Quantification and physiological significance of the rightward shift of the V-slope during incremental cardiopulmonary exercise testing

Characteristics of cardiopulmonary exercise capacity in adults with different degrees of obesity

Objective

To explore the characteristics of cardiopulmonary exercise capacity in adults with different degrees of obesity through cardiopulmonary exercise test (CPET).

Methods

From September 2019 to January 2024, the data of patients undergoing CPET in the Rehabilitation Department of the Affiliated Wuxi People's Hospital of Nanjing Medical University were analyzed retrospectively. A total of 231 cases were included. They were categorized into five groups based on their body mass index (BMI): the control group (18.5 ≤ BMI < 24 kg/m2, n = 28), the overweight group (24.0 ≤ BMI < 28 kg/m2, n = 48), the mild obesity group (28 ≤ BMI < 35 kg/m2, n = 75), the moderate obesity group (35.0 ≤ BMI < 40 kg/m2, n = 47), and the severe obesity group (BMI ≥ 40 kg/m2, n = 33). Collected informations on the age, gender, height, and weight of five groups of participants. The VO2 at anaerobic threshold (VO2AT), percentage of predicted VO2AT (VO2AT% Pred), peak oxygen consumption (VO2peak), percentage of predicted VO2peak (VO2peak% Pred), peak kilogram oxygen consumption (VO2peak/kg), maximum exercise power (WRmax), breathing reserve (BR), maximum heart rate (HRmax), percentage of predicted HRmax (HRmax% Pred), maximum O2 pulse (VO2/HRmax), percentage of predicted maximum O2 pulse (VO2/HRmax%Pred), maximum relative O2 pulse (VO2/HRmax/kg),heart rate response (HRr), forced vital capacity (FVC), ratio of forced expiratory volume to vital capacity in 1 s (FEV1/FVC), percentage of predicted forced vital capacity (FVC% Pred), percentage of predicted forced expiratory volume ratio of 1 s (FEV1% Pred), peak expiratory flow rate (PEF), maximum exercise ventilation (VEmax), maximum voluntary ventilation (MVV) and other indicators during the CPET were collected. Single factor analysis of variance was used to compare the mean of each index between groups. Spearman correlation analysis was used to analyze the correlation between BMI and various indicators.

Results

There was no statistical significance in gender composition, age, height, and exercise habit of the five groups of participants (P > 0.05). The body mass and BMI of the five groups had significant differences (P < 0.001). In terms of cardiopulmonary exercise capacity, there were statistical differences among the five groups in the overall distribution of VO2AT (H = 37.370,P < 0.001), VO2AT/kg (H = 34.747, P < 0.001), VO2peak (H = 23.018,P< 0.001), VO2peak/kg (H = 66.606, P < 0.001) and WRmax%Pred (H = 45.136, P < 0.001). There was no significant difference among the five groups in the overall distribution of VO2AT%Pred, VO2peak%Pred and WRmax. There were statistical significant difference among the five groups in HRmax (F = 2.443, P = 0.048), HRmax%Pred (F = 6.920, P < 0.001), VO2/HRmax (F = 8.803, P < 0.001), VO2/HRmax%Pred (F = 11.354, P < 0.001), VO2/HRmax/kg (F = 18.688, P < 0.001) and BR (F = 6.147, P < 0.001) and HRr (F = 9.467, P < 0.001). There were no significant differences among the five groups in RERmax (F = 0.336, P > 0.05). In terms of static pulmonary function, there were significant differences among the five groups in FVC%Pred (F = 4.577, P = 0.001), FEV1%Pred (F = 3.681, P = 0.006) and FEV1/FVC (F = 3.344, P = 0.011). There was no differences among the five groups in MVV(P> 0.05), and there were significant differences among the five groups in VEmax (P = 0.005) In terms of correlation analysis, BMI was positively correlated with VO2AT,VO2peak, VEmax and VO2/HRmax, and negatively correlated with VO2AT/kg, VO2peak/kg,WRmax%Pred, HRmax%Pred, VO2/HRmax%Pred, VO2/HRmax/kg,BR and HRr. In terms of static pulmonary function, BMI was negatively correlated with FVC%Pred, FEV1%Pred.

Conclusion

With the aggravation of obesity, the maximum exercise ability of adults decreases, VO2peak/kg and VO2/HRmax%Pred decreases, and the breathing reserve decreases.

