R M Sayers

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° 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 mothers 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 SDΔRR. 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 SDΔRR 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 SDΔRR) 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.

Participation in research: Informed consent, motivation and influence

Objective: To investigate the process and quality of informed consent, motivation and influence in parents who were invited to enrol their baby in a research project.

Vasoconstriction following spontaneous sighs and head-up tilts in infants sleeping prone and supine

The cutaneous vasoconstrictor responses following a 60 degrees head-up tilt and a spontaneous sigh were measured in 36 infants at 1 and 3 months age to investigate the effects of age, sleep state and sleep position on these responses. The vasoconstrictor response was determined by a measure of cutaneous blood flow using a laser Doppler flowmeter. The mean reduction in blood flow (vasoconstriction) was 52% following the tilt, and 33% following the sigh. Prone positioning 1-month-old infants as compared to supine, reduced the degree of vasoconstriction following the tilt (P=0.027) and sigh (P=0.026). The supine to prone reduction was: tilt, -11% in quiet sleep (QS) (from 55.1 to 49.1% vasoconstriction) and -18% in active sleep (AS) (from 52.0 to 42.9%) and; sigh, -26% in QS (35-26%), and -15% in AS (31-26%). The degree of vasoconstriction following the sigh was significantly greater in 3- compared to 1-month-old infants (+26%, P=0.040). The mean response to the tilt in the older age group was 12% greater but this did not reach significance (P=0.069). Sleep state did not affect the degree of vasoconstriction but influenced transmission of the response so that latency to minimal vasoconstriction was 1 s shorter in AS than QS. This study provides data on two simple measures of sympathetic activity during sleep that have not previously been described in any detail in infant studies, and add more evidence that autonomic activity is reduced in the prone position compared to supine during sleep.

Ventilatory sensitivity to mild asphyxia: prone versus supine sleep position.

AIMS To compare the effects of prone and supine sleep position on the main physiological responses to mild asphyxia: increase in ventilation and arousal. METHODS Ventilatory and arousal responses to mild asphyxia (hypercapnia/hypoxia) were measured in 53 healthy infants at newborn and 3 months of age, during quiet sleep (QS) and active sleep (AS), and in supine and prone sleep positions. The asphyxial test mimicked face down rebreathing by slowly altering the inspired air: CO2, maximum 5% and O2, minimum 13.5%. The change in ventilation with inspired CO2 was measured over 5–6 minutes of the test. The slope of a linear curve fit relating inspired CO2 to the logarithm of ventilation was taken as a quantitative measure of ventilatory asphyxial sensitivity (VAS). Sleep state and arousal were determined by behavioural criteria. RESULTS At 3 months of age, prone positioning in AS lowered VAS (0.184 prone v0.269 supine, p = 0.050). At newborn age, sleep position had no effect on VAS. Infants aged 3 months were twice as likely to arouse to the test than newborns (p = 0.013). Placing infants prone as opposed to supine increased the chances of arousal 1.57-fold (p = 0.035). CONCLUSION Our findings show 3 month old babies sleeping prone compared to supine have poorer ventilatory responses to mild asphyxia, particularly in AS, but the increased prevalence of arousal is a protective factor.

A matched case control study of orthostatic intolerance in children/adolescents with chronic fatigue syndrome.

This study aimed to define cardiovascular and heart rate variability (HRV) changes following head-up tilt (HUT) in children/adolescents with chronic fatigue syndrome (CFS) in comparison to age- and gender-matched controls. Twenty-six children/adolescents with CFS (11–19 y) and controls underwent 70-degree HUT for a maximum of 30 min, but returned to horizontal earlier at the participants request with symptoms of orthostatic intolerance (OI) that included lightheadedness. Using electrocardiography and beat-beat finger blood pressure, a positive tilt was defined as OI with 1) neurally mediated hypotension (NMH); bradycardia (HR <75% of baseline), and hypotension [systolic pressure (SysP) drops >25 mm Hg)] or 2) postural orthostatic tachycardia syndrome (POTS); HR increase >30 bpm, or HR >120 bpm (with/without hypotension). Thirteen CFS and five controls exhibited OI generating a sensitivity and specificity for HUT of 50.0% and 80.8%, respectively. POTS without hypotension occurred in seven CFS subjects but no controls. POTS with hypotension and NMH occurred in both. Predominant sympathetic components to HRV on HUT were measured in CFS tilt–positive subjects. In conclusion, CFS subjects were more susceptible to OI than controls, the cardiovascular response predominantly manifest as POTS without hypotension, a response unique to CFS suggesting further investigation is warranted with respect to the pathophysiologic mechanisms involved.

