Novel Computerized Method for Automated Determination of Ventilatory Threshold and Respiratory Compensation Point

Introduction: The ventilatory threshold (named as VT1) and the respiratory compensation point (named as VT2) describe prominent changes of metabolic demand and exercise intensity domains during an incremental exercise test.Methods: A novel computerized method based on the optimization method was developed for automatically determining VT1 and VT2 from expired air during a progressive maximal exercise test. A total of 109 peak cycle tests were performed by members of the US astronaut corps (74 males and 35 females). We compared the automatically determined VT1 and VT2 values against the visual subjective and independent analyses of three trained evaluators. We also characterized VT1 and VT2 and the respective absolute and relative work rates and distinguished differences between sexes.Results: The automated compared to the visual subjective values were analyzed for differences with t test, for agreement with Bland–Altman plots, and for equivalence with a two one-sided test approach. The results showed that the automated and visual subjective methods were statistically equivalent, and the proposed approach reliably determined VT1 and VT2 values. Females had lower absolute O2 uptake, work rate, and ventilation, and relative O2 uptake at VT1 and VT2 compared to men (p ≤ 0.04). VT1 and VT2 occurred at a greater relative percentage of their peak VO2 for females (67 and 88%) compared to males (55 and 74%; main effect for sex: p < 0.001). Overall, VT1 occurred at 58% of peak VO2, and VT2 occurred at 79% of peak VO2 (p < 0.0001).Conclusion: Improvements in determining of VT1 and VT2 by automated analysis are time efficient, valid, and comparable to subjective visual analysis and may provide valuable information in research and clinical practice as well as identifying exercise intensity domains of crewmembers in space.

A Cloth Facemask Causes No Major Respiratory or Cardiovascular Perturbations during Moderate to Heavy Exercise

Objectives: To investigate whether wearing a cloth facemask could affect physiological and perceptual responses to exercise at distinct exercise intensities in non-trained men and women. Methods: In a crossover design, participants (17 men and 18 women) underwent a progressive square-wave test at four intensities (i. at 80% of the ventilatory anerobic threshold [80%VAT]; ii. at VAT; iii. at the respiratory compensation point [RCP]; iv. at exercise peak [Peak] to exhaustion), with or without a triple-layered cloth mask (Mask or No-Mask). Several physiological, metabolic and perceptual measures were analyzed. Results: Mask reduced inspiratory capacity at all exercise intensities vs. No-Mask (p<0.0001), irrespective of sex. Mask reduced respiratory frequency vs. No-Mask (p=0.001) at Peak (-8.3 breaths/min; CI: -5.8, -10.8), RCP (-6.9 breaths/min; CI: -4.6, -9.2) and VAT (-6.5 breaths/min; CI: -4.1, -8.8), but not at Baseline or at 80%VAT. Mask also reduced tidal volume (p<0.0001) at both RCP (-0.5L; CI: -0.3, -0.6) and Peak (-0.8L; CI: -0.6, -0.9), but not at Baseline, 80%VAT or VAT. Shallow breathing index was increased with Mask at Peak compared to No-Mask (11.3; CI: 7.5, 15.1), but not at any other intensities. Mask did not change heart rate, lactate, ratings of perceived exertion, blood pressure or oxygen saturation. Conclusions: Wearing a cloth facemask during exercise at moderate to heavy intensities is unlikely to incur significant respiratory or cardiovascular changes, irrespective of sex. These data can inform new exercise recommendations for health during the COVID-19 pandemic and debunk unfounded allegations of harmful effects of masks during exercise. ClinicalTrials.gov: NCT04887714

Dissociation between exercise intensity thresholds: mechanistic insights from supine exercise

Introduction/purpose: This study tested the hypothesis that the respiratory compensation point (RCP) and breakpoint in deoxygenated [heme] (deoxy[heme]BP, assessed via near-infrared spectroscopy (NIRS)) during ramp incremental exercise would occur at the same metabolic rate in the upright (U) and supine (S) body positions. Methods: Eleven healthy men completed ramp incremental exercise tests in U and S. Gas exchange was measured breath-by-breath and time-resolved-NIRS was used to measure deoxy[heme] in the vastus lateralis (VL) and rectus femoris (RF). Results: RCP (S: 2.56 ± 0.39, U: 2.86 ± 0.40 L.min-1, P = 0.02) differed from deoxy[heme]BP in the VL in U (3.10 ± 0.44 L.min-1, P = 0.002), but was not different in S in the VL (2.70 ± 0.50 L.min-1, P = 0.15). RCP was not different from the deoxy[heme]BP in the RF for either position (S: 2.34 ± 0.48 L.min-1, U: 2.76 ± 0.53 L.min-1, P > 0.05). However, the deoxy[heme]BP differed between muscles in both positions (P < 0.05), and changes in deoxy[heme]BP did not relate to delta RCP between positions (VL: r = 0.55, P = 0.080, RF: r = 0.26, P = 0.44). The deoxy[heme]BP was consistently preceded by a breakpoint in total[heme], and was, in turn, itself preceded by a breakpoint in muscle surface electromyography (EMG). Conclusions: RCP and the deoxy[heme]BP can be dissociated across muscles and different body positions and, therefore, do not represent the same underlying physiological phenomenon. The deoxy[heme]BP may, however, be mechanistically related to breakpoints in total[heme] and muscle activity.

