Biomedical subjects

G M Davis

Publications and source records attributed to G M Davis.

At least 55 records · Page 3Linked to original sources

PubMed1998

Dexamethasone for pulmonary interstitial emphysema in preterm infants.

The efficacy of a 3-day course of dexamethasone (0.5 mg/kg/ day) in 10 preterm infants (< or = 30 weeks gestation) with pulmonary interstitial emphysema (PIE) was studied in a retrospective case review. PIE was diagnosed at a median age of 7.5 days and treatment with dexamethasone began at 8.5 days. Seven of the 10 subjects had at least 2 days of conservative treatment (lowered mean airway pressure) preceding dexamethasone during which the mean airway pressure (MAP), oxygenation index (OI) and mechanical ventilation index (MVI) were not significantly different although within 3 days of dexamethasone each variable improved significantly (p < 0.05). Similarly, for all 10 infants, OI and MAP were significantly lower at 3 and 7 days from baseline (p < 0.005). By day 7, FiO2 (p = 0.022) and MVI (p = 0.011) were significantly lower and PIE had resolved on chest X-ray in 7/9 (78%) and improved in the remaining 2/9 (22%). Nine of the 10 infants survived to term. Three days of dexamethasone was associated with significant clinical improvement in most of these infants. The mechanism may relate to reduced airway oedema and inflammation and reduced airway obstruction.

Dexamethasone↗

PubMed1998

Pediatric reference values for respiratory resistance measured by forced oscillation.

OBJECTIVES: To determine, in North American children, reference values for respiratory resistance measurements by the forced oscillation (Rfo) technique and to examine whether sitting height, as index of truncal length, is a better determinant of resistance, less influenced by race and gender, than standing height. DESIGN/SETTING: A prospective cross-sectional study of healthy nonobese children, carefully selected for absence of atopy, exposure to tobacco smoke, and recent upper respiratory tract infection. MEASUREMENTS: Three measurements of respiratory resistance by forced oscillation were obtained at the fixed frequencies of 8 Hz (Rfo8), 12 Hz (Rfo12), and at 16 Hz (Rfo16) using the Custo Vit R (Custo Med GMBH; Munich, Germany). In cooperative children, routine spirometry (FEV1, FVC, and peak expiratory flow rate [PEFR]) was also performed. RESULTS: We recruited 217 healthy children aged 3 to 17 years. Reproducible measurements of Rfo8 were obtained for 206 children, Rfo12 for 197 children, and Rfo16 for 209 children. Normal FEV1, FVC, and PEFR values were documented in all 69 subjects who were able to reproducibly cooperate with spirometry. Multiple linear regression identified measurements of either sitting or standing height as the best, and equally strong, determinants of respiratory resistance at all three frequencies. Gender and race were not important factors once either sitting or standing height measurement was considered. Our regression equations at 8 Hz are comparable to published reference values obtained at fixed frequencies of 6, 8, and 10 Hz using other instruments. However, in comparison to our results, prior values tended to underestimate resistance in the shortest children or to overestimate it in the tallest ones. Our regression equation for Rfo12 is similar to the only previously published one, while no reference values at 16 Hz were available for comparison. CONCLUSIONS: Height is the best predictor for total respiratory resistance at 8, 12, and 16 Hz in children aged > or = 3 years. Use of sitting height does not appear to be a stronger determinant of resistance than standing height.

Adolescent↗

PubMed1998

Respiratory resistance in the emergency department: a reproducible and responsive measure of asthma severity.

OBJECTIVES: To determine, in preschool children with an acute asthma exacerbation, the responsiveness to change of respiratory resistance measurements obtained by the forced oscillation (Rfo) technique, and to identify the magnitude of change indicative of airway obstruction reversibility. DESIGN/SETTING: A prospective observational study of 114 children, aged 3 to 17 years, untrained in the Rfo technique and treated for acute asthma in a tertiary-care pediatric emergency department (ED). MEASUREMENTS: A physical examination followed by three measurements of respiratory resistance by forced oscillation were obtained at 8 Hz (Rfo8) and at 16 Hz (Rfo16). In cooperative children, routine spirometry that included FEV1 was also performed on the Custo Vit R (Custo Med; Munich, Germany). All measurements were obtained twice during the course of the ED treatment, before and after treatment with nebulized bronchodilators. RESULTS: The Rfo8 and Rfo16 measurements were highly reproducible (reproducibility coefficients >0.85). Both the Rfo8 and Rfo16 were at least as responsive to change (responsiveness coefficients of 2.3 and 1.2, respectively) as was FEV1 (2.0) and the four clinical signs most sensitive to change (0.6 to 1.0). A 19% change in Rfo8 was suggestive of significant reversibility. CONCLUSIONS: In the assessment of children aged > or =3 years with acute asthma exacerbation, the respiratory resistance measurements are highly reproducible and responsive to change, particularly when obtained at 8 Hz. A 19% change from baseline Rfo8 is suggestive of reversibility. This technique appears to be an attractive alternative in the evaluation of children who are too young or too sick to perform spirometry reproducibly.

