Considerations in the evaluation of surrogate endpoints in clinical trials. summary of a National Institutes of Health workshop.

We report on recommendations from a National Institutes of Health Workshop on methods for evaluating the use of surrogate endpoints in clinical trials, which was attended by experts in biostatistics and clinical trials from a broad array of disease areas. Recent advances in biosciences and technology have increased the ability to understand, measure, and model biological mechanisms; appropriate application of these advances in clinical research settings requires collaboration of quantitative and laboratory scientists. Biomarkers, new examples of which arise rapidly from new technologies, are used frequently in such areas as early detection of disease and identification of patients most likely to benefit from new therapies. There is also scientific interest in exploring whether, and under what conditions, biomarkers may substitute for clinical endpoints of phase III trials, although workshop participants agreed that these considerations apply primarily to situations where trials using clinical endpoints are not feasible. Evaluating candidate biomarkers in the exploratory phases of drug development and investigating surrogate endpoints in confirmatory trials require the establishment of a statistical and inferential framework. As a first step, participants reviewed methods for investigating the degree to which biomarkers can explain or predict the effect of treatments on clinical endpoints measured in clinical trials. They also suggested new approaches appropriate in settings where biomarkers reflect only indirectly the important processes on the causal path to clinical disease and where biomarker measurement errors are of concern. Participants emphasized the need for further research on development of such models, whether they are empirical in nature or attempt to describe mechanisms in mathematical terms. Of special interest were meta-analytic models for combining information from multiple studies involving interventions for the same condition. Recommendations also included considerations for design and conduct of trials and for assemblage of databases needed for such research. Finally, there was a strong recommendation for increased training of quantitative scientists in biologic research as well as in statistical methods and modeling to ensure that there will be an adequate workforce to meet future research needs.

Localization of two distinct type III phosphatidylinositol 4-kinase enzyme mRNAs in the rat.

Inositol lipid kinases generate polyphosphoinositides, important regulators of several cellular functions. We have recently cloned two distinct phosphatidylinositol (PI) 4-kinase enzymes, the 210-kDa PI4KIIIalpha and the 110-kDa PI4KIIIbeta, from bovine tissues. In the present study, the distribution of mRNAs encoding these two enzymes was analyzed by in situ hybridization histochemistry in the rat. PI4KIIIalpha was found predominantly expressed in the brain, with low expression in peripheral tissues. PI4KIIIbeta was more uniformly expressed being also present in various peripheral tissues. Within the brain, PI4KIIIbeta showed highest expression in the gray matter, especially in neurons of the olfactory bulb and the hippocampus, but also gave a signal in the white matter indicating its presence in glia. PI4KIIIalpha was highly expressed in neurons, but lacked a signal in the white matter and the choroid plexus. Both enzymes showed expression in the pigment layer and nuclear layers as well as in the ganglion cells of the retina. In a 17-day-old rat fetus, PI4KIIIbeta was found to be more widely distributed and PI4KIIIalpha was primarily expressed in neurons. These results indicate that PI4KIIIbeta is more widely expressed than PI4KIIIalpha, and that the two enzymes are probably coexpressed in many neurons. Such expression pattern and the conservation of these two proteins during evolution suggest their nonredundant functions in mammalian cells.

Isolation and molecular cloning of wortmannin-sensitive bovine type III phosphatidylinositol 4-kinases.

Agonist-sensitive phosphoinositide pools are maintained by recently-identified wortmannin (WT)-sensitive phosphatidylinositol (PI) 4-kinase(s) (Nakanishi, S., Catt, K. J., and Balla, T. (1995) Proc. Natl. Acad. Sci. U.S.A. 92, 5317-5321). Two loosely membrane-associated WT-sensitive type III PI 4-kinases were isolated from bovine adrenal cortex as [3H]WT-labeled 110- and 210-kDa proteins. Based on peptide sequences from the smaller enzyme, a 3. 9-kilobase pair (kb) cDNA with an open reading frame encoding a 90-kDa protein was isolated from a bovine brain cDNA library. Expression of this cDNA in COS-7 cells yielded a 110-kDa protein with WT-sensitive PI 4-kinase activity. Northern blot analysis of a human mRNA panel showed a single approximately 3.8-kb transcript. Peptide sequences obtained from the 210-kDa enzyme corresponded to those of a recently described rat 230-kDa PI 4-kinase. A 6.5-kb cDNA containing an open reading frame of 6129 nucleotides that encoded a 230-kDa protein, was isolated from brain cDNA. Northern blot analysis of human mRNA revealed a major 7.5-kb transcript. The molecular cloning of these novel WT-sensitive type III PI 4-kinases will allow detailed analysis of their signaling and other regulatory functions in mammalian cells.

