Compliance Of The Respiratory System Research Articles

Lung function in infants with chronic pulmonary disease after severe adenoviral illness

Objective: To evaluate pulmonary function and bronchodilator responses in young children with chronic pulmonary disease (CPD) after a severe adenoviral lower respiratory tract infection. Methods: Pulmonary function tests were performed in 13 patients (mean age, 1.32 ± 0.8 years) with CPD and were compared with a control group of 13 healthy infants (mean age, 1.16 ± 0.4 years). Results: Respiratory rate, peak tidal expiratory flow (PTEF), PTEF/tidal volume, absolute time up to PTEF, time percentage to PTEF, volume percentage for PTEF, and compliance and resistance of the respiratory system were significantly affected in the CPD group. Similarly, maximal flow at functional residual capacity (V ́maxFRC) was 56.0 ± 42 mL/s and 373 ± 107 mL/s in the CPD and control groups, respectively ( P = .001). No within-group differences with baseline values or between-group differences were noted in response to treatment with ipratropium bromide or albuterol. Conclusion: Young children with CPD caused by adenovirus have pulmonary function changes characterized by severe obstruction and diminished lung distensibility not responsive to the administration of inhaled ipratropium bromide or albuterol. (J Pediatr 134:730-3)

Decrease in Lung Volume Depends on End-Expiratory Pressure in a Rabbit Model of Airway Lavage

Background: In the past, the rabbit model of repeated airway lavage has been extensively used to induce a decrease in lung volume accompanied by impairment in lung mechanics and gas exchange. Objectives: The rationale of our study was to investigate the influence of different end-expiratory pressure (EEP) levels (0.4–4.2 cm H₂O) on changes in functional residual capacity (FRC) and the efficacy of lavages administered. Methods: Forty-five rabbits were subjected to 2–8 lavages with 20 ml/kg warm normal saline until arterial/alveolar oxygen tension (a/A ratio) had decreased to ≤0.12. Results: FRC and dynamic compliance of the respiratory system (C_rs) decreased significantly (both p < 0.001; from 19.1 ± 4.2 to 10.5 ± 5.6 ml/kg and from 1.17 ± 0.27 to 0.47 ± 0.10 ml/cm H₂O, respectively, means ± SD). The decrease in FRC was significantly influenced by EEP (–28.6 ± 15.8% at EEP = 1 cm H₂O vs. –58.7 ± 12.9% at EEP = 3 cm H₂O, p < 0.0001). There was a significant correlation between the number of lavages and EEP (p < 0.01), indicating that successive lavages at higher EEP became ineffective in lowering FRC compared to those at lower EEP. Conclusions: We conclude that the EEP levels used in this model are of critical importance for the prediction of a decrease in lung volume (FRC) and the efficacy of lavages.

Combined effects of inhaled nitric oxide and hyperoxia on pulmonary vascular permeability and lung mechanics.

To determine whether inhaled nitric oxide (NO) may alter pulmonary vascular permeability and respiratory function in an in vivo model. Prospective, randomized, controlled, experimental study. University experimental pharmacology laboratory. Mechanically ventilated newborn piglets, 1 to 2 days old, exposed to 100% oxygen for 76 hrs. The piglets were randomly assigned either to a treatment group receiving 20 ppm inhaled NO from the onset of ventilation (n = 5) or to a control group (n = 6) receiving no treatment. The main variables studied were gas exchange (PaO2/F(IO2) ratio, lung diffusing capacity), respiratory mechanics (static compliance of the respiratory system, stat, quasi-static hysteresis area, functional residual capacity), and pulmonary vascular permeability assessed by simultaneous intravenous administration of iodine-125-labeled albumin and chromium-51-labeled red blood cells. Extravascular albumin space of the lung and dry lung weight were significantly higher in the NO group vs. the control group (albumin space, 1.08+/-0.16 vs. 0.70+/-0.26 [SD] mL/kg body weight [p < .05]; dry lung weight, 3.20+/-0.34 vs. 2.66+/-0.14 g/kg body weight [p < .05]). Moreover, the hysteresis area was higher from 24 hrs of NO exposure. Conversely, NO inhalation altered neither the extravascular lung water content (12.98+/-2.79 mL/kg body weight in the NO group vs. 12.18+/-2.26 mL/kg body weight in the control group [not significant]) nor the main respiratory mechanical variables (static compliance, functional residual capacity) and gas exchange (lung diffusing capacity, PaO2/F(IO2) ratio). These results do not support the hypothesis that NO inhalation combined with hyperoxia can alter the main lung-function variables in neonates. However, it may induce an increase in lung vascular protein leakage. The pathophysiologic consequences of this finding remain to be elucidated.

