Thorpe tube and oxygen flow restrictor: what's flow accuracy?

Oxygen gas flowmeters (OGF) are used to regulate the oxygen flow in acute and chronic care. In hospitals, Thorpe tubes (TT) are the classical systems most used for delivering oxygen. In recent years, the oxygen flow restrictor (OFR) has appeared. These devices use a series of calibrated openings in a disk that can be adjusted to deliver different flow rates. These devices have a reputation for delivering more accurate oxygen flow rates compared to classical OGFs. However, to our knowledge, few study has examined this supposition. This study aimed to compare and evaluate the accuracy and precision of the ready-to-use TTs and OFRs. OGFs were selected from hospitals in Belgium and France. Before performing the flow measurements, the inlet pressure was checked. The accuracy of the OGF was analyzed with a calibrated thermal mass flowmeter (RED Y COMPACT™ GCM-0 to 20 L/min-VÖGTLIN Instruments). Different flows (2, 4, 6, 9 or 12 L/min) were evaluated. Linear regression analysis, bias (with confidence interval) and lower and upper limit of the agreement were calculated for TTs and OFRs. All measurements are expressed in absolute values. Four-hundred-seventy-six TTs and 96 OFRs were analyzed. The intra-class correlation coefficient calculated for the calibrated thermal mass flowmeter was > 0.99 and reflected the excellent reliability of our measurements. For TTs, the bias value was - 0.24 L/min (± 0.88), and the limits of agreement were - 1.97 to 1.48 L/min. For OFRs, the bias value was - 0.30 L/min (± 0.54), and the limits of agreement were - 1.36 to 0.77 L/min. As the flow increased, the accuracy of all analyzed OGFs decreased. With the increasing flow, some data fell outside the limits of agreement, and the trend increased with the elevated oxygen flow. TTs were less accurate compared to OFRs due to the increased flow variability. However, for TTs and OFRs, as the required flow is elevated, the dispersion of values increases on both sides of the actual flow.

Cannabidiol in sport: Ergogenic or else?

In the sports domain, cannabis is prohibited by the World Anti-Doping Agency (WADA) across all sports in competition since 2004. The few studies on physical exercise and cannabis focused on the main compound i.e. Δ9-tetrahydrocannabinol. Cannabidiol (CBD) is another well-known phytocannabinoid present in dried or heated preparations of cannabis. Unlike Δ9-tetrahydrocannabinol, CBD is non-intoxicating but exhibits pharmacological properties that are interesting for medical use. The worldwide regulatory status of CBD is complex and this compound is still a controlled substance in many countries. Interestingly, however, the World Anti-Doping Agency removed CBD from the list of prohibited substances - in or out of competition - since 2018. This recent decision by the WADA leaves the door open for CBD use by athletes. In the present opinion article we wish to expose the different CBD properties discovered in preclinical studies that could be further tested in the sport domain to ascertain its utility. Preclinical studies suggest that CBD could be useful to athletes due to its anti-inflammatory, analgesic, anxiolytic, neuroprotective properties and its influence on the sleep-wake cycle. Unfortunately, almost no clinical data are available on CBD in the context of exercise, which makes its use in this context still premature.

Plasma asymmetric dimethylarginine concentrations are not related to differences in maximal oxygen uptake in endurance trained and untrained men.

