Control of laryngeal muscle activity in preterm infants

Control of upper airway muscles, such as those in the larynx, appears important for optimizing airflow patterns during normal respiration. Electromyograms (EMGs) of the laryngeal (LAR) area and diaphragm (DIA) were recorded with esophageal and skin electrodes, respectively, in 12 unsedated sleeping preterm infants during changes in chemical and mechanical feedback. Onset of phasic inspiratory LAR EMG preceded both DIA EMG and inspiratory airflow by 70 +/- 60 and 180 +/- 80 ms, respectively. Inhalation of 4% CO2 increased both peak LAR and DIA EMGs but did not alter their temporal relationships. End expiratory occlusion prolonged both LAR (600 +/- 120 to 930 +/- 290 ms, p less than 0.05) and DIA EMGs (690 +/- 180 to 940 +/- 270 ms, p less than 0.005) as well as mechanical inspiratory time. Early braking of expiratory flow was accompanied by persistence of DIA EMG into the expiratory phase, while termination of mid- to late expiratory braking was associated with onset of the LAR EMG of the subsequent inspiration. We conclude that respiratory activity of the LAR EMG is altered by both chemical and mechanoreceptor stimulation. Furthermore, simultaneous recording of LAR and DIA EMGs suggests that upper airway and chest wall muscles have different effects on expiratory flow patterns in human infants.     

Upper airway dynamic responses in children with the obstructive sleep apnea syndrome

Normal children have a smaller upper airway than adults, but, nevertheless, snore less and have less apnea. We have previously shown that normal children have an upper airway that is resistant to collapse during sleep. We hypothesized that this resistance to collapse is due to preservation of upper airway neuromotor responses during sleep. Furthermore, we hypothesized that upper airway responses would be diminished in children with the obstructive sleep apnea syndrome (OSAS). We therefore compared the upper airway pressure-flow relationship during sleep between children with OSAS and controls. Measurements were made by correlating maximal inspiratory airflow with the level of nasal pressure applied via a mask. Neuromotor upper airway activation was assessed by evaluating the upper airway response to 1) hypercapnia and 2) intermittent, acute negative pressure. We found that children with OSAS had no significant response to either hypercapnia or negative pressure during sleep, compared with the normal children. After treatment of OSAS by tonsillectomy and adenoidectomy, there was a trend for normalization of upper airway responses. We conclude that upper airway dynamic responses are decreased in children with OSAS but recover after treatment. We speculate that the pharyngeal airway neuromotor responses present in normal children are a compensatory response for a relatively narrow upper airway. Further, we speculate that this compensatory response is lacking in children with OSAS, most likely due to either habituation to chronic respiratory abnormalities during sleep or to mechanical damage to the upper airway.     

阻塞性睡眠呼吸暂停低通气综合征婴幼儿肺功能测定的诊断意义

目的观察鼾症患儿的潮气呼吸分析、呼吸力学指标的改变，探讨其对婴幼儿阻塞性睡眠呼吸暂停低通气综合征（OSAHS）的诊断价值。方法鼾症患儿48例按有无扁桃体、腺样体肥大分2组，采用MS-BABY—BODY测定，并与55例正常儿童对照组比较。主要测定指标：达峰容量比（VPTEF／VE）、达峰时间比（tPTEF／tE）、吸气时间与呼气时间比（TI／tE）、吸气时间分数（TI／rtot）、50％潮气量时吸气流量与潮气量比（TIF如／VT）、平均吸气流速（VT／TI）、功能残气量（FRCp）、呼吸道阻力（Reff）。结果Ⅰ、Ⅱ组TI／Tt0t、50％潮气量时呼气流量与吸气流量比（TEF50／TIF50）、FRCp、Reff均较正常对照组增高，VT／TI、TIF50／VT均较正常对照组减低（P均〈0．01）。Ⅰ组部分有呼吸暂停、脉搏血氧饱和度[Sp（O2）]下降、吸气流速减低、吸气环异常等改变。结论肺功能测定反映鼾症患儿的呼吸气流、呼吸力学变化及程度，VPEF／VE、tPTEF／tE、TI／tE、TI／Ttot、VT／TI可作为上呼吸道阻塞的判断指标，结合呼吸暂停及Sp（O2）下降等，对婴幼儿OSAHS诊断及病变程度的判断有重要意义。     

Assessment of pulmonary mechanics and breathing patterns during posturally induced glossoptosis in infants.

