Microphonic versus end-tidal carbon dioxide nasal airflow detection in neonates with apnea.

Impedance pneumography in combination with expired CO2 monitoring are commonly used techniques for detecting central and obstructive apnea in infants. In this investigation an American Telephone and Telegraph StarSet-1 3000-ohm self-actuating microphone connected to the end of an infant cannula was used to monitor neonatal nasal airflow to detect breaths and apnea. The microphone was placed in a soundproof container to eliminate environmental sound artifacts. Analyses of 100 breaths from five patient samples during active and quiet sleep showed that there was no significant difference between microphone and expired CO2 recording of respiration. The techniques were 98% and 96% sensitive, respectively. Microphonic detection of nasal airflow identified 27 of the 32 episodes of upper airway obstruction (84.2%) registered by end-tidal CO2 recording. Inspiratory and expiratory events could also be well documented. Microphonic recording of nasal airflow is a reliable and inexpensive technique to detect apnea.

Effects of maternal smoking and caffeine habits on infantile apnea: a retrospective study.

To evaluate the relationship of antecedent maternal smoking and caffeine consumption habits on the occurrence of apnea in their offspring, rates for central and obstructive apnea were analyzed in a cohort of mother-infant pairs. The mothers of 298 infants with apnea responded to a questionnaire completed prior to a nine-hour polysomnogram performed as part of the patients' evaluations. Cigarette consumption estimates were computed on a 20-cigarette per pack basis, and caffeine intake, based on dietary sources (coffee, tea, chocolate, and colas), was summarized as milligrams of caffeine consumed per day. Rates of central and obstructive apnea of 6 to 10 seconds in duration were calculated. Multiple linear regression analysis determined that smokers tended to be younger and have lower birth weight infants who presented earlier with apnea than infants of nonsmokers. Increased rates of central apnea occurred in infants of smokers as compared with infants of nonsmokers. During pregnancy, a pack per day increase in maternal smoking habit was associated with a 1.88/h increase in central apneas in their offspring (P less than .01). Maternal smoking after delivery had a similar relationship. Obstructive apnea rates were similar in both groups. Both central and obstructive apnea rates associated positively with increasing maternal caffeine consumption. Smoking habits and caffeine ingestion were correlated (P less than .01). Infants with apnea have greater rates of central apnea when their mothers smoke during pregnancy. Therefore, a history of nicotine consumption should be included in the medical history of infants presenting with apnea.

Effect of sleep state and position on the incidence of obstructive and central apnea in infants.

Sixty-four infants with a history of apnea were studied to determine the effects of sleeping position and sleep state (rapid eye movement [REM]) v (non-rapid eye movement [NREM]) on the occurrence of central and obstructive apneas. All-night polysomnographic studies were conducted on each infant, and the spontaneous occurrence of central and obstructive apneic events was determined in the prone, supine, and side positions. Sleeping position did not significantly affect the rate or duration of central or obstructive apneas. Furthermore, neither central nor obstructive apneic episodes were significantly altered by sleep state. These data suggest that, in spite of an ostensible predisposition to upper airway obstruction in the supine position and during rapid eye movement sleep, neither sleeping position nor sleep state appears to affect the rate of duration of apneic events.

Prediction of the acute response to surfactant therapy by pulmonary function testing.

We tested the hypothesis that pretreatment pulmonary function values would be predictive of the response to the synthetic pulmonary surfactant, Exosurf (Burroughs Wellcome Co.) treatment of infants with respiratory distress syndrome (RDS). Pulmonary compliance and resistance were measured prior to Exosurf treatment in 40 infants with severe RDS. In 36 patients who survived for at least 24 hr the acute response to therapy was quantitated by calculated post-treatment/pretreatment ratios of ventilator efficiency index (VEI) and arterial/alveolar oxygen tension ratios [Pa/AO2]. The values of these calculated response ratios 24 and 48 hr after treatment varied widely among individual patients. The magnitude of the response was not related to birthweight, gestational age, age at treatment, pretreatment VEI, pretreatment Pa/AO2, or pretreatment pulmonary compliance. However, the response to Exosurf as measured by improvements in Pa/AO2 at 24 and 48 hr was related to pretreatment pulmonary resistance (r = -0.34, P less than 0.05 and r = -0.60, P less than 0.001), high pretreatment pulmonary resistance was associated with a poor response to Exosurf 24 and 48 hr after treatment.

Latency to enter a mirrored chamber: a novel behavioral assay for anxiolytic agents.