Beta-adrenoceptor activation-induced placental prorenin secretion is mediated by increased renin messenger RNA and protein synthesis.

Activation of beta-adrenoceptors has been shown to promote renin secretion in both human kidney and placenta. In kidney, the enhanced secretion is immediately observed, and mobilization of renin in the storage granules accounts for such a rapid response. In contrast, the enhanced secretion in placenta is delayed for 6-12 hr after receptor activation and consists almost entirely of the renin precursor prorenin. It is hypothesized that newly synthesized rather than stored enzyme is responsible for the enhanced secretion in human placenta. To test this hypothesis, placental explants were cultured in the presence or absence of the protein synthesis inhibitor cycloheximide, and prorenin concentrations in the tissue and medium were measured. Dobutamine and terbutaline, beta1- and beta2-adrenoceptor agonists, evoked 17- and 5-fold increases in secretion, respectively. Tissue content of prorenin in response to the treatment was increased by a similar magnitude, yet values were consistently <10% of medium concentrations. The increases in prorenin concentrations in both medium and tissue, however, were markedly attenuated by cycloheximide, suggesting that prorenin synthesis in response to beta-adrenoceptor activation is required. Reverse transcription coupled with polymerase chain reaction revealed that renin mRNA levels were increased by 3-8-fold and occurred before increases in tissue and medium prorenin, indicating that increased renin mRNA levels are responsible for the increased synthesis of prorenin. Explants cultured in the presence of actinomycin D, an inhibitor of transcription, did not show the agonist-induced prorenin mRNA levels or enhancement of its secretion. The peak levels of renin mRNA were reached after 6 hr of incubation, were sustained at similar levels after 24 hr, and were not affected by cycloheximide. These findings are consistent with the notion that enhancement of renin mRNA and de novo protein synthesis are required for prorenin secretion induced by activation of placental beta-adrenoceptors.

Modification of native collagen reduces antigenicity but preserves cell compatibility.

Porcine intestinal collagen (ICL), derived from processed small intestine, is used as a part of a remodelable bilaminate biosynthetic vascular prosthesis. The process for the production of ICL involves mechanical cleaning of non-crosslinked porcine intestine (NC-ICL), disinfection with peracetic acid (PA-ICL), and crosslinking with 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (PA/EDC-ICL). Two model systems were investigated to evaluate the effect of these agents on the humoral response to NC-ICL. First, the antibody titers of rabbits immunized with NC-ICL, PA-ICL, and PA/EDC-ICL were determined, and second, the humoral response of canines receiving collagenous vascular implants was examined. Collagenous and noncollagenous fractions were extracted from NC-ICL, PA-ICL, and PA/EDC-ICL and separated by SDS-PAGE. PA and EDC treatment decreased the number of extractable proteins as compared to NC-ICL. Immunoblot techniques demonstrated anti-NC-ICL antibodies recognized multiple immunoreactive proteins in NC-ICL, but not in PA-ICL or PA/EDC-ICL; and rabbits immunized with NC-ICL produced higher antibody titers to ICL proteins than rabbits immunized with either PA-ICL or PA/EDC-ICL. It was, therefore, apparent that NC-ICL was more antigenic than either PA-ICL or PA/EDC-ICL. The humoral immune response of canines to PA/EDC-ICL fabricated vascular grafts was determined. At 4 weeks, 8 weeks, and 12 weeks postimplant, serum antibodies to ICL proteins or type I collagen could not be detected. These data demonstrate a reduced humoral immune response to PA/EDC-ICL. (c) 1996 John Wiley & Sons, Inc.

Human chorionic gonadotropin stimulates placental prorenin secretion: evidence for autocrine/paracrine regulation.

