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Hemorrhage at high altitude: impact of sustained hypobaric hypoxia on cerebral blood flow, tissue oxygenation, and tolerance to simulated hemorrhage in humans. Eur J Appl Physiol 2024:10.1007/s00421-024-05450-1. [PMID: 38489034 DOI: 10.1007/s00421-024-05450-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2023] [Accepted: 02/22/2024] [Indexed: 03/17/2024]
Abstract
With ascent to high altitude (HA), compensatory increases in cerebral blood flow and oxygen delivery must occur to preserve cerebral metabolism and consciousness. We hypothesized that this compensation in cerebral blood flow and oxygen delivery preserves tolerance to simulated hemorrhage (via lower body negative pressure, LBNP), such that tolerance is similar during sustained exposure to HA vs. low altitude (LA). Healthy humans (4F/4 M) participated in LBNP protocols to presyncope at LA (1130 m) and 5-7 days following ascent to HA (3800 m). Internal carotid artery (ICA) blood flow, cerebral delivery of oxygen (CDO2) through the ICA, and cerebral tissue oxygen saturation (ScO2) were determined. LBNP tolerance was similar between conditions (LA: 1276 ± 304 s vs. HA: 1208 ± 306 s; P = 0.58). Overall, ICA blood flow and CDO2 were elevated at HA vs. LA (P ≤ 0.01) and decreased with LBNP under both conditions (P < 0.0001), but there was no effect of altitude on ScO2 responses (P = 0.59). Thus, sustained exposure to hypobaric hypoxia did not negatively impact tolerance to simulated hemorrhage. These data demonstrate the robustness of compensatory physiological mechanisms that preserve human cerebral blood flow and oxygen delivery during sustained hypoxia, ensuring cerebral tissue metabolism and neuronal function is maintained.
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The effect of oscillatory hemodynamics on the cardiovascular responses to simulated hemorrhage during isocapnia. J Appl Physiol (1985) 2023; 135:1312-1322. [PMID: 37881852 PMCID: PMC10911761 DOI: 10.1152/japplphysiol.00241.2023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2023] [Revised: 10/17/2023] [Accepted: 10/20/2023] [Indexed: 10/27/2023] Open
Abstract
During cerebral hypoperfusion induced by lower body negative pressure (LBNP), cerebral tissue oxygenation is protected with oscillatory arterial pressure and cerebral blood flow at low frequencies (0.1 Hz and 0.05 Hz), despite no protection of cerebral blood flow or oxygen delivery. However, hypocapnia induced by LBNP contributes to cerebral blood flow reductions, and may mask potential protective effects of hemodynamic oscillations on cerebral blood flow. We hypothesized that under isocapnic conditions, forced oscillations of arterial pressure and blood flow at 0.1 Hz and 0.05 Hz would attenuate reductions in extra- and intracranial blood flow during simulated hemorrhage using LBNP. Eleven human participants underwent three LBNP profiles: a nonoscillatory condition (0 Hz) and two oscillatory conditions (0.1 Hz and 0.05 Hz). End-tidal (et) CO2 and etO2 were clamped at baseline values using dynamic end-tidal forcing. Cerebral tissue oxygenation (ScO2), internal carotid artery (ICA) blood flow, and middle cerebral artery velocity (MCAv) were measured. With clamped etCO2, neither ICA blood flow (ANOVA P = 0.93) nor MCAv (ANOVA P = 0.36) decreased with LBNP, and these responses did not differ between the three profiles (ICA blood flow: 0 Hz: 2.2 ± 5.4%, 0.1 Hz: -0.4 ± 6.6%, 0.05 Hz: 0.2 ± 4.8%; P = 0.56; MCAv: 0 Hz: -2.3 ± 7.8%, 0.1 Hz: -1.3 ± 6.1%, 0.05 Hz: -3.1 ± 5.0%; P = 0.87). Similarly, ScO2 did not decrease with LBNP (ANOVA P = 0.21) nor differ between the three profiles (0 Hz: -2.6 ± 3.3%, 0.1 Hz: -1.6 ± 1.5%, 0.05 Hz: -0.2 ± 2.8%; P = 0.13). Contrary to our hypothesis, cerebral blood flow and tissue oxygenation were protected during LBNP with isocapnia, regardless of whether hemodynamic oscillations were induced.NEW & NOTEWORTHY We examined the role of forcing oscillations in arterial pressure and blood flow at 0.1 Hz and 0.05 Hz on extra- and intracranial blood flow and cerebral tissue oxygenation during simulated hemorrhage (using lower body negative pressure, LBNP) under isocapnic conditions. Contrary to our hypothesis, both cerebral blood flow and cerebral tissue oxygenation were completely protected during simulated hemorrhage with isocapnia, regardless of whether oscillations in arterial pressure and cerebral blood flow were induced. These findings highlight the protective effect of preventing hypocapnia on cerebral blood flow under simulated hemorrhage conditions.
