Mechanical properties of the upper airway wall in children and their influence on respiratory impedance measurements.

The upper airway wall impedance (Zuaw) may be responsible for a large artifact in the measurement of respiratory system impedance (Zrs) in children. In 17 normal children aged 3.5-13 years Zuaw and Zrs were estimated by varying transrespiratory pressure directly at the mouth (conventional method: Z1) and around the subject's head (head generator method: Z2) from 4 to 32 Hz. Zrs and Zuaw were calculated from Z1 = Zrs.Zuaw/(Zrs+Zuaw) and Z2 = Zrs (1 + Zp/Zuaw), where Zp is the impedance of the pneumotachograph. From the real and imaginary part of Z1, Z2, Zrs, and Zuaw, the corresponding resistance, inertance, compliance and resonant frequency were calculated assuming simple RIC models. No significant difference was found between the mean +/- SE of parameters derived from Zrs (respectively, 6.8 +/- 0.4 cmH2O.L-1.s, 0.034 +/- 0.001 cmH2O.L-1.s2, 10.4 +/- 0.8 m.cmH2O-1, 9.1 +/- 0.3 Hz) and Z2 (6.8 +/- 0.4 cmH2O.L-1.s, 0.038 +/- 0.002 cmH2O.L-1.s2, 10.7 +/- 0.7 ml.cmH2O-1, 8.7 +/- 0.4 Hz). All but the compliance, derived from Z1 were significantly different (P less than 0.01) from those derived from Zrs (5.3 +/- 0.3 cmH2O.L-1.s, 0.008 +/- 0.001 cmH2O.L-1.s2, 11.9 +/- 1.2 ml.cmH2O-1, and 20.3 +/- 1.6 Hz). Respiratory resistance and compliance correlated significantly with height (r = -0.56 and 0.86, respectively), in contrast to upper airway wall resistance (Ruaw) and compliance (Cuaw). Ruaw (8.6 +/- 0.8 cmH2O.L-1.s), Cuaw (1.2 +/- 0.2 m.cmH2O-1), and upper airway wall inertance (0.030 +/- 0.004 cmH2O.L-1.s2) were close to those obtained by direct measurements in adults. The mechanical properties of the upper airway wall are responsible for a significant error in the measurement of Zrs by the conventional method in normal children. Most of the artifact may be corrected for by applying pressure around the child's head.     

Input respiratory impedance measured by head generator in preschool children

The upper airway wall motion represents a serious problem when measuring the input impedance of the respiratory system (Zrs) by the forced oscillation technique, particularly in young children. To minimize this error, it has been proposed to vary transrespiratory pressure around the head rather than directly at the mouth, using the head generator technique (HGT). The aim of this study was to collect normative data in preschool children in whom the technique may prove most useful. Zrs was measured using HGT and 4-32-Hz pseudorandom noise input in 127 healthy children. Age ranged from 2. 8 to 7.4 years and height (H) from 0.89 to 1.29 m. The fast Fourier transforms of pressure and flow allowed us to calculate respiratory system resistance (Rrs(f)) and reactance (Xrs(f)) at each frequency (f). Resonant frequency (fn), respiratory system inertance (Irs), and compliance (Crs) were derived from the Xrs(f) data. The technique was accepted by more than 95% of the children. A coherence function 相似文献   

Measurement of ventilatory system resistance in infants and young children

The mechanics of the ventilatory system were studied in 29 sleeping infants and young children by the analysis of a passive expiration following an end-inspiratory airway occlusion ('single breath' method). The ventilatory system time constant (tau rs) to compliance ratio yielded the value of ventilatory system resistance (Rrs). The calculated ventilatory system compliance correlated well with the slope of the quasi static pressure-volume curve (r = 0.97). The allometric relationship between Rrs and height (Rrs = 81.9.10(3).Ht (cm)-1.76, r = -0.82) is in agreement with forced oscillation measurements during the first year of life (Wohl et al., 1969). tau rs was found to increase significantly over the first months of life (P less than 0.01).     

