Aortic stretch and recoil create wave-pumping effect: the second heart in the systemic circulation

Figures

• 

  Figure 1.. (A) The in vitro hydraulic circuit to conduct the experiments. The pressure and flow measurements are collected at the location of the sensors. (B) Time profile of the aortic root displacement for three cases: healthy individual of 41 years old, healthy individual of 65 years old and heart failure patient who was 43 years old. Design of the cam in the cam-follower mechanism for modelling the longitudinal stretch of the aorta is also shown in this figure.

• 

  Figure 2.. Clinical motivation and relevancy of investigating aortic wave pumping due to the longitudinal stretch. (A) Two pairs of magnetic resonance images captured at the end-diastole (when the aortic elements are relaxed) and the end-systole (where the maximal downward force is applied to the aortic elements, and they are positioned at their maximal stretch) for a control individual (top row) and a heart failure patient (bottom row). (B) The difference in the longitudinal aortic root displacement between control population and heart failure patients. p values suggest significant statistical differences.

• 

  Figure 3.. In vitro flow modelling and sample measurements of the aortic longitudinal wave pumping. Figures on the top panel demonstrate the generated flow direction due to the aortic stretch and recoil, excited at the frequency of 1.0 Hz at various snapshots in time that leads to reverse pumping. The installed silicone aorta is the phantom model 5. The figures on the bottom panel present the flow direction for the same aorta excited at the frequency of 1.5 Hz, leading to the forward pumping. The installed silicone aorta is the phantom model 5. Sample pressure and flow time profiles are also demonstrated at both frequencies.

• 

  Figure 4.. Mean flow–frequency relationship due to the aortic longitudinal stretch and recoil. (A) Measured mean flow rates of the aortic wave pumping against the excitation frequency for low levels of PWV (elastic region) of 7.2 and 10.0 m s−1. (B) Measured mean flow rates of the aortic wave pumping against the excitation frequency for low levels of PWV (rigid region) of 14.8 and 22.7 m s−1. The bidirectionality of the flow as a function of frequency exists for both cases.

• 

  Figure 5.. The effect of aortic stiffness, quantified by wave speed, and frequency on mean generated flow due to aortic longitudinal wave pumping. (A) Measured mean flow rates of the aortic wave pumping against the wave speed inside the aorta for low levels of frequency. The elastic and rigid regions are categorized based on the wave speed value. (B) Measured mean flow rates of the aortic wave pumping against the wave speed inside the aorta for high levels of frequency. (C) Interpolation mapping of the mean generated flow, Q-, with respect to the aortic stiffness and the stretching frequency. The trend shows nonlinearity in terms of both stiffness and frequency (independent variables).

• 

  Figure 6.. The effect of stretching amplitude on mean flow–frequency pattern due to aortic longitudinal wave pumping. Measured mean flow rates due to the aortic wave pumping against the excitation frequency for different levels of stretching amplitude of 0.5, 1.0, 1.5 and 2.0 cm for two phantom models with aortic wave speeds of (A) 10.3 and (B) 22.7 m s−1. For both phantom models, the flow-stretching relation follows a parabolic-like curve as demonstrated for sample case of frequency 2 Hz in (C) and (D) for wave speeds of 10.3 and 22.7 m s−1, respectively.

• 

  Figure 7.. WI and time derivative of the pressure waveform patterns at different wave states. Figure demonstrates the patterns at the stretching frequency of 1 Hz for the left panel and 2 Hz for the right panel in all the phantom models with different wave speeds.