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Biomedical subjects

G M Stokes

Publications and source records attributed to G M Stokes.

At least 19 recordsLinked to original sources
PubMed1992

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.

Apnea↗
PubMed1992

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.

Airway Obstruction↗
PubMed1992

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.

Abdomen↗
PubMed1992

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.

Apnea↗
PubMed1992

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.

Apnea↗
PubMed1991

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.

Apnea↗
PubMed1990

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.

Aging↗
PubMed1990

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.

Carbon Dioxide↗
PubMed1990

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).

Female↗
PubMed1990

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.

Apnea↗
PubMed1989

Do lung volumes change with sleep state in the neonate?

We have studied 12 healthy full-term babies, mean age 3.2 days, using physiological criteria--EEG, electrooculogram, electromyogram, respiratory regularity and visible movement--to assess sleep state, and a respiratory jacket to record changes in functional residual capacity (FRC). A total of 593 min of sleep data were analysed. Of the recordings, 39% were scored as quiet sleep, 40% as active and 21% as indeterminate sleep. The mean maximum variation in FRC overall was 29 ml (SD +/- 15.4 ml). Examination of these figures showed that FRC variations during sleep state changes were smaller than those seen within a defined sleep state. We conclude that changes in sleep state are not associated with variations in FRC.

Functional Residual Capacity↗
PubMed1989

Interferon alfa, infectious virus, and virus antigen secretion in respiratory syncytial virus infections of graded severity.

Interferon alfa was measured by an immunoradiometric assay in the nasopharyngeal secretions of a group of infants admitted to hospital with respiratory syncytial virus infection. Virus replication in the upper respiratory tract was assessed by infectivity assay and by an enzyme linked immunoadsorbent assay for the viral fusion protein on the same nasopharyngeal secretions. All infants were examined daily while in hospital and allocated a score based upon a subjective assessment of the severity of their illness. There was no significant correlation between interferon, virus, or fusion (F) protein secretion and severity of illness or age of infant. It is concluded that poor interferon alfa secretion does not underly the susceptibility of infants to severe infections with this virus.

Antigens, Viral↗
PubMed1989

IgG and IgM antibodies to viral glycoproteins in respiratory syncytial virus infections of graded severity.

Serum antibodies to the fusion (F) and large glycoprotein (G) of respiratory syncytial virus in the serum of 57 infected infants were measured by enzyme linked immunosorbent assay (ELISA). Most serum samples taken at the time of admission to hospital contained antibodies to both glycoproteins, and overall there was no significant evidence of a selective deficiency of antibody to either viral antigen. Less than a quarter of the infants showed rising IgG antibody titres to either glycoprotein after infection, whereas over threequarters produced an IgM response. There was a significant correlation between IgG response to viral glycoproteins and the age of the infant. The correlation of age with the IgM response was less pronounced, and there was no correlation between serum IgG antibody derived transplancentally in the acute phase of infection and IgM response to either glycoprotein. Neither IgG or IgM responses correlated with a clinical assessment of the severity of infection in the infants. IgM responses, however, were weakly correlated with reduced secretion of infectious virus in the upper respiratory tract.

Antibodies, Viral↗
PubMed1985

Continuing respiratory problems three and a half years after acute viral bronchiolitis.

We reviewed the clinical progress of 81 children as part of a prospective study three and a half years after admission to hospital with acute viral bronchiolitis in infancy. Fifty six (69%) reported episodes of lower respiratory symptoms continuing over the preceding year, 25 (31%) had symptoms lasting for longer than two weeks on two or more occasions, 14 (17%) had symptoms for more than 100 days, and six (7%) required readmission to hospital with acute respiratory illness. Two years previously, these percentages had been 82%, 36%, 33%, and 13% respectively. Forty six (57%) children were said to be improving or to have become asymptomatic, but eight (10%) were deteriorating. There was no difference in the personal or family history of atopy, nor in the rate of skin test positivity between those with and without continuing symptoms, suggesting that atopy does not play an important role in the persistence of symptoms. Less than half the symptomatic children had received bronchodilator treatment during the preceding 12 months.

Acute Disease↗
PubMed1984

Nebulised ipratropium bromide and sodium cromoglycate in the first two years of life.

In a double blind crossover trial, we compared sodium cromoglycate, ipratropium bromide, and water in 23 asthmatic children less than 2 years old (mean age 11.8 months). Each child received nebulised solutions containing 20 mg of sodium cromoglycate, 250 micrograms of ipratropium bromide, or 2 ml water three times a day for three two month periods. Daily symptom scores did not show significant differences between the treatments but parental preferences indicated that both sodium cromoglycate and ipratropium bromide were superior to placebo. Sodium cromoglycate was prophylactic and was more likely to help the older patients. Ipratropium bromide produced an immediate clinical benefit and the response was not age dependent. We were unable to pick responders from non-responders on the basis of lung function tests performed on a routine outpatient basis. Both ipratropium bromide and sodium cromoglycate help some but not all asthmatic children aged less than 2 years.

Aerosols↗