Functional regulation of the placental renin-angiotensin system remains incompletely defined. Evidence indicates that synthesis and secretion of prorenin in the placenta and gestational sac decrease with advancing gestational age. Possible explanations for this developmental effect include the regulatory influences by locally released hormones, such as CG. To address this question, the effect of CG on prorenin secretion was evaluated in a human placental explant model. In this study, prorenin concentrations were measured in the media and tissue of cultured explants from term placentas. In addition, the role of cAMP in mediating hormone-regulated prorenin secretion was evaluated. Media and tissue concentrations of prorenin increased (2- and 3-fold, respectively) in a concentration-dependent fashion after 48 h of incubation with CG (0.03-300 IU/ml). Selective inhibition of phosphodiesterases by Ro 20-1724 (type IV) and cilostamide (type III) resulted in a marked potentiation of CG-induced prorenin secretion. Media concentrations of cAMP were also elevated with CG treatment and correlated with prorenin values. Prorenin secretion induced by CG was markedly attenuated by the cAMP-dependent protein kinase inhibitor, H-89. These results indicate that placental prorenin secretion may be locally regulated by CG and mediated by cAMP signal transduction mechanisms.

Characterization of a soluble adrenal phosphatidylinositol 4-kinase reveals wortmannin sensitivity of type III phosphatidylinositol kinases.

Phosphorylation of phosphatidylinositol (PtdIns) by PtdIns 4-kinases is the first step in the synthesis of polyphosphoinositides, the lipid precursors of intracellular signaling molecules. We have recently identified a cytosolic PtdIns 4-kinase (cPI4K) in the bovine adrenal cortex that is distinguished from previously known PtdIns 4-kinases by its sensitivity to the PtdIns 3-kinase inhibitor wortmannin (WT). The present study has further characterized this soluble enzyme and compared its properties to those of the membrane-bound, type II PtdIns 4-kinase activity of the adrenal cortex and the type III enzyme of bovine brain. The enzymatic activity of adrenal cPI4K was inhibited not only by WT (IC50 approximately 50 nM) but also by LY-294002 (IC50 approximately 100 microM), another inhibitor of PtdIns 3-kinase, and neither compound affected type II PtdIns 4-kinase at concentrations that inhibited cPI4K. In contrast to the type II enzyme, cPI4K had a significantly higher Km for ATP, was relatively insensitive to inhibition by adenosine (Ki approximately 800 microM vs approximately 40 microM), had lower affinity for PtdIns, and was not inhibited by Ca2+ ions. These properties identify the WT-sensitive adrenal cPI4K as a type III PtdIns 4-kinase that is distinct from the tightly membrane-bound, Ca2+- and adenosine-sensitive, type II PtdIns 4-kinase. The type III PtdIns 4-kinase prepared from bovine brain exhibited similar kinetic parameters as the adrenal cPI4K, and was also inhibited by WT with an IC50 of 30-50 nM. Since WT inhibits the synthesis of agonist-regulated phosphoinositide pools in intact cells at micromolar concentrations, these findings indicated that type III rather than type II PtdIns 4-kinases are responsible for the maintenance of the precursor phospholipids required for intracellular signaling through the inositol phosphate/Ca2+ pathway.

Stimulation of placental prorenin secretion by selective inhibition of cyclic nucleotide phosphodiesterases.

Prorenin secretion by human villous placenta is known to be stimulated by activation of adenylate cyclase and enhanced cyclic AMP (cAMP) generation. Placental tissue contains predominantly type III (cGMP-inhibited) and type IV (cAMP-specific) phosphodiesterases (PDEs), which inactivate cAMP. To evaluate the role of PDE subtypes in the regulation of prorenin secretion by human placenta, explants were cultured in the presence of isobutylmethylxanthine (IBMX), a non-selective PDE inhibitor, and selective inhibitors for various PDE subtypes. Inhibition of PDE subtypes with cilostamide (type III), Ro 20-1724 (type IV) and zardaverine (types III and IV) increased prorenin release. Inhibition of type I (Ca(2+)/calmodulin-dependent) PDE by 8-MeoM-IBMX and of type V (cGMP-specific) PDE by zaprinast or dipyridamole did not affect prorenin secretion. The stimulation of prorenin secretion by PDE inhibitors was attenuated by cAMP-dependent protein kinase inhibition. The selective PDE inhibitors caused a parallel increase in media cAMP and prorenin and also increased tissue prorenin levels. These studies demonstrate that cAMP degradation by type III and IV PDE isoenzymes is a major regulatory mechanism for placental prorenin secretion. It is suggested that enhancers of adenylate cyclase activity are constitutively present in placenta and influence prorenin synthesis and release.

