Pulmonary mechanics in ventilated preterm infants with respiratory distress syndrome after exogenous surfactant administration: A comparison between two surfactant preparations

The effects of two surfactant preparations on lung mechanics have been studied on 24 ventilated premature infants with respiratory distress syndrome (RDS): 13 were given artificial surfactant (Exosurf Neonatal, Burroughs–Wellcome) and 11 natural porcine surfactant (Curosurf, Laboratoire Serono France). Measurements of respiratory system compliance (C_dyn C_rs) and resistance (R_rs) were performed immediately before surfactant administration and repeated 6, 18, 24, 48, and 72 hours later. With Exosurf treatment, 6 hours after surfactant administration inhaled O₂ concentration (F_IO₂) could be lowered from (0.72 ± 0.20, to 0.62 ± 0.33; P < 0.05), whereas (C_rs)did not change (0.37 mL/cmH₂O/kg, ± 0.14 vs. 0.39 ± 0.12, NS). After 24 hours and during the following days a significant increase in (C_rs) occurred (24 hours post-Exosurf: 0.51 ± 0.18, P < 0.05). With Curosurf treatment, the improvement in oxygenation was greater and F_IO₂ could be lowered much more after 6 hours (from (F_IO₂), 0.78 2 ± 0.23 to 0.34 ± 0.11, P < 0.01). This was associated with an increase in (C_rs) (from 0.39 ± 0.09 to 0.59 ± 0.17, P < 0.05). During the following days, (C_rs) was significantly higher in the group treated with Curosurf. Resistance was not altered by the type of surfactant preparation used except after 72 hours, when R_rs increased in the group treated with Exosurf. In conclusion, Curosurf appears to be more effective than Exosurf with regard to immediate pulmonary changes in ventilator treated premature infants with RDS. A rapid increase in (C_rs) after Curosurf treatment indicates that recruitment of new functional areas of the lung is likely to be associated with a stabilization of small airways and alveolar units. Pediatr Pulmonol. 1994;18:273–278 © Wiley-Liss, Inc. © Wiley-Liss, Inc.     

Comparison of dynamic and passive measurements of respiratory mechanics in ventilated newborn infants

Pulmonary mechanics may differ in intubated and ventilated infants depending on whether they are measured by a dynamic or passive method. The objective of this study was to compare respiratory mechanics measured by a dynamic technique with those obtained by a single-breath occlusion technique in ventilated newborn infants. Thirty-one preterm and 15 term infants (mean ± SD: gestational age, 29.3 ± 2.3 and 39.5 ± 1.4 weeks; birth weight, 1.2 ± 0.5 and 3.4 ± 0.4 kg; postnatal age, 12 ± 13 and 5 ± 4 days, respectively) were studied. Flows were measured through a pneumotachometer placed between the endotracheal tube and the ventilator circuit: tidal volume by integration of flow, and airway pressure directly with a pressure transducer. Airway occlusion was performed with a Neonatal Occlusion Valve (Bicore pulmonary monitor) at the end of inspiration, and the following relaxed exhalation was analyzed to give passive respiratory system compliance (C_rs) and resistance (R_rs). These values were compared with dynamic respiratory system compliance (C_dyn) and dynamic expiratory resistance (R_e) obtained with the PEDS system (P) within 1 hour, without an esophageal balloon and on the same ventilator settings. Dynamic respiratory system compliance and resistance measured with the PEDS and the Bicore systems did not differ significantly and were well correlated. Mean C_dyn(P) values in preterm and term infants were 77% and 77% of C_rs the equation of the regression line was c_dyn = 0.75 c_rs + 0.02 and C_dyn = 0.78 c_dyn ? 0.02; and standard error of the estimate (SEE) was 0.2 and 0.3 mL/cmH₂O with a correlation coefficient (r) of 0.89 and 0.89 (P < 0.0001), respectively. The mean R_e (P) values in preterm and term infants were 68% and 64% of R_rs and the equation of the regression line was R_e = 0.3 R_rs + 63 and R_e = 0.5 R_rs + 20, with SEE of 25 and 20 cmH₂O/Lsec, and r of 0.65 and 0.69 (P < 0.0001, P < 0.005). respectively. The two methods are non-invasive and were well tolerated. We conclude that passive and dynamic respiratory compliance and resistance measured in intubated infants are highly correlated, although the values measured by the passive technique are higher than those obtained by the dynamic technique. Pediatr Pulmonol. 1995; 20:258–264 . © 1995 Wiley-Liss, Inc.     