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The potential therapeutic benefits of low frequency haemodynamic oscillations. J Physiol 2022; 600:3905-3919. [PMID: 35883272 PMCID: PMC9444954 DOI: 10.1113/jp282605] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2022] [Accepted: 07/22/2022] [Indexed: 11/08/2022] Open
Abstract
Haemodynamic oscillations occurring at frequencies below the rate of respiration have been observed experimentally for more than a century. Much of the research regarding these oscillations, observed in arterial pressure and blood flow, has focused on mechanisms of generation and methods of quantification. However, examination of the physiological role of these oscillations has been limited. Multiple studies have demonstrated that oscillations in arterial pressure and blood flow are associated with the protection in tissue oxygenation or functional capillary density during conditions of reduced tissue perfusion. There is also evidence that oscillatory blood flow can improve clearance of interstitial fluid, with a growing number of studies demonstrating a role for oscillatory blood flow to aid in clearance of debris from the brain. The therapeutic potential of these haemodynamic oscillations is an important new area of research which may have beneficial impact in treating conditions such as stroke, cardiac arrest, blood loss injuries, sepsis, or even Alzheimer's disease and vascular dementia.
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The reciprocal relationship between cardiac baroreceptor sensitivity and cerebral autoregulation during simulated hemorrhage in humans. Auton Neurosci 2022; 241:103007. [PMID: 35716525 PMCID: PMC10424721 DOI: 10.1016/j.autneu.2022.103007] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2021] [Revised: 04/07/2022] [Accepted: 06/09/2022] [Indexed: 11/16/2022]
Abstract
A reciprocal relationship between the baroreflex and cerebral autoregulation (CA) has been demonstrated at rest and in response to acute hypotension. We hypothesized that the reciprocal relationship between cardiac baroreflex sensitivity (BRS) and CA would be maintained during sustained central hypovolemia induced by lower body negative pressure (LBNP), and that the strength of this relationship would be greater in subjects with higher tolerance to this stress. Healthy young adults (n = 51; 23F/28M) completed a LBNP protocol to presyncope. Subjects were classified as high tolerant (HT; completion of -60 mmHg LBNP stage, ≥20-min) or low tolerant (LT; did not complete -60 mmHg LBNP stage, <20-min). R-R intervals (RRI), systolic arterial pressure (SAP), mean arterial pressure (MAP), and middle cerebral artery velocity (MCAv) were measured continuously. Cardiac BRS was calculated in the time domain (ΔHR/ΔSAP) and frequency domain (RRI-SAP low frequency (LF) transfer function gain), and CA was calculated in the time domain (ΔMCAv/ΔMAP) and frequency domain (MAP-mean MCAv LF transfer function gain). There was a moderate relationship between cardiac BRS and CA for the group of 51 subjects in both the time (R = -0.54, P < 0.0001) and frequency (R = 0.61, P < 0.001) domains; there was a stronger relationship in the HT group (R = 0.73) compared to the LT group (R = 0.31) in the frequency domain (P = 0.08), but no difference between groups in the time domain (HT: R = -0.73 vs. LT: R = -0.63; P = 0.27). These findings suggest that an interaction between BRS and CA may be an important compensatory mechanism that contributes to tolerance to simulated hemorrhage in young healthy adults.