Acute Disease↗

PubMed1998

A medial linkage orthosis to assist ambulation after spinal cord injury.

A "proof of concept" prototype of a new device to link bilateral knee-ankle-foot orthoses, the Mooring Medial Linkage Orthosis (Moorong MLO), is presented. The device consists of an arcuate sliding link centred on the hip joints with rolling element bearings to minimise friction. A single repeated-measures case study is reported in which a woman with an incomplete C6 tetraplegia ambulated over different surfaces and gradients using both the Moorong MLO and the Walkabout orthosis. Results demonstrated a slight increase in gait velocity in the Moorong MLO (between 0.36-1.02 m/min faster) and a consistently lower oxygen cost across all conditions (between 18-61% reduction) compared to the Walkabout orthosis. The reduction was most noticeable on sloping surfaces. These preliminary results suggest an improved efficiency of ambulation in this new device.

Adult↗

PubMed1997

Functional outcomes attained by T9-12 paraplegic patients with the walkabout and the isocentric reciprocal gait orthoses.

OBJECTIVE: To compare the functional outcomes attained by persons with paraplegia using the Walkabout Orthosis (WO) and the Isocentric Reciprocal Gait Orthosis (IRGO). DESIGN: A randomized crossover design. PATIENTS: Ten subjects with complete lesions between T9-T12. INTERVENTIONS: Over two 8-week periods, subjects were taught to use each orthosis in conjunction with elbow crutches. MAIN OUTCOME MEASURES: After each 8-week training period, subjects were assessed on their ability to perform five different sets of key skills associated with functional ambulation. RESULTS: There were no differences between orthoses in the ability of subjects to don and doff the orthoses, get up and down stairs and curbs, or walk on a flat surface. Subjects required significantly more assistance when using the WO to walk over inclined surfaces (median IRGO = "independent," median WO = "minimal assistance"; p = .03) but less assistance when using the WO to get from sitting to standing and standing to sitting (median IRGO = "moderate assistance," median WO = "minimal assistance"; p = .03). In addition, subjects walked significantly faster with the IRGO both on the flat (mean IRGO = .34 m/sec +/- .18, mean WO = .14 m/sec +/- .12; p = .002) and on inclined surfaces. CONCLUSIONS: Although it is easier to stand up and sit down with the WO, the IRGO facilitated a faster and more independent gait. Neither orthosis enabled subjects to be fully independent in the key skills necessary for functional ambulation after 8 weeks of training.

Activities of Daily Living↗

PubMed1997

Empyema thoracis in children: a 26-year review of the Montreal Children's Hospital experience.

The appropriate management of pediatric empyema thoracis remains controversial. The authors reviewed 47 cases of empyema thoracis over a 26-year period. The management of empyema included initial diagnostic thoracentesis and classification as acute, fibropurulent, or chronic. If the empyema was "acute," therapeutic tap, tube thoracostomy, or no surgical intervention was performed. "Fibropurulent" empyemas were uniformly treated with tube thoracostomy. The lung was decorticated when the empyema was encased by a thick peel, had recurred and was multiloculated, was refractory and the patient remained clinically unwell, or had occurred as a complication of previous thoracotomy. All patients with acute empyemas responded to antibiotics irrespective of drainage (average duration of fever, 17 days; average stay in hospital, 27 days). Of the fibropurulent empyemas in our review, complete drainage was attained in seven of 39 (18%), and decortication was not required in any empyema that was completely drained. Loculations persisted in 25 of 39 (64%) after tube thoracostomy but nonetheless resolved. The remaining seven of 39 (18%) with persistent loculations required formal decortication. Of the patients with fibropurulent empyemas that responded to tube thoracostomy, the average duration of fever was 13 days and hospitalization, 23 days. Of those requiring decortication the average duration of fever was 24 days and hospitalization, 40 days. These results will allow a baseline for comparison of new strategies (fibrinolytics and early thoracoscopy) that may reduce days of fever, hospitalization, and risk of formal decortication.