Measurement of lung volumes and pulmonary mechanics during weaning of newborn infants with intractable respiratory failure from extracorporeal membrane oxygenation

Newborn infants with intractable respiratory failure who require extracorporeal membrane oxygenation (ECMO) experience diffuse pulmonary atelectasis shortly after initiation of ECMO. Atelectasis is likely due to the primary lung injury and the reduction of applied inspiratory ventilator pressure when the respirator settings are changed to the “rest settings.” These pathophysiologic changes result in a decrease in lung compliance and lung volumes. We hypothesized that improving lung functions observed during ECMO and indicated by an increase in lung volumes will predict successful weaning from ECMO. Sixteen infants (mean SEM: gestational age, 40.3 ± 0.3 weeks; birth weight, 3.5 ± 0.1 kg) with meconium aspiration syndrome (n = 13), sepsis (n = 2), and persistent pulmonary hypertension (n = 1) were studied. We measured passive respiratory system mechanics and lung volumes initially during full ECMO support (115 ± 18 h on ECMO, Study I), and then within 24 h prior to weaning from ECMO (Study 11). Respiratory system compliance (C_rs), respiratory system resistance (Rrs), functional residual capacity (FRC), and tidal volume (V_T) were measured. Prior to Study I lung volumes were too small to be detected. C, increased between Study I and Study II (0.41±0.05 to 0.63±0.05 mL/cmH₂O/kg, P < 0.05), and V_T, increased between Study I and Study II (5.6 ± 0.6 to 10.4 ± 0.8mL/kg, P = 0.0005). FRC increased from 3.6 ± 1.0 to 7.9 ± 0.9mL/kg(P = 0.0001). There was no change in R_rs (88±8 to 89 ± 6 cm H₂O/Us, P = 0.9). The combination of C_rs > 0.5 mL/cmH₂O/kg and FRC > 5 mL/kg was a better predictor (P = 0.0002) of readiness to wean from ECMO than either C (>0.5 mL/cmH₂O/kg, P = 0.057) or FRC (>5 mL/kg, P = 0.007) alone. The combination of FRC and C_rs had a sensitivity of 73.3% and specificity of 100% for successful decannulation. We conclude that repeated measurements of FRC and C_rs can assess lung recovery and may assist in establishing criteria for successful weaning from ECMO. Pediatr Pulmonol. 1995; 20:145–151 . © 1995 Wiley-Liss, Inc.     

Low-frequency vs. High-frequency respiratory mechanics after methacholine challenge in artificially ventilated rabbits

Respiratory system resistance (R_rs) and elastance (E_rs) were estimated by two methods, before and after methacholine in six anesthetized, paralyzed, and artificially ventilated rabbits. R_rs and E_rs, were obtained (1) by multiple linear regression analysis of the relationship between tracheal pressure and tidal volume and flow [R_rs (mlr)], E_rs (mlr), and (2) by analysis of the Fourier transforms of tracheal pressure and flow resulting from 4 to 30 Hz pseudorandom pressure oscillations delivered by an Infant Star respirator [R_rs(os), E_rs(os)]. R_rs (os) was significantly lower than R_rs (mlr). For instance, R_rs (os) at 20 Hz [R_rs (os)20] was (mean±SD) 17.3±3.5 vs 21.4±3.6 cm H₂O · L^?1 · s (P < 0.01) for R_rs (mlr). E_rs (os) was significantly higher than the respective value obtained by multiple linear regression (718.2±81.0 vs 403.7±43.0 cm H₂O L^?1; P < 0.01). After methacholine, the changes of respiratory mechanics were similar with both methods. R_rs (mlr) and R_rs (os)20 increased respectively by 131±45 and 134±76%, and E_rs(mlr) and E_rs(os) increased respectively by 63±7 and 54±13%. A significant correlation was observed between R_rs(mlr) and R_rs (os)20 (r = 0.97) and between E_rs (mlr) and E_rs(os) (r = 0.96). We conclude that positive response to methacholine may be detected by forced oscillation as well as by multiple linear regression. However, the identified physiological components of the lung response (alteration in lung viscoelastic properties, increased lung inhomogeneity or increased intrathoracic airway shunt) are likely to be different with each method. Pediatr Pulmonol. 1993; 16:297–302. © 1993 Wiley-Liss, Inc.     