Evaluation of airway complications in high-risk preterm infants: application of flexible fiberoptic airway endoscopy.

OBJECTIVES: We sought to determine factors that would predict the development of subglottic stenosis (SGS) and tracheomalacia (TM) in preterm infants. The utility of a semiquantitative measurement of airway dimensions was assessed in relation to signs of airway complications. We also sought to determine from a high-risk population of infants those likely to have abnormal findings identified by bronchoscopic examination. METHODS: Prospective airway endoscopy was performed for preterm infants who were intubated for 7 days or more or who demonstrated chronic oxygen needs beyond 28 days after birth and 36 weeks postconceptional age. Subjects were 117 preterm (less than 36 weeks' gestation) infants from two level III intensive care nurseries. Endoscopy was used to classify the type and degree of airway injury. Subglottic stenosis was defined subjectively and compared with an objective measurement using subglottic spatial relations described as a trans-subglottic/vocal cord ratio (TSG/VC). Clinical signs and symptoms and other risk factors were evaluated as significant predictors of SGS and TM, identified by bronchoscopy. RESULTS: Moderate or severe airway abnormalities were identified in 32 patients (27.3%); 13 with SGS, 17 with TM, and 2 with both. All but one infant with TSG/VC less than 0.83 had signs and symptoms of airway dysfunction. Variables more commonly found in patients with SGS included greater number of intubations, use of inappropriately large endotracheal tubes, and longer duration of intubation. Higher averaged mean airway pressure during the first week after birth and lower gestational age were clinical features associated with TM. CONCLUSIONS: Flexible bronchoscopic evaluation of a high-risk population demonstrated a higher incidence of moderate or severe SGS or TM than previously suspected. Subglottic stenosis and TM appear to have different etiologies based on different factors associated with their development. The TSG/VC ratio correlated well with obstructive symptoms and may represent a means to quantitate clinically subglottic narrowing. Infants with chronic lung disease who have persistently elevated partial pressure of carbon dioxide, apnea, or phonation abnormalities are most likely to have airway abnormalities identifiable by bronchoscopy.

First-trimester villous placenta has high prorenin and active renin concentrations.

OBJECTIVE: Term villous placental concentrations of prorenin are known to be very low, whereas those of decidua and fetal membranes are high. It has been demonstrated that prorenin synthesis is modulated by hormones in other reproductive tissues, thus suggesting a means for paracrine regulation in the placenta. This study was performed to test the hypothesis that placental tissue prorenin concentrations may be influenced by gestational age and are temporally related to alterations in the hormonal milieu. STUDY DESIGN: Decidua and villous placental tissue were obtained from term and first-trimester human pregnancies, and concentrations of prorenin, active renin, prolactin, and human chorionic gonadotropin were measured. Values were compared between gestational periods, and relationships between renin and hormone values were analyzed. RESULTS: Prorenin concentrations in first-trimester placenta were nearly 200-fold higher than at term. The proportion of active renin was higher with early gestation. Decidual prorenin and active renin concentrations were similar in both groups. Placental prorenin correlated with chorionic gonadotropin but not prolactin in both groups. CONCLUSIONS: This study demonstrates large differences in placenta prorenin and active renin in villous placental tissue between first-trimester and term gestation tissues, yet these differences were not observed in decidual tissues. The contrast in placental prorenin values observed at the extremes of pregnancy parallel those of placental human chorionic gonadotropin.

cAPK mediates placental renin secretion stimulated by beta-adrenoceptor activation.