Effect of sleep stages on measurements of passive respiratory mechanics in infants with bronchiolitis.

The measurement of passive respiratory mechanics by the single-breath occlusion technique is one of the more frequently used tests of infant lung function. Measurements are routinely done under chloral hydrate sedation, and a possible influence of sleep stages on these measurements has not been evaluated so far. We combined the assessment of passive respiratory mechanics with sleep stage monitoring in 44 infants and toddlers with mild to moderately severe bronchiolitis. In 31 infants, only nonrapid eye movement (NREM) sleep was recorded. In 13 patients who showed both NREM and rapid eye movement (REM) sleep, compliance of the respiratory system was significantly lower during REM than NREM sleep (73.2 +/- 19.7 vs. 81.2 +/- 21.3 mL/kPa, P = 0.0007), while resistance remained essentially unchanged. This finding was explained by an unchanged airway opening pressure in combination with a significantly decreased extrapolated volume. As tidal volume did not change from NREM to REM, this indicates reduced dynamic elevation of lung volume during REM sleep and thus supports previous observations of decreased lung volume in this sleep stage. From a practical perspective, these findings argue for the monitoring of sleep stage during measurements of passive respiratory mechanics, thereby increasing the complexity of these measurements significantly.

CHANGES IN LUNG AND CHEST-WALL COMPLIANCES DURING LAPAROSCOPIC CHOLECYSTECTOMY

S419 INTRODUCTION: It has been shown that pneumoperitoneum (PP) can produce significative alterations in the compliance of the respiratory system (Crs). The goal of this study was to assess the changes in its two components, lung compliance (CL) and chest-wall compliance (Ccw), that occur during laparoscopic cholecystectomy. METHODS: After informed consent and approval of ethics committee, we prospectively included seventeen ASA I-II consecutive patients (3 males, 14 females) scheduled for laparoscopic cholecystectomy. The anesthetic technique were standard general anesthesia: premedication with fentanyl and atropine, induction with propofol (2-3 mg/kg) and vecuronium (0.12 mg/kg), maintenance with O2/N2 O (40/60 %), isoflurane (0.5-1%) and fentanyl-vecuronium bolus when necessary. Patients were ventilated with a tidal volume of 10 ml/kg and a rate of 12 breaths/min, employing the Ergotronic[registered sign] (Temel, Spain) ventilator (internal compliance = 1,1 ml/cmH2 O). Respiratory monitoring included the standard, plus Paw and esophageal pressure via a balloon-catheter placed in the inferior portion of the esophagus (Pulmonary monitor CP-100, Bicore MS, Irvine, USA), and position was confirmed by observing the esophageal pressure waveform and respirations. Compliances were measured using standard formulae (Ccw =VT/Pes, CL=VT/Paw-Pes). Measurements were made: T1) immediately after induction of anesthesia in supine position (SP), T2) 10[prime] after performance of the PP (insuflation to 15 mmHg with CO2) in anti-Tren position (aTDLP), T3) 10[prime] after abdominal deflation in SP. Statistical analysis was performed using Student's t test for paired data; values are presented as means +/- SD (p<0,05 significance). RESULTS: After PP in SP, Crs was significantly decreased. Ccw and CL were significantly reduced too, but the decrement was more important in Ccw than in CL (47% vs 27%). The values returned to baseline after release of PP (no differences between T3 - T1). Results are shown in Table 1.Table 1DISCUSSION: The induction of PP + aTDL position for performing laparoscopic cholecystectomy decreases Crs, mainly because the reduction in Ccw, whereas CL are reduced in a low percentage. After deflation of PP and recovery of SP, the Crs, Ccw and CL returns to prior values.