Respiratory mechanics were studied in nine infants with glossoptosis-apnoea syndrome to determine whether glossoptosis may account for signs of both inspiratory and expiratory airway obstruction. Airflow, oesophageal pressure, inspiratory and expiratory time (Ti and Te), and inspiratory and expiratory resistance (Ri and Re) were measured before and during ventilatory phases characterised by glossoptotic pharyngeal obstruction, induced by turning the infants onto their backs. In addition, an attempt was made to correlate the abnormalities in pulmonary mechanics with the clinical features. During partial glossoptotic pharyngeal obstruction, a significant increase was observed in Te and Re and variable changes in Ti and Ri. During severe obstruction, the infants displayed obstructed inspiratory efforts often associated with stridor, as well as obstructed expiratory efforts often associated with audible grunting and retarded expiratory flow pattern. The expiratory grunt was loudest over the neck and mimicked bronchospasm over the chest. These findings indicate that glossoptotic pharyngeal obstruction induces functional airway obstruction which may affect both inspiration and expiration. Expiratory airway obstruction seems, at least in part, to be due to active braking of expiratory flow.     

Assessment of pulmonary mechanics and breathing patterns during posturally induced glossoptosis in infants

Respiratory mechanics were studied in nine infants with glossoptosis-apnoea syndrome to determine whether glossoptosis may account for signs of both inspiratory and expiratory airway obstruction. Airflow, oesophageal pressure, inspiratory and expiratory time (Ti and Te), and inspiratory and expiratory resistance (Ri and Re) were measured before and during ventilatory phases characterised by glossoptotic pharyngeal obstruction, induced by turning the infants onto their backs. In addition, an attempt was made to correlate the abnormalities in pulmonary mechanics with the clinical features. During partial glossoptotic pharyngeal obstruction, a significant increase was observed in Te and Re and variable changes in Ti and Ri. During severe obstruction, the infants displayed obstructed inspiratory efforts often associated with stridor, as well as obstructed expiratory efforts often associated with audible grunting and retarded expiratory flow pattern. The expiratory grunt was loudest over the neck and mimicked bronchospasm over the chest. These findings indicate that glossoptotic pharyngeal obstruction induces functional airway obstruction which may affect both inspiration and expiration. Expiratory airway obstruction seems, at least in part, to be due to active braking of expiratory flow.     

Upper airway radiographs in infants with upper airway insufficiency

Upper airway measurements in nine infants considered to be at risk of upper airway insufficiency, six of whom presented after an apnoeic episode, were compared with measurements taken in two age groups of healthy infants. Paired, inspiratory and expiratory, lateral upper airway radiographs were obtained while the infants were awake and breathing quietly. The radiographs of all nine infants demonstrated narrowing in the oropharyngeal portion of the airway during inspiration and in six infants there was ballooning of the upper airway during expiration. Seven of the nine infants subsequently experienced recurrent apnoeic episodes which required vigorous stimulation to restore breathing. Experience suggests that respiratory phase timed radiographs are a useful adjunct to the evaluation of infants who are suspected of having upper airway dysfunction. They provide information regarding both the dimensions and compliance of the upper airway as well as the site of any restriction.     

Upper airway radiographs in infants with upper airway insufficiency.