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 (R_rs), compliance (C_rs), and expiratory time constants (TC_rs), 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 beatshin 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 R_rs, C_rs, and TC_rs, values, and a second compartment with a very high R_rs. 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. We propose that in such patients the two compartment analysis of passive exhalation mechanics measurements can provide better information about R_rs. © 1993 Wiley-Liss, Inc.     

Role of positive end-expiratory pressure changes on functional residual capacity in surfactant treated preterm infants

Both surfactant replacement and positive end-expiratory pressure (PEEP) increase lung volume in infants with respiratory distress syndrome (RDS). We measured pulmonary mechanics and functional residual capacity (FRC) in 21 preterm infants with RDS, > 48 hr post-surfactant therapy (BW, 1,168 ± 441 g; GA, 28.3 ± 2.8 weeks; postnatal age, 3–7 days). A non-linear but significant increase in mean FRC was noted as PEEP increased from 2 to 5 cmH₂O: 18.4 ± 4.7mL/kg at 2 cmH₂O; 19.7 ± 4.3 mL at 3 cm H₂O; 22.6 ± 5.5ml/kg at 4 cmH₂O; and 26.2 ± 6.2 mL/kg at 5 cmH₂O (P < 0.01). Because of the synergistic combined effect on lung volume, surfactant treated neonates should be weaned cautiously from PEEP during ventilatory management. Our study also suggests that the occurrence of inadvertent end-distending pressure during FRC measurement in the ventilated neonate lead to erroneous results. Pediatr Pulmonal. 1994;18:89–92. © 1994 Wiley-Liss, Inc.     

Biochemical lung maturity,static respiratory compliance,and pulmonary gas transfer in intubated preterm infants with and without respiratory distress syndrome

We investigated the relationship between tests of biochemical lung maturity [lecithin/ sphingomyelin ratio (L/S ratio)], static compliance of the respiratory system (C_rs), and estimates of pulmonary gas transfer [venous admixture and arterial/alveolar (a/A) ratio] in a group of intubated preterm infants with and without respiratory distress syndrome (RDS). Thirty infants were studied once (n = 26) or twice (n = 4). The L/S ratio was obtained by means of high-performance thin-layer chromatography and determination of the phosphorus content. C_rs was obtained by the multiple occlusion technique. Transcutaneous blood gases and the percentage of oxygen in the inspired gas were recorded and estimates of pulmonary gas transfer were calculated using algorithms. L/S ratio and C_rs correlated well (r = 0.73), indicating a higher compliance in biochemically more mature lungs. Both the a/A ratio and venous admixture correlated significantly with the L/S ratio and C_rs (P < 0.001). C_rs L/S ratio, and a/A ratio decreased with increasing severity of radiological RDS, and the percentage venous admixture increased (P < 0.001). Sequential measurements in four infants during the acute phase and after RDS resolved indicated that clinical improvement coincided with improvements in biochemical lung maturity, C_rs, and estimates of pulmonary gas transfer. Pediatr Pulmonol. 1995; 20:152–159 . © 1995 Wiley-Liss, Inc.     

