Compliance measurement in respiratory distress syndrome: the prediction of outcome

Dynamic compliance (Cdyn) measurements within the first three days of life predicted survival in 60 preterm infants suffering from respiratory distress syndrome. Cdyn was measured in 47 survivors at 2.3 +/- 1.4 days of life and in 13 nonsurvivors on 2.7 +/- 1.7 days. All nonsurvivors died from respiratory failure within the first two weeks of life. Mean Cdyn of the survivors was 0.83 +/- 0.33 ml/cm H2O and of the nonsurvivors 0.35 +/- 0.19 ml/cm H2O (p less than 0.001). Cdyn values below 0.45 ml/cm H2O predicted 11 of 13 deaths in infants, and Cdyn measurements above this value predicted 45 of 47 survivals, with a specificity of 81% and a sensitivity of 89%. Eleven of the survivors, who subsequently developed bronchopulmonary dysplasia (BPD), had a mean Cdyn of 0.56 +/- 0.23 ml/cm H2O. When these infants were matched with infants of comparable weight without evidence of BPD, the BPD group had a significantly lower Cdyn (p less than 0.05). Cdyn measurements during the first three days of life are useful in predicting outcome of respiratory failure secondary to respiratory distress syndrome.     

Pulmonary mechanics and outcome of neonates on ECMO.

Deciding when to wean neonates from extracorporal membrane oxygenation (ECMO) can be difficult. The usefulness of simple measurements of pulmonary mechanics e.g., dynamic compliance (Cdyn) has been questioned. We investigated the pulmonary mechanics of eight neonates using the interrupter technique, which allows the partitioning of pulmonary mechanics into compartments representing the conducting airways and more peripheral phenomena (viscoelastic properties and "pendelluft"). Three neonates required ECMO for a congenital diaphragmatic hernia (CDH), two for hyaline membrane disease (HMO), two for meconium aspiration syndrome (MAS), and one for pneumonia. All neonates with MAS, HMD, and pneumonia were successfully weaned from ECMO when their Cdyn was 0.3 mL/cmH2O/kg or greater [mean 0.34 +/- 0.06 (SEM)]. All three neonates with CDH died and their highest Cdyn was 0.21, 0.19, and 0.09 mL/cmH2O/kg respectively (mean, 0.16 +/- 0.037). The airway resistance (Raw) and the slower component of pressure change after interruption (delta Pdiff), a measure of the more peripheral phenomena of the lung, were not significantly different in those neonates who survived and those who did not. The values for delta Pdiff in all patients were higher than those in healthy neonates. However, the Raw was not different. This suggests that the major disturbance in pulmonary mechanics was distal to the conducting airways. Those neonates who were successfully weaned from ECMO had a significantly higher Cdyn 24-48 hours prior to decannulation. Considering the lung as a two-compartment model offers no advantages when compared to the one-compartment model for the prediction of the outcome of a neonate on ECMO.     

慢性阻塞性肺疾病患者长期人工通气撤机指标的临床研究

目的评价床边综合肺功能作为长期人工通气的慢性阻塞性肺疾病（COPD）患者脱机指标的指导意义。方法监测58例（成功组：43例，失败组：15例）通气时间＞72h的COPD呼衰患者达到临床脱机标准后的血气分析、肺功能及呼吸力学的改变情况。结果两组患者的血气分析、急性生理、慢性健康评分（APACHEⅡ）、氧合指数、动态顺应性及气道阻力均无显著差异（P均＞0．05）；成功组患者的肺活量／潮气量（VC／V_T）、最大吸气负压（Pi_(max)）和浅快呼吸指数（f／V_T）分别为：2．10±0．20、（－21±4）cmH_2O及（74±30）次·min~(-1)·L~(-1)；失败组患者则依次为1．30±0．20、（－13±3）cmH_2O及（115±20）次·min~(-1)·L~(-1)，两组结果比较差异有显著性，P均＜0．05。以VC／V_T＞1．8、Pi_(max)＜－18cmH_2O和f／V_T＜105次·min~(-1)·L~(-1)作为临界值预测此类患者脱机成功与否，具有较高的敏感性（84％）和特异性（90％）。结论　综合肺功能指标（VC／V_T、Pi_(max)及f／V_T）可用于指导长期通气的COPD患者选择脱机时机，适宜在我国目前条件下推广普及。     

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.     