Upper airway measurements in nine infants considered to be at risk of upper airway insufficiency, six of whom presented after an apnoeic episode, were compared with measurements taken in two age groups of healthy infants. Paired, inspiratory and expiratory, lateral upper airway radiographs were obtained while the infants were awake and breathing quietly. The radiographs of all nine infants demonstrated narrowing in the oropharyngeal portion of the airway during inspiration and in six infants there was ballooning of the upper airway during expiration. Seven of the nine infants subsequently experienced recurrent apnoeic episodes which required vigorous stimulation to restore breathing. Experience suggests that respiratory phase timed radiographs are a useful adjunct to the evaluation of infants who are suspected of having upper airway dysfunction. They provide information regarding both the dimensions and compliance of the upper airway as well as the site of any restriction.     

The basomedial hypothalamus modulates the ventilatory response to hypoxia in neonatal rats

We sought to examine the role of the basomedial hypothalamus in the regulation of breathing in neonatal rats. Small basomedial hypothalamic lesions were produced by a lesioning agent, goldthioglucose, in 5-d-old male rat pups, and 2 d later, baseline ventilation and the ventilatory responses to hypoxia and hypercapnia were examined. When compared with vehicle-injected controls, goldthioglucose-lesioned rat pups had a significantly slower respiratory rate and longer expiratory time at baseline. Lesioned rats displayed an impaired increase in breathing frequency in response to hypoxia, and augmented increases in tidal volume and respiratory drive (the ratio of tidal volume to inspiratory time) during hypoxia relative to controls. Hypercapnic responses were not affected. These data demonstrate that cells in a restricted area of the hypothalamus specifically influence the respiratory response to hypoxia.     

Dynamics of respiration during rapid rate mechanical ventilation in anesthetized and paralyzed rabbits

Infants with respiratory failure are often ventilated at rates exceeding 60 breath X min-1. To obtain insight into the factors controlling the delivery and distribution of tidal volume at these ventilatory rates, we analyzed the inspiratory and expiratory pressure-flow relationships of the respiratory system and its components (lungs, endotracheal tube, and chest wall) in anesthetized, paralyzed rabbits ventilated at 60, 90, and 120 breath X min-1. Inspiratory times were 0.3, 0.2, and 0.1 s. Driving pressure was maintained constant. We expressed the effect of ventilatory rate and flow direction on the pressure-flow relationships as changes in compliance, mean resistance, and inertance. We found a nonlinear pressure-flow relationship in both endotracheal tube and respiratory system. This nonlinearity could be accurately described as a function of gas flow and volume acceleration with similar coefficients for tube and respiratory system. Although the inspiratory and expiratory compliance and the mean inspiratory resistance of the lungs were lower at the higher ventilatory rates, the constant resistive behavior of the endotracheal tube and the constant elastic behavior of the chest wall caused a relatively rate-independent pressure-flow behavior of the respiratory system. The lower inspiratory resistance of the lungs was offset by the higher inspiratory resistance of the endotracheal tube, resulting in the resistance of the respiratory system being independent of the direction of gas flow. The rate-dependency of compliance and inspiratory resistance of the lungs suggests an heterogeneous distribution of inspiratory flow at rapid ventilatory rates.(ABSTRACT TRUNCATED AT 250 WORDS)     

Respiratory function monitoring in a child on mechanical respiratory ventilation. 2: compliance, resistance, dynamic hyperinflation, pulmonary dead-space, work of breathing

Several parameters can be used to study respiratory mechanics in children on mechanical ventilation. Compliance is a measure of the distensibility of the respiratory system. In mechanical ventilation two measures of compliance can be used. Static compliance (pulmonary distensibility) can be measured in volume modes by the application of an inspiratory pause with the respiratory system at rest (sedated patients without inspiratory effort). Dynamic compliance does not require an inspiratory pause and the respiratory system need not be at rest. Compliance can be calculated numerically or expressed graphically in the volume-pressure curve. Many respirators can calculate inspiratory and expiratory airway resistance (including endotracheal tube resistance). Several measures can be used to detect dynamic hyperinflation (intrinsic PEEP, auto-PEEP, trapped air volume) after application of an expiratory pause. The latest respirators can perform these measurements almost automatically. Work of breathing and respiratory effort can also be analyzed by measuring several parameters (pressure-time product, imposed work of breathing, P 0.1, maximum inspiratory pressure). However, these measures have not yet been standardized in children.     

