1
|
Mismatch between Tissue Partial Oxygen Pressure and Near-Infrared Spectroscopy Neuromonitoring of Tissue Respiration in Acute Brain Trauma: The Rationale for Implementing a Multimodal Monitoring Strategy. Int J Mol Sci 2021; 22:ijms22031122. [PMID: 33498736 PMCID: PMC7865258 DOI: 10.3390/ijms22031122] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2020] [Revised: 01/18/2021] [Accepted: 01/19/2021] [Indexed: 12/21/2022] Open
Abstract
The brain tissue partial oxygen pressure (PbtO2) and near-infrared spectroscopy (NIRS) neuromonitoring are frequently compared in the management of acute moderate and severe traumatic brain injury patients; however, the relationship between their respective output parameters flows from the complex pathogenesis of tissue respiration after brain trauma. NIRS neuromonitoring overcomes certain limitations related to the heterogeneity of the pathology across the brain that cannot be adequately addressed by local-sample invasive neuromonitoring (e.g., PbtO2 neuromonitoring, microdialysis), and it allows clinicians to assess parameters that cannot otherwise be scanned. The anatomical co-registration of an NIRS signal with axial imaging (e.g., computerized tomography scan) enhances the optical signal, which can be changed by the anatomy of the lesions and the significance of the radiological assessment. These arguments led us to conclude that rather than aiming to substitute PbtO2 with tissue saturation, multiple types of NIRS should be included via multimodal systemic- and neuro-monitoring, whose values then are incorporated into biosignatures linked to patient status and prognosis. Discussion on the abnormalities in tissue respiration due to brain trauma and how they affect the PbtO2 and NIRS neuromonitoring is given.
Collapse
|
2
|
Merz T, Denoix N, Huber-Lang M, Singer M, Radermacher P, McCook O. Microcirculation vs. Mitochondria-What to Target? Front Med (Lausanne) 2020; 7:416. [PMID: 32903633 PMCID: PMC7438707 DOI: 10.3389/fmed.2020.00416] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2020] [Accepted: 06/29/2020] [Indexed: 01/02/2023] Open
Abstract
Circulatory shock is associated with marked disturbances of the macro- and microcirculation and flow heterogeneities. Furthermore, a lack of tissue adenosine trisphosphate (ATP) and mitochondrial dysfunction are directly associated with organ failure and poor patient outcome. While it remains unclear if microcirculation-targeted resuscitation strategies can even abolish shock-induced flow heterogeneity, mitochondrial dysfunction and subsequently diminished ATP production could still lead to organ dysfunction and failure even if microcirculatory function is restored or maintained. Preserved mitochondrial function is clearly associated with better patient outcome. This review elucidates the role of the microcirculation and mitochondria during circulatory shock and patient management and will give a viewpoint on the advantages and disadvantages of tailoring resuscitation to microvascular or mitochondrial targets.
Collapse
Affiliation(s)
- Tamara Merz
- Institute for Anesthesiological Pathophysiology and Process Engineering, Ulm University Medical Center, Ulm, Germany
| | - Nicole Denoix
- Clinic for Psychosomatic Medicine and Psychotherapy, Ulm University Medical Center, Ulm, Germany
| | - Markus Huber-Lang
- Institute for Clinical and Experimental Trauma-Immunology, University Hospital of Ulm, Ulm, Germany
| | - Mervyn Singer
- Bloomsbury Institute for Intensive Care Medicine, University College London, London, United Kingdom
| | - Peter Radermacher
- Institute for Anesthesiological Pathophysiology and Process Engineering, Ulm University Medical Center, Ulm, Germany
| | - Oscar McCook
- Institute for Anesthesiological Pathophysiology and Process Engineering, Ulm University Medical Center, Ulm, Germany
| |
Collapse
|
3
|
Keeley TP, Mann GE. Defining Physiological Normoxia for Improved Translation of Cell Physiology to Animal Models and Humans. Physiol Rev 2019; 99:161-234. [PMID: 30354965 DOI: 10.1152/physrev.00041.2017] [Citation(s) in RCA: 169] [Impact Index Per Article: 33.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
The extensive oxygen gradient between the air we breathe (Po2 ~21 kPa) and its ultimate distribution within mitochondria (as low as ~0.5-1 kPa) is testament to the efforts expended in limiting its inherent toxicity. It has long been recognized that cell culture undertaken under room air conditions falls short of replicating this protection in vitro. Despite this, difficulty in accurately determining the appropriate O2 levels in which to culture cells, coupled with a lack of the technology to replicate and maintain a physiological O2 environment in vitro, has hindered addressing this issue thus far. In this review, we aim to address the current understanding of tissue Po2 distribution in vivo and summarize the attempts made to replicate these conditions in vitro. The state-of-the-art techniques employed to accurately determine O2 levels, as well as the issues associated with reproducing physiological O2 levels in vitro, are also critically reviewed. We aim to provide the framework for researchers to undertake cell culture under O2 levels relevant to specific tissues and organs. We envisage that this review will facilitate a paradigm shift, enabling translation of findings under physiological conditions in vitro to disease pathology and the design of novel therapeutics.
