Background: While extremely vulnerable in the initial extrauterine period (<72h), cardiovascular control improves such that preterms graduate NICU with apparently healthy cardiovascular function. However, cohort studies demonstrate persistent cardiovascular dysfunction throughout childhood, adolescence and adulthood.
Aim: Investigate maturation of cardiovascular control using static and dynamic cardiovascular challenges from infancy to juvenility.
Method: Cardiovascular function (three-lead ECG, non-invasive blood pressure, and laser Doppler flowmetry) was assessed in term-born guinea pigs at 24h, 7d and 40d postnatal age within a temperature-controlled environment. Doppler probes (ear and interscapular skin sites) were set at 36OC for baseline measures. Probe temperature was raised to 40OC and increased 1OC/min to 44OC to elicit maximal vasodilatation.
Results: Term animals displayed an ability to dilate ear vessels in response to local heating throughout the study period (24 hours: males P=0.001, females P=0.0004; 7d: males P=0.004, females P=0.002; 40d, males P=0.02, females P=0.2). This response was not observed in interscapular skin. In males, dilation of ear vasculature in response to heating was accompanied by a reduction in heart rate at 24h (P=0.001) and 7d (P=0.01), but was not observed at 40d. No effect of this peripheral challenge on heart rate was observed in females at any age. Longitudinally, central changes were inverse to peripheral perfusion, with heart rate reducing after 7d (P<0.0001), but ear and interscapular flow increasing (P=0.19, P<0.0001, respectively).
Discussion: In the early postnatal period, microvascular reactivity is associated with significant changes in central cardiovascular function, even in term-born individuals. With advancing postnatal age, both responsiveness to mild stimuli and the impact of peripheral microvascular tone on central cardiovascular function decreases. We have established methods for minimally-invasive, repeated assessment of cardiovascular function in guinea pigs from birth. Results will be compared with preterm-born animals in order to better understand long-term consequences of preterm birth.