Changes in oxygenation and heart rate after administration of artificial surfactant (ALEC) to preterm infants.

To determine if changes in oxygenation and heart rate occur after surfactant, changes in these variables were recorded continuously for 15 minutes before, during, and 15 minutes after the administration of the artificial surfactant ALEC to 21 preterm infants ventilated for respiratory distress syndrome. Median (range) birth weight and gestation were 1199 (561-2680) g and 28 (21-43) weeks, respectively. The mean (SD) time taken for administration was 17.6 (3.8) seconds. No clinically important changes resulted from the administration of ALEC in the mean (SD) values for oxygen saturation (before 91.3 (3.4)%, during 90.7 (3.2)%, after 90.4 (3.7)% and heart rate (before 143 (15), during 138 (17), after 142 (16)). The maximum change in mean arterial oxygen saturation (SaO2) was a fall of 4.8%.     

A developmental study on types and frequency distribution of short apneas (3 to 15 seconds) in term and preterm infants

We measured the frequency distribution and the ventilatory correlates of the various types of apneas 3 to 15 s long during sleep in eight term infants (birth weight 3.65 +/- 0.16 kg; gestational age 39.5 +/- 0.3 wk) and eight preterm infants (birth weight 2.07 +/- 0.18 kg; gestational age 34.3 +/- 0.4 wk). Each infant was studied on five to seven occasions from birth to 56 wk of postconceptual age using a modified flow-through system. Sixty-six paired epochs of quiet sleep (1163 min) and rapid eye movement sleep (829 min) were analyzed in term infants and 85 paired epochs of quiet sleep (1553 min) and rapid eye movement sleep (1328 min) in preterm infants. Of the 783 apneas recorded in term infants 82% were central, 1.5% obstructive, 0.5% mixed, and 16% were of the breath-holding type; the corresponding figures for the 4086 apneas recorded in preterm infants were 93, 0.5, 1.0, and 5.5%. This distribution was similar in the two sleep states but term infants had a higher percentage of breath-holding apneas than preterm infants (p less than 0.01). In preterm infants the rate of central apneas decreased with postnatal age (p less than 0.01); in term infants the rate did not change significantly. The duration of apneas showed a modal distribution for central apneas at about 8 s for both groups during the 1st month of life (p less than 0.05). The findings suggest: 1) apneas in the newborn and early infancy are primarily central and are more frequent in preterm than in term infants.(ABSTRACT TRUNCATED AT 250 WORDS)     

运动后心率恢复的研究进展

摘要：心率恢复（HRR）指数显示运动停止后心率下降的速度,运动后HRR异常是预测心血管疾病及其主要心血管事件发生的有效独立危险因子。HRR减慢指运动后心率下降不足,与交感神经功能缺陷和（或）迷走神经激活有关。临床主要用于评价冠心病、心衰、高血压、糖尿病、代谢综合征与肥胖、睡眠呼吸暂停综合征、风湿免疫病、慢性阻塞性肺病与肺动脉高压等儿童的心脏自主神经功能。研究表明有望通过药物治疗与运动训练等提高自主神经功能的干预措施改善异常的HRR。     

Patterns of oxygenation during periodic breathing in preterm infants

The characteristics of the arterial oxygen saturation (SaO2) signal during episodes of hypoxaemia (SaO2 less than or equal to 80% for greater than or equal to 4 s) associated with periodic and non-periodic apnoeic pauses were studied in 16 preterm infants with cyanotic episodes (patients). and 15 asymptomatic preterm infants (controls), matched on birthweight and gestational age. The patients showed a significantly higher percentage of apnoeic pauses followed by a hypoxaemic episode (25 vs. 6%, P less than 0.01), and a two-fold increase in the slope of the desaturation curve (8.4 vs. 4.3% per s, P less than 0.005) in periodic compared with non-periodic breathing. All other characteristic of oxygenation (baseline SaO2 before episodes of hypoxaemia, delay between onset of apnoeic pause and onset of desaturation, lowest SaO2 during episodes of hypoxaemia) were similar for periodic and non-periodic breathing patterns. Similar, but not significant, differences between isolated and periodic apnoeic pauses were also present in the controls. An analysis of episodes of bradycardia (less than or equal to 100 beats per minute (bpm] showed that out of 121 episodes in the patients 118 were accompanied by a fall in SaO2 to less than or equal to 80%, and in the remaining three SaO2 fell to 82%, 85% and 86%, respectively. Thus all episodes of bradycardia (less than or equal to 100 bpm) were associated with a fall in SaO2 detected by beat-to-beat pulse oximetry. Examination of hypoxaemic episodes and their relationship with bradycardia and with apnoeic pauses, periodic and non-periodic, may help the further understanding of the control of arterial oxygenation in preterm infants with cyanotic episodes.     

