Lower Crs Research Articles

Optimization and impact of modified operating parameters of a diesel engine emissions characteristic utilizing waste fat biodiesel/di-tert-butyl peroxide blend

This study comprehensively investigated the transesterification process of converting waste pork fat oil into biodiesel as a fuel for the common rail direct injection (CRDI) diesel engine. In addition, Di-tert-butyl peroxide (DTBP) is used as an ignition enhancer to minimize exhaust gas emissions. The test fuels are diesel and diesel-waste pork fat biodiesel (WPFB)-DTBP blend (B20DTBP10 by volume), were used to analyze the engine outcome parameters with modified engines operating conditions like various compression ratios (CRs 16, 17.5, and 19) and injection pressures (IPs 400, 500 and 600 bar) at maximum load. The experiment results revealed that higher CRs and IPs, the heat release rate (HRR) and cylinder pressure increased. The brake thermal efficiency (BTE) is enhanced by increasing CRs and IPs but lowered than neat diesel. Smoke opacity decreased while increasing CRs and IPs. At CR 19 and IP 600 bar, smoke opacity decreased by 18.29%, related to baseline diesel. Increasing CRs and IPs lowered HC and CO emissions, but increasing IPs increased both emissions. HC and CO emissions were lowered in CR 19 and IP 500 bar by 21.73% and 28.49% more than neat diesel. The lower CRs and IPs, the oxides of nitrogen (NOx) emissions decreased, but further increasing CRs and IPs, the NOx emissions increased. Compared to baseline diesel, NOx emissions decreased in CR 16 and IP 400 bar by 15.49%. It was discovered that with increasing CRs and IPs, the emissions decreased with a minor rise in NOx emissions. Furthermore, the experimental results matched the predictions of an artificial neural network (ANN) model. The research concluded that the blend B20DTBP10 with modified engine operating conditions CRs and IPs suits diesel engine operation.

Neoadjuvant chemotherapy for high-grade serous ovarian cancer: radiologic-pathologic correlation of response assessment and predictors of progression.

Neoadjuvant chemotherapy is often administered for high-grade serous ovarian carcinoma (HGSC) prior to cytoreductive surgery. We evaluated treatment response by CT (simplified peritoneal carcinomatosis index [S-PCI]), pathology (chemotherapy response score [CRS]), laboratory markers (serum CA-125), and surgical outcomes, to identify predictors of disease-free survival. For this retrospective, HIPAA-compliant, IRB-approved study, we identified 396 women with HGSC receiving neoadjuvant chemotherapy between 2010 and 2019. Two hundred and ninety-nine patients were excluded (surgery not performed; imaging/pathology unavailable). Pre- and post-treatment abdominopelvic CTs were assigned CT S-PCI scores 0-24 (higher score indicating more tumor). Specimens were assigned CRS of 1-3 (minimal to complete response). Clinical data were obtained via chart review. Univariate, multivariate, and survival analyses were performed. Ninety-seven women were studied, with mean age of 65years ± 10. Interreader agreement was good to excellent for CT S-PCI scores (ICC 0.64-0.77). Despite a significant decrease in CT S-PCI scores after treatment (p < 0.001), mean decrease in CT S-PCI did not differ significantly among CRS categories (p = 0.20) or between patients who were optimally versus suboptimally debulked (p = 0.29). In a survival analysis, lower CRS (more viable tumor) was associated with shorter time to progression (p < 0.001). A joint Cox proportional-hazard models showed that only residual pathologic disease (CRS 1/2) (HR 4.19; p < 0.001) and change in CA-125 (HR 1.79; p = 0.01) predicted progression. HGSC response to neoadjuvant therapy by CT S-PCI did not predict pathologic CRS score, optimal debulking, or progression, revealing discordance between imaging, pathologic, biochemical, and surgical assessments of tumor response.

Response to Prone Position in COVID-19 and Non-COVID-19 Patients with Severe ARDS Supported by vvECMO.

