摘要:

ABSTRACT.The combined system of ventilator circuit, endotracheal tube, and lung commonly imposes a resistive load on spontaneous breathing efforts. It is possible to compensate for this positive resistance by a device generating a “negative ventilator resistance” (NVR),i.e.delivering a positive pressure during inspiration and a negative pressure during expiration in constant proportion to the instantaneous flow of the spontaneous breathing. The concept of NVR implies that there must not be any phase lag between flow and pressure signals. In eight anesthetized, intubated, spontaneously breathing rabbits (mean body wt 3570 g, range 2900‐4600 g), challenged either by aerosolized histamine or an extrapulmonary resistive load, lung mechanical data were calculated from esophageal pressure and flow signals. Each animal served as its own control with and without NVR. In a total of 39 experiments, NVR was applied in amounts between 1 and 15 kPa.s/L. During both types of additional resistive load, NVR immediately reduced the resistive work of breathing. There was a strong linear correlation between the amount of NVR applied and the decrease in total resistance, where the total resistance equals the resistive load on the animal's respiratory muscles (sum of the resistances of all components of the combined respirator‐lung system):r= 0.93,p< 0.001. The relationship between NVR and the drop in resistive work per mL of tidal volume was similar:r= 0.85,p< 0.001. Throughout the experiments, NVR operated in perfect synchronization with the animal's spontaneous breathing activity. (28: 79‐82, 1990)AbbreviationsCPAP, continuous positive airway pressureNVR, negative ventilator resistancePes, esophageal pressurePm, pressure at the mouthpiece levelRext, extrapulmonary resistive load&OV0622;, flow

ISSN:0031-3998    

出版商:OVID    

年代:1990

数据来源: OVID

摘要:

ABSTRACT.The respiratory responses to theophylline during normoxia and hypoxia were determined in 13 unanesthetized fetal sheep. Theophylline (plasma levels ∼ 111 &mgr;mol/L) increased the incidence of fetal breathing movements measured over 120 min from 37.7 ± 4.8% to 61.1 ± 5.7% (SEM) in normoxic fetuses. In isocapnic hypoxia (arterial O2tension ∼ 1.86 kPa), theophylline increased the incidence from 20.0 ± 6.3 to 52.0 ± 6.1%. Theophylline also resulted in an increase in the slope of inspiration during both normoxia and hypoxia. We conclude that adenosine modulates fetal respiratory drive during normoxia and hypoxia. (Pediatr Res28:83‐86, 1990)AbbreviationsECOG, electrocorticogram

ISSN:0031-3998    

出版商:OVID    

年代:1990

数据来源: OVID

摘要:

ABSTRACT.The maturation of the process of spontaneous recovery from hypoxic apnea by gasping (autoresuscitation) was characterized in adult, weanling (18‐22 d), and infant (5 and 10 d) BALB/c mice. ECG and respiration were recorded and hypoxic apnea was induced with 97% N2‐3% CO2. Administration of 21% O2at onset of hypoxic apnea resulted in successful autoresuscitation in all 63 animals tested. In all mice, three sequential stages occurred:1) gasping with marked bradycardia,2) rapid increase in heart rate (cardiac resuscitation), and3) increase in respiratory rate (respiratory resuscitation). Despite these similar stages, marked maturational differences were apparent. The times to cardiac and respiratory resuscitation were longer in the pups than in the older mice, whereas the gasp frequency before cardiac resuscitation was lower in the infants. Resuscitation time correlated with gasp interval (1/gasp frequency). In addition, the initial bradycardia at onset of gasping was more pronounced in the pups. A 30‐ or 60‐s delay in oxygen administration after onset of hypoxic apnea caused a marked decrease in the adults' ability to autoresuscitate, without affecting that of the pups. A comparison of gasp frequency in 21% O2versus97% N2‐3% CO2showed that the presence of oxygen increased gasp frequency in the pups, but had no effect on gasp frequency in the weanlings or adults. We conclude that autoresuscitation is equally effective in both infant and adult BALB/c mice but only when oxygen is available before the onset of hypoxic gasping. Accordingly, the adult's ability to autoresuscitate rapidly can be viewed as an adaptation required by a limited tolerance for prolonged hypoxia. In contrast, it appears that the infant mouse's greater tolerance of hypoxia allows a slower autoresuscitation with a lower heart rate and gasp frequency. This conserves energy, thus facilitating prolonged survival and enabling recovery when O2availability is delayed. (Pediatr Res28: 87‐93, 1990)AbbreviationsHR, heart rateRR, respiratory rateANOVA, analysis of variancePao2, arterial oxygen tension

