Occlusion pressure and breathing pattern in healthy children

Pulmonary function testing in children's interstitial lung disease

The use of pulmonary function tests (PFTs) has been widely described in airway diseases like asthma and cystic fibrosis, but for children's interstitial lung disease (chILD), which encompasses a broad spectrum of pathologies, the usefulness of PFTs is still undetermined, despite widespread use in adult interstitial lung disease. A literature review was initiated by the COST/Enter chILD working group aiming to describe published studies, to identify gaps in knowledge and to propose future research goals in regard to spirometry, whole-body plethysmography, infant and pre-school PFTs, measurement of diffusing capacity, multiple breath washout and cardiopulmonary exercise tests in chILD. The search revealed a limited number of papers published in the past three decades, of which the majority were descriptive and did not report pulmonary function as the main outcome.PFTs may be useful in different stages of management of children with suspected or confirmed chILD, but the chILD spectrum is diverse and includes a heterogeneous patient group in all ages. Research studies in well-defined patient cohorts are needed to establish which PFT and outcomes are most relevant for diagnosis, evaluation of disease severity and course, and monitoring individual conditions both for improvement in clinical care and as end-points in future randomised controlled trials.

Monitoring of Respiratory Muscle Function in Critically Ill Children

OBJECTIVES

This review discusses the different techniques used at the bedside to assess respiratory muscle function in critically ill children and their clinical applications.

DATA SOURCES

A scoping review of the medical literature on respiratory muscle function assessment in critically ill children was conducted using the PubMed search engine.

STUDY SELECTION

We included all scientific, peer-reviewed studies about respiratory muscle function assessment in critically ill children, as well as some key adult studies.

DATA EXTRACTION

Data extracted included findings or comments about techniques used to assess respiratory muscle function.

DATA SYNTHESIS

Various promising physiologic techniques are available to assess respiratory muscle function at the bedside of critically ill children throughout the disease process. During the acute phase, this assessment allows a better understanding of the pathophysiological mechanisms of the disease and an optimization of the ventilatory support to increase its effectiveness and limit its potential complications. During the weaning process, these physiologic techniques may help predict extubation success and therefore optimize ventilator weaning.

CONCLUSIONS

Physiologic techniques are useful to precisely assess respiratory muscle function and to individualize and optimize the management of mechanical ventilation in children. Among all the available techniques, the measurements of esophageal pressure and electrical activity of the diaphragm appear particularly helpful in the era of individualized ventilatory management.

A New Method for Measuring Bell-Shaped Chest Induced by Impaired Ribcage Muscles in Spinal Muscular Atrophy Children

The involvement of the respiratory muscular pump makes SMA children prone to frequent hospitalization and morbidity, particularly in type 1. Progressive weakness affects ribcage muscles resulting in bell-shaped chest that was never quantified. The aims of the present work were: (1) to quantify the presence of bell-shaped chest in SMA infants and children and to correlate it with the action of ribcage muscles, assessed by the contribution of pulmonary ribcage to tidal volume (ΔV_{RC, p}); (2) to verify if and how the structure of the ribcage and ΔV_{RC, p} change after 1-year in SMA type 2. 91 SMA children were studied in supine position during awake spontaneous breathing: 32 with type 1 (SMA1, median age: 0.8 years), 51 with type 2 (SMA2, 3.7 years), 8 with type 3 (SMA3, 5.4 years) and 20 healthy children (HC, 5.2 years). 14 SMA2 showed negative ΔV_{RC, p} (SMA2px), index of paradoxical inspiratory inward motion. The bell-shaped chest index was defined as the ratio between the distance of the two anterior axillary lines at sternal angle and the distance between the right and left 10th costal cartilage. If this index was < < 1, it indicated bell shape, if ~1 it indicated rectangular shape, while if >> 1 an inverted triangle shape was identified. While the bell-shaped index was similar between HC (0.92) and SMA3 (0.91), it was significantly (p < 0.05) reduced in SMA2 (0.81), SMA2px (0.74) and SMA1 (0.73), being similar between the last two. There was a good correlation (Spearman's rank correlation coefficient, ρ = 0.635, p < 0.001) between ribcage geometry and ΔV_{RC, p}. After 1 year, ΔV_{RC, p} reduced while bell-shaped chest index did not change being significantly lower than HC. The shape of the ribcage was quantified and correlated with the action of ribcage muscles in SMA children. The impaired ribcage muscles function alters the ribcage structure. HC and SMA3 show an almost rectangular ribcage shape, whereas SMA2, SMA2px and SMA1 are characterized by bell-shaped chest. In SMA, therefore, a vicious cycle starts since infancy: the disease progressively affects ribcage muscles resulting in reduced expansion of lung and ribcage that ultimately alters ribcage shape. This puts the respiratory muscles at mechanical disadvantage.

Effects of detraining on breathing pattern and ventilatory efficiency in young soccer players

BACKGROUND

This study investigated the effects of detraining on breathing pattern. The aim of this study was to evaluate the effect of a six-week detraining period on breathing patterns and ventilatory efficiency.