For moderate to severe acute respiratory distress syndrome (ARDS), lung-protective ventilation combined with prolonged and repeated prone position (PP) is recommended. For the most severe patients for whom this strategy failed, venovenous extracorporeal membrane oxygenation (vv-ECMO) allows a reduction in ventilation-induced lung injury and improves survival. Some aggregated data have suggested a benefit regarding survival in pursuing PP during vv-ECMO. The combination of PP and vv-ECMO has been also documented in COVID-19 studies, although there is scarce evidence concerning respiratory mechanics and gas exchange response. The main objective was to compare the physiological response of the first PP during vv-ECMO in two cohorts of patients (COVID-19-related ARDS and non-COVID-19 ARDS) regarding respiratory system compliance (CRS) and oxygenation changes. This was a single-center, retrospective, and ambispective cohort study in the ECMO center of Marseille, France. ECMO was indicated according to the EOLIA trial criteria. A total of 85 patients were included, 60 in the non-COVID-19 ARDS group and 25 in the COVID-19-related ARDS group. Lung injuries of the COVID-19 cohort exhibited significantly higher severity with a lower CRS at baseline. Concerning the main objective, the first PP during vv-ECMO was not associated with a change in CRS or other variation in respiratory mechanic variables in both cohorts. By contrast, oxygenation was improved only in the non-COVID-19 ARDS group after a return to the supine position. Mean arterial pressure was higher during PP as compared with a return to the supine position in the COVID-19 group. We found distinct physiological responses to the first PP in vv-ECMO-supported ARDS patients according to the COVID-19 etiology. This could be due to higher severity at baseline or specificity of the disease. Further investigations are warranted.

Rapidly and slowly progressive neuromuscular disease: differences in pulmonary function, respiratory tract infections and response to lung volume recruitment therapy (LVR)

IntroductionReduced lung volumes are a hallmark of respiratory muscle weakness in neuromuscular disease (NMD). Low respiratory system compliance (Crs) may contribute to restriction and be amenable to lung volume recruitment...

Characterization of compliance phenotypes in COVID-19 acute respiratory distress syndrome

BackgroundCoronavirus disease 2019-associated acute respiratory distress syndrome (COVID-19 ARDS) seems to differ from the “classic ARDS”, showing initial significant hypoxemia in the face of relatively preserved compliance and evolving later in a scenario of poorly compliant lungs. We tested the hypothesis that in patients with COVID-19 ARDS, the initial value of static compliance of respiratory system (Crs) (1) depends on the previous duration of the disease (i.e., the fewer days of illness, the higher the Crs and vice versa) and (2) identifies different lung patterns of time evolution and response to prone positioning.MethodsThis was a single-center prospective observational study. We enrolled consecutive mechanically ventilated patients with a diagnosis of COVID-19 who met ARDS criteria, admitted to intensive care unit (ICU). Patients were divided in four groups based on quartiles of initial Crs. Relationship between Crs and the previous duration of the disease was evaluated. Respiratory parameters collected once a day and during prone positioning were compared between groups.ResultsWe evaluated 110 mechanically ventilated patients with a diagnosis of COVID-19 who met ARDS criteria admitted to our ICUs. Patients were divided in groups based on quartiles of initial Crs. The median initial Crs was 41 (32–47) ml/cmH2O. No association was found between the previous duration of the disease and the initial Crs. The Crs did not change significantly over time within each quartile. Positive end-expiratory pressure (PEEP) and driving pressure were respectively lower and greater in patients with lower Crs. Prone positioning significantly improved PaO2/FiO2 in the 4 groups, however it increased the Crs significantly only in patients in lower quartile of Crs.ConclusionsIn our cohort, the initial Crs is not dependent on the previous duration of COVID-19 disease. Prone positioning improves oxygenation irrespective to initial Crs, but it ameliorates respiratory mechanics only in patients with lower Crs.

Paradoxical Positioning: Does "Head Up" Always Improve Mechanics and Lung Protection?

