Combined effects of sleeping position and prenatal risk factors in sudden infant death syndrome: the Nordic Epidemiological SIDS Study

OBJECTIVE

Prone sleeping is a strong risk factor for sudden infant death syndrome (SIDS). We investigated whether the combined effect of prone sleeping position and prenatal risk factors further increased the SIDS risk.

METHODS

In the Nordic Epidemiological SIDS Study, parents of SIDS victims in Denmark, Norway, and Sweden completed a questionnaire on potential risk factors for SIDS. Forensic pathologists verified the SIDS diagnosis. Four controls of the same gender, age, and place of birth were selected. This matched case-control study, which included 244 SIDS cases and 869 controls from 1992 to 1995, was analyzed by conditional logistic regression.

RESULTS

Odds ratios (ORs) for prone and side sleeping compared with supine sleeping for the last sleep were 13.9 (95% confidence interval 8.2-24) and 3.5 (2.1-5.7). Infants 13 to 24 weeks old had particularly high risk in prone and side sleeping, at 28.5 (7.9-107) and 5.9 (1.6-22). OR for prone sleeping was higher in girls, at 30.4 (11-88), than in boys, 10.3 (5.5-19). We found strong combined effects of sleeping position and prenatal risk factors (more than multiplicative). The OR for prone and side sleeping was increased for infants with birth weight <2500 g, at 83 (25-276) and 36.6 (13-107); for preterm infants, at 48.8 (19-128) and 40.5 (14-115); and for intrauterine growth retarded, at 38.8 (14-108) and 9.6 (4.3-22), compared with supine position in infants without these prenatal factors. The combined effect of nonsupine positions and intrauterine growth retarded was highest among 13- to 24-week-old infants. Effects of combined presence of nonsupine sleeping positions and each of the factors of smoking in pregnancy, young maternal age, higher parity, low level of maternal education, and single motherhood were more than additive. Attributable fractions in the population for prone and side sleeping were 18.5% and 26.0%.

CONCLUSIONS

Both prone and side sleeping increased the risk of SIDS. The risk was increased further in low birth weight infants, preterm infants, and infants at the age of 13 to 24 weeks, suggesting that SIDS may be triggered by nonsupine sleeping in infants with prenatal risk factors during a vulnerable period of postnatal development.

The decline in the incidence of SIDS in Scandinavia and its relation to risk-intervention campaigns. Nordic Epidemiological SIDS Study

A prospective case-control study of sudden infant death syndrome (SIDS) in Norway, Denmark and Sweden between September 1, 1992 and August 31, 1995 comprised 244 cases and 869 matched controls. After the introduction of risk-intervention campaigns, the SIDS incidence decreased from 2.3/1000 live births in Norway, 1.6 in Denmark and 1.0 in Sweden to 0.6/1000 or fewer in all the Scandinavian countries in 1995. The decrease paralleled a decline in the prone sleeping position and there was an accompanying parallel fall in total postneonatal mortality in all three countries. Thus, the risk-reducing campaigns for SIDS have been successful not only in Norway and Denmark, starting from relatively high incidences, but also in Sweden, starting from a low incidence. During the study period, a gradual increase was observed for the effects of prone sleeping, smoking and bottle-feeding as risk factors for SIDS.

Cytokines in nasal fluids from school children with seasonal allergic rhinitis

Allergic rhinitis is a particularly good model for studies of cytokine production in vivo. In this study the occurrence of the cytokines IL-4, IL-5, IL-10 and IFN-gamma as well as the soluble receptor for IL-4 in nasal lavage fluids were assayed in 38 school children, with seasonal allergic rhinitis, and 19 healthy age-matched, non-atopic controls, using highly sensitive enzyme immunoassays. IL-4 levels in patients with seasonal allergic rhinitis were markedly increased in comparison with those in non-atopic controls or in atopic patients before the start of the pollen season. In controls, but not in the atopic patients, levels of IFN-gamma and IL-5 were significantly higher in specimens obtained during the pollen season than in those obtained outside the season. The IL-4/IFN-gamma ratios were significantly higher in atopic than in non-atopic subjects and further increased in atopic patients during the season. In addition to IL-4, elevated levels of IL-10 were observed in association with seasonal rhinitis. Following treatment with a topical steroid (budesonide) there was a statistically significant increase of the levels of soluble IL-4 receptor. These findings indicate that nonatopic and atopic individuals react to pollen exposure with distinct cytokine patterns in agreement with the Th1/Th2 concept. Topical steroids may possibly decrease inflammation by increasing the formation of soluble IL-4 receptor.

Wheezing bronchitis reinvestigated at the age of 10 years

We have reinvestigated 92/101 children aged 10, who before the age of 2 years were admitted to a paediatric ward due to wheezing bronchitis. At the present time, 70% are symptom-free without medication, 20% have mild asthma, 8% moderate and 2% severe asthma. Persistent asthma correlated significantly to the presence of some other atopic disease in recent years, to early start of wheezing during infancy and to intense obstructive disease as a young child, while initial respiratory syncytial virus infection did not. A clear-cut relationship between smoking in the home in infancy and persistent asthma emerged (not visible at a preschool follow-up). The histamine challenge results correlated to the clinical picture. A normal histamine challenge was seen in 63%, mild hyperresponsiveness in 19%, moderate in 12% and pronounced hyperresponsiveness in 6%. The figures for persistent asthma and bronchial hyperresponsiveness are high compared with the prevalence of asthma in the overall population of schoolchildren.

