Carbon dioxide absorbers allow the use of fresh gas flow below minute ventilation (V˙E). Models are developed and tested in vitro to quantify their performance with variable carbon dioxide load ...(V˙CO2), fresh gas flow, V˙E, end-tidal carbon dioxide (ETco2) fraction, and the type of workstation used.
First principles are used to derive a linear relationship between fresh gas flow and fractional canister usage or FCU0.5 (the reciprocal of the time for the inspiratory carbon dioxide fraction to reach 0.5%). This forms the basis for two basic models in which V˙E was measured by spirometry or calculated. These models were extended by multiplying V˙E with an empirical workstation factor. To validate the four models, two hypotheses were tested. To test whether the FCU0.5 intercept varied proportionally with V˙CO2 and was independent of V˙E, FCU was measured for 10 canisters tested with a fixed 0.3 l/min fresh gas flow and a range of V˙CO2 while V˙E was either constant or adjusted to maintain ETco2 fraction. A t test was used to compare the two groups. To confirm whether a change in V˙CO2 accompanied by a change in V˙E to maintain ETco2 fraction would shift the linear fresh gas flow-FCU0.5 relationship in a parallel manner, 19 canisters were tested with different combinations of V˙CO2 and fresh gas flow. These measured FCU values were compared to those predicted by the four models using Varvel's performance criteria.
With 0.3 l/min fresh gas flow, FCU0.5 was proportional with V˙CO2 and independent of whether V˙E was adjusted to maintain ETco2 fraction or not (P = 0.962). The hypothesized parallel shift of the fresh gas flow-FCU0.5 relationship was confirmed. Both extended models are good candidate models.
The models predict prepacked canister performance in vitro over the range of V˙E, fresh gas flow, and V˙CO2 likely to be encountered in routine clinical practice. In vivo validation is still needed.
Measurements of aerobic scope the difference between minimum and maximum oxygen consumption rate ( and , respectively) are increasing in prevalence as a tool to address questions relating to fish ...ecology and the effects of climate change. However, there are underlying issues regarding the array of methods used to measure aerobic scope across studies and species. In an attempt to enhance quality control before the diversity of issues becomes too great to remedy, this paper outlines common techniques and pitfalls associated with measurements of , and aerobic scope across species and under different experimental conditions. Additionally, we provide a brief critique of the oxygen- and capacity-limited thermal tolerance (OCLTT) hypothesis, a concept that is intricately dependent on aerobic scope measurements and is spreading wildly throughout the literature despite little evidence for its general applicability. It is the intention of this paper to encourage transparency and accuracy in future studies that measure the aerobic metabolism of fishes, and to highlight the fundamental issues with assuming broad relevance of the OCLTT hypothesis.
Continuous real-time monitoring of the adequacy of cerebral perfusion can provide important therapeutic information in a variety of clinical settings. The current clinical availability of several ...non-invasive near-infrared spectroscopy (NIRS)-based cerebral oximetry devices represents a potentially important development for the detection of cerebral ischaemia. In addition, a number of preliminary studies have reported on the application of cerebral oximetry sensors to other tissue beds including splanchnic, renal, and spinal cord. This review provides a synopsis of the mode of operation, current limitations and confounders, clinical applications, and potential future uses of such NIRS devices.
Cardiac muscle hypercontractility is a key pathophysiological abnormality in hypertrophic cardiomyopathy, and a major determinant of dynamic left ventricular outflow tract (LVOT) obstruction. ...Available pharmacological options for hypertrophic cardiomyopathy are inadequate or poorly tolerated and are not disease-specific. We aimed to assess the efficacy and safety of mavacamten, a first-in-class cardiac myosin inhibitor, in symptomatic obstructive hypertrophic cardiomyopathy.
