Increased Prevalence of Blood Pressure Instability Over Twenty-Four Hours in Chronic Spinal Cord Injury

Figures

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  FIG. 1.. Representative 24-h blood pressure (BP) data from the Ambulatory-NI (Participant ID: N206, panels A and B) and SCI groups (Participant ID: A80, panels C and D) while awake (white background) and asleep (gray background), illustrating methods used to analyze BP stability relative to a target range (110–120 mmHg) and fluctuations between measurements. Systolic BP (SBP) measurements are represented with black circles (panels A and C, top); green line represents the middle of the target range (i.e., 115 mmHg), and dashed blue lines represent upper and lower deviation of SBP (mmHg, right). SBP measurements within and without the target range are plotted in a cumulative distribution curve (triangles, panels B and C) to quantify area under the curve (AUC), percentage of measurements within 110–120 mmHg (highlighted in green), and the percentage of measurements within 90–140 mmHg (highlighted in green). Fluctuations between successive SBP measurements (A and C, bottom) were used to calculate average real variability (ARV; right) and coefficient of variation (COV; right).

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  FIG. 2.. Hourly means of systolic blood pressure (BP; A), diastolic BP (B), and heart rate (HR; C) measured over 24 h are represented for the Ambulatory-NI (open circles), Wheelchair-NI (gray circles), and SCI (blue circles) groups. Evident is the absence of the nocturnal dip in persons with SCI compared with Ambulatory-NI and Wheelchair-NI groups. NI, non-injured; SCI, spinal cord injury.

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  FIG. 3.. Mean systolic blood pressure (BP; A), diastolic BP (B), and heart rate (HR; C) while awake (left) and asleep (right) is represented for each participant in the Ambulatory-NI (open circles), Wheelchair-NI (gray circles), and SCI (blue circles) groups. Gray lines connect the awake and asleep values; box plots illustrate median and interquartile range. Systolic BP was significantly increased while awake compared with asleep in Ambulatory-NI (p < 0.01), but not in the Wheelchair-NI or SCI groups. Diastolic BP and HR were significantly increased while awake compared with asleep in the Ambulatory-NI (p < 0.001) and Wheelchair-NI (p < 0.05), but not the SCI group. Systolic BP while awake was significantly decreased and asleep systolic BP was significantly increased in participants with SCI (p < 0.05) compared with Ambulatory-NI, but not Wheelchair-NI. Diastolic BP while awake was significantly decreased in participants with SCI (p < 0.01) compared with both NI groups. *p < 0.05 between two groups. NI, non-injured; SCI, spinal cord injury.

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  FIG. 4.. Mean systolic blood pressure (SBP) total deviation around (A), deviation above (B), and deviation below (C) the middle of the target range (115 mmHg) while awake is represented for participants in the Ambulatory-NI (open circles) and SCI (blue circles) groups; box plots illustrate median and interquartile range. Bars illustrate deviation above (light green) and below (dark green) 115 mmHg for each participant in the Ambulatory-NI (D) and SCI (E) groups with median (open circle) and interquartile range. Total deviation (p < 0.01) and deviation below 115 mmHg (p < 0.001) were significantly greater in participants with SCI compared with Ambulatory-NI. Additionally, whereas the total deviation of SBP was evenly distributed around the median in Ambulatory-NI (D), this was not the case in most participants with SCI (E), where the median SBP was skewed toward the lower deviation despite a homogenous group of injuries. *p < 0.05 between two groups. NI, non-injured; SCI, spinal cord injury.

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  FIG. 5.. Mean ± SE awake systolic blood pressure (SBP) measurements within and outside the target range are plotted in a cumulative distribution curve (A) for the Ambulatory-NI (open triangles) and SCI (blue triangles) groups. Green dashed line indicates the SBP range 90–140 mmHg. Percentage of SBP measurements within 90–140 mmHg (B) while awake is represented for the Ambulatory-NI (open circles) and SCI (blue circles) groups; box plots illustrate median and interquartile range. Awake AUC (p < 0.05) and percentage of SBP measurements within 90–140 mmHg (p < 0.05) were significantly decreased in participants with SCI compared with the Ambulatory-NI group. *p < 0.05 between two groups. NI, non-injured; SCI, spinal cord injury; SE, standard error.