Differential diagnosis of apneas in preterm infants

Clinically relevant apneas, which are common in preterm infants, may adversely affect later neuropsychological condition in this group of patients. Pharmacotherapy to stimulate respiratory functions may be unsuccessful. Polygraphic recording may help in the differential diagnosis of these clinically relevant events. Twenty-nine preterm neonates born before 36 weeks of gestational age were examined using polygraphic recording (respiration—two channels, perioral electromyography, oxygen saturation, heart rate, electroencephalography, electrocardiography, electrooculography). The examination was ordered by the attending physician after an unsuccessful treatment of apnea by Aminophylline, and it should contribute to the clarification of the causes of these events. In the course of the polygraphic examinations, altogether 63 episodes were recorded during which the pulse oximeter alarm signal was set off. In 42 cases, the alarm signal was set off in events during which SaO₂ fell below 85%. In the remaining 21 cases, the alarm signal was set off in episodes during which early bradycardia below 90/min occurred. The onset of apnea was very often associated with the phasic increase of the perioral electromyography and with electroencephalography arousal reaction. Because of suspicion that these apneas may be triggered by episodes of gastroesophageal reflux, the interruption of the Aminophylline treatment and setting up an antireflux regimen were recommended. These therapeutic measures had a positive effect: The frequency of alarm signals decreased within 48 h by a statistically significant 50%. In cases where the pharmacotherapy of apnea by stimulation of respiratory functions is not successful, differential diagnostic analysis should be performed. Polygraphy may contribute to the clarification of the causes underlying clinically relevant apneas in a view of newly described polygraphic signs. It is feasible to suspect, based on these signs, that gastroesophageal reflux is the cause for clinically significant apneas in that case.     

Neurological status, sleep apnea frequency and blood oxygenation in six weeks old infants

A study was carried out to investigate the correlation between sleep apnea frequency, blood oxygenation and neurological condition in 21 infants at six weeks of age with inconspicuous medical history. Polygraphic recordings of respiratory behaviour and transcutaneous blood gas monitoring lasted for at least five hours. To quantify the results of the neurological examination we established a neurological optimality score (NOS). We found statistically significant correlations between several indexes of apneas and indexes of blood oxygenation and NOS. Thus, a reduced NOS was strongly correlated with higher apnea frequencies and with pronounced drops of transcutaneous PO2-values. In addition all but one infant who were diagnosed as having a sleep apnea syndrome showed a greater than ten percent reduction of NOS. Some pathophysiological considerations to explain our findings are put forward and the possible role of the neuromodulator adenosine is emphasized.     

Relationship between heart rate, left ventricular output, and stroke volume in preterm infants during fluctuations in heart rate.

The relationship between changes in heart rate, left ventricular output, and left ventricular stroke volume was studied in 18 preterm infants, with mean gestational age 29 wk (range 26-33 wk) and mean postnatal age 10 d (range 1-21 d). To yield left ventricular output, the blood flow velocity in the ascending aorta was measured by range-gated Doppler technique and multiplied by the aortic cross-sectional area measured by cross-sectional and M-mode echocardiography. Stroke volume was calculated by dividing left ventricular output by heart rate. The individual mean left ventricular output correlated poorly with heart rate (r2 = 0.17), and, accordingly, there was a closer relationship between stroke volume and left ventricular output. In only four of the 18 infants was a significant correlation between heart rate changes and left ventricular output found. Substantial changes in stroke volume were seen in most infants, and in 13 of the 18 infants the changes exceeded 25%. These variations in stroke volume were closely related to left ventricular output. In 15 of the 18 infants, the maximum heart rate change was associated with a stroke volume change in the opposite direction. The group average of the maximum heart rate increase in each individual, 24 bpm (18%), corresponded to a decrease in stroke volume of 0.15 mL.kg-1 (9%) (p less than 0.05) and an increase in left ventricular output of 22.7 mL.min-1.kg-1 (9%) (p less than 0.05). A reciprocal relationship was seen between afterload and left ventricular output.(ABSTRACT TRUNCATED AT 250 WORDS)     