In this phase 3, randomised, double-blind, placebo-controlled trial (EXPLORER-HCM) in 68 clinical cardiovascular centres in 13 countries, patients with hypertrophic cardiomyopathy with an LVOT gradient of 50 mm Hg or greater and New York Heart Association (NYHA) class II–III symptoms were assigned (1:1) to receive mavacamten (starting at 5 mg) or placebo for 30 weeks. Visits for assessment of patient status occurred every 2–4 weeks. Serial evaluations included echocardiogram, electrocardiogram, and blood collection for laboratory tests and mavacamten plasma concentration. The primary endpoint was a 1·5 mL/kg per min or greater increase in peak oxygen consumption (pVO2) and at least one NYHA class reduction or a 3·0 mL/kg per min or greater pVO2 increase without NYHA class worsening. Secondary endpoints assessed changes in post-exercise LVOT gradient, pVO2, NYHA class, Kansas City Cardiomyopathy Questionnaire-Clinical Summary Score (KCCQ-CSS), and Hypertrophic Cardiomyopathy Symptom Questionnaire Shortness-of-Breath subscore (HCMSQ-SoB). This study is registered with ClinicalTrials.gov, NCT03470545.
Between May 30, 2018, and July 12, 2019, 429 adults were assessed for eligibility, of whom 251 (59%) were enrolled and randomly assigned to mavacamten (n=123 49%) or placebo (n=128 51%). 45 (37%) of 123 patients on mavacamten versus 22 (17%) of 128 on placebo met the primary endpoint (difference +19·4%, 95% CI 8·7 to 30·1; p=0·0005). Patients on mavacamten had greater reductions than those on placebo in post-exercise LVOT gradient (−36 mm Hg, 95% CI −43·2 to −28·1; p<0·0001), greater increase in pVO2 (+1·4 mL/kg per min, 0·6 to 2·1; p=0·0006), and improved symptom scores (KCCQ-CSS +9·1, 5·5 to 12·7; HCMSQ-SoB −1·8, −2·4 to −1·2; p<0·0001). 34% more patients in the mavacamten group improved by at least one NYHA class (80 of 123 patients in the mavacamten group vs 40 of 128 patients in the placebo group; 95% CI 22·2 to 45·4; p<0·0001). Safety and tolerability were similar to placebo. Treatment-emergent adverse events were generally mild. One patient died by sudden death in the placebo group.
Treatment with mavacamten improved exercise capacity, LVOT obstruction, NYHA functional class, and health status in patients with obstructive hypertrophic cardiomyopathy. The results of this pivotal trial highlight the benefits of disease-specific treatment for this condition.
MyoKardia.
Hernando, D, Garatachea, N, Almeida, R, Casajús, JA, and Bailón, R. Validation of heart rate monitor Polar RS800 for heart rate variability analysis during exercise. J Strength Cond Res 32(3): ...716-725, 2018-Heart rate variability (HRV) analysis during exercise is an interesting noninvasive tool to measure the cardiovascular response to the stress of exercise. Wearable heart rate monitors are a comfortable option to measure interbeat (RR) intervals while doing physical activities. It is necessary to evaluate the agreement between HRV parameters derived from the RR series recorded by wearable devices and those derived from an electrocardiogram (ECG) during dynamic exercise of low to high intensity. Twenty-three male volunteers performed an exercise stress test on a cycle ergometer. Subjects wore a Polar RS800 device, whereas ECG was also recorded simultaneously to extract the reference RR intervals. A time-frequency spectral analysis was performed to extract the instantaneous mean heart rate (HRM), and the power of low-frequency (PLF) and high-frequency (PHF) components, the latter centered on the respiratory frequency. Analysis was done in intervals of different exercise intensity based on oxygen consumption. Linear correlation, reliability, and agreement were computed in each interval. The agreement between the RR series obtained from the Polar device and from the ECG is high throughout the whole test although the shorter the RR is, the more differences there are. Both methods are interchangeable when analyzing HRV at rest. At high exercise intensity, HRM and PLF still presented a high correlation (ρ > 0.8) and excellent reliability and agreement indices (above 0.9). However, the PHF measurements from the Polar showed reliability and agreement coefficients around 0.5 or lower when the level of the exercise increases (for levels of O2 above 60%).
