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T N Hansen

Publications and source records attributed to T N Hansen.

At least 37 records · Page 2Linked to original sources
PubMed1993

A nonlinear regression analysis of nonlinear, passive-deflation flow-volume plots.

When studying lung mechanics of intubated premature infants, by the passive-deflation technique we noted that in many flow-volume plots the descending limb was curvilinear with a convexity toward the volume axis. By conventional linear analysis lung mechanics of these patients did not change after the administration of terbutaline, but Mead's tangent-chord slope ratio method for quantifying the amount of curvature showed that the shape of the flow-volume plots did change. Because of the limitations of this method, we developed a microcomputer-based, reiterative regression algorithm which optimizes a nonlinear function for the best fit to any given set of data. We then studied six very low birth weight infants with clinical evidence of pulmonary gas trapping (weight at study, 1.22 +/- 0.29 kg; age, 26 +/- 16 days). We measured respiratory system resistance (Rrs), compliance (Crs), and expiratory time constants (TCrs) by the passive deflation technique before and after subcutaneous administration of 0.02 mg/kg of terbutaline. No effect of terbutaline in a dose sufficient to increase heart rate > 25 beats/min was observed. The same data analyzed using the nonlinear regression technique with a function based upon a two compartment model of parallel inhomogeneities revealed one compartment with relatively normal Rrs, Crs, and TCrs values, and a second compartment with a very high Rrs. The latter fell by 50% after terbutaline. These data suggest that abnormalities of airway resistance in ventilated preterm infants are not easily identifiable by classic linear analysis of lung mechanics.(ABSTRACT TRUNCATED AT 250 WORDS)

Airway Resistance↗
PubMed1993

Expression of recombinant human glutathione reductase in eukaryotic cells after DNA-mediated gene transfer.

Glutathione reductase (EC 1.6.4.2) protects tissues from oxidant stress by catalyzing the NADPH-mediated reduction of glutathione disulfide to glutathione. We describe construction of a vector for DNA-mediated gene transfer and successful transient overexpression of human glutathione reductase cDNA in CHO cells. No expression was observed when the same vector was transiently transfected into NIH3T3 or LA4 cells or stably integrated in CHO cells. These results demonstrate the ability to constitute recombinant glutathione reductase expression in eukaryotic cells but suggest that this expression may be toxic.

3T3 Cells↗
PubMed1993

Hyperoxic lung injury in Fischer-344 and Sprague-Dawley rats in vivo.

Supplemental oxygen remains an important therapy for pulmonary insufficiency, despite the potential adverse effects of hyperoxic exposures. Recently, He et al. reported that hyperoxic ventilation more readily damaged isolated perfused lungs from Fischer-344 rats than from Sprague-Dawley rats (Am. J. Physiol. 259:L451), which correlates with the previously reported strain differences in hepatic responses to diquat-induced oxidant stress in vivo (J. Pharmacol. Exp. Ther. 235:172). We therefore examined the differences in hyperoxic lung injury in Fischer-344 and Sprague-Dawley rats in vivo. Adult male rats were exposed to > 95% O2 and were sacrificed after 24, 48, or 60 h. Control animals were maintained in room air. Dramatically greater increases in pleural effusions and bronchoalveolar lavage protein concentrations in response to hyperoxia were observed in the Fischer-344 rats than in the Sprague-Dawley rats (p < .05 at both 48 and 60 h for both measurements). Additionally, the glutathione concentrations in alveolar lining fluid decreased from 800 microM to 115 microM in Fischer-344 rats after 60 h of > 95% O2, but did not change in Sprague-Dawley rats. We conclude that the greater susceptibility of Fischer-344 than of Sprague-Dawley rats to hyperoxic lung injury in vitro reported previously also is observed in vivo and that this strain difference offers unique opportunities to study mechanisms of hyperoxic lung injury.