ISSN:0031-3998    

出版商:OVID    

年代:1990

数据来源: OVID

摘要:

ABSTRACTHind limb blood flow and O2uptake, mean blood pressure, and heart rate were measured in six fetal sheep at 127‐141 d gestation in the control state and at different levels of hypoxia that were induced by partial occlusion of the maternal terminal aorta. Blood flow was measured by an ultrasonic flow transducer. Control fetal arterial O2content ([O2]a) in the descending aorta was 3.25 + 0.17 mM. In response to graded acute hypoxia, blood flow first increased (22.2versus19.9 mL.min−1.100 g−1,p= 0.003) and then decreased abruptly at approximately 1.5 mM [O2]a.O2uptake decreased about 12% (14.74versus16.71,p= 0.03) as [O2]adecreased to 1.5 mM, and then fell markedly, tending toward zero for [O2]a= 0.9 mM. In the 2.7‐ to 1.5‐mM [O2]arange, heart rate increased above control (194versus169 min−1,p= 0.0024), whereas mean blood pressure did not change significantly. For [O2]a< 1.5 mM, heart rate decreased to 148 min−1(p= 0.0005) and mean blood pressure increased above baseline (55versus47 torr,p= 0.0001). In conjunction with previous evidence, these results define a state of acute moderate hypoxia in which the whole fetus can sustain a relatively high rate of oxidative metabolism, and a state of acute severe hypoxia ([O2]abetween 1.5 and 1.0 mM) in which O2uptake by some fetal organs is selectively and markedly decreased. (Pediatr Res28: 94‐100, 1990)Abbreviation[O2]a, fetal arterial O2content

ISSN:0031-3998    

出版商:OVID    

年代:1990

数据来源: OVID

摘要:

ABSTRACTPast studies have found that total‐body O2extraction during hypoxia was less in 1‐wk‐old lambs than in older animals. It was proposed that reduced O2extraction was secondary to suppression of growth‐related oxygen consumption (&OV0312;o2) in tissues such as skeletal muscle, bone, kidney, and skin, rather than a defect in peripheral O2use. To determine the capacity of immature skeletal muscle to extract O2, we isolated the hind limb circulation of eight ketamine‐anesthetized, 7‐ to 18‐d‐old lambs exposed to stagnant hypoxia by inflation of a right atrial balloon catheter. Femoral arterial and venous Po2, Pco2, pH, Hb concentration, O2saturation, and femoral arterial blood flow (Q) were measured and hind limb O2delivery (Do2), extraction ratio, and &OV0312;o2calculated. Individual critical levels of Do2below which Vo2was dependent on O2supply were determined by dual‐line best‐fit regression analysis, In six of eight animals, &OV0312;o2was clearly independent of supply until Do2reached critically low levels. However, O2extraction during extreme hypoxia appeared submaximal (baseline O2extraction ratio, 0.22 ± 0.06; at critical levels of Do2, 0.51 ± 0.11; at the lowest level of Q, 0.64± 0.15). When 2,4‐dinitrophenol, an uncoupler of oxidative phosphorylation, was administered to four additional lambs exposed to stagnant hypoxia, O2extraction below critical levels of Do2increased from 0.48 ± 0.15 to 0.79 ± 0.10 (p< 0.001, unpairedttest). These data suggest that initial limitations in O2extraction were a result of the suspension of O2‐consuming processes, not an irreversible defect in peripheral O2use. (Pediatr Res28: 101‐105, 1990)AbbreviationsDNP, 2,4‐dinitrophenolDo2, O2deliveryDo2crit, critical level of Do2Q, blood flowVo2, O2consumptionP50, Po2at which Hb was 50% saturatedANOVA, analysis of variance[Hb], Hb concentrationpHa, arterial pH

