Increasing tidal volumes and pulmonary overdistention adversely affect pulmonary vascular mechanics and cardiac output in a pediatric swine model

OBJECTIVES: In a pediatric swine model, the effects of increasing tidal volumes and the subsequent development of pulmonary overdistention on cardiopulmonary interactions were studied. The objective was to test the hypothesis that increasing tidal volumes adversely affect pulmonary vascular mechanics and cardiac output. An additional goal was to determine whether the effects of pulmonary overdistention are dependent on delivered tidal volume and/or positive end-expiratory pressure (PEEP, end-expiratory lung volume). DESIGN: Prospective, randomized, controlled laboratory trial. SETTING: University research laboratory. SUBJECTS: Eleven 4- to 6-wk-old swine, weighing 8 to 12 kg. INTERVENTIONS: Piglets with normal lungs were anesthetized, intubated, and paralyzed. After median sternotomy, pressure transducers were placed in the right ventricle, pulmonary artery, and left atrium. An ultrasonic flow probe was placed around the pulmonary artery. MEASUREMENTS AND MAIN RESULTS: The swine were ventilated and data were collected with delivered tidal volumes of 10, 15, 20, and 25 mL/kg and PEEP settings of 5 and 10 cm H2O in a random order. Pulmonary overdistention was defined as a decrease in dynamic compliance of > or =20% when compared with a compliance measured at a baseline tidal volume of 10 mL/kg. At this baseline tidal volume, airway pressure-volume curves did not demonstrate pulmonary overdistention. Tidal volumes and airway pressures were measured by a pneumotachometer and the Pediatric Pulmonary Function Workstation. Inspiratory time (0.75 sec), FIO2 (0.3), and minute ventilation were held constant. We evaluated the pulmonary vascular and cardiac effects of the various tidal volume and PEEP settings by measuring pulmonary vascular resistance, pulmonary characteristic impedance, and cardiac output. When compared with a tidal volume of 10 mL/kg, a tidal volume of 20 mL/kg resulted in a significant decrease in dynamic compliance from 10.5 +/- 0.9 to 8.4 +/- 0.6 mL/cm H2O (p = .02) at a constant PEEP of 5 cm H2O. The decrease in dynamic compliance of 20% indicated the presence of pulmonary overdistention by definition. As the tidal volume was increased from 10 to 20 mL/kg, pulmonary vascular resistance (1351 +/- 94 vs. 2266 +/- 233 dyne x sec/cm5; p = .004) and characteristic impedance (167 +/- 12 vs. 219 +/- 22 dyne x sec/cm5; p = .02) significantly increased, while cardiac output significantly decreased (951 +/- 61 vs. 708 +/- 48 mL/min; p = .001). Each of these effects of pulmonary overdistention were further magnified when the tidal volume was increased to 25 mL/kg. The tidal volume-induced alterations in pulmonary vascular mechanics, characteristic impedance, and cardiac output occurred to a greater degree when the PEEP was increased to 10 cm H2O. Pulmonary vascular resistance and characteristic impedance were significantly increased and cardiac output significantly decreased for all tidal volumes studied at a PEEP of 10 cm H2O as compared with 5 cm H2O. CONCLUSIONS: Increasing tidal volumes, increasing PEEP levels, and the development of pulmonary overdistention had detrimental effects on the cardiovascular system by increasing pulmonary vascular resistance and characteristic impedance while significantly decreasing cardiac output. Delivered tidal volumes of >15 mL/kg should be utilized cautiously. Careful monitoring of respiratory mechanics and cardiac function, especially in neonatal and pediatric patients, is warranted.     

Suicidal behavior in bipolar and unipolar affective disorders: a meta-analysis

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.     

Radiotherapy of bone metastases of a spinal meningeal hemangiopericytoma

We evaluated pulmonary function status in healthy, nonventilated very-low-birth-weight (VLBW) infants at 40 weeks postconception because little is known about the pulmonary function status of these infants at the time of discharge. Seven normal VLBW infants were evaluated at 40 weeks postconception, and five normal term infants were examined as a control. The neonates were placed supine with their heads in the neutral position. Data were obtained while the infant was resting quietly and breathing spontaneously prior to feeding. Pulmonary mechanics and energetics were measured with a CP-100 pulmonary monitor (Bicore Co. Ltd.). Pulmonary mechanics and energetics were determined by the least mean square technique. Dynamic compliance (Cdyn), resistance (Rtot, Re), and work of breathing (WOB) were calculated for the total breath, and tidal volume, minute ventilation, ratio of inspiratory time to respiratory period (Ti/Ttot), and respiratory rate were measured. There were no significant differences between normal VLBW infants and term infants in regard to ventilation, mechanics, or energetics. Although the respiratory system of normal VLBW infants is immature at birth, its development caught up to term infants by the time of discharge.     