Inflammatory markers in childhood asthma

The importance of airway inflammation in the pathogenesis of asthma is clearly established. Studies in adults as well as in children have led to the concept that asthma is a chronic inflammatory disease. Airway inflammation is found even in mild asthma. Bronchoconstriction and hyper-reactivity appear to be secondary to the release of inflammatory mediators. The changed view of the pathogenesis of asthma and current emphasis on anti-inflammatory treatment have raised a need for markers that reflect the inflammatory status in the airways. This is of special importance in paediatric practice because lung function tests are less easily performed in young children, and it is preferable to keep steroid doses as low as possible. The eosinophil granulocyte has a multitude of proinflammatory functions and plays a key role in the asthmatic inflammation. It secretes toxic proteins and produces cytokines, which have important roles in airway inflammation. Use of eosinophil granula proteins to monitor inflammation is now finding its place. Measurement of eosinophil cationic protein (ECP) seems to be a valuable complement to the recording of lung function. For paediatric use, measurement of urinary eosinophil protein X (EPX) is promising because it does not require blood sampling.

Urinary eosinophil protein X in children with atopic asthma: a useful marker of antiinflammatory treatment

BACKGROUND

Bronchial asthma is associated with elevated serum levels of eosinophil products, such as eosinophil protein X (EPX), but the occurrence in urine of this substance in patients with asthma has not previously been studied.

OBJECTIVE

This study was performed to clarify whether increased amounts of eosinophil granulocyte proteins in urine and serum reflect ongoing asthmatic inflammation and whether decreasing values reflect successful treatment.

METHODS

Twelve children with a median age of 12.5 years who had mild or moderate atopic asthma were studied for 3 months. At the time of inclusion in the study, treatment with inhaled budesonide was initiated. Nine children of the same age without atopic disease served as control subjects. Levels of EPX, eosinophil cationic protein (ECP), and myeloperoxidase in serum and in urine (urinary EPX) were determined at inclusion and then after 3 months of treatment. Spirometry was performed on the same occasions.

RESULTS

At the time of inclusion, urinary EPX and serum ECP were significantly higher in children with atopic asthma than in the control subjects (mean, 116.4 vs 43.0 micrograms/mmol creatinine [p = 0.004] and 37.0 vs 14.8 micrograms/L [p = 0.004]). In the asthma group urinary EPX, as well as serum ECP, decreased significantly after 3 months of treatment with budesonide (116.4 to 68.4 micrograms/mmol creatinine [p = 0.005] and 37.0 to 24.0 micrograms/L [p = 0.04]). At the same time, peak expiratory flow values increased significantly in the children with asthma (76.0% to 87.8% of predicted value [p = 0.005]) but not in the control subjects (87.0% to 90.1%). In the asthma group the levels of myeloperoxidase were similar to those in the control group, both at inclusion and after 3 months.

CONCLUSION

Increased urinary EPX and serum ECP levels seem to reflect active atopic asthma, whereas decreased levels after antiinflammatory treatment probably reflect normalization of airway inflammation, and indirectly, improved lung function.

Decrease in hospitalization for treatment of childhood asthma with increased use of antiinflammatory treatment, despite an increase in prevalence of asthma

BACKGROUND

During the past 15 years, the prevalence of asthma in children in Sweden has doubled. However, since 1985, antiinflammatory treatment with inhaled steroids has increased continuously.

OBJECTIVE

The aim of this study was to analyze the net effect of these changes in terms of hospitalization of children for treatment of asthma.

METHODS

The numbers of hospital days, admissions, and individual patients admitted to the Children's Hospital in Göteborg because of acute asthma were recorded from 1985 through 1993. all the in-patient treatment of children is centralized at this hospital (i.e., the study was population-based). Göteborg has half a million inhabitants. Hospitalization policies were not altered during the study period.

RESULTS

In children aged 2 to 18 years, the number of hospital days per year gradually decreased to less than a third (r = 0.9; p less than 0.001), and admissions decreased by 45% (r = 0.7; p less than 0.05). The decrease in hospitalization was most marked in the group older than the age of 5 years in which hospital days were reduced to one fifth (r = 0.9; p less than 0.0001) and admissions were halved (r = 0.8; p less than 0.05). A decreasing trend in number of hospital days was also seen in the 2- to 5-year-old group. The number of individual patients admitted did not show a statistically significant decreasing trend. In children under the age of 2 years, the number of hospital days fluctuated, and there was no clear-cut change with time.

CONCLUSION

Although increased concentration on the education of parents and patients may have been a contributing factor, the major reason for the decrease in hospitalization in the group of children aged 2 to 18 years is most probably antiinflammatory treatment with inhaled steroids. The results suggest that this is a very cost-effective therapeutic approach.