Effect of tidal volume and positive end-expiratory pressure on compliance during mechanical ventilation.

In 12 patients requiring therapy with mechanical ventilation for acute respiratory failure, total static compliance (Cst) increased from 29 +/- 4 ml/cm H2O at a tidal volume (TV) of 5 ml/kg to 42 +/- 7 ml/cm H2O at a TV of 15 ml/kg. Similarly, Cst increased from 42 +/- 7 ml/cm H2O to 52 +/- 8 ml/cm H2O between 0 and 6 cm H2O of positive end-expiratory pressure (PEEP). At high levels of pulmonary inflation (ie, high PEEP and large TV) compliance decreased. The changes of total respiratory compliance with TV were mainly due to changes in pulmonary compliance. With PEEP, the functional residual capacity increased, and specific compliance did not change. Two mechanisms may be responsible for the changes in compliance. First, varying TV or PEEP will alter the position of tidal ventilation on the pressure-volume curve, resulting in an increase in compliance with increasing TV and PEEP up to a point, where overdistention occurs and compliance decreases. Secondly, the function of the surface-lowering substance may be altered in acute pulmonary parenchymal disease, thus disturbing the regulation of surface tension over the range of pulmonary inflation studied.     

Pulmonary antigen challenge in rats passively sensitized with a monoclonal IgE antibody induces immediate but not late changes in airway mechanics

Pulmonary antigen challenge in sensitized individuals results in isolated immediate, isolated late, or dual reactions consisting of both an immediate and late change in airway function. The immediate response appears to be dependent on the presence of IgE antibody and mast cell mediator release. Although the late phase of dual responses is considered to be related to or a continuum of the immediate hypersensitivity response, its precise pathogenesis remains to be determined. To increase both the sensitivity and specificity of analyzing the pathogenesis of IgE-dependent pulmonary responses, we have used a Sprague-Dawley rat model system in which rats are passively sensitized with a murine monoclonal IgE anti-dinitrophenol (DNP) antibody prior to challenge with DNP-bovine serum albumin (DNP-BSA). Pathogen-free rats were injected with IgE or saline in a randomized blinded protocol, and in 24 to 48 h were anesthetized with urethane (1.2 g/kg intraperitoneally) and instrumented to measure lung resistance (RL) and dynamic compliance (Cdyn). Rats were then challenged with aerosolized DNP-BSA (10 mg/ml), and RL and Cdyn monitored through 7 h after challenge. Both RL (0.30 +/- 0.10 versus 0.13 +/- 0.02 cm H2O/ml.sec-1) and Cdyn (0.41 +/- 0.10 versus 0.25 +/- 0.08 ml/cm H2O) were significantly different (p less than 0.05) in sensitized rats compared to control rats immediately after challenge. No late changes were observed in either the treated or control animals.(ABSTRACT TRUNCATED AT 250 WORDS)     

Pulmonary mechanics in normal infants and young children during first 5 years of life

To characterize lung function in young children we measured lung compliance and pulmonary conductance in 40 normal infants and children ranging in age from the newborn period to 5 years. Inspiratory and expiratory flow was measured by a pneumotachograph, esophageal pressure through a water-filled feeding tube, and functional residual capacity (FRC) by a N2 washout technique. The esophageal pressure change per breath [(mean +/- SD) 7.3 +/- 1.4 cm H2O] and specific compliance (75 +/- 13 ml/cm H2O/L-FRC) did not change with growth. Specific conductance was high (0.60 L/s/cm H2O/L-FRC) in preterm infants, decreasing rapidly with initial growth but minimally beyond 10 kg of body weight, and stabilizing at 0.10 L/s/cm H2O/L-FRC. During the age period studied, compliance increased approximately x 25 whereas conductance only rose five-fold. The changes in compliance and conductance were well correlated to FRC, body weight, and length. These findings suggest that in the last trimester of pregnancy the airways are already well developed and postnatal lung growth occurs mainly by formation of new alveoli, leading to a proportional increase in FRC and lung compliance. Postnatally, conductance increases much more slowly than FRC, resulting in a rapid drop in specific conductance.     