Animals↗
PubMed1993

Calorimetric determination of inhibition of ice crystal growth by antifreeze protein in hydroxyethyl starch solutions.

Differential scanning calorimetry and cryomicroscopy were used to investigate the effects of type I antifreeze protein (AFP) from winter flounder on 58% solutions of hydroxyethyl starch. The glass, devitrification, and melt transitions noted during rewarming were unaffected by 100 micrograms/ml AFP. Isothermal annealing experiments were undertaken to detect the effects of AFP-induced inhibition of ice crystal growth using calorimetry. A premelt endothermic peak was detected during warming after the annealing procedure. Increasing the duration or the temperature of the annealing for the temperature range from -28 and -18 degrees C resulted in a gradual increase in the enthalpy of the premelt endotherm. This transition was unaffected by 100 micrograms/ml AFP. Annealing between -18 and -10 degrees C resulted in a gradual decrease in the premelt peak enthalpy. This process was inhibited by 100 micrograms/ml AFP. Cryomicroscopic examination of the samples revealed that AFP inhibited ice recrystallization during isothermal annealing at -10 degrees C. Annealing at lower temperatures resulted in minimal ice recrystallization and no visible effect of AFP. Thus, the 100 micrograms/ml AFP to have a detectable influence on thermal events in the calorimeter, conditions must be used that result in significant ice growth without AFP and visible inhibition of this process by AFP.

Animals↗
PubMed1993

Increases in lung tissue expression of intercellular adhesion molecule-1 are associated with hyperoxic lung injury and inflammation in mice.

Lung injury caused by breathing enriched oxygen continues to be a major problem in clinical medicine. Experimentally, hyperoxic lung injury is characterized by pulmonary edema and associated neutrophil accumulation. Although extensively investigated, the mechanisms for neutrophil accumulation and the role of this accumulation in hyperoxic lung injury remain controversial. Intercellular adhesion molecule-1 (ICAM-1) is an adhesion molecule that when increased on endothelium by inflammatory cytokines leads to increased adhesion of neutrophils to the inflamed endothelium and transendothelial migration. The purpose of this study was to examine the role of inflammation in hyperoxia-induced lung injury by investigating ICAM-1 expression in the lungs of mice exposed to > 95% oxygen continuously. Lung tissue from mice exposed to > 95% oxygen was analyzed for ICAM-1 mRNA by slot blot analysis and for ICAM-1 protein expression. We also examined lungs from mice exposed to hyperoxia for up to 96 h by light microscopy to correlate pulmonary inflammation with ICAM-1 expression. We found that mRNA for ICAM-1 increased 56% over baseline after 48 h of exposure to hyperoxia, that ICAM-1 protein increased by more than 5-fold over baseline after 96 h of exposure to hyperoxia, and that lung inflammation and injury were not evident until 96 h of exposure. Our data demonstrate that exposure to hyperoxia causes an increase in ICAM-1 gene transcription and/or mRNA stability in mouse lungs, and that this increase is followed by an increase in ICAM-1 protein.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Oxidant stress responses in premature infants during exposure to hyperoxia.

To assess oxidant stress responses in newborn infants treated with elevated concentrations of oxygen, we measured plasma concentrations of glutathione (GSH) and glutathione disulfide (GSSG) in newborn infants ranging from 23 to 42 wk gestational age. All infants recruited into the study were mechanically ventilated and had catheters placed in their umbilical arteries as part of their normal clinical management. Blood samples were obtained on d 1, 3, and 5 and weekly thereafter or until the catheters were removed. We observed plasma concentrations of GSSG in these infants that were frequently an order of magnitude higher than the 0.1 to 0.3 microM we find in adults. Interestingly, plasma GSSG concentrations were inversely correlated to the inspired oxygen tensions. This effect appeared to arise from the patient selection criteria whereby, of the infants studied, those breathing the lowest partial pressures of oxygen were the smallest and gestationally youngest. A second observation was that plasma concentrations of GSH in the premature infants were substantially, indeed often dramatically, lower than we have observed in adult humans (6 to 10 microM). Finally, we found that in patients with both umbilical arterial and umbilical venous catheters arterial GSSG concentrations were consistently higher than venous concentrations; conversely, arterial GSH concentrations were lower than venous concentrations. The elevated GSSG concentrations we observed in these infants indicate marked oxidant stress responses in prematurely born infants, even in those infants exposed only to room air. The positive arteriovenous gradients of GSSG concentrations across the lungs of these infants suggest that at least some of the increased plasma GSSG originates in the lung.(ABSTRACT TRUNCATED AT 250 WORDS)

