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

Abstract

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.

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“…The ventilatory threshold (VT) and the respiratory compensation point (RC) were determined using different criteria. VT is commonly described as the point at which pulmonary ventilation and carbon dioxide (CO 2 ) output begin to increase exponentially 21 , while RC represents the point at which lactate is rapidly increasing with intensity and is associated with hyperventilation. The VT was determined through the V-Slope method, the point at which the increase in the rate of elimination of carbon dioxide ( CO 2 ) is greater than the increase in O 2 .…”

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“…Excess CO2 was calculated as (VCO2 2 / VO 2 ) -VCO 2 , with all values in L/min, and the ventilatory equivalents of O2 and CO2 were calculated as VE/VO2 and VE/VCO2. [95][96][97] Automated threshold detection was then applied separately to the excess CO2 and VE/VO2 time series [95][96][97] using the R 98 package 'mcp' 99 to identify the posterior distribution likelihood of the ventilatory threshold at each 5 second time point. This was performed separately after smoothing the data using 0, 10 and 20 second rolling averages.…”

“…The ventilatory threshold was identified by an upward break point in the excess CO2 and VE/VO2 data, disproportionate to any VE/VCO2 increase, where the slope of the VCO2 by VO2 relationship increased above 1. [95][96][97] If no threshold occurred during the test, time to threshold was set at the end of the GXT. Inter-rater reliability was excellent (ICC2,1: 0.98 [95%CI: 0.97-0.99], mean absolute error: 0.47 ± 0.87 minutes) despite a small systematic difference in mean time-to-threshold between raters (10.2 ± 4.9 versus 10.5 ± 4.7 minutes, p<0.0001).…”

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“…VT2 is considered the second breakpoint at which arterial CO 2 partial pressure begins to decrease during intense exercise, where the energy production comes from 100% carbohydrates. 78 In some athletes, high-intensity endurance exercise (at VT2 or above) induces a time-dependent decrease in sO 2 of more than 5% compared with resting levels (∼98%), where extreme declines in the 80% range have been reported. 79 The desaturation of O 2 Hb during exercise is based on respiratory and non-respiratory factors.…”