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Ventilatory and lactate threshold determinations in healthy normals and cardiac patients: methodological problems
K Meyer1, R Hajric, S Westbrook
1Herz-Zentrum, Bad Krozingen, Germany.
Summary
This study compared four ventilatory threshold (VT) methods against lactate threshold (LAT) in healthy individuals and heart patients. While most VT methods showed good reproducibility, standardized procedures are recommended for optimal determination.
Area of Science:
- Cardiopulmonary Exercise Testing
- Exercise Physiology
- Clinical Exercise Science
Background:
- Accurate determination of ventilatory threshold (VT) is crucial for assessing exercise capacity in various populations.
- Established methods for VT determination include V-slope, ventilatory equivalent for O2 (EqO2), gas exchange ratio (R), and end-tidal partial pressure of oxygen.
- Comparison with lactate threshold (LAT) provides a benchmark for VT accuracy.
Purpose of the Study:
- To analyze the success rate, comparability, reproducibility, and interobserver variability of four VT determination methods.
- To compare oxygen uptake (VO2) at VT with VO2 at LAT across different subject groups.
- To evaluate the impact of different exercise testing protocols (ramp-like vs. graded steady-state) on VT determination.
Main Methods:
- Four VT methods (V-slope, EqO2, R, end-tidal PO2) were applied to healthy individuals, coronary patients with myocardial ischemia, and patients with chronic heart failure (CHF).
- Lactate threshold (LAT) was determined using log-log plots of lactate vs. VO2.
- Exercise testing was performed using both ramp-like and graded steady-state protocols on a cycle ergometer.
Main Results:
- Successful VT determination occurred in 82% of trials for healthy and ischemic heart patients using ramp-like protocols.
- CHF patients exhibited a lower success rate for VT determination.
- VO2 at VT was significantly higher than VO2 at LAT for healthy and ischemic heart patients using R and EqO2 methods, but not for CHF patients.
Conclusions:
- While VT methods demonstrate good reproducibility in healthy individuals, interobserver variability increases in CHF patients.
- The choice of VT determination method can influence VO2 values, particularly in healthy and ischemic heart patients when compared to LAT.
- Standardized procedures are recommended to optimize and ensure consistency in ventilatory threshold determination across different clinical populations.