Effects of Training on Running Cost and Aerobic Capacity in Individuals with Obesity

This study investigated running cost (CRun), peak oxygen consumption (V̇ O2peak), and ventilatory threshold (VT1) responses to exercise programs for individuals with obesity. Ninety-four individuals (38.2±7.7 years; 33.4±2.9 kg/m²) were assigned into strength (n=24), endurance (n=26), combined (n=22), and physical activity (control, n=22) groups for 22 weeks, plus diet recommendation. The V̇ O2peak, VT1, and CRun were assessed through a maximal incremental step test. The change of V̇ O2peak in combined (9.9%) differed from the other groups, with lower values in women than men (0.7% vs. 6.2%). The VT1 change in combined (16.4%) differed from the strength (4.9%) and physical activity (1.2%) groups, with the change in endurance (12.7%) also being higher than the physical activity group. Only men in the combined group increased absolute V̇ O2peak, while both sexes increased VT1 in the endurance and combined groups. No effects for groups and sex were significant for CRun in moderate (VT1) running zones, despite CRun changes in VT1 zones correlated with the alterations of V̇ O2peak and VT1 (r²=0.29-0.59). Therefore, moderate aerobic exercise stimulus is suitable for VT1 improvement in individuals with obesity, with the increase in CRun associated to the chances of increasing V̇ O2peak in men and when combining strength with aerobic exercises.

Prolonged mean response time in older adults with cardiovascular risk compared to healthy older adults

BACKGROUND

During incremental exercise (Inc-Ex), the mean response time (MRT) of oxygen uptake (V̇O2) represents the time delay before changes in muscle V̇O2 reflect at the mouth level. MRT calculation by linear regression or monoexponential (τ') fitting of V̇O2 data are known to be highly variable, and a combination of incremental and constant load exercise (CL-Ex) is more reproducible.

METHODS

We evaluated MRT in older adults using linear regression and combination methods. We recruited 20 healthy adults (male: 9, 69.4 ± 6.8 years) and 10 cardiovascular risk subjects (male: 8, 73.0 ± 8.8 years). On day 1, they performed Inc-Ex using a 10W/min ramp protocol, for determination of the ventilatory anaerobic threshold (VAT) using the V-slope method. On day 2, they performed Inc-Ex to VAT exercise intensity and CL-Ex for 25min total. The MRT was calculated from the CL-Ex V̇O2 average and the time at equivalent V̇O2 in the Inc-Ex. We also assessed the amount of physical activity using the International Physical Activity Questionnaire short form (IPAQ-SF).

RESULTS

The MRT of healthy participants and those at cardiovascular risk were 49.2 ± 36.3 vs. 83.6 ± 45.4s (p = 0.033). Total physical activity in the IPAQ-SF was inversely correlated with MRT.

CONCLUSION

The MRT was significantly prolonged in cardiovascular risk participants compared to healthy participants, possibly related to the amount of daily physical activity. Individual MRT may be useful for adjustment of exercise intensity, but this should also be based on daily physical activity and individual condition during exercise.

Exploration of an Inflection Point of Ventilation Parameters with Anaerobic Threshold Using Strucchange

(1) Background: When measuring anaerobic work threshold (AT), the conventional V-slope method includes the subjectivity of the examiner, which cannot be eliminated completely. Therefore, we implemented an engineering method using strucchange to objectively search for the inflection point of AT. (2) Methods: Seventeen subjects (15 men and 2 women) were included in the study. The subjects rode an ergometer and performed a ramp load test for 18 min and 30 s. (3) Results: In VE (Ventilation), 11 out of 12 subjects had the same results with 95% confidence intervals for the AT by the strucchange and respiratory metabolic apparatus. In VCO₂ (Carbon dioxide emissions), 9 out of 12 subjects had the same results with 95% confidence intervals for the AT with the strucchange and respiratory metabolic apparatus. In VE, 3 out of 12 subjects showed the same results for respiratory metabolic analysis and the AT by the V-slope method. In VCO₂, 3 out of 12 subjects showed the same results for the respiratory metabolic analysis and AT by the V-slope method in VCO₂. (4) Conclusions: Strucchange was more objective and significant in identifying the AT than the V-slope method.

The Ratio of Oxygen Uptake From Ventilatory Anaerobic Threshold to Respiratory Compensation Point Is Maintained During Incremental Exercise in Older Adults

Introduction

The period from ventilatory anaerobic threshold (VAT) to respiratory compensation point (RCP) during incremental exercise (isocapnic buffering phase) has been associated with exercise tolerance and skeletal muscle composition. However, several reports compare younger and older healthy adults, and specific age-related changes are unclear. This study aimed to examine the oxygen uptake (VO₂) from VAT to RCP and its change over time in younger and older healthy adults.

Methods

A total of 126 consecutive participants were divided into two groups (95 younger and 31 older than 50 years of age) who underwent cardiopulmonary exercise testing, and VAT and RCP were determined. The ratio (RCP/VAT) and difference (ΔVO₂ RCP-VAT) were calculated from the VO₂ of VAT and RCP and compared between groups and ages. Statistical analyses included t-tests and Spearman’s correlation tests, and the significance level was set at <5%.

Results

RCP/VAT was not significantly different (1.40 ± 0.19 vs. 1.59 ± 0.24, p = 0.057) but weakly correlated with age (r = −0.229, p = 0.013, y = −0.0031x + 1.7588, lowering rate: 0.185%/year). Conversely, ΔVO₂ RCP-VAT was significantly lower in the older group (7.7 ± 3.1 vs. 13.8 ± 4.9 ml/kg/min, p < 0.001) and correlated significantly with age (r = −0.499; p < 0.001; y = −0.1303x + 16.855; lowering rate, 0.914%/year).