Total respiratory system compliance in asymptomatic infants with cystic fibrosis

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

An acute reduction in the fraction of inspired oxygen increases airway constriction in infants with chronic lung disease

Infants with chronic lung disease have acute episodes of hypoxemia that are often accompanied by wheezing. To test whether a sudden reduction in FIO2 might increase airway obstruction in such infants, we measured the flow-volume relationship, O2 saturation, and skin-surface CO2 tension in 19 sedated infants, 11 with chronic lung disease, and 8 control infants, before and during 10 min of continuous hypoxemia. In the infants with chronic lung disease, a 20 to 25% reduction in FIO2 caused acute hypoxemia (O2 saturation, 77 +/- 8%) and an associated decrease in mid-expiratory flow from 103 +/- 55 to 69 +/- 37 ml/s (mean +/- SD; p less than 0.05) in the absence of a significant change in tidal volume or skin-surface CO2 tension. In the infants without lung disease, breathing 17% O2 led to a significant increase in minute ventilation (26 +/- 25%; p = 0.05), but there was no consistent change in mid-expiratory flow. To further study the effects of an acute reduction in FIO2 on pulmonary function in infants with chronic lung disease, we measured lung mechanics in 6 infants and end-expiratory lung volume in 5. Baseline lung resistance was high (49 +/- 35 cm/l/s) and increased by 55 +/- 30% (p less than 0.05) in response to hypoxemia. Baseline dynamic lung compliance was low (2.5 +/- 1.5 ml/cm) and decreased by 24 +/- 10% (p less than 0.05). Functional residual capacity increased from 26 +/- 13 to 33 +/- 14 ml/kg (p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)     

Mechanisms of late hemodynamic and airway dynamic responses to endotoxin in awake sheep

The mechanism of sustained alterations in pulmonary hemodynamics and lung mechanics after endotoxin infusion in sheep remains unclear. We examined the effects of metaproterenol, propranolol, atropine, and ibuprofen on pulmonary artery pressure (Ppa), dynamic compliance (Cdyn), resistance to airflow across the lungs (RL), specific airway conductance (SGaw), and alveolar-arterial oxygen difference (delta AaPO2) (room air) given 2.5 h after endotoxemia (except for propranolol, which was given 1 h after metaproterenol) in awake sheep. Atropine infusion had no effect on any of the variables measured. Ibuprofen infusion immediately reduced mean Ppa from 31 +/- 2 (mean +/- SEM) to 24 +/- 2 cm H2O (p less than 0.05). Metaproterenol and ibuprofen immediately increased Cdyn and SGaw and decreased RL to near baseline (p less than 0.05). No intervention affected delta AaPO2 (p greater than 0.05). In sheep treated with metaproterenol, propranolol immediately returned lung mechanics (p less than 0.05) to premetaproterenol levels without affecting delta AaPO2 (p greater than 0.05). Ibuprofen reduced lung lymph thromboxane-B2 towards baseline levels (p less than 0.05). We conclude that endotoxemia causes prolonged bronchoconstriction and pulmonary hypertension in sheep, which is largely mediated by constrictor prostanoids rather than by cholinergic mechanisms and is reversible with ibuprofen given 2.5 h after endotoxin.     

Airway occlusion pressure. An important indicator for successful weaning in patients with chronic obstructive pulmonary disease

