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Frequency domain analysis and clinical outcomes of pulsatile and non-pulsatile blood flow energy during cardiopulmonary bypass

Dr. Jiang et al.1 investigated the impact of perfusion modes on the endothelial function, inflammatory response, and renal and cerebral injury in 60 adult valve disease patients (n = 30 in pulsatile and n = 30 in the non-pulsatile groups) during cardiopulmonary bypass (CPB) procedures. More importantly, Dr. Jiang and colleagues precisely quantified the pressure-flow waveforms in terms of Energy Equivalent Pressure (EEP) and Surplus Hemodynamic Energy (SHE) in the CPB circuitry (after the arterial filter) and the patient’s radial artery. They also applied the Fast Fourier Transform (FFT) to analyze the waveforms in power spectral density and power density ratios. Investigators concluded that pulsatile flow is superior to non-pulsatile perfusion in energy levels and specific biomarkers in their study. It is great to see that the authors included the blood flow, pressure, and EEP waveforms at 20 minutes after aortic clamping for both perfusion groups (Figure 3 in Jiang et al.). Although non-pulsatile pulsatile waveforms also show significant pulsatility (Figure 3A), the readers should be aware that the authors used different scales (Figure 3A and 3B in Jiang et al.) for different groups, which is a limitation of this particular figure. For example, the scale for flow waveforms of the non –pulsatile group was from 3.5 to 4.5 L/min, while the scale was from 0 to 6 L/min for the pulsatile group. If the authors use the identical scale (0–6 L/ min) for both groups, then the pulsatility of non-pulsatile group flow could be diminished. Scales for pressure (300 mmHg vs 400 mmHg) and EEP (60–160 vs 0–300) waveforms in the non-pulsatile and pulsatile groups should also not be different. An identical scale should be used to validate waveforms for each non-pulsatile (Figure 3A in Jiang et al.) and pulsatile group (Figure 3B in Jiang et al.). To the best of my knowledge, most of the CPB components, including oxygenators and arterial cannulae, were not evaluated by the device manufacturers for pulsatile flow, and these devices are not approved by the Food and Drug Administration (FDA) for clinical practice with pulsatile flow. Therefore, translational research studies are required to do additional validation and pre-clinical safety protocols for hemodynamic parameters and microemboli generation and delivery during CPB procedures.2–4 It is also documented that the manufacturer’s recommended maximum blood flow rates of the oxygenators may be exceeded under pulsatile perfusion.5 Therefore, pre-clinical circuit optimization and validation are required. Finally, to justify the sample size (n = 30 patients in each group), a power analysis should be completed for this critical clinical study. To end this long-lasting controversy on perfusion modes, multicenter doubleblinded randomized clinical trials are highly recommended. Again, I congratulate Dr. Jiang and colleagues for their promising results.