Attending Physician Hospital for Sick Children Toronto, Ontario, Canada
Abstract:
Introduction: Harnessing cardiopulmonary interactions in critically ill patients is essential to maximize patient care and outcomes. Patients who require cannulation to extracorporeal support with ventricular assist devices (VADs) represent a particularly challenging group at high risk of poor outcomes. The importance of VAD-pulmonary interactions and cardio-VAD interactions are an acknowledged but understudied phenomenon. We sought to evaluate whether measurable VAD-pulmonary interactions existed and could be quantified in the extreme setting of a patient with an implanted, non-compliant Total Artificial Heart (TAH) with a fixed stroke volume (Figure A).
Methods: Archived patient waveform data was extracted from AtriumDB, a custom time series database at SickKids. Arterial waveforms were sampled at 125Hz, and respiratory impedance was sampled at 62.5Hz. Using MATLAB (Mathworks, Inc), we extracted all systolic peaks from the arterial blood pressure (ABP) waveform using the synchrosqueezed wavelet transform technique for a period of 30 minutes. We then analyzed how these ABP values were modulated as a function of the respiratory cycle during inspiration (I) and exhalation (E) relative to the mean systolic BP over 10 heart beats while mechanically ventilated with a TAH. Lastly, we compared the VAD-pulmonary interaction to a 30-minute time window during which the same patient was mechanically ventilated with a transplanted heart to assess whether measured interactions differed in magnitude and/or direction (Figure B)
Results: The respiratory cycle clearly modulated the systolic blood pressure (sBP) at both timepoints. With the more compliant transplanted heart, variation induced by the respiratory cycle was significant with an up to 20% change in sBP during the different phases of breathing (Figure C). The same direction of change in sBP was induced by breathing while cannulated to the TAH for this patient, but these interactions were attenuated by the non-compliant TAH (Figure D).
Conclusions: Predictable, measurable cardiopulmonary interactions exist even in a non-compliant TAH with a fixed stroke volume. These interactions provide targets for clinical optimization of this high-risk patient group that may improve care and device support outcomes.
