Alexsandria Odoi

Cerebral Oxygenation in Preterm Infants

BACKGROUND AND OBJECTIVE: Prone sleeping is a major risk factor for sudden infant death syndrome (SIDS) and preterm infants are at significantly increased risk. In term infants, prone sleeping is associated with reduced mean arterial pressure (MAP) and cerebral tissue oxygenation index (TOI). However, little is known about the effects of sleeping position on TOI and MAP in preterm infants. We aimed to examine TOI and MAP in preterm infants after term-equivalent age, during the period of greatest SIDS risk. METHODS: Thirty-five preterm and 17 term infants underwent daytime polysomnography, including measurement of TOI (NIRO-200 spectrophotometer, Hamamatsu Photonics KK, Japan) and MAP (Finapress Medical Systems, Amsterdam, Netherlands) at 2 to 4 weeks, 2 to 3 months, and 5 to 6 months postterm age. Infants slept prone and supine in active and quiet sleep. The effects of sleep state and position were determined by using 2-way repeated measures analysis of variance and of preterm birth by using 2-way analysis of variance. RESULTS: In preterm infants, TOI was significantly lower when prone compared with supine in both sleep states at all ages (P < .05). Notably, TOI was significantly lower in preterm compared with term infants at 2 to 4 weeks, in both positions (P < .05), and at 2 to 3 months when prone (P < .001), in both sleep states. MAP was also lower in preterm infants in the prone position at 2 to 3 months (P < .01). CONCLUSIONS: Cerebral oxygenation is reduced in the prone position in preterm infants and is lower compared with age-matched term infants, predominantly in the prone position when MAP is also reduced. This may contribute to their increased SIDS risk.

The Effect of Gestational Age at Birth on Post-Term Maturation of Heart Rate Variability.

STUDY OBJECTIVE Preterm birth delays maturation of autonomic cardiovascular control, reflected in reduced heart rate variability (HRV) in preterm compared to term infants at term-equivalent age. It has been suggested that immature cardiovascular control contributes to the increased risk for the sudden infant death syndrome (SIDS) in preterm infants. However, the effects of prone sleeping, the major SIDS risk factor, and of gestational age (GA) at birth on HRV have not been assessed in preterm infants beyond term-equivalent age. SUBJECTS AND METHODS Very preterm (n = 21; mean GA 29.4 ± 0.3 weeks), preterm (n = 14; mean GA 33.5 ± 0.3 weeks), and term (n = 17; mean GA 40.1 ± 0.3 weeks) infants were recruited and underwent daytime polysomnography at 2-4 weeks, 2-3 months, and 5-6 months post-term corrected age (CA). Infants slept both supine and prone. HRV was assessed in the low frequency (LF) and high frequency (HF) ranges. RESULTS There was no effect of prone sleeping on HRV parameters in either preterm group. In term infants LF/HF was significantly elevated in the prone position in AS at 2-4 weeks (P < 0.05). HF HRV was significantly reduced (P < 0.05) and LF/HF increased (P < 0.05) in very preterm compared to both preterm and term infants at 2-3 months CA. CONCLUSION Prone sleeping did not significantly impact on heart rate variability (HRV) in preterm infants. However, reduced maturation of high frequency HRV in very preterm infants resulted in significantly altered sympathovagal balance at 2-3 months corrected age, the age of peak sudden infant death syndrome (SIDS) risk. This may contribute to the increased risk of SIDS in infants born at earlier gestational age.

The longitudinal effects of persistent periodic breathing on cerebral oxygenation in preterm infants

OBJECTIVES Periodic breathing is common in preterm infants, but is thought to be benign. The aim of our study was to assess the incidence and impact of periodic breathing on heart rate (HR), oxygen saturation (SpO2), and brain tissue oxygenation index (TOI) over the first six months after term-equivalent age. STUDY DESIGN Twenty-four preterm infants (27-36 weeks gestational age) were studied with daytime polysomnography in quiet sleep (QS) and active sleep (AS) and in both the prone and supine positions at 2-4 weeks, 2-3 months, and 5-6 months post-term corrected age. HR, SpO2, and TOI (NIRO-200 spectrophotometer) were recorded. Periodic breathing episodes were defined as greater than or equal to three sequential apneas each lasting ≥3 s. RESULTS A total 164 individual episodes of periodic breathing were recorded in 19 infants at 2-4 weeks, 62 in 12 infants at 2-3 months, and 35 in 10 infants at 5-6 months. There was no effect of gestational age on periodic breathing frequency or duration. Falls in HR (-21.9 ± 2.7%) and TOI (-13.1 ± 1.5%) were significantly greater at 2-3 months of age compared to 2-4 weeks of age. CONCLUSIONS The majority of preterm infants discharged home without clinical respiratory problems had persistent periodic breathing. Although in most infants periodic breathing was not associated with significant falls in SpO2 or TOI, several infants had significant desaturations and reduced cerebral oxygenation especially during AS. The clinical significance of this on neurodevelopmental outcome is unknown and warrants further investigations.