Biomarkers↗
PubMed1992

Antifreeze protein modulates cell survival during cryopreservation: mediation through influence on ice crystal growth.

Antifreeze proteins (AFPs) are extremely efficient at inhibiting ice recrystallization in frozen solutions. Knight and Duman [Knight, C. A. & Duman, J. G. (1986) Cryobiology 23, 256-263] have proposed that this may be an important function of the proteins in freeze-tolerant organisms. We have tested this proposal in vitro by characterizing the influence of AFP on the recovery of cryopreserved cells, which often can survive cooling and yet subsequently be damaged by ice crystal growth during warming. Relatively low concentrations (e.g., 5-150 micrograms/ml) of winter flounder (Pseudopleuronectes americanus) AFP enhance survival of red blood cells cryopreserved in hydroxyethyl starch solutions. This effect is most apparent in samples warmed at suboptimal rates, i.e., where ice recrystallization would be exaggerated. Cryomicroscopy demonstrates that AFP inhibits ice recrystallization in the extracellular regions during the latter stages of the warming cycle. AFP concentrations that enhance survival of red cells confer partial inhibition of recrystallization. Relatively high concentrations of AFP (e.g., 1.54 mg/ml) are much more effective at inhibiting extracellular recrystallization. However, extensive growth of ice around the cell, and concomitant cell damage, is noted. The mechanism for this AFP-induced ice growth is unknown. We propose that there is a delicate balance between AFP-induced enhancement of cell preservation and AFP-induced enhancement of cell preservation and AFP-induced enhancement of cell damage and that this balance hinges on the degrees of inhibition of ice recrystallization and of preferential growth of ice around the cells. We conclude that, under appropriate conditions, one of the proposed functions of AFPs in nature can be emulated, and perhaps have application, in cryopreservation of materials of biomedical interest.

Animals↗
PubMed1992

The effect of blood flow and left atrial pressure on the DLCO in lambs and sheep.

Previous studies suggest that pulmonary capillary distensibility and recruitment may differ in lambs and sheep. To study the effect of pulmonary blood flow (PBF) and vascular pressure on capillary hemodynamics in lambs and sheep we measured the diffusing capacity for carbon monoxide (DLCO) as an index of pulmonary capillary blood volume during a baseline period, after increasing PBF, and during left atrial hypertension. In the lamb, DLCO did not change significantly either with a 65% increase in PBF or with an increase in left atrial pressure (Pla) of 1.33 kPa at constant PBF. In the sheep on the other hand, doubling PBF led to a 28% increase in DLCO (P less than 0.02), and an increase in Pla of 1.87 kPa at constant PBF led to a 19% increase in DLCO (P less than 0.01). These results suggest that the neonatal lamb has a nearly fully recruited and relatively non-compliant pulmonary capillary bed at rest, unlike the adult sheep which can respond to hemodynamic changes with distension and recruitment of the pulmonary capillary bed.

Animals↗
PubMed1992

Time dependence of lung mechanics in preterm lambs.

