Key result
Positive pressure mechanical ventilation inverted systolic blood pressure variability and exerted complex influences on heart rate variability compared to simulated spontaneous breathing.
Why the study?
Does positive pressure mechanical ventilation alter heart rate and blood pressure variability compared to spontaneous breathing patterns in mechanically ventilated patients?
Observational (n=17)
Does positive pressure mechanical ventilation alter heart rate and blood pressure variability compared to spontaneous breathing patterns in mechanically ventilated patients?
Positive pressure ventilation exerts mainly a mechanical effect on systolic blood pressure variability, while its influence on heart rate variability involves complex neural influences.
Ventilation mode confounds variability metrics in monitoring; hypothesis-generating, prospective validation needed before practice implications.
Heart rate and blood pressure variations during spontaneous ventilation are related to the negative airway pressure during inspiration. Inspiratory airway pressure is positive during mechanical ventilation, suggesting that reversal of the normal baroreflex-mediated pattern of variability may occur. We investigated heart rate and blood pressure variability and baroreflex sensitivity in 17 mechanically ventilated patients. ECG (RR intervals), invasive systolic blood pressure (SBP), and respiratory flow signals were recorded. High-frequency (HF) amplitude of RR and SBP time series and HF phase differences between RR, SBP, and ventilatory signals were continuously computed by Complex DeModulation (CDM). Cross-spectral analysis was used to assess the coherence and the gain functions between RR and SBP, yielding baroreflex sensitivity indices. The HF phase difference between SBP and ventilatory signals was nearly constant in all patients with inversion of SBP variability during the ventilator cycle compared with cycling with negative inspiratory pressure to replicate spontaneous breathing. In 12 patients (group 1), the phase difference between RR and ventilatory signals changed over time and the HF-RR amplitude varied. In the remaining five patients (group 2), RR-ventilatory signal phase and HF-RR amplitude showed little change; however, only one of these patients exhibited a RR-ventilatory signal phase difference mimicking the normal pattern of respiratory sinus arrhythmia. Spectral coherence between RR and SBP was lower in the group with phase difference changes. Positive pressure ventilation exerts mainly a mechanical effect on SBP, whereas its influence on HR variability seems more complex, suggesting a role for neural influences.
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Louw et al. (2008) conducted an observational in Mechanically ventilated patients (n=17). Positive pressure mechanical ventilation vs. Cycling with negative inspiratory pressure (replicating spontaneous breathing) was evaluated on Heart rate and blood pressure variability and baroreflex sensitivity. Positive pressure mechanical ventilation inverted systolic blood pressure variability and exerted complex influences on heart rate variability compared to simulated spontaneous breathing.
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