Muscle oxygenation assessment during talk test to determine the anaerobic threshold in individuals with cardiovascular disease
Authors: Vieira AM , Althoff A , Martins EM , Mortimer FM , Roque ABAO , Silveira LS , Karsten M 
Published: May 2021

Abstract

Funding Acknowledgements
Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - Brasil (CAPES) - Finance Code 001.

Background
Cardiopulmonary exercise test (CPET) is the reference method for assessing gas exchange threshold (GET), a surrogate of the anaerobic threshold (AnT). However, muscle oxygenation has been shown as an additional tool for AnT determination, using the lower limb threshold (LLT). Besides, Talk Test (TT), a tool used to assess, prescribe, and monitor exercise intensity through speech comfort level, has shown a correlation with GET as well.

Purpose
To identify the AnT obtained from the traditional method from CPET (GET) and the LLT; to compare heart rate (HR) and tissue saturation index (TSI) data at AnT (GET and LLT); to compare the parameters of LLT on CPET and TT, and to correlate LLT and TT stages in cardiovascular disease (CVD) patients.

Methods
CVD patients underwent CPET and TT, both on a treadmill, in two distinctive days. During those tests, peripheral muscle oxygenation was assessed by the near-infrared spectroscopy method. GET (CPET) was determined by the V-slope method; LLT (CPET and TT) was determined by the visual inspection of oxyhemoglobin and deoxyhemoglobin curves. A TT protocol based on the prediction equation for the covered distance of the six-minute walk test (6MWD) was applied. TT protocol was incremental, with two-minutes stages starting at 70% of the average velocity predicted and 2% of inclination, increasing velocity in 10 percentage points (p.p.) at each stage, until the fifth stage, at which the inclination was increased in 2 p.p. until test completion. At the end of each stage, patients read a standardized paragraph and were asked about speech comfort. Shapiro-Wilk test was performed to assess data distribution. Wilcoxon test was applied to compare physiological variables (HR and TSI) at GET and LLT. Repeated measures analysis of variance (ANOVA), followed by Bonferroni post-hoc test was assessed to compare the variables at LLT and TT stages (last TT+ and first TT±). Spearman correlation coefficient was used to assess the relationship between variables. Statistical significance was set at 5%.

Results
24 cardiovascular patients were included. Similar values of HR (GET vs. LLT: 102 ± 15 bpm vs. 99 ± 14 bpm, p = 0,08), and TSI (GET vs. LLT: 64,6 ± 8,2% vs. 66,4 ± 7,8%, p = 0,09) were observed during CPET. Regarding LLT at CPET and TT, there was no difference between HR (CPET vs. TT: 99 ± 14 bpm vs. 100 ± 12 bpm, p = 1,00) and TSI (CPET vs. TT: 66,4 ± 7,8% vs. 65,3 ± 4,9%, p = 1,00). Furthermore, good relationship between HR in LLT and TT stages (LLT vs. TT+: r = 0,79; LLT vs. TT±: r = 0,76; p &lt; 0,05 for both) was found.

Conclusions
Our results showed similarity between LLT and GET. Besides, TT showed a similar response of muscle oxygenation and heart rate comparing to CPET, with a good correlation between LLT and TT stages. These results endorse the validity of TT as an auxiliary and low-cost tool to identify the AnT.