ISSN:0031-3998    

出版商:OVID    

年代:1990

数据来源: OVID

摘要:

ABSTRACTMost previous efforts to characterize electrocortical states in the unanesthetized fetal lamb have relied on descriptive measures of amplitude and frequency; those that used quantitative parameters did not draw upon data from a cohort of subjects for contiguous time segments. We have used Fourier analysis to quantitate amplitude and frequency characteristics of records of 2‐3 h for a group of fetuses. Four electrocortical states, including two types of transitional activity, have been identified and quantitated. Additionally, we have developed a method that automates the assignment of data to these four electrocortical states. This has enabled us to monitor transitions among states and indicates that epochs that appear homogeneous by descriptive measures may actually encompass several patterns of electrocortical activity. (Pediatr Res28: 106‐110, 1990)AbbreviationsECoG, electrocorticogramHVSA, high‐voltage, slow activityLVFA, low‐voltage, fast activityFFT, Fast Fourier Transform

ISSN:0031-3998    

出版商:OVID    

年代:1990

数据来源: OVID

摘要:

ABSTRACTTolazoline is used in neonatal intensive care to treat hypoxia secondary to persistent pulmonary hypertension of the newborn. Its use is often complicated by systemic hypotension. We compared the effect of tolazo‐line‐induced hypotension on organ blood flow, regional brain blood flow, and cerebral metabolism in hypoxic newborn dogs whose mean arterial pressure fell by more than 20% with a second group whose blood pressure fell by less than 20%. Blood flows were measured by the radioactive microsphere technique. We found no changes in organ blood flow, regional brain blood flow, and cerebral metabolism in hypoxic animals whose mean arterial blood pressure decreased less than 20% during tolazoline administration. However, in those animals whose mean arterial blood pressure decreased more than 20%, we found a decrease in cerebral blood flow. As a consequence of decreased cerebral blood flow, cerebral oxygen delivery decreased. However, oxygen extraction increased so that cerebral metabolic rate was preserved. (Pediatr Res28: 111‐115, 1990)AbbreviationsPao2, arterial O2tensionPaco2, arterial CO2tension

ISSN:0031-3998    

出版商:OVID    

年代:1990

数据来源: OVID

摘要:

ABSTRACTIn two children with familial erythrophagocytic lymphohistiocytosis accompanied by neurologic symptoms, total neopterin concentrations in cerebrospinal fluid were 200 times higher than in controls and 10 to 20 times higher than in five children with presumed neurologic disease due to primary viral infections (human immunodeficiency virus, herpes simplex, measles) of the CNS. In one child with familial erythrophagocytic lymphohistiocytosis, clinical remission was accompanied by a fall in neopterin concentrations to normal; in a second child, who died, total neopterin concentrations remained high. In two other children with a diagnosis of infection‐associated hemophagocytic syndrome without any neurologic disturbance, neopterin concentrations were also elevated but only to 10 times the concentrations in controls. Total neopterin concentrations in cerebrospinal fluid provide a measure of the severity of macrophage infiltration and activation within the CNS, and are useful in assessing the need for intensive chemotherapy and monitoring the response to treatment. (Pediatr Res28: 116‐119, 1990)AbbreviationsCSF, cerebrospinal fluidFEL, familial erythrophagocytic lymphohistiocytosisIAHS, infection‐associated hemophagocytic syndromeMTX, methotrexateNH2, dihydroneopterinVP16, etoposide

ISSN:0031-3998    

出版商:OVID    

年代:1990

数据来源: OVID

摘要:

