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The Cochrane Database of Systematic... Feb 2019Conventional mechanical ventilation (CMV) is a common therapy for neonatal respiratory failure. While CMV facilitates gas exchange, it may simultaneously injure the... (Meta-Analysis)
Meta-Analysis
BACKGROUND
Conventional mechanical ventilation (CMV) is a common therapy for neonatal respiratory failure. While CMV facilitates gas exchange, it may simultaneously injure the lungs. Positive end-expiratory pressure (PEEP) has received less attention than other ventilation parameters when considering this benefit-risk balance. While an appropriate PEEP level may result in clinical benefits, both inappropriately low or high levels may cause harm. An appropriate PEEP level may also be best achieved by an individualized approach.
OBJECTIVES
1. To compare the effects of PEEP levels in preterm infants requiring CMV for respiratory distress syndrome (RDS). We compare both: zero end-expiratory pressure (ZEEP) (0 cm HO) versus any PEEP and low (< 5 cm HO) vs high (≥ 5 cm HO) PEEP.2. To compare the effects of PEEP levels in preterm infants requiring CMV for bronchopulmonary dysplasia (BPD). We compare both: ZEEP (0 cm HO) vs any PEEP and low (< 5 cm HO) versus high (≥ 5 cm HO) PEEP.3. To compare the effects of different methods for individualizing PEEP to an optimal level in preterm newborn infants requiring CMV for RDS.
SEARCH METHODS
We used the standard search strategy of Cochrane Neonatal to search the Cochrane Central Register of Controlled Trials, MEDLINE via PubMed, Embase, and CINAHL to 14 February 2018. We also searched clinical trials databases, conference proceedings, and the reference lists of retrieved articles for randomized controlled trials and quasi-randomized trials.
SELECTION CRITERIA
We included all randomized or quasi-randomized controlled trials studying preterm infants born at less than 37 weeks' gestational age, requiring CMV and undergoing randomization to either different PEEP levels (RDS or BPD); or, two or more alternative methods for individualizing PEEP levels (RDS only). We included cross-over trials but limited outcomes to those from the first cross-over period.
DATA COLLECTION AND ANALYSIS
We performed data collection and analysis according to the recommendations of the Cochrane Neonatal Review Group. We used the GRADE approach to assess the quality of evidence for prespecified key clinically relevant outcomes.
MAIN RESULTS
Four trials met the inclusion criteria. Two cross-over trials with 28 participants compared different PEEP levels in infants with RDS. Meta-analysis was limited to short-term measures of pulmonary gas exchange and showed no differences between low and high PEEP.We identified no trials comparing PEEP levels in infants with BPD.Two trials enrolling 44 participants compared different methods for individualizing PEEP in infants with RDS. Both trials compared an oxygenation-guided lung-recruitment maneuver (LRM) with gradual PEEP level titrations for individualizing PEEP to routine care (control). Meta-analysis showed no difference between LRM and control on mortality by hospital discharge (risk ratio (RR) 1.00, 95% confidence interval (CI) 0.17 to 5.77); there was no statistically significant difference on BPD, with an effect estimate favoring LRM (RR 0.25, 95% CI 0.03 to 2.07); and a statistically significant difference favoring LRM for the outcome of duration of ventilatory support (mean difference -1.06 days, 95% CI -1.85 to -0.26; moderate heterogeneity, I = 67%). Short-term oxygenation measures also favored LRM. We graded the quality of the evidence as low for all key outcomes due to risk of bias and imprecision of the effect estimates.
AUTHORS' CONCLUSIONS
There continues to be insufficient evidence to guide PEEP level selection for preterm infants on CMV for RDS or BPD. Low-quality data suggests that selecting PEEP levels through the application of an oxygenation-guided LRM may result in clinical benefit. Well-conducted randomized trials, particularly to further evaluate the potential benefits of oxygenation-guided LRMs, are needed.
Topics: Bronchopulmonary Dysplasia; Humans; Infant, Newborn; Infant, Premature; Positive-Pressure Respiration; Pulmonary Gas Exchange; Randomized Controlled Trials as Topic; Respiration, Artificial; Respiratory Distress Syndrome, Newborn
PubMed: 30820939
DOI: 10.1002/14651858.CD004500.pub3 -
Vibration and bubbles: a systematic review of the effects of helicopter retrieval on injured divers.Diving and Hyperbaric Medicine Dec 2018Vibration from a helicopter during aeromedical retrieval of divers may increase venous gas emboli (VGE) production, evolution or distribution, potentially worsening the...
