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C S Beardsmore

Publications and source records attributed to C S Beardsmore.

53 records · Page 3Linked to original sources
PubMed1987

A non-invasive method for measuring inspiratory muscle fatigue during progressive isocapnic hyperventilation in man.

Eleven normal adults each performed a ten minute progressive isocapnic hyperventilation (PIHV) test in which ventilatory levels were increased every two minutes. All subjects exhibited mechanical fatigue by failing to maintain the target of 80% of maximum voluntary ventilation (MVV). The mean ventilation at this level was 67.5 +/- 1.4% MVV. This fatigue was accompanied by a fall in transdiaphragmatic pressure. During the test the EMG of the sternomastoid (SM) was monitored by surface electrodes and was analyzed using fast-fourier transform. The centroid frequency (Fc) fell as ventilation increased, and correlated negatively with the inability to achieve target ventilation(r = -0.99, p less than 0.015). Five subjects performed the test while the diaphragmatic EMG was recorded from an oesophageal electrode (DIes) and from surface electrodes (DIs). The Fc of DIes fell with increasing ventilation levels (r = -0.95, p less than 0.05) and there was a correlation between the Fc changes of both DIes and the SM (r = -0.92, p less than 0.001). The Fc of DIs did not correlate with either mechanical performance or the Fc of DIes, because of contamination of surface signals by signals from expiratory muscles. It is concluded that the PIHV along with surface monitoring of EMG activity from the sternomastoid can serve as a non-invasive method for evaluating inspiratory muscle fatigue.

Adult↗
PubMed1987

Partial forced expiratory flow-volume curves in young children during ketamine anesthesia.

Maximal flows at functional residual capacity (VmaxFRC) from partial forced expiratory flow-volume (PEFV) curves were obtained in 14 normal preschool children (8 boys, 6 girls) of average age 44 mo, under general anesthesia before elective surgery. PEFV curves were generated from end inspiration by rapid compression of the chest wall with an inflatable jacket. VmaxFRC, expressed in milliliter per second, correlated linearly with height, weight, age, and FRC in milliliter and milliliters per kilogram. The best correlation of VmaxFRC (ml/s) was to height to the power of 2.47, which agrees with the results predicted by wave-speed theory. Mean FRC-corrected VmaxFRC was 2.42 +/- 0.50 (SD) FRC's/s with no significant difference between boys (2.35 FRC's/s) and girls (2.51 FRC's/s). There was no correlation between lung-size corrected VmaxFRC and height, weight, or age, but it tended to decrease with increasing FRC. The intersubject variability for VmaxFRC was reduced by normalizing for FRC, and was significantly better than that reported for awake children. This can be attributed to the greater control over volume history and more reliable maximal flow generation during anesthesia. The intrasubject coefficient of variation (CV) for VmaxFRC was 12.2%, and the intersubject CV was 20.0%. The difference may represent the variability due to dysanapsis. It is concluded that dysanapsis is not a prominent factor in children of this age group. In addition, the similarity of the regression equation for VmaxFRC vs. height to that of FRC vs. height supports the concept of equidimensional growth of the airways and lung parenchyma.

Anesthesia, General↗
PubMed1987

Functional residual capacity in healthy preschool children lying supine.

Functional residual capacity (FRC) was measured by the closed-circuit helium dilution method in 41 supine healthy children 1 month to 8 yr of age. In 20 children, the measurement was carried out while they were awake, and in the others, who were less cooperative, testing was done during ketamine anesthesia before elective surgery. There was no significant difference in the FRC values between these groups, and they were subsequently analyzed as a single group. For males and females separately and combined, FRC correlated significantly with height, age, and weight, both with linear and nonlinear regression analyses. No significant difference between the sexes was found. The best correlation of FRC was with height; the linear equation being FRC (ml) = -457.3 + 8.8 X height (cm) (r2 = 0.662), and the nonlinear equation being FRC (ml) = 0.0052 X [height (cm)]2.44 (r2 = 0.827).

Child↗
PubMed1986

Airway resistance measurements throughout the respiratory cycle in infants.