The effects of long-term prone positioning in patients with trauma-induced adult respiratory distress syndrome

Prone positioning improves gas exchange in some patients with adult respiratory distress syndrome (ARDS), but the effects of repeated, long-term prone positioning (20 h duration) have never been evaluated systemically. We therefore investigated 20 patients with ARDS after multiple trauma (Injury Severity Score [ISS] 27.3 +/- 10, ARDS score 2.84 +/- 0.42). Patients who fulfilled the entry criteria (bilateral diffuse infiltrates, severe hypoxemia, pulmonary artery occlusion pressure [PAOP] < 18 mm Hg, and PaO2/fraction of inspired oxygen [FIO2] < 200 mm Hg at inverse ratio ventilation with positive end-expiratory pressure [PEEP] > 8 mm Hg for more than 24 h) were turned to the prone position at noon and were turned back to the supine position at 8:00 AM on the next day. Thus only two turns per day were necessary, and the risk of disconnecting airways or medical lines was minimized. Prone positioning was repeated for another 20 h if the patients fulfilled the entry criteria. Except for FIO2, the ventilator settings remained unchanged during the study period. All patients were sedated and, if needed paralyzed to minimize patient discomfort. One hour before and after each position change, ventilator settings and pulmonary and systemic hemodynamics were recorded and blood was obtained for blood gas analysis. Derived cardiopulmonary and ventilatory variables were calculated using standard formulas. Overall mortality was 10%. Oxygenation variables improved significantly each time the patients were placed prone. Immediately after the first turn from the supine to the prone position the following changes were observed: PaO2 increased from 97 +/- 4 to 152 +/- 15 mm Hg, intrapulmonary shunt (Qva/Qt) decreased from 30.3 +/- 2.3 to 25.5 +/- 1.8, and the alveolar-arterial oxygen difference decreased from 424 +/- 24 to 339 +/- 25 mm Hg. All these changes were statistically significant. Most of these improvements were lost when the patients were turned supine, but could be reproduced when prone positioning was repeated after a short period (4 h) in the supine position. Short periods in the supine position were necessary to allow for nursing care, medical evaluation, and interventions such as placement of central lines. No position-dependent changes of systemic hemodynamic variables were observed. We conclude that, in trauma patients with ARDS undergoing long-term positioning treatment, lung function improves significantly during prone position compared to short phases of conventional supine position during which the beneficial effects are partly lost.     

Computer-controlled minute ventilation in preterm infants undergoing mechanical ventilation

INTRODUCTION: Computer-controlled minute ventilation (CCMV) continuously adjusts the ventilator rate to changes in spontaneous respiratory drive and pulmonary mechanics to maintain a preset total minute ventilation. HYPOTHESIS: We hypothesized that CCMV would maintain ventilation and oxygenation with fewer mechanical breaths than conventional intermittent mandatory ventilation in very low birth weight infants. METHODS: Very low birth weight infants in clinically stable condition who were undergoing mechanical ventilation were enrolled. The number of mechanical breaths, total and mechanical expiratory minute ventilation, mean airway pressure, oxygen hemoglobin saturation by pulse oximetry, and transcutaneous partial carbon dioxide and partial oxygen tensions were obtained during intermittent mandatory ventilation and CCMV (45 to 60 minutes) and compared by paired t test. RESULTS: Fifteen infants were studied. Birth weight (median, range) was 700 gm (550 to 1205 gm), gestational age 26 weeks (23 to 34 weeks), age 21 days (3 to 50 days). When switched from intermittent mandatory ventilation to CCMV, the number of mechanical breaths was reduced (15 +/- 2.8 to 8.6 +/- 2.9 breaths per minute, p < 0.001), leading to lower airway pressure (3.97 +/- 1.00 to 3.45 +/- 1.00 cm H2O, p < 0.001) and lower expiratory minute ventilation generated by the mechanical ventilator (116 +/- 31 to 65 +/- 28 ml/min per kilogram, p < 0.001), while total expiratory minute ventilation remained unchanged. Mean transcutaneous partial carbon dioxide and oxygen tensions, oxygen hemoglobin saturation, and the time spent within different oxygen hemoglobin saturation ranges did not differ between both ventilatory modes. CONCLUSION: CCMV maintained adequate ventilation and oxygenation with lower mechanical ventilatory support than IMV. CCMV may reduce barotrauma and chronic lung disease during long-term use.     