The objective of this study was to determine whether airway occlusion pressure (P0.1) is a useful predictor for successful weaning during discontinuation of assisted ventilation (AV) in patients with chronic obstructive pulmonary disease (COPD). We studied 12 patients with COPD receiving AV with maximal inspiratory pressure (MIP) less than or equal to -20 cm H2O and FVC greater than or equal to 10 ml/kg. The P0.1, VT, frequency, mean inspiratory flow rate (VT/TI), inspiratory time to total breath cycle duration (TI/Ttot), and arterial blood gases were determined just prior to weaning, within 5 min after discontinuing AV (Time 0), and at 30, 60, 90, 120, 180, and 240 min. Five of the 12 patients failed to wean, defined as requiring AV within 24 h after discontinuing AV. At Time 0, all patients who subsequently failed to wean had a P0.1 of greater than 6 cm H2O, and those who were successfully weaned had a P0.1 of less than 6 cm H2O (p less than 0.001), although the arterial blood gas determinations were comparable in both groups. Throughout the study period, P0.1 in the patients who failed to wean was persistently higher than in the successfully weaned patients. Despite the high P0.1, VT and VT/TI decreased significantly at the termination of the study compared with those at Time 0 in 3 of the patients who failed to wean. Tachypnea was not useful in predicting failure to wean. The TI/Ttot in the patients who failed to wean was persistently lower than in the successfully weaned patients. We conclude that P0.1 is an important indicator for successful weaning.     

Effect of a beta-agonist nebulization on lung function in neonates with increased pulmonary resistance

Pulmonary resistance is elevated early in preterm infants who later develop chronic lung disease. This early increase in pulmonary resistance may play a role in the development of severe bronchopulmonary dysplasia (BPD). A beta-2-agonist (isoetharine HCl) was used as an aerosol in 13 preterm infants with elevated pulmonary resistance. Their birthweight ranged from 880 to 1630 g, their gestational age from 27 to 34 weeks, and their post natal age from 3 to 18 days. All infants had required mechanical ventilation for respiratory distress syndrome and therefore were at risk to develop BPD. Pulmonary mechanics were measured before and 30 minutes after aerosol treatment, determining inspiratory and expiratory flow with a pneumotachometer and esophageal pressure through a water-filled feeding tube. The treatment was well tolerated with no significant changes in blood pressure, heart rate, or respiratory rate. Pulmonary resistance decreased significantly from 130 +/- 35 cm H2O/L/sec to 89 +/- 24 cm H2O/L/sec after the treatment. Dynamic lung compliance increased in 11 of the 13 infants. It is concluded that beta-2-agonist nebulization is effective in reducing the early increase in pulmonary resistance that occurs in preterm infants who are at risk of developing BPD. This effect may be due to relaxation of bronchial smooth muscle, to improved mucociliary transport, and to a reduction in peribronchial edema.     

Ascaris suum ova-induced bronchoconstriction, eosinophilia, and IgE antibody responses in experimentally infected primates did not lead to histamine hyperreactivity

The hypothesis that active immunization of primates to give airway allergic responses would also confer on them a hyperreactivity to a nonspecific stimulus such as histamine was tested in 29 normal rhesus primates. At 6 wk after immunization, specific primate IgE (Rast) to Ascaris antigen had increased from 0.35 +/- 0.17 to 0.98 +/- 0.35 units/ml x 10(2) (p less than 0.05). Histamine released from bronchial alveolar lavage cells in response to antigen increased from 5.4 +/- 0.67 to 24 +/- 1.8ng/10(6) cells (p less than 0.05). In a subgroup of seven animals, airway resistance RL and compliance before and after feeding embryonated Ascaris ova increased from RL 3.5 +/- 3.1 to 275 +/- 212 cm H2O/L/s (p = 0.02) and Cdyn fell from 81 +/- 10 to 11.3 +/- 12 ml/cm H2O (p less than 0.05). The bronchial lavage fluid contained a very high percentage of eosinophils after infection, 8 +/- 3.1 to 24 +/- 13% per 500 cells counted, and did not increase appreciably upon later antigen challenge, 24 +/- 13 to 31 +/- 11% of the cells at 9.5 h after antigen challenge (p = NS). When a group of seven of these 29 animals were compared for their histamine responsiveness before and after acquired Ascaris airway reactivity, there was no difference in 19 animals. Pulmonary response to histamine delivered from freon canisters at doses of 0.005, 0.01, 0.025, and 0.05% did not change (RL, 141 +/- 102 to 93 +/- 62; Cdyn, 49 +/- 7 to 46 +/- 11% change before and after, respectively) (p = NS).(ABSTRACT TRUNCATED AT 250 WORDS)     