Observations on gastro-oesophageal reflux,central apnoea and heart rate in infants

Respiratory movements and heart rate were monitored continuously during the course of 2 h radionuclide studies to detect gastro-oesophageal reflux (GOR) in 22 infants following a milk feed. Twenty infants had GOR, to upper oesophageal/pharyngeal level in 19, and 17 had central apnoea between 3 and 15s. Prolonged central apnoea (greater than 20s) was not observed. Bradycardia, defined as a heart rate less than 80 beats/min for 10s or more, was observed in only 1 infant who did not have GOR. No correlation was found between the number or duration of reflux episodes and the frequency of respiratory pauses between 3 and 17s. When data from individual infants were examined a possible temporal relation between the occurrence of GOR and central apnoea was seen in only two infants; in each case, detailed examination suggested that apnoea was more closely associated with sleep than with GOR. Although the respiratory monitoring system did not include airflow sensors, the almost complete absence of bradycardia suggested that prolonged obstructive apnoeas did not occur. We conclude that any relation between GOR and central apnoeas less than 15 s is not of a direct cause/effect nature.     

Respiratory modulation of heart rate in newborn infants

Spectral analysis was performed on ventilation and instantaneous heart rate data recorded in 15 term infants during quiet sleep in the first week after delivery, and in 11 of these infants during active sleep. There was a close relation between the main peaks of the ventilation spectra and the corresponding histograms of the reciprocals of Ttot. The spectra for instantaneous heart rate showed power at the rate of breathing (HF) and also at lower frequencies, 0.04-0.2 Hz (LF). During quiet sleep, the relative magnitudes of the HF and LF peaks for heart rate were found to depend on the respiratory rate and the variability of Ttot. During active sleep, most of the power in the heart rate spectrum was concentrated in the LF region. Weighted coherences between ventilation and heart rate were higher during quiet than active sleep, both in the HF and LF spectra. LF power was higher during active than quiet sleep in both ventilation and heart rate. The results suggest that the pattern of breathing has a marked effect on the shape of the heart rate spectrum. In most infants, however, there is no fixed phase relationship between oscillations in ventilation and heart rate, at high or low frequencies. These oscillations are affected by sleep state and hence, by implication, by central nervous system rhythm generators.     

Patterns of blood pressure and pulse frequency in infants during Vojta therapy

In twenty infants aged seven weeks on average blood pressure and pulse frequency were measured during physiotherapy according to Vojta. At one of the exercises ("reflex reversion") blood pressure increased at an average of 60 mm Hg compared with the basic value under rest conditions. At another exercise ("reflex supporting") blood pressure reached about 52 mm Hg higher values as under rest conditions. The pulse frequency, however, showed a less impressive increase: it corresponded approximately to the value measured during crying. As probable causes for the increase of blood pressure are discussed: sustained muscle contractions, varied intrathoracal pressure conditions, and the emotional irritations of the infants. In infants with cardiovascular disease the increased strain during physiotherapy according to Vojta should be taken into account as an additional risk.     

Heart rate and heart rhythm in healthy infants and children

Cardiac rate and rhythm in 141 healthy infants, toddlers and schoolchildren during 24 hour ambulatory electrocardiographic monitoring are reported. Maximal and minimal heart rate (1/min) in infants 1 to 5 months of age were 204 +/- 17 and 105 +/- 13, in infants 6 to 12 months of age 187 +/- 19 and 101 +/- 15; in toddlers 177 +/- 17 and 66 +/- 10; in schoolchildren 158 +/- 24 and 54 +/- 6. A sizeable proportion of children of all age groups showed patterns of sinus arrhythmias indistinguishable from second degree sinuatrial block. Supraventricular escape beats and escape rhythms were frequent as well. The longest RR interval was 1.03 +/- 0.16 sec. in infants, 1.20 +/- 0.25 sec. in toddlers, and 1.35 +/- 0.15 sec., respectively, in schoolchildren. Two % of infants, 7% of toddlers, and 6% of schoolchildren had episodes of second degree atrioventricular block type I (Wenckebach) at rest. Supraventricular extrasystoles were found in 38%, 13% and 26%, respectively, and uniform ventricular extrasystoles in 18%, 20% and 16%, respectively, of infants, toddlers and schoolchildren. These data, together with similar information in the literature, can be taken as basis for the evaluation of ambulatory electrocardiograms in children.     

