Browsing by Author "Hudson, Lindsey"
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Item Evaluating the efficacy of wireless near infrared spectroscopy sensors for detecting central hypovolemia during simulated hemorrhage in humans(2024-03-21) Muthyala, Ritika; Davis, K. Austin; Hudson, Lindsey; Dinh, Viet Q.; Roumengous, Thibault; Wallner, Josephine; Boutwell, Casey; Rickards, Caroline A.Background: Early identification of blood loss is essential to decrease mortality from hemorrhage, a major cause of death in the military and civilian trauma settings. An industry partner has created noninvasive and wireless near infrared spectroscopy (NIRS) sensors to measure somatic tissue oxygenation (StO₂) for early detection of blood loss. In this study, we investigated the efficacy of these sensors for tracking the reduction in central blood volume (indexed by stroke volume) in humans undergoing simulated hemorrhage. We hypothesized that each NIRS sensor will progressively track the reduction in central blood volume during simulated hemorrhage in humans. Methods: Eight healthy humans (3 F, 5M; 25.3 ± 2.0 y) participated in a simulated hemorrhage protocol induced via application of lower body negative pressure (LBNP) to presyncope. Following baseline, the LBNP chamber pressure was decreased every 5-min to -15, -30, -45, -60, -70, -80, -90 and -100 mmHg, or until the onset of presyncopal symptoms (defined as a systolic arterial pressure <80 mmHg or subjective symptoms). Heart rate (via lead II ECG) and arterial pressure (via finger photoplethysmography) were monitored continuously. Stroke volume was estimated from pulse contour analysis of the finger photoplethysmography waveform. A total of five NIRS sensors measured StO2 at different anatomical locations including the sternum, forearm, deltoid, thigh, and calf. Data were analyzed over the final 3-min of each LBNP stage and the 1-min immediately prior to the onset of presyncope. Correlations between the relative changes in StO₂ of each sensor and stroke volume were assessed. Results: Stroke volume decreased by 46.9± 16.3 % at presyncope. StO₂ decreased by 1.5 ± 7.8 % at the sternum, 9.6 ± 7.4 % at the forearm, 1.5 ± 3.6 % at the deltoid, 21.3 ± 15.8 % at the thigh, and 30.4 ± 27.5 % at the calf. Of all the sites, the strongest relationship between decreases in StO₂ and stroke volume was at the calf (R-value range: 0.70-0.99, R-value mean: 0.89 ± 0.11). The sensors located at each of the other sites tracked stroke volume with high inter-participant variability (sternum, R-value range: -0.71-0.99, R-value mean: 0.24 ± 0.79; forearm, R-value range: -0.09-0.99, R-value mean: 0.61 ± 0.40; deltoid, R-value range: -0.97-0.96, R-value mean: 0.26 ± 0.83; thigh, R-value range: -0.75-0.99; R-value mean: 0.68 ± 0.64). Conclusion: Unexpectedly, the NIRS sensor on the calf, which was inside the LBNP chamber, performed the best out of the five sites in tracking the progressive reduction in central blood volume in healthy human participants. This may be due to the pooling of blood volume in the lower limbs with the LBNP stimulus, which increased deoxygenated hemoglobin, resulting in an overall lower measurement of tissue oxygen saturation. This finding is interesting, and further modifications and testing of these sensors are required to reliably track blood volume loss in patient populations.Item Interactions Between Carotid Arterial Stiffness, Amplitude of Cerebral Blood Flow Oscillations, and Cerebral Tissue Oxygenation During Simulated Hemorrhage in Humans(2024-03-21) Hudson, Lindsey; Davis, Austin; Anderson, Garen; Rosenberg, Alexander; McKeefer, Haley; Bird, Jordan; Pentz, Brandon; Byman, Britta; Jendzjowsky, Nicholas; Wilson, Richard; Day, Trevor; Rickards, CarolineIntroduction: Inducing 0.1 Hz (10-s cycle) oscillations in cerebral blood flow attenuates the reduction in cerebral tissue oxygenation during simulated hemorrhage in humans. It is unknown, however, how stiffness of the cerebral feed arteries influences the magnitude of cerebral blood flow oscillations, and/or the protection of cerebral tissue oxygenation. When 0.1 Hz oscillations are induced during simulated hemorrhage, we hypothesize that: 1) arterial stiffness of the internal carotid artery (ICA) will increase from rest; 2) the amplitude of 0.1 Hz oscillations in cerebral blood flow will be higher in individuals with stiffer arteries, and; 3) the reduction in cerebral tissue oxygenation will be smaller with higher amplitude of cerebral blood flow oscillations. Methods: 8 healthy human participants (age: 30.1±7.6 y) underwent a 10-min hypovolemic oscillatory lower body negative pressure (OLBNP) protocol, where chamber pressure oscillated every 5-s between -30 mmHg and -90 mmHg (i.e., 0.1 Hz). ICA beta stiffness index was calculated from measurements of ICA diameter (via ultrasound imaging), and arterial pressure (via finger photoplethysmography). Middle cerebral artery velocity (MCAv) was measured using transcranial doppler ultrasound, and cerebral tissue oxygenation (ScO2) was measured with near infrared spectroscopy. Fast Fourier transformation was used to quantify oscillations in mean MCAv at ~0.1 Hz. Results: While Mean MCAv 0.1 Hz oscillations increased from baseline to OLBNP (N=8, 34.0±33.9 (cm/s)2vs. 104.7±58.1(cm/s)2, p=0.01), ICA beta stiffness did not increase (N=5, 6.1±0.7 au vs. 8.2±2.7 au, p=0.21). There was no relationship between baseline ICA beta stiffness and the percent change in mean MCAv 0.1 Hz oscillations (N=5; r=0.44, p=0.46). ScO2 decreased from baseline to OLBNP (N=8, 66.5±2.9 % vs. 64.8±2.9%,p=0.03), but there was also no relationship between the percent change in mean MCAv 0.1 Hz oscillations and the decrease in ScO2(r=0.28, p=0.50). Conclusions: Based on these data, 0.1 Hz OLBNP does not affect ICA stiffness, and there is no relationship between ICA stiffness, amplitude of induced 0.1 Hz cerebral blood flow oscillations, and the reduction in cerebral tissue oxygenation during simulated hemorrhage. However, as this analysis was performed retrospectively, and arterial stiffness was not initially an outcome measure, there was limited data available for analysis. This limitation will be addressed in a project currently in progress in our laboratory.