NEW FINDINGS: What is the central question of this study? Is there an association of plasma concentration of asymmetric dimethylarginine, which is related to exercise capacity in patients with cardiovascular diseases, with oxygen delivery and subsequently exercise capacity in healthy subjects in the absence of the potentially confounding influence of inflammation and oxidative stress? What is the main finding and its importance? Plasma asymmetric dimethylarginine concentrations are not related to exercise capacity in healthy subjects, while O2 delivery in the working skeletal muscle during the maximal graded-exercise test is not associated with any of the l-arginine analogues. ADMA alone does not play a crucial role in local muscle perfusion and in maintaining exercise capacity. ABSTRACT: Asymmetric dimethylarginine (ADMA) is an endogenous inhibitor of nitric oxide (NO) synthesis that could limit oxygen (O2 ) delivery in the working skeletal muscles by altering endothelium-dependent vasodilatation. Exercise capacity is associated with plasma ADMA concentrations in patients with cardiovascular diseases, but this issue has still not been investigated in healthy subjects. We aimed to determine whether plasma ADMA concentrations were negatively associated with exercise capacity in young healthy male subjects. Ten men with maximal oxygen uptake ( V ̇ O 2 max ) > 65 mL kg-1  min-1 were included in the high exercise capacity group (HI-FIT), and 10 men with V ̇ O 2 max  < 45 mL kg-1  min-1 were included in the low exercise capacity group (LO-FIT). Plasma ADMA and other l-arginine analogue concentrations were measured before and after a maximal graded-exercise test by liquid chromatography-tandem mass spectrometry. Microvascular O2 delivery during exercise was estimated through the pattern from the sigmoid model of muscle deoxygenation in the vastus lateralis measured by near infrared spectroscopy. V ̇ O 2 max was 60% higher in the HI-FIT group (median: 70.2 mL kg-1  min-1 ; IQR: 68.0-71.9 mL kg-1  min-1 ) than in the LO-FIT group (median: 43.8 mL kg-1  min-1 ; IQR: 34.8-45.3 mL kg-1  min-1 ). Plasma ADMA concentrations did not differ between the LO-FIT and HI-FIT groups before (0.50 ± 0.06 vs. 0.54 ± 0.07 µmol L-1 , respectively) and after the maximal incremental exercise test (0.49 ± 0.08 vs. 0.55 ± 0.03 µmol L-1 , respectively). There was no significant association of plasma ADMA concentrations with the pattern of local muscle deoxygenation and exercise capacity. Exercise capacity and microvascular O2 delivery are not related to plasma ADMA concentrations in young healthy male subjects. Our findings show that ADMA does not play a crucial role in local muscle perfusion and in maintaining exercise capacity without pathological conditions.

Beetroot Juice Does Not Enhance Supramaximal Intermittent Exercise Performance in Elite Endurance Athletes.

Objective: Nitrate (NO3-)-rich beetroot juice (BR) is recognized as an ergogenic supplement that improves exercise tolerance during submaximal to maximal intensity exercise in recreational and competitive athletes. A recent study has investigated the effectiveness of BR on exercise performance during supramaximal intensity intermittent exercise (SIE) in Olympic-level track cyclists, but studies conducted in elite endurance athletes are scarce. The present study aimed to determine whether BR supplementation enhances the tolerance to SIE in elite endurance athletes.Methods: Eleven elite endurance athletes (age: 21.7 ± 3.7 years, maximal oxygen uptake [Formula: see text] 71.1 ± 5.2 mL·kg-1·min-1) performed an SIE test until exhaustion following either a 3-day BR supplementation (340 mg/d) or a placebo (PL) supplementation (<2.5 mg/d) in a randomized, single blind, placebo-controlled, and crossover study. The exercise test consisted of 15-second cycling exercise bouts at 170% of the maximal aerobic power interspersed with 30-second passive recovery periods. Gas exchange was measured during SIE tests as local muscle O2 delivery and extraction were assessed by near infrared spectroscopy.Results: The number of repetitions completed was not significantly different between BR (13.9 ± 4.0 reps) and PL conditions (14.2 ± 4.5 reps). BR supplementation did not affect oxygen uptake ([Formula: see text]) during SIE tests (BR: 3378.5 ± 681.8 mL·min-1, PL: 3466.1 ± 505.3 mL·min-1). No significant change in the areas under curves was found for local muscle total hemoglobin (BR: 6816.9 ± 1463.1 arbitrary units (a.u.), PL: 6771.5 ± 3004.5 a.u.) and deoxygenated hemoglobin (BR: 6619.7 ± 875.8 a.u., PL: 6332.7 ± 1336.8 a.u.) during time-matched work + recovery periods from SIE tests following BR supplementation.Conclusions: BR supplementation does not enhance the tolerance to SIE in elite endurance athletes and affects neither [Formula: see text] nor local muscle O2 delivery and extraction.

Effect of dietary nitrate supplementation on metabolic rate during rest and exercise in human: A systematic review and a meta-analysis.

