Multicenter experience with perventricular device closure of muscular ventricular septal defects

Hybrid procedures are becoming increasingly important, especially in the management of congenital heart lesions for which there are no ideal surgical or interventional options. This report describes a multicenter experience with perventricular muscular venticular septal defect (VSD) device closure. Three groups of patients (n = 12) were identified: infants with isolated muscular VSDs (n = 2), neonates with aortic coarctation and muscular VSDs (n = 3) or patients with muscular VSDs and other complex cardiac lesions (n = 2), and patients with muscular VSDs and pulmonary artery bands (n = 5). Via a sternotomy or a subxyphoid approach, the right ventricle (RV) free wall was punctured under transesophageal echocardiography guidance. A guidewire was introduced across the largest defect. A short delivery sheath was positioned in the left ventricle cavity. An Amplatzer muscular VSD occluding device was deployed across the VSD. Cardiopulmonary bypass was needed only for repair of concomitant lesions, such as double-outlet right ventricle, aortic coarctation, or pulmonary artery band removal. No complications were encountered using this technique. Discharge echocardiograms showed either mild or no significant shunting across the ventricular septum. At a median follow-up of 12 months, all patients were asymptomatic and 2 patients had mild residual ventricular level shunts. Perventricular closure of muscular VSDs is safe and effective for a variety of patients with muscular VSDs.

Efficacy and safety of dry powder fluticasone propionate in children with persistent asthma

BACKGROUND

Flovent Diskus is a powder formulation of the inhaled corticosteroid fluticasone propionate (FP) delivered via a breath-actuated, multidose inhaler.

OBJECTIVE

To determine the efficacy and safety of dry powder FP administered once or twice daily (200 microg per day) to children with persistent asthma.

METHODS

Twelve-week, randomized, double-blind, placebo-controlled, multicenter trial with a 52-week, open-label extension. Children aged 4 to 11 were required to have pulmonary function 50% to 85% of predicted values. The population was stratified for baseline therapy (inhaled corticosteroid/cromolyn or bronchodilators only). After a 2-week placebo run-in, 242 patients received dry powder FP 200 microg each morning, dry powder FP 100 microg BID, or placebo for 12 weeks; 192 were rerandomized to the QD or BID regimen for an additional 52 weeks of open-label treatment. Primary endpoints were mean changes in FEV1 and morning PEF recorded at clinic visits.

RESULTS

Both dry powder FP regimens significantly improved FEV1, evening PEF, and asthma symptoms at the double-blind phase endpoint (P < or = .017 compared with placebo). The BID regimen also significantly improved morning PEF and nighttime awakenings due to asthma (P < or = .005). Among patients previously treated with inhaled corticosteroids/cromolyn, improvements observed with the QD and BID regimens were similar. Patients switched from BID to open-label QD treatment showed additional improvements at week 52 generally comparable to patients who received the BID regimen during both phases. Fluticasone propionate was well tolerated for up to 64 weeks with few reports of drug-related adverse events or morning plasma cortisol abnormalities.

CONCLUSIONS

Once daily dosing of dry powder FP 200 microg is an effective and convenient alternative for children whose asthma is controlled with a more frequent dosing regimen of inhaled corticosteroids.

Adaptive responses to Na(+)-coupled solute transport and osmotic cell swelling in salamander proximal tubule

Measurements of basolateral membrane potential and relative K+ conductance were performed in isolated perfused proximal tubules from Ambystoma. To investigate adaptive increases in basolateral membrane K+ conductance (gK) associated with Na(+)-solute cotransport, measurements were made comparing transport of glucose and alanine, with changes caused by hypotonicity- and solute-induced cell swelling. Luminal perfusion with alanine produced results consistent with an adaptive increase in gK; perfusion with glucose failed to show this response. Hypotonic peritubular solutions also produced results consistent with an adaptive increase in gK, but isosmotic increases of peritubular glucose sufficient to swell the cells failed to produce this. No changes in the responses to luminal perfusion with alanine or glucose were induced by hypotonic peritubular solutions. With a high concentration of glucose in isosmotic peritubular solutions, perfusion of the lumen with glucose now produced results consistent with an adaptive increase in gK. Isosmotic peritubular solutions containing urea produced adaptive changes similar to those observed using hypotonic peritubular solutions, but when glucose was subsequently added to the lumen, no further adaptive response occurred. We conclude that cell swelling alone is insufficient to explain the mechanisms involved in the adaptive responses of gK occurring during Na(+)-solute cotransport in the salamander proximal tubule.