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Effects of Sustained Hypobaric Hypoxia on Amplitude of Forced Hemodynamic Oscillations During Central Hypovolemia. FASEB J 2022. [DOI: 10.1096/fasebj.2022.36.s1.r5720] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Peaks and valleys: oscillatory cerebral blood flow at high altitude protects cerebral tissue oxygenation. Physiol Meas 2021; 42:10.1088/1361-6579/ac0593. [PMID: 34038879 PMCID: PMC11046575 DOI: 10.1088/1361-6579/ac0593] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2021] [Accepted: 05/26/2021] [Indexed: 01/21/2023]
Abstract
Introduction.Oscillatory patterns in arterial pressure and blood flow (at ∼0.1 Hz) may protect tissue oxygenation during conditions of reduced cerebral perfusion and/or hypoxia. We hypothesized that inducing oscillations in arterial pressure and cerebral blood flow at 0.1 Hz would protect cerebral blood flow and cerebral tissue oxygen saturation during exposure to a combination of simulated hemorrhage and sustained hypobaric hypoxia.Methods.Eight healthy human subjects (4 male, 4 female; 30.1 ± 7.6 year) participated in two experiments at high altitude (White Mountain, California, USA; altitude, 3800 m) following rapid ascent and 5-7 d of acclimatization: (1) static lower body negative pressure (LBNP, control condition) was used to induce central hypovolemia by reducing chamber pressure to -60 mmHg for 10 min(0 Hz), and; (2) oscillatory LBNP where chamber pressure was reduced to -60 mmHg, then oscillated every 5 s between -30 mmHg and -90 mmHg for 10 min(0.1 Hz). Measurements included arterial pressure, internal carotid artery (ICA) blood flow, middle cerebral artery velocity (MCAv), and cerebral tissue oxygen saturation (ScO2).Results.Forced 0.1 Hz oscillations in mean arterial pressure and mean MCAv were accompanied by a protection of ScO2(0.1 Hz: -0.67% ± 1.0%; 0 Hz: -4.07% ± 2.0%;P = 0.01). However, the 0.1 Hz profile did not protect against reductions in ICA blood flow (0.1 Hz: -32.5% ± 4.5%; 0 Hz: -19.9% ± 8.9%;P = 0.24) or mean MCAv (0.1 Hz: -18.5% ± 3.4%; 0 Hz: -15.3% ± 5.4%;P = 0.16).Conclusions.Induced oscillatory arterial pressure and cerebral blood flow led to protection of ScO2during combined simulated hemorrhage and sustained hypoxia. This protection was not associated with the preservation of cerebral blood flow suggesting preservation of ScO2may be due to mechanisms occurring within the microvasculature.
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The impact of acute central hypovolemia on cerebral hemodynamics: does sex matter? J Appl Physiol (1985) 2021; 130:1786-1797. [PMID: 33914663 DOI: 10.1152/japplphysiol.00499.2020] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Trauma-induced hemorrhage is a leading cause of disability and death due, in part, to impaired perfusion and oxygenation of the brain. It is unknown if cerebrovascular responses to blood loss are differentiated based on sex. We hypothesized that compared to males, females would have reduced tolerance to simulated hemorrhage induced by maximal lower body negative pressure (LBNP), and this would be associated with an earlier reduction in cerebral blood flow and cerebral oxygenation. Healthy young males (n = 29, 26 ± 4 yr) and females (n = 23, 27 ± 5 yr) completed a step-wise LBNP protocol to presyncope. Mean arterial pressure (MAP), stroke volume (SV), middle cerebral artery velocity (MCAv), end-tidal CO2 (etCO2), and cerebral oxygen saturation (ScO2) were measured continuously. Unexpectedly, tolerance to LBNP was similar between the sexes (males, 1,604 ± 68 s vs. females, 1,453 ± 78 s; P = 0.15). Accordingly, decreases (%Δ) in MAP, SV, MCAv, and ScO2 were similar between males and females throughout LBNP and at presyncope (P ≥ 0.20). Interestingly, although decreases in etCO2 were similar between the sexes throughout LBNP (P = 0.16), at presyncope, the %Δ etCO2 from baseline was greater in males compared to females (-30.8 ± 2.6% vs. -21.3 ± 3.0%; P = 0.02). Contrary to our hypothesis, sex does not influence tolerance, or the central or cerebral hemodynamic responses to simulated hemorrhage. However, the etCO2 responses at presyncope do suggest potential sex differences in cerebral vascular sensitivity to CO2 during central hypovolemia.NEW & NOTEWORTHY Tolerance and cerebral blood velocity responses to simulated hemorrhage (elicited by lower body negative pressure) were similar between male and female subjects. Interestingly, the change in etCO2 from baseline was greater in males compared to females at presyncope, suggesting potential sex differences in cerebral vascular sensitivity to CO2 during simulated hemorrhage. These findings may facilitate development of individualized therapeutic interventions to improve survival from hemorrhagic injuries in both men and women.