METHODS

Fourteen young soccer players were evaluated at the end of a competitive season and after a six-week detraining period. Assessment of respiratory efficiency was based on VE/VCO2 slope changes below 70% of exercise intensity. All participants underwent twice an incremental graded exercise test up to exhaustion.

RESULTS

No differences in breathing frequency and inspiratory time/total time ratio (Ti/Ttot) were found after detraining (P>0.05). Differences in tidal volume (VT), VT/Ti quotient and VE were significant (P<0.05) at between 40 to 100% of exercise intensity. The VE/VCO2 slope did not change (P>0.05) during a postdetraining maximal incremental test.

CONCLUSIONS

A six-week detraining period causes changes in inspiratory flow but does not affect the inspiratory time/total respiratory cycle time ratio. The overall ventilatory efficiency of the respiratory system remains constant and is not affected by detraining.

Cerebrovascular and ventilatory responses to acute normobaric hypoxia in girls and women

Physiological responses to hypoxia in children are incompletely understood. We aimed to characterize cerebrovascular and ventilatory responses to normobaric hypoxia in girls and women. Ten healthy girls (9.9 ± 1.7 years; mean ± SD; Tanner stage 1 and 2) and their mothers (43.9 ± 3.5 years) participated. Internal carotid (ICA) and vertebral artery (VA) velocity, diameter and flow (Duplex ultrasound) was recorded pre- and post-1 h of hypoxic exposure (FIO2 = 0.126;~4000 m) in a normobaric chamber. Ventilation (V˙E) and respiratory drive (VT/TI) expressed as delta change from baseline (∆%), and end-tidal carbon-dioxide (PETCO2) were collected at baseline (BL) and 5, 30 and 60 min of hypoxia (5/30/60 HYP). Heart rate (HR) and oxygen saturation (SpO2) were also collected at these time-points. SpO2 declined similarly in girls (BL-97%; 60HYP-80%, P < 0.05) and women (BL-97%; 60HYP-83%, P < 0.05). Global cerebral blood flow (gCBF) increased in both girls (BL-687; 60HYP-912 mL·min-1, P < 0.05) and women (BL-472; 60HYP-651 mL·min-1, P < 0.01), though the ratio of ICA:VA (%) contribution to gCBF differed significantly (girls, 75:25%; women, 61:39%). The relative increase in V˙E peaked at 30HYP in both girls (27%, P < 0.05) and women (19%, P < 0.05), as did ∆%VT/TI (girls, 41%; women, 27%, P's < 0.05). Tidal volume (VT) increased in both girls and women at 5HYP, remaining elevated above baseline in girls at 30 and 60 HYP, but declined back toward baseline in women. Girls elicit similar increases in gCBF and ventilatory parameters in response to acute hypoxia as women, though the pattern and contributions mediating these responses appear developmentally divergent.

Spontaneous Breathing Pattern as Respiratory Functional Outcome in Children with Spinal Muscular Atrophy (SMA)

Introduction

SMA is characterised by progressive motor and respiratory muscle weakness. We aimed to verify if in SMA children 1)each form is characterized by specific ventilatory and thoraco-abdominal pattern(VTAp) during quiet breathing(QB); 2)VTAp is affected by salbutamol therapy, currently suggested as standard treatment, or by the natural history(NH) of SMA; 3)the severity of global motor impairment linearly correlates with VTAp.

Materials and methods

VTAp was analysed on 32 SMA type I (SMA1,the most severe form), 51 type II (SMA2,the moderate), 8 type III (SMA3,the mildest) and 20 healthy (HC) using opto-electronic plethysmography. Spirometry, cough and motor function were measured in a subgroup of patients.

Results

In SMA1, a normal ventilation is obtained in supine position by rapid and shallow breathing with paradoxical ribcage motion. In SMA2, ventilation is within a normal range in seated position due to an increased respiratory rate(p<0.05) with reduced tidal volume(p<0.05) secondary to a poor contribution of pulmonary ribcage(%ΔV_RC,P, p<0.001). Salbutamol therapy had no effect on VTAp during QB(p>0.05) while tachypnea occurred in type I NH. A linear correlation(p<0.001) was found between motor function scales and VTAp.

Conclusion

A negative or reduced %ΔV_RC,P, indicative of ribcage muscle weakness, is a distinctive feature of SMA1 and SMA2 since infancy. Its quantitative assessment represents a non-invasive, non-volitional index that can be obtained in all children, even uncollaborative, and provides useful information on the action of ribcage muscles that are known to be affected by the disease.Low values of motor function scales indicate impairment of motor but also of respiratory function.

Parasternal intercostal electromyography: a novel tool to assess respiratory load in children

BACKGROUND

Parasternal intercostal muscle electromyography (EMGpara) represents a novel tool to assess respiratory load when volitional techniques are not possible. This study examined the application of EMGpara in healthy, wheezy, and critically ill children.

METHODS

Surface EMGpara was measured during tidal breathing in 92 healthy children, 20 wheezy preschool children (with measurements repeated following bronchodilator), and 25 mechanically ventilated children during supported ventilation and on continuous positive airways pressure.