The passive exhalation flow-volume plots of preterm lambs exhibit curvature. To explain this curvature, we proposed two mathematical models that could predict the measured passive exhalation flow-volume data well. One model takes into account the flow and volume dependence of resistance and compliance. The second model emphasizes the time dependence of lung mechanics and considers the respiratory system viscoelastic properties and the analogy of the lung to two electronic resistor-capacitor circuits connected in parallel. We attempted to determine which of the two models is more valid by analyzing passive exhalation flow-volume data that were obtained while briefly obstructing flow midway through deflation. In 14 preterm lambs (130 d gestation), the flow of exhaled gas increased from 76 +/- 35 mL/s when measured just before obstruction to 90 +/- 30 mL/s when measured immediately after release of the obstruction (p less than 0.0001). This finding suggests that a time-dependent phenomenon was taking place during obstruction and is inconsistent with the model based upon the flow and volume dependence of resistance and compliance. We made similar measurements in four near-term (143-146 d gestation) and four full-term lambs (9-12 d of age). Their flow-volume curves were relatively linear, and they showed no increases in flow after removal of the obstruction. The results of this study strongly suggest that time-dependent phenomena caused the curvilinearity in the passive exhalation flow-volume plots of preterm lambs. We suspect that the time-dependent phenomena is associated with the premature lung and with parenchymal lung disease.(ABSTRACT TRUNCATED AT 250 WORDS)

Airway Resistance↗
PubMed1991

Calorimetric analysis of antifreeze glycoproteins of the polar fish, Dissostichus mawsoni.

Solutions of antifreeze glycoproteins 1 through 5 and 8 were analyzed for activity by differential scanning calorimetry. With a scan rate of 1 degree C min-1, antifreeze glycoproteins 1-5 (20 mg/ml) revealed antifreeze activity with a delay in the freeze exotherm during cooling in the presence of ice. Antifreeze glycoprotein 8 (60 mg/ml), however, did not reveal antifreeze activity. When a 0.1 degree C min-1 scan rate was used, glycoproteins 1-5 again yielded a delay in the freeze onset, but the exotherm consisted of multiple events. At the slower scan glycoprotein 8 revealed an initial freeze followed by multiple exothermic events resembling those of glycoproteins 1-5. Thermograms exhibiting antifreeze activity had an initial shoulder in the exotherm direction upon cooling followed by a delay before the exotherm. The shoulders were correlated with c-axis ice growth observed in visual methods. The glycoprotein antifreezes had a linear increase in activity with decreased ice content.

Animals↗
PubMed1991

Expression of SV40 T antigen under control of rabbit uteroglobin promoter in transgenic mice.

The rabbit uteroglobin gene is expressed in the lungs and reproductive tracts of male and female rabbits. To examine whether the promoter region of the uteroglobin gene could be used to target a heterologous gene to the lungs of transgenic mice, a fusion gene consisting of 3.3 kb of the 5'-flanking region of the rabbit uteroglobin gene and the large T antigen gene of the SV40 virus was constructed and microinjected into the pronuclei of one-cell mouse embryos. Eleven founder transgenic mice (5 female and 6 male) were generated. Seven of these mice developed bronchioalveolar neoplasms. Four of the founder males also developed primitive undifferentiated urogenital tract tumors. One founder female and one female offspring of a founder male developed glandular paraovarian tumors. Northern analysis revealed that the predominant site of expression of the transgene was the lung. Immunohistochemical staining showed T antigen predominantly in epithelial cells lining the bronchioles, the submucosal glands of the trachea, and the neoplasms. There appeared to be a high level of mosaicism for the transgene in the founder mice, with poor transmission of the transgene to subsequent generations. This suggests that, under the control of the uteroglobin promoter, the T antigen gene may be lethal to the fetus.

Animals↗
PubMed1991

Expression and regulation of the rabbit uteroglobin gene in transgenic mice.