Collapse
Affiliation(s)
- Thomas P Keeley
- King's British Heart Foundation Centre of Research Excellence, School of Cardiovascular Medicine and Sciences, Faculty of Life Sciences and Medicine, King's College London , London , United Kingdom
| | - Giovanni E Mann
- King's British Heart Foundation Centre of Research Excellence, School of Cardiovascular Medicine and Sciences, Faculty of Life Sciences and Medicine, King's College London , London , United Kingdom
| |
Collapse
|
4
|
Moon-Massat P, Mullah SHER, Abutarboush R, Saha BK, Pappas G, Haque A, Auker C, McCarron RM, Arnaud F, Scultetus A. Cerebral Vasoactivity and Oxygenation with Oxygen Carrier M101 in Rats. J Neurotrauma 2017; 34:2812-2822. [PMID: 26161914 DOI: 10.1089/neu.2015.3908] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
The severity of traumatic brain injury (TBI) may be reduced if oxygen can be rapidly provided to the injured brain. This study evaluated if the oxygen-carrier M101 causes vasoconstricton of pial vasculature in healthy rats (Experiment 1) and if M101 improves brain tissue oxygen (PbtO2) in rats with controlled cortical impact (CCI)-TBI (Experiment 2). M101 (12.5 mL/kg intravenous [IV] over 2 h) caused a mild (9 mm Hg) increase in the mean arterial blood pressure (MAP) of healthy rats without constriction of cerebral pial arterioles. M101 (12 mL/kg IV over 1 h) caused a modest (27 mm Hg) increase in MAP (peak, 123 ± 5 mm Hg [mean ± standard error of the mean]) of CCI-TBI rats and restored PbtO2 to near pre-injury levels. In both M101 and untreated control (NON) groups, PbtO2 was ∼30 ± 2 mm Hg pre-injury and decreased (p ≤ 0.05) to ∼16 ± 2 mm Hg 15 min after CCI. In NON, PbtO2 remained ∼50% of baseline but M101 administration resulted in a sustained increase in PbtO2 (peak, 25 ± 5 mm Hg), which was not significantly different from pre-injury until the end of the study, when it decreased again below pre-injury (but was still higher than NON). Histopathology showed no differences between groups. In conclusion, M101 increased systemic blood pressures without concurrent cerebral pial vasoconstriction (in healthy rats) and restored PbtO2 to 86% of pre-injury for at least 80 min when given soon after CCI-TBI. M101 should be evaluated in a clinically-relevant large animal model for pre-hospital treatment of TBI.