ABSTRACTDevelopmental defects in neutrophil function, including diminished expression of plasma membrane receptors, may play an important role in the susceptibility of the newborn infant to infection. We used monoclonal antibodies and flow cytometry to study the expression of complement receptor type one (CR1), complement receptor type three (CR3), and Fc&ggr;receptor type three (FcRIII) on neutrophils from six fetuses with Rh disease, 10 preterm infants, nine term infants, and nine adults. Expression of the complement receptors on unstimulated cells was similar for all groups, but significant diffences in complement receptor expression were observed after stimulation withN‐formyl‐methionyl‐leucyl‐phenylalanine (FMLP). Fetal, preterm, and term infant neutrophils expressed less CR3 than FMLP‐stimulated neutrophils of adults [61 ± 2, 48 ± 4, and 66 ± 4% (mean ± SEM) of the mean for adults,p< 0.05]. FMLP‐stimulated CR1 expression for these groups was 61 ± 6, 73 ± 6, and 91 ± 9% of the adult mean (p< 0.05, fetalversusterm infant and adult). Expression of both CR3 and CR1 increased with postconceptional age in the infants (r2= 0.49,p< 0.001 for CR3;r2= 0.23,p< 0.05 for CR1). Neutrophils of the preterm and term infants expressed less FcRIIIthan adult neutrophils (68 ± 10 and 77 ± 7% of the adult mean,p< 0.05, for FMLP‐stimulated cells), whereas fetal neutrophil FcRIIIexpression did not differ from that of the adult. The fluorescence distributions showed a peak for eosinophils that was distinct from the FMLP‐stimulated neutrophil peak, allowing separate analysis for the two cell types. Eosinophils constituted an unexpectedly large proportion of granulocytes in fetuses with Rh disease, averaging 61% of granulocytes in seven specimens at 20 to 26 wks gestation and 37% in 11 specimens at 28 to 34 wks. (Pediatr Res28: 120‐126, 1990)AbbreviationsCR1, complement receptor type one (CD35)CR3, complement receptor type three (CD11b/CD18)FcRIII, Fc&ggr;receptor type three (CD16)FMLP,N‐formyl‐methionyl‐leucyl‐phenylalanine

ISSN:0031-3998    

出版商:OVID    

年代:1990

数据来源: OVID

摘要:

ABSTRACTThe effect of red cell transfusion and polyethylene glycol‐modified adenosine deaminase therapy on biochemical abnormalities, clinical status, and immunologic function in an adenosine deaminase‐deficient child was investigated. After red cell transfusions, erythrocyte deoxyadenosine triphosphate (dATP) concentrations decreased about 95% and were closely related to adenosine deaminase activities; deoxyadenosine diphosphate concentrations decreased only approximately 30%. The evolution of dATP levels was also closely related to the improvement in clinical status of the patient. However, immune function was not restored. After polyethyelene glycol‐modified adenosine deaminase therapy, the concentration of erythrocyte dATP decreased to undetectable levels correlated with an increase of T lymphocyte counts and an increase of lymphocyte responses to mitogens. Immune functions were restored only when dATP levels were below 15 &mgr;mol/L. It appears that red cell transfusion therapy is not sufficiently effective to reduce and maintain erythrocyte dATP levels at values compatible with normal immune function. On the contrary, polyethylene glycol‐modified adenosine deaminase therapy is a suitable treatment to reduce dATP levels to near undetectable values, allowing the immune function to be restored. dATP measurement is a very useful tool for monitoring and evaluating the degree of efficiency of therapy in adenosine deaminase deficiency. (Pediatr Res28: 127‐130, 1990)AbbreviationsADA, adenosine deaminasedADP, deoxyadenosine diphosphatedATP, deoxyadenosine triphosphatePEG‐ADA, polyethylene glycol‐modified adenosine deaminaseSAH, S‐adenosyl homocysteineSCID, severe combined immunodeficiency disease

ISSN:0031-3998    

出版商:OVID    

年代:1990

数据来源: OVID