Page 35 - JSOM Spring 2025

Findings from a recent systematic review (18 studies included) As previously mentioned, we attempted to reduce partici-
also suggest no differences in VO or exercise capacity at sub- pant bias by blindfolding participants to hide their BD status.
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maximal exercise intensities at any time point following BD; Given that participants were aware of their donation status,
however, they do indicate that VO decreased by 7% during this could have influenced their perceptions of each condition
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maximal exercise, which is in alignment with the findings of and should be considered when interpreting the results. Future
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Panebianco et al. Given these conclusions, it is plausible that studies may consider different approaches to successfully blind
the submaximal exercise intensity in the current study was too participants during venipuncture needle sticks.
low to elucidate differences between BD and control seen at
maximal exercise; however, the ruck march intensity, if not the Blood volume per unit removed from each participant was
duration, in this study was considered appropriate for a simu- confirmed by two instructors independently using field mea-
lated military operational setting given the rucksack weights, surement techniques as outlined in the Methods, namely bag
elevation, and grade of the route. 17 circumference and bag fill line, which should indicate a blood
volume of 450mL; however, the exact volume per unit was not
We proposed that a single unit BD at high altitude would limit confirmed with weight. This potential variation in blood vol-
oxygen-carrying capacity by reducing circulating red blood ume per unit donated limits our study but reflects real-world
cells, thus limiting exercise capacity, but this was not observed. variability when using field measuring techniques during
Others also hypothesized this effect, stating that “the loss of whole blood transfusion.
red blood cells will logically reduce oxygen delivery and may
lower energy production in muscles.” Studies conducted at Participants were asked to complete the ruck as quickly as pos-
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sea level do confirm that SpO (under resting conditions) is sible but were not incentivized to do so within a certain time.
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unchanged by BD. Despite unchanged SpO following BD at This could have influenced their motivation, and the physical
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sea level, studies show that hemoglobin decreases 7%–9% in performance findings must be considered with this in mind.
the days following BD. 19,20 Hill et al. analyzed hemoglobin im-
mediately before and 2 hours after a 500-mL BD and observed Also, on the first day of the training event, a storm produced
no changes, but they measured again after 2 days and noted a snow, cold temperatures, wind, and low visibility, whereas on
6% hemoglobin reduction. Therefore, the timing of exercise the second day, it was sunny and clear with milder tempera-
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following BD may play an important role, at least with respect tures. These changes in weather and route conditions possibly
to changes in hemoglobin and oxygen delivery. improved trail conditions and rucking times on the second day
which would have masked a decrease in performance among
Not surprisingly, there are thresholds to BD volume, wherein those who donated on the second day. The improved condi-
greater volumes of BD produce more pronounced physiological tions on the second day may have also impacted the reported
responses and are more likely to impact exercise performance. temperature sensation and SpO of participants. This lim-
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Ekblom et al. evaluated submaximal exercise performance at itation is also observed in our results, wherein we observed
30% and 60% of VO max with and without an 800mL BD. slower ruck march times on the first day of testing (poor
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They observed HRs 18bpm higher (for 30% VO max) and weather conditions) relative to the second day of testing, re-
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24bpm higher (60% VO max) with an 800mL BD; this in- gardless of whether participants donated or did not donate
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dicates that BD volumes greater than 500mL are capable of blood. Although we did capture many aspects of physiology,
significantly altering physiological outcomes, even during sub- we did not collect measurements of hemoglobin, which could
maximal exercise. 22 have helped explain performance differences between partici-
pants and between conditions.
Perhaps one of the greatest contributing factors to similar
responses between BD and control may have been that our The current BD equipment available for FWBT is inadequate
participants were fully acclimatized to high elevations, given for cold temperatures and prolonged the BD process in these
the duration they spent living and/or working at altitude. As austere conditions, requiring changes in patient and material
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mentioned previously, all participants worked and/or lived at positioning during BD to maximize blood flow while limit-
an elevation of at least 2,100m for at least 60 days prior to ing blood coagulation. These limitations should be considered
participating in the study. This acclimatization is a key fac- when evaluating the findings of this study and conducting fu-
tor in interpreting our findings and replicates the expected ture research efforts on this topic.
acclimatization status of warfighters conducting high-alti-
tude operations from bases at similar elevations. Fulco et al. Following this study demonstrating the safety of BD at alti-
demonstrated that consistent altitude exposure elevates arte- tude for acclimatized personnel (i.e., no negative impacts to
rial SpO and improves oxygen transport to working muscles performance and no increase in AMS symptoms), future stud-
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during submaximal exercise. Additionally, acclimatization to ies should consider evaluating the impact and safety of BD on
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altitude improves exercise performance through increased ex- donors unacclimatized to high altitude as they are more sus-
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ercise tolerance and enhanced exercise economy. Data from ceptible to the physiological strains of a high-altitude environ-
the current study suggest that performing BD in a high-alti- ment. Such a study would better replicate combat operations
tude environment with acclimatized persons appears to have conducted at high-altitude from sea-level bases.
minimal impact on submaximal exercise performance.
Additionally, this study attempted to mirror previous sea-level
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Limitations and Future Research studies with a timed combat load carry march within 2 hours
Several study limitations must be acknowledged and ad- of BD. Future studies could focus on the physiologic or com-
dressed. To our knowledge, no other studies have investigated bat readiness impacts of BD on warfighters across days rather
the effects of BD on physical performance at altitude, and this than hours, when recruitment of extravascular fluid results in
topic requires further investigation. a decrease in hemoglobin concentration. 19-21

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