Adolescent↗

PubMed1997

A comparison of the attitude of paraplegic individuals to the walkabout orthosis and the isocentric reciprocal gait orthosis.

This study compared the attitude of paraplegic individuals to the Isocentric Reciprocal Gait Orthosis (IRGO) and the Walkabout Orthosis (WO), after they had been given the opportunity of using both. Ten complete T9-12 paraplegic patients participated in this randomised cross-over design. Initially the subjects learned to walk with the first orthosis before taking it home for a 14 week home trial period. The same process of training an trialing the orthosis at home was then repeated with the second orthosis. Attitudes to specific aspects of the orthoses were assessed by an 18 point questionnaire and overall attitudes were inferred after determining the amount of time that subjects used the orthoses at home and determining which orthosis the majority of subjects wanted to keep at the end of the study. The main finding was that subjects did not perceive any significant differences between the two orthoses. That is: (i) the questionnaire did not detect significant differences in attitudes to the two orthoses; (ii) there was no significant difference in the number of subjects tat preferred one orthosis to the other, at the end of the study, and (iii) subjects did not derive more use from one orthosis than the other over the two 14 week home trial periods. In addition, it was found that few subjects wore either orthosis more than once every 2 weeks and that subjects were primarily using the orthoses for therapeutic purposes. This latter finding was supported by the results of the questionnaire that revealed that subjects found both orthoses to be useful for standing but not useful for performing more purposeful tasks. It was concluded that when subjects are primarily using the WO and IRGO for therapeutic purposes, they do not readily perceive differences between the two.

Adult↗

PubMed1997

Oxygen uptake and heart rate responses during arm vs combined arm/electrically stimulated leg exercise in people with paraplegia.

The purpose of this study was to compare the oxygen uptake and heart rate responses during submaximal arm cranking to combined arm cranking + electrical stimulation (ES)-induced leg cycling in individuals with spinal cord injury (SCI). Seven subjects with paraplegia (T4-T12) performed combined arm and leg cycling exercise for 5 min, followed by arm cranking alone at the same power output for a further 5 min. During both exercise conditions, steady state oxygen consumption (VO2), carbon dioxide output (VCO2), expired ventilation (VE) and heart rate (HR) were determined. The respiratory exchange ratio (RER) and oxygen pulse were calculated from the measured variables. During combined arm + electrical stimulation-induced leg cycling exercise, the VO2 was 25% higher (1.58 l min-1 vs 1.26 l min-1), but the HR was 13% lower (132 b min-1 vs 149 b min-1), than during arm cranking exercise alone. Oxygen pulse and VCO2 were also significantly higher (by 42% and 25%, respectively) during combined arm + ES-induced leg exercise, but there were no differences between the two exercise conditions for VE or RER. These data suggest that the absence of the leg 'muscle pump' and a reduced venous return of blood to the heart elevate exercise heart rates during submaximal arm cranking. Conversely, combined arm cranking + ES-induced leg cycling exercise provides the body with a greater metabolic stress than arm cranking alone, while reducing the cardiac stress. The mechanism explaining the heart rate response, however, remains unclear, but may have been influenced by the blood pressure variations across the range of lesions. The findings from this study may have implications for the relative benefit of combined arm + ES-induced leg cycling training for people with paraplegia.

Adult↗

PubMed1997

Impaired calcium pump function does not slow relaxation in human skeletal muscle after prolonged exercise.

This study examined the effects of prolonged exercise on human quadriceps muscle contractile function and homogenate sarcoplasmic reticulum Ca2+ uptake and Ca2+-adenosinetriphosphatase activity. Ten untrained men cycled at 75 +/- 2% (SE) peak oxygen consumption until exhaustion. Biopsies were taken from the right vastus lateralis muscle at rest, exhaustion, and 20 and 60 min postexercise. Peak tension and half relaxation time of the left quadriceps muscle were measured during electrically evoked twitch and tetanic contractions and a maximal voluntary isometric contraction at rest, exhaustion, and 10, 20, and 60 min postexercise. At exhaustion, homogenate Ca2+ uptake and Ca2+ adenosinetriphosphatase activity were reduced by 17 +/- 4 and 21 +/- 5%, respectively, and remained depressed after 60 min recovery (P </= 0.01). Muscle ATP, creatine phosphate, and glycogen were all depressed at exhaustion (P </= 0.01). Peak tension during a maximal voluntary contraction, a twitch, and a 10-Hz stimulation were reduced after exercise by 28 +/- 3, 45 +/- 6, 65 +/- 5%, respectively (P </= 0.01), but no slowing of half relaxation times were found. Thus fatigue induced by prolonged exercise reduced muscle Ca2+ uptake, but this did not cause a slower relaxation of evoked contractions.

