Key result
Exercise at and above critical power in patients with severe COPD decreased the LF/HF ratio compared to rest (1.6 vs 4.1; p=0.01), suggesting a shift toward parasympathetic tone dominance.
Why the study?
How does exercise at and above critical power affect heart rate variability in patients with severe COPD?
Observational (n=9)
How does exercise at and above critical power affect heart rate variability in patients with severe COPD?
Absolute Event Rate: 1.6% vs 4.1%
p-value: p=0.01
In patients with severe COPD, heavy exercise shifts autonomic balance toward parasympathetic dominance, which correlates with increasing respiratory rate and ventilatory effort.
HRV shifts during heavy exercise in severe COPD warrant caution in intensity prescription; leaves open autonomic modulation as a limiter.
Heart rate variability is useful in evaluating cardiac autonomic balance. We investigated cardiac autonomic modulation in patients with severe chronic obstructive pulmonary disease (COPD) during heavy and very heavy exercise at and above the critical power (CP). Nine nonhypoxemic patients with COPD (mean forced expiratory volume in 1 second: 1.2 ± 0.5 L; forced expiratory volume in 1 second/forced vital capacity: 37.6 ± 12%) completed an initial incremental exercise test on a cycle ergometer followed by four constant work rate tests to define their CP. In addition, patients underwent a test at their calculated CP for a target of 20 minutes. The CP test plus a test above CP of sufficient duration to allow heart rate variability analysis were studied further. In these tests, R-R interval data were analyzed for variability in the frequency domain before and during exercise. Compared with rest, the power of the normalized low-frequency component (nuLF) decreased (73.0 ± 20.9 vs. 54.2 ± 20.1; p = 0.01) and the power of normalized high-frequency component (nuHF) increased (27.0 ± 20.9 vs. 45.8 ± 20.1; p = 0.01) during exercise, resulting in a decrease in LF/HF (4.1 ± 2.3 vs. 1.6 ± 1.2; p = 0.01) suggesting a relative increase in parasympathetic tone during exercise. When compared with exercise at CP, exercise above CP featured significantly higher values for the square root of the mean squared differences of the successive R-R intervals, the baseline width of the minimum square difference triangular interpolation of the highest peak of the histogram of all N-N intervals and the nuHF, as well as significantly lower values for the nuLF and LF/HF. During exercise above and at the CP, both LF and HF negatively correlated with the respiratory rate (r = −0.76 and r = −0.70, p < 0.005) and the Vmax/PEF (ratio of end-exercise peak expiratory flow and peak expiratory flow during a forced maneuver at rest) (r = −0.52 and r = −0.49, p < 0.05). The decrease in nuLF and LF/HF with increasing nuHF in very heavy exercise domains suggests that the autonomic balance is shifted toward parasympathetic tone dominance in patients with severe COPD. This correlates with increasing respiratory rate and ventilatory effort (Vmax/PEF) during heavy and very heavy exercise in COPD patients.
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Chang et al. (2011) conducted an observational in Severe chronic obstructive pulmonary disease (COPD) (n=9). Exercise at and above critical power vs. Rest was evaluated on LF/HF ratio (p=0.01). Exercise at and above critical power in patients with severe COPD decreased the LF/HF ratio compared to rest (1.6 vs 4.1; p=0.01), suggesting a shift toward parasympathetic tone dominance.
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