Time‐course analysis of cerebral circulation and cardiorespiratory responses to acute central blood volume reduction in healthy young males

Figures

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  FIGURE 1. Temporal changes in physiological variables during one of three trials in a representative subject. This figure presents data from a single trial, illustrating the temporal changes in various physiological variables from 2 min before the intervention to 2 min after its onset. The variables displayed are (from top to bottom): LBNP, lower‐body negative pressure; blood pressure (filled circles, systolic; open circles, diastolic; filled triangles, mean; the blood pressure values are averaged over 30 s); flow; HR, heart rate; ECG; MCA V mean, middle cerebral artery blood flow velocity; FLOW, respiratory flow; and F CO2, fraction of inspired CO2. The x‐axis represents time, with zero marking the onset of LBNP, clearly distinguishing the baseline period from the LBNP application period.

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  FIGURE 2. Time courses of cerebrocardiovascular and respiratory variables during baseline and lower‐body negative pressure (LBNP) periods. The graphs display percentage changes from baseline for the following variables: central blood volume; systolic BP, systolic blood pressure; diastolic BP, diastolic blood pressure; mean BP, mean blood pressure; HR, heart rate; MCA V mean, middle cerebral artery mean blood velocity; V˙E, minute ventilation; V T, tidal volume; RR, respiratory rate; and PETCO2, end‐tidal PCO2. Data points represent mean values averaged over 30 s intervals: baseline, 0–30 s, 30–60 s, 60–90 s and 90–120 s of LBNP application. Error bars indicate the SD. The horizontal line at 0% on the y‐axis represents baseline values. Statistical significance was assessed using one‐way repeated‐measures ANOVA followed by Tukey's post hoc tests comparing each time point to baseline. Multiple comparison correction was applied using the Benjamini–Hochberg false discovery rate (FDR) method. Symbols indicate significance after FDR correction: * p < 0.05, ** p < 0.01 and *** p < 0.001. Total number of comparisons for FDR correction: 10 parameters × 4 time points = 40 comparisons. Non‐significant…

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  FIGURE 3. Temporal relationships between changes in mean blood pressure and respiratory variables during lower‐body negative pressure (LBNP). Scatter plots show correlations between changes in mean blood pressure (BP) (x‐axis) and respiratory variables (y‐axis) for each 30 s period. Variables are expressed as delta values from baseline. Pearson correlation analysis with Benjamini–Hochberg false discovery rate (FDR) correction was applied (12 comparisons: 3 variables × 4 time periods). Significant correlations after FDR correction are marked with asterisks and shown with regression lines: V T at 0–30 s (r = −0.78, 95% CI: −0.92 to −0.47, p = 0.004). Non‐significant correlations after FDR correction are shown without regression lines. Dotted lines indicate zero reference. n = 11 for all analyses.

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  FIGURE 4. Cross‐correlation analysis between middle cerebral artery mean blood velocity (MCA V mean) and respiratory parameters during lower‐body negative pressure. Cross‐correlation coefficients are shown for MCA V mean and minute ventilation (V˙E), tidal volume (V T) and respiratory rate (RR). Data were collected 1 s for 2 min following lower‐body negative pressure onset (time 0) and averaged over 10 s intervals for analysis. Dotted horizontal lines represent 95% confidence intervals (±0.17). Negative time lags indicate that respiratory changes precede MCA V mean changes. Significant negative correlations (p < 0.05) are observed for V˙E and V T at time lags of 10–20 s, indicating that respiratory changes temporally precede cerebrovascular responses. This temporal pattern suggests respiratory‐mediated modulation of cerebrovascular function during circulatory stress.