INTRODUCTION
Vibration from a helicopter during aeromedical retrieval of divers may increase venous gas emboli (VGE) production, evolution or distribution, potentially worsening the patient's condition.
AIM
To review the literature surrounding the helicopter transport of injured divers and establish if vibration contributes to increased VGE.
METHOD
A systematic literature search of key databases was conducted to identify articles investigating vibration and bubbles during helicopter retrieval of divers. Level of evidence was graded using the Oxford Centre for Evidence-Based Medicine guidelines. A modified quality assessment tool for studies with diverse designs (QATSDD) was used to assess the overall quality of evidence.
RESULTS
Seven studies were included in the review. An in vitro research paper provided some evidence of bubble formation with gas supersaturation and vibration. Only one prospective intervention study was identified which examined the effect of vibration on VGE formation. Bubble duration was used to quantify VGE load with no difference found between the vibration and non-vibration time periods. This study was published in 1980 and technological advances since that time suggest cautious interpretation of the results. The remaining studies were retrospective chart reviews of helicopter retrieval of divers. Mode of transport, altitude exposure, oxygen and intravenous fluids use were examined.
CONCLUSION
There is some physical evidence that vibration leads to bubble formation although there is a paucity of research on the specific effects of helicopter vibration and VGE in divers. Technological advances have led to improved assessment of VGE in divers and will aid in further research.
Topics: Air Ambulances; Decompression Sickness; Diving; Embolism, Air; Humans; Prospective Studies; Retrospective Studies; Vibration
PubMed: 30517957
DOI: 10.28920/dhm48.4.241-251 -
The Cochrane Database of Systematic... Oct 2018Croup is an acute viral respiratory infection with upper airway mucosal inflammation that may cause respiratory distress. Most cases are mild. Moderate to severe croup... (Meta-Analysis)
Meta-Analysis
BACKGROUND
Croup is an acute viral respiratory infection with upper airway mucosal inflammation that may cause respiratory distress. Most cases are mild. Moderate to severe croup may require treatment with corticosteroids (from which benefits are often delayed) and nebulised epinephrine (adrenaline) (which may be short-lived and can cause dose-related adverse effects including tachycardia, arrhythmias, and hypertension). Rarely, croup results in respiratory failure necessitating emergency intubation and ventilation.A mixture of helium and oxygen (heliox) may prevent morbidity and mortality in ventilated neonates by reducing the viscosity of the inhaled air. It is currently used during emergency transport of children with severe croup. Anecdotal evidence suggests that it relieves respiratory distress.This review updates versions published in 2010 and 2013.
OBJECTIVES
To examine the effect of heliox compared to oxygen or other active interventions, placebo, or no treatment, on relieving signs and symptoms in children with croup as determined by a croup score and rates of admission and intubation.
SEARCH METHODS
We searched CENTRAL, which includes the Cochrane Acute Respiratory Infections Group's Specialised Register; MEDLINE; Embase; CINAHL; Web of Science; and LILACS in January and February 2018. We also searched the World Health Organization International Clinical Trials Registry Platform (apps.who.int/trialsearch/) and ClinicalTrials.gov (clinicaltrials.gov) on 8 February 2018. We contacted British Oxygen Company, a leading supplier of heliox (BOC Australia 2017).
SELECTION CRITERIA
Randomised controlled trials (RCTs) and quasi-RCTs comparing the effect of heliox in comparison with placebo or any active intervention(s) in children with croup.
DATA COLLECTION AND ANALYSIS
We used standard methodological procedures expected by Cochrane. We reported data that could not be pooled for statistical analysis descriptively.