Measurement of ventilatory mechanical impedance in infants using a head pressure generator

Two methods of measuring ventilatory mechanical impedance (Z) by forced oscillations between 6 and 20 Hz were compared in 24 infants aged 2 to 49 months: 1) the application of pressure oscillations at the airway opening (Z1); and 2) the application of pressure oscillations around the head (Z2). The latter has been recently proposed to minimize the influence of compliant upper airway walls (Peslin et al., J Appl Physiol. 1985, 59:1790-1795). Ventilatory resistance and compliance (Rsb, Csb) were also obtained with the single breath method. The real part of Z1 (R1) was markedly lower than that of the corresponding Z2 (R2), at any frequency. R1 exhibited a systematic negative frequency dependence, in contrast with R2. At any frequency, the slope of the regression equation on Rsb was closer to unity for R2 than for R1. The imaginary part of Z1 (X1) was negative over the whole frequency interval, and negative values of inertance were derived from X1. X2 was negative at low and positive at high frequencies. Resonant frequency (mean +/- SD = 10.5 +/- 3.5 Hz) was always reached with Z2 and correlated negatively with body weight (r = -0.61). Inertance estimated from X2 was positive and correlated negatively with body height (r = -0.66). The compliance derived from Z1 (C1 = 3.35 +/- 2.32 10(-3) L.cm H2O-1) was not significantly different from that derived from Z2 (C2 = 2.99 +/- 2.02 10(-3) L.cm H2O-1). The marked difference observed between Z1 and Z2 is related to the importance of the upper airway shunt and may be explained by inaccuracies of both methods.(ABSTRACT TRUNCATED AT 250 WORDS)     

Respiratory mechanics in mechanically ventilated newborns: a comparison between passive inflation and occlusion methods.

A passive inflation method was described for measuring total respiratory elastance and resistance during mechanical ventilation in adult patients (Rossi et al., J Appl Physiol 58:1849, 1985). We applied this method to preterm and full-term mechanically ventilated newborn infants and we compared the results with those obtained by the occlusion method. We performed 37 tests in 16 newborn infants (B.W. 880-4,500 g; G.A. 28-42 weeks), between 1 and 45 days of postnatal age, ventilated with a Servo Ventilator 900C, set in controlled-volume mode. Flow was measured through a pneumotachograph inserted between the endotracheal tube (ETT) and the breathing circuit, tidal volume by integration of flow and airway pressure directly at the airway opening. Flow, volume, and pressure were recorded on an X/Y plotter to obtain pressure-volume (P/V), flow-volume (V/V) loops, and pressure-time curves. Occlusion was performed by using the end-inspiratory and the end-expiratory pause buttons of the ventilator. Analysis of P/V and V/V loops provided respiratory system compliance (Crs, infl.), resistance (Rrs, infl.), and "intrinsic positive end-expiratory pressure" (PEEPi, infl.). These values were compared with Crs, occl., Rrs, occl., and PEEPi, occl. measured by the occlusion method. The measurements were well correlated (Crs, infl./Crs, occl.: r = 0.90; Rrs, infl./Rrs, occl.: r = 0.91; PEEPi, infl./PEEPi, occl.: r = 0.91). Rrs, infl./Rrs, occl. and PEEPi, infl./PEEPi, occl. did not differ significantly. However, Crs, occl. was 15% higher than Crs, infl. (P less than 0.01). The passive inflation method is simple to use and well tolerated in preterm and full-term ventilated newborn infants, it provides accurate results, and can be a good alternative to occlusion methods. It requires, however, a constant inflation flow and adaptation to the ventilator.     

Components of respiratory resistance monitored in mechanically ventilated patients.