Cerebrovascular control is altered in healthy term infants when they sleep prone

STUDY OBJECTIVES Sudden infant death syndrome (SIDS) is a leading cause of infant death, and prone sleeping is the major risk factor. Prone sleeping impairs arousal from sleep and cardiovascular control in infants at 2-3 months, coinciding with the highest risk period for SIDS. We hypothesized that prone sleeping would also alter cerebrovascular control, and aimed to test this hypothesis by examining responses of cerebral oxygenation to head-up tilts (HUTs) over the first 6 months after birth. STUDY DESIGN AND PARTICIPANTS Seventeen healthy full-term infants were studied at 2-4 weeks, 2-3 months, and 5-6 months of age using daytime polysomnography, with the additional measurements of blood pressure (BP, Finometer™, Finometer Medical Systems, The Netherlands) and cerebral tissue oxygenation index (TOI, NIRO 200, Hamamatsu Photonics KK, Japan). HUTs were performed in active sleep (AS) and quiet sleep (QS) in both prone and supine positions. RESULTS When infants slept in the prone position, a sustained increase in TOI (P < 0.05) occurred following HUTs, except in QS at 2-3 months when TOI was unchanged. BP was either unchanged or fell below baseline during the sustained TOI increase, signifying cerebro-vasodilatation. In contrast, when infants slept supine, TOI did not change after HUTs, except in QS at 2-3 and 5-6 months when TOI dropped below baseline (P < 0.05). CONCLUSIONS When infants slept in the prone position, cerebral arterial vasodilation and increased cerebral oxygenation occurred during head-up tilts, possibly as a protection against cerebral hypoxia. Absence of the vasodilatory response during quiet sleep at 2-3 months possibly underpins the decreased arousability from sleep and increased risk for sudden infant death syndrome at this age.

Gestational Age at Birth Affects Maturation of Baroreflex Control

OBJECTIVES To assess the effect of prone sleeping, the major risk factor for sudden infant death syndrome, in the control of blood pressure (BP) in preterm infants born across a range of gestational ages. STUDY DESIGN Daytime polysomnography was performed at 2-4 weeks, 2-3 months, and 5-6 months postterm age. The participants were 21 very preterm (mean gestation 29.4 ± 0.3 weeks), 14 preterm (mean gestation 33.1 ± 0.3 weeks), and 17 term (mean gestation 40.1 ± 0.3 weeks). BP was measured via a Finometer cuff (Finapres Medical Systems, Amsterdam, The Netherlands) placed around the wrist. Data were recorded both supine and prone. Baroreflex sensitivity (BRS) was calculated via cross-spectral analysis of spontaneous fluctuations in BP. RESULTS BRS was lower in the prone position in very preterm infants at 2-4 weeks in active sleep (P < .05). Maturation of BRS was delayed in very preterm compared with both preterm and term infants. CONCLUSIONS Maturation of BRS after term-equivalent age is altered in very preterm infants. Reduced BRS may result in an impaired ability of very preterm infants to respond to cardiovascular stress during infancy and may predispose them to cardiovascular disease later in life.

Preterm infants exhibit greater variability in cerebrovascular control than term infants

STUDY OBJECTIVES Sudden infant death syndrome (SIDS) remains an important cause of infant death, particularly among infants born preterm. Prone sleeping is the major risk factor for SIDS and this has recently been shown to alter cerebrovascular control in term infants. As preterm infants are at greater risk for SIDS than those born at term, we hypothesized that their cerebrovascular control in the prone position would be reduced compared to term infants. PATIENTS OR PARTICIPANTS There were 35 preterm (mean gestation 31.2 ± 0.4 w) and 17 term (mean gestation 40.1 ± 0.3 w) infants. DESIGN Infants underwent daytime polysomnography at 2-4 w, 2-3 mo, and 5-6 mo postterm age. Infants slept both prone and supine and were presented with cardiovascular challenges in the form of 15° head-up tilts (HUT). MEASUREMENTS AND RESULTS Cerebral tissue oxygenation index (TOI) was recorded using near-infrared spectroscopy (NIRO-200 spectrophotometer, Hamamatsu Photonics KK, Japan) and mean arterial pressure (MAP) was recorded using a Finometer cuff (Finapres Medical Systems, Amsterdam, The Netherlands). In the prone position TOI increased following the HUT (P < 0.05), whereas no change was seen in the supine position. The overall pattern of response was similar in both groups, but more variable in preterm than term infants (P < 0.05). CONCLUSIONS Cerebrovascular control differs between the prone and supine positions in preterm infants. Although overall the responses to head-up tilts were similar between term and preterm infants, greater variability of responses in preterm infants suggests persisting immaturity of their cerebrovascular control in the first year of life, which may contribute to their increased risk of sudden infant death syndrome.