Nebulized budesonide for the treatment of moderate to severe asthma in infants and toddlers

Maintenance treatment with nebulized budesonide was studied in young children with asthma not controlled without steroids. In a blind parallel-group study for 18 weeks, 102 children, mean age 22 (5- 47) months, were randomized for treatment starting with 0.25 or 1 mg b.i.d. The patients were reviewed every 3 weeks, and if symptom control had been achieved the dose was reduced, otherwise it was kept. The clinical effect was very good with both dose regimens. The median time to 7 consecutive days without any asthma symptoms was about 1 month with both, highlighting the importance of the duration of therapy rather than the benefits of a high starting dose. In 18 of 24 children who attained the placebo stage, symptoms had reappeared at the last visit. Although an overall minimal effective maintenance dose could not be demonstrated, 47% achieved symptom control on 0.25 mg b.i.d., i.e. fulfilled criteria for further dose reduction. No significant side effects were seen. On average, 25% of the nominal dose reached the patients.

Leukotriene B4 and C4 generation by human leukocytes after ex vivo stimulation with Ca-ionophore and opsonized zymosan in children with atopic asthma

The ex vivo release of leukotriene B4 (LTB4) and leukotriene C4 (LTC4) from leukocytes was evaluated after stimulation with both Ca-ionophore (Ca-I) and opsonized zymosan (OZ) in children with atopic asthma. Twenty-seven patients with asthma of varying severity were evaluated and divided into three groups: 1) moderate to severe asthma using inhaled steroids and symptom-free for the last 3 weeks (n = 8), 2) mild asthma with sporadic symptoms, only using inhaled beta 2-agonists < 3 times/week (n = 8), and 3) acute asthmatic attacks admitted to hospital (n = 11). A group of children without atopic disease or any other known disease served as controls (n = 15). Total serum IgE levels were significantly increased in the children with asthma compared with the control group. LTC4 production was only significantly increased in the group of children with moderate to severe asthma after stimulation with Ca-I, when compared with controls. In the same group, a trend towards increased LTC4 production after stimulation with OZ was found. LTB4 was not significantly increased in any patient group compared with the control group. A significant correlation between LTC4 production after stimulation with Ca-I, but not OZ, and the relative blood eosinophil count was found in all subjects. LTC4 generation per eosinophilic cell after stimulation with Ca-I or OZ was not statistically different in any patient group compared with the controls. We conclude that the increased leukotriene (LT) levels found after the stimulation of peripheral white blood cells sampled from atopic children with asthma are mainly the result of increased numbers of LT-producing cells, rather than due to increased releasability from these cells.

Eosinophil cationic protein, myeloperoxidase and tryptase in children with asthma and atopic dermatitis

Serum levels of eosinophil cationic protein (ECP), myeloperoxidase (MPO), tryptase, total IgE and differential blood cell counts were studied in atopic children with: 1) moderate to severe asthma using inhaled steroids and symptom-free for the last 3 weeks (n = 13), 2) mild asthma with sporadic symptoms, using only inhaled beta 2-agonists < 3 times/week (n = 15), 3) acute asthmatic attacks admitted to hospital (n = 12), 4) mild to moderate atopic dermatitis (n = 14). Fifteen children without any history of atopy served as controls. ECP, MPO, tryptase and IgE were measured in serum by radioimmunoassays (RIA). The symptom-free children with inhaled steroids had similar median ECP and MPO values as the controls, 8.0 and 360 micrograms/l, vs. 9.0 and 310 micrograms/l, while both ECP and MPO were significantly (p < 0.001) increased in the symptom-free children without anti-inflammatory treatment, 32 and 887 micrograms/l and in those with acute asthma, 28 and 860 micrograms/l. The children with atopic dermatitis had increased ECP but normal MPO levels, 16.0 and 455 micrograms/l. Tryptase in serum was not measurable in any patient. All groups except the control group had significantly elevated total IgE levels. The results indicate that in atopic children serum ECP is a good marker of ongoing asthma or atopic dermatitis. The normal levels of ECP and MPO in the children with asthma using inhaled steroids seem to reflect successful anti-inflammatory treatment. The increased levels of ECP and MPO in the children with mild asthma and no anti-inflammatory treatment may indirectly reflect airway inflammation.

Inhibitory effects of theophylline, terbutaline, and hydrocortisone on leukotriene B4 and C4 generation by human leukocytes in vitro

Leukotriene B4 (LTB4) and leukotriene C4 (LTC4) are considered to be important mediators in the pathophysiology of asthma. Theophylline, terbutaline, and hydrocortisone are drugs commonly used in the treatment of asthma. In the present study we have investigated the in vitro inhibitory effects of theophylline, terbutaline, and hydrocortisone on LTB4 and LTC4 generation from human leukocytes. After preincubation in the presence of these drugs, the cells were stimulated with the calcium ionophore A 23187 and the supernatants were analyzed for their LTB4 and LTC4 content using reverse-phase high-performance liquid chromatography (HPLC). Total leukotriene (LT) production (the combined amounts of LTB4 and LTC4) was dose-dependently inhibited by pretreatment with theophylline, terbutaline or hydrocortisone. Therapeutic levels of hydrocortisone (5 x 10(-6) M) plus theophylline (5 x 10(-5) M) inhibited LTB4 and LTC4 production in an additive way, as did the combination of hydrocortisone plus terbutaline (5 x 10(-8) M). A statistically significant effect of diminished LTB4 generation was obtained after preincubation with therapeutic levels of theophylline plus terbutaline, but no such effect was seen for LTC4 levels. The in vitro inhibitory effects on LTB4 and LTC4 generation from human leukocytes by theophylline, terbutaline, and hydrocortisone, as well as the additive effect of hydrocortisone plus theophylline or terbutaline, add to our understanding of the therapeutic effects of these drugs in the treatment of bronchopulmonary obstruction.