The interrupter technique is commonly adopted to monitor respiratory resistance (Rrs,int) during mechanical ventilation; however, Rrs,int is often interpreted as an index of airway resistance (Raw). This study compared the values of Rrs,int provided by a Siemens 940 Lung Mechanics Monitor with total respiratory impedance (Zrs) parameters in 39 patients with normal spirometric parameters, who were undergoing elective coronary bypass surgery. Zrs was determined at the airway opening with pseudorandom oscillations of 0.2-6 Hz at end inspiration. Raw and tissue resistance (Rti) were derived from the Zrs data by model fitting; Rti and total resistance (Rrs,osc=Raw+Rti) were calculated at the actual respirator frequencies. Lower airway resistance (Rawl) was estimated by measuring tracheal pressure. Although good agreement was obtained between Rrs,osc and Rrs,int, with a ratio of 1.07+/-0.19 (mean+/-SD), they correlated poorly (r2=0.36). Rti and the equipment component of Raw accounted for most of Rrs,osc (39.8+/-11.9 and 43.0+/-6.9%, respectively), whereas only a small portion belonged to Rawl (17.2+/-6.3%). It is concluded that respiratory resistance may become very insensitive to changes in lower airway resistance and therefore, inappropriate for following alterations in airway tone during mechanical ventilation, especially in patients with relatively normal respiratory mechanics, where the tissue and equipment resistances represent the vast majority of the total resistance.     

Dynamic respiratory mechanics in monkeys measured by forced oscillations

We measured impedances of the lungs (Zl) and respiratory system (Zrs) by discrete frequency (f) forced oscillations in adult bonnet monkeys at two lung volumes, FRC at transrespiratory system pressure (Prs) of −5 cm H₂O. Measurements were made from 2 to 32 Hz to study f dependence of effective resistance (Reff) and reactances, and from 1 to 8 Hz to study f dependence of effective pulmonary compliance (Ceff, l). Estimates of resistances (R) , inertances (I) and compliances (C)_ of the lungs (l), chest wall (w) and respiratory system (rs)_were obtained by fitting the 2−32 Hz data to a series RIC network model. Reff, l, Reff, w and Reff, rs were found to be f dependendt. The magnitude of Zl was small relative to that of Zrs at all f with Rl only 30% of Rrs and Cl six times Crs. Decreasing lung volume from FRC to Prs = −5 cm H₂O increased Rl, Rw and Rrs, slightly decreased Cl, Cw and Crs, slightly increased resonance frequencies, and increased the f dependent behavior of Ceff, l. Our results indicate both similarities and differences between the respiratory system of these primates and man.     

Total respiratory impedance in healthy children

Impedance of the total respiratory system was measured in 121 healthy children aged 4-16 years during spontaneous breathing by pseudo-random forced oscillations between 3 and 10 Hz. Total respiratory resistance (Rrs), inertance (Irs) and compliance (Crs) were determined by least-mean-squares fitting. Estimates for inertance were reliable only for the larger children, where the values of Irs (0.0127 +/- 0.0034 SD) were similar to those reported for normal adults. Rrs correlated significantly (P less than 0.001) with height (r = -0.868), age (r = -0.865), and, in a subpopulation of the 6- to 16-year-old children, with forced vital capacity (r = -0.803). The corresponding correlation coefficients for Crs were 0.873, 0.844, and 0.853, respectively. Crs amounted to about a third of the static total compliance values of Sharp et al. (J Appl Physiol 1970; 29: 775-779) over the same interval of heights. In these relationships no significant difference was found between boys and girls.     

Forced Oscillation Technique and Childhood Asthma

Most infants and preschool children are not able to voluntarily perform the physiological maneuvers required to complete the pulmonary function tests that are used in adults and older children. Recently, commercial devices using forced oscillation technique (FOT) suitable for young children have become available. In devices with FOT, an oscillation pressure wave is generated by a loud speaker, is applied to the respiratory system, usually at the mouth, and the resulting pressure-flow relationship is analyzed in terms of impedance (Zrs). Zrs encompasses both resistance (Rrs) and reactance (Xrs). Rrs is calculated from pressure and flow signals, and is a measure of central and peripheral airway caliber. Xrs is derived from the pressure in the phase with volume and is related to compliance (Crs) and inertance (Irs). These parameters individually indicate the condition of the small and large airways in each patient and indirectly suggest the presence of airway inflammation. It is agreed that the clinical diagnostic capacity of FOT is comparable to that of spirometry. One of the advantages of FOT is that minimal cooperation of the patient is needed and no respiratory maneuvers are required. The use of FOT should be considered in patients in whom spirometry or other pulmonary function tests cannot be performed or in cases where the results of other tests appear to be unreliable. In addition, this approach is effective in assessing bronchial hyperresponsiveness. Considering these qualities, FOT is a useful method to study pulmonary function in preschool children with asthma.     