Using a constant-volume infant whole-body plethysmograph containing a heated rebreathing bag, we have been able to measure airway resistance (Raw) throughout the respiratory cycle using a computer-based technique. Data from the plethysmograph transducers are sampled at 60 Hz for the calculations and Raw is calculated at each point sampled during the breath, with appropriate corrections for absolute lung volume. It was found that in most cases Raw varied less with respect to tidal volume than to tidal flow. Various patterns of Raw change in relation to tidal volume were found. These included an elevated but relatively constant resistance, a progressively rising expiratory resistance, and in 3 infants with laryngomalacia, a progressively rising inspiratory resistance. It was also found that the dynamic performance of the rebreathing bag was such that considerable errors would occur if apparatus resistance was assumed to be constant and so the actual apparatus resistance at each point was subtracted from the total resistance to give Raw. In conclusion, Raw is not constant throughout the respiratory cycle in infants and the pattern of change conveys additional information.

Airway Resistance↗
PubMed1986

Can thoracic gas volume be measured in infants with airways obstruction?

Thoracic gas volume (Vtg) was measured in a whole-body, infant plethysmograph in 46 infants with recurrent wheezing after bronchiolitis, 25 infants with cystic fibrosis, and 6 infants without overt lung disease during the first 13 months of life. When related to weight or length, 56.5% of the bronchiolitic infants had low Vtg values, which were more than 2 SD below their predicted normal. The Vtg of the other groups was normal or above. The bronchiolitic infants with Vtg values in the normal range had more severe airways obstruction and it is probable that their Vtg values were also underestimated. Investigation of possible sources of technical or experimental error failed to reveal any explanation for the low Vtg in the bronchiolitic infants. In 5 infants, Vtg determined plethysmographically was correlated linearly to functional residual capacity determined by helium dilution, although Vtg values were greater in all. The administration of albuterol or treatment with steroids failed to make significant changes in Vtg in the bronchiolitic infants. It is suggested that there is a physiologic basis for the presumed underestimation of Vtg in wheezy infants after bronchiolitis, either because of uneven alveolar pressure changes within the chest leading to the effective exclusion of a portion of the lung volume or because there are some alveolar units with very low compliance that change little in volume during respiratory efforts against an occlusion. These results call into question the validity of the plethysmographic measurement of Vtg or airway resistance in these infants. If the error in Vtg is due to uneven alveolar pressure changes, it is suggested that the calculated specific airway conductance is probably correct.

Airway Obstruction↗
PubMed1985

The effect of ketamine on the functional residual capacity in young children.

The effect of ketamine on the functional residual capacity (FRC) was measured in nine ASA class I children prior to elective surgery. FRC was determined by the closed-circuit helium dilution method on the day prior to surgery in the awake state and also following induction of anesthesia on the day of the operation. Anesthesia consisted of ketamine by continuous intravenous infusion following preanesthetic sedation with atropine and triclofos or flunitrazepam. There were no significant differences in FRC between the measurements in the awake state and anesthetized (392 +/- 43 SEM ml, and 411 +/- 53 SEM ml, respectively), and the authors conclude that ketamine does not affect resting lung volume in young children.

Anesthesia, General↗
PubMed1983

Esophageal pressure in infants at elevated lung volumes and positive airway pressure.

The measurement of esophageal pressure changes (delta Pes) under conditions of elevated lung volume or continuous positive airway pressure (CPAP) was investigated in a group of 17 infants by use of an esophageal balloon. Eleven of the infants were studied in a whole-body plethysmograph, and lung volume was increased by a volume injection technique. Reproducible measurements of lung volume in the plethysmograph showed that changes in mask pressure (delta Pm) were accurate during airway occlusion in 10 of the 11 infants. A progressive elevation of the ratio delta Pes/delta Pm during respiratory efforts against occlusion at lung volumes above the tidal range was observed in 8 of the 11 infants. In only one of these infants could the error have been in delta Pm measurement. Of seven infants (including one common to both studies) studied under CPAP, six also showed this effect, which occurred predominantly in very young or preterm infants. Changes in esophageal pressure in infancy, measured at high lung volumes or pressures, may not be representative of mean pleural pressure changes.

Esophagus↗
PubMed1982

Bronchial hypersecretion in preterm neonates.