BACKGROUND: Recent randomized controlled trials have suggested that dietary nitrate (NO3(-)), found in beetroot and other vegetables, and inorganic NO3(-) salts decrease metabolic rate under resting and exercise conditions. OBJECTIVE: Our aim was therefore to determine from a systematic review and meta-analysis whether dietary NO3(-) supplementation significantly reduces metabolic rate, expressed as oxygen uptake (VO2), under resting and exercise conditions in healthy humans and those with cardiorespiratory diseases. DESIGN: A systematic article search was performed on electronic databases (PubMed, Scopus and Web of Science) from February to March 2015. The inclusion criteria included 1) randomized controlled trials; 2) studies reporting the effect of NO3(-) on VO2 under resting and/or exercise conditions; 3) comparison between dietary NO3(-) supplementation and placebo. Random-effects models were used to calculate the pooled effect size. RESULTS: Twenty nine randomized placebo-controlled trials were included in the systematic review, and 26 of which were included in the meta-analysis. Dietary NO3(-) supplementation significantly decreases VO2 during submaximal intensity exercise [-0.26 (95% IC: -0.38, -0.15), p < 0.01], but not in the sub-analysis of subjects with chronic diseases [-0.09 (95% IC: -0.50, 0.32), p = 0.67]. When data were separately analyzed by submaximal intensity domains, NO3(-) supplementation reduces VO2 during moderate [-0.29 (95% IC: -0.48,-0.10), p < 0.01] and heavy [-0.33 (95% IC: -0.54,-0.12), p < 0.01] intensity exercise. When the studies with the largest effects were excluded from the meta-analysis, there is a trend for a VO2 decrease under resting condition in dietary NO3(-) supplementation [-0.28 (95% IC: -0.62, 0.05), p = 0.10]. CONCLUSION: Dietary NO3(-) supplementation decreases VO2 during exercise performed in the moderate and heavy intensity domains in healthy subjects. The present meta-analysis did not show any significant effect of dietary NO3(-) supplementation on metabolic rate in subjects with chronic diseases, despite enhanced exercise tolerance.

Effect of dietary nitrate supplementation on tolerance to supramaximal intensity intermittent exercise.

Dietary nitrate (NO3(-)) supplementation has been shown to increase exercise tolerance and improve oxidative efficiency during aerobic exercise in healthy subjects. We tested the hypothesis that a 3-day supplementation in beetroot juice (BJ) rich in NO3(-) would improve the tolerance to supramaximal intensity intermittent exercise consisting of 15-s exercise periods at 170% of the maximal aerobic power interspersed with 30-s passive recovery periods. The number of repetitions completed before reaching volitional exhaustion was significantly higher in the BJ than in the placebo condition (26.1 ± 10.7 versus 21.8 ± 8.0 respectively, P < 0.05). In contrast to previous findings during exercise performed at intensity below the peak oxygen uptake (VO2peak), oxygen uptake (VO2) was unaffected (BJ: 2735 ± 345 mL kg(-1) min(-1) vs. placebo: 2787 ± 346 mL kg(-1) min(-1), NS). However, the Area Under the Curve for microvascular total hemoglobin (AUC-THb) in the vastus lateralis muscle assessed by near infrared spectroscopy during 3 time-matched repetitions was significantly increased with NO3(-) supplementation (BJ: 9662 ± 1228 a.u. vs. placebo:8178 ± 1589 a.u.; P < 0.05). Thus, increased NO3(-) (BJ: 421.5 ± 107.4 µM vs placebo:39.4 ± 18.0 µM) and NO2(-) (BJ: 441 ± 184 nM vs placebo: 212 ± 119 nM) plasma levels (P < 0.001 for both) are associated with improved muscle microvascular Red Blood Cell (RBC) concentration and O2 delivery during intense exercise, despite no effect on resting femoral artery blood flow, and vascular conductance. Maximal voluntary force during an isometric leg extensor exercise, and blood lactate levels were also unaffected by NO3(-) supplementation. To conclude, dietary NO3(-) supplementation enhances tolerance to exercise at supramaximal intensity, with increased microvascular total RBC concentration in the working muscle, in the absence of effect on contractile function and resting hemodynamic parameters.

The Double-Trunk Mask Improves Oxygenation During High-Flow Nasal Cannula Therapy for Acute Hypoxemic Respiratory Failure.

BACKGROUND: High-flow nasal cannula (HFNC) oxygen therapy is used to deliver an FIO2 from 0.21 to 1.0. The double-trunk mask (DTM) is a device designed to increase the FIO2 in patients with a high inspiratory flow demand. The aim of our study was to evaluate the effect of DTM in hypoxemic subjects already receiving HFNC. METHODS: We report a prospective multi-center crossover pilot study including 15 subjects treated with HFNC for acute hypoxemic respiratory failure. Measurements were performed at the end of 30-min periods with HFNC only, with HFNC + DTM, and again with HFNC only. RESULTS: Compared with HFNC alone, HFNC + DTM increased PaO2 from 68 ± 14 mm Hg to 85 ± 22 mm Hg (P < .001) and did not affect PaCO2 (P = .18). In the 11 responders, the PaO2 increased from 63 ± 12 mm Hg to 88 ± 23 mm Hg (P < .001). No complications were reported during DTM use. CONCLUSION: In subjects receiving oxygen via HFNC, the addition of the DTM over the HFNC increased PaO2 without changing the PaCO2 .

A New Formula for Predicting the Fraction of Delivered Oxygen During Low-Flow Oxygen Therapy.