RESULTS

EMGpara was related to age, height, and weight in the healthy group (r = -0.623, -0.625, -0.641 respectively, all P < 0.0001). An age-based equation for predicted EMGpara was developed and patient data expressed as z-scores. EMGpara was higher in wheezy children prebronchodilator than healthy controls (median interquartile range (IQR) z-score 0.53 (0.07-1.94), P = 0.0073), falling to levels not different to healthy children postbronchodilator (-0.08 (-0.50-1.00)). In the critically ill children, EMGpara was higher (P < 0.0001) than in healthy subjects during both mechanical ventilation (median (IQR) z-score 1.14 (0.33-1.93)) and continuous positive airways pressure (1.88 (0.91-3.03)).

CONCLUSION

EMGpara is feasible in children and infants both healthy and diseased, is raised in those with elevated respiratory load, and is responsive to clinical interventions. EMGpara represents a potential method to assess respiratory status in patients conventionally challenging to assess.

Respiratory muscle function in patients with cystic fibrosis

Respiratory muscle function in patients with cystic fibrosis (CF) can be assessed by measurement of maximal inspiratory pressure (Pimax ), maximal expiratory pressure (Pemax ), and pressure-time index of the respiratory muscles (PTImus ). We investigated the differences in maximal respiratory pressures and PTImus between CF patients with no gross hyperinflation and healthy controls and described the effects of pulmonary function and nutrition impairment on respiratory muscle function in this group of CF patients. Forced expiratory volume in 1 sec (FEV1 ), forced vital capacity (FVC) and maximal expiratory flow between 25% and 75% of VC (MEF25-75 ), body mass index (BMI), upper arm muscle area (UAMA), Pimax , Pemax , and PTImus were assessed in 140 CF patients and in a control group of 140 healthy subjects matched for age and gender. Median Pimax and Pemax were significantly lower in CF patients compared to the controls [Pimax  = 74 (57-94) in CF vs. 84 (66-102) in controls, P = 0.009], [Pemax  = 71 (50-95) in CF vs. 84 (66-102) in controls, P < 0.001]. Median PTImus in CF patients compared to controls was significantly increased [PTImus  = 0.110 (0.076-0.160) in CF vs. 0.094 (0.070-0.137) in controls, P = 0.049] and it was significantly higher in CF patients with impaired pulmonary function. In CF patients, PTImus was significantly negatively related to upper arm muscle area (r = 0.184, P = 0.031). These findings suggest that CF patients with no severe lung disease compared to healthy subjects exhibit impaired respiratory muscle function, while CF patients with impaired pulmonary function and nutrition indices exhibit higher PTImus values.

Modeling regional deposited dose of submicron aerosol particles

We developed a simple model to calculate the regional deposited dose of submicron aerosol particles in the respiratory system. This model incorporates measured outdoor and modeled indoor particle number size distributions, detailed activity patterns of three age groups (teens, adults, and the elderly), semi-empirical estimation of the regional deposition fraction, hygroscopic properties of urban aerosols, and reported breathing minute volumes. We calculated the total and regional deposited dose based on three concentration metrics: particle number (PN), mass (PM), and surface area (PSA). The 24-h total deposited dose of fine particles in adult males was around 40 μg (57×109 particles, 8×102 mm(2)) and 41 μg (40×109 particles, 8×102 mm(2)) on workdays and weekends, respectively. The total and regional 24-h deposited dose based on any of the metrics was at most 1.5 times higher in males than in females. The deposited dose values in the other age groups were slightly different than in adults. Regardless of the particle size fraction or the deposited dose metric, the pulmonary/alveolar region received the largest fraction of the deposited dose. These values represent the lowest estimate of the deposited dose and they are expected to be higher in real-life conditions after considering indoor sources of aerosol particles and spatial variability of outdoor aerosols. This model can be extended to youngsters (<12 years old) after gaining accurate information about the deposition fraction inside their respiratory system and their breathing pattern. This investigation is foreseen to bridge the gap between exposure and response in epidemiological studies.

Pulmonary gas exchange and acid-base balance during exercise

As the first step in the oxygen-transport chain, the lung has a critical task: optimizing the exchange of respiratory gases to maintain delivery of oxygen and the elimination of carbon dioxide. In healthy subjects, gas exchange, as evaluated by the alveolar-to-arterial PO2 difference (A-aDO2), worsens with incremental exercise, and typically reaches an A-aDO2 of approximately 25 mmHg at peak exercise. While there is great individual variability, A-aDO2 is generally largest at peak exercise in subjects with the highest peak oxygen consumption. Inert gas data has shown that the increase in A-aDO2 is explained by decreased ventilation-perfusion matching, and the development of a diffusion limitation for oxygen. Gas exchange data does not indicate the presence of right-to-left intrapulmonary shunt developing with exercise, despite recent data suggesting that large-diameter arteriovenous shunt vessels may be recruited with exercise. At the same time, multisystem mechanisms regulate systemic acid-base balance in integrative processes that involve gas exchange between tissues and the environment and simultaneous net changes in the concentrations of strong and weak ions within, and transfer between, extracellular and intracellular fluids. The physicochemical approach to acid-base balance is used to understand the contributions from independent acid-base variables to measured acid-base disturbances within contracting skeletal muscle, erythrocytes and noncontracting tissues. In muscle, the magnitude of the disturbance is proportional to the concentrations of dissociated weak acids, the rate at which acid equivalents (strong acid) accumulate and the rate at which strong base cations are added to or removed from muscle.