Many animal species exhibit approach-avoidance responses upon the novel placement of a mirror into an individual animal's environment. With a view toward identifying new behavioral measures with qualitatively or quantitatively different responses to anxiolytic agents, we developed a mirrored chamber apparatus for which adult male BALB/cByJ mice showed an extended latency to enter. Administration of diazepam significantly reduced this latency to enter a mirrored chamber in a dosage-dependent manner. The psychomotor stimulant, methylphenidate, had no effect on latency to enter the mirrored chamber at a dose which stimulated locomotor activity to the same extent as diazepam. Thus, the decreased latency to enter the mirrored chamber brought about by diazepam seems unlikely to reflect the motor effects of this benzodiazepine. The potency of diazepam was significantly lower in the mirrored chamber assay than it was on three other measures of exploratory activity--"head-dipping" performance, plus-maze performance and locomotor activity stimulation. The findings of our study indicate that the mirrored chamber method is simple to carry out, nonpunishing, rapid and quantitative and that it possesses pharmacological attributes which distinguish its response to anxiolytics from other assays of exploratory behavior.

Apnea in subsequent asymptomatic siblings of infants who had an apparent life-threatening event.

Infants experiencing apparent life-threatening events (ALTE) have been reported to have elevated frequencies of periodic breathing and obstructive apnea when compared to presumably normal control groups. Whether these characteristics extend to the siblings of ALTE infants remains unknown. This study compared, retrospectively, the apnea indices of 13 first-born infants experiencing an ALTE with their subsequent asymptomatic siblings who had undergone polygraphic sleep apnea evaluations (including electrocardiogram, chest wall movements, expired CO2, and transcutaneous pulse oximetry). Gestation, birthweight, age at study, apnea and periodic breathing indices, and oxygen desaturations were compared. Regression analyses revealed that adjustments for gestational and postnatal age eliminated differences in apnea indices. ALTE infants and their subsequent siblings experienced similar rates of apnea. Neither group had elevated rates of prolonged central apneas (greater than 10 seconds duration) or periodic breathing (greater than 5% sleep time). Neither group had subsequent severe apneas. The use of polygraphic study and cardiac/apnea monitors in subsequent siblings of ALTE are unnecessary and should be considered only when there is parental disagreement.

Environmental tobacco smoke exposure and gastroesophageal reflux in infants with apparent life-threatening events.

OBJECTIVE: To study the hypothesis that environmental tobacco smoke exposure in infants diagnosed with an apparent life-threatening event (ALTE) could be a contributing factor to gastroesophageal reflux. METHODS: Thirty-four polygraphic recordings of combined esophageal pH study and respiration in infants with ALTE, age 4.1 +/- 4.9 months, range 0.4-27 months, were studied. This group of children had uncomplicated perinatal history, no congenital anomalies, no neuropathology, and no drug exposure. A written questionnaire was administered to the parents to determine the following: environmental variables, degree of environmental tobacco smoke (ETS) exposure (number of cigarettes/day), and nutrition (breast vs. bottle feeding). RESULTS: There was a strong correlation between pH study parameters and ETS exposure (p < 0.005). The esophageal pH parameters were markedly elevated in the ETS-exposed group and in this group there was a linear relation between the number of cigarettes smoked per day and reflux index, as well as reflux > 5 min/hr (p < 0.05, r = 0.46). Nursing mothers were less likely to be smokers (18.2% vs. 34.0%). The only significant respiratory finding was in the obstructive/mixed apnea group; there was strong association between ETS exposure and high reflux index (p < 0.05). CONCLUSION: We conclude that ETS exposure represents a significant contributing factor to GER. Pediatricians should systematically ask questions about the infant environment, explain the risk of ETS exposure to the caretaker, and recommend that children should remain in a smoke-free environment.

Morphine stimulates rapid, regular, deep, and sustained breathing efforts in fetal lambs.

We gave morphine (1-4 mg) to 11 unanesthetized lamb fetuses at 123-141 days of gestation. After a delay of 28 +/- 7 min (mean +/- SE), the fetuses began forceful, frequent, regular, and sustained inspiratory efforts lasting continuously for 105 +/- 15 min and continuing intermittently for a total of 155 +/- 13 min. The induced breathing motions are more forceful, frequent, and regular than the naturally occurring efforts of the fetus and resemble neonatal breathing motions. The phenomenon is blocked by 0.5 mg of naloxone but not by 0.1 mg of atropine. We conclude that the mechanism of action involves the opiate receptor system. We speculate that endorphins may have a role in the regulation of breathing in the fetal and newborn lamb.

Clinical usefulness of maternal odor in newborns: soothing and feeding preparatory responses.