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Cerebrovascular control: What's so base-ic about it? J Physiol 2021; 599:2787-2788. [PMID: 33675092 DOI: 10.1113/jp281398] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2021] [Accepted: 03/02/2021] [Indexed: 01/18/2023] Open
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A comparison of protocols for simulating hemorrhage in humans: step versus ramp lower body negative pressure. J Appl Physiol (1985) 2021; 130:380-389. [PMID: 33211600 DOI: 10.1152/japplphysiol.00230.2020] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Lower body negative pressure (LBNP) elicits central hypovolemia, and it has been used to simulate the cardiovascular and cerebrovascular responses to hemorrhage in humans. LBNP protocols commonly use progressive stepwise reductions in chamber pressure for specific time periods. However, continuous ramp LBNP protocols have also been utilized to simulate the continuous nature of most bleeding injuries. The aim of this study was to compare tolerance and hemodynamic responses between these two LBNP profiles. Healthy human subjects (N = 19; age, 27 ± 4 y; 7 female/12 male) completed a 1) step LBNP protocol (5-min steps) and 2) continuous ramp LBNP protocol (3 mmHg/min), both to presyncope. Heart rate (HR), mean arterial pressure (MAP), stroke volume (SV), middle and posterior cerebral artery velocity (MCAv and PCAv), cerebral oxygen saturation (ScO2), and end-tidal CO2 (etCO2) were measured. LBNP tolerance, via the cumulative stress index (CSI, summation of chamber pressure × time at each pressure), and hemodynamic responses were compared between the two protocols. The CSI (step: 911 ± 97 mmHg/min vs. ramp: 823 ± 83 mmHg/min; P = 0.12) and the magnitude of central hypovolemia (%Δ SV, step: -54.6% ± 2.6% vs. ramp: -52.1% ± 2.8%; P = 0.32) were similar between protocols. Although there were no differences between protocols for the maximal %Δ HR (P = 0.88), the %Δ MAP during the step protocol was attenuated (P = 0.05), and the reductions in MCAv, PCAv, ScO2, and etCO2 were greater (P ≤ 0.08) when compared with the ramp protocol at presyncope. These results indicate that when comparing cardiovascular responses to LBNP across different laboratories, the specific pressure profile must be considered as a potential confounding factor.NEW & NOTEWORTHY Ramp lower body negative pressure (LBNP) protocols have been utilized to simulate the continuous nature of bleeding injuries. However, it unknown if tolerance or the physiological responses to ramp LBNP are similar to the more common stepwise LBNP protocol. We report similar tolerance between the two protocols, but the step protocol elicited a greater increase in cerebral oxygen extraction in the presence of reduced blood flow, presumably facilitating the matching of metabolic supply and demand.
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White Mountain Expedition 2019: Peaks and Valleys ‐ Oscillatory cerebral blood flow at high altitude. FASEB J 2020. [DOI: 10.1096/fasebj.2020.34.s1.05888] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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White Mountain Expedition 2019: The Impact of Sustained Hypoxia on Cerebral Blood Flow Responses and Tolerance to Simulated Hemorrhage. FASEB J 2020. [DOI: 10.1096/fasebj.2020.34.s1.05889] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Responses of cerebral blood velocity and tissue oxygenation to low-frequency oscillations during simulated haemorrhagic stress in humans. Exp Physiol 2019; 104:1190-1201. [PMID: 31090115 PMCID: PMC11022286 DOI: 10.1113/ep087358] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2018] [Accepted: 05/14/2019] [Indexed: 04/19/2024]
Abstract
NEW FINDINGS What is the central question of this study? Do low-frequency oscillations in arterial pressure and cerebral blood velocity protect cerebral blood velocity and oxygenation during central hypovolaemia? What is the main finding and its importance? Low-frequency oscillations in arterial pressure and cerebral blood velocity attenuate reductions in cerebral oxygen saturation but do not protect absolute cerebral blood velocity during central hypovolaemia. This finding indicates the potential importance of haemodynamic oscillations in maintaining cerebral oxygenation and therefore viability of tissues during challenges to cerebral blood flow and oxygen delivery. ABSTRACT Tolerance to both real and simulated haemorrhage varies between individuals. Exaggerated low-frequency (∼0.1 Hz) oscillations in mean arterial pressure and brain blood flow [indexed via middle cerebral artery velocity (MCAv)] have been associated with improved tolerance to reduced central blood volume. The mechanism for this association has not been explored. We hypothesized that inducing low-frequency oscillations in arterial pressure and cerebral blood velocity would attenuate reductions in cerebral blood velocity and oxygenation during simulated haemorrhage. Fourteen subjects (11 men and three women) were exposed to oscillatory (0.1 and 0.05 Hz) and non-oscillatory (0 Hz) lower-body negative pressure profiles with an average chamber pressure of -60 mmHg (randomized and counterbalanced order). Measurements included arterial pressure and stroke volume via finger photoplethysmography, MCAv via transcranial Doppler ultrasound, and cerebral oxygenation of the frontal lobe via near-infrared spectroscopy. Tolerance was higher during the two oscillatory profiles compared with the 0 Hz profile (0.05 Hz, P = 0.04; 0.1 Hz, P = 0.09), accompanied by attenuated reductions in stroke volume (P < 0.001) and cerebral oxygenation of the frontal lobe (P ≤ 0.02). No differences were observed between profiles for reductions in mean arterial pressure (P = 0.17) and MCAv (P = 0.30). In partial support of our hypothesis, cerebral oxygenation, but not cerebral blood velocity, was protected during the oscillatory profiles. Interestingly, more subjects tolerated the oscillatory profiles compared with the static 0 Hz profile, despite similar arterial pressure responses. These findings emphasize the potential importance of haemodynamic oscillations in maintaining perfusion and oxygenation of cerebral tissues during haemorrhagic stress.