Immunosuppression in infants with short bowel syndrome undergoing isolated liver transplantation

BACKGROUND: Little data exist on immunosuppressive drug absorption in children with short bowel syndrome and intestinal failure associated liver disease (SBS-IFALD). AIM: To evaluate the absorption of immunosuppressive medications in children with SBS-IFALD undergoing isolated liver transplantation (iLTx). METHODS: A retrospective review was performed in children with SBS-IFALD undergoing LTx and comparison made with weight, age-matched children undergoing iLTX (extra-hepatic biliary atresia (EHBA) and normal intestinal length and function). RESULTS: Seven children with SBS-IFALD undergoing iLTx (median residual bowel length, 60 cm, range 40-80) were compared with 15 children undergoing LTx for EHBA. SBS-IFALD children had significantly lower trough tacrolimus levels at three months (5.8 vs. 7.9 ng/mL, p<0.05) and six months (5.0 vs. 8.0 ng/mL, p<0.05), but equivalent levels at 12 months after iLTx. The median calculated dose-normalized concentrations indicated that systemic availability of tacrolimus was comparable in two groups at 3, 6, 12 months (33.1 vs. 23.3; 42.4 vs. 36; 51 vs. 52.9) despite the differences in enteral function. The incidence of acute rejection was 1/7 (SBS-IFALD) and 10/15 (EHBA) group (p = 0.06). CONCLUSION: Children with SBS-IFALD demonstrated adequate absorption of oral tacrolimus without significant acute rejection rate after iLTx suggesting that modification of immunosuppression is not necessary.     

Factors affecting heart rate variability and heart rate responses to tilting in infants aged 1 and 3 months

Heart rate variability (HRV) and heart rate (HR) responses following a 60 degree head-up tilt were measured in 60 infants at 1 and 3 mo of age to investigate the effects on these of age, sleep state, sleep position, and mother's smoking status. HRV was determined from Poincaré plots of 500 sequential RR intervals to measure overall variability derived from the SDRR of this plot, and instantaneous variability derived from the SDdeltaRR. HR responses to the tilt were measured as changes in RR interval length from rest to immediately following the tilt and again once a stable pattern was reached. SDRR and SDdeltaRR increased 20 and 40%, respectively, with age (p < 0.0001), SDRR was higher in active sleep (AS) than quiet sleep (QS, +72%, p < 0.0001) but both measures of variability (SDRR and SDdeltaRR) were lower in the prone position compared with supine (-18%, p < 0.0001). However, several findings were dependent on the basal RR interval, thus the age effect disappeared once RR interval was taken into account, sleep state remained an important factor and the lower variability when prone now became a difference of -3% (p = 0.034). The tilt generally provoked a reflex tachycardia followed by a bradycardia and settling to a stable HR level below, at, or above baseline within 30 s. The more unusual responses were no HR change, sustained tachycardia or sustained bradycardia (15% of total). These were more likely to occur in younger infants (p = 0.008) and in AS (p < 0.0001). No changes were seen in any of the cardiac indices related to maternal smoking status. The findings confirm several reports indicating that prone sleeping damps some physiologic responses. The data emphasize the need to consider basal heart rate, and sleep position as well as sleep state in autonomic function testing during infant sleep.     