OBJECTIVES:Head-elevated body positioning, a default clinical practice, predictably increases end-expiratory transpulmonary pressure and aerated lung volume. In acute respiratory distress syndrome (ARDS), however, the net effect of such vertical inclination on tidal mechanics depends upon whether lung recruitment or overdistension predominates. We hypothesized that in moderate to severe ARDS, bed inclination toward vertical unloads the chest wall but adversely affects overall respiratory system compliance (Crs).DESIGN:Prospective physiologic study.SETTING:Two medical ICUs in the United States.PATIENTS:Seventeen patients with ARDS, predominantly moderate to severe.INTERVENTION:Patients were ventilated passively by volume control. We measured airway pressures at baseline (noninclined) and following bed inclination toward vertical by an additional 15°. At baseline and following inclination, we manually loaded the chest wall to determine if Crs increased or paradoxically declined, suggestive of end-tidal overdistension.MEASUREMENTS AND MAIN RESULTS:Inclination resulted in a higher plateau pressure (supineΔ: 2.8 ± 3.3 cm H2O [p = 0.01]; proneΔ: 3.3 ± 2.5 cm H2O [p = 0.004]), higher driving pressure (supineΔ: 2.9 ± 3.3 cm H2O [p = 0.01]; proneΔ: 3.3 ± 2.8 cm H2O [p = 0.007]), and lower Crs (supine Δ: 3.4 ± 3.7 mL/cm H2O [p = 0.01]; proneΔ: 3.1 ± 3.2 mL/cm H2O [p = 0.02]). Following inclination, manual loading of the chest wall restored Crs and driving pressure to baseline (preinclination) values.CONCLUSIONS:In advanced ARDS, bed inclination toward vertical adversely affects Crs and therefore affects the numerical values for plateau and driving tidal pressures commonly targeted in lung protective strategies. These changes are fully reversed with manual loading of the chest wall, suggestive of end-tidal overdistension in the upright position. Body inclination should be considered a modifiable determinant of transpulmonary pressure and lung protection, directionally similar to tidal volume and positive end-expiratory pressure.

Compliance Phenotypes in Early Acute Respiratory Distress Syndrome before the COVID-19 Pandemic.

Rationale: A novel model of phenotypes based on set thresholds of respiratory system compliance (Crs) was recently postulated in context of coronavirus disease (COVID-19) acute respiratory distress syndrome (ARDS). In particular, the dissociation between the degree of hypoxemia and Crs was characterized as a distinct ARDS phenotype.Objectives: To determine whether such Crs-based phenotypes existed among patients with ARDS before the COVID-19 pandemic and to closely examine the Crs–mortality relationship.Methods: We undertook a secondary analysis of patients with ARDS, who were invasively ventilated on controlled modes and enrolled in a large, multinational, epidemiological study. We assessed Crs, degree of hypoxemia, and associated Crs-based phenotypic patterns with their characteristics and outcomes.Measurements and Main Results: Among 1,117 patients with ARDS who met inclusion criteria, the median Crs was 30 (interquartile range, 23–40) ml/cm H2O. One hundred thirty-six (12%) patients had preserved Crs (≥50 ml/cm H2O; phenotype with low elastance [“phenotype L”]), and 827 (74%) patients had poor Crs (<40 ml/cm H2O; phenotype with high elastance [“phenotype H”]). Compared with those with phenotype L, patients with phenotype H were sicker and had more comorbidities and higher hospital mortality (32% vs. 45%; P < 0.05). A near complete dissociation between PaO2/FiO2 and Crs was observed. Of 136 patients with phenotype L, 58 (43%) had a PaO2/FiO2 < 150. In a multivariable-adjusted analysis, the Crs was independently associated with hospital mortality (adjusted odds ratio per ml/cm H2O increase, 0.988; 95% confidence interval, 0.979–0.996; P = 0.005).Conclusions: A wide range of Crs was observed in non–COVID-19 ARDS. Approximately one in eight patients had preserved Crs. PaO2/FiO2 and Crs were dissociated. Lower Crs was independently associated with higher mortality. The Crs–mortality relationship lacked a clear transition threshold.

Respiratory Mechanics and Outcomes in Immunocompromised Patients With ARDS: A Secondary Analysis of the EFRAIM Study