Collapse
Affiliation(s)
- Paula Moon-Massat
- 1 Department of Neurotrauma, Naval Medical Research Center , Operational and Undersea Medicine Directorate, Silver Spring, Maryland
| | - Saad Habib-E-Rasul Mullah
- 1 Department of Neurotrauma, Naval Medical Research Center , Operational and Undersea Medicine Directorate, Silver Spring, Maryland
| | - Rania Abutarboush
- 1 Department of Neurotrauma, Naval Medical Research Center , Operational and Undersea Medicine Directorate, Silver Spring, Maryland
| | - Biswajit K Saha
- 1 Department of Neurotrauma, Naval Medical Research Center , Operational and Undersea Medicine Directorate, Silver Spring, Maryland
| | - Georgina Pappas
- 1 Department of Neurotrauma, Naval Medical Research Center , Operational and Undersea Medicine Directorate, Silver Spring, Maryland
| | - Ashraful Haque
- 1 Department of Neurotrauma, Naval Medical Research Center , Operational and Undersea Medicine Directorate, Silver Spring, Maryland
| | - Charles Auker
- 1 Department of Neurotrauma, Naval Medical Research Center , Operational and Undersea Medicine Directorate, Silver Spring, Maryland
| | - Richard M McCarron
- 1 Department of Neurotrauma, Naval Medical Research Center , Operational and Undersea Medicine Directorate, Silver Spring, Maryland.,2 Department of Surgery, Uniformed Services University of the Health Sciences , Bethesda, Maryland
| | - Francoise Arnaud
- 1 Department of Neurotrauma, Naval Medical Research Center , Operational and Undersea Medicine Directorate, Silver Spring, Maryland.,2 Department of Surgery, Uniformed Services University of the Health Sciences , Bethesda, Maryland
| | - Anke Scultetus
- 1 Department of Neurotrauma, Naval Medical Research Center , Operational and Undersea Medicine Directorate, Silver Spring, Maryland.,2 Department of Surgery, Uniformed Services University of the Health Sciences , Bethesda, Maryland
| |
Collapse
|
5
|
Perfluorocarbon NVX-108 increased cerebral oxygen tension after traumatic brain injury in rats. Brain Res 2016; 1634:132-139. [PMID: 26794250 DOI: 10.1016/j.brainres.2016.01.012] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2015] [Revised: 12/23/2015] [Accepted: 01/08/2016] [Indexed: 11/23/2022]
Abstract
BACKGROUND Hypoxia is a critical secondary injury mechanism in traumatic brain injury (TBI), and early intervention to alleviate post-TBI hypoxia may be beneficial. NVX-108, a dodecafluoropentane perfluorocarbon, was screened for its ability to increase brain tissue oxygen tension (PbtO2) when administered soon after TBI. METHODS Ketamine-acepromazine anesthetized rats ventilated with 40% oxygen underwent moderate controlled cortical impact (CCI)-TBI at time 0 (T0). Rats received either no treatment (NON, n=8) or 0.5 ml/kg intravenous (IV) NVX-108 (NVX, n=9) at T15 (15 min after TBI) and T75. RESULTS Baseline cortical PbtO2 was 28±3 mm Hg and CCI-TBI resulted in a 46±6% reduction in PbtO2 at T15 (P<0.001). Significant differences in time-group interactions (P=0.013) were found when comparing either absolute or percentage change of PbtO2 to post-injury (mixed-model ANOVA) suggesting that administration of NVX-108 increased PbtO2 above injury levels while it remained depressed in the NON group. Specifically in the NVX group, PbtO2 increased to a peak 143% of T15 (P=0.02) 60 min after completion of NVX-108 injection (T135). Systemic blood pressure was not different between the groups. CONCLUSION NVX-108 caused an increase in PbtO2 following CCI-TBI in rats and should be evaluated further as a possible immediate treatment for TBI.
Collapse
|
6
|
Meng F, Tsai AG, Intaglietta M, Acharya SA. PEGylation of αα-Hb using succinimidyl propionic acid PEG 5K: Conjugation chemistry and PEG shell structure dictate respectively the oxygen affinity and resuscitation fluid like properties of PEG αα-Hbs. ARTIFICIAL CELLS NANOMEDICINE AND BIOTECHNOLOGY 2014; 43:270-81. [PMID: 24597567 DOI: 10.3109/21691401.2014.885443] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
PEGylation of intramolecularly crosslinked Hb has been studied here to overcome the limitation of dissociation of Hb tetramers. New hexa and deca PEGylated low oxygen affinity PEG-ααHbs have been generated. Influence of PEG conjugation chemistry and the PEG shell structure on the functional properties as well as PEGylation induced plasma expander like properties of the protein has been delineated. The results have established that in the design of PEG-Hbs as oxygen therapeutics, the influence of conjugation chemistry and the PEG shell structure on the oxygen affinity of Hb needs to be optimized independently besides optimizing the PEG shell structure for inducing resuscitation fluid like properties.