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A Comparison of Protocols for Simulating Hemorrhage in Humans: Step vs. Ramp Lower Body Negative Pressure. FASEB J 2019. [DOI: 10.1096/fasebj.2019.33.1_supplement.838.22] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Effect of Acute Leg Heating on Neurovascular Control in Aged Humans. FASEB J 2019. [DOI: 10.1096/fasebj.2019.33.1_supplement.541.8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Are Spontaneous Low Frequency Oscillations in Arterial Pressure and Cerebral Blood Flow Associated with the Protection of Cerebral Tissue Oxygenation during Simulated Hemorrhage? FASEB J 2019. [DOI: 10.1096/fasebj.2019.33.1_supplement.838.23] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Hemorrhage simulated by lower body negative pressure provokes an oxidative stress response in healthy young adults. Exp Biol Med (Maywood) 2019; 244:272-278. [PMID: 30727766 DOI: 10.1177/1535370219828706] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
IMPACT STATEMENT We characterize the systemic oxidative stress response in young, healthy human subjects with exposure to simulated hemorrhage via application of lower body negative pressure (LBNP). Prior work has demonstrated that LBNP and actual blood loss evoke similar hemodynamic and immune responses (i.e. white blood cell count), but it is unknown whether LBNP elicits oxidative stress resembling that produced by blood loss. We show that LBNP induces a 29% increase in F2-isoprostanes, a systemic marker of oxidative stress. The findings of this investigation may have important implications for the study of hemorrhage using LBNP, including future assessments of targeted interventions that may reduce oxidative stress, such as novel fluid resuscitation approaches.
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Responses of cerebral blood flow and tissue oxygenation to low frequency oscillations during simulated hemorrhagic stress in humans. FASEB J 2018. [DOI: 10.1096/fasebj.2018.32.1_supplement.910.6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Oxidative Stress During Simulated Hemorrhage Elicited by Lower Body Negative Pressure. FASEB J 2018. [DOI: 10.1096/fasebj.2018.32.1_supplement.910.5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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The effect of polymer addition on granulation in an anaerobic baffled reactor (ABR). Part II: compartmentalization of bacterial populations. WATER RESEARCH 2002; 36:944-955. [PMID: 11848365 DOI: 10.1016/s0043-1354(01)00316-5] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
The microbial ecology of wastewater treatment plants remains one of the least understood aspects in both aerobic and anaerobic systems, despite the fact that both processes are ultimately dependent on an active biomass for operational efficiency. Ultimately, future developments in anaerobic treatment processes will require a much greater understanding of the fundamental relationships between bacterial populations within the biomass if optimum process efficiency is to be fully realised. This study assesses the influence of polymer addition on granule formation within an ABR and compares the ecology of the biomass in each compartment of two ABRs treating ice-cream wastewater. To our knowledge, this is the first reported characterisation of the microbiology of acidogenic and methanogenic bacteria in the individual compartments of an ABR. The polymer-amended reactor contained sludge that had a greater density of anaerobic bacteria and larger and denser granules than the control reactor, indicating that polymer addition possibly contributed to the retention of active biomass within the ABR. The average fraction of autofluorescent methanogens was lower, with 1.5% being in the initial compartments of the ABRs, compared to the last compartment which had 15%, showing that each compartment of an ABR had a unique microbial composition. Partial spatial separation of anaerobic bacteria appeared to have taken place with acidogenic bacteria predominating in the initial compartments and methanogenic bacteria predominating in the final compartments. Scanning electron micrographs have revealed that the dominant bacteria in the initial compartments of the ABR (Compartments 1 and 2) were those which could consume H2/CO2 and formate as substrate, i.e. Methanobrevibacter, Methanococcus, with populations shifting to acetate utilisers, i.e. Methanosaeta, Methanosarcina, in the final compartments (Compartments 3 and 4). In addition, there appeared to be a stratified structure to the bacterial genera present within the granules.