In view of the high mortality rate of immunocompromised patients with ARDS, it is important to identify targets for improvement. This study investigated factors associated with mortality in this specific ARDS population, including factors related to respiratory mechanics (plateau pressure [Pplat,rs], compliance [Crs], and driving pressure [ΔPrs]). This study consisted of a predefined secondary analysis of the EFRAIM data. Overall, 789 of 1,611 patients met the Berlin criteria for ARDS, and Pplat,rs, ΔPrs, and Crs were available for 494 patients. A hierarchical model was used to assess factors at ARDS onset independently associated with hospital mortality. Hospital mortality was 56.3%. After adjustment, variables independently associated with hospital mortality included ARDS of undetermined etiology (OR, 1.66; 95%CI, 1.01-2.72), need for vasopressors (OR, 1.91; 95%CI, 1.27-2.88), and need for renal replacement therapy (OR, 2.02; 95%CI, 1.37-2.97). ARDS severity according to the Berlin definition, neutropenia on admission, and the type of underlying disease were not significantly associated with mortality. Before adjustment, higher Pplat,rs, higher ΔPrs, and lower Crs were associated with higher mortality. Addition of each of these individual variables to the final hierarchical model revealed a significant association with mortality: ΔPrs (OR, 1.08; 95%CI, 1.05-1.12), Pplat,rs (OR, 1.07; 95%CI, 1.04-1.11), and Crs (OR, 0.97; 95%CI, 0.95-0.98). Tidal volume was not associated with mortality. In immunocompromised patients with ARDS, respiratory mechanics provide additional prognostic information to predictors of hospital mortality. Studies designed to define lung-protective ventilation guided by these physiological variables may be warranted in this specific population.

Forage grasses with lower uptake of caesium and strontium could provide 'safer' crops for radiologically contaminated areas.

Substitution of a species or cultivar with higher uptake of an element by one with lower uptake has been proposed as a remediation strategy following accidental releases of radioactivity. However, despite the importance of pasture systems for radiological dose, species/cultivar substitution has not been thoroughly investigated for forage grasses. 397 cultivars from four forage grass species; hybrid ryegrass (Lolium perenne L. x Lolium multiflorum Lam.), perennial ryegrass (Lolium perenne L.), Italian ryegrass (Lolium multiflorum Lam.) and tall fescue (Festuca arundinacea Shreb.); were sampled from 19 field-based breeding experiments in Aberystwyth and Edinburgh (UK) in spring 2013 and analysed for caesium (Cs) and strontium (Sr) concentrations. In order to calculate concentration ratios (CRs; the concentration of an element in a plant in relation to the concentration in the soil), soils from the experiments were also analysed to calculate extractable concentrations of Cs and Sr. To test if cultivars have consistently low Cs and Sr concentration ratios, 17 hybrid ryegrass cultivars were sampled from both sites again in summer 2013 and spring and summer 2014. Tall fescue cultivars had lower Cs and Sr CRs than the other species. Three of the selected 17 hybrid ryegrass cultivars had consistently low Cs CRs, two had consistently low Sr CRs and one had consistently low Cs and Sr CRs. Cultivar substitution could reduce Cs CRs by up to 14-fold and Sr CRs by 4-fold in hybrid ryegrass. The identification of species and cultivars with consistently low CRs suggests that species or cultivar substitution could be an effective remediation strategy for contaminated areas.

Lung function at follow‐up of infants with surgically correctable anomalies

Infants with congenital diaphragmatic hernia (CDH) or anterior wall defects (AWD) can suffer abnormal antenatal lung growth, the risk, however, may be greater for CDH infants. The objectives of this study were to test the hypothesis that following surgical correction, CDH infants would have worse lung function at follow-up than AWD infants and to determine whether fetal lung volume (FLV) results correlated with the lung function results at follow-up. Thirteen infants with CDH and 13 infants with AWD had lung function measurements at a median age of 11 (range 6-24) months; 17 of the infants had had their FLV assessed. Lung function was assessed by plethysmographic measurement of lung volume (FRCpleth) and airway resistance (Raw). In addition, functional residual capacity was assessed by a helium gas dilution technique (FRCHe); tidal breathing parameters (T(PTEF) :Te) and compliance and resistance of the respiratory system (Crs and Rrs, respectively) were also determined. FLV was assessed using three-dimensional (3D) ultrasound and virtual organ computer aided analysis. The CDH compared to the AWD infants had a higher median FRCpleth (41 ml/kg vs. 37 ml/kg, P = 0.043) and a lower median Crs (1.45 ml/cm H(2) O/kg vs. 2.78 ml/cm H(2) O/kg, P = 0.041). FRCpleth results correlated significantly with FLV results (r = 0.721, P < 0.001). In conclusion, infants with CDH had significantly different lung function at follow-up than AWD infants. Our findings suggest FLV results may predict lung function abnormalities at follow-up in infants with surgically correctable anomalies.