Tumor necrosis factor-alpha in serum of macaques during SIVmac251 acute infection

Peripheral chemoreceptors may be immature in neonatal animals, exhibiting maturational changes in the perinatal period. Even though methylxanthines are respiratory stimulants, many premature neonates do not respond to them. Thus, we hypothesized that carotid body activity is necessary for aminophylline to reverse hypoxia-induced respiratory depression. We exposed 16 anesthetized newborn piglets (age 2-7 days) to hypoxia (inhalation of 12% oxygen) for 5 min. Aminophylline (15 mg/kg iv) was administered either prior to (11 piglets) or following (5 piglets) carotid body denervation (CBD). Before CBD, hypoxia elicited transient initial increases in tidal volume (from 79 +/- 4 to 99 +/- 1% of maximum, mean +/- SE), minute ventilation (from 64 +/- 5 to 93 +/- 4%), and peak phrenic electroneurogram (from 63 +/- 8 to 91 +/- 6%, all P < 0.05). This was followed by a decrease in tidal volume, minute ventilation and phrenic electroneurogram (all P < 0.05). Prior to CBD, aminophylline pretreatment prevented the decrease in all the measures of respiratory output during late hypoxia. After CBD, hypoxia induced an initial and sustained depression of ventilation (tidal volume from 100 to 33 +/- 14%; frequency from 94 +/- 4 to 42 +/- 17%; minute ventilation from 100 to 32 +/- 14%, all P < 0.05) and phrenic electroneurogram (peak phrenic from 100 to 47 +/- 18%; minute phrenic from 85 +/- 6 to 55 +/- 21%, both P < 0.05). Administration of aminophylline after CBD did not prevent the profound respiratory depression elicited by hypoxia in the chemodenervated piglets.(ABSTRACT TRUNCATED AT 250 WORDS)     

Sleep position, autonomic function, and arousal

AIMS: To investigate and compare heart rate variability (HRV) and responses of heart rate and arousal to head-up tilting in infants sleeping prone and supine. METHODS: Thirty seven healthy infants aged 2-4 months were studied. HRV was measured for 500 beats while they were in a horizontal position. Subjects were then tilted 60 degrees head-up, and heart rate recorded over 1 minute and arousal responses observed. Data were collected during both quiet and active sleep for both prone and supine sleep positions. RESULTS: HRV, as assessed by the point dispersion of Poincaré plots, was significantly reduced in the prone position for both sleep states. Sleep position did not influence the changes in heart rate seen during a head-up tilt. Full awakening to the tilt was common in active sleep but significantly less so in the prone position (15% of prone tests vs 54% supine). Full awakening to the tilt rarely occurred during quiet sleep in either sleep position. CONCLUSION: This study provides some evidence that blunted arousal responses and/or altered autonomic function are a feature of the prone sleeping position. Decreased HRV may be a sign of autonomic impairment. It is seen in many disease states and in infants who later die of sudden infant death syndrome (SIDS).     

Does airway pressure release ventilation alter lung function after acute lung injury?