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The effect of polymer addition on granulation in an anaerobic baffled reactor (ABR). Part I: process performance. WATER RESEARCH 2002; 36:933-943. [PMID: 11848364 DOI: 10.1016/s0043-1354(01)00315-3] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
The stability and performance of an anaerobic baffled reactor (ABR) treating an ice-cream wastewater at several organic loading rates have been investigated. Specifically, it was determined whether an ABR would promote phase separation and if a polymer additive was capable of enhancing granule formation in an ABR. In order to achieve these goals, two ABRs, having identical dimensions and configurations, were used to study the above objectives using a synthetic ice-cream wastewater. The ABR proved to be an efficient reactor configuration for the treatment of a high-strength synthetic ice-cream wastewater. An organic loading rate of around 15 kg CODm(-3) d(-1) was treated with a 99% COD removal efficiency. From the jar test and inhibition assay, it was concluded that Kymene SLX-2 was the most effective and least inhibitory polymer tested. The methane yield was higher in the polymer-amended reactor compared to the control reactor. In addition, polymer addition resulted in a considerably higher degree of biomass retention and lower solids washout from the ABR. Consequently, it demonstrated that there was a considerable potential for sludge conditioning in ABRs by facilitating better biomass retention within the reactor which in turn led to better process performance. Granulation was achieved in both ABRs within 3 months. However, the granules from the polymer-amended reactor appeared earlier and were generally larger and more compact, although this was not quantified in detail during the present study. The main advantage of using an ABR comes from its compartmentalised structure. The first compartment of an ABR may act as a buffer zone to all toxic and inhibitory material in the feed thus allowing the later compartments to be loaded with a relatively harmless, balanced and mostly acidified influent. In this respect, the latter compartments would be more likely to support active populations of the relatively sensitive methanogenic bacteria and partly explains why the best granules and the highest methane yield were obtained in Compartment 2. It is unlikely that a complete separation of phases (acidogenic and methanogenic) occurred within the ABRs since methane production was observed in all compartments, although this was low (approximately 40% of all gas composition) in Compartment 1, becoming higher (approximately 70%) in the following compartments.
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Improved split feed anaerobic baffled reactor (SFABR) for shorter start-up period and higher process performance. WATER SCIENCE AND TECHNOLOGY : A JOURNAL OF THE INTERNATIONAL ASSOCIATION ON WATER POLLUTION RESEARCH 2002; 46:223-230. [PMID: 12361014] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
In this paper, the Split Feed Anaerobic Baffled Reactor (SFABR) is introduced and investigations into the use of modified seed material are described. It was shown that shorter and reliable start-up times could be achieved with SFABR when using improved seed material, even for the treatment of particularly problematic wastewater, i.e. ice-cream wastewater. Scanning electron photo-micrographs (SEM) revealed that granulation process occurs relatively rapidly in the SFABR compared with other reactor configurations, and that the reactor contained a highly mixed population of methanogens in all compartments. The use of polymer-conditioned anaerobic sludge and granular sludge as seed proved advantageous over the use of suspended growth anaerobic sludge, and the "improved" SFABR consequently performed more efficiently and also showed greater stability than the conventional ABR.
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Ulcerative colitis and colonic lymphoma: a theoretical link. Am Surg 2001; 67:654-6. [PMID: 11450782] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/20/2023]
Abstract
Ulcerative colitis (UC) is an inflammatory disease of the colon and rectum. Although colonic adenocarcinoma is a recognized complication of UC there have been few reported cases of gastrointestinal lymphoma arising in this setting. We describe our experience with such a case and review the literature that attempts to explain possible genetic etiologies for the malignant transformation of gastrointestinal lymphoid tissue to lymphoma as well as a link between UC and lymphoma.
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Abstract
Significant gastrointestinal complications have been observed in patients following heart- and lung transplantation. These complications can occur in the immediate post-operative period or remote from the time of transplantation. We retrospectively reviewed the medical records of 268 consecutive patients who received either heart- or lung transplants at Henry Ford Hospital between 1985 and 1998. Two hundred and thirty-three patients received heart transplants and 35 underwent lung transplantation. Two patients developed acute diverticulitis post transplant, both requiring surgery. Management of acute diverticulitis in the heart- and lung transplant population requires a high index of suspicion. Early and aggressive diagnosis is mandatory. Surgical intervention must be prompt when indicated, with meticulous attention to surgical technique. With appropriate intervention, reasonable outcomes can be expected.