Dexamethasone therapy for bronchopulmonary dysplasia: improved respiratory mechanics without adrenal suppression.

The purpose of the present study was to examine the pattern of changes in respiratory system mechanics induced by dexamethasone (Dex) in infants with bronchopulmonary dysplasia (BPD) and to determine whether dosages that produce these changes induce adrenal suppression. We examined mechanics in seven ventilator-dependent premature infants (age, 33 +/- 4.8 days) with BPD, before and daily during Dex therapy. Dex (0.5 mg/kg/day) was given intravenously for 7 days unless complications necessitated early termination. Respiratory system resistance (Rrs) and compliance (Crs) were measured by the passive expiratory flow-volume technique during the course of dexamethasone therapy or until extubation. Adrenocorticotrophic hormone (ACTH) stimulation tests were done at baseline and following Dex therapy to evaluate adrenal function. Dex therapy caused a 77 +/- 18% increase in Crs (from 0.97 +/- 0.09 SEM mL/cmH2O to 1.6 +/- 0.16 mL/cmH2O; P less than 0.025) and a 33 +/- 5% decrease in Rrs (from 0.20 +/- 0.02 cmH2O/mL/s to 0.14 +/- 0.01 cmH2O/mL/s; P less than 0.01). Concurrently, ventilator rate, mean airway pressure, and FIO2 all decreased significantly (P less than 0.025). Extubation occurred later in infants with the lowest Crs and highest Rrs at baseline. At extubation, all Crs values were greater than 1.33 mL/cmH2O and Rrs values were less than 0.15 cmH2O/mL/s. Systolic blood pressure increased from 61 +/- 6.3 mmHg to 84 +/- 17 mmHg, 72-96 h after the start of Dex (P less than 0.025). There were no episodes of culture-positive sepsis. Neither basal nor ACTH-stimulated levels of cortisol were suppressed as a result of Dex therapy (P greater than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)     

Evaluation of a simplified oscillation technique for assessing airway obstruction in sleep apnoea.

The forced oscillation technique (FOT) is a noninvasive method that is useful for assessing airway obstruction and for titrating continuous positive airway pressure (CPAP) in patients with sleep apnoea. The aim was to evaluate the routine applicability of a simplified FOT set-up based on recording pressure and flow at the level of the CPAP device, i.e. obviating the need for connecting the transducers to the nasal mask. A correction to account for the tubing and the exhaust port was applied. This simplified FOT was evaluated on nine patients with moderate or severe sleep apnoea during routine CPAP titration. Patient impedance measured by the simplified FOT ([Z]) was compared with actual patient impedance ([Zrs]) measured simultaneously with a reference FOT based on recording pressure and flow at the nasal mask. An excellent agreement was found between [Z] and [Zrs] over the wide range of airway obstruction explored (4.8-72.1 cmH2O x s x L(-1)): [Z] = [Zrs] x 0.86 + 1.3 cmH2O x s x L(-1) (r = 0.99). Moreover, the simplified and the conventional FOT settings detected the same respiratory events during sleep. These results demonstrate that this simplified FOT is applicable for measuring airway obstruction during routine sleep studies in patients with sleep apnoea.     