The rabbit uteroglobin (UG) gene, with varying lengths of 5' flanking sequence, was introduced into the mouse genome to investigate the DNA sequences required for tissue-specific expression and regulation by steroid hormones. The pattern of expression and steroid hormone regulation of the transgene was compared to the expression and regulation of the endogenous mouse UG-like gene. In the rabbit, UG is induced in the uterus by progesterone and is expressed constitutively in the lungs, where it is weakly regulated by glucocorticoids. Genomic DNA fragments containing the complete UG-coding sequence with 4.0 (UG4.0), 3.0 (UG3.0), 2.3 (UG2.3), or 0.6 (UG0.6) kilobases of 5' flanking sequence were used to establish lines of transgenic mice. Expression of UG mRNA was observed in the lungs of UG4.0 (2/4 lines), UG3.0 (4/4 lines), UG2.3 (1/2 lines), and UG0.6 (4/4 lines) mice. Uterine expression was observed in UG3.0 (3/4 lines), UG2.3 (1/2 lines), and UG0.6 (2/4 lines). In the lungs of UG3.0 and UG2.3 mice, RNA expression was stimulated by treatment with dexamethasone. In the one line of UG3.0 mice examined, UG was regulated by ovarian steroids in the uterus. The endogenous mouse UG-like gene showed the major site of expression to be in the lung. Unlike the transgene, the endogenous gene was more strongly stimulated by glucocorticoids. Thus, we conclude that the cis elements needed for pulmonary expression of UG are contained within the UG2.3 fragment used to generate transgenic mice, but that other elements are required for full glucocorticoid regulation. Also, the transgene did not show the full uterine expression observed in the rabbit, but regulation by the ovarian steroids was observed.

Animals↗
PubMed1990

Atrial tachycardia causes hydrops in fetal lambs.

The purpose of this project was to study mechanisms responsible for edema formation in fetuses with hydrops. We produced hydrops fetalis in 28 fetal sheep [gestational age of 125 +/- 5 days (mean +/- SD)] by pacing their atria at 300-320 beats/min for 68 +/- 40 (SD) h. All fetuses developed peripheral edema and ascites [volume of ascitic fluid was 134 +/- 75 (SD) ml; total protein concentration was 3.10 +/- 0.6 (SD) g/dl, and total albumin concentration was 1.68 +/- 0.3 (SD) g/dl]. Pacing did not affect aortic pressure but increased venous pressure from 4 +/- 1 to 8 +/- 1 (SE) Torr. Pacing did not affect pH, arterial partial pressure of O2 (PaO2), or Na+ but increased PaCO2 from 53 +/- 1 to 55 +/- 1 (SE) Torr and K+ from 3.9 +/- 0.1 to 4.3 +/- 0.1 (SE) meq/l. Hematocrit increased from 29 +/- 1 to 32 +/- 1 (SE)% acutely with pacing but returned to base line by the last day of the experiment. Plasma protein concentration decreased slightly from 3.7 +/- 0.1 to 3.5 +/- 0.1 (SE) g/dl by the last day of the experiment; plasma albumin concentration did not change. Plasma volume decreased acutely from 271 +/- 19 to 238 +/- 16 (SE) ml and then remained decreased throughout the experiment. Red blood cell mass and the turnover time for albumin were not affected by pacing. We found no consistent relationship between edema formation and changes in arterial blood gas tensions, plasma protein concentrations, or the turnover time for albumin.2

Animals↗
PubMed1990

Passive deflation time constant of 7-week-old rabbits.

