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Biomedical subjects

P D Sly

Publications and source records attributed to P D Sly.

At least 19 recordsLinked to original sources
PubMed1992

The role of corticosteroids in the management of childhood asthma. The Thoracic Society of Australia and New Zealand.

OBJECTIVE: To formulate recommendations for the role of corticosteroid therapy in the management of childhood asthma. DATA SOURCES: The recommendations are based on a review of the available literature and a variety of review articles on the efficacy and safety of corticosteroid therapy supplemented by personal experience in managing children with asthma. DATA SYNTHESIS: 1. Preventive therapy. Sodium cromoglycate should be considered first-line treatment. Inhaled corticosteroids are indicated in children who fail to achieve control on this therapy or those with severe disease. An initial dosage of 400-600 micrograms/day is recommended with subsequent variation in dosage related to clinical response. Large volume spacers can be used to improve aerosol delivery and minimise side effects. Indications for specialist assessment include: use of inhaled corticosteroids in children under 3 years of age; the requirement for high dose therapy (greater than 600 micrograms/day); or the need for regular oral corticosteroids. 2. Acute severe asthma. Systemic corticosteroid therapy is a valuable adjunct in the treatment of acute severe asthma and can be used safely in the short term. The efficacy of high dose inhaled corticosteroids in the management of acute severe asthma requires further evaluation. The need for systemic corticosteroid therapy signals the need for reassessment of that child's usual maintenance therapy. CONCLUSION: These recommendations are presented as a guide to the use of corticosteroid therapy in childhood asthma. In the individual child, the benefits of therapy need to be weighted against the possible risks, with the aim of maintaining good asthma control with the minimum dose of corticosteroid.

Asthma↗
PubMed1992

Correcting for the Bernoulli effect in lateral pressure measurements.

Measurement of airway pressure is essential in the study of respiratory mechanics, and is usually done via a lateral tap in the conduit (e.g., endotracheal tube, cannula, or mouthpiece) leading into the subject's airway. Such pressure measurements, however, may be severely affected by the Bernoulli effect if the diameter of the conduit is small and the gas flow through it sufficiently high. We present in this note a simple method of assessing whether or not the Bernoulli effect is important in any particular situation. The technique involves comparing the pressure-flow relationships of the conduit obtained both by blowing air through it from one end and sucking air in the reverse direction by applying negative pressure at the same end. If the resistance of the conduit is the same for gas flow in both directions, then half the magnitude of the difference between the two pressure-flow relationships gives the magnitude of the Bernoulli effect pressure. We give results of an experimental situation in which this was the case. We also show that those conditions under which the Bernoulli effect is likely to be a problem are also those under which the velocity profile is likely to be approximately flat, thereby permitting the magnitude of the Bernoulli effect to be easily calculated.

Air Pressure↗
PubMed1992

Validation of respiratory inductance plethysmography ("Respitrace") for the measurement of tidal breathing parameters in newborns.

INTRODUCTION: The ratio of the time to reach peak (maximum) tidal expiratory flow (Tme) to total expiratory time (Te) is smaller in infants who later develop lower respiratory tract disease. In previous studies infants have been sedated and flow measured using a pneumotachograph with face-mask. These methodological factors are known to affect tidal breathing, and the frequent need for sedation limits the use of the technique to relatively small studies. The aim of this study was to validate uncalibrated respiratory inductance plethysmography (Respitrace) to measure Tme/Te in unsedated newborns. METHODS: Nineteen normal term infants were studied during quiet sleep. Agreement between Tme/Te measured directly using a pneumotachograph and with Respitrace was assessed in 15 infants. Repeatability of the Respitrace technique was assessed in 10 infants. RESULTS: The mean Tme/Te for the 19 infants using Respitrace was 0.46 (S.D. 0.14). The mean difference between Tme/Te obtained using Respitrace and that measured with a pneumotachograph was 0.014; 95% of Respitrace readings were between -0.042 and 0.070 of the pneumotachograph values. The mean difference between repeat Respitrace values was 0.02 with 95% of the second measurements within 0.066 of the first. CONCLUSIONS: These results indicate that Respitrace can be used to determine Tme/Te accurately.