BACKGROUND: During airway pressure release ventilation (APRV), tidal ventilation occurs between the increased lung volume established by the application of continuous positive airway pressure (CPAP) and the relaxation volume of the respiratory system. Concern has been expressed that release of CPAP may cause unstable alveoli to collapse and not reinflate when airway pressure is restored. OBJECTIVE: To compare pulmonary mechanics and oxygenation in animals with acute lung injury during CPAP with and without APRV. DESIGN: Experimental, subject-controlled, randomized crossover investigation. SETTING: Anesthesiology research laboratory, University of South Florida College of Medicine Health Sciences Center. SUBJECTS: Ten pigs of either sex. INTERVENTIONS: Acute lung injury was induced with an intravenous infusion of oleic acid (72 micrograms/kg) followed by randomly alternated 60-min trials of CPAP with and without APRV. Continuous positive airway pressure was titrated to produce an arterial oxyhemoglobin saturation of at least 95% (FIO2 = 0.21). Airway pressure release ventilation was arbitrarily cycled to atmospheric pressure 10 times per minute with a release time titrated to coincide with attainment of respiratory system relaxation volume. MEASUREMENTS: Cardiac output, arterial and mixed venous pH, blood gas tensions, hemoglobin concentration and oxyhemoglobin saturation, central venous pressure, pulmonary and systemic artery pressures, pulmonary artery occlusion pressure, airway gas flow, airway pressure, and pleural pressure were measured. Tidal volume (VT), dynamic lung compliance, intrapulmonary venous admixture, pulmonary vascular resistance, systemic vascular resistance, oxygen delivery, oxygen consumption, and oxygen extraction ratio were calculated. MAIN RESULTS: Central venous infusion of oleic acid reduced PaO2 from 94 +/- 4 mm Hg to 52 +/- 9 mm Hg (mean +/- 1 SD) (p < 0.001) and dynamic lung compliance from 40 +/- 6 mL/cm H2O to 20 +/- 6 mL/cm H2O (p = 0.002) and increased venous admixture from 13 +/- 3% to 32 +/- 7% (p < 0.001) in ten swine weighing 33.3 +/- 4.1 kg while they were spontaneously breathing room air. After induction of lung injury, the swine received CPAP (14.7 +/- 3.3 cm H2O) with or without APRV at 10 breaths per minute with a release time of 1.1 +/- 0.2 s. Although mean transpulmonary pressure was significantly greater during CPAP (11.7 +/- 3.3 cm H2O) vs APRV (9.4 +/- 3.8 cm H2O) (p < 0.001), there were no differences in hemodynamic variables. PaCO2 was decreased and pHa was increased during APRV vs CPAP (p = 0.003 and p = 0.005). PaO2 declined from 83 +/- 4 mm Hg to 79 +/- 4 mm Hg (p = 0.004) during APRV, but arterial oxyhemoglobin saturation (96.6 +/- 1.4% vs 96.9 +/- 1.3%) did not. Intrapulmonary venous admixture (9 +/- 3% vs 11 +/- 5%) and oxygen delivery (469 +/- 67 mL/min vs 479 +/- 66 mL/min) were not altered. After treatment periods and removal of CPAP for 60 min, PaO2 and intrapulmonary venous admixture returned to baseline values. DISCUSSION: Intrapulmonary venous admixture, arterial oxyhemoglobin saturation, and oxygen delivery were maintained by APRV at levels induced by CPAP despite the presence of unstable alveoli. Decrease in PaO2 was caused by increase in pHa and decrease in PaCO2, not by deterioration of pulmonary function. We conclude that periodic decrease of airway pressure created by APRV does not cause significant deterioration in oxygenation or lung mechanics.     

Bone mineral density in pediatric patients with idiopathic hypercalciuria

Between October 1993 and April 1995, a total of 77 neonates requiring mechanical ventilation were enrolled in this study and were randomly divided into two groups. Group A consisted of 31 premature infants (mean birthweight 1.36 +/- 0.29 kg) with respiratory distress syndrome (RDS) and seven neonates (mean birthweight 3.2 +/- 0.5 kg) with meconium aspiration syndrome (MAS). Group B consisted of 31 premature infants (mean birthweight 1.31 +/- 0.3 kg) with RDS and eight neonates (mean birthweight 3.3 +/- 0.5 kg) with MAS. Infants in group A received synchronized intermittent mandatory ventilation (SIMV) and infants in group B received conventional intermittent mandatory ventilation (CIMV) therapy. In premature infants with RDS, our data showed: (i) the duration of ventilation was significantly shorter (P < 0.05) in the synchronized group (156 +/- 122 h) compared to the conventional group (242 +/- 175 h); (ii) significantly fewer (P < 0.05) patients required reintubation in the synchronized group than in the conventional group (three vs 11 patients); (iii) incidence of severe intraventricular hemorrhage (grades 3 and 4) was significantly lower (P < 0.05) in the synchronized group compared to the conventional group (one vs seven patients); (iv) incidence of bronchopulmonary dysplasia was significantly lower (P < 0.05) in the synchronized group than in the control group (one vs seven patients). In neonates with MAS, our data showed no significant difference (P < 0.05) on duration of ventilation, incidence of reintubation, incidence of pneumothorax or mortality rate between synchronized and control groups.     

Expiratory flow limitation and intrinsic positive end-expiratory pressure in obesity