Cluster analysis of behavioural and event-related potentials during a contingent negative variation paradigm in remitting-relapsing and benign forms of multiple sclerosis

BackgroundEvent-related potentials (ERPs) may be used as a highly sensitive way of detecting subtle degrees of cognitive dysfunction. On the other hand, impairment of cognitive skills is increasingly recognised as a hallmark of patients suffering from multiple sclerosis (MS). We sought to determine the psychophysiological pattern of information processing among MS patients with the relapsing-remitting form of the disease and low physical disability considered as two subtypes: 'typical relapsing-remitting' (RRMS) and 'benign MS' (BMS). Furthermore, we subjected our data to a cluster analysis to determine whether MS patients and healthy controls could be differentiated in terms of their psychophysiological profile.MethodsWe investigated MS patients with RRMS and BMS subtypes using event-related potentials (ERPs) acquired in the context of a Posner visual-spatial cueing paradigm. Specifically, our study aimed to assess ERP brain activity in response preparation (contingent negative variation -CNV) and stimuli processing in MS patients. Latency and amplitude of different ERP components (P1, eN1, N1, P2, N2, P3 and late negativity -LN) as well as behavioural responses (reaction time -RT; correct responses -CRs; and number of errors) were analyzed and then subjected to cluster analysis.ResultsBoth MS groups showed delayed behavioural responses and enhanced latency for long-latency ERP components (P2, N2, P3) as well as relatively preserved ERP amplitude, but BMS patients obtained more important performance deficits (lower CRs and higher RTs) and abnormalities related to the latency (N1, P3) and amplitude of ERPs (eCNV, eN1, LN). However, RRMS patients also demonstrated abnormally high amplitudes related to the preparation performance period of CNV (cCNV) and post-processing phase (LN). Cluster analyses revealed that RRMS patients appear to make up a relatively homogeneous group with moderate deficits mainly related to ERP latencies, whereas BMS patients appear to make up a rather more heterogeneous group with more severe information processing and attentional deficits.ConclusionsOur findings are suggestive of a slowing of information processing for MS patients that may be a consequence of demyelination and axonal degeneration, which also seems to occur in MS patients that show little or no progression in the physical severity of the disease over time.

Sugarcane Responses to Water‐Table Depth and Periodic Flood

Sugarcane (Saccharum spp.) is exposed to periodic floods and shallow water tables in Florida due to practices that reduce P discharge to the Everglades. This study examined the yields and juice quality of four sugarcane cultivars (CP 88‐1762, CP 89‐2143, CP 89‐2376, and CP 96‐1252) maintained at constant water‐table depths near 20 (20CWT) and 45 cm (45CWT) and with periodic summer flooding. Prescribed lysimeters were flooded for the first 7 d of five, five, and four 21‐d cycles in 2005 (plant‐cane crop), 2006 (first‐ratoon crop), and 2007 (second‐ratoon crop), respectively. These treatments generally remained flooded during the next 7 d while they received no irrigation or drainage, and were drained to 20 (20FWT) or 45 cm (45FWT) for the final 7 d of each cycle. Water treatment affected CRS only in the plant‐cane crop, where 45CWT had lower CRS than 20CWT, 20FWT, and 45FWT. Yields of cane and sucrose of CP 89‐2143 were least affected by water treatments. Reductions in cane and sucrose yields at a 20 compared with a 45 cm water‐table depth were common for the other three cultivars, but yields under the 20CWT vs. 20FWT or 45CWT vs. 45FWT treatments were generally similar. These results suggest that sugarcane roots function well in flood for up to 14 d, but do not grow well into saturated soil. This provides new options for sustaining high yields of sugarcane exposed to shallow water tables and floods; verification of root responses could enhance strategies to sustain yields while reducing P discharge.