Sleep apneas and acid esophageal reflux in control infants and in infants with an apparent life-threatening event

Clinical experience shows that episodes of apnea can occur during regurgitations or vomiting. We questioned whether sleep apneas could be related temporally to documented falls in esophageal pH, when no clinical symptoms of emesis are witnessed. Twenty infants admitted after an apparently life-threatening event ('ALTE') during sleep, but with no clinical symptoms of vomiting or regurgitations at the time of the event, and ten control infants were studied. All infants had occasional episodes of regurgitations. Polygraphic monitoring of state of alertness, cardiorespiratory activity and low esophageal pH was performed continuously during 1 night. The data were analyzed blindly. A total of 334 central and 36 obstructive apneas were monitored, mainly in the ALTE group, during NREM sleep. A total of 116 falls in esophageal pH below 4 units were seen in 18 infants; 50% occurred during wakefulness, and 31% in REM sleep. Arousals or body movements preceded the pH fall in 50% of the cases. Within 5 min following the reflux onset, 18 central apneas (7.2% of the apneas) were seen. There was no correlation between the duration, or the lowest values of esophageal pH measured, and the number or duration of apneas. No obstructive apnea, bradycardia or arousal followed the falls in esophageal pH. Acid esophageal reflux did not play a significant role in the development of apnea in our population.     

Resting heart rate does not predict growth in preterm infants

Background

Previous reports indicate that preterm infants with higher baseline heart rate (HR) have greater weight gain than preterm infants with lower baseline HR. To verify this correlation and the potential utility of resting HR as a bench mark for risk of extrauterine growth restriction (EUGR), we studied preterm infants born between 32 and 36 weeks gestation. Earlier gestation infants (27 to 31 weeks) were included.

Methods

In retrospective chart review we collected heart rate (HR) and growth data on 156 infants between 27.0 and 34.0 weeks gestation from birth to hospital discharge.

Results

There was a significant increase in weight gain from day 10 of life in infants with higher resting HR compared to infants with lower resting HR. However, upon controlling for birth weight and gestational age, there was no significant relationship between HR and weight gain for any gestational age group of premature infants.

Conclusions

Contrary to previous reports, there was no significant relationship between HR and growth at any gestational age after controlling for birth weight and gestational age. It is important to continue to search for a clinical marker of risk for poor growth in preterm infants and to give an opportunity for nutritional interventions which may support better growth and developmental outcomes.     

Unchanged heart rate-respiratory frequency ratio in preterm infants during spontaneous arousals

Aim: To find out whether a correlation of heart rate (HR) and respiratory frequency (RF) defined as HR-RF-ratio (HRR) may be helpful to identify arousals in term and preterm infants.
Methods: Polygraphic recordings were performed in 25 term infants (gestational age 40.1 ± 1.1 weeks) and 25 preterm infants (gestational age 31.1 ± 1.3 weeks) during undisturbed daytime sleep. Arousals were scored as suggested by the 'International Paediatric Work Group on Arousals' and divided into cortical arousals and subcortical arousals. HRR was defined as HR over RF. Arousals were compared to a 30-sec period preceding an arousals.
Results: Two hundred arousals were scored (100 cortical arousals and 100 subcortical arousals). HRR increased during arousals in term infants (p < 0.001). This was true for cortical arousals (p < 0.001) and subcortical arousals (p < 0.05) of term infants. In contrast, in preterm infants HRR remained unchanged during cortical arousals and subcortical arousals.
Conclusion: An increase of HRR during arousals is a simple parameter to identify arousals in term infants, but not in preterm infants suggesting that an unchanged HRR might be an indicator of an immature arousal response.     

健康足月新生儿生后10分钟内血氧饱和度及心率研究

目的探讨健康足月新生儿在出生后10 min内血氧饱和度(SpO2)及心率(HR)的变化及参考值。方法采用脉压氧饱和度仪测定203例正常足月新生儿(阴道产97例,剖宫产106例)在正常呼吸时的血SpO2及HR,描绘SpO2及HR在生后1~10分钟的第10~95百分位图表。结果生后第1分钟,健康新生儿血SpO2的P10、P50和P95分别为62%、71%和85%;HR的P10、P50和P95分别为66次/min、98次/min和126次/min。SpO2上升至90%的中位数时间为5 min。健康新生儿在出生后1~5 min HR随时间上升趋势明显,之后趋于平稳。结论可参考SpO2及HR,并结合临床表现综合评估新生儿,谨慎用氧,避免高氧或低氧血症对新生儿造成的损伤。