Prediction of prolonged ventilator dependence in children byrespiratory function measurements

Complications of ventilatory support are more common if this assistance is prolonged. Our aim was to determine if results of respiratory function measurement on the first day of ventilation identified children who would develop prolonged ventilatory dependence (4 days) and whether such results were a more accurate predictor than readily available clinical data. Thirty three children, median age 2 years (range 0.1-13.6), who were supported by a constant flow ventilator and hence had measurements of compliance of the respiratory system (CRS) and resistance of the respiratory system (RRS) on the first day of ventilatory support, were retrospectively identified. Those who needed prolonged ventilatory support had a lower CRS on day one (p<0.01) and required at any time during their ventilatory career both a higher maximum inspired oxygen concentration (p<0.01) and peak inspiratory pressure (PIP) (p<0.01). Logistic regression analysis demonstrated that only a low CRS and high maximum PIP were significantly correlated with prolonged ventilator dependence. A low CRS (<0.4 (ml/cmH2O) kg-1) and a high maximum PIP (>27 cmH2O) had similar sensitivities (83%) and specificities (71% and 67% respectively) in predicting prolonged ventilatory dependence. The CRS results, unlike the maximum PIP results, however, were always available on the first day of ventilatory support. We therefore conclude that respiratory function measurements have a role in identifying children who would benefit from strategies to prevent prolonged ventilator dependence.

Pressure-controlled mechanical ventilation: a simplified titration method of the extrinsic positive expiratory pressure

Extrinsic positive end-expiratory pressure (PEEPe) may improve gas distribution within the lungs, induce alveolar recruitment or, conversely, produce pulmonary overdistension, and modify the respiratory impedance. Under pressure-controlled mechanical ventilation (PCV) this phenomenon modifies the minute ventilation and the dynamic compliance of the respiratory system (Crs,dyn). This study was aimed to assess the incidence of a significant gain in Crs,dyn under the effect of PEEPe during PCV. Prospective, open, descriptive, case series study. Surgical intensive care unit patients, under sedation, neuromuscular blockade and PCV because of severe hypoxaemia (ARDS or acute lung injury). Four incremental levels of PEEPe (4 to 16 cmH2O) of 30 minute duration were applied. Crs,dyn, and PaO2/FIO2 were recorded at the end of each level of PEEPe. The resulting gain in Crs,dyn was calculated and considered as significant if it was greater than the upper limit of confidence (at 99.8%) of the statistical distribution of all the recorded gains. Thirty patients were included, median and extreme values (within brackets) of PaO2/FIO2 of 117 [53-230] and Crs,dyn without PEEPe of 29 [14.3-46.8] mL.cmH2O-1. Among the 120 recorded gains, a gain in Crs,dyn was found significant at least once in 15 tests of PEEPe out of 30. Within the two groups of patients, the increase in PaO2/FIO2 with incremental PEEPe was similar. The levels of PEEPe producing the greatest increase in Crs,dyn were not correlated with the increase in PaO2/FIO2. In 50% of the studied patients a significant gain in Crs,dyn was found, allowing a less traumatic PCV. These results suggest the clinical usefulness of this method of titration of PEEPe, which requires neither specific devices nor a disconnection of the patient.

Combined Surfactant Therapy and Inhaled Nitric Oxide in Rabbits with Oleic Acid-induced Acute Respiratory Distress Syndrome

Intratracheal administration of surfactant and inhaled nitric oxide (INO) have had variable effects in clinical trials on patients with acute respiratory distress syndrome (ARDS). We hypothesized that combined treatment with exogenous surfactant and INO may have effects in experimental ARDS. After intravenous infusion of oleic acid in adult rabbits and 4-6 h of ventilation, there was more than a 40% reduction in both dynamic compliance (Cdyn) of the respiratory system and functional residual capacity (FRC), a 50% increment of respiratory resistance (Rrs), a 70% reduction in PaO2 /FIO2, and an increase in intrapulmonary shunting (Q S/Q T) from 4.4 to 33.5%. The animals were then allocated to groups receiving (1) neither surfactant nor INO (control), (2) 100 mg/kg of surfactant (S) administered intratracheally, (3) 20 ppm INO (NO), or (4) 100 mg/kg of surfactant and 20 ppm INO (SNO), and subsequently ventilated for 6 h. After the period of ventilation, the animal lungs were used for analysis of disaturated phosphatidylcholine (DSPC) and total proteins (TP) in bronchoalveolar lavage fluid (BALF), and for determination of alveolar volume density (VV). The animals in the control group had the lowest survival rate, and no improvement in lung mechanics and blood oxygenation, whereas those in the S group had a modest but statistically significant improvement in Cdyn, Rrs, PaO2 and FRC, reduced Q S/Q T, lowered minimum surface tension (gammamin) of BALF, and increased DSPC/ TP and alveolar VV. The NO group had increased PaO2 and reduced Q S/Q T. The SNO group showed improved Cdyn, Rrs, FRC, DSPC/TP, alveolar VV, and gammamin of BALF comparable to the S group, but there was a further increase in survival rate and PaO2, and additional reduction in Q S/Q T and TP in BALF. These results indicate that, in this animal model of ARDS, a combination of surfactant therapy and INO is more effective than either treatment alone.