Responses to an increasing asphyxia in infants: effects of age and sleep state

Infants aged 0-6 months were assessed for respiratory and arousal responses to mild asphyxia during sleep. Ventilatory sensitivity was assessed from the relationship between inspired carbon dioxide (FICO2) and ventilation. Arousal and ventilatory sensitivity were significantly related. Respiratory response increased with age and was greater in quiet sleep than in REM sleep. Arousal occurred more frequently in REM sleep (55/102) than quiet sleep (38/165, P < 0.05) and more frequently at the newborn age (54/117) than at 6 months (13/58, P < 0.05). Arousal in quiet sleep occurred in babies with high ventilatory sensitivities (mean ventilatory asphyxial sensitivity (VAS) 0.476 +/- 0.288) and in REM sleep was more associated with low ventilatory sensitivities (mean VAS 0.194 +/- 0.334, P <0.05). We conclude infants respond to mild asphyxia during sleep with an increase in ventilation, an arousal or both. The exact response is dependent on age and sleep state.

Respiratory responses to hypoxia/hypercapnia in small for gestational age infants influenced by maternal smoking

Aim: To determine any variation in the respiratory responses to hypoxia/hypercapnia of infants born small for gestational age (SGA) to smoking and to non-smoking mothers. Methods: A total of 70 average for gestational age (AGA) infants (>36 weeks gestation, >2500 g, >25th centile for gestational age, and no maternal smoking), and 47 SGA infants (<10th centile for gestational age) were studied at 1 and 3 months of age, in quiet and active sleep. Respiratory test gases were delivered through a Perspex hood to simulate face down rebreathing by slowly allowing the inspired air to be altered to a CO2 maximum of 5% and O2 minimum of 13.5%. The change in ventilation with inspired CO2 was measured over 5–6 minutes of the test. The slope of a linear curve fit relating inspired CO2 to the logarithm of ventilation was taken as a quantitative measure of ventilatory asphyxial sensitivity (VAS). Results: There was no significant difference in VAS between the AGA and SGA infants (0.25 v 0.24). However within the SGA group, VAS was significantly higher (p = 0.048) in the infants whose mothers smoked during pregnancy (0.26 (0.01); n = 24) than in those that did not (0.23 (0.01); n = 23). The change in minute ventilation was significantly higher in the smokers than the non-smokers group (141% v 119%; p = 0.03) as the result of a significantly larger change in respiratory rate (8 v 4 breaths/min; p = 0.047) but not tidal volume. Conclusions: Maternal smoking appears to be the key factor in enhancing infants’ respiratory responses to hypoxia/hypercapnia, irrespective of gestational age.

Targeting Sleep, Food, and Activity in Infants for Obesity Prevention: An RCT

An RCT comparing effects of a conventional food and activity intervention versus a sleep behavior intervention on infant growth from birth to 2 years. OBJECTIVE: The few existing early-life obesity prevention initiatives have concentrated on nutrition and physical activity, with little examination of sleep. METHODS: This community-based, randomized controlled trial allocated 802 pregnant women (≥16 years, <34 weeks’ gestation) to: control, FAB (food, activity, and breastfeeding), sleep, or combination (both interventions) groups. All groups received standard well-child care. FAB participants received additional support (8 contacts) promoting breastfeeding, healthy eating, and physical activity (antenatal–18 months). Sleep participants received 2 sessions (antenatal, 3 weeks) targeting prevention of sleep problems, as well as a sleep treatment program if requested (6–24 months). Combination participants received both interventions (9 contacts). BMI was measured at 24 months by researchers blinded to group allocation, and secondary outcomes (diet, physical activity, sleep) were assessed by using a questionnaire or accelerometry at multiple time points. RESULTS: At 2 years, 686 women remained in the study (86%). No significant intervention effect was observed for BMI at 24 months (P = .086), but there was an overall group effect for the prevalence of obesity (P = .027). Exploratory analyses found a protective effect for obesity among those receiving the “sleep intervention” (sleep and combination compared with FAB and control: odds ratio, 0.54 [95% confidence interval, 0.35–0.82]). No effect was observed for the “FAB intervention” (FAB and combination compared with sleep and control: odds ratio, 1.20 [95% confidence interval, 0.80–1.81]). CONCLUSIONS: A well-developed food and activity intervention did not seem to affect children’s weight status. However, further research on more intensive or longer running sleep interventions is warranted.