Collapse
Affiliation(s)
- Fantao Meng
- Hematology Division, Department of Medicine, Albert Einstein College of Medicine of Yeshiva University , Bronx, NY , USA
| | | | | | | |
Collapse
|
7
|
Hypoxia and hypoxia mimetics inhibit TNF-dependent VCAM1 induction in the 5A32 endothelial cell line via a hypoxia inducible factor dependent mechanism. J Dermatol Sci 2011; 65:86-94. [PMID: 22093255 DOI: 10.1016/j.jdermsci.2011.10.003] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2011] [Revised: 08/29/2011] [Accepted: 10/06/2011] [Indexed: 12/25/2022]
Abstract
BACKGROUND We previously reported that iron chelators inhibit TNFα-mediated induction of VCAM-1 in human dermal microvascular endothelial cells. We hypothesized that iron chelators mediate inhibition of VCAM-1 via inhibition of iron-dependent enzymes such as those involved with oxygen sensing and that similar inhibition may be observed with agents which simulate hypoxia. OBJECTIVE We proposed to examine whether non-metal binding hypoxia mimetics inhibit TNFα-mediated VCAM-1 induction and define the mechanisms by which they mediate their effects on VCAM-1 expression. METHODS These studies were undertaken in vitro using immortalized dermal endothelial cells, Western blot analysis, ELISA, immunofluorescence microscopy, quantitative real-time PCR, and chromatin immunoprecipitation. RESULTS Hypoxia and the non-iron binding hypoxia mimetic dimethyl oxallyl glycine (DMOG) inhibited TNFα-mediated induction of VCAM-1. DMOG inhibition of VCAM-1 was dose-dependent, targeted VCAM-1 gene transcription independent of NF-κB nuclear translocation, and blocked TNFα-mediated chromatin modifications of relevant elements of the VCAM-1 promoter. Combined gene silencing of both HIF-1α and HIF-2α using siRNA led to a partial rescue of VCAM expression in hypoxia mimetic-treated cells. CONCLUSION Iron chelators, non-metal binding hypoxia mimetics, and hypoxia all inhibit TNFα-mediated VCAM-1 expression. Inhibition is mediated independent of nuclear translocation of NF-κB, appears to target TNFα-mediated chromatin modifications, and is at least partially dependent upon HIF expression. The absence of complete VCAM-1 expression rescue with HIF silencing implies an important regulatory role for an Fe(II)/α-ketoglutarate dioxygenase distinct from the prolyl and asparagyl hydroxylases that control HIF function. Identification of this dioxygenase may provide a valuable target for modulating inflammation in human tissues.
Collapse
|
8
|
Opdahl H, Strømme TA, Jørgensen L, Bajelan L, Heier HE. The acidosis-induced right shift of the HbO₂ dissociation curve is maintained during erythrocyte storage. Scandinavian Journal of Clinical and Laboratory Investigation 2011; 71:314-21. [PMID: 21476827 PMCID: PMC3156439 DOI: 10.3109/00365513.2011.565366] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Background and objectives. In fresh blood, tissue hypoxia increases microcirculatory acidosis, which enhances erythrocyte O2 unloading and increases the amount of available O2. Storage of eryfhrocytes increases the HbO2 affinity and reduces O2 unloading. We examined the development of the affinity change during a period of 5 weeks of storage by present blood bank standards, and investigated to what extent acidosis offsets the affinity change. Materials and methods. Blood from volunteer donors was processed and stored as erythrocyte concentrates (EC). At 2–5 day intervals, EC were drawn from the bags and suspended in plasma and crystalloids to an Hb ≈ 10 g/dL. The suspensions were adjusted to give a pH of 7.40, 7.10, 6.80 or 6.30 and equilibrated with different gas mixtures to SO2 0, 25, 50, 75 and 100%. Measurements of the PO2/SO2 pairs at each pH were used to calculate the position of the HbO2 curve and its P50 value. Results. A significant leftward shift in the HbO2 curve was established after 1 week of storage; after 2.5 weeks only minor further changes were observed. Acidification right-shifted the HbO2 curve, after 2.5 weeks of storage the curve at pH 7.10 was similar to that for fresh blood at pH 7.40. Calculations of extractable O2 showed that the left-shifted HbO2 curve of stored EC could be advantageous at a low arterial PO2. Conclusions. The rightward shift of the HbO2 curve due to acidosis is well maintained in stored eryfhrocytes, a moderate pH decrease offsets the storage-induced increased HbO2 affinity.
