Modeling Arterial Pulse Pressure From Heart Rate During Sympathetic Activation by Progressive Central Hypovolemia

Figures

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  Figure 1. Arterial pressure parameters. Pulse pressure (PP) is indicated for each beat at the root of each beat (in mmHg). Note the effect of increased interbeat interval (IBI) (and thus decreased heart rate) on diastolic pressure runoff (indicated in bold) increasing PP. The preceding beat shows the reverse effect: due to a premature ventricular contraction (reducing the IBI, increasing heart rate), PP decreases.

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  Figure 2. Steps in analysis. Visual representation of the steps required to obtain model performance.

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  Figure 3. Cardiovascular response to sympathetic stimulation by lower body negative pressure (LBNP). With subjects becoming pre-syncopal the number of subjects within this figure decreases over time. Values normalized to the values in baseline rest preceding LBNP. First minute was tested (paired t-test) for statistical significance and noted with an asterisk when different from baseline (P < 0.05). (A) PP, pulse pressure; (B) HR, heart rate; (C) SV, stroke volume (D) MAP, mean arterial pressure; Mean and standard deviation for each minute during LBNP.

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  Figure 4. Relationship between heart rate and systolic, diastolic, mean and pulse pressure during LBNP. Scatter plots of the raw data of systolic, diastolic, and mean blood pressure, and pulse pressure vs. heart rate (HR). There is a more distinct decrease of pulse pressure (PP, bottom right) between baseline (filled circles) and during lower body negative pressure (LBNP, open circles) compared to systolic and mean arterial pressure (SAP and MAP).

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  Figure 5. Model performance. Pulse pressure estimated with linear mixed effect model of heart rate in one subject (A) and the entire study population (B). Measured (filled circles) and estimated (open circles) pulse pressure (PP) during lower body negative pressure (LBNP). Horizontal axis shows the progress of LBNP in seconds (A) and normalized to total duration of LBNP (B), i.e., till pre-syncope or LBNP lasting 30 min. Note that the model misses initial non normally distributed part of the group mean PP due to the onset of LBNP with rapid decrease in PP in the first minute (as noted in Figure 3A). Mean and standard errors in 41 subjects.

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  Figure 6. Visualization of the difference in trend assessment during LBNP for both measures of pulse pressure. Bland-Altman (A) and polar plot (B,C) representation of the difference between the measured and estimated pulse pressure trends. The visualized delta was computed using the mean during LBNP subtracted from the mean during baseline. The angle φ toward the line of identity is either positive (overestimation) or negative (underestimation). φ and the mean of both methods is translated to the polar plot (Critchley et al., 2011) (C).The shaded areas in panels (B,C) indicate overestimation of pulse pressure, whereas the hashed areas indicate underestimation of the pulse pressure. The green shaded area indicates the sector including 95% of the samples.