Spleen contraction during 20 min normobaric hypoxia and 2 min apnea in humans.
Level 3 - non-randomized controlled study
non-randomized within-subject comparative physiological study in humans
PubMed 20540444 · doi:10.3357/asem.2682.2010
What was done
Nine healthy volunteers (5 female, 4 male) underwent two separate experimental exposures on different days: 20 minutes of normobaric hypoxic breathing (14.2% oxygen) and 2 minutes of apnea following a deep inspiration. Both protocols included 10-minute rest periods before and after the exposure. Spleen volume was assessed intermittently with 3D ultrasound, while arterial oxygen saturation (SaO2) and heart rate were continuously monitored with pulse oximetry.
What was found
Nadir SaO2 reached similar levels in both conditions: 87% in normobaric hypoxia and 89% in apnea. Spleen volume decreased by 16% during normobaric hypoxia and by 34% during apnea. Heart rate increased by 7% during normobaric hypoxia but decreased by 25% during apnea.
Why it matters
This study indicates that splenic contraction is not triggered solely by the absolute level of arterial hypoxia. Apnea evokes a substantially stronger contractile response, suggesting that additional factors such as hypercapnia, rate of desaturation, or the breath-hold stimulus itself drive human splenic emptying.
Limits
The study had a very small sample size (n = 9). The abstract does not report whether the condition order was randomized. Blood carbon dioxide levels and sympathetic nerve activity were not directly measured to confirm the mechanisms underlying the difference between exposures.
Cited by
- context Sleep disturbances such as mild sleep apnea trigger splenic contractions at night, causing iron biomarkers to fluctuate significantly on blood tests.