Lung mechanics and gas exchange in ventilated preterm infants during treatment of hyaline membrane disease with multiple doses of artificial surfactant (Exosurf)

Eight premature infants ventilated for hyaline membrane disease and enrolled in the OSIRIS surfactant trial were studied. Lung mechanics, gas exchange [PaCO2, arterial/alveolar PO2 ratio (a/A ratio)], and ventilator settings were determined 20 minutes before and 20 minutes after the end of Exosurf instillation, and subsequently at 12-24 hour intervals. Respiratory system compliance (Crs) and resistance (Rrs) were measured by means of the single breath occlusion method. After surfactant instillation there were no significant immediate changes in PaCO2 (36 vs. 37 mmHg), a/A ratio (0.23 vs. 0.20), Crs (0.32 vs. 0.31 mL/cm H2O/kg), and Rrs (0.11 vs. 0.16 cmH2O/mL/s) (pooled data of 18 measurement pairs). During the clinical course, mean a/A ratio improved significantly each time from 0.17 (time 0) to 0.29 (time 12-13 hours), to 0.39 (time 24-36 hours) and to 0.60 (time 48-61 hours), although mean airway pressure was reduced substantially. Mean Crs increased significantly from 0.28 mL/cmH2O/kg (time 0) to 0.38 (time 12-13 hours), to 0.37 (time 24-38 hours), and to 0.52 (time 48-61 hours), whereas mean Rrs increased from 0.10 cm H2O/mL/s (time 0) to 0.11 (time 12-13 hours), to 0.13 (time 24-36 hours) and to (time 48-61 hours) with no overall significance. A highly significant correlation was found between Crs and a/A ratio (r = 0.698, P less than 0.001). We conclude that Exosurf does not induce immediate changes in oxygenation as does the instillation of (modified) natural surfactant preparations. However, after 12 and 24 hours of treatment oxygenation and Crs improve significantly.(ABSTRACT TRUNCATED AT 250 WORDS)     

Thoracoabdominal compression and respiratory system compliance in HIV-infected infants

The thoracoabdominal compression technique (TAC) is used to measure expiratory flow in infants. We investigated whether TAC caused a change in total thoracic compliance (Crs), resistance (Rrs), and respiratory system time constant (Trs). We studied 41 infants (mean age, 12.4 mo; SD, 7.5) from five centers studying longitudinal lung and cardiovascular function of infants from HIV-infected mothers. We measured Crs, Rrs, and Trs before and after TAC. Changes in Crs, Rrs, and Trs after TAC were not dependent on the length of time since TAC. Crs and Trs were reduced after TAC, p = 0.013 and p = 0.003, respectively, whereas Rrs did not change. When compared with uninfected infants, HIV-infected infants had a larger post-pre TAC percent decline in Crs (p = 0.003) and a post-pre TAC rise in mean Rrs (p = 0.03). These differences remained significant after adjusting for sex and age. When performing infant pulmonary function testing, TAC itself produces a temporary decrease in Crs and Trs that is more significant in infants at risk for abnormal lung volume or compliance. Therefore, the sequence of performing the infant lung function parameters should be the same each time the testing is repeated with TAC as the last parameter tested at each testing session.     

Effects of a clinically detectable PDA on pulmonary mechanics measures in VLBW infants with RDS.

We examined the effect of a clinically detectable patent ductus arteriosus (PDA) and its successful treatment with indomethacin on serial measures of pulmonary mechanics in 10 very-low-birthweight (VLBW) intubated infants with respiratory distress syndrome (RDS). Pulmonary mechanics were measured by the passive expiratory flow technique. Total respiratory system compliance (Crs) gradually improved as RDS resolved. However, a significant decrease in mean Crs was associated with the development of a clinically detectable PDA, ranging from 1.51 +/- 0.21 to 0.90 +/- 0.08 mL/cmH2O/m (P less than 0.05). We also noted an increase in mean Crs, from 0.90 +/- 0.08 to 1.49 +/- 0.21 mL/cmH2O/m (P less than 0.05), after successful treatment of a PDA with indomethacin. Total respiratory system resistance (Rrs) did not change. We conclude that a clinically significant PDA is associated with a decreased Crs and that successful treatment of a PDA with indomethacin is associated with an improvement in lung compliance. These findings imply that the development of a clinically detectable PDA and its subsequent treatment complicates the interpretation of pulmonary mechanics data in VLBW infants with RDS.     

