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Initiation of spleen contraction resulting in natural blood boosting in humans
Mid Sweden University, Faculty of Science, Technology and Media, Department of Ecotechnology and Sustainable Building Engineering.
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The spleen has been shown to contract in apneic situations in humans as well as in other diving mammals, expelling its stored red blood cell content into circulation. This natural blood boosting may increase the circulating hemoglobin concentration (Hb) by up to 10%, which would enhance the oxygen carrying capacity and likely increase performance. However, the triggers of this response in humans have not been fully clarified. Study I was therefore focused on the effect of hypoxia as a trigger of spleen contraction. It was found that 20 min of normobaric hypoxic breathing evoked a substantial reduction in spleen volume showing that hypoxia is an important trigger for spleen contraction. Knowing the role of hypoxia, Study II compared two different hypoxic situations – a 2 min apnea and 20 min normobaric hypoxic breathing – which resulted in the same level of arterial hemoglobin desaturation. Apnea evoked a twice as great spleen volume reduction, implying that variables other than hypoxia were likely involved in triggering spleen contraction. This may be hypercapnia which is present during apnea but not during normobaric hypoxic breathing. Study III therefore investigated the effects of breathing gas mixtures containing different proportions of CO2 prior to maximal apneas. Pre-breathing mixtures with higher percentages of CO2 resulted in greater spleen contraction, thus demonstrating hypercapnia's likely role as a trigger in addition to hypoxia. Study IV explored whether an all-or-nothing threshold stimulus for triggering spleen contraction existed, or if contraction was graded in relation to the magnitude of triggering stimuli. Exercise was therefore performed in an already hypoxic state during normobaria. Rest in hypoxia produced a moderate spleen volume reduction, with an enhanced spleen contraction resulting after hypoxic exercise, with a concomitant increase in Hb. This implies that spleen contraction is a graded response related to the magnitude of the stimuli. This could be beneficial in environments with varying oxygen content or work loads. Study V examined the possibility that spleen contraction is part of the acclimatization to altitude, during an expedition to summit Mt Everest. The long-term high altitude exposure, combined with physical work on the mountain, had no effects on resting spleen volume but resulted in a stronger spleen contraction, when provoked by apnea or exercise. This indicates that acclimatization to altitude may enhance the contractile capacity of the spleen, which may be beneficial for the climber. From these studies I concluded that hypoxia is an important trigger for spleen contraction but that hypercapnia also contributes in apneic situations. The spleen contraction likely provides a graded expulsion of erythrocytes in response to these stimuli, causing a temporary increase in gas storage capacity that may facilitate activities such as freediving and climbing. The storage of erythrocytes during rest serves to reduce blood viscosity, which would also be beneficial for the climber or diver. The human spleen contraction appears to become stronger with acclimatization, with beneficial effects at altitude. Such an upgraded response could be beneficial both in sports and diseases involving hypoxia.

Place, publisher, year, edition, pages
Östersund: Mid Sweden University , 2015. , 87 p.
Mid Sweden University doctoral thesis, ISSN 1652-893X ; 217
Keyword [en]
Acclimatization, altitude, apnea, breath-hold diving, hemoglobin, hypercapnia, hypoxia, triggers
National Category
Health Sciences
URN: urn:nbn:se:miun:diva-25518ISBN: 978-91-88025-10-4OAI: diva2:841470
Available from: 2015-07-13 Created: 2015-07-13 Last updated: 2015-08-24Bibliographically approved
List of papers
1. Short-term effects of normobaric hypoxia on the human spleen
Open this publication in new window or tab >>Short-term effects of normobaric hypoxia on the human spleen
2008 (English)In: European Journal of Applied Physiology, ISSN 1439-6319, E-ISSN 1439-6327, Vol. 104, no 2, 395-399 p.Article in journal (Refereed) Published
Abstract [en]