The purpose of our study was to determine the effects of insufflation time (TI) and of tidal volume (VT) on the passive deflation time constant (tau) of juvenile rabbits. We sedated and paralyzed nine 7-wk-old New Zealand rabbits (wt 1.2 +/- 0.2 SD kg) and placed them on a time-cycled, pressure-limited mechanical ventilator. Measurements of tau and dynamic compliance of the respiratory system were made at nine ventilator settings. TI was adjusted to 0.2, 0.4, and 0.6 s and VT was adjusted to 10, 15, and 20 mL so that the effects of TI and VT on tau could be determined independently. Respiratory system quasi-static and static compliances were also measured and served as a basis for discussing the physiologic explanations for the effects of TI and VT on tau. In general, increases in TI resulted in increases in tau and increases in VT also resulted in increases in tau. Increasing TI from 0.2 to 0.6 s plus increasing VI from 10 to 20 mL resulted in an increase in tau from 0.220 +/- 0.007 to 0.282 +/- 0.010 s (mean +/- SEM) (p less than 0.05, student Newman-Kuels), which is a 28% increase. At a VT of 10 mL, dynamic compliance increased from 1.95 +/- 0.10 to 2.14 +/- 0.10 mL/cm H2O (p less than 0.05) when TI was increased from 0.2 to 0.6 s; however, dynamic compliance decreased 19% as VT was increased from 10 to 20 mL.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Reversal of venous blood flow with atrial tachycardia and hydrops in fetal sheep.

The purpose of this project was to characterize the reversal of blood flow in the proximal inferior vena cava (IVC) seen in fetal sheep with pacing-induced atrial tachycardia and hydrops. We successfully operated on seven pregnant ewes at 118-130 d gestation to attach ECG and pacing wires, insert vascular catheters, and place Doppler flow probes around the common aortic trunk and the IVC. We also performed two-dimensional and Doppler ultrasonographic exams at baseline, after initiation of pacing, and daily thereafter. All fetuses developed hydrops. Ultrasonographic appearance of ascites and pleural effusion occurred within 4 h in four fetuses and within 48 h in all fetuses. Atrial pacing did not affect arterial pH or arterial O2 tension, but arterial CO2 tension increased by a small amount. Mean IVC pressure increased 75%, whereas mean aortic pressure remained the same. Concentrations of plasma protein and albumin and the hematocrit did not change with atrial pacing. Doppler ultrasound examination and Doppler IVC flow tracings showed that flow reversal began immediately with atrial pacing and disappeared immediately with cessation of pacing. Reversed flow was 21% of forward flow. Inspection of simultaneous recordings of ECG, Doppler aortic and IVC flows, and aortic and IVC pressure tracings revealed that the reversed blood flow occurred in diastole in conjunction with atrial contraction and, therefore, could not be due to tricuspid insufficiency. Our findings of increased venous pressure and reversed venous blood flow suggest that ventricular function is impaired and further suggest that oxygen supply to the ventricles may not be sufficient for the increased demand.

Animals↗
PubMed1990

Biochemical manifestations of oxygen toxicity in the newborn lamb.

The purpose of this project was to study the role of lipid peroxidation in oxygen-induced lung injury in the newborn lamb. It was our hypothesis that injury to the microvascular bed of the lung by oxygen would coincide with a burst of peroxidative activity and would be accompanied by an increased rate of excretion of ethane and pentane in expired gas. We measured vascular pressures, the rate of lung lymph flow and concentrations of ethane and pentane in exhaled gas in 10 newborn lambs that breathed greater than 95% oxygen continuously. Our marker for oxygen-induced lung injury was an increase in the permeability of the microvascular bed of the lung to protein (an increase in the rate of lung lymph flow accompanied by an increase in the protein concentration in lymph). Although all 10 lambs demonstrated an abrupt increase in microvascular permeability to protein within 48 to 96 h of exposure to greater than 95% oxygen, the rates of ethane and pentane excretion remained unchanged throughout the entire experimental period. Lung tissue concentrations of glutathione decreased by 40% in the oxygen-exposed lambs and the concentrations of glutathione disulfide increased 85% relative to air-breathing controls. Activities of glutathione reductase and superoxide dismutase were lower in the lungs of the oxygen-exposed lambs than in controls, whereas the activities of glutathione peroxidase and catalase were not changed. We conclude that, in the lamb, changes in the rates of excretion of ethane and pentane do not correlate with the timing of injury to the microvascular bed of the lung.

Animals↗