1. Characterization of the ER-REBOA and Coda occlusion balloons
Volume-pressure-diameter relations for the unconstrained ER-REBOA and Coda balloons were
characterized prior to the study (Figure S1). Both balloons exhibited similar inflation characteristics in the pressure- diameter domain up to 200 mmHg (Figure S1C), but the ER-REBOA balloon exhibited a slightly larger diameter (Figure S1A) and higher pressure (Figure S1B) than the Coda balloon under the same inflation volumes.
Interestingly, at higher (>20 ml) inflation volumes, our measurements of the volume-diameter relationship for the ER-REBOA balloon deviated from the manufacturer-provided values1 (Figure S1A).
Figure S1. Volume-pressure-diameter relations for the unconstrained ER-REBOA and Coda balloons inflated in air.
Whiskers extend to one standard deviation.
2. Donor information and experimental setup
Donor information, risk factors, and cause of death are summarized in Table S1. Schematic representation of the experimental setup and distribution of aortic specimens by age are illustrated in Figure S2. A total of 76 aortas included the segment of the descending thoracic aorta (TA) spanning from the left subclavian artery to the celiac artery, and 67 aortas included the abdominal segment (AA) – Figure S2B.
Table S1. Subject demographics, risk factors, and cause of death.
Age, years 51 ± 18 (range 13-75)
Gender 52 M, 27 F (66/34%)
Body Mass Index 32 ± 8 (range 18.0-57.5)
Hypertension 34 (43%)
Diabetes Mellitus 17 (22%)
Dyslipidemia 20 (25%)
Coronary Artery Disease 20 (25%)
Smoking, pack-years 14 ± 23 (49% ever smokers) Cause of death Cardiac related: 37 (47%)
Trauma: 10 (13%)
Intracranial hemorrhage: 8 (10%) Vehicle-related: 7 (9%)
Respiratory/anoxia 6 (8%) Self-inflicted 4 (5%) Other and N/A: 7 (9%)
Figure S2. Experimental setup (A) and distribution of aortic specimens by age groups (B). TA = Descending Thoracic Aorta (red), AA = Abdominal Aorta (violet). Please note that since some aortas only included the TA or the AA segment, the total number of donors in most age groups is higher than the number of TA and AA tests.
3. Data acquisition during occlusion and rupture
Figure S3A is a representative example of upstream, downstream, and balloon pressures when occluding the 100/40 mmHg pulsatile flow in a 64-year-old male thoracic aorta (TA). It illustrates the timeline required to
achieve stable systolic and balloon pressures. As the balloon inflated and occluded the flow (Figure S3A, time = 10 sec), upstream systolic pressure increased above 150 mmHg. To compensate for this increase, the flow bypass resistance was reduced, and the balloon inflation was adjusted. At time = 25 sec, the system reached equilibrium with 100/40 mmHg upstream flow pressures. Figure S3B illustrates deformations of the TA during the rupture test with a Coda balloon at 0, 20, and 40 ml balloon inflation volumes, and eventual rupture of the aorta at 40 ml balloon inflation.
Figure S3. Pressure during occlusion (A) and rupture events (B) in a 64-year-old male TA using a Coda balloon. Note that the upstream systolic pressure (red) increases as the distal systolic pressure (dashed blue) decreases during the aortic occlusion (A). To compensate for this increase, pump stroke volume and balloon inflation (green) were adjusted accordingly, resulting in 100/40 mmHg systolic/diastolic flow pressure equilibrium upstream from the balloon. Red arrows in panel B indicate balloon location.
4. Aortic morphometry
The mean unpressurized inner diameter (ID) was larger in TAs than in AAs (14.2 ± 2.1 vs 11.1 ± 2.1 mm, p
< 0.01), while differences in the wall thickness (WT) between TAs and AAs were not statistically significant (2.3 ± 0.5 vs 2.2 ± 0.7, p = 0.33). The ID and WT values in all age groups are summarized in Figure S4. The IDs increased significantly with age for both TAs (r = 0.71, p < 0.01) and AAs (r = 0.60, p < 0.01) (Figure S4 A), and the IDs of TAs were larger than those of AAs in all age groups (p < 0.01). However, the IDs of AAs in the oldest age group, on
average, were larger than the IDs of TAs in the youngest age group (12.5 ± 2.0 mm vs. 9.7 ± 0.9 mm, p < 0.01).