Previous studies have indicated that activation of placental beta-adrenoceptors stimulates renin secretion, whereas basal secretion is extremely low. This response is potentiated by inhibition of types III and IV phosphodiesterases, implicating a role for adenosine 3',5'-cyclic monophosphate (cAMP). Described are experiments aimed at defining the regulatory influence of cAMP and cAMP-dependent protein kinase (cAPK) isotypes in renin secretion. Human placental explants were cultured with dobutamine, a beta 1-agonist, and cAPK activity, renin, and cAMP concentrations were determined. After 48 h of incubation, media concentrations of renin and cAMP increased and were positively correlated. Tissue cAPK activity was positively correlated with renin secretion associated with dobutamine. Renin secretion was measured in response to substituted cAMP analogues selective for a unique cAMP binding site (site A or B) for cAPK regulatory subunits. A fivefold stimulation of renin secretion by the type II site B activators occurred, whereas a threefold increase was seen with a type I site B analogue. Site A-selective analogues for cAPK types I and II produced no stimulation. Dobutamine-induced renin secretion was attenuated by selective inhibitors of cAPK regulatory and catalytic subunits. These findings indicate that placental renin secretion associated with beta-adrenoceptor activation is correlated with cAMP generation and mediated predominantly by the type II isoform of cAPK.

Prorenin secretion from villous placenta: regulation by cyclic AMP and angiotensin.

Renin synthesis and secretion from human chorion and decidua have previously been shown to be stimulated by agents which increase cellular cyclic adenosine monophosphate (cAMP). We have now used organ culture of villous placenta, incubated for periods up to 72 h, to investigate the cellular regulation of renin in this tissue. The placental tissues release renin (92-96% in the form of prorenin) and human chorionic gonadotrophin (hCG), but not prolactin. We found that cholera toxin and forskolin markedly stimulate the synthesis and release of renin in a time-dependent manner. This stimulation was potentiated by phosphodiesterase inhibitors and inhibited by an angiotensin II agonist, sar-1-angiotensin II. The inhibitory action of the angiotensin agonist on renin release was blocked by sar-1-leu-8-angiotensin II, a selective angiotensin receptor antagonist. The potential for stimulation of renin expression by cyclic AMP-regulated elements is supported by the dramatic (two-orders of magnitude) increase in renin release observed with cholera and forskolin at 72 h. There are several possible candidates for primary signals for adenylyl cyclase-coupled renin secretion from the placenta, including relaxin and epinephrine. The extremely low concentration of renin in term villous placenta may be related to activation of negative regulatory elements on the renin gene. We propose that angiotensin II is one negative regulator of this system.

Pulmonary vasculature changes associated with idiopathic closure of the ductus arteriosus and hydrops fetalis.

Antenatal closure of the ductus arteriosus has been considered as a potential risk factor for the development of hydrops fetalis and persistent fetal circulation of the newborn. We present an infant with antenatal ductal closure who had not received prenatal prostaglandin synthetase inhibitors. The pulmonary vascular morphological findings are described and compared to three additional infants in whom the ductus arteriosus was known to be patent; one with neonatal sepsis and two others with hydrops fetalis. The infants with fetal hydrops, regardless of etiology, had increased muscularization of the acinar pulmonary arteries. In addition, the infant with antenatal closure of the ductus arteriosus also had both a significant decrease in preacinar arterial external diameter and an increase in medial wall thickness. Antenatal closure of the ductus arteriosus appears to enhance in utero pulmonary blood flow and this may be the cause of pulmonary vascular remodeling.

Beta-adrenoceptor activation stimulates, and phosphodiesterase inhibition potentiates, placental prorenin synthesis and release.

