Spleen contraction elevates hemoglobin concentration at high altitude during rest and exercise

Abstract

Purpose: Hypoxia 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.

Methods: Eleven 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.

Results: Resting 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.

Conclusions: The 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.

Keywords: Hematocrit; Hemoconcentration; High altitude; Spleen size; Spleen volume.

Fig. 1

The field measurements were conducted during 10 days at three different locations in the Rolwaling valley in the Nepali Himalayas. All subjects followed the same ascent profile. Altitudes for the locations where participants slept are shown. Arrows mark measurement days; 1: collection of background data and 2: step test in Kathmandu; 3: step test in Beding; 4: step test in Naa

Fig. 2

Mean (SE) spleen volume across the exercise test at 3 altitudes for 11 participants. Difference between the last minute value during rest and first value after exercise is indicated by *P < 0.05 and **P < 0.01

Fig. 3

Mean (SE) spleen volumes during 5-min rest before step test, directly after the 5-min step test, and after 10-min rest at 3 altitudes for 11 participants; Kathmandu 1370 m, Beding 3700 m and Naa 4200 m. Significant difference between baseline value and first post-exercise value within altitudes is indicated with **P < 0.01 and *P < 0.05. At 10 min post-exercise, spleen volumes were back to baseline at all altitudes (all NS). Differences between baseline volumes at Kathmandu and other altitudes is indicated with a above columns (a for P < 0.05; aa for P < 0.01). There was no difference between Beding and Naa for rest and exercise (NS). Post-exercise volumes were different between Beding and Naa (b for P < 0.05)

Fig. 4

Mean (SE) hemoglobin concentration (Hb) during rest before exercise, during the last minute of the step test, and 10 min after exercise for 11 participants at 3 altitudes; in Kathmandu 1370 m, Beding 3700 m and Naa 4200 m. Significant difference between baseline value and first post-exercise value within altitudes is indicated with **P < 0.01 and *P < 0.05. At 10 min post-exercise, spleen volumes were back to baseline at all altitudes (all NS). Differences between baseline volumes at Kathmandu and other altitudes are indicated with a above columns for P < 0.05. There was also a difference between Beding and Naa for exercise and post-exercise volumes (b for P < 0.05; bbb for P < 0.001)

Fig. 5

Mean (SE) change from baseline in spleen volume and hemoglobin concentration (Hb) at three altitudes; 1370 m, 3700 m and 4200 m. Values are means from 11 participants. Significant difference between Hb elevation at 3700 and 4200 m is indicated by *P < 0.05, while other differences were not significant. P value for spleen volume comparison between 3700 and 4200 m is shown above column

Fig. 6

Mean (SE) values for cardiorespiratory variables before, during and 10 min after exercise at three altitudes; Kathmandu 1370 m, Beding 3700 m and Naa 4200 m. Means are based on 11 participants, except for RR, where n = 10. Arterial oxygen saturation (SaO₂); end-tidal carbon dioxide (ETCO₂); heart rate (HR) and respiratory rate (RR) were affected by altitude and by exercise. Significant differences between exercise and post-exercise values compared to baseline values within altitudes are indicated with *P < 0.05; **P < 0.01 and ***P < 0.001. Differences between baseline values at Kathmandu and other altitudes are indicated with a above columns for P < 0.05; aa for P < 0.01 and aaa for P < 0.001. There was also a difference between 3700 and 4200 m values for exercise and post-exercise ETCO₂ indicated by bb for P < 0.01