Leukotriene B4 and C4 generation by blood leukocytes after ex vivo stimulation by Ca-ionophore and opsonized zymosan in children with atopic dermatitis

The ex vivo release of leukotrienes B4 (LTB4) and C4 (LTC4) from the leukocytes of children with atopic dermatitis (AD) was evaluated after stimulation with Ca-ionophore and opsonized zymosan and compared with that of control children of similar ages. The blood eosinophil counts and total serum IgE levels in AD children were significantly higher than those in control children. The production of LTC4, but not LTB4, was significantly higher in AD children than in control children. There was a significant correlation between the relative blood eosinophil count and LTC4 generation after stimulation with both Ca-ionophore and opsonized zymosan in all subjects. Calculations of the amount of LTC4 produced per eosinophilic cell showed that there was no significant difference between cells from AD children and control children in terms of their ability to produce LTC4. These findings suggest that the enhanced LTC4 generation is due to increased numbers of eosinophils rather than to enhanced releasability of these cells.

Nebulised racemic adrenaline in the treatment of acute bronchiolitis in infants and toddlers

The effect of inhaled nebulised racemic adrenaline upon symptoms of acute bronchiolitis was investigated in 29 infants and toddlers aged 2-17.5 months by transcutaneous oxygen tension (TcPO2), oxygen saturation, transcutaneous carbon dioxide tension (TcPCO2), and clinical evaluation in a double blind placebo controlled study. Clinical score and TcPO2 improved significantly at 30, 45, and 60 minutes after inhalation of racemic adrenaline, with an increase in TcPO2 > or = 0.5 kPa in 72% of the children < 1 year of age. No significant improvement was observed after inhalation of placebo. No significant changes in heart rate or TcPCO2 were observed from before to after inhalation, but a small increase in mean systolic blood pressure was observed immediately and 45 minutes after racemic adrenaline inhalation. This study demonstrates that treatment with nebulised racemic adrenaline improved oxygenation and clinical signs in hospitalised children aged less than 18 months with bronchiolitis.

SIDS outdoors and seasonality in Sweden 1975-1987

In order to link the reported increasing incidence of SIDS in Sweden to environmental or other risk factors, we compared birth records and circumstances of deaths in infants who died in 1975-1977 with those who died a decade later, 1985-1987. The number of liver births differed by only 6850 in these two periods. Data were acquired from autopsy records of the decreased infants and matched with their respective birth certificates which were obtained from the National Board of Health and Welfare. The reported postperinatal incidence of SIDS increased from 0.51 per 1000 in 1975-1977 to 0.93 per 1000 in 1985-1987. No significant differences in boy/girl ratio, birth weight, gestational age or age at death were found in the two periods. While the number of infants who died at night indoors in their own bed remained almost unchanged, the number of infants who died outdoors in baby carriages during the cold season increased almost four-fold. The observed increase in incidence could, to a large extent, be related to the increase in outdoor deaths. We speculate that increased incidence of smoking among young women as well as other changes in lifestyle may have been contributing factors.

Longitudinal follow-up of growth in children born small for gestational age

Postnatal growth was followed in a population-based group of 123 small-for-gestational-age (SGA, birth weight < -2 SD) children (66 boys and 57 girls) to four years of age in order to determine the incidence and time of catch-up growth. Gestational age was determined by ultrasound in gestational weeks 16-17 in all pregnancies, thus eliminating the problem of distinguishing between SGA and preterm infants. Infants with well-defined causes for slow growth rate, i.e. those infants with chromosomal disorders, severe malformations, intrauterine viral infections or cerebral palsy, were excluded. The boys showed an extremely fast weight catch-up, 85% of them reaching weights greater than -2 SD at the age of three months and remaining above this level to the end of the study period. Such a fast catch-up growth was observed in only two-thirds of the girls, but at four years of age 85% of the girls were also above -2 SD. Length catch-up was more gradual than weight catch-up. Of the boys, 54% had lengths below -2 SD at birth, 26% at 1 year of age, 22% at 2 years of age, 17% at 2.5 years of age and 11% (n = 8) at 4 years of age. Corresponding figures for girls were: 69% at birth, 28% at 1 year, 15% at 2 years, 12% at 2.5 years and 5% (n = 3) at 4 years. At 4 years of age, only six boys and three girls remained below -2 SD for both weight and height.(ABSTRACT TRUNCATED AT 250 WORDS)

Transcutaneous blood gas monitoring during salbutamol inhalations in young children with acute asthmatic symptoms

The effect of salbutamol inhalations on transcutaneous blood gases was investigated in 23 children (aged 11 months-2.5 years) with asthmatic symptoms. After one salbutamol inhalation there was a mean increase in transcutaneous PO2 (tcPO2) of 0.5 kPa (P less than 0.01); after a second dose given 30 minutes later, the mean increase was 1.2 kPa (P less than 0.001). The increase in tcPO2 after only one dose of salbutamol was significantly correlated to age (P less than 0.01). No such correlation was observed after a second dose. The overall increase in tcPO2 after two salbutamol inhalations showed a negative correlation to the duration of the current symptomatic period (P less than 0.05). We conclude that salbutamol inhalations have beneficial effects in young children with acute asthmatic symptoms, even below the age of 18 months, provided that an adequate dose reaches the lung and preferably at an early stage of obstruction.