Collapse
Affiliation(s)
- Helge Opdahl
- Department of Acute Medicine and the Norwegian National Center for NBC Medicine, Oslo University Hospital, Ullevål, Oslo, Norway.
| | | | | | | | | |
Collapse
|
9
|
Tsai AG, Cabrales P, Intaglietta M. The physics of oxygen delivery: facts and controversies. Antioxid Redox Signal 2010; 12:683-91. [PMID: 19757988 PMCID: PMC2834451 DOI: 10.1089/ars.2009.2519] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/19/2009] [Revised: 09/15/2009] [Accepted: 09/16/2009] [Indexed: 11/13/2022]
Abstract
At the microvascular level, the radial oxygen gradient is greater in arterioles than in any other vascular segment and thus drives the oxygen from the blood (high concentration, source) into the perivascular tissue (low concentration, sink). Thus, arterioles appear to be the main suppliers of oxygen to the tissue, in contrast to the capillaries, where the oxygen gradient is only a few millimeters of mercury. However, longitudinal oxygen loss from arteriolar blood is higher than can be solely accounted for by diffusion. This discrepancy becomes evident when determining how oxygen is distributed in the microvascular network, an approach that requires confirmation of the data in terms of mass balance and thermodynamic considerations. A fundamental difficulty is that measuring tissue Po 2 is complicated by methods, exposure of tissue, interpretation, and resolution. The literature reports mean tissue Po 2 as low as 5 and up to 50 mm Hg. This large variability is due to the differences in techniques, species, tissue, handling, and interpretation of signals used to resolve Po 2 levels. Improving measurement accuracy and physiological interpretation of the emerging Po 2 data is ongoing. We present an analysis of our current understanding of how tissue is supplied by oxygen at the microscopic level in terms of present results from laboratories using differing methods. Antioxid. Redox Signal. 12, 683–691.
Collapse
Affiliation(s)
- Amy G. Tsai
- Department of Bioengineering, University of California, San Diego, La Jolla, California
| | | | - Marcos Intaglietta
- Department of Bioengineering, University of California, San Diego, La Jolla, California
| |
Collapse
|
10
|
Lee CM, Genetos DC, Wong A, Yellowley CE. Prostaglandin expression profile in hypoxic osteoblastic cells. J Bone Miner Metab 2010; 28:8-16. [PMID: 19471853 DOI: 10.1007/s00774-009-0096-0] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/04/2008] [Accepted: 04/09/2009] [Indexed: 11/28/2022]
Abstract
Conditions such as fracture and unloading have been shown to be associated with tissue and cellular hypoxia in bone. The effects of hypoxia on bone cell physiology and ultimately its impact on bone tissue repair and remodeling are not well understood. In this study, we investigated the role of hypoxia on prostaglandin release from osteoblastic cells cultured in 2% (hypoxia), 5% (potentially cellular normoxia), and 21% (normoxia for standard cell culture conditions) oxygen for up to 24 h. We quantified the effects of reduced oxygen tension on the release of prostaglandin (PG)E(2), PGF(2alpha), PGD(2), and PGI(2). The mechanism by which hypoxia increases PG production was investigated by examining the various regulatory components of the PG biosynthetic pathway. Our data show that PGE(2) levels alone are significantly elevated under hypoxic conditions. Also, we show that cyclooxygenase (COX)-1 and COX-2 play an important role in hypoxia-induced PGE(2) production, possibly via a mechanism involving changes in their respective activity levels under low oxygen conditions. The effect of hypoxia on PGE(2) levels was mimicked by dimethyloxaloglycine, a known activator of the HIF pathway. In addition, we confirmed that HIF-1alpha was stabilized in osteoblastic cells under hypoxia. Taken together these data suggest a role for the HIF pathway in regulation of PGE(2) levels under hypoxic conditions. Previous studies have detected release of prostaglandins from areas of damaged bone, such as a fracture site, and our data may contribute to an understanding of how this release is regulated.
