related to high B-line counts at discharge was higher in patients with lower TAPSE.

CONCLUSIONS

In patients with acutely decompensated HF, impaired RV function and RV-PA coupling were associated with severe pulmonary congestion on admission, and less resolution of pulmonary congestion during hospital stay. Worse prognosis related to residual pulmonary congestion was enhanced in patients with RV dysfunction. TAPSE, tricuspid annular plane systolic excursion; PASP, pulmonary artery systolic pressure.

Methylprednisolone reduces vascular resistance in hypoxic and atelectatic lungs

The effect of pharmacological doses of methylprednisolone (MP) on the pulmonary vasoconstrictor response to hypoxia has been investigated in two groups of isolated rat lung preparations, one consisting of ventilated, and the other of atelectatic lungs. In both groups, MP reduced the vasoconstrictor response to hypoxia in a dose-dependent fashion. At a perfusate concentration of 3 mmol/l of MP, the response was reduced by about 80%. On the contrary, the vasoconstrictor response to injections of standardized doses of angiotensin II, used as an independent vasoconstrictor substance, were not significantly changed by MP, even when administered at a concentration which completely abolished the response to hypoxia. We suggest that MP inhibits the pulmonary vasoconstrictor response to hypoxia without influencing the general reactivity of the pulmonary vascular bed.

Vascular resistance in atelectatic lungs: effects of inhalation anesthetics

We have investigated the relative contribution of mechanical obstruction and hypoxia-induced vasoconstriction to the increased pulmonary vascular resistance (PVR) in atelectatic lungs. For this purpose we have utilized the previous observation that inhalation anesthetics inhibit the vasoconstrictor response to pulmonary hypoxia. The effects of halothane, enflurane and ether on PVR in atelectatic lungs have been explored. Two pairs of isolated rat lungs were perfused in series at constant flow. One of the preparations was made atelectatic by airway occlusion subsequent to ventilation with a high PO2 gas (95% O2). Ventilation of the other preparation continued with hypoxic gas (2% O2), resulting in a gradual increase in PVR in both preparations. When maximum PVR was reached, one of the above inhalation anesthetics was administered to the atelectatic lungs via the ventilated lung preparation. This caused a dose-dependent, reversible reduction of PVR. The same effect was observed when pulmonary arterial PO2 was increased (greater than 66.5 kPa). Histological examination revealed that two out of four preparations were completely atelectatic 1 h after airway occlusion, whereas atelectasis was nearly complete in the other two. In two groups, airways were occluded for 1 h. In the first group PVR increased to 163% (median) above baseline level, as found during ventilation with high PO2. High arterial PO2 reduced PVR in the atelectatic lungs to 50% (median) above baseline, whereas papaverine induced a further PVR reduction, to 7% (median) above baseline. In the other group, papaverine was given before airway occlusion, and PVR increased to 10% (median) above baseline. Comparison of the two groups shows that mechanical obstruction accounts for about 6% (10/163) of the overall rise in PVR during atelectasis.

Changes in the pulmonary circulation after bronchial occlusion in anesthetized dogs and cats

The effects of bronchial occlusion on the pulmonary circulation were studied in anesthetized cats and dogs. Immediately after occlusion, blood flow fell rapidly at normal pulmonary arterial pressure (–71% cats, –54% dogs), and in constant flow perfusion experiments, perfusion pressure rose (+50% cats, +28% dogs). These resistance changes were reversed by vasodilator drugs, alkali, or perfusion of the lung with arterial blood. We concluded that an active mechanism, probably an increase in vasomotor tone, was involved; a mechanical process would not be reversed in this way. Pulmonary venous Po 2 was the factor most closely related to the increase in resistance. In collapsing "oxygen-filled" lobes, compared with "air-filled" lobes the resistance change was delayed until the pulmonary venous Po 2 fell. Hypoventilation and ventilation with hypoxic mixtures causing a fall in pulmonary venous Po 2 similar to that due to collapse caused equivalent changes in blood flow. Changes in pH, Pco 2 and lung volume played a relatively minor role in resistance changes following collapse. The increase in resistance may be caused by a mechanism regulating ventilation-perfusion ratios in both normal and diseased lung.