Conclusion
COPD patients responded properly to the upper limb IC and to the VM; however, HR recovery during VM was impaired in these patients. The severity of the disease and MIP were associated with increased parasympathetic modulation and higher chronotropic response.
Methods
Twenty-two stable moderate to severe COPD patients were evaluated. R-R intervals were recorded (monitor Polar® S810i) during dominant upper limb IC (2 minutes). Stable signals were analyzed by Kubios HRV® software. Indices of HRV were computed in the time domain (mean HR; square root of the mean squared differences of successive RR intervals [RMSSD] and HRV triangular index [RR tri index]) and in the frequency domain (high frequency [HF]; low frequency [LF] and LF/HF ratio). The HR responses were evaluated at rest, at the peak and at the nadir of the VM (15 seconds). The Valsalva index was also calculated.
Purpose
To evaluate the heart rate variability (HRV) indices and heart rate (HR) responses during isometric contraction (IC) and Valsalva maneuver (VM) in COPD patients.
Results
During IC: time domain indices (mean HR increased [P=0.001], RMSSD, and RR tri index decreased [P=0.005 and P=0.005, respectively]); frequency domain indices (LF increased [P=0.033] and HF decreased [P=0.002]); associations were found between forced expiratory volume in 1 second (FEV1) vs RMSSD (P=0.04; r=-0.55), FEV1 vs HR (P=0.04; r=-0.48), forced vital capacity (FVC) vs RMSSD (P=0.05; r=-0.62), maximum inspiratory pressure (MIP) vs HF (P=0.02; r=0.68). FEV1 and FVC justified 30% of mean HR. During VM: HR increased (P=0.01); the nadir showed normal bradycardic response; the Valsalva index was =0.7.