European early experience with a novel 3D mapping system

Funding Acknowledgements Type of funding sources: None. Introduction Catheter navigation and 3-dimensional (3D) cardiac mapping are critical for successful electrophysiological ablation procedures. A novel 3D mapping system received CE Mark in July 2020. The system offers two imaging modalities: magnetic-based (VoXel) and impedance-based (NavX). Real-time display of 3D location and catheter movements is achieved via a magnetic field frame and magnetic sensors with supplemental impedance data when operating in VoXel mode or primarily via an impedance field generated from surface electrodes in NavX mode. To address limitations in data collection commonly experienced during 3D mapping, a new respiratory compensation algorithm, patient movement detection module, and metal compensation algorithm have been developed to enable consistent data collection throughout the full respiratory cycle even in challenging cases and lab environments. Purpose To examine the clinical utility and procedural characteristics associated with the use of this novel 3D mapping system among participating centers. Methods Procedural data was collected in cases utilizing the newly cleared mapping system during the initial evaluation phase in Europe. Procedural characteristics recorded included indication for mapping and ablation, rhythm mapped, chambers mapped, and procedure time. Results Procedural data was collected from over 250 cases across 12 European centers. A total of 12 indications for mapping and ablation were represented including de novo and redo atrial fibrillation (paroxysmal, persistent, long-standing persistent), ventricular tachycardia (ischemic, non-ischemic) or premature ventricular contraction, and supraventricular arrhythmias (typical and atypical atrial flutter, atrioventricular nodal reentrant tachycardia, atrioventricular reentrant tachycardia). Over 70% of the cases were performed in VoXel mode. Impedance mode was mostly used in SVT cases or when the case was intended to be completed with minimal fluoroscopy. The most commonly mapped rhythms were sinus rhythm during voltage mapping and atrial tachycardia. The majority of cases (over 65%) were completed under conscious sedation; general anesthesia was used in 20% of the cases (15% not reported). The respiratory compensation algorithm was utilized in over 90% of the cases. For cases in which pre-procedural computed tomography or magnetic resonance imaging were available, operators indicated that the model shape was accurate when compared to pre-procedural imaging in 96% of the cases performed in VoXel mode. Conclusions Initial European experience with this novel 3D mapping system included a wide variety of arrhythmias in the atria and ventricles. This new mapping system offered operators the flexibility to tailor to specific procedure needs with two imaging modalities which were both widely utilized.

Respiratory compensation point

This chapter describes how acidaemia stimulates ventilation in the later stages of a cardiopulmonary exercise test (CPET). This happens after the anaerobic threshold, once the capacity of the blood to buffer lactic acid has been used up. The respiratory compensation point (RCP) can be identified from an increase in the slope when minute ventilation (VE) is plotted against carbon dioxide output (VCO2), or from a rise in the ventilatory equivalents for carbon dioxide (VeqCO2). The presence of a clear RCP indicates that the subject has made a fairly maximal effort during the CPET. An RCP also argues against significant lung disease, since it implies the ability to increase ventilation in response to acidaemia.

Prescribing and Self-Regulating Heated Water-Based Exercise by Rating of Perceived Exertion in Older Individuals With Hypertension

We aimed to analyze the usefulness of the 6–20 rating of perceived exertion (RPE) scale for prescribing and self-regulating high-intensity interval (HIIE) and moderate-intensity continuous (MICE) aerobic exercise performed in a heated swimming pool (32 °C). Fifteen older individuals (65 ± 3 years) treated for hypertension underwent a symptom-limited maximal graded exercise test to determine their heart rate at anaerobic threshold, and respiratory compensation point. On different days, participants were randomized to HIIE (walking/jogging between 11 and 17 of RPE; 25 min) and MICE (walking at 11–13 of RPE; 30 min). Heart rate during the low-intensity intervals of HIIE and MICE remained below the graded exercise test’s heart rate at anaerobic threshold (−7 ± 18 bpm/−16 ± 15 bpm) and respiratory compensation point (−18 ± 18 bpm/−30 ± 16 bpm), respectively, and maintained in the aerobic training zone during the high-intensity intervals of HIIE (+8 ± 18 bpm/−4 ± 19 bpm). The RPE scale at 15–17 is a useful tool for prescribing and self-regulating heated water-based HIIE and may have important implications for water-based exercise in older individuals with hypertension.

NIRS-derived skeletal muscle oxidative capacity is correlated with aerobic fitness and independent of sex

Near-infrared spectroscopy (NIRS) can be used to measure skeletal muscle oxidative capacity. Here, we demonstrated that NIRS-derived skeletal muscle oxidative capacity of the vastus lateralis was independent of sex, reliable across and within days, and correlated with maximal and submaximal indices of aerobic fitness, including maximal oxygen uptake, lactate threshold, and respiratory compensation point. These findings highlight the utility of NIRS for investigating skeletal muscle oxidative capacity in females and males.