The effect of independent variations in inspiratory-expiratory ratio and end expiratory pressure during mechanical ventilation in hyaline membrane disease: the significance of mean airway pressure.

The specific aspects of the respiratory cycle during mechanical ventilation that allow for optimum gas exchange are still controversial. To further clarify the relationship of inspiratory:expiratory ratio and positive end expiratory pressure to optimum ventilation and oxygenation, five premature lambs with severe hyaline membrane disease were ventilated with volume-present infant ventilators at I:E ratios of 1:4 and 1:1 and PEEP levels of 0, 5, and 10 cm H2O. For each I:E ratio/PEEP combination, pH, Pao2, PaCO2, PAO2, PACO2, peak inspiratory pressure, mean inspiratory pressure, and mean airway pressure were measured and compared. Optimum ventilation and oxygenation were related to MAP, but not to I:E ratio, PIP, or MIP. As MAP increased from 6 to 14 cm H2O, progressive improvement in Pao2, PaCO2 (A-a) DO2 and (a-A) DCO2 was evident. Above 14 cm H2O, there was progressive deterioration in these measurements. There was also a direct relationship between MAP and mean pleural pressure. These results indicate that during mechanical ventilation there is an optimum MAP at which gas exchange is best. Since MAP changes with any change in PIP, PEEP, or I:E ratio, it provides a useful composite measure of all pressures transmitted to the airways by the ventilator.     

Proximal airway function 8 to 16 years after laryngomalacia: follow-up using flow-volume loop studies

Twenty children who had endoscopically confirmed laryngomalacia were reviewed at 8 to 16 years of age. All had developed stridor in the first 6 weeks of life; stridor had stopped or largely resolved by age 4 years. Proximal airway function was assessed by expiratory and inspiratory flow volume loops and compared with control values. These children as a group had variable extrathoracic obstruction to inspiratory airflow, as indicated by a significantly low maximal inspiratory flow at 50% of vital capacity and a high mean ratio of maximal expiratory to maximal inspiratory flow at 50% vital capacity. Although limitation to inspiratory airflow was detectable in later childhood, it was not associated with troublesome symptoms. Significant stridor always resolved by 4 years of age, but some children experienced minor stridor under stress in later childhood.     

Recurrent cyanotic episodes with severe arterial hypoxaemia and intrapulmonary shunting: a mechanism for sudden death.

The pathophysiology of recurrent cyanotic episodes has been investigated in 51 infants and children. Episodes began at a median age of 7 weeks (range 1 day to 22 months, 39 at less than 4 months). They were characterised by the rapidity of onset and progression of severe hypoxaemia with early loss of consciousness from cerebral hypoxia. The most common precipitating factor was a sudden naturally occurring stimulus from pain, fear, or anger. In uncontrolled trials, cyanotic episodes were reduced in frequency and severity by tetrabenazine (n = 15) and additional inspired oxygen (n = 10). Eight patients died suddenly and unexpectedly (four during cyanotic episodes). Twenty eight patients underwent physiological studies during cyanotic episodes. There was no evidence of seizure activity at the onset and although prolonged absence of inspiratory effort with continued expiratory efforts was common, breathing sometimes continued. Episodes were not caused by upper airway obstruction and sometimes occurred during positive airway pressure ventilation. The rapidity of fall in arterial oxygen pressure and continued breathing suggested a right to left shunt of sudden onset. The results of contrast echocardiography and lung imaging studies confirmed that this was occurring within the lungs. These cyanotic episodes included both intrapulmonary shunting and prolonged expiratory apnoea. They are best explained by interactions between central sympathetic activity, brainstem control of respiration and vasomotor activity, reflexes arising from around and within the respiratory tract, and the matching of ventilation to perfusion in the lungs. They are a cause of sudden unexpected death in infancy and early childhood.     