Evidence that alteration of charge modifies proximal tubular shunt pathway permselectivity

Experiments were performed to test the hypothesis that membrane charge is an important determinant of paracellular pathway ion permselectivity in the proximal tubule. Net negative charge in or around the paracellular pathway should favor cation permeability; net positive charge should favor anion permeability. Therefore compounds such as amiloride and 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid (SITS), capable of changing net membrane charge, should predictably change the diffusive permselectivity of the paracellular pathway to anions and cations. In the first group of experiments amiloride, a compound capable of increasing net positive membrane charge, inhibited cation and enhanced anion diffusive permeability. In a second group of experiments, SITS, a compound capable of increasing net negative membrane charge, inhibited anion and enhanced cation diffusive permeability. The effects of amiloride and SITS were symmetrical; the lumen-to-bath and the bath-to-lumen diffusion potentials were not significantly different in magnitude. In addition these effects were completely and rapidly reversible. Our results suggest that amiloride increases net positive charge, and SITS increases net negative charge within the paracellular pathway. The most likely site for the actions of SITS and amiloride is the tight junction because the effects of the inhibitors were symmetrical. Both compounds act at low concentrations and reversibly such that removal of the inhibitor rapidly reverses its effects. We propose, on the basis of the ease with which these alterations in charge and thus paracellular pathway permselectivity occurred, that the permselectivity of this pathway may not be fixed and constant for any given proximal tubular segment. In fact, permselectivity may vary and thus serve as an important physiological control mechanism for proximal tubular solute and water reabsorption.

Effect of renal allograft dysfunction upon cyclosporine trough levels in host blood

Cyclosporine (CsA) dose adjustment after renal transplantation is generally based on serum, plasma, or whole-blood trough level values. In the face of increased levels, the dosage is reduced in order to prevent CsA-induced nephrotoxicity. There is a paucity of data, however, on the kinetics of CsA in association with dysfunction of the transplanted kidney. This study documents dramatic rises in serum cyclosporine trough levels at the time of rejection crises, as well as following periods of nonimmunological allograft oliguria. Decreases in CsA dosage in such patients failed to result in a significant lowering in trough levels. Therapeutic CsA trough levels were generally at the 70-140 ng/ml level; at the time of rejection, the same doses of CsA resulted in a rise of trough levels to 300-500 ng/ml. As the rejection crises resolved and kidney function improved, the CsA serum trough levels returned to their lower levels. These results suggest that the urinary elimination of CsA and its metabolites may be a key determinant of CsA trough levels, and that the status of renal function at the time of testing must be considered in the interpretation of the data. In support of this observation, the CsA concentrations in 4-6 hr post-CsA-administration urine samples ranged from 400 ng/ml to 4500 ng/ml, as measured by high pressure liquid chromatography. The data suggest that rising CsA trough levels in a previously stable recipient may serve as a valuable early warning index of impending allograft dysfunction (rejection, infection, and obstruction). This appears particularly true during the first 30 days after renal transplantation, when the incidence of rejection is the greatest in this patient population.

Evidence for electroneutral chloride transport in rabbit renal cortical brush border membrane vesicles

Controversial evidence exists as to whether electroneutral Cl-OH exchange occurs across the proximal tubular brush border membrane of the mammalian kidney. To help resolve this controversy, we carried out a series of experiments using rabbit renal cortical brush border membrane vesicles to determine the effect of changes in pH on 36Cl uptake across this membrane. Reducing pH equally inside and outside of the vesicle stimulated Cl-Cl exchange as well as chloride uptake. A proton gradient (out greater than in) stimulated and caused an overshoot in unidirectional Cl uptake. All three of these processes were inhibited by 4-acetoamido-4-isothiocyano-2,2-disulfonic stilbene. Valinomycin with K+ out-in added to shunt any proton diffusion potential, minimally inhibited pH gradient-dependent Cl uptake, and carbonyl cyanide p-trifluoro-methoxyphenyl hydrazone (FCCP), added to increase the proton diffusion potential, minimally stimulated pH gradient-dependent Cl uptake. Sodium-glucose cotransport (an electrogenic system) was used to assess the efficacy of these ionophores. FCCP markedly enhanced and valinomycin markedly inhibited pH gradient stimulated sodium-glucose cotransport. Valinomycin added to vesicles with a 180/0 meq K+ out greater than in gradient stimulated less Cl uptake than a 6.0/7.5 pH out greater than in gradient. We conclude that these results provide strong evidence for the existence of an electroneutral Cl-OH exchanger or Cl-H symporter in this membrane.