BACKGROUND: During O2 therapy at low flow in patients who breathe spontaneously, the fraction of delivered O2 (FDO2 ) is unknown. In recent years, FDO2 prediction formulas have been proposed. However, they do not take into account the effect of inspiratory flow (V̇I) on the FDO2 . The aim of this study was to validate a new FDO2 prediction formula, which takes into account the V̇I and compares it with other FDO2 prediction formulas. METHODS: During a bench study, spontaneous breathing was generated with a mechanical test lung connected to a mechanical ventilator set to volume control mode. O2 flow from a wall-mounted tube was delivered through a heat-and-moisture exchanger filter. A flow sensor recorded each breath of the V̇I in ambient temperature and barometric pressure conditions. Three parameters [O2 flow at 2, 3, 4, 5, 6 L/min; minute ventilation at 5, 10, 15, 20 L/min; and ratio of the inspiratory time (TI) to the total breathing cycle time (Ttot) (TI/Ttot) of 0.33 (TI/Ttot value) and 0.50 (TI/Ttot value)] were modified to generate many ventilatory patterns. An O2 analyzer continuously examined the FDO2 . RESULTS: When the O2 flow and/or TI/Ttot increased, the FDO2 increased. When the minute ventilation increased, the FDO2 decreased. The results of the Bland-Altman method for the FDO2 , calculated by using our mathematical model and the measured FDO2 , showed that the mean ± SD bias value was equal to 1.49 ± 0.84%, and the limits of agreement ranged from -0.17% to 3.14%. The intraclass correlation coefficients were 0.991 for TI/Ttot = 0.33 and 0.994 for TI/Ttot = 0.50, and the coefficient of variation was 2.1% for TI/Ttot = 0.33 and 1.3% for TI/Ttot = 0.50. The results of the Bland-Altman method for the FDO2 calculated by using the Shapiro formula and the FDO2 measured on the bench indicated that the bias value was 0.075 ± 8.66% and the limits of agreement ranged from -16.89% to 17.04%. For the Vincent formula, the bias value was 3.08% ± 8.56% and the limits of agreement ranged from -13.69% to 19.84%. CONCLUSIONS: The V̇I has a major impact on FDO2 during O2 therapy at low flow. FDO2 comparisons between frequently used prediction formulas and FDO2 measured on the bench indicated greater differences. Uncritical use of these formulas should be used cautiously to predict FDO2 . In this study, our prediction formula indicated a good accuracy for predicting FDO2 during supplemental oxygenation through a heat-and-moisture exchanger in patients who breathe spontaneously.

Accuracy of Oxygen Flow Delivered by Compressed-Gas Cylinders in Hospital and Prehospital Emergency Care.

BACKGROUND: Oxygen cylinders are widely used both in hospital and prehospital care. Excessive or inappropriate FIO2 may be critical for patients with hypercapnia or hypoxia. Moreover, over-oxygenation could be deleterious in ischemic disorders. Supplemental oxygen from oxygen cylinder should therefore be delivered accurately. The aim of this study was to assess the accuracy of oxygen flows for oxygen cylinder in hospital and prehospital care. METHODS: A prospective trial was conducted to evaluate accuracy of delivered oxygen flows (2, 4, 6, 9 and 12 L/min) for different oxygen cylinder ready for use in different hospital departments. Delivered flows were analyzed randomly using a calibrated thermal mass flow meter. Two types of oxygen cylinder were evaluated: 78 oxygen cylinder with a single-stage regulator and 70 oxygen cylinder with a dual-stage regulator. Delivered flows were compared to the required oxygen flow. The residual pressure value for each oxygen cylinder was considered. A coefficient of variation was calculated to compare the variability of the delivered flow between the two types of oxygen cylinder. RESULTS: The median values of delivered flows were all ≥ 100% of the required flow for single stage (range 100-109%) and < 100% of required flow for dual stage (range 95-97%). The median values of the delivered flow differed between single and dual stage. It was found that single stage is significantly higher than dual stage (P = .01). At low flow, the dispersion of the measures for single stage was higher than with a high oxygen flow. Delivered flow differences were also found between low and high residual pressures, but only with single stage (P = .02). The residual pressure for both oxygen cylinders (no. = 148) ranged from 73 to 2,900 pounds per square inch, and no significant difference was observed between the 2 types (P = .86). The calculated coefficient of variation ranged from 7% (±1%) for dual stage to 8% (±2%) for single stage. CONCLUSIONS: This study shows good accuracy of oxygen flow delivered via oxygen cylinders. This accuracy was higher with dual stage. Single stage was also accurate, however, at low flow this accuracy is slightly less. Moreover, with single stage, when residual pressure decreases, the median value of delivered flow decreased.