Noninvasive determination of the tension-time index in Duchenne muscular dystrophy

OBJECTIVE

Noninvasive determination of the tension-time index of the inspiratory muscles (TT MUS) can identify predisposition to respiratory muscle fatigue in neuromuscular disease. We correlated TT MUS with age and extent of need of ventilator use for patients with Duchenne muscular dystrophy.

DESIGN

Maximal inspiratory pressure, inspiratory pressure 0.1 sec after the onset of inspiration (P 0.1), and the breathing pattern during spontaneous breathing were measured in 46 subjects with Duchenne muscular dystrophy and in 46 healthy males of the same age. TT MUS (TT MUS = T I/T TOT x P I/MIP) was determined by calculating P I from P 0.1 (P I = 5 x P 0.1 x T I). The data were compared with normal values and related to age and ventilator use.

RESULTS

TT MUS was significantly higher in the entire Duchenne muscular dystrophy group than in controls (0.21 +/- 0.11 vs. 0.06 +/- 0.02, P < 0.001) and increased with age in the patients (P < 0.001). TT MUS was significantly higher in subjects ventilated 8-20 hrs per day than in nocturnal-only users and in patients ventilated >20 hrs per day than in those ventilated 8-20 hrs per day (P < 0.001). TT MUS surpassed 0.23 in 95% of subjects ventilated 8-20 hrs. TT MUS exceeded 0.37 in 95% of individuals ventilated >20 hrs per day, whereas it was less than this value in 95% of patients ventilated 8-20 hrs.

CONCLUSIONS

TT MUS increases significantly with disease progression and is a sensitive indicator of risk of inspiratory muscle fatigue and ventilator use. Longitudinal determination of TT MUS in patients with Duchenne muscular dystrophy may help to justify the extent of need for mechanical ventilation.

Measurement of maximal inspiratory pressure in ventilated children

Maximal inspiratory pressure (PIMAX), the maximum negative pressure generated during temporary occlusion of the airway, is commonly used to measure inspiratory muscle strength in mechanically ventilated infants and children. There are, however, no guidelines as to how the PIMAX measurement should be made. We compared the maximum inspiratory pressure generated during airway occlusion (PIMAX(OCC)) to that when a unidirectional valve (PIMAX(UNI)), which allowed expiration, but not inspiration was used. Twenty-two mechanically ventilated children (mean (SD) age 4.8 (4.5) years) were studied. Three sets of end expiratory occlusions were performed for each method in random order. The expired volume during PIMAX(UNI) was assessed and related to the functional residual capacity (FRC) measured using a helium dilution technique.The mean (SD) PIMAX(UNI) (45.5 (15.2) cmH(2)O) was significantly greater than mean (SD) PIMAX(OCC) (30.9 (9.0) cmH(2)O) (P < 0.0001). The mean (SD) expired volume during PIMAX(UNI), was 98 ml (62.3), a mean reduction in FRC of 33.1% (SD 13.9). There were no significant differences between techniques in the baseline respiratory drive, the number of efforts required and the time to reach PIMAX. Regardless of technique, PIMAX was reached in 10 inspiratory efforts or 15 sec of airway occlusion.A unidirectional valve allowing expiration, but not inspiration yields greater PIMAX values in children. Occlusions should be maintained for 12 sec or eight breaths (99% CI of mean).

Exercise-induced breathing patterns of youth are related to age and intensity

The influences of sex, age, exercise intensity, and end-tidal CO(2) on the inspiratory drive ([V(T) kg(-1)] x T(i)(-1)) and respiratory timing (T(i) x T(tot)(-1)) components of ventilation were examined in 295 youth (138 females, 157 males); similarly distributed 8-18 years of age. Ventilatory and metabolic measures were collected breath-by-breath at rest and during a slow walk (4.0 km h(-1)), fast walk (5.6 km h(-1)) and run (8.0 km h(-1)). Regression modeling for drive (age, sex, and P(ET)CO(2)) found that sex was significant (R (2) < 0.017; P < 0.05) for rest and running, but not walking. Compared to rest, drive increased by 120% for the slow walk, 217% for the fast walk and 258% for the run (P < 0.0001). Drive decreased with age (P < 0.0001): rest = 0.41 ml kg(-1) s(-1) year(-1); slow walk = 0.90 ml kg(-1) s(-1) year(-1); fast walk = 1.30 ml kg(-1) s(-1) year(-1); and run = 1.47 ml kg(-1) s(-1) year(-1). In the regression models for timing, sex provided approximately 1% of the variance during the run, but was not significant during rest or walking. Timing increased with exercise intensity by approximately 0.02 units (P < 0.001), but decreased by approximately 0.002 units year(-1) with age for all conditions (P < 0.003). Changes in drive and timing were marginally related to end-tidal CO(2) (exercise R(2) < 0.063 for all models). These results suggest that in the control of inspiratory drive and timing during exercise in youth, sex is of minor importance but there are age-related changes which are marginally associated with CO(2).

