ABSTRACT
Interstitial fluid (ISF) flow through vascular adventitia has been discovered recently. However, its kinetic pattern was unclear. We used histological and topographical identification to observe ISF flow along venous vessels in rabbits. By magnetic resonance imaging (MRI) in live subjects, the inherent pathways of ISF flow from the ankle dermis through the legs, abdomen, and thorax were enhanced by paramagnetic contrast. By fluorescence stereomicroscopy and layer-by-layer dissection after the rabbits were sacrificed, the perivascular and adventitial connective tissues (PACTs) along the saphenous veins and inferior vena cava were found to be stained by sodium fluorescein from the ankle dermis, which coincided with the findings by MRI. The direction of ISF transport in a venous PACT pathway was the same as that of venous blood flow. By confocal microscopy and histological analysis, the stained PACT pathways were verified to be the fibrous connective tissues, consisting of longitudinally assembled fibers. Real-time observations by fluorescence stereomicroscopy revealed at least two types of spaces for ISF flow: one along adventitial fibers and another one between the vascular adventitia and its covering fascia. Using nanoparticles and surfactants, a PACT pathway was found to be accessible by a nanoparticle of <100 nm and contained two parts: a transport channel and an absorptive part. The calculated velocity of continuous ISF flow along fibers of the PACT pathway was 3.6‒15.6 mm/s. These data revealed that a PACT pathway was a "slit-shaped" porous biomaterial, comprising a longitudinal transport channel and an absorptive part for imbibition. The use of surfactants suggested that interfacial tension might play an essential role in layers of continuous ISF flow along vascular vessels. A hypothetical "gel pump" is proposed based on interfacial tension and interactions to regulate ISF flow. These experimental findings may inspire future studies to explore the physiological and pathophysiological functions of vascular ISF or interfacial fluid flow among interstitial connective tissues throughout the body.
ABSTRACT
Objective:To observe the drainage effects of the venous and arterial perivascular and adventitial connective tissues(PACT)on edema of lower limbs in mice model, and to provide a new understanding of the drainage for the elderly lower extremity edema.Methods:Different doses of fluorescent sodium(FluoNa)were injected into the venous and arterial perivascular connective tissues in the feet and ankles of the lower limbs to create a model of lower extremity edema in mice.Then, at the level of the femoral artery and vein sheath, a stereoscopic fluorescence microscope was used to observe and record the drainage effect of vascular PACT pathways on the edema.Results:By tracking the diffusion and flowing of FluoNa in the interstitial space of ankle and foot, we found that(1)in addition to the local diffusion at the injection site, FluoNa can also flow along the venous and arterial PACT and the interstitial spaces between the corresponding vein and artery.(2)The flowing process along the vascular adventitia included transmission along the vascular long axis, and the long axis-perpendicular diffusion into the vascular peripheral tissue.(3)When low-dose and high-dose FluoNa were administered into the venous adventitia of the lower extremities, the venous PACT imaging was observed.(4)When low-dose and high-dose FluoNa were administered into the arterial adventitia of the lower extremities, the arterial PACT imaging was observed; (5)When low-dose and high-dose of FluoNa were administered into the near the arteriovenous-accompanying blood vessels, not only the venous PACT pathway and the arterial PACT pathway are imaged, but also the interstitial space between the pathway of the accompanying vein and artery was also visualized at the same time; (6)Histological analysis showed that the tissues stained by FluoNa were the venous and arterial adventitia and perivascular connective tissues.Conclusions:The interstitial fluid in lower extremity tissue edema can not only be drained by the venous or arterial PACT pathway, but also be drained through the interstitial space between the accompanying vein and artery when a large amount of the interstitial fluid accumulates.
ABSTRACT
Objective To investigate the correlation of PICC tip position and weight gaining in very low birth weight infants.Methods We performed a retrospective study using chest X-ray films of very low birth weight infants in NICU who had PICCs inserted in a tertiary hospital.We recorded the tip positions on plain radiographs and calculated the position change,and calculated weight gaining ratio.Spearman regression model was used to analyze the relationship between tip position migration and weight gaining ratio.Results A total of 57 cases of very low birth weight infants were included,containing 246 X-ray films.On the first day of taking X-ray,weight was 0.6-1.46 (1.06±0.25) kg,the median and interquartile spacing are 5(3,7)d.The last time of taking X-ray was(24.0±9.1) dafter PICC placement;weight gaining ratio was 11.8％～114.8％,the median and interquartile spacing are 41.5％ (27.1％,65.3％).All PICCs tip position changed,75％ of which migrated more than 2 vertebrae,50％ of which migrated 3 vertebrae,and the median and interquartile spacing are 3 (1.8,3.5) vertebrae.The distances of tip migration were correlated with weight gaining ratio.With an approximate 2,3 and 4 vertebrae of PICC tip migration,the corresponding weight gaining ratio was about 40％,70％ and 100％.The correlation coefficient between PICC tip position migration and weight gaining ratio was-0.7(P＜0.01),but there was difference in different insertion sites.Conclusion PICC tip position is greatly influenced by weight gaining among very low birth weight infants.By considering the initial placement position,the crucial moment to assess catheter location is at 40％ and 70％ weight gaining ratio.After 100％ weight gaining,PICCs should be removed or replaced.PICCs can easily be affected by bone growth and limb movement,require higher frequency of catheter localization.