Efficacy of surfactant therapy in infants managed with CPAP

Surfactant rescue therapy can be utilized effectively early in the course of respiratory distress syndrome (RDS) in infants weighing > 1,000 g and treated exclusively with continuous positive airway pressure (CPAP) therapy. Thirteen infants (BW, 1,774 ± 580 g; GA, 31 ± 3 weeks) comprising the CPAP/SURFACTANT group were compared with 12 infants (BW, 1,753 ± 556 g; GA, 31 ± 2 weeks) who comprised the intermittent mandatory ventilation (IMV)/ surfactant group, and with 14 infants (BW, 1,776 ± 332 g; GA, 32 ± 2 weeks) treated with CPAP before surfactant was clinically available. A 5 mL/kg dose of Exosurf Neonatal (Burroughs-Wellcome) was administered to infants intratracheally when the F_iO₂ requirement reached 0.40 to maintain the PO₂ above 50 torr. Infants in the CPAP/surfactant group were intubated solely for surfactant administration and extubated within 18 ± 6 min of treatment. The CPAP/surfactant group was treated at a mean age of 12.3 ± 9.3 h, and the IMV/surfactant group at 10.2 ± 9.8 h. Alveolar-arterial oxygen gradient (AaDO₂), oxygenation index (OI), and mean airway pressure (MAP) were determined immediately before and after surfactant therapy, and at comparable times for the CPAP- only group. A significant difference was found in pre-treatment AaDO₂, OI, and MAP between the CPAP/ surfactant group and IMV/surfactant group, but not between the CPAP/surfactant group and the CPAP-only group. Similarly, a significant difference in AaDO₂, OI, and MAP continued post-treatment was noted. However, a significant difference was also found at this time between the CPAP/surfactant group and the CPAP- only group. In addition, a significant difference was noted in AaDO₂ and OI pre- and post-treatment within each surfactant-treated group. Furthermore, in the CPAP-only group AaDO₂ and OI actually worsened (212 ± 70 vs. 239 ± 68; 4.0 ± 1 vs. 4.5 ± 2, respectively). There was a significant reduction in the duration of oxygen therapy (3 ± 2 vs. 5 ± 2 vs. 4.5 ± 2 days, respectively) as well as in the total days of hospitalization (30 ± 10 vs. 42 ± 15 vs. 43 ± 12 days, respectively). We conclude that in this small group of infants surfactant administration was effective and safe. It appeared to improve the course of RDS and shorten the duration of oxygen exposure and days of hospitalization. Pediatr Pulmonol. 1995; 20:172–176 . © 1995 Wiley-Liss, Inc.     

Respiratory system reactance as an indicator of the intrathoracic airway response to methacholine in children

The upper airways may contribute to increases in airway resistance in response to a bronchial challenge, and thus decrease the specificity of such challenge tests to diagnose airway hyperresponsiveness when forced oscillation techniques are used to evaluate changes in respiratory system resistance (R_rs). A concomitent decrease in respiratory system reactance (X_rs) may indicate a change in the intrathoracic airways and/or lung parenchyma, provided that extrathoracic airway wall motion is prevented. To test the value of X_rs in the evaluation of bronchial hyperresponsiveness, we studied the respiratory impedance response to methacholine in 38 children with a history of asthma (aged 6–14.5 years), and compared the results to changes in the forced expiratory volume in one second (FEV₁). R_rs and X_rs were measured by the forced oscillation technique with pseudorandom (11 subjects) or sinusoidal (27 subjects) pressure variations applied around the child's head to minimize upper airway wall motion. Changes in R_rs and in X_rs at 12 Hz (R_rs12, X_rs12) correlated significantly with changes in FEV₁ (P < 0.005). A decrease in FEV₁ ≥20% was observed in 23 subjects. When these 23 subjects were compared with the 15 children who did not show significant changes in FEV₁, the responding group had larger mean ±SEM changes in R_rs (116.0 ± 13.2% vs 60.4 ± 11.4%;, P < 0.006) and in X_rs (−2.1 ± 0.4 hPa · s/L vs −0.9 ± 0.3 hPa·s/L, P < 0.03) than the nonresponders. The receiver operating characteristics (ROC) curve analysis was used to assess the diagnostic value, i.e., specificity and sensitivity, of different levels of change in R_rs and X_rs, with reference to FEV₁. The overall incidence of false results was similar for R_rs and X_rs. The optimum diagnostic value for R_rs was a 70% increase, which corresponded to a sensitivity of 87% and a specificity of 67%. For X_rs the optimum decision level was −1 hPa·s/L, corresponding to a sensitivity of 70% and a specificity of 80%. It is concluded that X_rs may improve the specificity of the forced oscillation technique in interpreting the airway response to methacholine. This may be of particular interest in young children unable to perform forced expirations. Pediatr Pulmonol. 1996;22:7–13. © 1996 Wiley-Liss, Inc.     