Kamandulis, S, Bruzas, V, Mockus, P, Stasiulis, A, Snieckus, A, and Venckunas, T. Sport-specific repeated sprint training improves punching ability and upper-body aerobic power in experienced amateur ...boxers. J Strength Cond Res 32(5): 1214-1221, 2018-High-intensity interval training improves endurance and performance, but it is unclear whether sprint-type upper-body interval training is similarly effective. This study explored the effects of 4-week sport-specific sprint interval training on punch characteristics and endurance capacity in boxers. Experienced male amateur boxers (n = 18) participated in this 4-week training study and were divided into an experimental group (EG) and a control group (CG) (n = 9 per group). Both groups completed standard low-intensity training. The EG also completed 3 rounds (14 sets of 3-second all-out punching with a 10-second rest) of a simulated fight using a punching bag with a 1-minute rest between rounds 3 times per week, whereas the CG performed the same 3 rounds of a simulated fight at low intensity. Three rounds of 14 sets of 3-second all-out punching of a bag ergometer with a 10-second rest were performed to measure punching abilities. Peak oxygen consumption and peak power were measured during progressive arm cranking before and after training. In response to training peak oxygen consumption and peak power in arm-cranking test increased in EG, also punching force increased and maintenance of punching frequency and punch force improved during the simulated fight, which resulted in greater cumulative force throughout the 3 rounds. There were no changes in the CG. The study shows that 1 month of all-out punching training (3 sessions per week with ∼2 minutes of all-out punching per session) improved both upper-body aerobic power and punching abilities in experienced amateur boxers.
Prescribing the frequency, duration, or volume of training is simple as these factors can be altered by manipulating the number of exercise sessions per week, the duration of each session, or the ...total work performed in a given time frame (e.g., per week). However, prescribing exercise intensity is complex and controversy exists regarding the reliability and validity of the methods used to determine and prescribe intensity. This controversy arises from the absence of an agreed framework for assessing the construct validity of different methods used to determine exercise intensity. In this review, we have evaluated the construct validity of different methods for prescribing exercise intensity based on their ability to provoke homeostatic disturbances (e.g., changes in oxygen uptake kinetics and blood lactate) consistent with the moderate, heavy, and severe domains of exercise. Methods for prescribing exercise intensity include a percentage of anchor measurements, such as maximal oxygen uptake (Formula: see text), peak oxygen uptake (Formula: see text), maximum heart rate (HR
), and maximum work rate (i.e., power or velocity-Formula: see text or Formula: see text, respectively), derived from a graded exercise test (GXT). However, despite their common use, it is apparent that prescribing exercise intensity based on a fixed percentage of these maximal anchors has little merit for eliciting distinct or domain-specific homeostatic perturbations. Some have advocated using submaximal anchors, including the ventilatory threshold (VT), the gas exchange threshold (GET), the respiratory compensation point (RCP), the first and second lactate threshold (LT
and LT
), the maximal lactate steady state (MLSS), critical power (CP), and critical speed (CS). There is some evidence to support the validity of LT
, GET, and VT to delineate the moderate and heavy domains of exercise. However, there is little evidence to support the validity of most commonly used methods, with exception of CP and CS, to delineate the heavy and severe domains of exercise. As acute responses to exercise are not always predictive of chronic adaptations, training studies are required to verify whether different methods to prescribe exercise will affect adaptations to training. Better ways to prescribe exercise intensity should help sport scientists, researchers, clinicians, and coaches to design more effective training programs to achieve greater improvements in health and athletic performance.
Protective masks impose variable breathing resistance (BR) on the wearer and may adversely affect exercise performance, yet existing literature shows inconsistent results under different types of ...masks and metabolic demands. The present study was undertaken to determine whether added BR impairs cardiopulmonary function and aerobic performance during exercise. Sixteen young healthy men completed a graded exercise test on a cycle ergometer under the four conditions of BR using a customized breathing resistor at no breathing resistance (CON), 18.9 (BR1), 22.2 (BR2), and 29.9 Pa (BR3). The results showed that BR significantly elevates respiratory pressure (
< 0.001) and impairs ventilatory response to graded exercise (reduced V
;
< 0.001) at a greater degree with an increased level of BR which caused mild to moderate exercise-induced hypoxemia (final mean SpO
: CON = 95.6%, BR1 = 94.4%, BR2 = 91.6%, and BR3 = 90.6%;
< 0.001). Especially, such a marked reduction in SpO
was significantly correlated with maximal oxygen consumption at the volitional fatigue (r = 0.98,
< 0.001) together with exaggerated exertion and breathing discomfort (
< 0.001). In conclusion, added BR commonly experienced when wearing tight-fitting facemasks and/or respirators could significantly impair cardiopulmonary function and aerobic performance at a greater degree with an increasing level of BR.
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