Impaired gas mixing and low lung volume in preterm infants with mild chronic lung disease.

The aim of this study was to assess the possible role of gas mixing inefficiency in spontaneously breathing infants with mild chronic lung disease (CLD) of prematurity in relation to changes in other functional parameters. A simple bedside technique for recording and analysis of multiple breath nitrogen washout curves was applied together with occlusion mechanics. Fifteen preterm infants with mild or moderately severe CLD were studied at a mean postconceptional age of 35 wk, together with 15 healthy preterm infants at the same maturity. All infants breathed spontaneously, and the test was performed by a continuous bypass flow system, connected to a face mask, a pneumotachograph, and a nitrogen meter. The results showed impaired gas mixing with moment ratios above the 95th percentile of the normal group in 11/15 infants with CLD. Functional residual capacity (FRC) was low in 13/15 infants, but specific compliance and resistance of the respiratory system did not differ between the groups. As FRC and moment ratios were not correlated, it is suggested that they may reflect different aspects of the pathophysiology in CLD. It is concluded that low FRC and disturbed gas mixing are characteristic disturbances in CLD at different degrees of severity. The multiple breath nitrogen washout test, followed by moment analysis of end-tidal nitrogen concentrations, is a simple and sensitive method for detection of these disturbances and for monitoring purposes.

Combined Effects of Inhaled Nitric Oxide and Hyperoxia on Pulmonary Vascular Permeability and Lung Mechanics 1751

Potential beneficial and/or detrimental effects of inhaled NO on oxidant-induced lung injury have not been fully investigated in newborn infants. The purpose of this investigation was to examine whether inhaled nitric oxide (NO) may alter pulmonary vascular permeability and respiratory function in mechanically ventilated newborn piglets -1 to 2 days old-, exposed to 100% O2 for 76 hours. They were randomly assigned to treatment with 20 ppm inhaled NO (n=5) from the onset of ventilation or control (n=6). Peak inspiratory pressure was set to maintain PaCO2 between 35 and 45 mmHg. The other ventilator parameters were not changed during the course of the study (FiO2=1; PEEP=5cmH2O; RR=25/min). The main studied parameters were gas exchange (PaO2/FiO2 ratio, lung diffusing capacity=DLCO), respiratory mechanics (static compliance of the respiratory system=Crs,stat measured at 5, 10, 15, and 20 ml/kg during inspiration and expiration, quasi-static hysteresis area, functional residual capacity=FRC) and pulmonary vascular permeability assessed by simultaneous intravenous administration of 125I-labeled albumin and 51Cr-labeled red blood cells. PaO2/FiO2 decreased significantly between 2 and 76 hours of 100% O2 exposure in the control and the NO groups (from 388±63 to 225±63 and from 375±84 to 200±64 mmHg respectively). The extravascular albumin space of the lung and the dry lung weight were significantly higher in the NO group versus control group (Alb space: 1.08 ± 0.16 ml / kg body weight versus 0.70 ±0.26 ml / kg body weight and dry lung weight: 3.20 ± 0.34 g / kg body weight versus 2.66 ± 0.14 g / kg body weight respectively). Moreover, hysteresis area was higher from 24 hours of NO exposure. Conversely, NO inhalation did alter neither the extravascular lung water content (12.98 ± 2.79 ml / kg body weight in the NO group versus 12.18 ± 2.26 ml / kg body weight in the control group; NS), nor the main respiratory mechanic parameters (Crs,stat, FRC) and gas exchange (DLCO, PaO2/FiO2 ratio). In conclusion, our results do not support the hypothesis that NO inhalation combined with hyperoxia may alter the main lung function parameters in neonates. However, it may induce an increase in lung vascular protein leakage. Pathophysiological consequences of this finding remain to be elucidated.