The effects of dummy/pacifier use on infant blood pressure and autonomic activity during sleep

BACKGROUND Dummy/pacifier use is protective for sudden infant death syndrome (SIDS); however, the mechanism/s for this are unknown. As impaired cardiovascular control may be the underlying cause of SIDS, we assessed the effects of dummy/pacifier use on cardiovascular control during sleep within the first 6 months of life. METHODS Term infants, divided into dummy/pacifier users and non-dummy/pacifier users, were studied at 2-4 weeks (n = 27), 2-3 months (n = 35) and 5-6 months (n = 31) using daytime polysomnography. Heart rate, blood pressure (BP), heart rate variability (HRV), blood pressure variability (BPV), and baroreflex sensitivity (BRS) were measured in triplicate 1-2-min epochs during quiet and active sleep in the supine and prone positions. RESULTS Overall, during the non-sucking periods, in the prone position, the BP was higher (10-22 mmHg) in dummy/pacifier users compared to non-users at 2-4 weeks and 5-6 months (p < 0.05 for both). HRV and BRS were higher in dummy/pacifier users compared to non-users at 2-4 weeks (p < 0.05). Active sucking increased HRV and BPV, consistent with increased sympathetic activity in dummy/pacifier users. CONCLUSIONS Higher BP and HRV in dummy/pacifier users indicate increased sympathetic tone, which may serve as a protective mechanism against possible hypotension leading to SIDS; however, these effects were not apparent at 2-3 months, when the risk of SIDS is highest.

Pacifier use does not alter sleep and spontaneous arousal patterns in healthy term‐born infants

Impaired arousal from sleep has been implicated in sudden infant death syndrome (SIDS). Sleeping in the prone position is a major risk factor for SIDS. Epidemiological studies have shown that pacifier use decreases the risk of SIDS, even when infants sleep prone. We examined spontaneous arousability in infants slept prone and supine over the first 6 months of life and hypothesised that spontaneous arousals would be increased in pacifier users, particularly in the prone position.

Autonomic cardiovascular control in hypotensive critically ill preterm infants is impaired during the first days of life.

BACKGROUND The first days after preterm birth are a critical period of cardiovascular instability, where hypotension is common. We assessed autonomic cardiovascular function by measuring heart rate variability (HRV), blood pressure variability (BPV) and baroreflex sensitivity (BRS) and hypothesised that these would be impaired in preterm infants born at younger gestational ages. In addition, we speculated that impaired cardiovascular control could be used as a marker of circulatory failure such as is manifest as hypotension. METHODS 23 preterm infants (11 M/12 F) born between 23 and 35 weeks (mean 27 ± 0.6 weeks) gestational age with indwelling arterial catheters were recruited. Infants were studied over the first 3 days of life with heart rate and blood pressure (BP) analysed beat to beat in the frequency domain in 2 minute epochs of artefact free data during active sleep. Data were compared with one way ANOVA. RESULTS Gestational age was correlated with all HRV indices but not BPV or BRS. 9 babies received inotropes. Gestational age between the inotrope group and the non-inotrope group was not different. BP and RR interval were lower in the inotrope group (40.7 ± 1.5 vs 47.1 ± 1.5 mmHg, p<0.05 and 395 ± 14 vs 426 ± 11 ms, p<0.08). BRS was also lower in the inotrope group (3.8 ± 0.9 vs 6.9 ± 1.6 ms/mmHg) as was LF/HF HRV (5.7 ± 1.3 vs 13.6 ± 2.8, p<0.05). CONCLUSIONS In the first 3 days after birth, infants receiving inotropes had significantly impaired cardiovascular control compared to those who did not receive treatment, indicating that these infants maybe predisposed to increased vulnerability to circulatory instability.

The Longitudinal Effects of Persistent Apnea on Cerebral Oxygenation in Infants Born Preterm

Objective To assess the incidence and impact of persistent apnea on heart rate (HR), oxygen saturation (SpO2), and brain tissue oxygenation index (TOI) over the first 6 months after term equivalent age in ex‐preterm infants. Study design Twenty‐four preterm infants born between 27 and 36 weeks of gestational age were studied with daytime polysomnography at 2‐4 weeks, 2‐3 months, and 5‐6 months post‐term corrected age. Apneas lasting ≥3 seconds were included and maximal percentage changes (nadir) in HR, SpO2, and tissue oxygenation index (TOI, NIRO‐200 Hamamatsu) from baseline were analyzed. Results A total of 253 apneas were recorded at 2‐4 weeks, 203 at 2‐3 months, and 148 at 5‐6 months. There was no effect of gestational age at birth, sleep state, or sleep position on apnea duration, nadir HR, SpO2, or TOI. At 2‐4 weeks, the nadirs in HR (−11.1 ± 1.2 bpm) and TOI (−4.4 ± 1.0%) were significantly less than at 2‐3 months (HR: −13.5 ± 1.2 bpm, P < .05; TOI: −7.5 ± 1.1 %, P < .05) and at 5‐6 months (HR: −13.2 ± 1.3 bpm, P < .01; TOI: −9.3 ± 1.2%, P < .01). Conclusions In ex‐preterm infants, apneas were frequent and associated with decreases in heart rate and cerebral oxygenation, which were more marked at 2‐3 months and 5‐6 months than at 2‐4 weeks. Although events were short, they may contribute to the adverse neurocognitive outcomes that are common in ex‐preterm children.