During an 18-month period, 11 preterm infants with birthweights between 700 and 1560 g (mean 1.2 kg) developed excessive tracheobronchial secretions during intensive care. No single obstetric factor was incriminated. Copious, viscous, tracheobronchial secretions were noted at about 5 days during mechanical ventilation via endotracheal tube causing recurrent segmental collapse, hypoxia, and hypercapnia (median peak PCO2 13.5 kPa). All infants were treated with frequent bronchial lavages and continued intermittent positive pressure ventilation, together with high concentrations of oxygen. No infant died, but morbidity was high. Tracheostomy was performed on 2 infants (one at age 3 months, because of severe croup) and 2 others had clinical or physiological evidence of upper airways narrowing. Follow-up studies showed that this group had more problems of airways obstruction throughout the first year of life as well as increased lung stiffness. The hypersecretion group showed a higher incidence of chronic lung disease. Likely aetiological factors were sought. Contamination of the mechanical ventilation equipment by detergent and activated glutaraldehyde was found; this could have been a contributory factor.

Airway Obstruction↗
PubMed1982

Pulmonary sequelae of neonatal respiratory distress in very low birthweight infants: a clinical and physiological study.

Twenty infants, mechanically ventilated in the neonatal period for respiratory distress syndrome, were compared with 15 healthy controls, matched for birthweight(less than 1501 g) but greater in mean gestational age. Clinical features and lung mechanics (by whole body plethysmography) were recorded at 6-monthly intervals until about one year. THe neonatal course of the mechanically ventilated infants was commonly complicated by tracheobronchial hypersecretion and the later course by a fairly high incidence of lower respiratory tract illness. In this group, thoracic gas volume, dynamic compliance, pulmonary and airways conductance were all abnormal during the middle 4 months of the first year and reverted towards normal towards the end of the first year. The control group had normal lung mechanics. Early lung function tests were of limited value in predicting later lower respiratory tract illness, which was more common in boys, after neonatal mechanical ventilation for longer than 24 hours or raised ambient oxygen for longer than 5 days. There were few predictive physical signs. In this group of very low birthweight infants, respiratory distress syndrome of sufficient severity to require mechanical ventilation led to significant physiological and clinical disturbances of lung function which lasted into the second 6 months of life and which were particularly severe in those who had recurrent lower respiratory tract illness.

Female↗
PubMed1982

Antenatal dexamethasone and subsequent lung growth.

Long-term effects on lung size and lung mechanics were sought in a 12-month follow-up study of 15 infants of very low birthweight (less than 1500 g), 7 of whom had been exposed to antepartum dexamethasone (mean dose 21 mg). None of the infants had significant neonatal respiratory disease. No differences were found between the dexamethasone-treated and control groups for thoracic gas volume, dynamic pulmonary compliance, or airways resistance during the first year of life. This suggests that the growth and development of the lungs are not adversely affected by antepartum exposure to dexamethasone.

Body Weight↗
PubMed1982

Problems in measurement of thoracic gas volume in infancy.

Thoracic gas volume (TGV) was measured with a whole-body plethysmograph in 20 infants at functional residual capacity (FRC) and at a series of higher lung volumes achieved by artificial inflation of the lungs with known volumes of air after airway occlusion. There was a discrepancy between the corrected values of TGV measured at high and low lung volumes in nine infants; in six cases TGV measured at high lung volumes exceeded that measured at FRC, and in three cases it was reduced when compared with the measurement made at FRC. These changes were not related to age, size, or clinical status and could be explained by airway closure at FRC, combined with an uneven distribution of pleural pressure.

Gases↗
PubMed1981

Absolute intraesophageal pressure at functional residual capacity in frequency.

Absolute intraesophageal pressure at functional residual capacity (FRC) has been estimated in 15 infants (age 1-30 wk) by the extrapolation of the esophageal pressure-volume relationships to zero balloon volume by use of air-filled balloons in their ranges of infinite compliance. The pressure-volume relationships of the esophageal balloons (length 3.5-5.0 cm, perimeter 1.7-2.5 cm, wall thickness 0.045-0.075 mm) were determined in air and in erect and horizontal positions under water, the behavior of the balloons placed horizontally under water closely approximated that of the balloons in vivo. The mean absolute intraesophageal pressure at FRC was -1.44 cmH2O in eight normal infants and -1.56 cmH2O in seven convalescent infants with a variety of cardiorespiratory disorders. The less negative absolute end-expiratory esophageal pressure in infants when compared with that in adults can be explained by changes in lung elastic recoil, chest wall recoil, or a combination of these factors during the development and growth of the respiratory system from birth to adulthood.