Proximal tubular Na, Cl, and HCO3 reabsorption and renal oxygen consumption

The majority of the oxygen consumed by the rat kidney appears to occur in the proximal tubule. Therefore changes in metabolically linked ion transport in this segment of the nephron should result in changes in renal oxygen consumption. To study the role of bicarbonate reabsorption in metabolically linked proximal tubular ion transport a series of micropuncture-clearance-extraction experiments were performed comparing the effects of the carbonic anhydrase inhibitor benzolamide and of hypertonic sodium bicarbonate infusion with control conditions in the rat. End-proximal tubular fluid and chloride reabsorption were measured. From these, the rates of sodium and bicarbonate reabsorption were estimated. Simultaneously with the tubular fluids, extraction collections were obtained for determination of renal oxygen consumption. Both benzolamide and hypertonic bicarbonate reduced proximal tubular fluid reabsorption while concomitantly reducing the transepithelial gradient for chloride. The mean rate of renal oxygen consumption did not differ from the control rate in either experimental group and could be dissociated from the calculated net rates of proximal tubular sodium, chloride, and bicarbonate reabsorption. We interpret these data as evidence that proximal tubular hydrogen ion secretion supporting bicarbonate reabsorption requires at most small amounts of oxidative energy, less than detectable by these techniques. The data, in contrast, support the conclusion that the chloride-bicarbonate transepithelial gradient appears to be an important passive driving force in vivo for proximal tubular fluid reabsorption.

Evidence for PAH extraction from superficial cortical efferent vessel plasma

Consistent with its anatomical association with the proximal tubule we have previously shown that superficial cortical efferent vessel blood contains an admixture of early and late proximal tubular reabsorbate. Since tubular secretion of p-aminohippurate (PAH) occurs predominantly in the late proximal tubule, extraction of this compound should occur preferentially from efferent vessel blood. As a result, the midportion of the proximal convoluted tubule supplied by the more downstream peritubular capillaries would receive blood containing a disproportionately reduced concentration of PAH. To study this, proximal and distal tubular fluid and efferent vessel blood samples were collected from rats. The data confirm that preferential secretion of PAH occurs in the pars recta and demonstrate that PAH is extracted from efferent vessel plasma by the pars recta. This in turn preferentially reduces PAH concentration in early postglomerular blood before it reaches the peritubular capillary network. We speculate that PAH and similar substances secreted by the pars recta are short-circuited by rapid extraction from early postglomerular blood, reducing their delivery to the mid-proximal convoluted tubule. Such circumstances must be considered in any analysis of organic compound secretion by the in vivo proximal tubule.

Evidence for an osmotic effect of glucose in the in vivo rat proximal tubule

A series of micropuncture experiments were performed to assess whether phlorizin inhibition of proximal tubular glucose reabsorption inhibits proximal tubular fluid reabsorption due to a change in the transepithelial osmotic gradient for glucose. End proximal tubular filtrate reabsorption was measured, control vs experimental, in the same rat. The effects of infusing phlorizin in one group were compared to those of graded small infusions of mannitol in a second group of rats. In the phlorizin series tubular fluid and peripheral plasma were analyzed for glucose. Net renal sodium and renal oxygen consumption were measured in these same rats. In the mannitol series tubular fluid and peripheral plasma mannitol concentrations were determined. The results show that phlorizin inhibits proximal tubular fluid and glucose reabsorption without changing renal oxygen consumption. Mannitol inhibits proximal fluid reabsorption per unit transepithelial concentration difference to the same extent as does glucose during phlorizin infusion. We interpret these data as most consistent with the conclusion that the reduction in proximal tubular fluid reabsorption during phlorizin infusion is primarily due to the resultant change in the effective transepithelial osmotic gradient for glucose. Normally this gradient favors net fluid reabsorption. During phlorizin it favors retention of fluid in the proximal tubular lumen.

Superficial nephron tubular-vascular relationships in the rat kidney

Silicone rubber injections of methyl salicylate-cleared rat kidneys were performed. In 50 of 56 injections of superficial nephrons with their accompanying blood supply, the efferent vessel and early proximal tubule were closely approximated. In 18 of 21 tubular injections filling through the pars recta, the proximal tubule folded upon itself with early and late proximal segments, in close contact, located over their parent glomerulus, and the midproximal segments separate and located over their parent interlobular artery. The distribution of blood was serially through the early-late proximal region above the glomerulus via a long unbranched efferent vessel, via branches over the capsular surface, via capillaries down through the midproximal region, then into the interlobular vein. The observed anatomical pattern of the superficial nephron appears to permit direct functional interactions between the juxtaposed early and late proximal tubule, and in turn may effect midproximal function via the distribution of blood (modified by early proximal) from the efferent vessel to midproximal convolutions. In addition, the relationship between specific segments of the proximal tubule and specific portions of the postglomerular peritubular blood supply may be important in determining the distribution of peritubular physical forces to these nephrons.