Spleen contraction resulting in an increase in circulating erythrocytes has been shown to occur during apnea. This effect, however, has not previously been studied during normobaric hypoxia whilst breathing. After 20 min of horizontal rest and normoxic breathing, five subjects underwent 20-min of normobaric hypoxic breathing (12.8% oxygen) followed by 10 min of normoxic breathing. Ultrasound measurements of spleen volume and samples for venous hemoglobin concentration (Hb) and hematocrit (Hct) were taken simultaneously at short intervals from 20 min before until 10 min after the hypoxic period. Heart rate, arterial oxygen saturation (SaO2) and respiration rate were recorded continuously. During hypoxia, a reduction in SaO2 by 34% (P < 0.01) was accompanied by an 18% reduction in spleen volume and a 2.1% increase in both Hb and Hct (P < 0.05). Heart rate increased 28% above baseline (P < 0.05). Within 3 min after hypoxia SaO2 had returned to pre-hypoxic levels, and spleen volume, Hb and Hct had all returned to pre-hypoxic levels within 10 min. Respiratory rate remained stable throughout the protocol. This study of short-term exposure to eupneic normobaric hypoxia suggests that hypoxia plays a key role in triggering spleen contraction and subsequent release of stored erythrocytes in humans. This response could be beneficial during early altitude acclimatization.

Hypoxia, Spleen, Hemoglobin, Hematocrit, Ultrasound
National Category
Biological Sciences Sport and Fitness Sciences Microbiology
urn:nbn:se:miun:diva-4361 (URN)10.1007/s00421-007-0623-4 (DOI)000258609300033 ()18043933 (PubMedID)2-s2.0-50449084381 (ScopusID)5527 (Local ID)5527 (Archive number)5527 (OAI)
2nd International Conference on Environmental Ergonomics, 2007, Piran, Slovenia
nd International Conference on Environmental Ergonomics, Piran, SLOVENIAAvailable from: 2008-11-29 Created: 2008-11-19 Last updated: 2015-07-13Bibliographically approved
2. Spleen contraction during 20 min normobaric hypoxia and 2 min apnea in humans
Open this publication in new window or tab >>Spleen contraction during 20 min normobaric hypoxia and 2 min apnea in humans
2010 (English)In: Aviation, Space and Environmental Medicine, ISSN 0095-6562, Vol. 81, no 6, 545-549 p.Article in journal (Refereed) Published
Abstract [en]

Introduction: Spleen contraction occurs in humans during exercise, apnea, and simulated altitude, resulting in ejection of stored red blood cells into circulation. The mechanisms responsible for initiating the contraction are not fully known: hypoxia is likely involved, but other, unknown factors may also contribute. To reveal the initiating factors, we studied its occurrence in two different situations involving similar reductions in arterial oxygen saturation (SaO2). We hypothesized that similar spleen responses would result if the level of hypoxia is the main factor involved. Methods: Five female and four male healthy volunteers performed two different trials on separate days: 1)20 min of normobaric hypoxic breathing (14.2% oxygen); and II) 2 min of apnea after a deep inspiration of air. Both trials started and ended with 10 min of sitting eupneic rest. Spleen diameter was intermittently measured via ultrasonic imaging in three dimensions to calculate volume. S aO2 and heart rate (HR) were recorded continuously with a pulse oximeter. Results: Exposures resulted in similar nadir SaO 2: 87% after normobaric hypoxia and 89% after apnea. During normobaric hypoxia, spleen volume was reduced by 16% and during apnea by 34%. HR increased by 7% during normobaric hypoxia, but fell by 25% during apnea. Discussion: Both normobaric hypoxia and apnea induced spleen contraction, but despite similar levels of SaO2 apnea evoked a significantly stronger response, possibly due to hypercapnia, faster desaturation, ortheapneic stimulus in itself. Spleen contraction may facilitate adaptation to altitude and to apneic diving by elevating blood gas storage capacity.

Altitude; Breath hold; Diving response; Hypoxia; Spleen contraction
National Category
urn:nbn:se:miun:diva-10766 (URN)10.3357/ASEM.2682.2010 (DOI)000278305400002 ()20540444 (PubMedID)2-s2.0-77952831855 (ScopusID)
Available from: 2009-12-22 Created: 2009-12-22 Last updated: 2015-07-13Bibliographically approved
3. Effect of hypercapnia on spleen-related haemoglobin increase during apnea
Open this publication in new window or tab >>Effect of hypercapnia on spleen-related haemoglobin increase during apnea
2012 (English)In: Diving and Hyperbaric Medicine, ISSN 1833-3516, Vol. 42, no 1, 4-9 p.Article in journal (Refereed) Published
Abstract [en]


Splenic contraction associated with apnea causes increased haemoglobin concentration and haematocrit (Hct), an effect that may promote prolonged breath-holding. Hypoxia has been shown to augment this effect, but hypercapnic influences have not been investigated previously.