This study evaluated activation of beta-adrenoceptors and the cAMP pathway on prorenin secretion from human placental explants. For comparative purposes, hCG secretion was also measured. Treatment with selective beta-adrenergic agonists (beta 1-dobutamine and beta 2-terbutaline) produced dose-dependent increases in prorenin secretion, with dobutamine yielding a greater response (10- vs. 6-fold). In contrast, hCG secretion was stimulated only by terbutaline (5-fold). Prorenin and hCG secretory responses were inhibited by corresponding selective receptor antagonists (beta 1-metoprolol and beta 2-ICI 118,551). Selective phosphodiesterase inhibitors were used to evaluate the role of cAMP in mediating these responses. Marked potentiation of beta-adrenoceptor-dependent prorenin secretion was observed with the type III inhibitor, cilostamide (63-76%), and the type IV inhibitor, Ro-201724 (32-43%). Type I (8-methoxymethyl-3-isobutylmethylxanthine) and type V inhibitors (dipyridamole and M&B 22,948) showed no potentiation. These studies demonstrate that activation of both beta 1- and beta 2-receptors stimulates placental prorenin release. The potentiation of beta-adrenergically activated prorenin release by selective inhibitors of phosphodiesterase indicates a coupling of beta-adrenoceptor and adenylate cyclase. The contrast in secretion of prorenin and hCG by selective beta-adrenergic agonists suggests differences in cellular localization. The results indicate that clinically used adrenergic agonists can affect the placental renin-angiotensin system. The role of endogenous activators of beta-adrenoceptors in this system remains to be determined.

Acquired subglottic cysts in the low-birth-weight infant. Characteristics, treatment, and outcome.

OBJECTIVE: To provide a descriptive summary of characteristics, including demographics, symptoms, risk factors, and outcome of acquired subglottic cysts identified in the neonatal period. DESIGN: Patient series. SETTING: A tertiary neonatal care unit and referral neonatal follow-up clinic. PARTICIPANTS: One hundred seventy-four preterm infants undergoing flexible bronchoscopy, 21 (12%) referred for airway evaluation because of symptoms and 153 (88%) examined consecutively following 7 days or more of endotracheal intubation. INTERVENTION: None. MEASUREMENTS/RESULTS: Subglottic cysts were identified in 11 (7.2%) of 153 preterm infants examined prospectively at discharge from the neonatal intensive care unit after prolonged intubation and two (10%) of 21 infants referred for airway evaluation. Infants with subglottic cysts were extremely preterm (mean +/- SEM gestation, 26.7 +/- 0.5 weeks) and very low birth weight (894.6 +/- 64.6 g). The mean duration of intubation was 28.5 +/- 5.0 days. Most infants, particularly those with large cysts, were symptomatic with stridor, hoarseness, or obstructive apnea. In two cases, airway symptoms began after discharge from the neonatal intensive care unit. Ten (91%) of the 11 patients were discharged receiving home oxygen. Generally, multiple cysts were present in the subglottic space, most prominently located in the posterior aspect of the trachea. Three of five patients with large cysts received a tracheostomy. Two additional patients had surgical marsupialization of the cysts, and six others experienced resolution without treatment. One patient with large cysts died of viral pneumonia 10 months after surgical intervention. An additional patient with large cysts died before surgical intervention secondary to chronic lung disease and cor pulmonale. All surviving infants had resolution of signs of airway obstruction and 10 of the 11 did not require supplemental oxygen or have symptoms of chronic pulmonary disease at age 1 year. CONCLUSION: Intubation-acquired subglottic mucous cysts in the neonate may occur more commonly than was previously recognized. Symptoms of this lesion may mimic features of chronic lung disease. Early identification of the cysts with flexible bronchoscopy is important since airway compromise may progress and surgical intervention may be lifesaving.

Echocardiographically guided balloon atrial septostomy during extracorporeal membrane oxygenation (ECMO).

Use of extracorporeal membrane oxygenation (ECMO) in infants with congenital heart disease is becoming more frequent. We present the first reported use of balloon atrial septostomy during ECMO support and describe possible complications of such procedures unique to ECMO therapy.

In vivo correlation of Doppler waveform analysis with arterial input impedance parameters.