Prostanoids counterbalance the bronchoconstrictor activity of endothelin-1 in pigs

In 12 anaesthetized spontaneously breathing pigs divided into two groups of six animals we evaluated the respiratory and haemodynamic responses to endothelin-1 (ET-1) administered by aerosol (200 pmol.kg −1 in 1 ml of saline solution). In the first group (control group), the responses to ET-1 were evaluated before and after the blocking of endogenous nitric oxide (NO) by N G-nitro-L-arginine methyl ester (L-NAME 5 mg.kg −1, i.v.). In the second group (indomethacin-pretreated group), the experimental protocol was similar to that of the control group, but the responses were evaluated after the blocking of endogenous prostanoids by indomethacin (3 mg.kg −1, i.v.). Results show that in the control group ET-1 administered before and after L-NAME did not change compliance (Crs) or resistances (Rrs) of the respiratory system. In indomethacin-pretreated pigs, ET-1 significantly increased Rrs and decreased Crs. This constrictor effect appearing only during the block of arachidonic acid metabolites showed that ET-1 activity can be counterbalanced by a release of dilator prostanoids. In this group after L-NAME pretreatment ET-1 did not alter the mechanical properties of the respiratory system, suggesting an involvement of other bronchodilator mechanisms. In the control group, aerosol administered ET-1 increased mean systemic (MAP) and pulmonary (MPAP) arterial pressures, while when ET-1 was administered after L-NAME pretreatment, MPAP decreased. In the indomethacin-pretreated group, the peptide did not modify MAP, but caused an early decrease in MPAP when administered after L-NAME. Therefore, our results show that ET-1 caused a bronchoconstrictor effect only in indomethacin-pretreated pigs and suggest that the intrinsic constrictor activity of the peptide can be modulated especially by the release of dilator prostanoids.

Rate of surfactant administration influences lung function and gas exchange in a surfactant‐deficient rabbit model

The aim of this study was to test whether the effect of surfactant treatment on lung function in a surfactant-deficient animal model can be influenced by the rate at which surfactant is administered. Surfactant deficiency was induced in 18 New Zealand white rabbits (weighing approx. 1 kg each) by lung lavage with normal saline. The arterial/alveolar oxygen ratio (a/A ratio), functional residual capacity (FRC), dynamic compliance of the respiratory system (Crs), tidal volume (VT), alveolar portion of the tidal volume (VA) and arterial PCO2 (Pa,CO2) were measured before and after lavage and 15, 30, 60, 90, and 120 min after administration of a single dose of surfactant (Survanta®, 100 mg/kg). Two surfactant administration protocols were compared over a 2-h interval: an infusion lasting 4 min and an infusion over 2 min. Both administrations were given during continuous mechanical ventilation. The six lung function and gas exchange parameters improved significantly following surfactant administration over 2 min compared with a control group. However, only the a/A ratio and VA improved following the 4-min protocol. Comparison of the two intervention protocols yielded significantly differences in VA and Pa,CO2, favoring the shorter administration. These results support the hypothesis that fast (2 min) administration of surfactant will improve its distribution to formerly collapsed alveoli and results in better lung function, improved ventilation, and (to a lesser extent) better oxygenation than prolonged infusions (4 min). Pediatr. Pulmonol. 1998; 25:196–204. © 1998 Wiley-Liss, Inc.

Comparative effects of theophylline and caffeine on respiratory function of prematurely bora infants

The aim of this study was to determine the relative effects of theophylline and caffeine on neonatal respiratory function. Fifty-three preterm infants (45 infants with a median gestational age of 28 weeks, range 24–34 weeks completed the protocol) were randomized to receive either theophylline (loading dose 4 mg/kg followed by 4 mg/kg/day) or caffeine (loading dose 10 mg/kg followed by 5 mg/kg/day). Compliance of the respiratory system ( C RS), strength of Hering Breuer reflex and the inspired oxygen concentration requirement were measured immediately prior to, 24 h and 7 days after commencing therapy. There was no statistically significant difference in the patient characteristics of the two groups, but only the theophylline group contained immature infants (i.e. < 26 weeks gestational age ( n = 7)). At 24 h, there was a significant improvement in C RS and reduction in supplementary oxygen requirements in the caffeine group ( p < 0.01), in the theophylline group no such significant effects were seen. In the study population overall, after 7 days of treatment in both the theophylline and caffeine groups there was an improvement in C RS ( p < 0.05 and p < 0.01 respectively) and a reduction in the inspired oxygen concentration ( p < 0.05 and p < 0.01 respectively). There was, however, a significant reduction in the strength of the Hering Breuer reflex only in the caffeine group ( p < 0.05) and this was a decrease which related to the change in C RS ( p < 0.05). The only statistically significant difference in the magnitude of change in C RS, reflex strength or supplementary oxygen requirements between the two groups was that the reduction in inspired oxygen requirement in the caffeine group was greater man that in the theophylline treated infants at 24 h ( p < 0.05). We conclude theophylline and caffeine have similar effects on neonatal respiratory function, but our results suggest caffeine administration may be associated with an earlier onset of action.