1~2岁和~3岁肺炎支原体肺炎肺功能的前瞻性对照研究

摘要 目的 观察1~3岁肺炎支原体（MP）肺炎患儿的肺功能改变情况并探讨其临床意义。方法 前瞻性选择2005年1月至2006年12月在广州市妇女儿童医疗中心儿童医院住院治疗的1～3岁MP肺炎患儿为研究对象,按年龄分为1~2岁和～3岁组。采用凝集法检测患儿血清特异性抗体MP IgM的浓度,滴度≥1∶160为阳性,提示MP现症感染。采用美国森迪公司2600幼儿肺功能仪测定MP肺炎患儿急性期肺功能,并以120名1～3岁（1～2岁组62例,~3岁组58例）健康儿童的肺功能数据作为正常对照组。结果 研究期间77例MP肺炎患儿入组,1～2岁43例、~3岁34例。1~2岁和～3岁MP肺炎亚组急性期潮气呼吸流速 容量（TBFV）环形态特点均表现为TBFV环变窄,呼气曲线升支陡、高峰提前、峰值增高,降支凹陷;1~2岁MP肺炎亚组急性期呼吸频率（RR）、潮气呼气峰流速（PTEF）较同龄正常对照亚组增加（P＜0.05）;吸气时间/总呼吸时间(Ti/Tt)、到达PTEF时的呼出气量/潮气量（%V PF）、呼出75%潮气量时的呼气流速/PTEF（25/PF）、潮气呼气中期流速/潮气吸气中期流速（ME/MI）、每千克体重功能残气量（FRC/kg）和每千克体重顺应性（Crs/kg）较同龄正常对照亚组减少（P＜0.05）。~3岁MP肺炎亚组急性期PTEF较同龄正常对照亚组增加（P＜0.05）,Ti/Tt、%V PF和25/PF较同龄正常对照亚组减少（P＜0.05）。1~2岁和~3岁MP肺炎亚组的临床表现与其肺功能检测的结果较吻合。1～2岁和～3岁MP肺炎亚组咳痰分别为22例（51.2％）和9例（26.5％）,肺部闻及湿啰音分别为19例（44.2％）和8例（23.5％）,胸部X线检查见斑片状影分别为36例（83.7％）和14例（41.2％）,差异均有统计学意义（P均＜0.05）;1～2岁和~3岁MP肺炎亚组发热、喘息或呼吸困难发生率差异均无统计学意义。结论 肺功能检测是监测幼儿MP肺炎急性期肺功能改变的较理想方法。1~2岁MP肺炎患儿急性期肺功能改变较大,呈现大、小气道阻力增高,FRC/kg和Crs/kg下降,RR增加;而~3岁MP肺炎患儿急性期肺功能改变相对较小,仅呈现小气道阻力增高改变。     

Microphonic versus end-tidal carbon dioxide nasal airflow detection in neonates with apnea

Impedance pneumography in combination with expired CO2 monitoring are commonly used techniques for detecting central and obstructive apnea in infants. In this investigation an American Telephone and Telegraph StarSet-1 3000-ohm self-actuating microphone connected to the end of an infant cannula was used to monitor neonatal nasal airflow to detect breaths and apnea. The microphone was placed in a soundproof container to eliminate environmental sound artifacts. Analyses of 100 breaths from five patient samples during active and quiet sleep showed that there was no significant difference between microphone and expired CO2 recording of respiration. The techniques were 98% and 96% sensitive, respectively. Microphonic detection of nasal airflow identified 27 of the 32 episodes of upper airway obstruction (84.2%) registered by end-tidal CO2 recording. Inspiratory and expiratory events could also be well documented. Microphonic recording of nasal airflow is a reliable and inexpensive technique to detect apnea.     