Tracheal occlusion decreases airway resistance but not lung tissue mechanics in fetal rabbits with diaphragmatic hernia

MECHANICS IN FETAL RABBITS WITH DIAPHRAGMATIC HERNIA JACQUES JANI, ANDREAS FLEMMER, FLORIAN BERGMANN, XENIA ROUBLIOVA, DENIS GALLOT, OLIVER MUENSTERER, LISBETH VERCRUYSSE, KERSTIN HAJEK, HOLGER TILL, JAN DEPREST, Catholic University of Leuven, Center for Surgical Technologies, Leuven, Belgium, Ludwig-Maximilians-University, Department of Neonatology, Munich, Germany, Dr. von Hauner Children’s Hospital, University of Munich, Department of Pediatric Surgery, Munich, Germany, Catholic University of Leuven, Laboratory of Experimental Gynecology, Leuven, Belgium OBJECTIVE: To document the effect of tracheal occlusion (TO) on ventilatory parameters in a rabbit surgical model for diaphragmatic hernia (DH) using the forced oscillation technique. STUDY DESIGN: In New Zealand white rabbits fetuses of 23 d (term = 31d) underwent either surgical creation of DH (n = 18) or sham thoracotomy (Sham; n = 6). Half of DH-fetuses were randomly chosen to undergo TO @ 28d (DHCTO; n = 8). Non-operated littermates served as controls (n = 15). After term delivery, pups were intubated and connected to a Flexivent ventilator for 1 h. Outcome measures were body weight, lung weight, lungbody-weight ratio (LBWR), dynamic lung mechanics (Resistance; Rrs and Compliance; Crs) and lung impedance. Airway resistance (Raw), elastance (HL), tissue damping (GL) and hysteresivity (GL/HL) were calculated from impedance data. Sections of ventilated lungs were stained with Sirius-red to determine collagen content. Statistics were done using ANOVA. RESULTS: LBWR was larger in DHCTO than DH (p!0.01) and Sham (p!0.05) but not than controls. Crs and Rrs were no different in DHCTO than DH and Sham fetuses, but lower (Crs) resp. no different (Rrs) than in controls. Raw was decreased in DHCTO compared to DH but not to Sham and controls. DHCTO had no effect on lung tissue mechanic parameters HL, GL and hysteresivity; those fetuses also had morphologically a lower lung collagen content than DH. CONCLUSION: TO increases LBWR and improves mechanical lung properties in fetal rabbits with DH. TO has an effect on airway resistance but not on lung tissue mechanics.

Significance of the changes in the respiratory system pressure-volume curve during acute lung injury in rats.

The hypothesis that the changes in the respiratory system pressure- volume (PV) curve during pulmonary edema mainly reflect distal airway obstruction was investigated in rats. Normal rats had a well-defined upper inflection point (UIP) at low airway pressure. Airway occlusion by liquid instillation decreased compliance (Crs) and the volume (Vuip) of the UIP, and increased end-inspiratory pressure. The same changes were observed during the progression of edema produced by high volume ventilation (HV). Changes in Vuip and in Crs produced by HV were correlated with edema severity in normal rats or rats with lungs preinjured with alpha-naphthylthiourea. Vuip and Crs changes were proportional, reflecting compression of the PV curve on the volume axis and suggesting reduction of the amount of ventilatable lung at low airway pressure. In keeping with this explanation, the lower Vuip and Crs were before HV, the more severe HV-induced edema was in alpha-naphthylthiourea-injected rats. When edema was profuse, PV curves displayed a marked lower inflection point (LIP), the UIP at low pressure disappeared but another was seen at high volume above the LIP, and the correlation between Vuip changes and edema severity was lost. These observations may have clinical relevance in the context of the "open lung" strategy. ventilator-induced lung injury; respiratory mechanics; acute respiratory distress syndrome

Pulmonary function in infants with neonatal chronic lung disease with or without hyaline membrane disease at birth.

