Characterizing Neurocardiovascular Responses to an Active Stand Test in Older Women: A Pilot Study Using Functional Data Analysis

Figures

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  Figure 1. Group-level mean trajectories with 95% confidence intervals for neurovascular and cardiovascular signals during the active stand test, stratified by age group. Participants were classified as younger (<70 years, n = 11; blue line) or older (≥70 years, n = 14; red line). The active stand was initiated at 50 s. Signals shown include tissue saturation index (TSI), oxygenated hemoglobin (O2Hb), deoxygenated hemoglobin (HHb), heart rate (HR), systolic blood pressure (sBP), and diastolic blood pressure (dBP).

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  Figure 2. Group-level mean trajectories with 95% confidence intervals for neurovascular and cardiovascular signals during the active stand test, stratified by the presence of initial orthostatic hypotension (IOH). Participants were classified as IOH-positive (n = 14; blue line) or IOH-negative (n = 11; red line) based on standard hemodynamic criteria. The active stand was initiated at 50 s. Signals shown include tissue saturation index (TSI), oxygenated hemoglobin (O2Hb), deoxygenated hemoglobin (HHb), heart rate (HR), systolic blood pressure (sBP), and diastolic blood pressure (dBP).

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  Figure 3. Group-level mean trajectories with 95% confidence intervals for neurovascular and cardiovascular signals during the active stand test, stratified by body mass index (BMI). Participants were classified as non-overweight (BMI < 25 kg/m2, n = 10; blue line) or overweight/obese (BMI ≥ 25 kg/m2, n = 15; red line). The active stand was initiated at 50 s. Signals shown include tissue saturation index (TSI), oxygenated hemoglobin (O2Hb), deoxygenated hemoglobin (HHb), heart rate (HR), systolic blood pressure (sBP), and diastolic blood pressure (dBP).

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  Figure 4. Group-level mean trajectories with 95% confidence intervals for neurovascular and cardiovascular signals during the active stand test, stratified by antihypertensive medication use. Participants were categorized as not using antihypertensive medication (n = 17; red line) or currently using antihypertensive medication (n = 8; blue line). The active stand was initiated at 50 s. Signals shown include tissue saturation index (TSI), oxygenated hemoglobin (O2Hb), deoxygenated hemoglobin (HHb), heart rate (HR), systolic blood pressure (sBP), and diastolic blood pressure (dBP).

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  Figure 5. Group-level mean trajectories with 95% confidence intervals for neurovascular and cardiovascular signals during the active stand test, stratified by physical frailty status. Participants were classified as less frail (SHARE-FI score < −0.5; n = 12; red curve) or more frail (SHARE-FI score ≥ −0.5; n = 13; blue curve). The active stand was initiated at 50 s. Signals shown include tissue saturation index (TSI), oxygenated hemoglobin (O2Hb), deoxygenated hemoglobin (HHb), heart rate (HR), systolic blood pressure (sBP), and diastolic blood pressure (dBP).

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  Figure 6. Functional data analysis (FDA) F2(t) statistic curves for neurovascular signals—tissue saturation index (TSI), oxygenated hemoglobin (O2Hb), and deoxygenated hemoglobin (HHb)—measured during the 200 s active stand test. Each solid colored line represents the observed F2(t) statistic for a specific group comparison (age, IOH, BMI, antihypertensive use, and frailty). The corresponding dashed colored lines indicate the permutation-derived critical thresholds for statistical significance (p < 0.05). The dotted gray horizontal line represents the conventional 95% parametric F cutoff, derived from the F-distribution under assumptions of normality and equal variances, and is included for reference. Periods where the observed F2(t) curve exceeds its permutation-derived threshold for at least 5 consecutive seconds are interpreted as clinically significant differences in signal trajectories between groups. The active stand began at 50 s. In the legend, “Fobs” denotes the observed F2(t) statistics, and “band” refers to the permutation-derived significance threshold for each group comparison.

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  Figure 7. Functional data analysis (FDA) F2(t) statistic curves for cardiovascular signals—heart rate (HR), systolic blood pressure (sBP), and diastolic blood pressure (dBP)—measured during the 200 s active stand test. Each solid colored line represents the observed F2(t) statistic for a specific group comparison (age, IOH, BMI, antihypertensive use, and frailty). The corresponding dashed colored lines indicate the permutation-derived critical thresholds for statistical significance (p < 0.05). The dotted gray horizontal line represents the conventional 95% parametric F cutoff, derived from the F-distribution under assumptions of normality and equal variances, and is included for reference. Periods where the observed F2(t) curve exceeds its permutation-derived threshold for at least 5 consecutive seconds are interpreted as clinically significant differences in signal trajectories between groups. The active stand began at 50 s. In the legend, “Fobs” denotes the observed F2(t) statistics, and “band” refers to the permutation-derived significance threshold for each group comparison.