Breathing at very low lung volumes might be affected by decreased expiratory airflow and air trapping. Our purpose was to detect expiratory flow limitation (EFL) and, as a consequence, intrinsic positive end-expiratory pressure (PEEPi) in grossly obese subjects (OS). Eight OS with a mean body mass index (BMI) of 44 +/- 5 kg/m2 and six age-matched normal-weight control subjects (CS) were studied in different body positions. Negative expiratory pressure (NEP) was used to determine EFL. In contrast to CS, EFL was found in two of eight OS in the upright position and in seven of eight OS in the supine position. Dynamic PEEPi and mean transdiaphragmatic pressure (mean Pdi) were measured in all six CS and in six of eight OS. In OS, PEEPi increased from 0.14 +/- 0.06 (SD) kPa in the upright position to 0.41 +/- 0.11 kPa in the supine position (P < 0.05) and decreased to 0.20 +/- 0.08 kPa in the right lateral position (P < 0.05, compared with supine), whereas, in CS, PEEPi was significantly smaller (<0.05 kPa) in each position. In OS, mean Pdi in each position was significantly larger compared with CS. Mean Pdi increased from 1.02 +/- 0.32 kPa in the upright position to 1.26 +/- 0.17 kPa in the supine position (not significant) and decreased to 1. 06 +/- 0.26 kPa in the right lateral position (P < 0.05, compared with supine), whereas there were no significant changes in CS. We conclude that in OS 1) tidal breathing can be affected by EFL and PEEPi; 2) EFL and PEEPi are promoted by the supine posture; and 3) the increased diaphragmatic load in the supine position is, in part, related to PEEPi.     

Quanolirones I and II, two new human cytomegalovirus protease inhibitors produced by Streptomyces sp. WC76535

The aim of the study was to assess whether changes in the interposition of body compartments affect the results of body composition measurements by dual-energy x-ray absorptiometry (DEXA) in the fan-beam mode. Thirty healthy subjects underwent two sequential measurements: the first was performed in the supine position as described by the manufacturer, and the second in the prone position. Estimates of body composition were compared between the two measurements. Mean body weight did not differ between measurements ([mean+/-SD] supine vprone, 68.561+/-12.461 v 68.589+/-12.469 kg). Mean bone mineral content (BMC) was lower in the prone position versus the supine position. When the head was excluded, this difference reached statistical significance (supine v prone, 1,738+/-361 v 1,688+/-360 g, P=.0001). The mean fat tissue mass (FTM) was lower and lean tissue mass (LTM) higher in the prone measurements. When the head was excluded, the mean FTM difference between the two measurements became greater (FTM supine v prone, 25.129+/-10.445 v 24.030+/-10.388 kg, P=.0001; LTM supine v prone, 37.309+/-9.357 v 38.246+/-9.150 kg, P=.0001). It is concluded that the positioning of the patient on the examination table affects DEXA body composition measurements by the fan-beam mode. This could imply a lack of accuracy of the method, which may be due to subtle changes in regional tissue depth and fat distribution caused by patient repositioning.     

Tidal volume measurements in newborns using respiratory inductive plethysmography

Respiratory inductive plethysmography (RIP) is a well-accepted noninvasive technology for monitoring breathing patterns in adults. Prior attempts to calibrate this device in babies have been fraught with technical difficulties, thereby limiting applications in this population. Recently, a new method, qualitative diagnostic calibration (QDC), has been shown to provide accurate calibration of tidal volume in adults. The QDC method is based upon principles of the isovolume maneuver and carried out during natural breathing without specialized respiratory maneuvers or postural changes. We calibrated RIP with QDC in the supine posture and compared tidal volume (VT) measured with RIP to VT by a face mask-pneumotachograph (PNT) in 21 healthy full-term newborns in supine and prone postures. Eleven of the babies were calibrated during active sleep and 10 in quiet sleep. The mean VT in the supine and prone postures were 19 and 25 ml, respectively. In the supine and prone postures, weighted mean difference between RIP (VT) and PNT (VT) and 95% confidence intervals were -0.05 ml (-0.27, 0.18) and -0.32 ml (-0.08, 0.55), respectively. There was no difference in the accuracy of RIP relative to PNT calibrated during active sleep when thoracoabdominal incoordination was present or quiet sleep when it was not in either the supine or the prone postures. Therefore, in full-term infants, RIP calibrated with QDC solely in the supine posture provides clinically acceptable measurements of VT in both supine and prone postures.     

Effects of partial liquid ventilation with perfluorocarbons on pressure-flow relationships, vascular compliance, and filtration coefficients of isolated blood-perfused rabbit lungs