Adult↗

PubMed1997

Exercise ability in survivors of severe bronchopulmonary dysplasia.

There is limited information concerning the exercise performance of long-term survivors of bronchopulmonary dysplasia (BPD), and much of what is available pertains to those with relatively mild disease. The present study was undertaken to describe exercise responses in patients with a history of severe BPD, defined as those patients with a clinical and radiographic diagnosis of BPD who required supplemental oxygen at least until they were 44 wk postconceptual age and who were discharged home on oxygen. Fifteen children with a history of severe BPD were matched for gestational age with 15 children who had previously had respiratory distress syndrome but who did not develop BPD (Prem). These Prem control children were subsequently compared with 13 healthy control children born at term (Control) who were of similar postnatal age. Participants underwent pulmonary function testing, progressive exercise testing on a cycle ergometer, and a steady-state exercise test with cardiac output determined by CO2-rebreathing. Despite the patients with BPD having a lower FEV1 than those in the Prem group, who had lower values than the Control group (BPD, 64 +/- 21%; Prem, 85 +/- 11%; Control, 95 +/- 8%), the exercise capacity did not differ between the BPD and the Prem and between the Prem and the Control groups (BPD, 84 +/- 15%; Prem, 81 +/- 17%; Control, 91 +/- 12%). However, the BPD patients used a greater percentage of their ventilatory reserve (VEmax/40 FEV1: BPD, 93 +/- 20%; Prem, 67 +/- 12%; Control, 59 +/- 13%). Of the four patients with BPD who had significant oxygen desaturation with exercise, three had the lowest values for FEV1. Cardiac output was appropriate for oxygen consumption in most patients.

Anthropometry↗

PubMed1997

Measurement of respiratory resistance in the emergency department: feasibility in young children with acute asthma.

OBJECTIVES: To assess, in acutely ill asthmatic children, the feasibility of obtaining reproducible measurements of two independent lung function tests, namely spirometry and respiratory resistance, using the forced oscillation technique (Rfo). DESIGN/SETTING: A prospective observational study of 150 previously untrained children, aged 2 to 17 years, treated for acute asthma in a tertiary-care pediatric emergency department. MEASUREMENTS: Following a standardized physical examination, three measurements of respiratory resistance by forced oscillation were attempted at 8 Hz (Rfo8) and at 16 Hz (Rfo16), followed by spirometry, all using the same instrument (Custo Vit R; Custo Med; Munich, Germany). RESULTS: On the initial assessment, 98 (65%) children, aged 2 to 17 years, were able to reproducibly perform the Rfo8 measurement, 77 (51%) were able to reproducibly perform the Rfo16 measurement, while only 65 (43%) subjects managed to reliably perform spirometry. A notable proportion of preschool-aged children cooperated with the Rfo8 technique: 19% of 3-year-olds, 40% of 4-year-olds, and 83% of 5-year-olds. The superior success rate with Rfo8 as compared with spirometry was seen in all age groups but was most striking both in preschoolers (relative risk [RR]=10.5; 95% confidence interval [CI], 8.0 to 13.8) and in children aged 6 to 9 years (RR= 1.28; 95% CI, 1.18 to 1.39). Rfo8 values correlated significantly with clinical markers of asthma severity such as respiratory rate (r=0.38) and heart rate (r=0.23) as well as with FEV1 values (r2=0.73). CONCLUSIONS: This study demonstrates the feasibility of obtaining reproducible measurements of respiratory resistance in a notable proportion of untrained, acutely ill, asthmatic children. The forced oscillation technique appears as an attractive alternative to objectively assess lung function in children too young or too ill to cooperate with spirometry.

Acute Disease↗

PubMed1997

Measurement of infant pulmonary mechanics: comparative analysis of techniques.