WTs also increased with age for both TA (r = 0.48, p < 0.01) and AA (r = 0.39, p < 0.01) specimens. The differences between the TA and AA WTs were not statistically significant, except in the youngest age group (p = 0.01).
Figure S4. Unpressurized inner diameter (A) and wall thickness (B) of Thoracic (TA – red) and Abdominal (AA – violet) aortas in seven age groups. Whiskers extend to the minimum and maximum values, boxes represent the interquartile range (IQR), the median is shown as a horizontal band within the box, the mean value is marked with an x, and statistical outliers (values that lie 1.5 IQRs or more outside the box) are shown as hollow circles. Statistical significance is marked with single (*, p
≤ 0.05) and double (**, p ≤ 0.01) asterisks.
Male donors were younger than female donors (47 ± 18 vs. 56 ± 18 years, p = 0.045), but male donors on average had larger unpressurized inner diameters (IDs) of the AA (11.6 ± 2.2 vs. 10.0 ± 1.8 mm, p < 0.01) and the TA (14.5 ± 1.9 vs. 13.7 ± 2.5 mm, p = 0.13) than female donors (Figure S5A). No significant differences were observed in the wall thicknesses (WTs) of the TA (2.3 ± 0.5 vs. 2.4 ± 0.6 mm, p = 0.51) or AA (2.2 ± 0.6 vs. 2.3 ± 0.8 mm, p = 0.43) between male and female specimens, respectively (Figure S5B).
Figure S5. Differences in unpressurized inner diameter (A) and wall thickness (B) between female (F – red) and male (M – violet) aortas. Whiskers extend to the minimum and maximum values, boxes represent the interquartile range (IQR), the median is shown as a horizontal band within the box, the mean value is marked with an x, and statistical outliers (values that lie 1.5 IQRs or more outside the box) are shown as hollow circlesStatistical significance (p ≤ 0.01) is marked double (**) asterisks.
5. Balloon inflation volumes versus manufacturers’ recommendations
Prytime Medical recommends starting with an 8 ml inflation volume when occluding the TA and increasing it gradually to no more than 24 ml, while the maximum indicated inflation volume for the 40 mm Coda balloon is 40 ml. Our results demonstrate that stable TA occlusion was achieved with inflation volumes < 8 ml in 10 (13%) subjects when using ER-REBOA and in 13 (16%) subjects when using the Coda balloon, suggesting that even smaller initial inflation volumes may be effective, particularly in younger aortas. In fact, 80% of the TAs in our youngest age group required < 8 ml ER-REBOA inflation volume to achieve stable occlusion, although the ER- REBOA balloon is currently contraindicated in patients younger than 18 years old1. Conversely, in 1.4% of cases that used the ER-REBOA balloon and in 2.9% of cases that used Coda, the flow occlusion in the TA required more than 24 ml of inflation volume, which is larger than the maximum indicated capacity for the ER-REBOA balloon.
6. An Outlier
Although most boxes in Figure 4 (main manuscript) include several points that appear to be statistical outliers, only one measurement seems to have a physical reason for exclusion. This particular measurement corresponds to 72 mmHg balloon pressure and 10 ml balloon volume (both lie more than 1.5 IQRs below the first
quartile) associated with the AA rupture from a 47-year old female donor. In this case, the balloon pressure was only about 5% of the median rupture pressure across all AAs (1394 mmHg). Also, this was the only case in which balloon pressure during rupture was smaller than the balloon pressure during occlusion at 150/40 and 200/40 flows, suggesting that aortic wall damage or weakening might have occurred before the rupture test.
Reference
1. Medical P. ER-REBOA TM Catheter Value Analysis Committee-Product Information Kit Resuscitative Endovascular Balloon Occlusion of the Aorta MINIMALLY INVASIVE SOLUTION FOR TEMPORARY OCCLUSION OF LARGE BLOOD VESSELS.; 2015. https://mtqip.org/sites/default/files/downloads/180306 REBOA Toolkit_0.pdf. Accessed September 26, 2019.