Characteristics and prognosis of hospital-treated obstructive bronchitis in children aged less than two years

In a prospective study 101 children aged less than 2 years (median age 10 months), were examined the first time they were admitted to a paediatric ward for asthmatic symptoms. Two-thirds were boys and 58 had parents or siblings with allergic symptoms. During winter-spring, respiratory syncytial (RS) virus was verified in 50% of children. Other viral agents were adenovirus, parainfluenza 3, coxsackie B 2, ECHO 6 and rotavirus. At the acute stage, 54% of the children displayed changes on pulmonary X-ray. The total IgE value was greater than or equal to +2 SD score units in 14 children. At reinvestigation after 3-4.5 years, when the children were aged 3.3-6.3 years, 53% were free from asthmatic symptoms; the median age for the last episode was 2 years. A total of 33% had mild asthma, 8% moderate and 6% severe asthma. The factors which correlated significantly with persistent asthma were: (1) The need for daily medication for at least 6 months. (2) A young age in conjunction with the first wheezing episode and on the first admission to a paediatric ward because of asthmatic symptoms. (3) Other past or present atopic symptoms. Heredity, tobacco smoking at home, having a furry pet, RS virus infection, or high total IgE at the time of the first admission did not correlate significantly with the persistence of asthma 3-4.5 years later. The results emphasize the good overall prognosis of wheezing in early childhood, even when the wheezing is severe enough to lead to inpatient treatment.

Clinical and neurophysiological development of Unverricht-Lundborg disease in four Swedish siblings

Four siblings aged 12-18 years with progressive myoclonus epilepsy demonstrated a subclinical stage at the age of 9-11 years, with visual blackouts and polyspike electroencephalographic (EEG) activity on photic stimulation, an early myoclonic stage at the age of 12-15 years, with increasing segmental, stimulus-sensitive myoclonus, occasional nocturnal buildup myoclonic "cascade" seizures, slowing of EEG alpha-activity, episodic 4-6 Hz bilateral sharp waves and polyspikes with myoclonias on photic stimulation, and a disabling myoclonic stage at the age of 16-18 years, with periodic generalized myoclonias, nocturnal myoclonic "cascade" seizures, ataxia, dysarthria, mental changes, intermittent wheelchair dependency, and continuous EEG slow waves with polyspikes and intense myoclonias on photic stimulation. One of the siblings died at the age of 18 years with no apparent cause of death. Treatment with antiepileptic drugs other than valproate may have contributed but none of the siblings were ever treated with phenytoin. Extensive clinical and laboratory investigations revealed no abnormalities and excluded other known possible causes of progressive myoclonus epilepsy. The diagnosis was consistent with Unverricht-Lundborg disease and rested on typical age of onset, clinical signs, EEG, and evoked response abnormalities. Buildup myoclonic seizures are typical in advanced stages of Unverricht-Lundborg disease. We have labeled these myoclonic "cascade" seizures. A typical seizure was studied with video-EEG and cardiorespiratory monitoring. Characteristics revealed were onset with continuous arrhythmic myoclonic jerks followed by intense rhythmic myoclonus with increasing muscle tone that successively reduced the amplitude of the jerks. The EEG during the whole seizure showed intense polyspike activity. Obstructive apnea was seen at the peak of the seizure. There were no cardiac dysrhythmias. Consciousness was normal or only slightly impaired. Postictal drowsiness was not observed. Myoclonic "cascade" seizures are easily confused with generalized tonic-clonic seizures.

Respiratory and arousal responses to hypoxia in apnoeic infants reinvestigated

Respiratory and arousal responses to mild hypoxia (15% oxygen in nitrogen) were recorded in 18 healthy infants and 33 infants who had sustained severe sleep related apnoeic events (ALTE). Respiratory movements and transcutaneous gas pressures (tcPO2 and tcPCO2) were continuously monitored during the 10 min test. The changes in tcPCO2 in relation to the decrease in tcPO2 were used as an index of the ventilatory and metabolic responses to hypoxia. We found that the response of apnoeic infants was within the range of the controls although the distribution of the individual response slopes was shifted towards the lower end of the range. Arousal was observed in 33% of apnoeic infants and 32% of the controls. Regular periodic breathing occurred in 42% of apnoeic infants compared to 28% of controls. In contrast to the controls, periodic breathing in apnoeic infants was not associated with a drop in tcPCO2 to below baseline levels. Apnoeic infants also alternated between regular and periodic breathing during the test. These findings are suggestive of a weak feed back control of breathing but do not support former views of a deficient hypoxic response in infants with ALTE.

Hypoxia reinforces laryngeal reflex bradycardia in infants

The laryngeal chemoreflex involves bradycardia, apnea, swallowing and peripheral vasoconstriction. This reflex was studied in twelve infants, aged 5 days-28 weeks, who had sustained an apparent life-threatening event or were siblings of infants who had died of the sudden infant death syndrome. The bradycardic and apneic components of the reflex were found to be significantly, and sometimes powerfully, reinforced when elicited by pharyngeal water instillation during acute, mild hypoxia (transcutaneous PO2 4.6-8.3 kPa). Apnea duration during normoxia was 0.7-15 sec, and during hypoxia 2-30 sec. Heart rate change ranged from +26% to -21% during normoxia, as compared with -4% to -63% during hypoxia. The percentage change in heart rate was found to inversely correlate with the transcutaneous PO2-level prevailing when the reflex was elicited. The conclusion is that there is a significant reinforcement of the cardiorespiratory adjustments when the laryngeal reflex is activated during simultaneous excitation of the peripheral arterial chemoreceptors. One infant, showing a particularly strong increase of the cardiorespiratory response to laryngeal receptor stimulation during hypoxia, later died of sudden infant death syndrome.