全氟化碳雾化吸入对急性呼吸窘迫综合征猪气体交换、呼吸力学和血流动力学的影响

目的探讨全氟化碳(PFC)雾化吸入对急性呼吸窘迫综合征(ARDS)猪气体交换、呼吸力学和血流动力学的影响。方法16只通过气管内吸入十六烷磺基丁二酸钠(DTG)制作的ARDS模型猪随机分为PFC治疗组和对照组。PFC治疗组在常规机械通气基础上,连接雾化器,以纯氧(氧流速3L/min)作为驱动气流推动雾化PFC治疗2h(7～8ml·kg-1·h-1);对照组在常规机械通气基础上,连接雾化器单独给予纯氧治疗2h(氧流速3L/min),在治疗期间每间隔15min测定动脉血气、血压、心率及平台压、顺应性、呼出潮气量和内源性呼气末正压(PEEPi),观察两组动物气体交换、呼吸力学和血流动力学参数的变化。结果DTG气管内吸入1h后,PFC治疗组动脉血氧分压(PaO2)从(377±55)mmHg(1mmHg=0.133kPa)下降至(56±13)mmHg[吸入气氧浓度(FiO2)100%],对照组PaO2从(383±53)mmHg下降至(49±12)mmHg(FiO2100%);PFC治疗组顺应性从(3.7±1.0)ml/cmH2O下降至(1.5±0.4)ml/cmH2O,对照组顺应性从(3.8±0.7)ml/cmH2O下降至(1.4±0.4)ml/cmH2O。PFC治疗2h后PFC治疗组PaO2上升至(189±133)mmHg,顺应性改善至(4.1±1.4)ml/cmH2O,呼出潮气量增加至(74.5±16.9)ml;对照组PaO2上升至(83±51)mmHg,顺应性改善至(2.8±1.8)ml/cmH2O,呼出潮气量增加至(50.1±4.1)ml;两组比较差异均有统计学意义(P均<0.05)。两组动物pH值、心率、血压、平台压、PEEPi和动脉血二氧化碳分压(PaCO2)比较差异均无统计学意义(P均>0.05)。结论PFC雾化吸入能明显改善ARDS家猪的氧合,提高损伤肺的顺应性,增加呼出潮气量。     

The role of airflow resistance in patients with the adult respiratory distress syndrome

Although reduced lung compliance is a hallmark of the adult respiratory distress syndrome (ARDS), the role of increased airflow resistance in this disorder has not been well studied. Because animal models of ARDS show marked increases in airflow resistance and because mediators known to participate in lung parenchymal injury have also been implicated in models of increased airway reactivity, we hypothesized that increased airflow resistance is a major contributor to altered lung mechanics in human ARDS. We studied 10 mechanically ventilated patients with ARDS (criteria: PaO2 less than or equal to 70 mm Hg breathing FIO2 greater than or equal to 0.4; bilateral pulmonary roentgenographic infiltrates; Ppaw less than or equal to 18 mm Hg) measuring dynamic (Cdyn) and static (Cstat) compliance, airflow resistance across the lungs (RL), shunt fraction (QS/QT breathing FIO2 = 1.0), minute ventilation (VE), (a/A)PO2, dead space to tidal volume ratio (VD/VT), airflow (pneumotachograph), transpulmonary pressure (intratracheal pressure minus esophageal pressure) and volume (integrated from flow) at 50 L/min peak flow rate. Airflow resistance was uniformly elevated and averaged six times normal (5.32 +/- 0.92 cm H2O/L/s versus 0.88 +/- 0.08) (p less than 0.05). Cdyn correlated directly with (a/A)PO2. RL correlated with peak pressure, but did not correlate with VE, shunt, (a/A)PO2, or VD/VT. We conclude that increased pulmonary airflow resistance contributes significantly to the altered lung mechanics in ARDS. These data are consistent with studies of animal models of ARDS and long-term survivors of ARDS and may be secondary to tissue factors, airway hyperreactivity, or airway inflammation.     

