Numerical modelling and analysis of peripheral airway asymmetry and ventilation in the human adult lung

We present a new one-dimensional model of gas transport in the human adult lung. The model comprises asymmetrically branching airways, and heterogeneous interregional ventilation. Our model differs from previous models in that we consider the asymmetry in both the conducting and the acinar airways in detail. Another novelty of our model is that we use simple analytical relationships to produce physiologically realistic models of the conducting and acinar airway trees. With this new model, we investigate the effects of airway asymmetry and heterogeneous interregional ventilation on the phase III slope in multibreath washouts. The model predicts the experimental trend of the increase in the phase III slope with breath number in multibreath washout studies for nitrogen, SF(6) and helium. We confirm that asymmetrical branching in the acinus controls the magnitude of the first-breath phase III slope and find that heterogeneous interregional ventilation controls the way in which the slope changes with subsequent breaths. Asymmetry in the conducting airways appears to have little effect on the phase III slope. That the increase in slope appears to be largely controlled by interregional ventilation inhomogeneities should be of interest to those wishing to use multibreath washouts to detect the location of the structural abnormalities within the lung.

Lung structure and function of infants with recurrent wheeze when asymptomatic

Infants with recurrent wheeze have repeated episodes of airways obstruction; however, relatively little is known about the structure and function of their lungs when not symptomatic. The current authors evaluated whether infants with recurrent wheeze have smaller airway lumens or thickened airway walls, as well as decreased airway function. High-resolution computed tomography images 1 mm thick were obtained at three anatomic locations at an elevated lung volume and at functional residual capacity. Forced expiratory flows were also measured in subjects with recurrent wheeze. Airway lumen, wall areas and lung tissue density were not significantly different for recurrent wheeze (n = 17) and control (n = 14) subjects; however, subjects with recurrent wheeze had lower forced expiratory flows than predicted. Similar findings were obtained when subjects were grouped by exposure to tobacco smoke. These findings indicate that infants with recurrent wheeze, as well as exposure to tobacco smoke, have lower airway function when not symptomatic. The lower forced expiratory flows may result from a degree of airway narrowing that could not be resolved with the methodology employed or from other mechanisms, such as more collapsible airways or decreased pulmonary elastic recoil.

Hyperhomocysteinemia in stable pediatric, adolescents, and young adult renal transplant recipients

BACKGROUND

High total plasma homocysteine (tHcy) levels are accompanied by an increased risk for premature development of atherosclerosis and atherothrombosis. Adult renal transplant recipients have elevated tHcy levels. Corresponding data in pediatric, adolescent, and young adult renal transplant recipients are scarce. We investigated whether tHcy levels were elevated in stable renal transplant recipients who received kidney grafts before age 18.

METHODS

This cross-sectional study was conducted during routine posttransplantation follow-up. Fasting tHcy levels, serum creatinine, and lipoprotein profile were measured in 38 clinically stable renal transplant recipients with different degrees of renal function. No patient was receiving B vitamin or folic acid supplementation. Estimated glomerular filtration rate (GFR) was assessed according to Schwartz's formula. All patients followed a triple-drug immunosuppressive regimen, with the exception of three patients (deflazacort and azathioprine). Forty-one apparently healthy subjects constituted the control group. tHcy levels were determined by fluorescence polarization immunoassay in an IMx analyzer.

RESULTS

Mean tHcy levels in transplant recipients were significantly higher than in controls (16.8+/-8.7 micromol/L and 9.5+/-2.3 micromol/L, respectively; P<0.01). A significant positive correlation between tHcy and serum creatinine levels was observed for both transplant recipients (rS=0.70, P<0.01) and controls (rS=0.54, P<0.01). In transplant recipients, tHcy correlated negatively with estimated GFR (rS=[minus]0.47, P<0.05). Fasting tHcy levels in excess of 14.6 micromol/L (>95th percentile in controls) were present in 19 (50%) patients; 14 of these patients had an estimated GFR<60 ml/min per 1.73 m2. When the renal transplant recipients were analyzed by renal function, mean tHcy was significantly higher in patients with an estimated GFR<60 ml/min per 1.73 m2 compared with patients with an estimated GFR> or =60 ml/min per 1.73 m2 (20.5+/-9.9 vs. 13.2+/-5.8 micromol/L, P<0.01). Both groups were significantly different from controls (P<0.01). No relationship was found between tHcy level and either cumulative cyclosporine or cumulative methylprednisone doses. No differences were observed in tHcy levels or lipoprotein profile between patients who were receiving deflazacort and those on methylprednisone.

CONCLUSIONS

Hyperhomocysteinemia in renal transplant recipients is a common condition. Testing for fasting tHcy level might be a useful tool to identify patients at increased risk for development of vascular disease.