In order to mitigate the effect of non-stationarity in frequency domain analysis of data, we propose a modification to the power spectral estimation, a widely used technique to characterize physiological signals. Spectral analysis requires partitioning data into smaller epochs determined by the desired frequency resolution. The modified approach proposed here involves dividing the data within each epoch by the standard deviation of the data for that epoch. We applied this modified approach to cardiac beat-to-beat interval data recorded from a newborn infant undergoing hypothermia treatment for birth asphyxia. The critically ill infant had episodes of tachyarrhythmia, distributed sporadically throughout the study, which affected the stationarity of the heart rate. Over the period of continuous heart rate recording, the infant’s clinical course deteriorated progressively culminating in death. Coinciding with this clinical deterioration, the heart rate signal showed striking changes in both low-frequency and high-frequency power indicating significant impairment of the autonomic nervous system. The standard spectral approach failed to capture these phenomena because of the non-stationarity of the signal. Conversely, the modified approach proposed here captured the deteriorating physiology of the infant clearly.
Although this study does not, by design, provide further evidence toward the questions of whether CHD is a defining feature of VACTERL association, the frequency of CHD in our cohort does lend support to it being an important medical consideration in patients with VACTERL association. Based on our experience, we strongly recommend a screening echocardiogram to evaluate for CHD in individuals with a potential diagnosis of VACTERL association.
OBJECTIVE: In this study, we validated the use of the FORE-SIGHT ® (CAS Medical Systems, Branford, CT USA) tissue oximeter monitor on abdominal tissue oxygenation in infants ≤4 kg using a stool-interference compensation algorithm. STUDY DESIGN: A total of 40 neonates with an umbilical venous catheter (UVC) were enrolled in this study. We measured abdominal tissue saturation (StO 2 ) values using FORE-SIGHT, and compared to a Reference StO 2 value derived from weighted co-oximetry values from the UVC and pulse oximeter measurements. RESULTS: There was a strong correlation between NIRS calculated StO 2 measurements when compared with the reference StO 2, with an overall bias (sd) of −0.77 (5.06)% and a concordance correlation coefficient (CCC) of 0.789. CONCLUSION: Data from this validation study suggest that the FORE-SIGHT monitor, which compensates for the optical properties of stools in neonates, can yield accurate measures of abdominal tissue oxygen saturation.
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