OBJECTIVES: The density of perfluorocarbons is almost twice that of blood. Therefore, we hypothesized that partial liquid ventilation with these fluids markedly affects pulmonary hemodynamics and filtration coefficients. To test these hypotheses we studied pressure-flow relationships, vascular compliances, capillary pressures, and filtration coefficients in normal and perfluorocarbon-ventilated rabbit lungs. DESIGN: Controlled animal study with an ex-vivo isolated lung preparation. SETTING: Research laboratory for experimental anesthesiology at the Heinrich-Heine-University of Düsseldorf. SUBJECTS: Fourteen New Zealand White rabbits. INTERVENTIONS: The lungs were perfused under zone 3 flow conditions with autologous blood at various flow rates (50 to 250 mL/min, closed circuit, roller pump, 37 degrees C) and ventilated with 5% CO2 in air (positive end-expiratory pressure: 2 cm H2O, tidal volume: 10 mL/kg, respiratory rate: 30 breaths/min) without (control group, n=7) and with (n=7) perfluorocarbon administered intratracheally (15 mL/kg). MEASUREMENTS AND MAIN RESULTS: Pulmonary arterial, left atrial, and airway pressures, as well as blood reservoir volume (reflecting changes in pulmonary blood volume) and lung weight, were measured continuously. Inconsistent with our hypothesis, we found no significant differences between both groups in the slopes and intercepts of the pressure-flow relationships. There were no significant differences in capillary pressures determined by double occlusion (6.7+/-1.2 vs. 6.3+/-1.3 cm H2O for control group, p=.53), vascular compliances (0.51+/-0.10 vs. 0.47+/-0.09 mL/cm H2O for control group, p=.38), and filtration coefficients (0.33+/-0.06 vs. 0.37+/-0.07 mL/min/mm Hg/100 g wet weight for control group, p=.80, Mann-Whitney). CONCLUSIONS: Partial liquid ventilation with perfluorocarbons has no relevant effects on pulmonary filtration coefficients and global hemodynamic variables of isolated zone 3 lungs. These findings suggest that right ventricular afterload is not changed with partial liquid ventilation. It is likely, however, that intrapulmonary blood flow is redistributed toward less-dependent regions, although relevant global hemodynamic changes are absent during partial liquid ventilation.     

N-Glycosylation affects endoplasmic reticulum degradation of a mutated derivative of carboxypeptidase yscY in yeast

BACKGROUND: Reports of short- and medium-term evolution of Lung Function Tests (LFT) in infants with bronchopulmonary dysplasia (BPD) are still scarce. POPULATION AND METHODS: The results of the first (before 3 months of corrected age) and the second (between 3 and 9 months of corrected age) LFT in 22 premature infants with BPD (gestational age 31 +/- 2.5 weeks; birth weight: 1570 +/- 440 g; duration of mechanical ventilation: 46 +/- 24 days, total duration of oxygen therapy: 88 +/- 47 days) were compared to those obtained in 27 normal infants for the first LEF and 10 normal infants for the second LFT, similar to the patients for birth weight and corporeal index (CI). RESULTS: In the first LFT, major abnormalities were an increased thoracic gaz volume (TGV) (16.5 +/- 42 vs 122 +/- 24 mL; P < 0.001) and TGV CI ratio (1.25 +/- 0.31 vs 0.89 +/- 0.17 ml/kg/m2; P < 0.0001) a decreased pulmonary compliance (2.49 +/- 1.46 vs 11.60 +/- 4.50 mL/cmH2O; P < 0.0001) and specific pulmonary compliance (0.015 +/- 0.10 vs 0.100 +/- 0.042 mL/cmH2O/mL de TGV; P < 0.0001), an increased total pulmonary resistance (20.4 +/- 12.1 vs 10.5 +/- 5.3 cmH2O/L/s; P < 0.001). In the second LFT, an increased TGV (235 +/- 62 vs 166 +/- 28 mL; P < 0.01) and TGV CI ratio (1.64 +/- 0.65 vs 0.98 +/- 0.11 ml/kg/m2; P < 0.05), a decreased pulmonary compliance (2.68 +/- 2.0 vs 15.2 +/- 5.7 mL/cmH2O; P < 0.0001) and specific pulmonary compliance (0.013 +/- 0.010 vs 0.106 +/- 0.050 mL/cmH2O/mL de TGV; P < 0.0001), an increased total pulmonary resistance (17.1 +/- 9.6 vs 8.6 +/- 4.9 cmH2O/L/s; P < 0.05) were noted when compared with the control group results. Major abnormalities of the blood gases were hypoxemia (63 +/- 10 vs 85 +/- 20 mmHg; P < 0.05), hypercapnia (38.5 vs 31 +/- 4 mmHg; P < 0.0001) during the first LFT. Hypoxemia (77 +/- 14 vs 90 +/- 14 mmHg and hypercapnia (37 +/- 4 vs 29 +/- 5 mmHg) continued in the second LFT. Thoracic distention and total pulmonary resistances in infants with BPD did not improve but their pulmonary compliance (P < 0.0001) and PaO2 (P < 0.01) between the first and second LFT did it. Infants who had been ventilated for a hyaline membrane disease (HMD) were more hypoxic on the second LFT (P < 0.05) than those who had been ventilated for other causes. Statistically significant relationships were found between thoracic distention and duration of positive inspiratory pressure (P < 0.05; r = 0.43), duration of positive expiratory pressure (P < 0.05, r = 0.45) total oxygen therapy duration; between total pulmonary resistance and duration of mechanical ventilation with high frequency (P < 0.05; r = 0.52); between hypoxemia and duration of oxygen therapy with FiO2 > or = 60% (P < 0.05; r = 0.54). CONCLUSIONS: This study shows prolonged clinical and functional abnormalities of the respiratory functions requiring longer follow-up.     