MAIN RESULTS
We included 3 RCTs with 91 children aged between 6 months and 4 years. Study duration was from 7 to 16 months; all studies were conducted in emergency departments in the USA (two studies) and Spain. Heliox was administered as a mixture of 70% heliox and 30% oxygen. Risk of bias was low in two studies and high in one study due to an open-label design. We added no new trials for this update.One study of 15 children with mild croup compared heliox with 30% humidified oxygen administered for 20 minutes. There may be no difference in croup score changes between groups at 20 minutes (mean difference (MD) -0.83, 95% confidence interval (CI) -2.36 to 0.70). The mean croup score at 20 minutes postintervention may not differ between groups (MD -0.57, 95% CI -1.46 to 0.32). There may be no difference between groups in mean respiratory rate (MD 6.40, 95% CI -1.38 to 14.18) and mean heart rate (MD 14.50, 95% CI -8.49 to 37.49) at 20 minutes. The evidence for all outcomes in this comparison was of low quality, downgraded for serious imprecision. All children were discharged, but information on hospitalisation, intubation, or re-presenting to emergency departments was not reported.In another study, 47 children with moderate croup received one dose of oral dexamethasone (0.3 mg/kg) with either heliox for 60 minutes or no treatment. Heliox may slightly improve croup scores at 60 minutes postintervention (MD -1.10, 95% CI -1.96 to -0.24), but there may be no difference between groups at 120 minutes (MD -0.70, 95% CI -4.86 to 3.46). Children treated with heliox may have lower mean Taussig croup scores at 60 minutes (MD -1.11, 95% CI -2.05 to -0.17) but not at 120 minutes (MD -0.71, 95% CI -1.72 to 0.30). Children treated with heliox may have lower mean respiratory rates at 60 minutes (MD -4.94, 95% CI -9.66 to -0.22), but there may be no difference at 120 minutes (MD -3.17, 95% CI -7.83 to 1.49). There may be no difference in hospitalisation rates between groups (OR 0.46, 95% CI 0.04 to 5.41). We assessed the evidence for all outcomes in this comparison as of low quality, downgraded due to imprecision and high risk of bias related to open-label design. Information on heart rate and intubation was not reported.In the third study, 29 children with moderate to severe croup received intramuscular dexamethasone (0.6 mg/kg) and either heliox with one to two doses of nebulised saline, or 100% oxygen with one to two doses of adrenaline for three hours. Heliox may slightly improve croup scores at 90 minutes postintervention, but may have little or no difference overall using repeated measures analysis. We assessed the evidence for all outcomes in this comparison as of low quality, downgraded due to high risk of bias related to inadequate reporting. Information on hospitalisation or re-presenting to the emergency department was not reported.The included studies did not report on adverse events, intensive care admissions, or parental anxiety.We could not pool the available data because each comparison included data from only one study.
AUTHORS' CONCLUSIONS
Due to very limited evidence, uncertainty remains about the effectiveness and safety of heliox. Heliox may not be more effective than 30% humidified oxygen for children with mild croup, but may be beneficial in the short term for children with moderate to severe croup treated with dexamethasone. The effect may be similar to 100% oxygen given with one or two doses of adrenaline. Adverse events were not reported, and it is unclear if these were monitored in the included studies. Adequately powered RCTs comparing heliox with standard treatments are needed to further assess the role of heliox in the treatment of children with moderate to severe croup.
Topics: Adrenal Cortex Hormones; Airway Obstruction; Airway Resistance; Bronchodilator Agents; Child, Preschool; Croup; Dexamethasone; Epinephrine; Helium; Humans; Infant; Oxygen; Oxygen Inhalation Therapy; Randomized Controlled Trials as Topic
PubMed: 30371952
DOI: 10.1002/14651858.CD006822.pub5 -
Translational Psychiatry Sep 2018Acid-sensitive ion channels, such as amiloride-sensitive cation channel (ACCN), transient receptor potential vanilloid-1 (TRPV1), and T-cell death-associated gene 8... (Meta-Analysis)
Meta-Analysis
Acid-sensitive ion channels, such as amiloride-sensitive cation channel (ACCN), transient receptor potential vanilloid-1 (TRPV1), and T-cell death-associated gene 8 (TDAG8) are highly related to the expression of fear and are expressed in several regions of the brain. These molecules can detect acidosis and maintain brain homeostasis. An important role of pH homeostasis has been suggested in the physiology of panic disorder (PD), with acidosis as an interoceptive trigger for panic attacks. To examine the effect of acid-sensitive channels on PD symptoms, we conducted a systematic review and meta-analysis of these chemosensors in rodents and humans. Following PRISMA guidelines, we systematically searched the Web of Science, Medline/Pubmed, Scopus, Science Direct, and SciELO databases. The review included original research in PD patients and animal models of PD that investigated acid-sensitive channels and PD symptoms. Studies without a control group, studies involving patients with a comorbid psychiatric diagnosis, and in vitro studies were excluded. Eleven articles met the inclusion criteria for the systematic review. The majority of the studies showed an association between panic symptoms and acid-sensitive channels. PD patients appear to display polymorphisms in the ACCN gene and elevated levels of TDAG8 mRNA. The results showed a decrease in panic-like symptoms after acid channel blockade in animal models. Despite the relatively limited data on this topic in the literature, our review identified evidence linking acid-sensitive channels to PD in humans and preclinical models. Future research should explore possible underlying mechanisms of this association, attempt to replicate the existing findings in larger populations, and develop new therapeutic strategies based on these biological features.