Previous studies have confirmed that Doppler waveform analysis (DWA) offers a valid reflection of changes in peripheral vascular resistance. However, the ability of the pulsatility index (PI), a parameter of DWA, to reflect the dynamic components of the circulation, as assessed by arterial input parameters, remains uncertain. In addition, the state of the central circulation is considered an important factor influencing the accuracy of this technique. This study evaluated the ability of the aortic PI to reflect alterations of input impedance in a chronically instrumented lamb model that was subjected to pharmacologic alteration of the circulation. Pressure, volumetric flow and continuous-wave Doppler frequency shift measurements were recorded from the infrarenal abdominal aorta. The parameters of input impedance, peripheral vascular resistance (Zpr), characteristic impedance (Zo) and reflection coefficient (Rc), were determined and then correlated with changes in the aortic PI. Initially, perturbations of the circulatory state were created with a vasodilator, hydralazine (HY) and a vasoconstrictor, phenylephrine (PE). During a second set of experiments, the effect of the reflex heart rate (HR) responses on the PI was evaluated. This was accomplished by inhibiting reflex HR responses to these vasoactive agents with either trimethophan (TM) or atropine methyl bromide (AMB). In response to HY and HY with TM, significant decreases in the PI and impedance parameters occurred. Administration of PE and PE with AMB resulted in significant increases in PI and each of the impedance parameters. HY and PE induced changes in PI correlated significantly with changes in volumetric flow (r = 0.82, 0.80; p < 0.001), mean arterial blood pressure (r = 0.64, 0.70; p < 0.001) and Zpr (r = 0.77, 0.80; p < 0.001), but not with Zo (r = 0.34, 0.36) and Rc (r = 0.26, 0.31). However, when reflex HR responses were inhibited during the administration of the vasoactive agents, HY with TM and PE with AMB, induced changes in PI correlated significantly with Zo (r = 0.93, 0.89; p < 0.001) and Rc (r = 0.84, 0.83; p < 0.001), and the correlation with mean arterial pressure (r = 0.78, 0.87; p < 0.05) and Zpr (r = 0.92, 0.91; p < 0.05) was significantly greater. These findings indicate that the PI accurately assesses pharmacologically induced changes in the downstream arterial input impedance. The accuracy of this assessment is enhanced further when central circulatory factors such as changes in HR are considered.

Antepartum fetomaternal hemorrhage. Report of a case with the use of cordocentesis in diagnosis and management.

Clinical recognition of antepartum fetomaternal hemorrhage (FMH) is most often achieved by the observation of characteristic fetal heart rate (FHR) patterns and positive Kleihauer-Betke acid elution staining. Both methods are noted to lack sensitivity and specificity. A case of suspected antepartum FMH occurred with intermittent sinusoidal FHR tracings. Fetal blood sampling by cordocentesis in situations with equivocal antenatal testing, such as in this case, allows not only confirmation of fetal anemia but assessment of fetal acid-base status. In pregnancies of less than 32 weeks' gestation complicated by severe antepartum FMH, intravascular transfusion may be offered via this technique. Cordocentesis is beneficial in the management of pregnancies with uncertain FHR patterns when antepartum FMH is suspected.

Kidney function in very low birth weight infants with furosemide-related renal calcifications at ages 1 to 2 years.

To determine whether long-term renal sequelae follow the use of furosemide in preterm infants, we evaluated renal function in 27 former very low birth weight infants (less than 1500 gm) at 1 to 2 years of age. Patients were classified into three groups on the basis of status at the time of discharge from the hospital: group 1 (n = 7) had no furosemide treatment or renal calcifications, group 2 (n = 10) had furosemide therapy but no calcifications, and group 3 (n = 10) had furosemide therapy with renal calcifications. Renal ultrasonography at the time of the study demonstrated resolution of the calcifications in six patients in group 3. No differences in renal function were observed between groups 1 and 2. Creatinine clearance (mean +/- SEM) in group 3 (83.6 +/- 7.8 ml/min per 1.73 m2) was significantly lower than clearance in groups 1 and 2 (103.2 +/- 6.5 and 109.1 +/- 5.1, respectively; p less than 0.05). Children in group 3 had significantly higher urinary calcium/creatinine ratios and fractional excretion of sodium and lower tubular reabsorption of phosphate than children in the two other groups had. Urine-blood difference in carbon dioxide tension after oral acetazolamide load, which indicates the ability of the distal tubule to secrete hydrogen ions, was 8.4 +/- 3.4 mm Hg in group 3, significantly lower than values in groups 1 and 2 (22.6 +/- 3.1 and 28.0 +/- 4.3 mm Hg, respectively, p less than 0.05). Within group 3 the four children with persistent renal calcifications had significantly lower urine-blood carbon dioxide tension differences than did those with resolution of calcifications (p = 0.02). We conclude that furosemide-related renal calcifications in very low birth weight infants may lead to glomerular and tubular dysfunction; further long-term follow-up of this population is recommended.