Biomedical subjects
H Simpson
Publications and source records attributed to H Simpson.
Gastro-oesophageal reflux and apnoeic pauses during sleep in infancy--no direct relation.
We studied the relation of gastro-oesophageal reflux with apnoea during sleep in 24 infants with antecedent respiratory abnormalities and/or proven gastrooesophageal reflux (GOR), by combined lower oesophageal pH and polygraphic monitoring. GOR, indicated by pH less than 4, was confirmed in 24 infants. There were no episodes of prolonged (greater than 20 s) central apnoea (CA). Fifty-six mixed or obstructive breathing episodes were identified in 12 infants (14 studies), of which 28 lasted between 3 and 6 s. Bradycardia (heart rate less than less than 80 beats/min for 10 s was not observed. There were 80 falls in transcutaneous oxygen (PtcO2 greater than 5 mmHg) but only 6 exceeded 10 mmHg and one 20 mmHg. There was no relationship between GOR and obstructive episodes in terms of frequency, duration or temporal occurrence, except in one infant. There were 1276 gross body movements, mainly during active or indeterminate sleep and, of these, 7% were associated with decreases in pH to less than 4. Movements occurred during the 60 s period preceding 83% of pH decreases greater than 1 pH unit compared to only 30% in the 60 s succeeding a pH drop. We conclude that, while GOR and obstructive episodes may co-exist in the patient groups studied, decreases in pH in the lower oesophagus do not usually induce either central or obstructive apnoea, and vice versa. Of the variables monitored, only gross body movements were temporally associated with pH drops, and usually preceded them.
Observations on gastro-oesophageal reflux, central apnoea and heart rate in infants.
Respiratory movements and heart rate were monitored continuously during the course of 2 h radionuclide studies to detect gastro-oesophageal reflux (GOR) in 22 infants following a milk feed. Twenty infants had GOR, to upper oesophageal/pharyngeal level in 19, and 17 had central apnoea between 3 and 15s. Prolonged central apnoea (greater than 20s) was not observed. Bradycardia, defined as a heart rate less than 80 beats/min for 10s or more, was observed in only 1 infant who did not have GOR. No correlation was found between the number or duration of reflux episodes and the frequency of respiratory pauses between 3 and 17s. When data from individual infants were examined a possible temporal relation between the occurrence of GOR and central apnoea was seen in only two infants; in each case, detailed examination suggested that apnoea was more closely associated with sleep than with GOR. Although the respiratory monitoring system did not include airflow sensors, the almost complete absence of bradycardia suggested that prolonged obstructive apnoeas did not occur. We conclude that any relation between GOR and central apnoeas less than 15 s is not of a direct cause/effect nature.
Reproducibility of 24 hour oesophageal pH studies in infants.
Thirteen infants who had undergone 24 hour oesophageal pH monitoring to diagnose gastro-oesophageal reflux had a second study carried out to see if the results were reproducible. The studies were done without restricting the babies' activities. Appreciable differences were found, the percentage of the total time during which the pH was less than 4 varying by up to 3.7-fold between the two tests. The differences were largely the result of biological rather than technical variability. From these results estimates were made of the reliability of a single diagnostic study and the size of changes that would be necessary to show the effect of treatment. These findings have a considerable impact on the diagnosis of abnormal gastro-oesophageal reflux and its response to treatment whether using 24 hour pH monitoring or any other method of measurement.
Airway function in infants with vascular rings: preoperative and postoperative assessment.
Aortic arch anomalies in infancy often cause intrathoracic airway obstruction. Airway function was assessed as part of the diagnostic evaluation in six symptomatic infants both by plethysmography and using a chest compression technique to obtain partial flow-volume loops. Two infants had normal intrathoracic airway function and their symptoms were unrelated to aortic arch abnormalities. The remaining four had complete vascular rings (three double aortic arch, one pulmonary sling) and had increased expiratory airway resistance (Raw) (mean Raw = 700% predicted) and greatly decreased maximum flow rates at functional residual capacity (VmaxFRC; mean VmaxFRC = 34% predicted) with gross shape abnormalities of the flow-volume loop. Postoperatively airway function was substantially improved (mean Raw = 175% predicted, VmaxFRC = 79% predicted) but some abnormality of flow-volume loop shape remained, suggesting that tracheal dynamics were not completely normal in the early postoperative period.
