Article Figures & Data
Figures
- Fig 1.
Mean CBF during the breath-hold experiment. False color maps of cohort mean cerebral blood flow during 5-minute breath-hold. Selected transverse brain sections of the cohort mean CBF before, during, and after the 5-minute breath-hold challenge. The mean total GM CBF over all participants and over all phases was scaled to 60 mL/100 g/min. Likewise, the mean total WM CBF for all participants over all phases was scaled to 20 mL/100 g/min for WM.
- Fig 2.
Cerebral blood flow and partial volume–corrected relative spatial coefficient of variation dynamics. Baseline scan with normal ventilation starts at 0 minutes, the second and third measurement points represent 2 minutes and 30 seconds and 5 minutes of breath-hold, and the fourth and fifth scan phases at 7 minutes and 30 seconds and 10 minutes represent the recovery phase. A, CBF in gray matter voxels only (n = 15 participants, each represented by a color dot). B, The same for white matter only. C, Partial volume–corrected relative spatial coefficient of variation dynamics in gray matter. Y-axis: relative CBF spatial coefficient of variation defined as the ratio of the actual spatial coefficient of variation divided by the spatial coefficient of variation expected on the basis of anatomy (in arbitrary units [au]).
- Fig 3.
Relationship of SpO2 and heart rate with CBF. A, Mean GM CBF (colored dots) and mean WM CBF (triangles) are both strongly correlated with absolute SpO2. Color encoding for A and C: green for baseline, orange for 2 minutes and 30 seconds breath-hold, red for 5-minute breath-hold, turquoise after 2 minutes and 30 seconds of recovery, and blue after 5 minutes of recovery. The same WM time points are right below. B, ΔCBF (here measured in GM) similarly correlates well to ΔSpO2 (all 75 single values). C and D, There is no strong correlation between heart rate and CBF in absolute values (C, mean) or ΔCBF and ΔSpO2 (D).
- Fig 4.
Scatterplot illustration of the relationship between cumulative breath-hold experience and CBF during the experiment. With the exception of 2 participants (divers 11 and 13, marked with arrows), there is a lower CBF during the experiment with more previous prolonged breath-hold events (cumulative breath-hold, >2 minutes and 30 seconds).
- Fig 5.
Energy metabolites and blood gases in brain and venous blood. A, Sample 31P-MR spectrum of 1 participant averaged over 2 minutes and 30 seconds of the late breath-hold phase (above), displayed together with AMARES-fitted spectral components (below). B, Brain pH as assessed by 31P-MR spectroscopy is near-constant during the entire breath-hold experiment. C, The PCr / (ATP + adenosine diphosphate) ratio measured by 31P-MR spectroscopy slightly decreases during breath-hold. D, PCr and β-ATP differences (Δ) from individual baseline values correlate with the pH differences from baseline, indicating that small tendencies toward acidosis and ATP depletion occur during breath-hold. E, Venous blood analyses reveal significant hypoxemia and hypercapnia development (left axis in millimeters of mercury) during breath-hold with fast recovery. Blood glucose (in milligrams/deciliter, left axis) and lactate (in mmol/L, right axis) rose during breath-hold and did not return to baseline. All values are expressed as differences from baseline.
Tables
Anthropometric data of freediver volunteersa
Participant Longest Breath-Hold until MRI (min) Start of Sport (yr before MRI) Estimated Breath-Holds >2 min 30 s per Session Sessions per Month Estimated Cumulative Lifetime Breath-Holds >2 min 30 s Age (yr) 1 10.6 11.3 30 0.4 1632 31 2 5.5 1.5 7 8 1008 36 3 5.4 2.0 1 1 24 20 4 5.4 11.0 ~0 8 4 33 5 5.0 2.0 0.125 8 24 40 6 5.5 10.0 ~0 4 4 38 7 5.0 8.0 5 8 3840 61 8 5.5 1.5 0.5 4 36 34 9 5.0 7.0 6 16 8064 47 10 6.2 9.0 6 7 4536 26 11 5.3 27.5 15 16 79,200 64 12 6.5 10.2 12 28 11,712 51 13 5.5 11.3 10 16 21,760 35 14 5.5 1.6 18 10 3420 32 15 5.0 5.0 0.083 4 20 50 Median 5.5 8.0 6 8 2526 36.0 95% CI 5.3–5.5 2.0–11.0 0.14–12.0 4.0–9.96 30–6300 32–50 Minimum 5.0 1.5 0 0.41 4 20 Maximum 10.6 27.5 30 28 79,200 64 ↵a Participants were interviewed concerning the duration (start of sport) and intensity (freediving sessions per month) and the estimated frequency of breath-holding for >2 minutes and 30 seconds per session. The latter could be near zero in freedivers specializing in short high-frequency breath-holds. Some participants breath-held for >2 minutes and 30 seconds only as a qualification for this study; hence, their cumulative lifetime breath-holds of >2 minutes and 30 seconds before MRI were 4, while others very frequently underwent prolonged breath-hold.