Evaluation of pulmonary functions during pressure-limited manual ventilation in preterm neonates

Manual ventilation (MAV) or handbagging is a frequent and often life—saving procedure for neonates; however, few studies allow for an objective evaluation of techniques or possible risks. We compared parameters of ventilation and pulmonary mechanics obtained during routine pressure—limited MAV to those obtained during spontaneous breathing (SPB) in the same infant at approximately the same time. We selected 20 preterm neonates in the recovery phase of respiratory distress syndrome who received periodic MAV and were capable of optimum spontaneous minute ventilation ( > 300 mL/kg/min). During MAV compared to SPB we measured higher tidal volume (8.1 ± 0.5 SE vs. 5.4 ± 0.4 SE mL/kg, P < 0.001), lower total pulmonary compliance (0.65 ± 0.05 vs. 1.16 ± 0.11 SE mL/cmH₂O, P < 0.001). end—inspiratory compliance, higher pulmonary resistance (121 ± 11 vs. 61 ± 7 SE cmH₂O/L/s, P < 0.001) and higher peak inspiratory airflow (2.8 ± 0.2 vs. 1.6 ± 0.1 L/s, P < 0.001). Inspiratory time (Ti) was consistently longer during MAV (0.49 ± 0.02 vs. 0.36 ± 0.02 SE, P < 0.001) such that during MAV the difference between actual Ti and minimal effective Ti (fivefold inspiratory time constant) was larger (0.29 ± 0.03 vs. 0.13 ± 0.03 s, P < 0.05). Our study suggests that operator—dependent ventilatory variables such as tidal volume, inspiratory time, frequency, and airflow need to be further evaluated in order to develop standardized guidelines for the safe administration of MAV. Until then the ventilator used for brief or augmented ventilatory support is a reasonable alternative to administering MAV by inconsistent standards. © 1993 Wiley-Liss, Inc.     

Influence of head-neck posture on airflow and pulmonary mechanics in preterm neonates

The influence of head-neck posture (neutral, 15°, 30°, and 45° extension and flexion) on airflow and pulmonary mechanics was evaluated in 10 spontaneously breathing healthy preterm neonates (mean ± SD; birth weight, 1.32 ± 0.23 kg; gestational age, 29.4 ± 2.4 weeks; study age, 36.6 ± 1.6 weeks) who had had respiratory distress syndrome. Head-neck postures were quantified using specially constructed wooden wedges. Airflow was measured by a pneumotachometer via face mask. Lung compliance (C_L) and resistance (R_L) were measured using an esophageal balloon. Airflow interruption was designated as mild (10–40%), moderate (40–80%), and severe (>80–00%) decrease of airflow. At neutral head-neck posture, 42.8 ± 7.5% SEM of breaths had airflow interruption (71.4% mild, 19.9% moderate, 8.7% severe). There was no significant change with 15° and 30° head-neck flexion and extension. However, at 45° flexion the overall incidence of airflow interruption (77.3 ± 4.8%, P < 0.05) and R, (86.6 ± 6.7 vs. 64.2 ± 3.9 cmH₂O/L/s, mean ± SEM; P < 0.05) significantly increased. Extension to 45° caused severe airflow interruption and increased R_L in some infants, but no statistically significant change for the whole group. The incidence of severe airflow interruption significantly increased (P < 0.05) from 8.7% at neutral head-neck posture to 26.3% at hyperflexion (45°). No changes in CL were observed. We conclude that minor (15–30°) deviations from neutral neck posture are insignificant, whereas hyperflexion, and in some infants, hyperextension, can significantly affect airflow and pulmonary mechanics. Pediatr Pulmonol. 1994; 17:149–154. © 1994 Wiley-Liss, Inc.     

