Abstract
PurposeHypoxia and exercise are known to separately trigger spleen contraction, leading to release of stored erythrocytes. We studied spleen volume and hemoglobin concentration (Hb) during rest and exercise at three altitudes.MethodsEleven healthy lowlanders did a 5-min modified Harvard step test at 1370, 3700 and 4200 m altitude. Spleen volume was measured via ultrasonic imaging and capillary Hb with Hemocue during rest and after the step test, and arterial oxygen saturation (SaO2), heart rate (HR), expiratory CO2 (ETCO2) and respiratory rate (RR) across the test.ResultsResting spleen volume was reduced with increasing altitude and further reduced with exercise at all altitudes. Mean (SE) baseline spleen volume at 1370 m was 252 (20) mL and after exercise, it was 199 (15) mL (P < 0.01). At 3700 m, baseline spleen volume was 231 (22) mL and after exercise 166 (12) mL (P < 0.05). At 4200 m baseline volume was 210 (23) mL and after exercise 172 (20) mL (P < 0.05). After 10 min, spleen volume increased to baseline at all altitudes (NS). Baseline Hb increased with altitude from 138.9 (6.1) g/L at 1370 m, to 141.2 (4.1) at 3700 m and 152.4 (4.0) at 4200 m (P < 0.01). At all altitudes Hb increased from baseline during exercise to 146.8 (5.7) g/L at 1370 m, 150.4 (3.8) g/L at 3700 m and 157.3 (3.8) g/L at 4200 m (all P < 0.05 from baseline). Hb had returned to baseline after 10 min rest at all altitudes (NS). The spleen-derived Hb elevation during exercise was smaller at 4200 m compared to 3700 m (P < 0.05). Cardiorespiratory variables were also affected by altitude during both rest and exercise.ConclusionsThe spleen contracts and mobilizes stored red blood cells during rest at high altitude and contracts further during exercise, to increase oxygen delivery to tissues during acute hypoxia. The attenuated Hb response to exercise at the highest altitude is likely due to the greater recruitment of the spleen reserve during rest, and that maximal spleen contraction is reached with exercise.
Highlights
To reveal if spleen contraction and hemoglobin concentration (Hb) elevation occur at high altitude, if this response is enhanced during whole-body exercise at high altitude, and whether the response is affected by the altitude
We suggest that the observed transient Hb elevation with spleen contraction during work at high altitude could help explain the association between individual spleen volume and acute mountain sickness (AMS) symptoms, as reported by Holmström et al (2019), with our limited LLQ data we could not support this association
We found that the spleen contracts during rest with increased altitude and mobilizes stored red blood cells, and suggest that this could be responsible for at least part of the transient early elevation in Hb often observed during ascent to high altitude
Summary
Spleen contraction with release of stored erythrocytes resulting in elevation of the circulating red blood cell volume occurs in various situations and species, including humans (Stewart and McKenzie 2002). This response has been observed in humans during exercise (Laub et al 1993), exposure to apnea (Schagatay et al 2001; Bacovic et al 2003; Richardson et al 2005) or a hypoxic environment (Richardson et al 2008). This natural blood-boosting was found to be active during exercise in chronically hypoxic patients with chronic obstructive pulmonary disease (COPD), where the most hypoxic patients were found to have the largest spleens and the most pronounced spleen contractions with exercise (Schagatay et al 2015)
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