Influence of airway pressure waveform on cardiac output during positive pressure ventilation of healthy newborn dogs

During positive pressure ventilation, increases in mean airway pressure produced by increases in end expiratory pressure are associated with reductions in cardiac output. Mean airway pressure may be increased not only by increasing end expiratory pressure, but also by increasing the inspiratory pressure or the inspiratory to expiratory time ratio. During positive pressure ventilation of 10 healthy newborn dogs, cardiac output and left ventricular dimensions were measured using radioactive microspheres and echocardiography, respectively. Baseline ventilation was produced using the least inspiratory pressure to maintain normocarbia (rate = 50 min-1, inspiratory to expiratory time ratio = 1:3, end expiratory pressure = 2 cm H2O). The mean airway pressure was increased 3-fold by independently changing the airway pressure waveform through increases in inspiratory pressure, inspiratory to expiratory time ratio, or end expiratory pressure. Despite differences in airway pressure waveform, similar reductions in left ventricular dimension, cardiac output, and stroke volume were seen. We conclude that at a given increased mean airway pressure during positive pressure ventilation, the reduction in cardiac output is independent of the airway pressure waveform.     

Lung function in children and adolescents with antecedents of acute rheumatic fever

Static lung volumes, CO-lung transfer, airway resistance, maximal expiratory flows and lung elastic properties were studied in 29 children and adolescents 1–10 years after recovery from acute rheumatic fever. There were essentially no changes in lung function even in the subjects with a residual valvular disease. The only abnormality was a tendency for the elastic lung recoil at TLC to be low, which is interpreted as probably reflecting a decrease in inspiratory muscle force.Abbreviations ARF acute rheumatic fever - VC vital capacity - TGV thoracic gas volume - Raw airway resistance - P-V pressure-volume - TLC total lung capacity - MEFV maximal expiratory flow-volume - T_LCO CO-lung transfer - FRC functional residual capacity     

Air trapping causes a Ca2(+)-channel-mediated increase in pulmonary vascular resistance in neonatal lambs.

Air trapping and alveolar hyperinflation may occur during mechanical ventilation in the presence of severe airway obstruction, during fast ventilator rates, and when expiratory time is compromised. Inadvertent positive end-expiratory pressure may occur with air trapping and increased mean airway pressure. The pulmonary artery pressure response to air trapping, produced during volume-regulated time-cycled ventilation, was studied in neonatal lamb lungs, isolated in situ, and perfused at a constant flow rate (50-75 ml.kg-1.min-1), both before and after Ca2(+)-channel blockade with verapamil (5 mg). The hub of the endotracheal tube was narrowed to a 1.5-mm orifice to produce fixed proximal airway obstruction. Air trapping was then produced by lengthening inspiratory time from 25 to 80%, at zero end-expiratory pressure. The magnitude of inadvertent positive end-expiratory pressure due to air trapping was estimated by end-expiratory occlusion pressure. End-expiratory occlusion pressure was 0.20 +/- 0.03 kPa (1.7 +/- 0.2 mm Hg) and 1.60 +/- 0.01 kPa (11.8 +/- 1.0 mm Hg), at 25 and 80% inspiratory times, respectively. On lengthening inspiratory time, mean pulmonary artery pressure (mPpa) increased briskly within 30 s followed by a gradual increase over the next 4 min. Verapamil blunted both the brisk and the gradual increase in mPpa on lengthening inspiratory time. Lengthening inspiratory time increased the mPpa by 2.0 +/- 0.1 kPa (14.7 +/- 0.8 mm Hg) from baseline, and verapamil reduced this increase to 1.3 +/- 0.1 kPa (10.1 +/- 0.6 mm Hg; p less than 0.05 by analysis of variance).(ABSTRACT TRUNCATED AT 250 WORDS)     

