The effect of venous and arterial occlusion of the arm on changes in tissue hemodynamics, oxygenation, and ultra-weak photon emission.

Ultra-weak photon emission (UPE) is a general feature of living -biological systems. To gain further insights into the origin of UPE and its physiological significance, the aim of the present study was to investigate the connection between hemodynamics (HD), oxygenation (OX), and UPE. Therefore, during venous and arterial occlusion (VO, AO), changes of UPE and surrogates of HD as well as OX were measured simultaneously using two photomultipliers and near-infrared spectroscopy, respectively. We showed that (1) changes in UPE correlate significantly nonlinearly with changes in oxyhemoglobin (Δ[O(2)Hb]), deoxyhemoglobin (Δ[HHb]), and hemoglobin difference (Δ[HbD] = Δ[O(2)Hb]-Δ[HHb]), indicating a complex association between UPE and tissue HD/OX; (2) UPE decreases significantly during AO but not during VO; (3) UPE increases significantly after AO; and (4) the view that ROS are the source of UPE is generally supported by the present study, although some findings remain unexplained in the context of the theory of ROS-mediated UPE generation. In conclusion, the present study revealed new insights into the interplay between HD, OX, and UPE and opens up new questions that have to be addressed by future studies.

Heartbeat-induced axial motion artifacts in optical coherence tomography measurements of the retina.

PURPOSE: To investigate the cause of axial eye motion artifacts that occur in optical coherence tomography (OCT) imaging of the retina. Understanding the cause of these motions can lead to improved OCT image quality and therefore better diagnoses. METHODS: Twenty-seven measurements were performed on 5 subjects. Spectral domain OCT images at the macula were collected over periods up to 30 seconds. The axial shift of every average A-scan was calculated with respect to the previous average A-scan by calculating the cross-correlation. The frequency spectrum of the calculated shifts versus time was determined. The heart rate was determined from blood pressure measurements at the finger using an optical blood pressure detector. The fundamental frequency and higher order harmonics of the axial OCT shift were compared with the frequency spectrum of blood pressure data. In addition, simultaneous registration of the movement of the cornea and the retina was performed with a dual reference arm OCT setup, and movements of the head were also analyzed. RESULTS: A correlation of 0.90 was found between the fundamental frequency in the axial OCT shift and the heart rate. Cornea and retina move simultaneously in the axial direction. The entire head moves with the same amplitude as the retina. CONCLUSIONS: Axial motion artifacts during OCT volume scanning of the retina are caused by movements of the whole head induced by the heartbeat.

The reliability of continuous noninvasive finger blood pressure measurement in critically ill children.

INTRODUCTION: Continuous noninvasive arterial blood pressure can be measured in finger arteries using an inflatable finger cuff (FINAP) with a special device and has proven to be feasible and reliable in adults. We studied prototype pediatric finger cuffs and pediatric software to compare this blood pressure measurement with intraarterially measured blood pressure (IAP) in critically ill children. METHODS: We included sedated and mechanically ventilated children admitted to our pediatric intensive care unit. We performed simultaneous arterial blood pressure measurements during a relatively stable hemodynamic period and compared FINAP, IAP, and the noninvasive blood pressure oscillometric technique. We also compared IAP to a reconstruction of brachial pressure from finger pressure. RESULTS: Thirty-five children between 2 and 22 kg body weight were included. In total, 152 attempts to record a FINAP pressure were performed of which 4.6% were unsuccessful. When comparing FINAP to IAP, bias was -16.2, -7.7, and -10.2 mm Hg for systolic arterial blood pressure, diastolic arterial blood pressure, and mean arterial blood pressure. Limits of agreement (LOA) were respectively 26.1%, 30.1%, and 22.6%. When reconstruction of brachial pressure from finger pressure was compared to IAP, these results were -11.8, 0.6, and -0.9 mm Hg for bias and 21.7%, 8.9%, and 8.9% for LOA. When noninvasive blood pressure oscillometric technique was compared to IAP, the results were: -6.8, -0.9, and -3.8 mm Hg for bias and 18.2%, 38.6%, and 22.1% for LOA. CONCLUSION: Beta type continuous noninvasive arterial blood pressure monitoring using a finger cuff with brachial arterial waveform reconstruction seems reliable in hemodynamically stable critically ill children.

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 designed a set of small-sized finger cuffs based on the assessment of finger circumference. Finger arterial BP measured by a volume clamp device (Finapres 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 feasible in very young children. However, cuff application is critical, and the current set-point algorithm needs to be revised in very young children.