Esophagus↗
PubMed1980

Improved esophageal balloon technique for use in infants.

Esophageal balloons of three different wall thicknesses, two different lengths, and two different diameters were made to assess which type of balloon gave the most consistent and reliable measurements of dynamic compliance (CL) and pulmonary resistance (Rp). The balloons were subjected to in vitro testing to determine their pressure-volume characteristics and working range and then used in infants to compare in vivo results from one balloon to another. The optimal balloon was found to have a length of 35--50 mm, a diameter of 7.6 mm, and a wall thickness of 0.045--0.075 mm. The use of unsuitable balloons or inappropriate volumes of air within the balloon resulted in applied pressures being under-recorded, both in vitro and in vivo, with consequent overestimation of CL and underestimation of Rp during infant lung function tests. Recommendations are made concerning the techniques of making and using esophageal balloons.

Esophagus↗
PubMedDate not supplied

Flow-pressure looping during plethysmography in wheezy infants.

Marked looping of the expiratory portion of the flow-pressure relationship was noted in some infants during measurements of airway resistance in a whole-body plethysmograph while the respired air was maintained at body temperature and humidity. An investigation of 13 infants who had varying degrees of airway obstruction showed that there was a negative correlation (r = 0.72) between the severity of the looping and specific airway conductance (SGaw). An even stronger correlation (r = 0.85) was found between the tangent of the angle of phase lag between flow and pressure (theta) and the forced expiratory time constant (t) obtained from the partial forced expiratory flow-volume curve. Such a relationship would be predicted from a model in which the lung behaved as a simple electrical resistance-capacitance network during expiration. It is suggested that the looping is the result of small airway closure during expiration in wheezy infants, with a consequent rise in resistance and prolongation of the time constant of the lung.

Airway Resistance↗
PubMedDate not supplied

Maximum voluntary cough: an indication of airway function.

Maximum voluntary coughing produces a flow-volume profile which incorporates the characteristics of a maximum expiratory flow-volume curve (MEFV). The cough flow-volume curve also has transient spikes of supramaximal flow, interspersed with portions of zero flow when the glottis is closed. The peak flow rates of the supramaximal flow transients during cough decrease in a linear fashion as lung volume goes down from total lung capacity to residual volume. Cough flow-volume curves have been recorded from forty-two subjects between the ages of 7 and 56 yr. The rate of change of cough peak flow shows a positive correlation with airway conductance measured plethysmographically in children. The ratio of forced expiratory flow to cough peak flow (the cough ratio) expresses the maximum expiratory flow rate during forced expiration as a proportion of that which can be achieved with a cough. The cough ratio declines during adult life, because although there is a fall in cough peak flow with age there is a proportionally greater fall in MEFV-equivalent flow. These investigations explore the information to be gained from cough flow-volume curves by examining the cough in a heterogeneous group of individuals.

Adolescent↗
PubMedDate not supplied

The total compliance of the respiratory system during the first year of life.

Respiratory system compliance (Crs) was measured in 34 spontaneously breathing infants during the first year of life. An occlusion technique was used whereby several expiratory occlusions were performed at different lung volumes within the tidal range. The airway opening pressure generated during a plateau after occlusion was related to the volume included above the end-tidal level by a regression equation. The slope of this equation represented the compliance of the infant's respiratory system; the intercept was significantly different for preterm (-0.5 ml) and post-term (-5.5 ml) infants and may represent the difference between end-expiratory lung volume during tidal breathing and the relaxed functional residual capacity. The values for respiratory system compliance were similar to those previously reported for infants during muscle relaxation. As a function of body length, Crs = 1.58 X length3.13 X 10(-4) ml . kPa-1. The technique described is simple to apply and is independent of oesophageal pressure measurements.

Body Height↗