Biomedical subjects
Publications and source records attributed to I E Hopkin.
We measured total respiratory system compliance (Crs) before and after instilling 25 mg artificial surfactant in 1 ml saline down the endotracheal tube of preterm babies requiring resuscitation at birth, and compared results with data from 6 similar babies receiving saline only. Surfactant did not produce a significant improvement in Crs.
Inflation and oesophageal pressures were recorded simultaneously during bag and mask resuscitation of 9 asphyxiated babies. After half a minute of standard inflation pressures, higher pressures were applied for at least 5 inflations by occluding the blow-off valve. No air entered the oesophagus until a high mean inflation pressure of 5.4 kPa was exceeded. These findings were confirmed in 4 fresh stillborn babies studied similarly. We conclude that resuscitation using bag and mask, applying pressures less than 3.5 kPa, should not lead to gastric distension.
We have investigated the effect of giving two 25 mg doses of dry surfactant powder to the airways of 10 preterm babies with severe idiopathic respiratory distress syndrome requiring intermittent positive pressure ventilation. No useful change in static total compliance or blood gases was seen. We conclude that dry surfactant powder does not have a role in the management of severe idiopathic respiratory distress syndrome.
Intrathoracic pressure and volume changes were measured during the spontaneous first breath in 11 healthy term neonates delivered by emergency caesarean section (CS). Although inspiratory and expiratory rates were higher than those found among babies delivered by elective CS, inspiratory volume was very similar and these babies, unlike those delivered by elective CS, had all formed a functional residual capacity at the end of the first breath. We obtained cord arterial and venous samples for catecholamine analysis concurrently, and found that most of the babies had concentrations of plasma noradrenaline similar to babies delivered by elective CS--high values were found only among infants who had suffered fetal distress. Both catecholamine excretion and method of delivery may be important in the formation of the functional residual capacity at birth.
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Measurements of thoracic volume, inflation pressure, and intrathoracic pressure have been recorded at the resuscitation of nine newborn babies. The initial inflation pressure was maintained for approximately five seconds which produced a twofold increase in inflation volume compared to standard resuscitation techniques and always led to formation of an FRC. When the inflation pressure was increased slowly over three to five seconds, the apparent opening pressure which occurred universally in square wave inflation was rarely seen.
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Nine studies were carried out on seven babies who were having repeated episodes of bradycardia without any clinically obvious apnoea. Their mean gestational age was 31.7 weeks (range 29 to 36 weeks) and the mean birth weight was 1.56 kg (range 1.08 kg to 2.16 kg). Investigations were carried out in a total body plethysmograph. Face mask with a pneumotachograph attached to it measured flow. Tidal volume was obtained by integrating these signals. An oesophageal balloon measured intrathoracic pressure changes and the heart rate was measured from ECG chest electrodes. A total of 172 episodes of apnoea were observed. In 50% of these apnoeas, the airway was closed as determined by the absence of cardiac artefact on the flow signals. Apnoea was associated with bradycardia in just over 25% of all apnoea. It tended to occur early (11 to 14 sec). Whether the apnoea was central or obstructive had no effect on the pattern provided the baby did not make any inspiratory efforts. Inspiration against a closed airway produced bradycardia in over 50% of obstructive apnoea, the heart rate falling precipitously within 1 to 2 sec. These findings indicate that often bradycardias occur too early in apnoea to be due to central hypoxia and must be due to a peripheral mechanism.
Measurements of tidal flow, volume, and oesophageal pressure were recorded on a group of 8 severely preterm infants with periodic respiration. Analysis of the flow trace for evidence of cardiac artefact, and the tidal volume trace to identify at what point of the tidal cycle apnoea starts, indicated that upper airways obstruction was associated with about half these attacks. It is surmised that this is produced by glottic closure.
Ventilatory exchange and endotracheal and esophageal pressures were measured during resuscitation of asphyxiated neonates born by cesarean section. In contrast to spontaneously breathing, vaginally born babies, an opening pressure had to be exceeded before lung expansion occurred. Subsequently there was usually a gradual increase in gaseous exchange over the first few lung inflations. A further rise in lung compliance occurred with the baby's inspiratory efforts. The functional residual capacity was formed with or without active inspiratory efforts by the baby, although gaseous retention occurred more rapidly as a result of the infant's inspiration.
Lung ventilation, endotracheal, and intraoesophageal pressures were measured during standard resuscitation of 20 asphyxiated babies born by caesarean section. The most common response to resuscitation was the production of a large positive intraoesphageal pressure. An opening pressure greater than 2.0 kPa was required to expand the lungs of most of these babies. The need for resuscitation was associated with prolonged maternal anaesthesia before delivery.
Serial measurements of thoracic gas volume revealed no evidence of air trapping in maintenance of functional residual capacity (FRC) in healthy term babies in the first days of life. Tidal pressue/volume and flow/volume analysis demonstrated intermittent air trapping in only 2 of 19 such babies. Artificial FRC reduction by continuous positive external pressure of 7 cm H20 induced grunting in 4 babies, but otherwise had no effect on spontaneous breathing pattern or on dynamic compliance. Group mean total pulmonary resistance rose by 52.9% but only one baby demonstrated evidence of air trapping. Our findings suggest that FRC is maintained in the immediate neonatal period by some means other than air trapping.
Pulmonary mechanics were measured in 22 normal, full-term babies as soon as quiet, regular breathing was established. The method included construction of tidal resistance profiles, by which it was demonstrated that 'air trapping' is probably not the major factor in establishing and maintaining the functional residual capacity immediately after birth.
1. Tidal pressure/volume and flow/volume respiratory loops were constructed from records obtained during 98 studies on 48 neonates of various ages and gestations. Records were obtained with a total body plethysmograph and an oesophageal balloon. Total pulmonary resistance was computed at five separate levels in the breathing cycle and results were expressed graphically as tidal resistance profiles by plotting total pulmonary resistance against percentage tidal volume above functional residual capacity. 2. Values obtained for standard pulmonary mechanical measurements and thoracic gas volume were similar to those of other workers. In addition six distinctive resistance profile patterns were found and related to different breathing patterns. 3. The technique appeared to be particularly useful in identifying air trapping and also demonstrated that total pulmonary resistance is open to misinterpretation when measured only at the mid-tidal-volume level, as is the present convention.
Lung function tests were carried out in the first 6 hours of life on 26 babies born by vaginal delivery and 10 born by caesarean section. The babies born by caesarean section had a mean thoracic gas volume of only 19.7 ml/kg body weight compared with 32.7 ml/kg for the babies born vaginally. We conclude that this is owing to an excess of lung fluid in the babies born by caesarean section.
Simple clinical measurements were performed on a group of 23 very low birth weight babies (less than 1500 g and less than 32 weeks gestation), and combined with pulmonary function studies in 13 cases. The studied included a special single-breath analysis, or Tidal Resistance Profile, which enabled us to detect air trapping. 2 infants developed classical Wilson-Mikity syndrome and 2 further infants exhibited a milder, shorter form of the same disorder. All 4 survived. Results suggest that all infants in this maturity group are at risk of developing Wilson-Mikity syndrome, and that it comprises a wide spectrum of respiratory dysfunction.
Total obstruction of the airways caused all respiratory efforts to stop on 15 occasions in 10 preterm babies. This was not seen in 60 studies on 38 term babies. These findings suggest that failure to achieve an oral airway may not be the only mechanism by which upper airway obstruction might cause the cot death syndrome.