Obstetric characteristics and neonatal performance in a four-year small for gestational age population

Obstetric and neonatal performance were analyzed in an ultrasound-dated small for gestational age (SGA) population from 1982-1985. Eighty-three percent of 160 SGA infants were identified antenatally by means of intrauterine growth retardation (IUGR) risk scoring, and the pregnancies were supervised at a high-risk clinic. Fifty percent were delivered electively, predominantly in gestational weeks 38-39. Thirty percent were born preterm. The cesarean section rate was 40%. Perinatal mortality was 6%, or 4% when lethal malformations were excluded, ten times higher than the corresponding total population figures. Eleven percent of the fetuses had severe malformations. In the remaining SGA population, one infant died after experiencing severe perinatal asphyxia and another developed cerebral palsy; no other major sequelae were found before the age of 18 months. Hypoglycemia and hypothermia occurred frequently, but these problems were managed satisfactorily. The mean hospital stay for term infants was twice that of appropriate for gestational age infants. We conclude that the extra attention paid to the SGA population is well motivated. Future efforts should be directed toward improving the diagnostic techniques for IUGR, as most of the perinatal mortality occurred among SGA infants not identified before birth.

The epidemiology of sudden infant death syndrome and attacks of lifelessness in Sweden

Infants who died showing the syndrome of sudden infant death (SIDS) and infants who survived attacks of lifelessness (AL) were examined in a prospective epidemiological multicentre study over 24 months covering close to 40% of all births in Sweden. Seventy SIDS cases and 34 cases of AL were observed, giving an incidence for SIDS of 0.94/1000 and for AL of 0.46/1000. This SIDS incidence is higher than that observed during the seventies. The boy/girl ratio was 1.4:1 for SIDS and 1.6:1 for AL. The age distribution for AL resembled that for SIDS. Similarities were also seen with regard to place of occurrence. Sixty per cent of the SIDS cases occurred during the daytime/evening. Twenty-nine per cent of the infants with AL had more than one apneic spell during the three-day-period around the attack, indicating a period of respiratory instability, but only 12% had such spells later on. None of the infants who had had AL died from SIDS. The possible relationship between AL and SIDS is discussed.

Transcutaneous oxygen and carbon dioxide levels and a clinical symptom scale for monitoring the acute asthmatic state in infants and young children

Measurement of transcutaneous PO2 and PCO2 in addition to a clinical symptom grading system was used to monitor the acute asthmatic attack in children under two years of age. tcPO2 was lowered already at signs of mild obstruction and decreased in parallel with clinical deterioration. tcPCO2 was almost unchanged at mild to moderate obstructive symptoms. With clinical deterioration tcPCO2 rose steadily. An increase of the oxygen concentration to 30-40% in the inspired air increased tcPO2, on the average by 70%, but did not change the tcPCO2, level. Continuous recording of tcPO2 and tcPCO2 as well as the clinical grading system are valuable tools when monitoring severely obstructive infants and young children.

Neonatal breathing control mediated via the central chemoreceptors

Respiratory changes elicited via the central chemoreceptor system have been studied in anesthetized newborn guinea pigs and newborn rabbits. Periodic breathing was induced by inhibition of the central chemoreceptors by superfusion with alkaline cerebrospinal fluid. The periodic breathing was promptly reversed to steady by increasing the oxygen or carbon dioxide concentration in the inspired air or by intravenous theophylline. Elicitation of periodic breathing simply by exposing the animals to hypoxia succeeded only when very low oxygen concentrations were given. Clearcut respiratory excitation was produced by small amounts of theophylline applied onto the ventral surface of the medulla. Not only theophylline intravenously but also theophylline topically applied on the ventral medullary surface normalized spontaneously developed periodic breathing. Application of meperidine onto the ventral medullary surface gave respiratory inhibition with dosages considerably lower than required when given intravenously. The results emphasize the importance of an adequate respiratory drive from the central chemoreceptors for the maintenance of a regular breathing pattern. The findings support a view that at least part of the respiratory effects seen in the newborn following administration of meperidine or theophylline is due to effect of the drugs on the central chemosensitive system.

A case of near-miss SIDS developing an abnormal respiratory reaction to hypoxia

A SIDS sibling is described who showed a normal respiratory regulation at 1.5 months but who was equipped with an apnea monitor at home on psychological indications. At 3 months he had a near-miss SIDS episode. He was then found to have developed a reaction to hypoxia with appearance of periodic breathing. With theophylline this response pattern was normalized but despite theophylline medication episodes of prolonged apnea occurred.