氮气洗入/洗出法测定急性肺损伤患者肺复张容积的研究

  目的 探讨氮气洗入/洗出法测急性肺损伤(ALI)患者肺复张容积的准确性及可行性。方法 将15例有创机械通气的ALI患者纳入本研究,根据ARDSnet法和跨肺压法滴定2种呼气末正压(PEEP) 水平,分别通气30 min,记录各PEEP水平下潮气量(Vt)、气道平台压等呼吸力学及血流动力学指标,并利用氮气洗入/洗出法测2种PEEP水平的呼气末肺容积(EELV),根据公式推算氮气洗入/洗出法测的肺复张容积,同时根据低流速压力-容积(P-V)曲线法获得肺复张容积,比较2种方法获得的肺复张容积的相关性及一致性。结果 (1)ARDSnet法滴定的PEEP为（7±2） cm H₂O（1 cm H₂O=0.098 kPa）,气道峰压为（23±5） cm H₂O,气道平台压为(17±4） cm H₂O;跨肺压法滴定的PEEP为（14±5 )cm H₂O,气道峰压为（28±6） cm H₂O,气道平台压为（22±6） cm H₂O,2种方法比较差异有统计学意义(P<0.05)。(2) 低流速P-V曲线法测的肺复张容积为100（-25~185）ml,氮气洗入/洗出法测的肺复张容积为180（-19~255）ml,两者具有较好的相关性,R²=0.755,P<0.0001,且测量误差为46（8~80）ml。结论 氮气洗入/洗出法可测定ALI患者的肺复张容积。        

Ability of new lung function tests to assess methacholine-induced airway obstruction in infants

We assessed the ability of innovative lung function tests to detect bronchial obstruction induced by methacholine bronchial challenge. Fifty-five recurrently wheezy infants (mean age 16 ± 5.2 months) free of respiratory symptoms underwent baseline lung function tests. Forty-two completed the methacholine challenge. Maximal flow at functional residual capacity (V?_maxFRC) was obtained using the squeeze technique; compliance and resistance of the respiratory system (C_rs, R_rs,) was measured with the passive expiratory flow volume technique; tidal volume breathing patterns were analyzed from recordings of respiratory rate (RR), tidal volume (V?_T), and inspiratory time divided by total cycle of duration (T_i/T_tot). Expiratory tidal flow volume (V?/V_T) curves were described with multiple indices such as the ratio of expiratory time necessary to reach peak tidal expiratory flow (F_pet) to expiratory time (T_me/T_e). Transcutaneous oxygen tension (P_ICO2) was measured as an indicator of response to methacholine challenge. Of 42 infants 41 responded to methacholine by a change 3. 2 standard deviations from baseline values. The mean SD unit changes were 9.8 in (P_ICO2), 3.7 for V?_maxFRC. 2.8 for C_rs, 2.09 for R_rs 3.1 for RR, 1.6 for T₁/T_tot, 2.2 for T_me/T_e, 3.9 for PF_vt. We conclude that these noninvasive lung function tests, especially V?_maxFRC and F_pet, can be used to detect minor or moderate airway obstruction. Further studies are needed to determine the value of the tests in assessing bronchial disease and effects of its treatment. Pediatr Pulmonol. 1994;18:308–316 © Wiley-Liss, Inc.     

Respiratory resistance and transcutaneous P during histamine provocation in children with bronchial asthma

Bronchial reactivity was assessed in 66 children with bronchial asthma (aged 8–15 years) by provocation with histamine-HCl during a symptom-free period. A significant bronchial reaction to histamine was defined as a 50% increase in the resistance of the respiratory system (R_rs) determined by the forced oscillation technique. The provocative dose causing a 50% increase in the R_rs (PD₅₀R_rs) was interpolated from the log dose-response curve. The mean PD₅₀R_rs was significantly lower in children with asthma (0.22 mg/mL) compared with a group of healthy children in the same age range (1.55 mg/mL) (P < 0.001). In children with clinically severe asthma, the mean PD₅₀R_rs was lower (0.13 mg/ml) than in children with mild asthma (0.34 mg/mL) (P < 0.001). Transcutaneous Po₂ (Ptco₂) was monitored in 25 of the children with asthma. In this group the proportion of mild and severe asthma, the baseline lung function variables, and the PD₅₀R_rs were not significantly different from those of the whole group of children. During the reaction, the Ptc_o2 fell on average by 29% of the baseline value (P < 0.001); in 88% of the children, the fall in Ptc_o2 was 20% or more of the baseline value. We conclude that histamine provocation tests using the forced oscillation technique and transcutaneous Po₂ to assess a bronchial reaction have a good discriminatory capacity for different degrees of clinical severity of asthma in children. © 1993 Wiley-Liss, Inc.     

