Severe developmental delay and multiple strawberry naevi: a new syndrome?

An 18 month old girl with dysmorphic features, severe developmental delay, multiple strawberry naevi, and capillary naevi is described. No previous report of a similar association of features has been identified.

Response to external obstruction in preterm infants with apnea.

A proportion of preterm infants respond to an external airway obstruction by becoming apneic. We have studied 23 infants (median birthweight, 1.14 kg; gestation, 29 weeks) on 80 occasions, to determine the time course of the response and its relationship with spontaneous apnea occurrence. Upper airway flow was measured with a face mask and pneumotachograph, and a tap was turned intermittently to produce an occlusion. A total of 380 occlusions were analyzed. The infants became apneic during the obstruction on 72 occasions (19%), and after the obstruction on 122 occasions (32%). Both of these events were significantly more common than immediately prior to the obstruction, when apnea occurred on 29 occasions (8%). Of the apneas following occlusion 57% were central in type. The point in the respiratory cycle at which obstruction occurred had no effect on the production of apnea. An obstruction score was calculated for each study. This was the mean of the number of apneas during and after each obstruction, expressed as a percentage of the number of obstructions per study. This score was positively correlated with the number of spontaneous apneas recorded. Obstruction score rose from a mean of 20% during days 0-14, to 34% during days 15-28, and thereafter it declined. This pattern may be relevant to the time course of apnea in susceptible infants.

Episodic bradycardia in preterm infants.

To analyse factors likely to precipitate bradycardia, 27 preterm infants born at 32 weeks' gestation or less were studied on 89 occasions. Polygraphic recordings of electrocardiography, oxygen saturation, and respiratory effort were made. Subsequently, upper airway flow was measured by a mask and pressure transducer. In 605 episodes detected during initial recordings, time of onset of bradycardia correlated positively with apnoea duration, with bradycardia often occurring as respiratory effort resumed. Airway closure occurred in 88% of apnoeas associated with bradycardia during flow measurements, and was significantly more common than in apnoea without bradycardia (64%). We suggest that bradycardia is most commonly a reflex response to the resumption of respiratory effort against a closed upper airway as apnoea is terminated, and that this reflex is potentiated by hypoxaemia.

Is thoraco-abdominal phase relationship an indicator of sleep state?

The phase relationship between ribcage and abdominal movement in 1440 breaths from 12 infants (mean age 3.2 days) showed statistically significant differences between sleep states as judged by physiological criteria. The mean phase difference (+/- 1 SD) was 20 (+/- 16)% in active sleep, 9 (+/- 17)% in indeterminate sleep and 3 (+/- 5)% in quiet sleep (P less than 0.0005). However, the wide scatter within sleep states meant that even the mean value from 50 breaths was not specific enough to delineate sleep state.

Upper airway patency during apnoea of prematurity.

Twenty four preterm infants (median birth weight 1120 g and gestation 29 weeks) were studied on 83 occasions by measuring upper airway airflow. Airway patency was detected by the transmission of cardiac impulse up the airway and airway closure by its absence. A total of 309 apnoeas of at least five seconds' duration were recorded. One hundred and eighty (58.0%) were central, 109 (35.5%) mixed, and 20 (6.5%) obstructive. Airway closure was noted in 47% of apparently central apnoeas. Airway closure occurred as apnoea lengthened; the airway remained patent in 38% of apnoeas of 5-9 seconds, 17% of those 10-14 seconds, and 11% of those 15-19 seconds' duration. Airway closure occurred in every apnoea of greater than or equal to 20 seconds. As a consequence, closed apnoeas were longer than open apnoeas (mean 9.7 v 6.6 seconds). In 72% of mixed apnoeas, airway closure was recorded during the central element and this usually preceded obstructive breaths. In 20% of mixed apnoeas and 15.5% of the total group the airways closed, having previously been patent. This occurred after a mean of 3.5 seconds (range 1-17). Mixed apnoea produced a significantly greater drop in arterial oxygen saturation than central apnoea, but only because of the greater duration of mixed apnoea. Airway closure occurs in both central and mixed apnoea and appears to be important in the pathophysiology of mixed apnoea. Central and mixed apnoea are part of a continuum of airway closure and not separate entities.

Response to tube breathing in preterm infants with apnea.

In order to analyze the effects of maturity and apnea frequency on the respiratory control of preterm infants, we studied their responses to tube breathing using tubes equivalent to two anatomical dead spaces. Ventilation during tube breathing was expressed as a percentage above baseline and compared to an "expected" value calculated from the volume of the added tube. Twenty-seven preterm infants (median birthweight, 1.14 kg.; and gestational age, 29 weeks) were studied on 86 occasions. The percentage of "expected" ventilation increased with post-conceptional age (r = 0.48, slope = 3.12, P less than 0.0005), from a mean of 73% at 26 weeks up to 104% at 36 weeks. Using multiple regression analysis, neither postnatal age nor apnea frequency had any effect once allowance had been made for post-conceptional age. Although the respiratory adaptation of the most immature infants was poor, this study suggests that infants with apnea show no gross deficit in respiratory control, compared to those without apnea.

Apnoea, bradycardia, and oxygen saturation in preterm infants.

To analyse the effects of apnoea and bradycardia on the oxygen saturation (SaO2) of preterm infants and to make recommendations for apnoea alarm limits, polygraphic recordings were made on 89 occasions of 27 preterm infants; 1029 apnoeic episodes were analysed. Reduction in SaO2 was positively correlated with duration of apnoea, but the scatter of results was such that reductions in SaO2 of up to 40% occurred with apnoeas of less than 10 seconds duration. The median initial SaO2 was significantly lower in those episodes that resulted in bradycardia (92% compared with 95%), and there was also a significantly greater reduction in median SaO2 (9% compared with 5%). This study illustrates the difficulty of setting alarm limits for the detection of apnoea. We suggest that rather than simply detecting apnoea it is more appropriate to monitor heart rate and SaO2 in infants with recurrent apnoea.