Single-nephron function and renal oxygen consumption during rapid volume expansion

Isotonic volume expansion reduces net filtrate reabsorption in the proximal tubule while increasing it in Henle's loop. To determine the role oxidative metabolism plays in these processes, experiments were performed on rats initially hydropenic and then rapidly volume expanded with isotonic Ringer solution. Whole-kidney sodium reabsorption, oxygen consumption, and single-nephron function were measured simultaneously. During volume expansion, net renal sodium reabsorption increased concomitantly with a fall in oxygen consumption and a reduction in proximal tubular absolute filtrate reabsorption. The increase in quantity of nonreabsorbed filtrate delivered into the loop of Henle greatly exceeded the amount excreted in the urine. Thus, filtrate reabsorption by the distal nephron segments increased. These data provide evidence that acute volume expansion reduces oxygen-dependent active solute transport in the proximal tubule. The increase noted in distal nephron sodium reabsorption appears nonoxygen dependent, energized by anaerobic glycolysis or occurring passively.

Early postglomerular plasma concentrations of chloride, sodium, and inulin in the rat kidney

Sodium, chloride, and inulin concentrations were measured in plasma collected from the terminal portions of long efferent vessels at the subcapsular surface of the rat kidney. Sodium concentration equaled and the concentrations of chloride and inulin were less than those in peripheral plasma. During benzolamide infusion, chloride concentration equaled while inulin concentration remained less than in peripheral plasma. In free-flow micropuncture samples collected randomly during control conditions, chloride concentration rose rapidly in the early proximal tubule and then remained elevated and constant throughout the remainder of the proximal tubule accessible to micropuncture. These experiments indicate that normally tubular reabsorbate low in chloride and inulin is added to the blood traversing the early postglomerular vessels before reaching the kidney surface. Bases on the analyses of proximal tubular fluid, this type of reabsorbate appears available only from the early proximal tubular segment. We conclude that a close functional relationship exists between the first segment of the proximal tubule and the early postglomerular blood supply characteristic of the superficial cortical nephron.

Effect of intraluminal bicarbonate and chloride on fluid absorption by the rat renal proximal tubule

In order to study mechanisms of fluid transport in the rat renal proximal convoluted tubule, the effects of large variations in intraluminal HCO3- and Cl- concentrations were measured by microperfusion techniques. No differences in rates of fluid transport were found when intraluminal HCO3- was varied from 4 to 30 mEq/liter and Cl- from 146 to 120 mEq/liter. Inhibition of H+ secretion with benzolamide had no effect on fluid absorption when little or no HCO3- was present in the lumen, but did reduce fluid transport when 25 mEq of HCO3- was present. If several different mechanisms are responsible for proximal fluid transport, such as nonelectrogenic active NaHCO3 transport, passive chloride diffusion and active sodium transport linked to H+ secretion, the above observations imply that they all operate at approximately the same rate, since the dominant driving force would have been different with each perfusion solution. The data seem more compatible with the view that active sodium transport is the major driving force for fluid absorption in the proximal tubule, that this is not linked to H+ secretion and that anions modify the rate of absorption only to the degree that they are able to accompany sodium across the epithelium. An additional observation was that absorption of isotonic NaCl was very slow in short segments of tubule, as compared to HCO3--containing perfusion solutions. Although the mechanism is uncertain, these data suggest that a finite amount of intraluminal HCO3- is necessary for optimal proximal fluid transport.

A microperfusion study of phosphate reabsorption by the rat proximal renal tubule. Effect of parathyroid hormone

To study the mechanism of phsophate reabsorption by the proximal tubule and the effect of parathyroid hormone (PTH), microperfusion experiments were carried out in rats. Segments of proximal tubule isolated by oil blocks were perfused in vivo with one of three solutions, each containing 152 meq/liter Na(+) and 2 mmol/liter phosphate, but otherwise differing in composition. The pH of solution 1 was 6.05-6.63, indicating that 60-85% of the phosphate was in the form of H(2)PO(4) (-). The pH of solution 2 was 7.56-7.85, and 85-92% of the phosphate was in the form of HPO(4) (=). Solution 3 contained HCO(3) (-) and glucose and had a pH of 7.50-7.65. When the proximal tubules were perfused with solution 1, the (32)P concentration in the collected perfusate was found to be consistently lower than in the initial perfusion solution. In sharp contrast, when the tubules were perfused with solutions 2 or 3, (32)P concentration usually rose above that in the initial solution. Water (and persumably Na(+)) reabsorption, as measured with [(3)H]inulin, was the same with the acid and alkaline solutions. Administration of partially purified PTH clearly prevented the fall in phosphate concentration with the acid solution, but had a less discernible effect on phosphate reabsorption with the two alkaline solutions. Measurements of pH within the perfused segments with antimony microelectrodes demonstrated that PTH enhanced alkalinization of the acid perfusion solution. The findings are consistent with the view that H(2)PO(4) (-) is reabsorbed preferentially over HPO(4) (=). This can be attributed to either an active transport mechanism for H(2)PO(4) (-) or selective membrane permeability to this anion. PTH appears to either inhibit an active transport process for H(2)PO(4) (-), or to interfere with passive diffusion of phosphate by alkalinizing the tubular lumen.