Evaluation Studies as Topic↗
PubMed1992

The epidemiology of acute epiglottitis in children in Western Australia.

A comprehensive case definition was used to study all cases of epiglottitis that occurred in children under 15 years of age in Western Australia during a 5 year period. There was microbiological evidence of Haemophilus influenzae type b infection in 71% of 103 cases of epiglottitis. Seventy-five per cent of cases occurred in children under 5 years of age. In this age group, the estimated annual incidence (13.5 episodes per 100,000) was significantly lower than that reported in Victoria (22.7 per 100,000). The case definition of invasive H. influenzae type b disease used for surveillance purposes in Canada was more sensitive than the definitions used in the United States or England and Wales, yet even the Canadian definition could have detected only 65% of the cases of epiglottitis that occurred in Western Australia. A simple and sensitive surveillance system which could be used to monitor the impact of H. influenzae type b immunization in Western Australia is proposed.

Acute Disease↗
PubMed1991

Do wheezy infants recovering from bronchiolitis respond to inhaled salbutamol?

Wheezy infants, less than 6 months of age, were given either inhaled salbutamol or saline in a double-blind study. A significant change in maximal flow at functional residual capacity (VmaxFRC) was defined as being greater than twice the coefficient of variation of the baseline measurements. There was no difference in the infants' response to saline or salbutamol. Wheezy infants, less than 6 months of age, do not have an increase in VmaxFRC following a single dose of inhaled salbutamol.

Acute Disease↗
PubMed1991

Pulmonary mechanics and outcome of neonates on ECMO.

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

Airway Resistance↗
PubMed1991

Lack of vagal influence on pulmonary visco-elasticity in puppies.

We recently demonstrated that most of the change in lung function following inhaled histamine in 8-10 week old puppies was due to changes in the tissue visco-elastic properties and argued that vagally-mediated reflexes may be responsible for this phenomenon (Sly and Lanteri, J. Appl. Physiol. 1990; 68: 1562-1567). To test this hypothesis we compared 5 puppies treated with inhaled lignocaine or bilateral cervical vagotomy did not alter baseline pulmonary mechanics and there were no differences in the response to histamine challenge between the three groups. These results show that vagal reflexes, mediated via the central nervous system, are not involved in the response of the pulmonary tissues to inhaled histamine, but do not exclude the possible involvement of local axonal reflexes.

Administration, Inhalation↗
PubMed1991

Inhaled therapy in paediatrics.

Inhalation of aerosols in the mainstay of treatment of asthma and can be useful in treating children with cystic fibrosis. The most efficient method of delivering aerosol to children depends on the age and clinical condition of the child. The most rational dosage schedule for nebulized drugs appears to be to weight-correct the dose added to the nebulizer solution.

Adrenergic beta-Antagonists↗
PubMed1991

Histamine-induced constriction of canine peripheral lung: an airway or tissue response?

We compared the histamine responsiveness of peripheral airways (less than 6.0 mm diam) and parenchymal tissues in eight anesthetized paralyzed open-chest mongrel dogs. We measured pressure in a peripheral bronchus by using an antegrade wedged catheter and pressure in the alveolar region subtended by the wedged bronchus by using an alveolar capsule. Sinusoidal volume oscillations at a frequency of 0.5 Hz were delivered by a linear motor pump into the segment through the wedged catheter. We calculated the resistance of the segment (Rseg) and partitioned Rseg into tissue viscance (i.e., proportional to the resistive pressure drop between the alveolus and the pleura) and peripheral airway resistance. Measurements were taken under baseline conditions and after delivery of increasing concentrations of aerosolized histamine (0.1 micrograms/ml to 100.0 mg/ml) into the segment. We found that the histamine responsiveness of the peripheral airways and lung tissues varied markedly within a given dog. In four of eight dogs the airways were more responsive to histamine, in three of eight the tissues were more responsive, and in one of eight the response was equivalent at the two sites. We conclude that in a given animal, there is marked heterogeneity in the histamine responsiveness of the peripheral airways and parenchymal tissues and that either may dominate responsiveness in the peripheral lung.