We studied whether neonatal chronic lung disease (NCLD), hyaline membrane disease (HMD) and differences in ventilatory support affected pulmonary function during the first year of life, in 65 infants born prematurely. The relationship between body weight and oxygen consumption (V'O2) was also analysed. The study comprised 14 infants without cardiorespiratory disease, 19 infants with HMD but without NCLD, 9 infants with NCLD without prior HMD, and 23 infants with NCLD following HMD. At 6 and 12 months corrected postnatal age, static respiratory system compliance (Crs) was measured by weighted spirometry and the functional residual capacity by closed circuit helium dilution (FRCHe) combined with assessment of ventilation distribution from the mixing index (MI). Ventilatory support during the first 5 days of therapy was quantified from peak inspiratory pressure (PIP), mean airway pressure (MAP) and fractional inspiratory concentration of oxygen (FI,O2). Infants with NCLD had a shorter duration of gestation and lower birth weight than those without NCLD (Wilcoxon, p=0.002 and p=0.001, respectively). Pulmonary function at 6 and 12 months corrected age was not different between NCLD infants with or without HMD at birth. Infants with NCLD had lower Crs and MI than those without NCLD (analysis of variance (ANOVA), p<0.011), but their FRCHe was not different. V'O2 adjusted for body weight was comparable in the four groups. PIP and FI,O2 were higher (Wilcoxon, p<0.01) in the NCLD infants than in those with HMD alone, but MAP was not different. Except for FI,O2, these indices were not different among the infants with NCLD. We conclude that birth weight is the major determinant of the development of neonatal chronic lung disease. At 6 and 12 months corrected age, the abnormal pulmonary function is not associated with prior hyaline membrane disease.

Referencing lung volume for measurements of respiratory system compliance in infants.

We propose a method for measurements of respiratory system compliance (Crs) in spontaneously breathing infants, which circumvents the potential problems introduced by the breath-by-breath oscillations in the end-expiratory level, i.e., functional respiratory capacity (FRC). Changes in lung volume (V) and pressure at the airway opening (P(ao)) were measured in 10 infants breathing through a face mask. A first brief occlusion was to establish a reference V and the corresponding static P(ao); a second occlusion was done at a different V, within the same expiration, or in the following breath. Both occlusions were sufficiently long for the establishment of a stable P(ao) value. From the V difference (delta V, where delta V was at least 20% tidal volume) and the corresponding difference in P(ao) (delta P(ao)) Crs was computed and averaged (Crs[REF.VOL.] = delta V/delta P(ao). Although, on average, the results were similar to those obtained by the traditional multiple occlusions technique with linear regression analysis of the P(ao)-V data points (Crs[MOT]), in several infants Crs[REF.VOL.] tended to be slightly higher than Crs[MOT]. Some possibilities for this discrepancy are discussed. It seems likely that breath-to-breath oscillation in FRC may potentially lower Crs[MOT] by introducing a bias on the V measurement at low P(ao). We conclude that referencing V for Crs measurements in spontaneously breathing infants is a simple approach, which does not require linear regression analysis and circumvents the effects of oscillation in FRC.

RAPID IMPROVEMENT IN RESPIRATORY COMPLIANCE AFTER PORCINE SURFACTANT

Treatment with surfactant is associated with a rapid improvement in oxygenation, but no work has yet demonstrated a rapid increase in respiratory compliance (Crs). Using a computerised passive expiratory flow technique, we measured respiratory compliance immediately before, at 3 hours and 12 hours after the first dose of surfactant (Curosurf) in 33 infants with respiratory distress syndrome and a/A ratio < 0.22. Using the same technique in an earlier reference population, no infant with Crs ≥ 2ml/cm H2O/m had biochemical evidence of surfactant deficiency. There was an increase of 6% in mean Crs at 3 hours after surfactant (NS: p = 0.227). Excluding 3 infants with initial Crs ≥ 2 ml/cm H2O/m, the increase in Crs at 3 hours was 13% (p = 0.016). In keeping with previous experience, there was rapid improvement in oxygenation, with a mean reduction in FiO2 of 45% of its initial value 3 hours after surfactant (p < 0.001). All 3 infants with an initial Crs of ≥2 ml/cm H2O/m had lower Crs 3 hours after surfactant. In the infants whose initial Crs was < 2 ml/cm H2O/m Crs increased by 38% (p<.001) and FiO2 decreased by 52% (p <.001) 12 hours after surfactant. These data suggest, for the first time, that porcine surfactant rapidly improves Crs, in parallel with improvements in oxygenation. This technique may identify infants who are most likely to benefit acutely from surfactant.