Latent sensitisation to respiratory syncytial virus during acute bronchiolitis and lung function after recovery.
To determine whether latent sensitivity to respiratory syncytial virus antigen(s) occurs after infection, 27 infants with acute bronchiolitis were studied and compared with 15 hospital controls. Blood was collected for whole blood challenge, and histamine release was measured by a high performance liquid chromatography technique with fluorometric detection. There was a significantly greater histamine release to respiratory syncytial virus antigen(s) in those with bronchiolitis than in controls, expressed either in amount (median 154 nmol/l compared with 104 nmol/l) or percentage release (median 20% compared with 3%). There was a significant difference between index and control groups in terms of individual histamine responses. These findings strongly suggest that infants develop latent sensitivity to respiratory syncytial virus antigen(s) during the course of acute bronchiolitis. Serial lung function tests were performed in 15 infants. All infants had abnormalities of lung function at some stage, but the small numbers of subjects precluded comparison between 'sensitised' and 'non-sensitised' infants. Further study is indicated to define the relation of latent sensitisation and subsequent bronchial hyper-responsiveness after respiratory syncytial virus infection in infants.
[Antilipemic agents and postprandial lipidemia].
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High-performance liquid chromatographic technique for the rapid determination of histamine in both the plasma and cellular components of blood.
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Cough flow-volume relationships in normal and asthmatic children.
The flow-volume profile of a maximum voluntary cough resembles that of a maximum expiratory flow-volume (MEFV) curve with superimposed transient peak flows at the onset of each cough effort and portions of zero flow corresponding to periods of glottis closure. A straight line (the cough slope) can be drawn through the transient peak flows, and the ratio of MEFV-equivalent flow to the cough peak flow can be calculated. This cough ratio has been shown to fall during adult life and may be related to changes in airway compliance and cross-sectional area with age. The present study investigated the cough ratio, cough slope, and maximum flows measured from the cough flow-volume curve in a group of normal children aged 7 to 16 years. Maximum flows and the cough slope increased with height, but the cough ratio did not change with growth or age. In a similar group of asthmatic children, baseline measurements of cough showed a reduction in cough peak flow rates, MEFV-equivalent flow, and the cough ratio. These changes are related to alterations in airway compliance and cross-sectional area and are partly reversed following inhalation of a bronchodilator.
Measurement of lung volumes during active and quiet sleep in infants.
The question of whether functional residual capacity (FRC) falls in infants during active sleep has been clouded by studies using different subject groups and techniques for measurements of lung volume and determination of sleep state. Twenty healthy full-term infants within the first week of life participated in the present study. Neurophysiological and behavioral criteria were used to define sleep state, and measurements of FRC were made using a specially constructed closed-circuit helium dilution system. Regularity of respiration was recorded using magnetometers on the chest and a modified respirator monitor. Results showed that no significant changes in FRC occurred, related either to sleep state or to regularity of respiration. In addition, we failed to detect any differences in FRC between the sexes.
Sleep phase and gastro-oesophageal reflux in infants at possible risk of SIDS.
The association between gastro-oesophageal reflux and sleep state in 24 infants with confirmed or suspected gastro-oesophageal reflux was studied by monitoring both the pH in the lower oesophagus and polygraphic tracings made during sleep at night. Gastro-oesophageal reflux during the night was confirmed in 20 infants. Three hundred and sixteen precipitous drops of more than one unit of pH were recorded during the studies, 186 during periods of wakefulness. Of 130 drops in pH during sleep, 62 (48%) began during active sleep and 62 during indeterminate sleep. Of the latter, 56 (90%) were associated with brief gross body movements. Only five of the drops in pH (4%) began during quiet sleep. Gastro-oesophageal reflux stopped during active sleep on 56 occasions (43%), in indeterminate sleep in 62 (47%), and in quiet sleep in 12 (9%). Episodes of gastro-oesophageal reflux starting or ending in quiet sleep were uncommon. The occurrence of gastro-oesophageal reflux during active sleep may partly explain why reflux during sleep is a risk factor for pulmonary disease.