Topics: Acid Sensing Ion Channels; Animals; Fear; Humans; Models, Animal; Panic Disorder; Polymorphism, Single Nucleotide; Receptors, G-Protein-Coupled
PubMed: 30194289
DOI: 10.1038/s41398-018-0238-z -
Danish Medical Journal Mar 2018During conventional cardiopulmonary bypass (CPB) there is no active perfusion of the pulmonary circulation and the mechanical ventilation is ceased leaving the lungs... (Review)
Review
During conventional cardiopulmonary bypass (CPB) there is no active perfusion of the pulmonary circulation and the mechanical ventilation is ceased leaving the lungs exposed to warm ischemia. Pulmonary dysfunction is seen in varying degrees after major surgery, but more severe in cardiac surgery patients probably due to the effects of CPB. The evidence for effect and safety are limited, but active pulmonary artery perfusion during CPB could be beneficial for the patients' postoperative oxygenation. Our aim was in a randomised clinical trial to assess primarily the effect of pulmonary artery perfusion during CPB on postoperative oxygenation in patients diagnosed with chronic obstructive pulmonary disease (COPD), secondarily to assess other possible benefits and harms. Furthermore, we wanted in a systematic review with meta-analyses of all randomised clinical trials to investigate the pooled effects of pulmonary artery perfusion during CPB. We planned and conducted a randomised, partly blinded, clinical trial assigning cardiac surgery patients diagnosed with COPD to receive pulmonary artery perfusion with oxygenated blood or histidine-tryptophan-ketoglutarate (HTK) solution compared to no pulmonary perfusion during CPB. The primary outcome was the oxygenation index measured during and after surgery. Secondary outcomes were intubation time, serious adverse events, days alive outside the intensive care unit and outside the hospital, 30- and 90-days mortality. Secondly, we conducted a systematic review of randomised clinical trials comparing benefits and harms of using pulmonary artery perfusion versus no pulmonary perfusion during CPB pooling results in meta-analyses and trial sequential analyses (TSA). Of the 90 randomised patients 89 were included in analysis of the primary outcome, the inverse oxygenation index, measured at a single time point 21 hours after CPB start and longitudinally 1, 3, 5, 7, and 21 hours after CPB start. At 21 hours, patients randomised to pulmonary artery perfusion with oxygenated blood had a higher inverse oxygenation index compared to patients randomised to no pulmonary perfusion during CPB (mean difference (MD) 0.94; 95% confidence interval (CI), 0.05 to 1.83; P=0.04). The inverse oxygenation index was also significantly higher at 21 hours after CPB start (MD 0.99; CI, 0.29 to 1.69; P=0.007), and longitudinally (P=0.009), for patients receiving pulmonary artery perfusion with oxygenated blood compared to pulmonary artery perfusion with HTK solution. This corresponds to a PaO difference of 23 mmHg with a median FiO of 0.32. We found no additional significant differences for the remaining comparisons of the inverse oxygenation index neither for any of the secondary outcomes. The systematic review identified 4 trials with a total of 210 patients. In meta-analyses pulmonary artery perfusion with blood versus no pulmonary perfusion during CPB was not associated with relative risk of death (1.7; 95% CI, 0.4 to 6.9; 210 patients in three trials with high and one trial with low risk of bias), serious adverse events (1.2; 95% CI, 0.8 to 1.8; 180 patients in two trials with high and one trial with low risk of bias) or intubation time (-0.4 hours; 95% CI, -1.1 to 0.4; 176 patients in three trials with high and one trial with low risk of bias). TSA on mortality, serious adverse events, and PaO/FiO ratio showed that required information sizes have not been reached, but pulmonary artery perfusion with blood was associated with a higher PaO/FiO ratio (27.8 mmHg; 95% CI, 5.7 to 50.0 mmHg; 119 patients in two trials with high and one trial with low risk of bias). TSA on intubation time showed that the boundary for lack of superiority (futility) was crossed refuting a shorten intubation time of 1.5 hours or more. Our trial provided additional knowledge about the use of pulmonary artery perfusion during CPB in cardiac surgery patients with COPD, and improved oxygenation for patients receiving pulmonary artery perfusion with oxygenated blood. Pulmonary artery perfusion with HTK solution did not result in an improved oxygenation. In line with this, the systematic review including data from additional trials showed a possible association between pulmonary artery perfusion with blood and improved oxygenation, but no significant associations with mortality, serious adverse events or intubation time. However, all data are too sparse to be conclusive.