不同通气模式下吸痰对呼吸力学和气体交换的影响

目的比较在压力控制通气（PCV）与容量控制通气（VCV）模式下吸痰对患者气体交换和呼吸力学的影响。方法采取自身交叉对照的方法，在PCV和VCV模式下分别对23例机械通气患者进行开放式吸痰，比较不同时间点气体交换、呼吸力学及血流动力学等指标的变化。结果在PCV模式下，吸痰后30min潮气量、顺应性分别为（6．60±1．95）mL／kg、（18±7）ml／cmH2O（1cmH2O=0．098kPa），与基础水平[（9．05±0．22）mL／kg、（24±6）ml／cmH2O]比较差异有统计学意义（F值分别为8．47、8．01，P均〈0．05）；而30min时动脉血氧分压（PaO2）、动脉血二氧化碳分压（PaCO2）分别为[（87±13）mmHg（1mmHg=0．133kPa）、（53±11）mmHg]，与0min[（113±22）mmHg、（41±10）mmHg]比较差异有统计学意义（，值分别为6．18、9．13，P均〈0．05）；在VCV模式下，吸痰后30min顺应性、气道平台压、气道峰压分别为[（18±7）ml／cmH2O、（27±8）cmH2O、（33±8）cmH2O]，与基础水平[（23±7）ml／cmH2O、（22±5）cmH2O、（27±8）cmH2O]比较差异有统计学意义（，值分别为6．83、6．97、7．08，P均〈0．05）；而30min时PaO2、PaCO2分别为（105±26）mmHg、（38±11）mmHg，与0min[（109±21）mmHg、（37±14）mmHg]比较差异无统计学意义（F值分别为1．88、1．32，P均〉0．05）；在PCV模式下，吸痰后5min心率、平均动脉压（MAP）分别为（109±20）次／min、（89±10）mmHg，与基础水平[（97±17）次／min、（83±12）mmHg]比较差异有统计学意义（F值分别为5．86、9．49，P均〈0．05）。在VCV模式下，吸痰后5min心率、MAP分别为（110±17）次／min、（87±11）mmHg，与基础水平[（96±17）次／min、（79±11）mmHg]比较差异有统计学意义（F值分别为7．33、7．96，P均〈0．05）。结论吸痰在PCV和VCV模式下均引起患者气体交换受损和顺应性下降，但对气体交换的影响在PCV模式下比VCV更严重和持久。     

Respiratory compliance of healthy newborn infants measured by endinspiratory airway occlusion technique in the first hours of life

The compliance of the respiratory system (Crs) has been measured by an airway occlusion technique in 78 healthy newborn infants [gestational age (GA) 36.2 +/- 2.9 weeks, range 28-41 weeks; birth weight (BW) 2.418 +/- 0.879 kg, range 0.830-4.350 kg; body height (BH) 45.2 +/- 4.4 cm, range 33-52 cm in the first 8 h after birth (206.2 +/- 100.8 min, range 45-480 min). The prediction equations were (Crs, ml/cm H2O): Crs = 0.087.GA -1.173 (r = 0.49, p less than 0.0001), Crs = 0.372.BW +1.067 (r = 0.62, p less than 0.0001), Crs = 0.076.BH -1.493 (r = 0.61, p less than 0.0001). The Crs values were very similar to the values measured in curarized newborn infants and quoted in the literature. There was only one newborn infant with a Crs of less than 1 ml/cm H2O (GA = 34 weeks, BW = 0.830 kg, BH = 33 cm, Crs = 0.909 ml/cm H2O).     

Evaluation of neonatal pulmonary mechanics and energetics: a two factor least mean square analysis

Pulmonary mechanics, using a two factor least mean square analysis technique, were determined in 22 preterm neonates with respiratory failure. The respiratory system is modelled as a linear mechanical system. Concurrent signals of airflow and transpulmonary pressure were utilized to calculate values of dynamic lung compliance and pulmonary resistances; these determinations were made over the entire tidal volume range. In addition, values of resistive work of breathing, pulmonary time constants, scalar records of sequential breaths, pressure-volume and flow-volume relationships were available for data review and interpretation. The mean +/- SEM value of tidal volume was 7.4 +/- 0.6 ml/kg; dynamic lung compliance was 0.44 +/- 0.04 ml/cmH2O/kg; and the pulmonary resistance of the whole breath was 106 +/- 9.1 cmH2O/liter/s. The resistive work of breathing (hysteresis) was 41.8 +/- 5.9 gm.cm/kg. In correlating the measured values of pressure and flow to those predicted by the model, the mean value of the correlation coefficient for the least mean square analysis for all 22 studies was 0.995 +/- 0.001; the standard error of estimate of the predicted pressure was less than 4.4% of the range of pressures measured. Thereby, the model was considered to be appropriate for the neonatal respiratory system. In addition to the traditional procedures of evaluating the respiratory status of a sick neonate, bedside analysis of pulmonary mechanics provide graphical information, and quantitative data which should be useful in day-to-day pulmonary management.     