Does taking endurance into account improve the prediction of weaning outcome in mechanically ventilated children?

INTRODUCTION

We conducted the present study to determine whether a combination of the mechanical ventilation weaning predictors proposed by the collective Task Force of the American College of Chest Physicians (TF) and weaning endurance indices enhance prediction of weaning success.

METHOD

Conducted in a tertiary paediatric intensive care unit at a university hospital, this prospective study included 54 children receiving mechanical ventilation (> or = 6 hours) who underwent 57 episodes of weaning. We calculated the indices proposed by the TF (spontaneous respiratory rate, paediatric rapid shallow breathing, rapid shallow breathing occlusion pressure [ROP] and maximal inspiratory pressure during an occlusion test [Pimax]) and weaning endurance indices (pressure-time index, tension-time index obtained from P(0.1) [TTI1] and from airway pressure [TTI2]) during spontaneous breathing. Performances of each TF index and combinations of them were calculated, and the best single index and combination were identified. Weaning endurance parameters (TTI1 and TTI2) were calculated and the best index was determined using a logistic regression model. Regression coefficients were estimated using the maximum likelihood ratio (LR) method. Hosmer-Lemeshow test was used to estimate goodness-of-fit of the model. An equation was constructed to predict weaning success. Finally, we calculated the performances of combinations of best TF indices and best endurance index.

RESULTS

The best single TF index was ROP, the best TF combination was represented by the expression (0.66 x ROP) + (0.34 x Pimax), and the best endurance index was the TTI2, although their performance was poor. The best model resulting from the combination of these indices was defined by the following expression: (0.6 x ROP) - (0.1 x Pimax) + (0.5 x TTI2). This integrated index was a good weaning predictor (P < 0.01), with a LR+ of 6.4 and LR+/LR- ratio of 12.5. However, at a threshold value < 1.3 it was only predictive of weaning success (LR- = 0.5).

CONCLUSION

The proposed combined index, incorporating endurance, was of modest value in predicting weaning outcome. This is the first report of the value of endurance parameters in predicting weaning success in children. Currently, clinical judgement associated with spontaneous breathing trials apparently remain superior.

Effect of body size on breathing pattern and fine-particle deposition in children

Interchild variability in breathing patterns may contribute to variability in fine particle lung deposition and morbidity in children associated with those particles. Fractional deposition (DF) of fine particles (2-microm monodisperse, carnauba wax particles) was measured in healthy children, age 6-13 yr (n = 36), while they followed a resting breathing pattern previously determined by respiratory inductance plethysmography. Interchild variation in DF, measured by photometry at the mouth, was most strongly predicted by their tidal volume (Vt) (r =0.79, P < 0.001). Multiple regression analysis further showed that, for any given height and age, Vt increased with increasing body mass index (BMI) (P < 0.001). The overweight children (> or =95th percentile BMI) (n = 8) had twice the DF of those in the lowest BMI quartile (<25th percentile) (n = 9; 0.28 +/- 0.13 vs. 0.15 +/- 0.06, respectively; P < 0.02). In the same groups, resting minute ventilation was also significantly higher in the overweight children (8.5 +/- 2.2 vs. 5.9 +/- 1.1 l/min; P < 0.01). Consequently, the rate of deposition (i.e., particles depositing/time) in the overweight children was 2.8 times that of the leanest children (P < 0.02). Among all children, the rate of deposition was significantly correlated with BMI (r = 0.46, P = 0.004). These results suggest that increased weight in children may be associated with increased risk from inhalation of pollutant particles in ambient air.

Prepubescents' ventilatory responses to exercise with reference to sex and body size

STUDY OBJECTIVES

To examine the ventilatory responses of prepubescent children to submaximal and peak exercise using appropriate allometric modeling to control for differences in body size.

DESIGN

Cross-sectional study of a representative sample of children.

SETTING

Middle schools (8 to 11 years) in Exeter, UK.

PARTICIPANTS

We studied 101 boys and 76 girls aged 11.1 (0.4) years and classified Tanner stage 1 for pubic hair (no true pubic hair).

MEASUREMENTS

At rest: stature, mass, sum of skinfolds, hemoglobin concentration, FVC, and FEV1. During treadmill exercise at 7, 8, 9, and 10 km/h, and at peak exercise: oxygen uptake (VO2), minute ventilation (VE), tidal volume (VT), and respiratory frequency (Rf).

RESULTS

At peak exercise, boys' VO2, VE, and VT were significantly (p<0.01) higher than girls' values and remained so even when the influence of body size was controlled using allometric principles. There were no significant (p>0.05) sex differences in Rf or the ratios VT/FVC or VE/VO2. When data were compared at the same relative exercise intensity (ie, 70 to 75% or 80 to 85% peak VO2), no significant (p>0.05) sex differences in Rf, VT/FVC, or VE/VO2 were detected. Boys' higher (p<0.001) VO2 values were reflected by their higher VE which remained higher than values for girls at both submaximal levels even when the influence of body size was covaried out.