Collapse
Affiliation(s)
- Christina M Lee
- Department of Anatomy, Physiology and Cell Biology, School of Veterinary Medicine, University of California Davis, 1321 Haring Hall, One Shields Ave, Davis, CA 95616, USA
| | | | | | | |
Collapse
|
11
|
MICROCIRCULATORY EFFECTS OF CHANGING BLOOD HEMOGLOBIN OXYGEN AFFINITY DURING HEMORRHAGIC SHOCK RESUSCITATION IN AN EXPERIMENTAL MODEL. Shock 2009; 31:645-52. [DOI: 10.1097/shk.0b013e31818bb98a] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
|
12
|
Golub AS, Pittman RN. Po2measurements in the microcirculation using phosphorescence quenching microscopy at high magnification. Am J Physiol Heart Circ Physiol 2008; 294:H2905-16. [DOI: 10.1152/ajpheart.01347.2007] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
In phosphorescence quenching microscopy (PQM), the multiple excitation of a reference volume produces the integration of oxygen consumption artifacts caused by individual flashes. We analyzed the performance of two types of PQM instruments to explain reported data on Po2in the microcirculation. The combination of a large excitation area (LEA) and high flash rate produces a large oxygen photoconsumption artifact manifested differently in stationary and flowing fluids. A LEA instrument strongly depresses Po2in a motionless tissue, but less in flowing blood, creating an apparent transmural Po2drop in arterioles. The proposed model explains the mechanisms responsible for producing apparent transmural and longitudinal Po2gradients in arterioles, a Po2rise in venules, a hypothetical high respiration rate in the arteriolar wall and mesenteric tissue, a low Po2in lymphatic microvessels, and both low and uniform tissue Po2. This alternative explanation for reported paradoxical results of Po2distribution in the microcirculation obviates the need to revise the dominant role of capillaries in oxygen transport to tissue. Finding a way to eliminate the photoconsumption artifact is crucial for accurate microscopic oxygen measurements in microvascular networks and tissue. The PQM technique that employs a small excitation area (SEA) together with a low flash rate was specially designed to avoid accumulated oxygen photoconsumption in flowing blood and lymph. The related scanning SEA instrument provides artifact-free Po2measurements in stationary tissue and motionless fluids. Thus the SEA technique significantly improves the accuracy of microscopic Po2measurements in the microcirculation using the PQM.
Collapse
|
13
|
Salazar Vázquez BY, Wettstein R, Cabrales P, Tsai AG, Intaglietta M. Microvascular experimental evidence on the relative significance of restoring oxygen carrying capacity vs. blood viscosity in shock resuscitation. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2008; 1784:1421-7. [PMID: 18502215 DOI: 10.1016/j.bbapap.2008.04.020] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/26/2007] [Revised: 04/15/2008] [Accepted: 04/24/2008] [Indexed: 11/24/2022]
Abstract
The development of volume replacement fluids for resuscitation in hemorrhagic shock comprises oxygen carrying and non carrying fluids. Non oxygen carrying fluids or plasma expanders are used up to the transfusion trigger, and upon reaching this landmark either blood, and possibly in the near future oxygen carrying blood substitutes, are used. An experimental program in hemorrhagic shock using the hamster chamber window model allowed to compare the relative performance of most fluids proposed for shock resuscitation. This model allows investigating simultaneously the microcirculation and systemic reactions, in the awake condition, in a tissue isolated from the environment. Results from this program show that in general plasma expanders such as Ringer's lactate and dextran 70 kDa do not sufficiently restore blood viscosity upon reaching the transfusion trigger, causing microvascular collapse. This is in part restored by a blood transfusion, independently of the oxygen carrying capacity of red blood cells. These results lead to the proposal that effective blood substitutes must be designed to prevent microvascular collapse, manifested in the decrease of functional capillary density. Achievement of this goal, in combination with the increase of oxygen affinity, significantly postpones the need for a blood transfusion, and lowers the total requirement of restoration of intrinsic oxygen carrying capacity.
