Structural and functional evidence for the scaffolding effect of alveolar blood vessels

Abstract

A contribution of pulmonary blood distension to alveolar opening was first proposed more than 100 years ago. To investigate the contribution of blood distension to lung mechanics, we studied control mice (normal perfusion), mice after exsanguination (absent perfusion) and mice after varying degrees of parenchymal resection (supra-normal perfusion). On inflation, mean tracheal pressures were higher in the bloodless mouse (4.0α2.5 cmH2O); however, there was minimal difference between conditions on deflation (0.7α0.9 cmH2O). To separate the peripheral and central mechanical effects of blood volume, multi-frequency lung impedance data was fitted to the constant-phase model. The presence or absence of blood had no effect on central airway resistance (p>.05). In contrast, measures of tissue damping (G), tissue elastance (H) and hysteresivity (η) demonstrated a significant increase in bloodless mice relative to control mice (p<.001). After varying amount of surgical resection and associated supra-normal perfusion of the remaining lung, there was an increase in G and H. Although the absolute difference in G and H increased with the amount of parenchymal resection, the proportional contribution of blood was identical in all conditions. The presence of blood in the pulmonary vasculature resulted in a constant 64α5% reduction in tissue damping (G) and a 55α4% reduction in tissue elastance (H). This nearly-constant contribution of blood to lung hysteresivity was only reduced by positive end-expiratory pressure (PEEP). To identify a distinct structural subset of vessels in the lung potentially contributing to these observations, vascular casting and scanning electron microscopy of the lung demonstrated morphologically distinct vascular rings at the alveolar opening. Our results suggest that intravascular blood distension, likely attributable to a subset of vessels in the alveolar entrance ring, contributes a measurable scaffolding effect to the functional recruitment of the peripheral lung.

Hierarchical imaging and computational analysis of three-dimensional vascular network architecture in the entire postnatal and adult mouse brain

“…In mice at the embryonic stage (8.5-13 days of gestation), vascular corrosion casting has been applied to investigate embryonic aortic development 85–87 and the fetal circulation in relation to the placenta 88,89 . In adult mice, vascular corrosion casting techniques are widely used in all major organs, shown for example to be particularly useful to study cochlear vasculature in age-related hearing loss 90–93 , the microvasculature in the urine bladder 94 , and to investigate alveolar anatomy during both physiological development 95,96 and in several diseases 97,98 .…”

Effect of preoperative pulmonary hemodynamic and cardiopulmonary bypass on lung function in children with congenital heart disease

“…The authors hypothesized that these mechanical deteriorations were probably caused by a diminished tethering effect of the lung periphery through a reduced filling of the pulmonary capillaries that seemed to be more pronounced in children with hypo-perfused lungs than in those with high Qp. Animal studies with restricted Qp supported this hypothesis [ 34 ]. The beneficial postoperative changes in lung mechanics occurring in the VSD infants were consequences of the reversal of the pulmonary vascular engorgement after surgical repair [ 10 ].…”

Effect of mechanical ventilation during cardiopulmonary bypass on end-expiratory lung volume in the perioperative period of cardiac surgery: an observational study

“…Indeed, experimental studies suggested that pulmonary vascularization is involved in maintaining the mechanical and architectural properties of the lung. Gibney et al, observed in animal models a decrease in pulmonary compliance if vascularization is stopped [24]. Thus, the mere maintenance of mechanical ventilation may not be able to counteract this "ischemic" closure of the lung.…”