Alternative Approaches to the Assessment of the Systemic Circulation and Left Ventricular Performance: A Proof-of-Concept Study

Figures

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  Figure 1. Head-capacity curves for 1/3 and 3 horsepower (HP) pumps. By comparing the 2 curves, the 1/3 HP pump can pump a 3 gallons per minute flow to a head of 250 feet, but to pump that flow to a head of 1200 feet requires 3 HP, 9× the HP. Also, notice that an increase in HP shifts the curve upward and to the right. The 0.002 HP curve corresponds to Figure 6. GPM, gallons per minute.

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  Figure 2. (A) Results from a representative experiment (Experiment 13). Cardiac index (CI) is plotted against the driving pressure across the systemic circulation (P¯Ao – P¯CV). (B) Pooled data from all the experiments. Isoproterenol (ISO) data are indicated in blue, sodium nitroprusside (NP) data are indicated in red, baseline data are indicated in black, phenylephrine (PE) data are indicated in violet, and constriction (CONST) data are indicated in green.

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  Figure 3. Conductance values for baseline measurements and each intervention. Solid lines represent mean values, and dashed lines represent upper and lower confidence intervals of the regression lines.

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  Figure 4. (A) Head (P¯LV) – capacity (CI) relations for a representative experiment.13 (B) Head (P¯LV) – capacity (CI) relations for pooled data. (C) Pooled data illustrating how the maximum head-capacity curve was determined. Vertical bins 12.5 mL/min/kg wide were constructed, and the maximum P¯LV value within that bin was identified and indicated by a red diamond. These values were then fitted as a polynomial (ie, quadratic) to define the maximum head-capacity curve. Other abbreviations as in Figure 2.

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  Figure 5. Head-capacity curve (from Fig. 3C) and mean conductance relations (Fig. 3). Right: The red line indicates NP, black line indicates baseline, and pink line indicates PE. Note that the CI axis is common to both relationships.

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  Figure 6. A plot of peak aortic systolic pressure vs cardiac output (CO) demonstrating an inverse curvilinear relationship. PE data are indicated in pink, cold-pressor data are indicated in green, baseline data are indicated in black, and upright-tilt data are indicated in gray. Data were measured using the noninvasive Modelflow technique from an individual subject in an ongoing study by Dr Raj et al. (www.clinicaltrials.gov, NCT02673996).

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  Figure 7. Regardless of the value of CI, it is the systemic conductance that determines the driving pressure across the circulation and, therefore, arterial pressure. Bottom: The red line indicates NP conductance, the black line indicates baseline conductance, and the pink line indicates PE conductance. (See the Results section of the text.)

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  Figure 8. A block diagram of the feedback loop involved in the interaction between the cardiac and vascular portions of the circulatory system. The block labelled Vascular (B) represents the resistance/conductance elements that define the arteriovenous pressure difference at any given GSV and CO. The block labelled Vascular (C) represents the capacitative elements that define the absolute values of P¯Ao and P¯CV.

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  Figure 9. (A) Systemic vascular conductance of the circulation at rest.26 (B) By assuming a 50% reduction in CO, (P¯Ao–P¯CV) decreases from 100 to 50 mm Hg (red line). If renal conductance is decreased to zero, (P¯Ao–P¯CV) increases from 50 to 62.5 mm Hg (orange line). If gut conductance is also decreased to zero, (P¯Ao–P¯CV) increases from 62.5 to 100 mm Hg (green line). This illustrates the compensatory effects of reducing renal and then gut flow to zero.