Postnatal development of baroreflex sensitivity in infancy

Baroreflex sensitivity (BRS) using spontaneous sequence analysis in the time domain is not fully applicable in infancy, as the time delay for heart period to change (heart period delay, HPD) after an arterial pressure change is unknown. We estimated and compared HPD and BRS in the frequency (BRSsp, HPDsp) and time domains (BRSseq, HPDseq) from systolic blood pressure (SBP) and heart period fluctuations. Continuous SBP, using photoplethysmography, and heart period measurements were performed on 30 term infants at 2–4 weeks, 2–3 months and 5–6 months postnatal age. Cross-spectral analysis between SBP and heart period fluctuations was used to estimate BRSsp and HPDsp. Spontaneous sequence analysis was used to estimate BRS using a fixed beat delay of 1–12 beats (BRSseq) or a variable delay identified by a novel method accounting for epoch–epoch variability in HPD (BRSseqvar). HPDsp averaged 3.4 s (∼7 beats); BRSsp averaged 11.4 ms mmHg−1. BRSseq and BRSseqvar were consistently lower than BRSsp (P < 0.05), but the three BRS estimates were strongly correlated using a HPD of ∼5–6 beats. BRSseqvar resulted in the average estimate (8.9 ms mmHg−1) closest to BRSsp and overall had the strongest correlation with BRSsp (R2= 0.61; P < 0.001). All three BRS estimates increased progressively with postnatal age, with BRSsp averaging 6.4, 10.5 and 16.0 ms mmHg−1 at 2–4 weeks, 2–3 months and 5–6 months, respectively (P < 0.05). Accounting for the HPD of infancy provides estimates of BRS in the time domain that closely parallel spectral estimates, and provides a novel analytical tool to assess normal development and dysfunction of the baroreflex in infants

Baroreflex dysfunction in sick newborns makes heart rate an unreliable surrogate for blood pressure changes.

BACKGROUND: Cerebral pressure passivity (CPP) in sick newborns can be detected by evaluating coupling between mean arterial pressure (MAP) and cerebral blood flow measured by NIRS hemoglobin difference (HbD). However, continuous MAP monitoring requires invasive catheterization with its inherent risks. We tested whether heart rate (HR) could serve as a reliable surrogate for MAP in the detection of CPP in sick newborns. METHODS: Continuous measurements of MAP, HR, and HbD were made and partitioned into 10-minute epochs. Spectral coherence (COH) was computed between MAP and HbD (COH(MAP-HbD)) to detect CPP, between HR and HbD (COH(HR-HbD)) for comparison, and between MAP and HR (COH(MAP-HR)) to quantify baroreflex function (BRF). The agreement between COH(MAP-HbD) and COH(HR-HbD) was assessed using ROC analysis. RESULTS: We found poor agreement between COH(MAP-HbD) and COH(HR-HbD) in left hemisphere (area under the ROC curve (AUC) 0.68) and right hemisphere (AUC 0.71). Baroreflex failure (COH(MAP-HR) not significant) was present in 79% of epochs. Confining comparison to epochs with intact BRF showed an AUC of 0.85 for both hemispheres. CONCLUSIONS: In these sick newborns, HR was an unreliable surrogate for MAP required for the detection of CPP. This is likely due to the prevalence of BRF failure in these infants

Feasibility of noninvasive continuous finger arterial blood pressure measurements in very young children, aged 0-4 years

Our goal was to study the feasibility of continuous noninvasive finger blood pressure (BP) monitoring in very young children, aged 0-4 y. To achieve this, we dedigned a set of smallsized finger cuffs based on the assessment of finger circumference. Finger arterial BP measured by a volume clamp device (Finapress technology) was compared with simultaneously measured intra-arterial BP in 15 very young children (median age, 5 mo; range, 0-48), admitted to the intensive care unit for vital monitoring. The finger cuff-derived BP waveforms showed good resemblance with the invasive arterial waveforms (mean root-mean-square error, 3 mm Hg). The correlation coefficient between both methods was 0.79 ± 0.19 systolic and 0.74 ± 0.24 diastolic. The correlation coefficient of beat-to-beat changes between both methods was 0.82 ± 0.18 and 0.75 ± 0.21, respectively. Three measurements were related to measurement errors (loose cuff application; wrong set-point). Excluding these erroneous measurements resulted in clinically acceptable measurement bias (-3.8 mm Hg) and 95% limits of agreement (-10.4 to + 2.8 mm Hg) of mean BP values. We conclude that continuous finger BP measurement is feasable in very young children. However, cuff application is critical, and the current set-point algorithm needs to be revised in very young children. (Pediatr Res 63: 691-696, 2008