Reflex cardiovascular responses to graded stimulations of low- and high-threshold afferents in the carotid sinus and aortic nerves in the cat

Reflex responses to electrical stimulation of low-threshold and high-threshold afferents in the aortic and carotid sinus nerves were investigated in chloralose-anesthetized cats. Changes in blood pressure, heart rate and muscle resistance were recorded. Low-threshold stimulation induced depressor responses of moderate magnitude. When stimulation intensity was increased to engage also the high threshold aortic nerve afferents a more pronounced reflex response was seen even with stimulation frequencies less than 10 Hz. Furthermore, stimulation of low- and high-threshold aortic nerve afferents induced different reflex patterns. For a given fall in blood pressure, the low-threshold afferents induced a greater reflex decrease in muscle vascular resistance compared with the high-threshold afferents, which reduced heart rate more. The effects seen at low frequency stimulation of high-threshold aortic nerve afferents were interpreted to reflect activation of the non-medullated baroreceptor afferents, while the depressor reflexes at low-threshold stimulation were induced by medullated baroreceptor afferents. Also the reflex effects of continuous and intermittent stimulation patterns of the various afferents were compared. At the same number of imp/s an intermittent stimulation of the low-threshold afferents induced greater reflex changes in blood pressure and muscle vascular resistance but smaller changes in heart rate. No such difference was observed when high-threshold afferents were similarly stimulated.

Cardiovascular effects elicited from the ventral surface of medulla oblongata in the cat

Cardiovascular adjustments induced by topical application of drugs on a restricted area on the ventral surface of the medulla oblongata, corresponding to the caudal part of the rostral chemoreceptor area and the intermediate area, have been studied in chloralose-anesthetized cats. Topical application of GABA or glycine on these structures resulted in blood pressure fall, bradycardia, vasodilatation in the kidney and the skeletal muscles and also depression of respiration. Similar responses except for a slight tachycardia occurred with application of physostigmine. Application of GABA resulted in a marked attenuation of the reflex vasoconstrictor responses to removal of arterial baroreceptor restraint (carotid occlusion), particularly in the kidney, and to disappearance of the reflex renal vasodilatation to baroreceptor stimulation. The findings suggest that GABA application leads to a general diminution of the tonic vasomotor neuron activity, and with regard to renal vasomotor neurons a virtual cessation. Atropine methylnitrate application induced blood pressure rise, increased peripheral resistance in both skeletal muscle and kidney and a strongly potentiated renal vasoconstrictor response to carotid occlusion. The results indicate that the studied superficial medullary structures play an important role for the maintenance of tonic vasomotor neuron activity, especially renal.

The role of cardiac receptors in clonidine-induced vagal bradycardia

In chloralosed, spinalized and beta-blocked cats, clonidine, 10 microgram/kg i.v. caused a vagally mediated bradycardia which was further analysed with particular attention to cardiopulmonary receptors. Cardiovascular deafferentiation, with preservation of vagal cardiac efferents, abolished the bradycardia. However, in animals with arterial baroreceptors denervated but with vagal cardiopulmonary pathways intact, clonidine decreased heart rate simultaneously with an increase in left atrial pressure to an extent known to activate cardiac receptors with unmyelinated vagal efferents. Clonidine somewhat enhanced the bradycardia to efferent vagal stimulation and also had a slight positive chronotropic effect on the non-innervated heart. The reflex bradycardia from electrical stimulation of unmyelinated cardiac afferents was augmented by the drug but not more than could be accounted for by the changed neuroeffector sensitivity. The data suggest that clonidine can reflexly augment vagal tone on the heart by an increased activity in vagal cardiac afferents, secondary to the drug's peripheral vasoconstrictor action, whereas no evidence for any central facilitation of these reflexes has been found.

Cardiac receptors activated during the hypothalamic defence reaction

The increases of arterial blood pressure, cardiac inotropy and venous return seen during the hypothalamic defence reaction are likely to lead to concomitant excitation of left ventricular receptors with nonmedullated afferents. The integrated efferent pattern of response resulting from the central interaction between the defence reaction and influences from the mentioned cardiac receptors was recently analyzed. These two, essentially opposing influences on the circulation were then seen to interact in such a way as to produce an optimal cardiovascular response with respect to increases in cardiac output and blood supply to the skeletal muscles. However, direct electrophysiological recordings from nonmedullated cardiac efferents during defence area stimulation have hitherto been lacking. The present experiments, performed on chloralose-anesthetized cats and utilizing electrophysiological recordings, clearly demonstrate that the left ventricular receptors are activated by the cardiovascular readjustments induced by the defence reaction. Defence area stimulation increased the activity of these receptors, which work within a very narrow, low frequency range, from 1.1 +/- 0.3 imp/s to 2.7 +/- 0.7 imp/s associated with rises in systolic blood pressure (afterload) and heart rate. Normally such a receptor activation would induce considerable bradycardia and sympathetic inhibition, but particularly the reflex bradycardia is centrally supressed by a concomitant defence area activation. The marked bradycardia often seen immediately upon interruption of the defence area stimulation is, however, probably to a great extent initiated from the excited ventricular receptors.