Lactation Consultant Support from Late Pregnancy with an Educational Intervention at 4 Months of Age Delays the Introduction of Complementary Foods in a Randomized Controlled Trial

BACKGROUND Although the WHO recommends that complementary feeding in infants should begin at 6 mo of age, it often begins before this in developed countries. OBJECTIVE Our objective was to determine whether lactation consultant (LC) support, with educational resources given at 4-mo postpartum, can delay the introduction of complementary foods until around 6 mo of age. METHODS A total of 802 mother-infant pairs were recruited from the single maternity hospital serving Dunedin, New Zealand (59% response rate) and randomly assigned to the following: 1) usual care (control group); 2) infant sleep education intervention (Sleep); 3) food, activity, and breastfeeding intervention (FAB); or 4) combination (both) intervention (Combo). Certified LCs delivered 3 intervention sessions (late pregnancy and 1-wk and 4-mo postpartum). The 4-mo contact used educational resources focused on developmental readiness for complementary foods. Age when complementary foods were introduced was obtained from repeated interviews (monthly from 3- to 27-wk postpartum). RESULTS A total of 49.5% and 87.2% of infants received complementary foods before 5 and 6 mo of age, respectively. There was evidence of group differences in the number of infants introduced to complementary foods before 5 mo (P = 0.006), with those receiving support and resources (FAB and Combo groups combined; 55.6%) more likely to wait until at least 5 mo compared with controls (control and Sleep groups combined; 43.3%) (OR: 1.52; 95% CI: 1.08, 2.16). However, there was no evidence they were more likely to wait until 6 mo of age (P = 0.52). Higher maternal age, higher parity, and a less positive attitude toward breastfeeding were positively associated, and drinking alcohol during pregnancy was negatively associated, with later age of introduction of complementary foods. CONCLUSIONS Providing an LC and educational resources at 4-mo postpartum to predominantly well-educated, mainly European, women can delay the introduction of complementary foods until 5 mo of age, but not until the WHO recommendation of 6 mo. This trial was registered at clinicaltrials.gov as NCT00892983.

Anticipatory guidance to prevent infant sleep problems within a randomised controlled trial: infant, maternal and partner outcomes at 6 months of age

Objective To evaluate the effectiveness of sleep education delivered antenatally and at 3 weeks postpartum to prevent infant sleep problems at 6 months of age. Design Sleep intervention within a randomised controlled trial for the Prevention of Overweight in Infancy (POI) study. Participants 802 families were randomly allocated to one of four groups: usual care (control), sleep intervention (sleep), food, activity and breastfeeding intervention (FAB), and combined group receiving both interventions (combination). Interventions All groups received standard Well Child care. The sleep intervention groups (sleep and combination) received an antenatal group education session (all mothers and most partners) emphasising infant self-settling and safe sleeping, and a home visit at 3 weeks reinforcing the antenatal sleep education. FAB and combination groups received four contacts providing education and support on breast feeding, food and activity up to 4 months postpartum. Outcome measures Here we report secondary sleep outcomes from the POI study: the prevalence of parent-reported infant sleep problems and night waking, and differences in sleep duration. Additional outcomes reported include differences in infant self-settling, safe sleep practices, and maternal and partner reports of their own sleep, fatigue and depression symptoms. Results Linear or mixed linear regression models found no significant intervention effects on sleep outcomes, with 19.1% of mothers and 16.6% of partners reporting their infant’s sleep a problem at 6 months. Actigraphy estimated the number of night wakings to be significantly reduced (8%) and the duration of daytime sleep increased (6 min) in those groups receiving the sleep intervention compared with those who did not. However, these small differences were not clinically significant and not observed in 24 hours infant sleep diary data. No other differences were observed. Conclusion A strategy delivering infant sleep education antenatally and at 3 weeks postpartum was not effective in preventing the development of parent-reported infant sleep problems.