广州地区1～3岁健康幼儿肺功能测定结果的探讨

目的 探讨广州地区1～3岁健康幼儿肺功能状况。方法 将120名1～3岁健康幼儿分成1～2岁组和～3岁组。用美国森迪公司2600型婴幼儿肺功能仪测定肺功能值，包括用潮气流速-容量(TBFV)环部分替代最大呼气流速容量曲线检测出的潮气量(TV)和反映大、小气道功能的指标；利用被动流速容量技术测定呼吸系统静态顺应性(Crs)、总气道阻力(Rrs)；用开放式氮冲洗法测定功能残气量(FRC)。结果 1～3岁健康幼儿各项肺功能测定值男、女间差异均无统计学意义(P均＞0.05)。1～2岁组和～3岁组呼吸频率差异无统计学意义（27 vs 26，t＝1.512，P＞0.01）。～3岁组TV水平显著高于1～2岁组（0.123 vs 0.091，t＝8.587，P<0.01），但经体重校正后，差异无统计学意义（0.009 1 vs 0.008 6，t＝1.959，P＞0.01）。～3岁组潮气呼气峰流速（PTEF）水平显著高于1～2岁组（0.159 vs 0.135，t＝3.787，P<0.01）。所测定的TBFV环是不典型椭圆形。呼气时间/总呼吸时间（Ti/Tt）、到达潮气呼气峰流速时的呼出气量/潮气量（%V-PF）、呼出75%潮气量时的呼气流速/潮气呼气峰流速（25/PF）和潮气呼气中期流速/潮气吸气中期流速（ME/MI）等指标，两组间差异均无统计学意义（P均＞0.05），而1～2岁组潮气呼气峰流速/潮气量（PF/Ve）水平显著高于～3岁组（1.257 vs 1.095，t＝2.098，P<0.05）。1～2岁组Rrs水平显著高于～3岁组（2.697 vs 2.071，t＝3.761，P<0.01）；～3岁组Crs水平显著高于1～2岁组（0.352 vs 0.254，t＝4.297，P<0.01），但经体重校正后，差异无统计学意义（0.026 vs 0.024，t＝1.051，P＞0.01）；～3岁组FRC水平显著高于1～2岁组（0.271 vs 0.211，t＝8.468，P<0.01），但经体重校正后，差异无统计学意义（0.019 8 vs 0.019 8，t＝0.000，P＞0.01）。由此可见，TV、FRC、Crs和PTEF随年龄增大而增大，尤与体重密切相关，两组间差异有统计学意义(P＜0.01＝，而反映大、小气道功能的所有指标相对稳定。结论 用TBFV环部分替代最大呼气流速容量曲线可反映大、小气道功能情况，其各项指标相对稳定，可作为观察呼吸系统疾患时肺功能变化情况较理想的指标。健康幼儿TV、FRC、Crs和PTEF与体重呈正相关，符合幼儿生长发育的规律,1～3岁幼儿体重发育较明显。     

Lung function in children of low birth weight.

Lung function was recorded in a cohort of 130 age specific children of low birth weight (under 2000 g) and a reference population of 120 unselected local schoolchildren at 7 years of age. Children of the cohort were similar in height and forced vital capacity to the reference group, but had significantly reduced forced expiratory volume in 0.75 second and expiratory flow indices. Although neonatal respiratory illness was associated with reduced airway function, we were unable to confirm that this was a consequence of oxygen treatment or mechanical ventilation. Low birth weight, however, was closely associated with poor airway function independent of neonatal respiratory illness. Other factors of importance included the male gender and maternal smoking. The reduction in airway function observed in the low birthweight children was associated with cough but not wheeze. The disparity between the relatively well preserved vital capacity and reduced airway function suggests that very low birth weight, and hence prematurity, has its greatest effect on the subsequent growth of airway function. The absence of an association between neonatal oxygen score or mechanical ventilation and childhood lung function suggests that the long term effect of neonatal respiratory treatment is small compared with that of birth weight, maternal smoking, and male sex.