In spontaneously breathing, intubated infants, lung elastance (E) and resistance (R) can be derived from the general equation of motion of the lung, Ptp = E.V + R.V + I.V + K, where P is the pressure applied to the system, E is the elastance (the reciprocal of the compliance), V is the volume, R is the resistance to airflow (V), I is the inertance, (V) is gas acceleration, and K is a constant representing alveolar pressure. However, differences in the methods of analysis may results in variations in the derived values of E and R. Eighteen non-sedated intubated infants, with a mean post-conceptual age of 32.3 weeks and mean weight of 1.51 kg, were studied to compare values in E and R derived by 7 different methods of analysis. For each infant, the same 7 consecutive breaths were analyzed by the following methods: 1) linear regression of Ptp on tidal volume (VT); 2) a Mead-Whittenberger analysis, 3) a 2-factor linear regression of Ptp with (V) and VT; 4) a 3-factor regression of Ptp with V, VT, and V; 5) a 3-factor linear regression model of Ptp with V, VT, and a (V)2 factor (to incorporate a turbulent flow factor); 6) a 4-factor regression of Ptp with V, VT, V, and (V)2; and 7) a transformation regression plot of Ptp/VT versus V/VT. In addition, the lung impedance was calculated from the values of E and R derived by each method. There was no significant difference between the measurements of E and R in methods 2-6 (by MANCOVA, with the subjects being covariates). Methods 1 and 7 had a significantly elevated E; in addition, Method 7 also had an elevated R. Furthermore, there were no differences between the impedance values derived from the different methods. We conclude that in this group of spontaneously breathing, intubated infants with a spectrum of pathology, the results of a 2-factor regression analysis are comparable to more complex models of the mechanics of the lung.

Airway Resistance↗

PubMed1997

Cardiovascular and metabolic responses to electrical stimulation-induced leg exercise in spinal cord injury.

Electrical stimulation-induced leg muscle contractions provide a useful model for examining the role of leg muscle neural afferents during low-intensity exercise in persons with spinal cord-injury and their able-bodied cohorts. Eight persons with paraplegia (SCI) and 8 non-disabled subjects (CONTROL) performed passive knee flexion/extension (PAS), electrical stimulation-induced knee flexion/extension (ES) and voluntary knee flexion/extension (VOL) on an isokinetic dynamometer. In CONTROLs, exercise heart rate was significantly increased during ES (94 +/- 6 bpm) and VOL (85 +/- 4 bpm) over PAS (69 +/- 4 bpm), but no changes were observed in SCI individuals. Stroke volume was significantly augmented in SCI during ES (59 +/- 5 ml) compared to PAS (46 +/- 4 ml). The results of this study suggest that, in able-bodied humans, Group III and IV leg muscle afferents contribute to increased cardiac output during exercise primarily via augmented heart rate. In contrast, SCI achieve raised cardiac output during ES leg exercise via increased venous return in the absence of any change in heart rate.

Electric Stimulation↗

PubMed1996

Molecular systematics and evolution of reproductive traits of North American freshwater unionacean mussels (Mollusca: Bivalvia) as inferred from 16S rRNA gene sequences.

North American freshwater unionacean bivalves are a diverse group of nearly 300 species. Unionaceans exhibit an array of conchological, anatomical, life history, and reproductive characteristics that have figured prominently in proposed classification schemes. Recently, two very different classifications of North American unionaceans have been proposed. Depending on the classification system utilized, a very different evolutionary trajectory of anatomical and reproductive features is obtained. The lack of a robust, well corroborated phylogeny of North American unionacean bivalves hinders the progress of evolutionary and ecological studies involving these species. Here we present a mitochondrial DNA (mtDNA) based phylogeny for North American unionacean mussels and compare it to previously proposed classifications. In addition, we present a 'total evidence' phylogeny which incorporates both the mtDNA sequence data and available morphological data. The molecular and total evidence phylogenies agree largely with the conclusions of a previous study based largely on immunoelectrophoretic data. North American unionaceans can be divided into two families: the Unionidae, which is comprised of most of the species and the Margaritiferidae. Within the Uniondae are two subfamilies, the Anodontinae and Ambleminae. The resultant phylogeny was used to examine the evolution of several key anatomical features including the number of gills (demibranchs) used by females to brood developing embryos, incubation length (bradytictic vs tachytictic), larval (glochidial) tooth structures, and shell texture. Both molecular and total evidence phylogenies indicate several of the aforementioned characters evolved independently or were subsequently lost or gained in several lineages.

Animals↗

PubMed1996

Diaphragmatic pacemaker failure in congenital central hypoventilation syndrome: a tale of two twiddlers.

