Walailak Frontier 09, December 2018

Periodicity ‒ A Characteristic of Heart Rate Variability Modified by the Type of Mechanical Ventilation

Heart rate variability (HRV) refers to the variation in beat-to-beat and is measured from the electrocardiogram (ECG). Multiple analytic tools have been applied to quantify HRV in both the frequency domain, time domains, and nonlinear methods. Many studies revealed that disease can reduce HRV. Biologically variable ventilation (BVV) refers to a method of mechanical ventilation that imposes variability in cycle duration and tidal volume. In contrast, continuous mechanical ventilation (CMV), refers to mechanical ventilation that imposes a nonvarying rate and tidal volume compared to CMV. This opened the field of critical care to the possibility that applied variability in ventilation patterns may benefit patients.

Assist. Prof. Dr. Anurak Thungtong, in collaboration with Matthew F. Knoch, Frank J. Jacono, Thomas E. Dick and Kenneth A. Loparo who are researcher from University hospital, Case Medical Center, Case Western Reserve University have a longstanding interest in autonomic and respiratory control, in particular whether changes cardio-respiratory coupling can persist in the absence of the forces driving that coupling. They recorded, analyzed and compared HRV in two groups of rats both of which sustained lung injury. One group was ventilated with CMV; the other, with BVV. While performing these experiments, they observed an obvious effect of the mode of ventilation on HRV. However, application of the basic analytical methods could not distinguish the structural differences in HRV between BVV and CMV.

Assist. Prof. Anurak Thungtong compared the relative power spectrum of the RR- interval signals as well as the instantaneous frequency of ventilator and breathing patterns from the BVV and CMV groups following lung injury. The power spectrum of the RR-interval time series from a BVV treated rat (2.5 min segment) had a wide frequency range; whereas that from the CMV treated rat had a narrow bandwidth with a dominant peak at the ventilator frequency. Differences between BVV- and CMV- treated rats were also observed in the autocorrelation plots of the RR-interval time series. The autocorrelation plot for the BVV treated rat was flat; indicating that the signal was irregular while that of the CMV treated rat fluctuated at a regular interval, implying that the signal was periodic. In summary, the RR-interval time series of rats treated with non-varying ventilation (CMV group) oscillated with a relatively constant frequency whereas that of the BVV group treated with variable lung inflation was irregular. Thus, we concluded that the RR-interval time series of the BVV group had more variability than the CMV group.

Sources:

• Thungtong A, Knoch MF, Jacono FJ, Dick TE and Loparo KA (2018) Periodicity: A Characteristic of Heart Rate Variability Modified by the Type of Mechanical Ventilation After Acute Lung Injury. Front. Physiol. 9:772

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