Collapse
Affiliation(s)
- Beatriz Y Salazar Vázquez
- Faculty of Medicine, Universidad Juárez del Estado de Durango, 34000 Victoria de Durango, Durango, Mexico
| | | | | | | | | |
Collapse
|
14
|
Abstract
Longitudinal Po2profiles in the microvasculature of the rat mesentery were studied using a novel phosphorescence quenching microscopy technique that minimizes the accumulated photoconsumption of oxygen by the method. Intravascular oxygen tension (Po2, in mmHg) and vessel diameter ( d, in μm) were measured in mesenteric microvessels ( n = 204) of seven anesthetized rats (275 g). The excitation parameters were as follows: 7 × 7-μm spot size; 410 nm laser; and 100 curves at 11 pulses/s, with pulse parameters of 2-μs duration and 80-pJ/μm2energy density. The mean Po2(± SE) was 65.0 ± 1.4 mmHg ( n = 78) for arterioles ( d = 18.8 ± 0.7 μm), 62.1 ± 2.0 mmHg ( n = 38) at the arteriolar end of capillaries ( d = 7.8 ± 0.3 μm), and 52.0 ± 1.0 mmHg ( n = 88) for venules ( d = 22.5 ± 1.0 μm). There was no apparent dependence of Po2on d in arterioles and venules. There were also no significant deviations in Po2based on d (bin width, 5 μm) from the general mean for both of these types of vessels. Results indicate that the primary site of oxygen delivery to tissue is located between the smallest arterioles and venules (change of 16.3 mmHg, P = 0.001). In conclusion, oxygen losses from mesenteric arterioles and venules are negligible, indicating low metabolic rates for both the vascular wall and the mesenteric tissue. Capillaries appear to be the primary site of oxygen delivery to the tissue in the mesenteric microcirculation. In light of the present results, previously reported data concerning oxygen consumption in the mesenteric microcirculation can be explained as artifacts of accumulated oxygen consumption due to the application of instrumentation having a large excitation area for Po2measurements in slow moving and stationary media.
Collapse
|
15
|
Ward JPT. Oxygen sensors in context. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2007; 1777:1-14. [PMID: 18036551 DOI: 10.1016/j.bbabio.2007.10.010] [Citation(s) in RCA: 149] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Subscribe] [Scholar Register] [Received: 09/13/2007] [Revised: 10/21/2007] [Accepted: 10/24/2007] [Indexed: 01/02/2023]
Abstract
The ability to adapt to changes in the availability of O2 provides a critical advantage to all O2-dependent lifeforms. In mammals it allows optimal matching of the O2 requirements of the cells to ventilation and O2 delivery, underpins vital changes to the circulation during the transition from fetal to independent, air-breathing life, and provides a means by which dysfunction can be limited or prevented in disease. Certain tissues such as the carotid body, pulmonary circulation, neuroepithelial bodies and fetal adrenomedullary chromaffin cells are specialised for O2 sensing, though most others show for example alterations in transcription of specific genes during hypoxia. A number of mechanisms are known to respond to variations in PO2 over the physiological range, and have been proposed to fulfil the function as O2 sensors; these include modulation of mitochondrial oxidative phosphorylation and a number of O2-dependent synthetic and degradation pathways. There is however much debate as to their relative importance within and between specific tissues, whether their O2 sensitivity is actually appropriate to account for their proposed actions, and in particular their modus operandi. This review discusses our current understanding of how these mechanisms may operate, and attempts to put them into the context of the actual PO2 to which they are likely to be exposed. An important point raised is that the overall O2 sensitivity (P50) of any O2-dependent mechanism does not necessarily correlate with that of its O2 sensor, as the coupling function between the two may be complex and non-linear. In addition, although the bulk of the evidence suggests that mitochondria act as the key O2 sensor in carotid body, pulmonary artery and chromaffin cells, the signalling mechanisms by which alterations in their function are translated into a response appear to differ fundamentally, making a global unified theory of O2 sensing unlikely.
Collapse
Affiliation(s)
- Jeremy P T Ward
- King's College London School of Medicine, Division of Asthma, Allergy and Lung Biology, London SE1 9RT, UK
| |
Collapse
|