Interaction between the hypothalamic defence reaction and cardiac ventricular receptor reflexes

The interference with regard to the cardiovascular and gastric motility responses which follows stimulation of the hypothalamic defence area (D.A.) and a simultaneous afferent input from cardiac ventricular receptors was analysed in chloralose-anesthetized cats. In spinalized animals with only the vagal efferent innervation of autonomic effectors from supraspinal structures intact, a D.A. stimulation increased the heart rate to the same level irrespective whether the cardiac receptor afferents were stimulated or not. This suggests that the vagal component of the reflex bradycardia of cardiac receptor origin was completely suppressed by the D.A. stimulation. The reflex gastric relaxation to cardiac receptor activation, mediated via vagal efferent non-adrenergic fibres, was similarly completely blocked by D.A. stimulation. In contrast, the reflex inhibition of the sympathetic outflow to the heart and vessels from cardiac receptors was still effective during a D.A. stimulation, a phenomenon which seems compatible with a simple summation of excitatory D.A. and inhibitory cardiac receptor influences on the sympathetic neurons. The modifying influence from ventricular receptors on D.A. responses closely resembles that exerted by the arterial baroreceptors. The two reflex mechanisms thus work in concert and synergistically with the hypothalamic influences to produce maximal cardiac output and skeletal muscle perfusion without undue increases of pressure load on the pump during a defence reaction.

Cardiac receptors in ducks--a link between vasoconstruction and bradycardia during diving

It has been demonstrated that cardiac receptors, most likely of the left ventricular type, are present also in the duck's heart. These receptors and their reflex responses (i.e. bradycardia and hypotension) could be blocked by intrapericardial administration of lidocaine. Initially, usch receptor blockade did not affect efferent vagal control of heart rate, as revealed by undiminished bradycardia in response to a standardized vagal stimulation. After cardiac receptor blockade, however, the duck's normal bradycardia response to head immersion was greatly reduced. The cardiovascular response to submersion was now instead characterized by a marked rise in arterial pressure, with superimposed bouts of intensified bradycardia and pressure reduction, evidently induced reflexly from the arterial baroreceptors. Meanwhile, the bradycardia response to standarized efferent vagal stimulation was still the same as before intrapericardial lidocaine injection. These results suggest that the marked rise in cardiac filling pressure following the intense shemo-receptor-induced constriction of both resistance and capacitance vessels, activates ventricular stretch receptors signalling in vagal afferents. Apparently, the activation of these receptors contributes crucially to the bradycardia and reduction of cardial output, which balance off the greatly increased peripheral resistance in the diving duck.

Studies on the central integration of excitatory chemoreceptor influences and inhibitory baroreceptor and cardiac receptor influences

Experiments were performed on cats to explore the integrated cardiovascular responses when excitatory (chemoreceptor) and inhibitory (baroreceptor or cardiac receptor) influences are simultaneously presented to the medullary cardiovascular areas. At a given sinus pressure in the low or medium pressure range, the systemic blood pressure and the vascular resistance were higher when the chemoreceptors were stimulated, while a high, pulsating sinus pressure, i.e.a strong baroreceptor stimulation, could suppress completely even an intense chemoreceptor activation. Thus, the set point and the gain of the baroreflex were increased by a concomitant chemoreceptor activation. These effects are compatible with a simple, mutual 'summation' of excitatory and inhibitory influences on a common population of central vasomotor neurons. The reflex vasodilator effects elicited via vagal cardiac afferents were found to be more effectively suppressed by a concomitant chemoreceptor stimulation than were the baroreceptor effects, provided a primary chemoreceptor response (bradycardia) was at hand, while the heart rate responses were essentially uninfluenced by the prevailing chemoreceptor activity. This chemoreceptor suppression of the reflex vasodilatation from cardiac receptors, which may be of great importance in hypoxic situations, e.g. during a dive, suggests a more complex, neuronal interaction between the two reflex mechanisms in the CNS.

The distribution of sodium in aortic walls from spontaneously hypertensive and normotensive rats

The contents of exchangeable sodium, bound sodium and total water and the extracellular space of thoracic aortas from normotensive and spontaneously hypertensive rats were measured. The aortas from the hypertensive rats contained more sodium than those from the normotensive animals while the total water content and extracellular space in the two groups were the same. The capacity to bind sodium in an osmotically inactive form was greater in the aortas from the hypertensives than in those from the normotensives. The difference in binding capacity was of the same order of magnitude as the difference in sodium content, indicating that the excess sodium in the thoracic aortas from the hypertensive rats was osmotically inactive and thus unable to cause water logging.

Aspects of the central integration of arterial baroreceptor and cardiac ventricular receptor reflexes in the cat

The possible central integrative mechanisms, responsible for the earlier reported, differentiated reflex engagement of the renal and muscle vessels and the heart from cardiac ventricular receptors and arterial baroreceptors, respectively, were analyzed in atropinized cats. The reflux renal vessel, muscle vessel and heart rate responses, expressed as per cent of maximum, to graded activations of arterial baroreceptors (sinus pressure variations) and stimulations of ventricular receptor afferents in the cardiac nerve were systematically compared. Cardiac nerve stimulation with low frequencies was found to elicit more pronounced reflex renal vessel responses than muscle vessel and heart rate responses. In contrast, elevations of sinus pressure induced equally pronounced renal and muscle vessel responses. High frequency cardiac nerve stimulation elicited maximal reflex renal vessel responses, but only submaximal effects on muscle vessels and heart rate, while intense baroreceptor stimulation induced maximal reflex effector responses throughout. The submaximal heart rate response to cardiac nerve stimulation is probably due to a simultaneous activation of excitatory afferents. On the other hand, the less pronounced muscle than renal vessel responses when the cardiac nerve was stimulated probably reflect a relatively sparse innervation of muscle vasomotor neurons by ventricular receptor afferents, which seem instead to be preferentially oriented towards renal vasomotor and, possibly, cardiac motor neurons.