Perioperative respiratory compliance in children undergoing repair of atrial septal defects

Children with atrial septal defects (ASD) have less respiratory compliance (Crs) than normal cohorts. There could be implications for anaesthetic management if these children also have decreased compliance during anaesthesia. To examine the changes in Crs before, during and following surgical correction of the atrial defect, Crs was measured in 29 infants and children, 15 undergoing correction of secundum type atrial septal defects, and a group of 14 children of similar weight undergoing non-thoracic surgery. During sedation, Crs was measured using the single breath technique (SBT) and during anaesthesia, both before and after the surgical procedure, an inflation technique was applied to determine Crs. To investigate the aetiology of the difference in Crs, the pulmonary to systemic flow ratio (Qp:Qs) was determined using echocardiography during sedation in the ASD patients. During sedation, Crs in the ASD group was 52.7 +/- 19.5% less than in the control group. The slope of the line of regression of Crs vs height for the ASD group was significantly less (P less than 0.05) than that of the control group during sedation. However, during anaesthesia, Crs in the ASD group was not significantly different from the control group either before or after surgery. The per cent decrease in Crs during sedation in the children with ASD, in comparison with the control group, did not correlate with the Qp:Qs ratio of the ASD group (r2 = 0.012,NS). We conclude that, in spite of lower Crs during sedation, infants and children with ASD do not have lower Crs during anaesthesia and cardiopulmonary bypass than normal controls undergoing non-thoracic surgery.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of dynamic and static measurements of respiratory mechanics in infants

The objective of this study was to compare the conventional method of measuring respiratory mechanics, which requires the passage of an esophageal tube, with the occlusion technique, which is less invasive. Thirty-nine preterm infants who received mechanical ventilation on the first day were studied before discharge (mean +/- SD: postnatal age 67 +/- 23 days; weight 1790 +/- 300 gm), and 27 of them again at 1 year (weight 8.1 +/- 1.4 kg). Flows were measured through a nosepiece by pneumotachometry, tidal volume by integration of flow, esophageal pressure through a water-filled tube, and airway pressure directly at the nasal piece. Airway occlusion was performed at the end of inspiration, and the following relaxed exhalation was analyzed to give compliance (Crs) and resistance (Rrs) of the respiratory system. These values were compared with dynamic lung compliance (Cdyn) and expiratory resistance (Re) of the previous unoccluded breath. In the younger infants, dynamic and static measurements did not differ significantly and were well correlated (Cdyn/Crs, r = 0.91; Re/Rrs, r = 0.95). In the older infants, Crs was 80% of Cdyn (p less than 0.001), and Rrs was 24% higher than Re (p less than 0.001). The measurements were well correlated (Cdyn/Crs, r = 0.94; Re/Rrs, r = 0.91). The regression line Cdyn versus Crs had a slope (0.77) significantly less than 1; the regression Re versus Rrs had an intercept (13.8) significantly greater than zero. The lower Crs and higher Rrs values can be expected because the static determinations include the chest wall. In the more immature infants, the very compliant chest wall, in combination with an underestimation of Cdyn because of the higher breathing frequency of these infants, may obscure this difference. We conclude that the occlusion technique gives accurate and reproducible results, is easily applied, does not need the passage of an esophageal tube, and is well tolerated by the infants.

Total respiratory system compliance in asymptomatic infants with cystic fibrosis.

Total respiratory system compliance (Crs) was assessed by the weighted spirometer method in 11 asymptomatic infants (mean age, 11.1 months) with cystic fibrosis (CF) who had normal chest radiographs. In addition to Crs, functional residual capacity (FRC), respiratory rate (RR), and mixing index (MI) were measured. There was no significant difference in FRC between normal controls (n = 36) and CF infants (190 +/- 69 versus 186 +/- 63 ml; p less than 0.8), although the CF group had a higher RR (32 +/- 7 versus 37 +/- 7 BPM; p less than 0.05) and a lower MI (45 +/- 7 versus 40 +/- 8%; p less than 0.05), reflecting an abnormal distribution of ventilation. The lower Crs (9.0 +/- 3.4 versus 5.7 +/- 2.8 ml/cm H2O; p less than 0.01) and the lower specific compliance, Crs/FRC (0.049 +/- 0.013 versus 0.029 +/- 0.007 1/cm H2O; p less than 0.0001), in the CF group were the parameters that best distinguished the normal control and CF infants. We conclude that the measurement of Crs represents a noninvasive method for detecting early pulmonary function abnormalities in CF infants.