Perioperative assessment of respiratory compliance and lung volume in infants with congenital diaphragmatic hernia: Prediction of outcome

Background/Purpose: Infants who have congenital diaphragmatic hernia (CDH) have high mortality and morbidity. The aim of this study was to determine the relative ability of the results of serial measurements of compliance of the respiratory system (CRS) and lung volume (functional residual capacity (FRC)) to predict poor outcome: death or oxygen dependency at 28 days. In addition, the authors wished to document the evolution of any lung function abnormalities during the perioperative period. Methods: Daily measurements of CRS and FRC were made in the first week of life and subsequently during week 2 in 16 infants who had a median gestational age of 38 weeks and birth weight of 3.2 kg. Results: Seven infants had a poor outcome: five died and two others remained oxygen dependent beyond 28 days. The infants who had a poor outcome were characterized on day 1 by a significantly lower CRS, but not FRC ( P < .05). In comparison with results from day 1, the median CRS of the infants overall had significantly improved only by week 2 ( P < .05), there was no such significant change in FRC with increasing postnatal age. At week 2, only the CRS results differed significantly between those infants who had and who did not have poor outcome ( P < .05). Conclusion: The results of serial measurements of CRS, rather than FRC are the more useful predictor of outcome in infants who have CDH.

Effect of volume recruitment on response to surfactant treatment in rabbits with lung injury.

We determined if surfactant treatment effect can be enhanced by mechanical volume recruitment during surfactant administration by measuring functional residual capacity, tidal volume, the alveolar portion of tidal volume, dynamic compliance of the respiratory system, a/A ratio, and PaCO2 by measuring before and after surfactant administration to rabbits with lung injury induced by airway lavage. There was improvement in all lung function indices when surfactant was given with volume recruitment, but when surfactant was given without volume recruitment, the only index to show significant improvement was a/A ratio of oxygenation. These results support the hypothesis that mechanical recruitment of terminal airspaces from a previously unventilated compartment will enhance the effectiveness of surfactant replacement by facilitating the distribution of instilled surfactant to this compartment.

In utero exposure to cigarette smoking influences lung function at birth.

To avoid the possible confounding effects of postnatal exposure to tobacco smoke, we investigated possible effects of uterine tobacco smoke (UTS) exposure upon infant lung function shortly after birth. Infants with no major disease, in one maternity ward in Oslo, Norway, participating in a cohort study established in 1992/1993, were included in the present study (n=803). Exposure information, assessed as maternal active and passive smoking during pregnancy and other personal and environmental factors, was obtained by questionnaire. Tidal flow-volume (TFV) loops (n=802) and compliance (Crs) and resistance (Rrs) of the respiratory system (n=663) were measured at a mean age of 2.7 days. In girls, the TFV ratio (time to reach peak expiratory flow to total expiratory time (tPEF/tE)), and Crs were significantly lower with active as well as passive maternal smoking compared to nonexposure to UTS. Respiratory rate and Rrs were not significantly influenced by UTS exposure. However, in linear regression analysis adjusted for confounding factors (including respiratory rate), tPEF/tE and Crs, but not Rrs, were related to maternal active but not passive daily smoking. One daily cigarette corresponded to a change in tPEF/tE of -0.0021 (95% confidence interval (95% CI) -0.0040 to -0.0002) and a change in Crs of -0.026 mL x cmH2O (95% CI -0.045 to -0.007 mL x cmH2O). The decrease was 0.023 and 0.29, respectively, in infants of an average smoker. Maternal smoking during pregnancy adversely affected tidal flow-volume ratios in healthy newborn babies, as well as the compliance of the respiratory system in girls, independently of the reduced body size also resulting from maternal smoking.

Delayed derecruitment after removal of PEEP in patients with acute lung injury.