Topics: Cardiac Surgical Procedures; Cardiopulmonary Bypass; Glucose; Hospital Mortality; Humans; Lung; Mannitol; Perfusion; Potassium Chloride; Procaine; Pulmonary Artery; Pulmonary Circulation; Pulmonary Disease, Chronic Obstructive; Pulmonary Gas Exchange; Randomized Controlled Trials as Topic
PubMed: 29510817
DOI: No ID Found -
Redox Report : Communications in Free... Dec 2018p53 is a tumor suppressor protein involved in regulating a wide array of signaling pathways. The role of p53 in the cell is determined by the type of imposed oxidative... (Review)
Review
BACKGROUND
p53 is a tumor suppressor protein involved in regulating a wide array of signaling pathways. The role of p53 in the cell is determined by the type of imposed oxidative stress, its intensity and duration. The last decade of research has unravelled a dual nature in the function of p53 in mediating the oxidative stress burden. However, this is dependent on the specific properties of the applied stress and thus requires further analysis.
METHODS
A systematic review was performed following an electronic search of Pubmed, Google Scholar, and ScienceDirect databases. Articles published in the English language between January 1, 1990 and March 1, 2017 were identified and isolated based on the analysis of p53 in skeletal muscle in both animal and cell culture models.
RESULTS
Literature was categorized according to the modality of imposed oxidative stress including exercise, diet modification, exogenous oxidizing agents, tissue manipulation, irradiation, and hypoxia. With low to moderate levels of oxidative stress, p53 is involved in activating pathways that increase time for cell repair, such as cell cycle arrest and autophagy, to enhance cell survival. However, with greater levels of stress intensity and duration, such as with irradiation, hypoxia, and oxidizing agents, the role of p53 switches to facilitate increased cellular stress levels by initiating DNA fragmentation to induce apoptosis, thereby preventing aberrant cell proliferation.
CONCLUSION
Current evidence confirms that p53 acts as a threshold regulator of cellular homeostasis. Therefore, within each modality, the intensity and duration are parameters of the oxidative stressor that must be analyzed to determine the role p53 plays in regulating signaling pathways to maintain cellular health and function in skeletal muscle.
ABBREVIATIONS
Acadl: acyl-CoA dehydrogenase, long chain; Acadm: acyl-CoA dehydrogenase, C-4 to C-12 straight chain; AIF: apoptosis-inducing factor; Akt: protein kinase B (PKB); AMPK: AMP-activated protein kinase; ATF-4: activating transcription factor 4; ATM: ATM serine/threonine kinase; Bax: BCL2 associated X, apoptosis regulator; Bcl-2: B cell Leukemia/Lymphoma 2 apoptosis regulator; Bhlhe40: basic helix-loop-helix family member e40; BH3: Borane; Bim: bcl-2 interacting mediator of cell death; Bok: Bcl-2 related ovarian killer; COX-IV: cytochrome c oxidase IV; cGMP: Cyclic guanosine monophosphate; c-myc: proto-oncogene protein; Cpt1b: carnitine palmitoyltransferase 1B; Dr5: death receptor 5; eNOS: endothelial nitric oxide synthase; ERK: extracellular regulated MAP kinase; Fas: Fas Cell surface death receptor; FDXR: Ferredoxin Reductase; FOXO3a: forkhead box O3; Gadd45a: growth arrest and DNA damage-inducible 45 alpha; GLS2: glutaminase 2; GLUT 1 and 4: glucose transporter 1(endothelial) and 4 (skeletal muscle); GSH: Glutathione; Hes1: hes family bHLH transcription factor 1; Hey1: hes related family bHLH transcription factor with YRPW motif 1; HIFI-α: hypoxia-inducible factor 1, α-subunit; HK2: Hexokinase 2; HSP70: Heat Shock Protein 70; HO: Hydrogen Peroxide; Id2: inhibitor of DNA-binding 2; IGF-1-BP3: Insulin-like growth factor binding protein 3; IL-1β: Interleukin 1 beta; iNOS: inducible nitric oxide synthase; IRS-1: Insulin receptor substrate 1; JNK: c-Jun N-terminal kinases; LY-83583: 6-anilino-5,8-quinolinedione; inhibitor of soluble guanylate cyclase and of cGMP production; Mdm 2/ 4: Mouse double minute 2 homolog (mouse) Mdm4 (humans); mtDNA: mitochondrial DNA; MURF1: Muscle RING-finger protein-1; MyoD: Myogenic differentiation 1; MyoG: myogenin; Nanog: Nanog homeobox; NF-kB: Nuclear factor-κB; NO: nitric oxide; NoxA: phorbol-12-myristate-13-acetate-induced protein 1 (Pmaip1); NRF-1: nuclear respiratory factor 1; Nrf2: Nuclear factor erythroid 2-related factor 2; P21: Cdkn1a cyclin-dependent kinase inhibitor 1A (P21); P38 MAPK: mitogen-activated protein kinases; p53R2: p53 inducible ribonucleotide reductase gene; P66Shc: src homology 2 domain-containing transforming protein C1; PERP: p53 apoptosis effector related to PMP-22; PGC-1α: Peroxisome proliferator-activated receptor gamma coactivator 1-alpha; PGM: phosphoglucomutase; PI3K: Phosphatidylinositol-4,5-bisphosphate 3-kinase; PKCβ: protein kinase c beta; PTEN: phosphatase and tensin homolog; PTIO: 2-phenyl-4, 4, 5, 5,-tetramethylimidazoline-1-oxyl 3-oxide (PTIO) has been used as a nitric oxide (NO) scavenger; Puma: The p53 upregulated modulator of apoptosis; PW1: paternally expressed 3 (Peg3); RNS: Reactive nitrogen species; SIRT1: sirtuin 1; SCO2: cytochrome c oxidase assembly protein; SOD2: superoxide dismutase 2; Tfam: transcription factor A mitochondrial; TIGAR: Trp53 induced glycolysis repulatory phosphatase; TNF-a: tumor necrosis factor a; TRAF2: TNF receptor associated factor 2; TRAIL: type II transmembrane protein.
Topics: Animals; Diet; Exercise; Humans; Muscle, Skeletal; Oxidative Stress; Oxygen; Proto-Oncogene Mas; Radiation Injuries; Tumor Suppressor Protein p53
PubMed: 29298131
DOI: 10.1080/13510002.2017.1416773 -
Frontiers in Physiology 2017The European Space Agency has recently announced to progress from low Earth orbit missions on the International Space Station to other mission scenarios such as... (Review)
Review
The European Space Agency has recently announced to progress from low Earth orbit missions on the International Space Station to other mission scenarios such as exploration of the Moon or Mars. Therefore, the Moon is considered to be the next likely target for European human space explorations. Compared to microgravity (μg), only very little is known about the physiological effects of exposure to partial gravity (μg < partial gravity <1 g). However, previous research studies and experiences made during the Apollo missions comprise a valuable source of information that should be taken into account when planning human space explorations to reduced gravity environments. This systematic review summarizes the different effects of partial gravity (0.1-0.4 g) on the human musculoskeletal, cardiovascular and respiratory systems using data collected during the Apollo missions as well as outcomes from terrestrial models of reduced gravity with either 1 g or microgravity as a control. The evidence-based findings seek to facilitate decision making concerning the best medical and exercise support to maintain astronauts' health during future missions in partial gravity. The initial search generated 1,323 publication hits. Out of these 1,323 publications, 43 studies were included into the present analysis and relevant data were extracted. None of the 43 included studies investigated long-term effects. Studies investigating the immediate effects of partial gravity exposure reveal that cardiopulmonary parameters such as heart rate, oxygen consumption, metabolic rate, and cost of transport are reduced compared to 1 g, whereas stroke volume seems to increase with decreasing gravity levels. Biomechanical studies reveal that ground reaction forces, mechanical work, stance phase duration, stride frequency, duty factor and preferred walk-to-run transition speed are reduced compared to 1 g. Partial gravity exposure below 0.4 g seems to be insufficient to maintain musculoskeletal and cardiopulmonary properties in the long-term. To compensate for the anticipated lack of mechanical and metabolic stimuli some form of exercise countermeasure appears to be necessary in order to maintain reasonable astronauts' health, and thus ensure both sufficient work performance and mission safety.