Measurement of ventilatory system compliance in infants and young children

Ventilatory system compliance (Crs) was measured in 32 sedated sleeping infants and young children aged 3-54 months breathing spontaneously through a face mask. Airways were occluded during expiration at different lung volumes above FRC and the corresponding airway pressure was measured. A pressure-volume relationship was then calculated by the least square method. To ensure the presence of the Breuer-Hering inspiratory inhibitory reflex, the percent increase of occluded expiratory time relative to the preceding unoccluded breath was calculated in 28 subjects where several end inspiratory occlusions had been maintained up to the next inspiratory effort. This index ranged from 4 to 100% and correlated negatively with age (r = -0.50, P less than 0.01). Crs ranged from 4.5 to 21.8 ml/cm H2O and correlated best with height (H) (Crs = 5.36 X 10(-4) H2.27, r = 0.94).     

Specific airway resistance,interrupter resistance,and respiratory impedance in healthy children aged 2–7 years

We report data on respiratory function in healthy children aged 2–7 years in whom we measured respiratory resistance by the interrupter technique (Rint); total respiratory impedance (Zrs), respiratory resistance (Rrs), and reactance (Xrs) by the impulse oscillation technique; and specific airway resistance (sRaw) by a modified procedure method in the whole body plethysmograph. Measurements were attempted in 151 children and were successfully obtained in 121 children with a mean (SD) age of 5.3 (1.5) years; no measurements were possible in 30 children (mean age 3 (0.9) years). The repeatability of measurements was independent of the age of the subjects, and the within-subject coefficient of variation was 11.1%, 8.1%, 10.8%, and 10.2% for sRaw, Rint, Zrs, and Rrs at 5 Hz (Rrs5), respectively. All lung function indices were linearly related to age, height, and weight. A significant negative correlation with age, height, and weight was found for Rint, Zrs, and Rrs5. Xrs5 was positively correlated to age and body size. The mean values of Rint, Rrs5, Xrs5, and Zrs in children younger and older than 5 years were 1.04, 1.38, −0.5, and 1.48 kPa · L⁻¹ · s and 0.9, 1.18, −0.37, and 1.23 kPa · L⁻¹ · s, respectively. sRaw showed no significant correlation with body size or age and the mean sRaw in children younger and older than 5 years was 1.09 and 1.13 kPa · s, respectively. None of the indices of respiratory function differed between boys and girls. Xrs and Rrs exhibited a significant frequency dependence in the range of 5–35 Hz. The techniques applied in this study require minimal cooperation and allow measurement of lung function in 80% of our population of awake young children. Further studies are needed to evaluate the potentials of the presently established reference values for clinical and epidemiological purposes. Pediatr Pulmonol. 1998; 25:322–331. © 1998 Wiley-Liss, Inc.     

Respiratory impedance and response to salbutamol in healthy Vietnamese children

A high incidence of childhood asthma has been reported in Ha Noi, Viet Nam, indicating a need to document lung function in these children. The degree of airway obstruction and reversibility may be evaluated from the forced oscillation assessment of respiratory resistance to reactance (Rrs, Xrs). Appropriate controls are necessary for a proper interpretation of patients. The aim of the study was to provide reference values on Rrs and Xrs and response to salbutamol in healthy Vietnamese children. One hundred seventy-five children aged 6-11 year recruited from one public school in Ha Noi were studied. Measurements were obtained at baseline and after 200 microg inhaled salbutamol. Significant correlations were disclosed between Rrs or Xrs and standing height (P < 0.0001). Salbutamol significantly decreased Rrs (from 7.1 +/- 1.9 hPa.sec/L to 6.2 +/- 1.8 hPa sec/L, P < 0.0001) and increased Xrs (from -1.22 +/- 0.64 to -0.91 +/- 0.61 hPa.sec/L, P < 0.0001). Rrs response to salbutamol lower limit of 95% confidence interval was -38% from baseline Rrs and, Xrs upper limit was +16% from baseline impedance. It is concluded that reference values for respiratory impedance (Zrs) and thresholds for clinically relevant response to bronchodilator are provided in primary school Vietnamese children. A smaller slope for the observed Rrs-body height relationship is suggested with reference to relevant studies in healthy Caucasians.     