Conclusion

ΔVO₂ RCP-VAT was considered to be a poor indicator of lactate buffering capacity in the IB phase because both VAT and RCP were greatly affected by age-related decline. Conversely, RCP/VAT was suggested to be an index not easily affected by aging.

Gas exchange threshold to guide exercise training intensity of older individuals during cardiac rehabilitation

The gas exchange threshold (GET), which is determined during incremental exercise (Inc-Ex) testing, is often considered a safe training intensity for cardiac rehabilitation. However, there are only a limited number of reports on the actual implementation of this method. We assessed the applicability of GET-guided exercise using a constant load exercise (CL-Ex) protocol.We recruited 20 healthy older individuals (healthy, age: 69.4 ± 6.8 years) and 10 patients with cardiovascular diseases or risk factors (patient, age: 73.0 ± 8.8 years). On day 1, we determined the GET during symptomatic maximal Inc-Ex. On day 2, CL-Ex at work rate (watt: W) where the GET manifested during Inc-Ex (therefore, not corrected for the known oxygen response delay) was maintained for 20 minute. Arterialized blood lactate (BLa) levels were also determined.Oxygen uptake reached a steady state in all participants, with a mean respiratory exchange ratio of < 1.0. The mean BLa at the GET during Inc-Ex was 1.51 ± .29 mmol·l-1 in the healthy group and 1.78 ± .42 mmol·L-1 in the patient group, which was about .5 mmol·L-1 above the resting level. During CL-Ex, BLa increased significantly over the value at the GET (Inc-Ex). However, it reached a steady-state level of 2.65 ± 1.56 (healthy) and 2.53 ± 0.95 (patient) mmol·L-1. The %peak oxygen uptake, %peak heart rate, and %heart rate reserve during CL-Ex were 58.8 ± 11.5, 71.8 ± 10.3, and 44.9 ± 17.4, respectively. All participants could complete CL-Ex with mean perceived exertion ratings (Borg/20) of 11.8 ± 1.3 (healthy) and 12.2 ± 1.3 (patient). These heart rate-related indices and exertion ratings were all within the recommended international guidelines for cardiac rehabilitation.CL-Ex at the GET appears to be the optimal exercise intensity for cardiac rehabilitation.

New method for the mathematical derivation of the ventilatory anaerobic threshold: a retrospective study

Background

Ventilatory anaerobic threshold (VAT) is a useful submaximal measure of exercise tolerance; however, it must be visually determined. We developed a new mathematical method to objectively determine VAT.

Methods

We employed two retrospective population data sets (A/B). Data A (from 128 healthy subjects, patients with cardiovascular risk factors, and cardiac subjects at institution A, who underwent symptom-limited cardiopulmonary exercise testing) were used to develop the method. Data B (from 163 cardiac patients at institution B, who underwent pre−/post-rehabilitation submaximal exercise testing) were used to apply the developed method. VAT (by V-slope) was visually determined (vVAT), assuming that the pre-VAT segment is parallel to the respiratory exchange ratio (R) = 1 line.

Results

First, from data A, exponential fitting of ramp V-slope data yielded the equation y = ba^x, where a is the slope of the exponential function: a smaller value signified a less steep curve, representing less VCO₂ against VO₂. Next, a tangential line parallel to R = 1 was drawn. The x-axis value of the contact point was the derived VAT, termed the expVAT (VCO₂) (calculated as LN (1/[b*LN(a)]/LN(a). This point represents an instantaneous ΔVCO₂/ΔVO₂ of 1.0. Second, in a similar way, the relation of VO2 vs. VE (minute ventilation) was fitted exponentially. The tangent line that crosses zero was drawn and the x-axis value was termed expVAT (VE) (calculated as 1/LN(a). For data A, the correlation coefficients (r) of vVAT versus VAT (CO₂), and VAT (VE) were 0.924 and 0.903, respectively (p < 0.001), with no significant difference between mean values with the limits of agreement (1.96*SD of the pair difference) being ±276 and ± 278 mL/min, respectively. expVAT (VCO₂) and expVAT (VE) significantly correlated with VO₂peak (r = 0.971, r = 0.935, p < 0.001). For data B, after cardiac rehabilitation, expVAT (CO₂) and exp. (VE) (mL/min) increased from 641 ± 185 to 685 ± 201 and from 696 ± 182 to 727 ± 209, respectively (p < 0.001, p < 0.008), while vVAT increased from 673 ± 191 to 734 ± 226 (p < 0.001). During submaximal testing, expVAT (VCO₂) underestimated VAT, whereas expVAT (VE) did not.

Conclusions

Two new mathematically-derived estimates to determine VAT are promising because they yielded an objective VAT that significantly correlated with VO₂peak, and detected training effect as well as visual VAT did.

Electronic supplementary material

The online version of this article (10.1186/s13102-019-0122-z) contains supplementary material, which is available to authorized users.