Animals↗
PubMed1991

Partitioning of pulmonary responses to inhaled methacholine in puppies.

Twelve open-chest mongrel puppies, 8-10 wk old, were studied to localize the site of action of inhaled methacholine within the lungs. Six puppies were challenged with methacholine aerosols and six were challenged with an equal number of nebulizations of normal saline (control group). Pulmonary mechanics were measured during mechanical ventilation and after midexpiratory flow interruptions. Alveolar pressure was measured to allow the partitioning of pulmonary mechanics into airway and tissue components. Good matching between airway opening and alveolar pressures was seen throughout the study. After methacholine challenge, lung resistance increased fivefold. Increases in airway resistance and in the parameters reflecting tissue viscoelastic properties contributed to this increase in lung resistance. Dynamic lung elastance also increased threefold. The response of the methacholine group was statistically different from that of the control group. These data indicate that both the airways and pulmonary parenchyma contribute to the response to inhaled methacholine in 8- to 10-wk-old puppies.

Administration, Inhalation↗
PubMed1991

Site of action of hypertonic saline in the canine lung.

The site of action of inhaled hypertonic saline was determined in 8- to 10-wk-old puppies by combining measurements of respiratory mechanics, made during mechanical ventilation and after midexpiratory flow interruptions, with direct measurements of alveolar pressure. Under both control conditions and after inhalation of 10% saline, we were able to partition lung mechanics into components representing the airways and tissue viscoelastic properties. Hypertonic saline challenge altered lung mechanics by increasing airway resistance and did not have any effect on elastic or viscoelastic properties of the lung.

Albuterol↗
PubMed1991

Disturbance in respiratory mechanics with extreme truncal flexion during anaesthesia in children.

Respiratory mechanics were studied in five anaesthetised children, aged 3 to 33 months undergoing urological surgery, in both the supine position and with extreme truncal flexion. Extreme truncal flexion was associated with a reduced respiratory system compliance. Dynamic compliance decreased significantly, by 30% (range 12-55%) and static compliance decreased significantly, by 40% (range 18-65%). There were no changes in respiratory system resistance. Tidal volume was also significantly reduced (mean 20%) despite a significant increase (mean 22%) in peak ventilator pressure. These changes in mechanics must be recognised to avoid alveolar hypoventilation, with a consequent decrease in gas exchange during surgery.

Anesthesia, General↗
PubMed1991

Pulmonary function in a hospital population of asthmatic children.

Traditionally, assessment of control of pediatric asthma has relied on symptoms reported by the child and his or her family, and on clinical examination at office visits. A survey of the pulmonary function of 100 clinically stable asthmatic children, recruited from the outpatient clinics of the Royal Children's Hospital, Melbourne, Australia for a clinical drug trial was performed. Correlation of baseline pulmonary function with symptom scores recorded at home and home monitoring of peak expiratory flow variability (PEFV) found that a third of these clinically stable asthmatic children had an abnormal FEV1 and half had an abnormal FEF25-75; however, there was no correlation between symptom scores and FEV1 or PEFV. Objective measurements of pulmonary function are needed to ensure good asthma control. Home monitoring of peak expiratory flow can provide a valuable aid for the management of pediatric asthma.

Administration, Inhalation↗
PubMed1991

Non-invasive determination of alveolar pressure during mechanical ventilation.