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[Ethylene-1,2-bis(diphenylphosphine)-P,P']dinitratoplatinum(II) and cis-bis[(diphenylphosphinomethyl)-diphenylphosphine oxide-O,P]-platinum (II) dinitrate dihydrate. Acta Crystallogr C 2001; 57:237-9. [PMID: 11250560 DOI: 10.1107/s0108270100017273] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2000] [Accepted: 11/14/2000] [Indexed: 11/11/2022] Open
Abstract
In [Pt(dppe)(NO(3))(2)], where dppe is ethylene-1,2-bis(diphenylphosphine) (C(26)H(24)P(2)), the Pt atom is coordinated by the two P atoms and by two O atoms of the two nitrate ions. The molecule has a distorted square-planar geometry, with one of the nitrate groups directed on each side of the plane. The cation in cis-[Pt(dppmO-O,P)(2)](NO(3))(2) x 2H(2)O, where dppmO is bis(diphenylphosphinomethyl)diphenylphosphine oxide (C(25)H(22)OP(2)), comprises two five-membered chelate rings, each dppmO ligand being coordinated to platinum through one P atom and the O atom. The larger P--Pt--P angle of 102.25 (4) degrees is due to steric interactions between the two phenyl groups on each P atom.
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Colour removal from a simulated dye wastewater using a two-phase anaerobic packed bed reactor. WATER RESEARCH 2001; 35:425-432. [PMID: 11228995 DOI: 10.1016/s0043-1354(00)00280-3] [Citation(s) in RCA: 81] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
In recent years, rapid technological advances in the textile and dyeing industry have yielded benefits to society but have also generated new and significant environmental problems. The treatment alternatives applicable for the removal of colour vary, depending upon the type of dye wastewater. A synthetic, simulated mixed dye waste (Basic Yellow 28, Basic Yellow 21, Basic Red 18.1, Basic Violet Red 16, Basic Red 46, Basic Blue 16, Basic Blue 41) representing a known waste from a fibre production factory, was investigated. The biological process of anaerobic digestion has been recognised as a simple and energy-efficient means of treating and stabilising a wide range of organic industrial wastewaters. This study sets out to demonstrate the effect of different loading rates, dye concentrations and hydraulic retention times (HRTs) on colour removal efficiency under mesophilic anaerobic conditions. The reactor was operated under mesophilic conditions at different organic loading rates (OLRs) and HRTs for nine months. The results of this study show that a 2-stage mesophilic anaerobic up-flow packed bed reactor can remove up to 90% of the colour from a mixed cationic dye containing 1000 mg/l of dye. Colour removal efficiency falls as the influent dye concentration increases, but rises with increased hydraulic retention time and increased organic loading. The primary colour removal mechanism was one of biosorption with subsequent biodegradation. Acetoclastic methanogens were moderately inhibited at low organic loading rates of 0.25 kg COD/m3 d, at which level, acidogenesis and acetogenesis appeared to be unaffected. Inhibition of acidogenesis became marked at higher OLRs (1 kg COD/m3 d) and when the HRT was reduced from 5 to 3 days.
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A decade of great progress in medical readiness. Mil Med 1990; 155:535-8. [PMID: 2126854] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
The 1980s were times of extensive real growth in military capability of the Armed Forces of the United States. In concert with this growth, the ability to provide direct medical mission support and combat casualty care was greatly enhanced. Because medical equipment and supplies are worth little without qualified health care personnel, enhanced medical readiness training programs were created early in the build. The training programs, coupled with expanded inventories of medical equipment and supplies, were key elements in the decade-long quest to enhance medical readiness. This decade must be remembered for the success in building medical readiness capability and for the lessons learned while doing it.
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Paper-free flight surgeon's office. AVIATION, SPACE, AND ENVIRONMENTAL MEDICINE 1988; 59:664-6. [PMID: 3408429] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Integration of evolving technology into the flight surgeon's daily practice offers revolutionary opportunities to improve professional effectiveness. The productivity of those involved in the practice of aerospace medicine will be enhanced through the use of information systems, including word processors, communications equipment, graphics displays, and computers. The use of these systems will eliminate "paper work" and add efficiency to the flight surgeon's office environment. The practice of medicine is changing with increasing emphasis on credentialing, activity tracking, incident reporting, and occurrence screening. These quality assurance measures are being followed through data base management. The implications regarding medical records management, productivity indicators, continuing medical education, preventive medicine and direct patient care are great. The ability to communicate electronically leads to potential consultant networks, allowing real-time advice on complex cases regardless of geography. Military physicians should also be mindful of the command, control, communications, and intelligence advantages offered by these systems. Although microcomputers exist in most flight surgeons' offices and new technical applications are planned, integrators and champions are needed.