Lack of effects of beta sympathetic blockade on the metabolic and respiratory responses to carbohydrate feeding

Increases in metabolic rate, heart rate and ventilation occur following carbohydrate feeding or during beta sympathetic stimulation. Furthermore, insulin secretion and hypokalemia are features common to both which raises the question as to whether these effects of carbohydrate depend upon an intact sympathetic nervous system. Accordingly, in the present study, we measured the effects of carbohydrate feeding (250 gram meal) before and after chronic beta sympathetic blockade in sex normal men. Before blockade metabolic rate (0₂ consumption) rose (P < 0.05) from a fasting mean of 248 ± 19.7 (SEM) ML 0₂/min to 292 ± 15.2 at 1 hr, 269 ± 13.7 at 2, and 262 ± 18.0 at 3 hr following the meal. During blockade (oral propranolol 80 mg p.o. Q 6 h for 3 days) the post-prandial increase in 0₂ consumption was also significant (P < 0.05) and almost identical to that found before blockade. A similar pattern was found for ventilation, heart rate, insulin secretion and hypokalemia, where the significant postprandial changes were not altered by blockade. A transient increase in serum triiodothyronine from a mean of 92 ± 8.4 μg/ML to 109 ± 9.4 occurred at 1 hr (P < 0.05) only during blockade. No other changes in thyroid hormonal concentrations occurred as a result of the meal. We conclude that although similarities exist between beta sympathetic stimulation and carbohydrate feeding, the post-prandial effects studied do not depend on intact beta sympathetic receptors.     

Disease severity and optimum mean airway pressure level on transfer to high frequency oscillation

The aim of this study was to assess whether the severity of the infant's lung disease determined the most appropriate change in mean airway pressure (MAP) level to use on transfer from conventional ventilation to high frequency oscillation (HFO). In addition, we wished to assess whether the oscillatory frequency employed affected gas exchange. Ten premature infants with respiratory distress syndrome (RDS) were studied at a mean postnatal age of 1.5 days. During HFO, the infants were studied at a MAP equivalent of that used during conventional ventilation (baseline MAP), then at 2 and 5 cmH₂O above baseline at 10 Hz. At the MAP identified as optimum, that is, the one associated with the best oxygenation, the infants were then studied at 10, 15 and 20 Hz. Each oscillatory setting was maintained for 20 minutes after which time arterial blood gases were measured. Prior to transfer to the oscillator, the peak inspiratory pressure was recorded, the P calculated and compliance of the respiratory system C_rs) measured. In nine infants, the optimum baseline MAP was +5 cmH₂O. Oxygenation at that level was better than on conventional ventilation (P < 0.05), but there was no significant change in CO₂ elimination. The optimum MAP was related to the peak pressure during conventional ventilation (P < 0.01) and inversely related to C_rs (P < 0.01). There was no significant relationship with the P. At the optimum MAP, the only significant effect of frequency was an impairment of oxygenation at 20 Hz. We conclude that if a volume optimization strategy is pursued among infants with stiff lungs due to RDS, the appropriate starting level of MAP can be identified by stepwise changes in MAP. Impairment of oscillator performance at high frequencies can affect gas exchange. Pediatr Pulmonol. 1994; 17:178–182. © 1994 Wiley-Liss, Inc.     

Variability of Airway Responses in Mice

We examined the effect of animal strain, type of spasmogen, and mode of spasmogen administration on the pattern of lung mechanical responses in intubated and mechanically ventilated mice. We determined the response in inspiratory respiratory system resistance (R_rs) and inspiratory static respiratory system compliance (C_rs) to increasing doses of inhaled or intravenous carbachol or serotonin in Balb/C and C57BL/6 mice. R_rs responsiveness was quantitated by calculating, by interpolation, the inhaled spasmogen concentration (PC₁₅₀) and intravenous spasmogen dose (PD₁₅₀) causing an increase in R_rs to 150% of baseline. C_rs responsiveness was calculated similarly for a decrease in C_rs to 85% of baseline (PC₈₅ for inhaled and PD₈₅ for intravenous spasmogen). Baseline R_rs and C_rs were similar in all groups. R_rs responsiveness to inhaled and intravenous carbachol and serotonin tended to plateau and was not different in the two strains. In contrast, C_rs responses were variable and had a greater mean PC₈₅ for inhaled serotonin than carbachol in both strains and a greater fall in mean C_rs at PC₁₅₀ for carbachol in Balb/C mice; no interstrain and interdrug differences in PD₈₅ were noted for intravenous spasmogens. Intravenous atropine attenuated the R_rs response to high-dose inhaled and intravenous serotonin, suggesting the involvement of a vagal reflex. In contrast, atropine attenuated C_rs responses only for intravenous serotonin in Balb/C mice. These results suggest that animal strain, spasmogen, and mode of administration determine the extent to which induced airflow resistance is accompanied by increases in elastic recoil. Accepted for publication: 24 June 1999     