CONCLUSIONS

Prepubescent boys demonstrate higher peak VO2 than girls and this is supported by a higher VE and VT, even when the influence of body size is accounted for using allometry. Other ventilatory responses to both peak exercise and exercise at the same relative intensity are remarkably similar in both boys and girls.

Lung function in infants with sickle cell disease

We performed pulmonary function testing in 20 infants (11 male and 9 female; ages 3-30 months) with sickle cell disease to assess whether abnormal lung function develops early in life. Respiratory system compliance (Crs) and resistance (Rrs) were measured by the passive occlusion technique, functional residual capacity (FRC) was measured by the nitrogen washout technique, and tidal flow-volume loops and partial expiratory flow-volume curves were obtained by the thoracoabdominal compression technique to detect airway obstruction. Patients with Hb SS (Group I, n = 12) had significantly lower hemoglobin levels and a higher (but not significant) incidence of acute chest syndrome (ACS), vasoocclusive crisis (VOC), splenic sequestration, transfusions, and history of intermittent bronchospasm compared to with patients with hemoglobinopathies Hb SC, Hb Sbt and Hb SF (Group II; n = 8). Both groups had elevated FRC, decreased maximum expiratory flows at FRC (V'max,FRC), and decreased time needed to reach peak expiratory flow (tme/tE), suggesting lower airway obstruction (LAO) and hyperinflation. Restrictive disease was found in only three patients of Group I. Our findings suggest that in sickle cell disease (especially among patients with Hb SS), abnormal lung function (predominantly LAO) may be present in early infancy. Airway reactivity may play a role in the pathogenesis, but the relation to VOC or ACS remains unclear.

Development of ventilatory responses to exercise in normal white children. A longitudinal study

Cross-sectional studies have indicated that the pattern of ventilatory responses to exercise evolves during the course of childhood. This 5-year study was designed to provide a longitudinal assessment of minute ventilation (VE), tidal volume (VT), and breathing frequency (fR) in 20 children (11 girls, nine boys) between the ages of 9 and 13 years. Subjects performed maximal and identical submaximal steady-state treadmill walking tests annually. No significant gender differences were observed in any of the three variables. At submaximal exercise, VT per kilogram remained stable, with a progressive fall in fR. As a result, submaximal VE per kilogram declined with age. A similar pattern was observed at maximal exercise, but the decrease in VE per kilogram was not statistically significant. Ventilatory equivalent for oxygen (VE/VO2) fell with age at submaximal exercise but declined only in the boys with maximal testing. VE/VO2 at maximal and submaximal exercise was greater in the girls at all ages. These findings support previous data derived from cross-sectional studies.

Predictors of extubation success and failure in mechanically ventilated infants and children

OBJECTIVE

To predict extubation success and failure in mechanically ventilated infants and children using bedside measures of respiratory function.

DESIGN

Prospective collection of data.

SETTING

A university-affiliated children's hospital with a 51-bed critical care unit.

PATIENTS

All infants and children who were mechanically ventilated for at least 24 hrs, except neonates < or = 37 wks gestation and patients with neuromuscular disease.

INTERVENTIONS

Bedside measurements of cardiorespiratory function were obtained immediately before extubation.

MEASUREMENTS AND MAIN RESULTS

Extubation failure was defined as reintubation within 48 hrs of extubation in the absence of upper airway obstruction. Failure rates were calculated for different ranges (selected a priori) of preextubation measures of breathing effort, ventilatory support, respiratory mechanics, central inspiratory drive, and integrated indices useful in adults. Effort of spontaneous breathing was assessed by the respiratory rate standardized to age, the presence of retractions and paradoxical breathing, inspiratory pressure, maximal negative inspiratory pressure (maximal negative inspiratory pressure), inspiratory pressure/maximal negative inspiratory pressure ratio, and tidal volume indexed to body weight of a spontaneous breath. Ventilatory support was measured by the fraction of inspired oxygen (F10(2)), mean airway pressure, oxygenation index, and the fraction of total minute ventilation provided by the ventilator. Respiratory mechanics were assessed by determination of peak ventilatory inspiratory pressure and dynamic compliance. Central inspiratory drive was assessed by mean inspiratory flow. Frequency to tidal volume ratio and the compliance, rate, oxygenation, and pressure indexed to body weight, the integrated indices useful in predicting extubation failure in adults, were also calculated. Thirty-four of the 208 patients who were studied were reintubated for an overall failure rate of 16.3% (95% confidence interval 11.3% to 21.4%). The reasons for reintubation were poor effort (n = 8), excessive effort (n = 14), altered mental status or absent airway reflexes (n = 2), cardiovascular instability (n = 3), inadequate oxygenation (n = 3), respiratory acidosis (n = 3), and undocumented (n = 1). Extubation failure increased significantly with decreasing tidal volume indexed to body weight of a spontaneous breath, increasing F10(2), increasing mean airway pressure, increasing oxygenation index, increasing fraction of total minute ventilation provided by the ventilator, increasing peak ventilatory inspiratory pressure, or decreasing mean inspiratory flow (p < .05). Dynamic compliance showed a trend of increasing failure rate with decreasing dynamic compliance but did not reach statistical significance (p = .116). Respiratory rate standardized to age, inspiratory pressure, maximal negative inspiratory pressure, inspiratory pressure/maximal negative inspiratory pressure ratio, frequency to tidal volume ratio, and compliance, rate, oxygenation, and pressure did not show any trend in failure rate with increasing or decreasing values. Threshold values that defined a low risk (< or = 10%) and a high risk (> or = 25%) of extubation failure could be determined for tidal volume indexed to body weight of a spontaneous breath, F10(2), mean airway pressure, oxygenation index, fraction of total minute ventilation provided by the ventilator, peak ventilatory inspiratory pressure, dynamic compliance, and mean inspiratory flow. Neither a low nor a high risk of failure could be defined for frequency to tidal volume ratio or the compliance, rate, oxygenation, and pressure (CROP) index.