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Chemical mechanism of the Gram stain and synthesis of a new electron-opaque marker for electron microscopy which replaces the iodine mordant of the stain. J Bacteriol 1983; 156:837-45. [PMID: 6195147 PMCID: PMC217902 DOI: 10.1128/jb.156.2.837-845.1983] [Citation(s) in RCA: 38] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023] Open
Abstract
Crystal violet (hexamethyl-para-rosaniline chloride) interacts with aqueous KI-I2 during the Gram stain via a simple metathetical anion exchange to produce a chemical precipitate. There is an apparent 1:1 stoichiometry between anion (I-) and cation (hexamethyl-para-rosaniline+) during the reaction and, since the small chloride anion is replaced by the bulkier iodide, the complex formed becomes insoluble in water. It is this same precipitate which forms in the cellular substance of bacteria (both gram-positive and gram-negative types) and which initiates the Gram reaction. Potassium trichloro(eta 2-ethylene)-platinum(II), as an electronopaque marker for electron microscopy, was chemically synthesized, and it produced an anion in aqueous solution which was compatible with crystal violet for the Gram stain. It interacted with crystal violet in a similar manner as iodide to produce an insoluble complex which was chemically and physically analogous to the dye-iodide precipitate. This platinum anion therefore allows the Gram staining mechanism to be followed by electron microscopy.
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Environmentally induced cholinergic urticaria and anaphylaxis. AVIATION, SPACE, AND ENVIRONMENTAL MEDICINE 1983; 54:551-3. [PMID: 6882317] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
Although urticaria is generally an uncomfortable condition, it is usually considered to be relatively benign. Recent evidence indicates that numerous environmental stimuli can initiate cholinergic urticaria, and severe systemic manifestations may be associated with the onset of the urticaria. Exercise-induced anaphylaxis is a specific life-threatening reaction that has been documented to occur very unpredictably in susceptible individuals with cholinergic urticaria. The occurrence of severe hypotension, syncope, or laryngeal edema poses specific limitations to optimum performance should it occur in individuals employed in critical occupations. Although treatment with appropriate medications is generally effective in control of symptoms, these medications frequently have side effects not tolerable in high-risk situations. Four cases of U.S. Air Force aircrewmen referred to the USAF School of Aerospace Medicine for aeromedical evaluation illustrate the spectrum of problems that can be associated with cholinergic urticaria. Exercise history should always be carefully evaluated in all individuals who present with urticaria.
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Treatment of carbon monoxide poisoning with hyperbaric oxygen. Mil Med 1978; 143:538-41. [PMID: 99694] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
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Heterogeneous condensation of BCl(3) in the presence of CO(2) laser irradiation. OPTICS LETTERS 1978; 3:10-12. [PMID: 19684679 DOI: 10.1364/ol.3.000010] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
Isotope-enrichment experiments were conducted in an attempt to measure the effect of laser excitation on the heterogeneous sticking coefficient of BCl(3). Our results indicate that the effect, if any, is very small. This is in contrast to the work of Gochelashvili et al. [Sov. Phys. JETP 43, 274-277 (1976)], who reported an enrichment ratio of alpha = 1.57 under very similar experimental conditions.
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Altitude decompression sickness: hyperbaric therapy results in 145 cases. AVIATION, SPACE, AND ENVIRONMENTAL MEDICINE 1977; 48:722-30. [PMID: 889546] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Most cases of decompression sickness that occur at altitude resolve upon descent to lower altitudes. Before the use of hyperbaric therapy, cases that did not resolve accounted for some of the most difficult medical management problems in military aerospace medicine. On 27 March, 1941, the U.S. Navy Diving School successfully used hyperbaric therapy for a case of altitude-induced decompression sickness that did not resolve on return to ground level. Since then, over 145 such cases have been treated by hyperbaric therapy. At first, treatments involved using compressed air, with varying success. Current medical management of altitude-induced decompression sickness requires immediate compression to 2.8 ATA, equivalent to 60 ft of sea water (FSW) pressure, and a series of intermittent oxygen and air breathing periods during the subsequent slow decompression to surface. This report confirms the treatment recommendations set forth by Behnke and Downey, and crystallized by Goodman in 1964. Conclusions are based on treatment experience in the management of 120 cases in U.S. Air Force hyperbaric chambers, and a survey of hyperbaric facilities which have treated 25 other cases.
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