Continued pulmonary recovery observed after discontinuing extracorporeal membrane oxygenation

Extracorporeal membrane oxygenation (ECMO) is a valuable therapy for the treatment of reversible lung disease in neonates. Associated with this treatment, however, are risks for complications that increase with the duration of therapy. We evaluated alveolar-arterial oxygen tension difference P pulmonary compliance (C_L), and functional residual capacity (FRC) in 20 infants immediately after ECMO was discontinued, and again 24 hours thereafter. We measured C, by pnemotachography and eosphageal manometry and FRC by helium dilution. Mean (±SEM) values for C_L and FRC increased (C_L from 0.28 ± 0.02 to 0.35 ± 0.03 mL/cmH₂O)/kg and FRC from 18.6 ± 1.4 to 22.2 ± 1.1 mL/kg; P < 0.05), and P and the oxygenation index (OI) decreased (200 ± 19 to 169 ± 14 mm Hg and 6.9 ± 0.44 to 5.4 ± 0.5, respectively; P < 0.02), over the 24 hour period following ECMO. Nineteen of 20 infants experienced improvement in at least two of these parameters. Improvements were found to be greatest in the infant with the worst lung function immediately after discontinuing ECMO, and in the ten infants who had not received pancuronium bromide for inducing skeletal muscle paralysis, following decannulation from ECMO. These data indicate that improvement in lung function following ECMO will generally continue over the 24 hour period following the termination of cardiopulmonary bypass, and that borderline pulmonary status may not preclude discontinuation of bypass therapy. Pediatr Pulmonol. 1994; 17:143–148. © 1994 Wiley-Liss, Inc.     

Home testing for pediatric obstructive sleep apnea syndrome secondary to adenotonsillar hypertrophy

The objective of this study was to determine the accuracy and practicality of home testing for pediatric obstructive sleep apnea syndrome (OSAS) secondary to adenotonsillar hypertrophy. Twenty-one children aged 2-12 years and referred for possible OSAS were studied twice, once at home and once in the sleep laboratory. The home test consisted of two parts: (1) a cardiorespiratory recording of saturation (SaO₂), pulse rate, pulse waveform, electrocardiogram, and respiratory inductive plethysmography; and (2) an 8-hour videotape recording of the sleeping child. In the laboratory, standard nocturnal polysomnography including electroencephalography was performed. Experiences with another 62 children who underwent home testing alone were also reviewed and are reported. At home, saturation, respiratory, and video data were obtained 96.4 ± 13.3% (mean ± SD) 99.4 ± 1.6%, and 90.0 ± 7.8% of the time, respectively. The sleep efficiency was greater at home than in the laboratory, 91.1 ± 3.9% vs. 86.1 ± 7.2%, with a mean difference of 5.0% (P < 0.01). The median environmentally induced movement/arousal index was lower in the home than in the laboratory, 0.0 (inter-quartile range, 0.0-0.3) vs. 2.4/hr (inter-quartile range 1.2–4.2), with a median difference of 2.4/hr (P < 0.001). Study duration, apne/dhypopnea index, desaturation index, respiratory and spontaneous movement/arousal indices, and oxygen saturation during sleep were similar for home and laboratory studies. Although neither sleep state nor PCO₂, (transcutaneous or end-tidal) was measured in the home, this information would have modified patient management in, at most, one case. In the second group of 62 children, exclusively studied at home, all studies were successfully recorded despite a wide range of sleep efficiencies, apne/dhypopnea indices, and desaturation indices. We conclude that home testing, using a simplified cardiorespiratory montage plus video recording, is accurate and of practical use in the routine evaluation of OSAS in patients with adenotonsillar hypertrophy. Pediatr Pulmonol. 1995; 20:241–252 . © 1995 Wiley-Liss, Inc.