Respiratory control in infants at increased risk for sudden infant death syndrome.
There is much debate relating to possible abnormalities in respiratory control mechanisms in infants considered at increased risk for sudden infant death syndrome (SIDS). The P0.1 occlusion technique was used to assess the central respiratory response to hyperoxic hypercapnia during quiet sleep in 21 normal infants, 13 siblings of SIDS victims, and 17 infants with apparent life threatening events. The slope of P0.1 plotted against carbon dioxide concentration increased exponentially with age, independent of body weight in each group. Birth weight has a significant effect on slope with a lower weight predisposing to a lower slope. Siblings as a group had a significantly lower slope at any given age than normal infants, whereas the infants who had had apparent life threatening events were not significantly different from the controls. As intragroup variation in both siblings and control groups greatly exceeded the significant intergroup differences observed, the technique cannot identify individual infants as belonging to one or other group.
Monitoring for central apnoea in infancy--limitations of single channel recordings.
Apparent central apnoea (absent breathing movements) detected by monitoring movement of the thoracic wall was compared with simultaneous detection by abdominal wall movement. Eighteen infants provided one or more 24 hour recording of heart rate (electrocardiography), thoracic respiration (transthoracic impedance), and abdominal wall movement (pressure sensitive capsule distortion). Detection of true apnoea, recognition of artefact, and measurement of the duration of true apnoea were all improved when two channels of respiratory monitoring were used in combination. We recommend that any study purporting to observe breathing patterns by indirect recording of respiratory movement will be more reliable if more than one channel of respiratory movements is recorded simultaneously. Further, in infants no estimation of duration of central apnoea can be made on the basis of either a transthoracic impedance record alone or an abdominal wall movement sensor alone. Comparison of findings among studies using different single channel recordings are unlikely to be meaningful.
Vomiting and gastro-oesophageal reflux.
During radionuclide scans in 82 infants and children gastro-oesophageal reflux extending to the upper oesophageal/laryngeal level was detected in 636 one minute frames. Only 61 (9.6%) of these frames were associated with vomiting, defined as the appearance of milk at the mouth. Thus the absence of vomiting does not preclude appreciable gastro-oesophageal reflux.
Infantile apnoea and home monitoring.
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Nocturnal cough in asthma.
The timing of nocturnal cough and its association with change in ambient temperature was documented in 11 asthmatic children, median age 5.1 years, while they were receiving continuous prophylaxis. Studies were performed in their homes on three nights. A voice activated system with electronic time signal recorded coughing. Ambient temperature was recorded every five minutes throughout the night on a Grant Squirrel data logger. Ten children coughed on 27 nights with a median of six bouts of coughing a night (range 0-272). The cough rate in the two hours after going to bed was significantly higher than the cough rate in the middle of the night (2-4 am or 4-6 am). Peak coughing times were 7-9 pm and 6-8 am. The room temperature was lowest between 5 and 7 am. There were no significant differences between cough rates during periods of rapid temperature change (more than 1 degree C an hour). The timing of nocturnal cough observed in this study differed from the known basophase of circadian cycles described for adults and children.
Vacuum extraction or forceps?
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Sleep apnoea during upper respiratory infection and metabolic alkalosis in infancy.
Three to four hour polygraphic sleep studies were carried out in 10 infants, five with upper respiratory infection and five with metabolic alkalosis secondary to vomiting during and after recovery from illness. During upper respiratory infection, the main abnormality detected was brief (greater than 3 less than 6 seconds) or prolonged (greater than 6 seconds) attacks of obstructive apnoea. Other indices of apnoea were similar to recovery data. Gross body movements were also increased. In infants with metabolic alkalosis indices of central apnoea were significantly increased when compared with recovery or case control data. Prolonged (greater than 15 seconds) attacks of central apnoea and obstructive apnoea (greater than 6 seconds) were only observed during illness. Gross body movements and periodic breathing were also increased. These findings suggest that the functional consequences of apparently 'mild' illnesses in young infants may be greater than is generally suspected and perhaps relevant to mechanism(s) of death in sudden infant death syndrome.