体位改变对急性肺损伤兔肺功能与CT及病理的影响

目的　通过观察不同体位下急性肺损伤 (ALI)肺的氧合功能、呼吸力学、肺CT以及病理等的变化 ,来探讨不同体位的效应和可能机制。方法　采用油酸型ALI兔模型 ,分为正常对照组(Ⅰ组 )、仰卧位油酸组 (Ⅱ组 )、俯卧位油酸组 (Ⅲ组 )、旋转体位油酸组 (Ⅳ组 ) ,观察各组兔实验过程中动脉血氧分压 (PaO2 )、呼吸力学的变化。并进行肺CT扫描加以分析 ,最后作病理切片检查。结果Ⅲ、Ⅳ组的PaO2 [(15 8± 5 1)、(16 6± 37)mmHg]、肺的顺应性 [(2 8± 0 9)、(2 6± 0 7)ml/cmH2 O]显著高于Ⅱ组 [PaO2 (87± 2 4 )mmHg、肺的顺应性 (1 6± 0 5 )ml/cmH2 O ,P均 <0 0 5 ];Ⅲ、Ⅳ组肺内分流 [(2 1± 5 ) %、(18± 5 ) % ]显著低于Ⅱ组 [(2 9± 8) % ,P <0 0 5 ];Ⅳ组的气道峰压 [(2 0± 2 )cmH2 O]显著高于Ⅲ组 [(16± 2 )cmH2 O ,P <0 0 5 ];3个实验组的PaO2 与肺的顺应性呈显著正相关 ,与肺内分流呈显著负相关。ALI兔肺CT呈明显的重力依赖效应 ,体位的变化对肺CT的影响非常迅速。肺水肿在重力依赖区重 ,旋转后 ,重力依赖现象减轻。结论　俯卧位和旋转体位都能改善兔油酸型ALI肺的氧合 ;ALI肺出现重力压迫性肺不张 ,旋转体位能减轻肺不张的程度和使肺水肿趋于均匀。     

A prospective comparison of IMV and T-piece weaning from mechanical ventilation

Two hundred (200) consecutive medical and surgical patients requiring mechanical ventilation were entered into a prospective randomized trial of weaning by either intermittent mandatory ventilation (IMV) or T-piece. Patients in these groups were of similar age and sex and had the same total ventilation time (TVT). The study design provided equal time for each weaning mode after specific criteria for oxygenation and ventilation were satisfied (PaO2 greater than 55 mm Hg on FIO2 less than 0.5; VE less than 12 L/min and two of the following four parameters: MVV greater than 2 VE, VT greater than 5 ml/kg, FVC greater than 10 ml/kg, NIF less than or equal to -20 cm H2O). Of the original 200 patients 165 were entered into the weaning phase; 35 patients were withdrawn prior to weaning due to the discretion of the attending physician or protocol error. Weaning time was not different between the IMV (5.3 +/- 1.2 h, mean +/- SEM) and T-piece groups (5.9 +/- 1.4 h, p = NS). Of the 165 patients, 155 (93 percent) were weaned successfully by protocol, 79 in the IMV and 76 in the T-piece group. Of 155 patients, 136 (88 percent) were weaned on the first attempt by protocol. Of the 19 who were not weaned, 11 were weaned successfully on the second and five on the third trial; three patients required three-day weans. We conclude that clinically stable patients who require short-term mechanical ventilation and meet standard bedside weaning criteria can be weaned efficiently by protocol using either IMV or T-piece techniques.