Role of vagus during exercise in thermal panting

In dogs anaesthetised with pentobarbitone sodium raising the body temperature from 37 degrees C during mild exercise increased the rate of respiration and pulmonary ventilation but decreased the tidal volume. Cold blocking the vagi during the exercise resulted in decrease in respiration rate and minute ventilation, but increase in tidal volume. At 40 degrees C body temperature vagal block was not effective in decreasing the respiration rate and minute ventilation, which may be due to stimulation of lung irritant receptors through hyperthermia.     

Physiological dead space/tidal volume ratio during face mask, laryngeal mask, and cuffed oropharyngeal airway spontaneous ventilation

OBJECTIVE: To compare the physiological dead space/tidal volume ratio and arterial to end-tidal carbon dioxide tension (ETCO2) difference during spontaneous ventilation through a face mask, a laryngeal mask (LMA), or a cuffed oropharyngeal airway. DESIGN: Prospective, randomized, cross-over study. SETTING: Inpatient anesthesia at a university department of orthopedic surgery. PATIENTS: 20 ASA physical status I and II patients, without respiratory disease, who underwent ankle and foot surgery. INTERVENTIONS: After a peripheral nerve block was performed, propofol anesthesia was induced and then maintained with a continuous intravenous (i.v.) infusion (4 to 6 mg/kg/h). A face mask, a cuffed oropharyngeal airway, or an LMA were placed in each patient in a random sequence. After 15 minutes of spontaneous breathing through each of the airways, ventilatory variables, as well as arterial, end-tidal, and mixed expired CO2 partial pressure, were measured, and physiological dead space/tidal volume ratio was calculated. MEASUREMENTS AND MAIN RESULTS: Expired minute volume and respiratory rate (RR) were lower with LMA (5.6 +/- 1.2 L/min and 18 +/- 3 breaths/min) and the cuffed oropharyngeal airway (5.7 +/- 1 L/min and 18 +/- 3 breaths/min) than the face mask (7.1 +/- 0.9 L/min and 21 +/- 3 breaths/min) (p = 0.0002 and p = 0.013, respectively). Physiological dead space/tidal volume ratio and arterial to end tidal CO2 tension difference were similar with the cuffed oropharyngeal airway (3 +/- 0.4 mmHg and 4.4 +/- 1.4 mmHg) and LMA (3 +/- 0.6 mmHg and 3.7 +/- 1 mmHg) and lower than with the face mask (4 +/- 0.5 mmHg and 6.7 +/- 2 mmHg) (p = 0.0001 and p = 0.001, respectively). CONCLUSION: Because of the increased dead space/tidal volume ratio, breathing through a face mask required higher RR and expired minute volume than either the cuffed oropharyngeal airway or LMA, which, in contrast, showed similar effects on the quality of ventilation in spontaneously breathing anesthetized patients.     

Evaluation of lung function after intratracheal perfluorocarbon administration in healthy animals