CONCLUSIONS

Bedside measurements of respiratory function can predict extubation success and failure in infants and children. Both a low risk and a high risk of failure can be determined using these measures. Integrated indices useful in adults do not reliably predict extubation success or failure in

Ability of new lung function tests to assess methacholine-induced airway obstruction in infants

We assessed the ability of innovative lung function tests to detect bronchial obstruction induced by methacholine bronchial challenge. Fifty-five recurrently wheezy infants (mean age 16 +/- 5.2 months) free of respiratory symptoms underwent baseline lung function tests. Forty-two completed the methacholine challenge. Maximal flow at functional residual capacity (VmaxFRC) was obtained using the squeeze technique; compliance and resistance of the respiratory system (Crs, Rrs) was measured with the passive expiatory flow volume technique; tidal volume breathing patterns were analyzed from recordings of respiratory rate (RR), tidal volume (VT), and inspiratory time divided by total cycle of duration (Ti/Ttot). Expiratory tidal flow volume (V/VT) curves were described with multiple indices such as the ratio of expiratory time necessary to reach peak tidal expiratory flow (Fpet) to expiratory time (Tme/Te). Transcutaneous oxygen tension (PtCO2) was measured as an indicator of response to methacholine challenge. Of 42 infants 41 responded to methacholine by a change > or = 2 standard deviations from baseline values. The mean SD unit changes were 9.8 in PtCO2, 3.7 for VmaxFRC, 2.8 for Crs, 2.09 for Rrs, 3.1 for RR, 1.6 for Ti/Ttot, 2.2 for Tme/Te 3.9 for PFVt. We conclude that these noninvasive lung function tests, especially VmaxFRC and Fpet, can be used to detect minor or moderate airway obstruction. Further studies are needed to determine the value of the tests in assessing bronchial disease and effects of its treatment.

Ventilatory response of prepubertal boys and adults to carbon dioxide at rest and during exercise

The aim of this study was to determine whether the greater ventilation in children at rest and during exercise is related to a greater CO2 ventilatory response. The CO2 ventilatory response was measured in nine prepubertal boys [10.3 years (SD 0.1)] and in 10 adults [24.9 years (SD 0.8)] at rest and during moderate exercise (VCO2 = 20 ml.kg-1.min-1) using the CO2-rebreathing method. Three criteria were measured in all subjects to assess the ventilatory response to CO2: the CO2 sensitivity threshold (Th), which was defined as the value of end tidal PCO2 (PETCO2) where the ventilation increased above its steady-state level; the reactivity slope expressed per unit of body mass (SBM), which was the slope of the linear relation between minute ventilation (VE) and PETCO2 above Th; and the slope of the relationship between the quotient of tidal volume (VT) and inspiration time (tI) and PETCO2 (VT.tI-1.PETCO2(-1)) values above Th. The VE, VT, breathing frequency (fR), oxygen uptake (VO2), and CO2 production (VCO2) were also measured before the CO2-rebreathing test. The following results were obtained. First, children had greater ventilation per unit body weight than adults at rest (P < 0.001) and during exercise (P < 0.01). Second, at rest, only VT.tI-1.PETCO2(-1) was greater in children than in adults (P < 0.001). Third, during exercise, children had a higher SBM (P < 0.02) and VT.tI-1.PETCO2(-1) (P < 0.001) while Th was lower (P < 0.02).(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of anthropometric characteristics on changes in maximal exercise ventilation and breathing pattern during growth in boys

The aim of this study was to investigate the effect of growth on ventilation and breathing pattern during maximal exercise oxygen consumption (VO2max) and their relationships with anthropometric characteristics. Seventy six untrained schoolboys, aged 10.5-15.5 years, participated in this study. Anthropometric measurements made included body mass, height, armspan, lean body mass, and body surface area. During an incremental exercise test, maximal ventilation (VEmax), tidal volume (VTmax), breathing frequency (fmax), inspiratory and expiratory times (tImax and tEmax), total duration of respiratory cycle (tTOTmax), mean inspiratory flow (VT/tImax), and inspiration fraction (tI/tTOTmax) were measured at VO2max. A power function was calculated between anthropometric characteristics and ventilatory variables to determine the allometric constants. The results showed firstly, that VEmax, VTmax, tImax, tEmax, tTOTmax, and VT/tImax increased with age and anthropometric characteristics (P less than 0.001), fmax decreased (P less than 0.001), and tI/tTOTmax remained constant during growth; secondly that lean body mass explained the greatest percentage of variance of VEmax (62.1%), VTmax (76.8%), and VT/tImax (70.6%), while anthropometric characteristics explained a slight percentage of variance of fmax and timing; and thirdly that VEmax, VTmax, and VT/tImax normalized by lean body mass did not change significantly with age. We concluded that at VO2max there were marked changes in ventilation and breathing pattern with growth. The changes in VEmax, VTmax, and VT/tImax were strongly related to the changes in lean body mass.