Eight non-divers performed three series of apneas on separate days after inspiration of oxygen with different carbon dioxide (CO₂) levels. Each series consisted of three apneas 2 minutes apart: one with pre-breathing of 5% CO₂ in oxygen (O₂, 'Hypercapnia'); one with pre-breathing of 100% O₂ ('Normocapnia'); and one with hyperventilation of 100% O₂ ('Hypocapnia'). The apnea durations were repeated identically in all trials, determined from the maximum duration attained in the CO₂ trial. A fourth trial, breathing 5% CO₂ in O₂ for the same duration as these apneas was also performed ('Eupneic hypercapnia'). In three subjects, spleen size was measured using ultrasonic imaging.


Haemoglobin increased by 4% after apneas in the 'Hypercapnia' trial (P = 0.002) and by 3% in the 'Normocapnia' trial (P = 0.011), while the 'Hypocapnia' and 'Eupneic hypercapnia' trials showed no changes. The 'easy' phase of apnea, i.e., the period without involuntary breathing movements, was longest in the 'Hypocapnia' trial and shortest in the 'Hypercapnia' trial. A decrease in spleen size was evident in the hypercapnic trial, whereas in the hypocapnia trial spleen size increased, while only minor changes occurred in the other trials. No differences were observed between trials in the cardiovascular diving response.


There appears to be a dose-response effect of CO₂ on triggering splenic contraction during apnea in the absence of hypoxia.

hypercapnia spleen contraction
National Category
urn:nbn:se:miun:diva-15820 (URN)000301886700002 ()22437969 (PubMedID)2-s2.0-84858788803 (ScopusID)
Available from: 2012-02-02 Created: 2012-02-02 Last updated: 2015-07-13Bibliographically approved
4. The effect of climbing mount everest on spleen contraction and increase in hemoglobin concentration during breath holding and exercise
Open this publication in new window or tab >>The effect of climbing mount everest on spleen contraction and increase in hemoglobin concentration during breath holding and exercise
2014 (English)In: High Altitude Medicine & Biology, ISSN 1527-0297, E-ISSN 1557-8682, Vol. 15, no 1, 52-57 p.Article in journal (Refereed) Published
Abstract [en]

Release of stored red blood cells resulting from spleen contraction improves human performance in various hypoxic situations. This study determined spleen volume resulting from two contraction-evoking stimuli: breath holding and exercise before and after altitude acclimatization during a Mount Everest ascent (8848m). Eight climbers performed the following protocol before and after the climb: 5min ambient air respiration at 1370m during rest, 20min oxygen respiration, 20min ambient air respiration at 1370m, three maximal-effort breath holds spaced by 2min, 10min ambient air respiration, 5min of cycling at 100 W, and finally 10min ambient air respiration. We measured spleen volume by ultrasound and capillary hemoglobin (HB) concentration after each exposure, and heart rate (HR) and arterial oxygen saturation (Sao2) continuously. Mean (SD) baseline spleen volume was unchanged at 213 (101) mL before and 206 (52) mL after the climb. Before the climb, spleen volume was reduced to 184 (83) mL after three breath holds, and after the climb three breath holds resulted in a spleen volume of 132 (26) mL (p=0.032). After exercise, the preclimb spleen volume was 186 (89) mL vs. 112 (389) mL) after the climb (p=0.003). Breath hold duration and cardiovascular responses were unchanged after the climb. We concluded that spleen contraction may be enhanced by altitude acclimatization, probably reflecting both the acclimatization to chronic hypoxic exposure and acute hypoxia during physical work. © Copyright 2014, Mary Ann Liebert, Inc. 2014.

Acclimatization, Apnea, Hematology, Hypobaric hypoxia, Red cell volume
National Category
Sport and Fitness Sciences Hematology Physiology
urn:nbn:se:miun:diva-22041 (URN)10.1089/ham.2013.1061 (DOI)000333464100008 ()2-s2.0-84897141698 (ScopusID)

Language of Original Document: English

Available from: 2014-06-02 Created: 2014-05-30 Last updated: 2015-07-13Bibliographically approved

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