Endotracheal resuscitation of neonates using a rebreathing bag.

Thirty asphyxiated neonates were resuscitated endotracheally with an anaesthetic rebreathing bag. The system was not limited either by pressure or by volume and chest movement was used as the criterion for adequate inflation. Inflation pressure and flow were recorded during resuscitation, and flow was integrated to obtain volume. Median mean pressure over the first 10 inflations was 40 cm H2O and this dropped during later resuscitation to 29 cm H2O. The volume delivered did not change significantly, so volume divided by pressure increased from a median of 0.18 to 0.35 ml/kg/cm H2O. Fourteen infants formed part of their functional residual capacity with artificial ventilation and five with spontaneous breaths. Eleven infants showed no evidence of functional residual capacity formation. In the 22 preterm infants there was a strong association between absence of functional residual capacity formation and later hyaline membrane disease that required ventilation. We suggest that pressures of more than than 30 cm H2O may be helpful during initial resuscitation and that there should be further study of devices using positive end expiratory pressure for resuscitation of preterm infants.

Combined impedance and inductance for the detection of apnoea of prematurity.

To compare two methods of detecting central apnoea, 27 preterm infants (median birth weight 1.14 kg, gestation 29 weeks) were studied on 89 occasions, using combined thoracic impedance and abdominal respiratory inductive plethysmography. During 353 h recording time, 946 apnoeic episodes were noted. In 651 of these, there was agreement between impedance and inductance traces, but apnoea appeared longer in 106 episodes on impedance, and in 189 on inductance. If a single system had been used 27 would have been missed by inductance and 112 by impedance (P less than 0.05). Failure of impedance monitoring was mainly due to technical reasons, especially cardiac artefact, and to movement. The use of a dual system of impedance and inductance offers improved detection of central apnoea, particularly for research purposes.

The effect of changes in inspiratory time on neonatal triggered ventilation.

Nine preterm infants with hyaline membrane disease were studied using a ventilator triggered from abdominal movement. It was possible to alter respiratory rate over a short space of time by adjustments of the inspiratory time setting. There was a marked inverse relationship between inspiratory time and both ventilator and baby's respiratory rate--mean baby respiratory rate was 62 breaths/min at an inspiratory time of 0.2 s and 45 breaths/min at 0.8 s. This drop was statistically significant (P less than 0.005). Mean tidal volume changed little over this range. This interaction meant that mean minute ventilation was optimal at inspiratory times of 0.2 to 0.4 s, being 269 and 258 ml/kg per minute, respectively, but at 0.8 s fell to 213 ml/kg per minute (P less than 0.05).

Dynamic responses to tube breathing during the first 10 days of life.

To assess whether there is a maturation of the response to tube breathing during the first 10 days of life, we have measured the dynamic ventilatory responses of nine term infants (34 studies) to added tubes equivalent to two anatomical dead spaces. Such a method allows an assessment of the baby's ability to increase dead space ventilation in response to an added stress. There was a significant improvement with age over the first 10 days in the babies' ability to reach "expected" values of minute ventilation when the tubes were added (P = 0.003). The rates at which 63% and maximum adaptation were achieved also increased significantly with age (P less than 0.005). The rate to 63% adaptation appeared to be faster in active compared with quiet sleep (P less than 0.05). The dynamic responses to tube breathing improve over the first 10 days of life. This is likely to be due to a maturation of peripheral chemoreceptor control, although improving lung mechanics may also be important.

What are the mechanisms producing increased ventilation in dead space studies in neonates?

In 21 studies on 15 infants an additional dead space tube produced a significant rise in end-tidal PCO2 and fall in end-tidal PO2, associated with a rise in minute ventilation (228 +/- 77 mL/kg/min at zero, 348 +/- 85 mL/kg/min at one, and 437 +/- 128 mL/kg/min at two anatomical dead spaces). The differences between end-inspiratory and end-expiratory PCO2 and PO2 did not change significantly, suggesting an increase in dead space, but not in alveolar ventilation. In a further 9 babies the rise in ventilation was unchanged when measurements were repeated in 30% oxygen (361 +/- 65 vs. 340 +/- 54 mL/kg/min at one anatomical dead space). Studies on 8 babies, with the added tube ventilated by a fan, showed that a mean 28% of the rise in minute ventilation was due to increased resistance. Although the response to tube breathing in neonates is complex, carbon dioxide appears to be the major factor producing increased ventilation.

Two minute walking distance in cystic fibrosis.

We have evaluated the 'two minute walking distance' in children with cystic fibrosis as an objective measurement of exercise tolerance. There was a strong correlation between walking distance and height in 89 normal children (r = 0.72). Fifty children with cystic fibrosis showed a similar correlation (r = 0.56) with a mean result of 94% of that expected for height compared with the normal children. There was a training effect in the normal children with the second walk being significantly better than the first, but this was not evident in children with cystic fibrosis. The test was reproducible with no significant change in 12 children retested after one to three months. Sixteen children with cystic fibrosis admitted for treatment of chest disease showed a significant improvement in walking distance with treatment. Children as young as 5 years old can perform a walking distance test. It seems to be an objective way of assessing exercise tolerance and can help in evaluating response to treatment.

Salbutamol and ipratropium in acute asthma.

Thirty seven children with acute asthma were given nebulised ipratropium or placebo 30 minutes after their first dose of salbutamol and eight hourly thereafter. There were no significant differences between the two groups in clinical scores, peak expiratory flow rates, length of stay in hospital, or the need for oral steroids.