Breathing pattern during exercise in untrained children

Breathing pattern during exercise on a cycle ergometer was studied in 18 untrained children aged from 6 to 15 years of age (9 boys, 9 girls). Oxygen uptake, tidal volume, minute ventilation, all normalized for body weight (VO2BW, VT BW, VE BW), respiratory frequency (f), inspiratory (TI) and expiratory (TE) times, ratio TI over total duration of the respiratory cycle (TI/TTOT) and mean inspiratory flow (VT BW/TI) were measured: (1) at rest (W0) and at the highest load (maximal cardiac rate) of an incremental exercise (W1); (2) in steady state conditions, at 50% of W1 (W1/2) and at 2/3 of W1 (W2/3). VO2BW, VT BW, VE BW, TI/TTOT, VT BW/TI increased significantly (P less than 0.01) from W0 to W1. Behaviour of f and TI were different from the latter parameters: f increased and TI decreased significantly from W0 to W1/2 (P less than 0.01) and from W1/2 to W2/3 (P less than 0.01) but remained similar at W2/3 and W1. We observed a relationship between VO2 BW and VT BW/TI, and between VT BW and TI/TTOT at each step of workload. We conclude that untrained children adapt the pattern of breathing during exercise, as at rest, to metabolic demand. However, the increase in f and the decrease in TI are limited at maximal workload.

Ventilatory and occlusion-pressure responses to exercise in trained and untrained children

Pattern of breathing and mouth occlusion pressure were investigated during an incremental and exhaustive ergocycle test in untrained and trained 11 to 13 year old boys. At each level of exercise, the trained group had lower ventilation, a lower respiratory equivalent, and a lower respiratory rate. These results suggest that trained subjects have more efficient ventilation. Lower ventilation coincided with a smaller mean inspiratory flow (VT/TI), while the ratio of inspiratory to total breath (TI/TTOT) was unchanged. In contrast, mouth occlusion pressure and the index of neuromuscular inspiratory drive were the same up to 60 W for the two groups, and tended to be slightly lower in the trained boys above this level.

Characteristics of a simple measure of respiratory impedance

The ratio of mouth pressure developed 0.1 sec after occlusion at end-expiration (P0.1) to average inspiratory flow rate (VT/TI) has been proposed as 'effective inspiratory impedance', Imeff. We have studied a simple mathematical model of lung mechanics, consisting of an effective resistance, an effective compliance and a single pressure generator, to learn how Imeff is altered by changes in resistance (R), compliance (C), inspiratory duration (TI), and the degree of curvature of the inspiratory pressure wave form. The degree of curvature was varied between concave with respect to the time axis to convex and included a linear inspiratory muscle pressure function. Assuming a linear pressure function, we obtained an explicit equation for Imeff as a function of R, C, and TI. Using the same model we also studied the classical impedance as a function of R, C and frequency (of a sinusoidal excitation pressure). We found that Imeff was increased by increases in R, increasing degrees of concavity, decreases in C, and by decreases in TI. For this model the classical impedance was about 5 times larger than Imeff. Classical impedance was increased by increases in R, decreases in C, and decreases in excitation frequency. In conclusion, measurements of effective inspiratory impedance need to be interpreted in terms of R, C, TI, and the shape of the inspiratory muscle pressure function.

Breathing pattern and occlusion pressure during exercise in pre- and peripubertal swimmers

In two groups of young swimmers (prepubertal stage: group A; peripubertal stage: group B), the ventilatory response to graded exercise work with a cycle ergometer was studied. Ventilatory variables (ventilation, VE, tidal volume, VT, respiratory frequency,f, ratio between inspiratory period and total breath duration, TI/TTOT, and mean inspiratory flow, VT/TI) as well as mouth occlusion pressure measured at 100 msec (P0.1), effective impedance of the respiratory system (P0.1/VT/TI), inspiratory power for breathing (W) and O2 uptake (VO2) were measured during the third minute of each work load. At the same level of exercise both groups showed identical values of VT/TI, but VE was higher in group A individuals. This resulted from higher values of respiratory frequency with higher TI/TTOT ratios. P0.1, P0.1(VT/TI) and W were also much higher during work load in group A than in peripubertal subjects. When the above results were related to the same percentage of VO2 max, P0.1, W, respiratory frequency and duty cycle did not differ within both groups. However, VE, VT and VT/TI were lower in group A subjects with a higher P0.1/(VT/TI) ratio. Further corrections of VT, VT/TI and P0.1/(VT/TI) ratios by body weight cancelled all these differences. In conclusion, our results strongly suggest that biometric factors only determined interindividual differences in ventilatory response to exercise in prepubertal and peripubertal swimmers.