Two patients with congenital central hypoventilation syndrome (CCHS) experienced phrenic nerve pacer failure due to deliberate manipulation of the internal receiver implant ("twiddling"). The patients, aged 7 and 12 years, presented with repeated episodes of pacer failure associated with local pain over a period of 18 months. They had progressively coiled the pacing wires to the point of breakage, which only became apparent at surgery. The breaks were not recognized radiologically, although in retrospect progressive twisting of the wires was evident on serial chest radiographs. Both patients required replacement of the internal receivers under general anesthesia. We recommend that the chest radiograph that is undertaken to investigate the cause of pacer dysfunction include the internal receiver. A plain chest radiograph that demonstrates progressive coiling of the subcutaneous pacing wire should raise suspicion of pacer wire breakage regardless of the patient's age.

Child↗

PubMed1996

Pedal forces produced during neuromuscular electrical stimulation cycling in paraplegics.

This study investigated forces applied to the pedal of a cycle ergometer by paraplegic subjects undergoing neuromuscular electrical-stimulation-induced leg exercise. The patterns of force application were compared with those of able-bodied subjects cycling under voluntary muscle control in order to investigate the effectiveness of the muscle stimulation parameters. Results show that paraplegic subjects applied significantly larger peak forces than the able-bodied subjects because of the short duration of neuromuscular stimulation. Able-bodied subjects were able to achieve the same average workload by applying smaller forces over a greater percentage of each crank revolution. It is suggested that the large forces produced by paraplegic subjects contribute to the low efficiency reported by previous studies, and that increasing the range of angles over which muscles are stimulated may provide a means to increase the efficiency of cycling for paraplegic individuals.

Journal Article↗

PubMed1996

Diaphragm pacing with a quadripolar phrenic nerve electrode: an international study.

We sought to determine the international experience with the quadripolar diaphragm pacer system and to test two hypotheses: the incidence of pacer complications would be (1) increased among pediatric as compared to adult patients; and (2) highest among active pediatric patients with idiopathic congenital central hypoventilation syndrome (CCHS). Data were collected via a questionnaire coupled with the Atrotech Registry data for a total of 64 patients (35 children and 29 adults) from 14 countries. Thoracic implantation of electrodes and bilateral pacer use each occurred in 94% of all subjects. Tetraplegic (vs pediatric CCHS) patients were more typically paced 24 hours/day (P = 0.001). Pacing duration averaged 2.0 +/- 1.0 years among children and 2.2 +/- 1.1 years among adults. Infections occurred among 2.9% of surgical procedures, all in pediatric CCHS patients (vs pediatric tetraplegic patients, P = 0.01). The incidence of mechanical trauma was 3.8%, without significant differences among patient groups. The incidence of presumed electrode and receiver failure were 3.1% and 5.9%, respectively, with internal component failure greater among pediatric CCHS than pediatric tetraplegic patients (P < 0.01). Intermittent or absent function of 0-4 electrode combinations occurred among 19% of all patients, with increased frequency among pediatric CCHS than pediatric tetraplegic patients (P < 0.03). Complication-free successful pacing occurred in 60% of pediatric and 52% of adult patients. In all, 94% of the pediatric and 86% of the adult patients paced successfully after the necessary intervention. Although pacer complications were not increased among pediatric as compared to adult patients, the incidence of complications was highest among the active pediatric patients with CCHS. Longitudinal study of these patients will provide invaluable information for modification and improvement of the quadripolar system.

Adult↗

PubMed1996

Do tidal expiratory flow patterns reflect lung mechanics in infants?

It has been suggested that during tidal breathing, the time to maximal expiratory flow, as a proportion of total expiratory time (Tme/TE), can be used as an index of airways obstruction. However, the relationship of Tme/TE to lung mechanics in infants is unclear. We examined this relationship in 42 premature infants (21 intubated and 21 not intubated) by comparing direct measures of pulmonary mechanics (lung resistance, dynamic lung compliance, and lung impedance) with Tme/TE measured over the same sample of tidal breathing. Tme/TE was positively correlated with lung compliance, expressed as a percent of the predicted value, in both intubated (r = 0.69, p < 0.005) and nonintubated (r = 0.64, p < 0.02) infants. There was no significant association between Tme/TE and lung resistance, expressed as a percent of the predicted value, in intubated (r = 0.32) and nonintubated (r = 0.23) infants. Tme/TE also showed, in nonintubated infants, a positive association with lung impedance, expressed as a percent of the predicted value, on the basis of the predictive values for compliance and resistance at the infant's unique respiratory rate, but this was significant only because of the influence of compliance on Tme/TE. These findings suggest that, in infants, the relationship between pulmonary mechanics and Tme/TE is complex, with Tme/TE being influenced by the elastic rather than the flow-resistive properties of the lungs.

Airway Resistance↗