The development of inadvertent positive end-expiratory pressure (PEEPi) in ventilated infants is of clinical relevance and difficult to measure non-invasively. A method for estimating end-expiratory alveolar pressure by applying a multiple regression analysis to airway opening pressure, flow and volume recordings during mechanical ventilation was evaluated. In eight open-chested, paralysed and mechanically ventilated mongrel dogs, alveolar pressure was measured directly with "alveolar capsules". Alteration of ventilation patterns and addition of a resistive element were used in three dogs to induce different levels of PEEPi. End-expiratory alveolar pressure measured directly and determined from multilinear regression of airway opening pressure correlated well (mean error 0.06 +/- 0.53 (+/- SD) hPa, limits of agreement -1.16 to +1.04 hPa). The other five dogs received inhalation challenges, two with histamine, two with hypertonic saline and one with methacholine resulting in a mean increase of respiratory system resistance of 230% (range 141-489%) of the baseline values. The mean error in determining PEEPi was 0.54 +/- 0.37 hPa, the limits of agreement were -0.20 to 1.28 hPa. The method was then applied to seven mechanically-ventilated children (aged 2 months to 8 yrs, weight 4.9-23.5 kg) and the results were compared to the pressure at which inspiration began (equalling PEEPi). Seventy eight measurements were performed during open heart surgery, while compliance changed by between 3 and 186% of baseline values due to the surgical procedures. PEEPi estimated by multiple regression agreed well with the pressure at which inspiration began (mean difference 0.25 +/- 0.68 hPa, limits of agreement -1.12 to 1.62 hPa).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Effect of the thermodynamics of an infant plethysmograph on the measurement of thoracic gas volume.

Adult plethysmographs have frequency responses that are essentially flat over the range of frequencies encountered in the measurement of thoracic gas volume (TGV). An infant plethysmograph is necessarily much smaller than an adult model. This means that there is a smaller mean distance over which heat diffusion must occur between the air in the plethysmograph and its walls. This in turn leads to a much reduced thermal time constant. We examined the effects of thermal time constant of a 60 L infant plethysmograph on measurements of TGV in infants. The thermal time constant was measured by rapidly injecting 20 mL of air into the plethysmograph, and found to be 0.16 +/- 0.09s when the box was empty. We calculated from this time constant that measurements of TGV should be quite dependent on the frequency at which the associated panting maneuvers are performed. TGV was measured in 5 infants less than 6 months old in the recovery phase following acute viral bronchiolitis. When we performed a digital correction of the measurements, to compensate for the thermal time constant of the plethysmograph, the TGV values decreased by a mean of 12%. Agitating the air in the plethysmograph with a fan decreased the thermal time constant of the box and reduced measured TGV by a mean of 8.4%. These results indicate that thermodynamics of infant plethysmographs can be an important source of error in TGV measurements.

Algorithms↗
PubMed1990

Should TGV be measured from end-inspiratory occlusions rather than end-expiratory occlusions in wheezy infants?

It has been suggested that thoracic gas volume (TGV) measured in infants in a plethysmograph most accurately represents true lung volume when calculated from end-inspiratory airway occlusions. The rationale proposed is that pressure measured at the mouth underestimates alveolar pressure more at end-expiration than at end-inspiration, presumably due to small airway closure, and this results in greater overestimation of TGV. To investigate this possibility we calculated TGV in 40 wheezy infants from occlusions at both end-inspiration (TGVei) and end-expiration (TGVee) using a 60 L whole body plethysmograph. TGV was corrected for equipment dead space and tidal volume. When a significant change in TGV was defined as lying outside the 95% confidence interval of the TGVee measurements, 8 of the 40 infants tested had significantly higher TGV values measured from occlusions made at end-expiration, while two infants had significantly lower TGV values measured from occlusions made at end-expiration. This trend was not more common in infants with "concave" flow-volume curves. Although it is technically easier to make occlusions at end-expiration, occluding at end-inspiration may minimize errors of TGV measures in a few individuals due to small airway closure at low lung volumes.

Bronchiolitis, Viral↗
PubMed1990

Effect of forced expiration on thoracic gas volume in wheezy infants.

Partial expiratory flow-volume curves are commonly used in infant pulmonary function testing. The flow measurements are volume dependent and thoracic gas volume (TGV) is often measured in conjunction with forced expiratory maneuvers. Since it is not possible to make continuous, simultaneous measurements of TGV during forced expiration, it is assumed that lung volume returns to its original value after forced expiration. To test this assumption we measured TGV using a whole body plethysmograph in 14 wheezy infants before and after a series of forced expirations produced with an inflatable jacket. Forced expiration did not cause a significant change in group mean TGV measurements. Examination of individual data did not show any systematic difference between TGV measured before and after forced expiration. These results suggest that repeated forced expirations do not alter TGV within the time scale of usual pulmonary function testing protocols.

Bronchiolitis, Viral↗