PubMed: 28860998
DOI: 10.3389/fphys.2017.00583 -
Journal of Applied Physiology... Dec 2017Exercise performance is determined by oxygen supply to working muscles and vital organs. In healthy individuals, exercise performance is limited in the hypoxic...
Exercise performance is determined by oxygen supply to working muscles and vital organs. In healthy individuals, exercise performance is limited in the hypoxic environment at altitude, when oxygen delivery is diminished due to the reduced alveolar and arterial oxygen partial pressures. In patients with pulmonary hypertension (PH), exercise performance is already reduced near sea level due to impairments of the pulmonary circulation and gas exchange, and, presumably, these limitations are more pronounced at altitude. In studies performed near sea level in healthy subjects, as well as in patients with PH, maximal performance during progressive ramp exercise and endurance of submaximal constant-load exercise were substantially enhanced by breathing oxygen-enriched air. Both in healthy individuals and in PH patients, these improvements were mediated by a better arterial, muscular, and cerebral oxygenation, along with a reduced sympathetic excitation, as suggested by the reduced heart rate and alveolar ventilation at submaximal isoloads, and an improved pulmonary gas exchange efficiency, especially in patients with PH. In summary, in healthy individuals and in patients with PH, alterations in the inspiratory Po by exposure to hypobaric hypoxia or normobaric hyperoxia reduce or enhance exercise performance, respectively, by modifying oxygen delivery to the muscles and the brain, by effects on cardiovascular and respiratory control, and by alterations in pulmonary gas exchange. The understanding of these physiological mechanisms helps in counselling individuals planning altitude or air travel and prescribing oxygen therapy to patients with PH.
Topics: Altitude; Exercise; Humans; Hyperoxia; Hypertension, Pulmonary; Hypoxia; Oxygen Consumption; Pulmonary Gas Exchange
PubMed: 28775065
DOI: 10.1152/japplphysiol.00186.2017 -
Journal of Applied Physiology... Oct 2017The aim of this systematic review and meta-analysis [International Prospective Register of Systematic Reviews (PROSPERO) CRD42017055619] was to assess the effects of... (Meta-Analysis)
Meta-Analysis Review
The aim of this systematic review and meta-analysis [International Prospective Register of Systematic Reviews (PROSPERO) CRD42017055619] was to assess the effects of strict prolonged bed rest (without countermeasures) on maximal oxygen uptake (V̇o) and to explore sources of variation therein. Since 1949, 80 studies with a total of 949 participants (>90% men) have been published with data on strict bed rest and V̇o The studies were conducted mainly in young participants [median age (interquartile range) 24.5 (22.4-34.0) yr]. The duration of bed rest ranged from 1 to 90 days. V̇o declined linearly across bed rest duration. No statistical difference in the decline among studies reporting V̇o as l/min (-0.3% per day) compared with studies reporting V̇o normalized to body weight (ml·kg·min; -0.43% per day) was observed. Although both total body weight and lean body mass declined in response to bed rest, we did not see any associations with the decline in V̇o However, 15-26% of the variation in the decline in V̇o was explained by the pre-bed-rest V̇o levels, independent of the duration of bed rest (i.e., higher pre-bed-rest V̇o levels were associated with larger declines in V̇o). Furthermore, the systematic review revealed a gap in the knowledge about the cardiovascular response to extreme physical inactivity, particularly in older subjects and women of any age group. In addition to its relevance to spaceflight, this lack of data has significant translational implications because younger women sometimes undergo prolonged periods of bed rest associated with the complications of pregnancy and the incidence of hospitalization including prolonged periods of bed rest increases with age. Large interindividual responses of maximal oxygen uptake (V̇o) to aerobic exercise training exist. However, less is known about the variability in the response of V̇o to prolonged bed rest. This systematic review and meta-analysis showed that pre-bed-rest V̇o values were inversely associated with the change in V̇o independent of the duration of bed rest. Moreover, we identified a large knowledge gap about the causes of decline in V̇o, particularly in postmenopausal women, which may have clinical implications.
Topics: Bed Rest; Body Composition; Cardiorespiratory Fitness; Humans; Oxygen Consumption; Space Flight
PubMed: 28705999
DOI: 10.1152/japplphysiol.00415.2017