Respiratory input impedance from 4 to 256 Hz in normals and chronic airflow obstruction: comparisons and correlations with spirometry.

Measurement of respiratory system input impedance (Zrs) by forced oscillation (FO) has generally been limited to frequencies less than or equal to 50 Hz, and correlations with spirometry have been variable. Using FO from 4 to 256 Hz in normals, Jackson and colleagues recently described a first acoustic antiresonance frequency (Far,1) at approximately 170 Hz. Using the same frequency range, we compared several Zrs spectral characteristics with spirometry in 12 chronic airflow obstruction (CAO) patients (range FEV1 0.8 to 2.0 L) and 10 matched controls. Compared with controls, patients had a higher first resonance frequency (Fr,1) (mean +/- SD = 15 +/- 5 versus 10 +/- 2 Hz, p less than 0.02) and a higher Far,1 (196 +/- 11 versus 172 +/- 13 Hz, p less than 0.0002). Good correlations occurred between % predicted FVC and the Far,1 (r = -0.81, p less than 0.0000), between FEV1/FVC and the reactance at 20 Hz (r = -0.6, p less than 0.003), between FEV1 and Far,1 (r = -0.74, p less than 0.0001). Because Far,1 may be affected by airway wall mechanical properties, the shift in Far,1 seen in these patients may be due to airway wall properties in CAO. We conclude that measurement of Zrs up to 256 Hz requires little patient cooperation and may be clinically useful. It can differentiate CAO patients from controls and correlates well with spirometry. The first acoustic antiresonance frequency may reflect airway mechanical properties and provide information not available from Zrs measured at lower frequencies.     

Reference values for resistance and compliance based on the single occlusion technique in healthy infants from Southeast China

Background

Respiratory disease is a major cause of morbidity and mortality in infants and has a large impact on health care. The aim of this study was to present the reference values of resistance and compliance by using a single occlusion technique (SOT) in healthy infants in Southeast China.

Methods

Respiratory compliance (Crs) and respiratory resistance (Rrs) were measured in healthy infants, aged 1–96 weeks, by using SOT in the Children’s Hospital of FuDan University (Shanghai, China). For comparison, the infants were grouped by age as follows: 1–24, 25–48, 49–72 and 73–96 weeks. Multiple regression analysis was performed using age, length, weight, and body mass index (BMI) as the independent variables to obtain predictive equations, separated according to sex.

Results

We measured 205 healthy infants from birth up to 96 weeks of age (112 boys, 93 girls). Height and weight increased significantly with age. The Rrs declined with length, whereas the Crs increased. The median Rrs was 5.04 kPa/L/sec (range, 3.73–6.82 kPa/L/sec), and the mean Crs was 119.52±60.47 mL/kPa. Regression equations for Rrs and Crs were obtained.

Conclusions

We obtained reference values for passive respiratory mechanics by using SOT in healthy infants from Southeast China. These data provide references for assessing the normality of SOT measurements in infants.     

Variability of dynamic compliance measurements in spontaneously breathing and ventilated newborn infants.

We studied reproducibility and variability of dynamic pulmonary compliance (Cdyn) by making measurements with the esophageal balloon at multiple locations within the esophagus, in both spontaneously breathing and mechanically ventilated newborn infants. Reliable measurements could be obtained over a range similar to that reported for measurements with a liquid-filled catheter. In spontaneously breathing infants Cdyn was found to be highly variable. This variability was unrelated to catheter position but was associated with concomitant changes in pulmonary resistance. Probably because of the high variability, the correlation of Cdyn with a measurement of respiratory system compliance (Crs) was rather poor (r = 0.63). Cdyn measured in mechanically ventilated infants was significantly less variable and compared favorably to Crs (r = 0.86), but its accuracy could not be adequately assessed since the comparison of esophageal and airway occlusion pressure was not feasible in all infants. In addition, significant differences in Cdyn were found between spontaneous and ventilated breaths during mechanical ventilation. Further studies in both ventilated and spontaneously breathing infants are needed to assess the variability of Cdyn over extended time periods.