OBJECTIVES: To investigate the effects of partial liquid ventilation (i.e., mechanical ventilation in combination with intratracheal administration of perfluorocarbon) on lung function, with particular attention to the integrity of the alveolocapillary membrane in healthy adult animals. DESIGN: Prospective, randomized, controlled study. SETTING: Laboratory at the Department of Experimental Anesthesiology, Erasmus University Rotterdam. SUBJECTS: Ten adult male New Zealand rabbits. INTERVENTIONS: Five rabbits were intratracheally treated with 12 mL/kg of perfluorocarbon while conventional mechanical ventilation (volume-controlled, tidal volume of 12 mL/kg, respiratory rate of 30 breaths/min, inspiration/expiration ratio of 1:2, positive end-expiratory pressure of 2 cm H2O, and an FIO2 of 1.0) was applied for 3 hrs. To assess the permeability of the alveolocapillary membrane, pulmonary clearance of inhaled technetium-99m-labeled diethylenetriamine pentaacetic acid (99mTc-DTPA) measurements were performed at 3 hrs and compared with data from the control group (n = 5) treated with mechanical ventilation only, using the same ventilatory parameters. MEASUREMENTS AND MAIN RESULTS: Pulmonary gas exchange and lung mechanical parameters were measured in both groups at 30-min intervals. Mean values for PaO2 in the perfluorocarbon group, although at adequate levels, were less than those values of the control group during the 3-hr study period (370 +/- 44 vs. 503 +/- 44 torr at 3 hrs [49.3 +/- 5.9 vs. 67.1 +/- 5.9 kPa]). Peak and mean airway pressures were higher in the perfluorocarbon group (ranging from 1.9 to 3.4 cm H2O and 0.7 to 1.3 cm H2O, respectively) compared with the control group, while end-inspiratory airway pressure was similar in both groups. The half-life of 99mTc-DTPA was 83.7 +/- 24.5 mins in the control group, which was significantly longer (p < .01) than in the perfluorocarbon group (49.8 +/- 6.1 mins). CONCLUSIONS: These findings suggest that partial liquid ventilation with perfluorocarbons lowers pulmonary gas exchange in healthy animals, and the increased pulmonary clearance of 99mTc-DTPA after 3 hrs of this type of ventilatory support may reflect minimal reversible changes in the lung surfactant system.     

Lyme disease--on the basis of our observations

We biologically assessed functions of several reconstituted surfactants with the same minimum surface tension (2-3 mN/m) as "complete" porcine pulmonary surfactant (natural surfactant) but with longer surface adsorption times. Administration of natural surfactant (adsorption time 0.29 s) into the lungs of surfactant-deficient immature rabbits brought a tidal volume of 16.1 +/- 4.4 (SD) ml/kg during mechanical ventilation with 40 breaths/min and 20 cmH2O insufflation pressure. In static pressure-volume recordings, these animals showed a lung volume of 62.4 +/- 9.7 ml/kg at 30 cmH2O airway pressure and maintained 55% of this volume when the pressure decreased to 5 cmH2O. With two reconstituted surfactants consisting of synthetic lipids or isolated lipids from porcine lungs plus surfactant-associated hydrophobic proteins (adsorption times 0.57 and 0.78 s, respectively), tidal volumes were < 38% of that with natural surfactant (P < 0.05), but static pressure-volume recordings were not different. Care is therefore needed in estimating the in vivo function of surfactant preparations from minimum surface tension or static pressure-volume measurements.     

Prone position favors motor development of infants

OBJECTIVE: To determine the motor development in infants sleeping in the supine position compared to infants sleeping in the prone position, and to compare the levels of motor development of infants playing only in the supine position and of infants playing in the prone position as well. DESIGN: Prospective blinded comparing study. SETTING: Department of Physical Therapy, Maasziekenhuis, Boxmeer, the Netherlands. METHODS: Various measuring instruments were used in the home environment to determine the levels of motor development at the age of 5 months of 21 healthy infants born at term selected from a group of 160 infants attending the infant welfare clinic. RESULTS: Infants sleeping in the prone position (n = 8) showed a higher motor development than infants sleeping in the supine position (n = 13). Infants playing in the prone and supine position (n = 5) had a higher motor development than infants who played exclusively in the supine position (n = 15). CONCLUSION: Sleeping and playing in the prone position was accompanied by a higher motor development in healthy mature-born infants at the age of 5 months.     

Oxygen cost of breathing and weaning process in newborn infants

Newborn infants may have a high oxygen cost of breathing (OCB) at the time of being weaned from mechanical ventilation. We hypothesized that this increase in oxygen consumption (V'O2) could be reduced by using certain weaning ventilatory modes. We designed a study to assess V'O2 during three weaning ventilatory modes: patient triggered ventilation, synchronous intermittent mandatory ventilation (SIMV) and continuous positive airway pressure in 16 newborn infants before being weaned from mechanical ventilation In seven infants whose OCB was high. V'O2 was not significantly different between CV and PTV (8.9+/-0.6 versus 9.5+/-0.8, respectively) whereas it tended to increase to 10.8+/-1.1 mL x min(-1) x kg(-1) during SIMV and increased significantly to 11.9+/-0.8 mL x min(-1) x kg(-1). In the other nine infants whose OCB was normal, no significant variation of V'O2 was observed. Patient triggered ventilation was a weaning ventilatory mode that significantly reduced the increase in oxygen consumption observed in infants with a high oxygen cost of breathing, as compared to synchronous intermittent mandatory ventilation or continuous positive airway pressure. Further investigations in newborn infants with a high oxygen cost of breathing should be performed prior to routine use of patient triggered ventilation.