This study assessed the responsiveness of newborn breast- and bottle-fed infants to presentations of maternal odor. Maternal odor was presented for 1 min to crying, sleeping or awake newborns. The odors were: (1) own mother's odor - presentation of a hospital gown worn by the baby's mother, (2) other mother's odor - presentation of a hospital gown of another newborn baby's mother, (3) clean gown - presentation of a clean hospital gown and (4) no gown - no gown presented. The results indicated that crying babies stopped crying when either own mother or other mother odor was presented. Awake babies responded specifically to their own mother's odor by increasing mouthing. These results suggest that the practice of presenting the mother's odor to a distressed infant is of clinical usefulness since it was capable of attenuating crying. The results also characterized a role for maternal odor with respect to feeding since presentation of the infant's own mother odor increased mouthing. Thus, presentation of maternal odor may also be useful in enhancing nipple acceptance and feeding in newborns.

In vitro model of human umbilical venous perfusion to study the effects of meconium staining of the umbilical cord.

Because meconium diffuses into placental and umbilical cord tissue, its bioactive components are potentially capable of entering the fetal circulation. Meconium diluted in Krebs solution produces vasoconstriction in human umbilical vein segments that are suspended in a milieu similar to that of the amniotic cavity. Based on published observations, we wanted to determine if very diluted meconium could induce vasospasm in intact umbilical cords. Human umbilical cords were obtained from full-term deliveries, cut into 2 equal segments, cannulated, and perfused continuously as test and control cords. The study included four parts: (1) intraluminal meconium (n = 6; 0.01-1% solution); (2) 4-hour exposure to 10% meconium-stained amniotic fluid of intact umbilical cords (n = 8); (3) 4-hour exposure to a 10% meconium-stained amniotic fluid of umbilical cords denuded of their epithelial layer (n = 5); (4) 24-hour exposure to a 10% meconium-stained amniotic fluid of intact umbilical cords (n = 9). Significant vasoconstriction of the umbilical vein occurred only with the intraluminal meconium solution exposure (p = 0.034). In this in vitro model meconium staining of the umbilical cord was not associated with vasoconstriction of the umbilical vein.

Effect of morphine on fetal electrocortical activity and breathing movements in fetal sheep.

Morphine (1 mg/kg) given to the lamb fetus near term induces a significant increase in low-voltage high-frequency (LVHF) electrical activity in the brain. This pattern of the electrocorticogram (ECOG) is associated with simultaneous continuous fetal breathing movements of greater amplitude than control. Naloxone prevents and reverses these morphine-induced changes. The observed phenomena suggest that opiate receptors may play a stimulant role in the control of fetal LVHF ECOG and fetal breathing movements.

Cardiovascular effects of acute hemorrhage in fetal lambs.

The effects of acute hemorrhage were studied in two groups each with six fetal lambs (100-116 amd 128-147 days gestation) 3-4 days after we implanted catheters. Fetal blood pressures, heart rate, arterial blood gases and pH, and combined ventricular output and its distribution (radionuclide-labeled microsphere technique) were measured before and 5 min after removal of 15% of fetal-placental blood volume measured by 125I-albumin dilution. Because there were no differences in responses in the two age groups, the data were pooled. Fetal arterial mean pressure fell significantly (50.7 +/- 2.5 to 45.5 +/- 2.6 mmHg) as did heart rate (186 +/- 6 to 151 +/- 13 beats/min) and arterial blood pH (7.39 +/- 0.02 to 7.30 +/- 0.02); arterial blood carbon dioxide tension rose (39.7 +/- 29 to 44.1 +/- 4.4). Combined ventricular output fell from 610 +/- 58 to 448 +/- 45 ml . kg-1 . min-1 (P < 0.05). Blood flow to the umbilical-placental circulation, as well as to the fetal body, fell significantly. Blood flow to the kidneys, gastrointestinal tracts, and lungs also fell, but flow to other organs was maintained. Blood volume reduction in the fetus markedly influences blood gas exchange, because it results in a reduction of umbilical-placental blood flow associated with the fall in arterial pressure.

Effects of hypothermia and rewarming on the neonatal circulation.

Thirteen unanesthetized lambs, aged 1-3 days, were cooled from 40 degrees to 30 degrees C and then rewarmed. During cooling, heart rate dropped from 196 +/- 47 to 140 +/- 42 beats per minute, a 29% change; cardiac output, femoral arterial and pulse pressures did not change significantly; but inferior vena cava pressure (IVC) increased from 5 to 9 mm of mercury, and left ventricular end diastolic pressure (LVEDP) increased from 8 to 25 mm/Hg. Mean pulmonary arterial pressure increased from 29 to 40 mm/Hg. Metabolic acidosis and hypoxia developed during the cooling. There were marked changes in the distribution of cardiac output; the proportion of cardiac output increased by 450% to brown fat, 66% to the skeletal muscles, and 30% to the right ventricular myocardium and atria. No significant change in the distribution to the left ventricule and septum was observed. Distribution to the other organs decreased markedly. After rewarming, all the previous parameters returned to normal except CVP and LVEDP, which remained elevated.