A step decrease in positive end-expiratory airway pressure (PEEP) is not followed by an instantaneous loss of the PEEP-induced increase in end-expiratory lung volume (EELV). Rather, the reduction of EELV is delayed, while adverse PEEP effects on hemodynamics are immediately attenuated upon the drop in airway pressure. Step PEEP increments were applied to the lungs of patients with acute lung injury. It was investigated retrospectively whether enlargement of end-expiratory lung volume and changes in lung mechanics persist 45 min after removal of the PEEP increment. In 14 patients with acute lung injury (LIS score 2.7) EELV and volume-dependent dynamic compliance of the respiratory system (Cdyn,rs) were determined 45 min after removal of an additional PEEP increment (0.64 kPa added to baseline PEEP of 1.0 kPa). Nine patients kept an EELV gain of 13% (SD 7) and showed improved Cdyn,rs. In 5 patients, EELV was reduced (by 9% (SD 6)) and Cdyn,rs unchanged after removal of the PEEP increment compared to baseline. A subgroup of patients with acute lung injury, the characteristics of which remain to be defined, benefit from prolonged recruitment effects up to 45 min after removal of a PEEP increment, while sequelae of continuously increased airway pressures are minimised.

A tube in the pharynx for emergency ventilation

If the endotracheal placement of a nasal advanced tube fails, ventilation via this tube could bridge the time until a fibreoptic bronchoscope is available. This study investigates the efficiency of ventilation via a tube resting with its tip in the pharynx near the glottis. In 20 patients respiratory data during ventilation via a pharyngeally placed tube were recorded by means of pulse oximetry, capnometry and side-stream spirometry. Results were compared with those measured previously in the same patients during conventional facemask ventilation. Oxygen saturation and end-tidal carbon dioxide concentration remained unchanged using ventilation via facemask (SO2 98.5 +/- 0.9%, FECO2 4.5 +/- 0.7 vol%) or pharyngeal tube (SO2 98.6 +/- 0.7%, FECO2 4.8 +/- 0.4 vol%). No significant differences were found between the two groups with regard to peak airway pressure, tidal volume leakage, compliance and resistance of the respiratory system. Our results suggest an effective ventilation and oxygenation via a tube placed with its tip in the pharynx. This technique may be helpful during difficult and prolonged nasal intubation.

Changes in lung volume, compliance and oxygenation in the first 48 hours of life in infants given surfactant.

Changes in lung volume (functional residual capacity) compliance and oxygenation in the first 48 h of life in infants given surfactant replacement therapy were studied. Fourteen infants, median gestational age 30 weeks (range 26-35), who were given two doses of an artificial surfactant (Exosurf) at approximately 2 h of age and 12 h later, were examined. Compared to baseline, functional residual capacity, compliance of the respiratory system and oxygenation, significantly improved at 24 and 48 hours, but specific compliance (compliance/functional residual capacity) decreased. The greater changes, however, were experienced between baseline and 24 h. These data suggest that the elevation of FRC over the first 48 hours of life may be due to increased distension as well as recruitment of alveoli.

Anaphylactic bronchoconstriction in immunized guinea pigs provoked by inhalation and intravenous administration of hexahydrophthalic anhydride and methyltetrahydrophthalic anhydride.

We established a guinea-pig model of anaphylactic bronchoconstriction provoked in immunized animals by inhalation and intravenous administration of 4,4-methyltetrahydrophthalic anhydride (MTHPA) and hexahydrophthalic anhydride (HHPA). Guinea pigs were immunized intradermally with either MTHPA (n = 8) or HHPA (n = 8) suspended in olive oil. Control animals (n = 8) were injected with olive oil alone. After 4 weeks, the animals were challenged during mechanical ventilation by inhalation or intravenous administration of MTHPA or HHPA conjugated with guinea-pig serum albumin (GPSA). Airway flow, and airway and esophageal pressures were measured. Resistance (R) and static compliance (Cst) of the respiratory system (rs), lung (1), and chest wall were studied with the flow-interruption technique. After challenge with MTHPA-GPSA or HHPA-GPSA, R,rs and R,1 increased dramatically while Cst,rs and Cst,1 decreased, and severe arterial hypoxia developed. The reaction occurred at a well-defined dose of anhydride and lasted about 30 min. When the same dose was repeated after 30 min, the response was much attenuated. MTHPA and HHPA can induce asthma in guinea pigs. The dose-response curve at antigen challenge is steep. Once a threshold dose is reached, a severe reaction occurs. The reactivity is then exhausted. This model may be suitable for assessing occupational asthma caused by acid anhydrides and possibly by other low-molecular-weight chemicals.