The Magnitude of Diving Bradycardia During Apnea at Low-Altitude Reveals Tolerance to High Altitude Hypoxia

Holmström, Pontus; Mulder, Eric; Sundström, Angelica Lodin; Limbu, Prakash; Schagatay, Erika

doi:10.3389/fphys.2019.01075

Cited by 13 publications

(41 citation statements)

References 36 publications

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“…However, the similar spleen contraction between SH and SL may indicate that some adaptation persists as a genetic predisposition to hypoxia tolerance in lowland Sherpa. Despite this, we found an overall association between resting spleen volume and spleen contraction, which has also been reported previously (Holmström et al, 2019).…”

Section: Figure 5 | (A)supporting

confidence: 81%

“…It could therefore be speculated that HA dwellers could benefit from a similar cardiovascular priority system, temporarily directing blood flow to vulnerable tissues during severe hypoxic stress (e.g., during work at HA). In line with this, it was recently found that the diving response, initiated by apnea at low altitude, was negatively associated with AMS symptoms and maintained SpO 2 at HA in non-acclimatized lowlanders (Holmström et al, 2019). Why then would the HA-tolerant Sherpa have a less developed diving response than lowlanders?…”

Section: Figure 5 | (A)mentioning

confidence: 79%

“…used to obtain the individual baseline spleen volume (Schagatay et al, 2012;Holmström et al, 2019). Spleen volume changes that occurred from apneas were calculated by comparing values obtained after apnea and after recovery with baseline volumes.…”

Section: Discussionmentioning

confidence: 99%

“…Taken together, these studies suggest that a pronounced spleen contraction could be adaptive at HA, by enhancing the overall oxygen-carrying capacity. Recently, spleen volume was also found to be negatively associated with acute mountain sickness (AMS), whereby non-acclimatized lowlanders at HA with bigger spleens developed less AMS symptoms compared to those with smaller spleens (Holmström et al, 2019). This indicates that individual spleen size affects tolerance to hypobaric hypoxia, just as it affects performance during apneic diving (Schagatay et al, 2012).…”

Section: Introductionmentioning

confidence: 99%

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Spleen Size and Function in Sherpa Living High, Sherpa Living Low and Nepalese Lowlanders

et al. 2020

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High-altitude (HA) natives have evolved some beneficial responses leading to superior work capacity at HA compared to native lowlanders. Our aim was to study two responses potentially protective against hypoxia: the spleen contraction elevating hemoglobin concentration (Hb) and the cardiovascular diving response in Sherpa highlanders, compared to lowlanders. Male participants were recruited from three groups: (1) 21 Sherpa living at HA (SH); (2) seven Sherpa living at low altitude (SL); and (3) ten native Nepalese lowlanders (NL). They performed three apneas spaced by a twomin rest at low altitude (1370 m). Their peripheral oxygen saturation (SpO 2), heart rate (HR), and spleen volume were measured across the apnea protocol. Spleen volume at rest was 198 ± 56 mL in SH and 159 ± 35 mL in SL (p = 0.047). The spleen was larger in Sherpa groups compared to the 129 ± 22 mL in NL (p < 0.001 compared to SH; p = 0.046 compared to SL). Spleen contraction occurred in all groups during apnea, but it was greater in Sherpa groups compared to NL (p < 0.001). HR was lower in Sherpa groups compared to NL both during rest (SL: p < 0.001; SH: p = 0.003) and during maximal apneas (SL: p < 0.001; SH: p = 0.06). The apnea-induced HR reduction was 8 ± 8% in SH, 10 ± 4% in SL (NS), and 18 ± 6% in NL (SH: p = 0.005; SL: p = 0.021 compared to NL). Resting SpO 2 was similar in all groups. The progressively decreasing baseline spleen size across SH, SL, and NL suggests a role of the spleen at HA and further that both genetic predisposition and environmental exposure determine human spleen size. The similar HR responses of SH and SL suggest that a genetic component is involved in determining the cardiovascular diving response.

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Section: Figure 5 | (A)supporting

confidence: 81%

Section: Figure 5 | (A)mentioning

confidence: 79%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Spleen Size and Function in Sherpa Living High, Sherpa Living Low and Nepalese Lowlanders

et al. 2020

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“…By necessity, a field study like this has restrictions on which laboratory equipment can be used, and has to rely on smaller monitors and often simpler methods than in a stationary laboratory, as all equipment has to be carried on the back to location, and the laboratory has to be rapidly mounted before tests can begin at every location. The data from the equipment in this study have, however, been compared to results obtained with more advanced monitors in stationary laboratories at high altitude (e.g., Holmström et al 2019) and been found to be in agreement.…”

Section: Study Limitationsmentioning

confidence: 63%

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

et al. 2020

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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.

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Larger spleens and greater splenic contraction during exercise may be an adaptive characteristic of Nepali Sherpa at high‐altitude

Brutsaert,

Harman,

Bigham

et al. 2024

American J Hum Biol

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ObjectivesThe Sherpa ethnic group living at altitude in Nepal may have experienced natural selection in response to chronic hypoxia. We have previously shown that Sherpa in Kathmandu (1400 m) possess larger spleens and a greater apnea‐induced splenic contraction compared to lowland Nepalis. This may be significant for exercise capacity at altitude as the human spleen responds to stress‐induced catecholamine secretion by an immediate contraction, which results in transiently elevated hemoglobin concentration ([Hb]).MethodsTo investigate splenic contraction in response to exercise at high‐altitude (4300 m; Pb = ~450 Torr), we recruited 63 acclimatized Sherpa (29F) and 14 Nepali non‐Sherpa (7F). Spleen volume was measured before and after maximal exercise on a cycle ergometer by ultrasonography, along with [Hb] and oxygen saturation (SpO2).ResultsResting spleen volume was larger in the Sherpa compared with Nepali non‐Sherpa (237 ± 62 vs. 165 ± 34 mL, p < .001), as was the exercise‐induced splenic contraction (Δspleen volume, 91 ± 40 vs. 38 ± 32 mL, p < .001). From rest to exercise, [Hb] increased (1.2 to 1.4 g.dl−1), SpO2 decreased (~9%) and calculated arterial oxygen content (CaO2) remained stable, but there were no significant differences between groups. In Sherpa, both resting spleen volume and the Δspleen volume were modest positive predictors of the change (Δ) in [Hb] and CaO2 with exercise (p‐values from .026 to .037 and R2 values from 0.059 to 0.067 for the predictor variable).ConclusionsLarger spleens and greater splenic contraction may be an adaptive characteristic of Nepali Sherpa to increase CaO2 during exercise at altitude, but the direct link between spleen size/function and hypoxia tolerance remains unclear.

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The Magnitude of Diving Bradycardia During Apnea at Low-Altitude Reveals Tolerance to High Altitude Hypoxia

Cited by 13 publications

References 36 publications

Spleen Size and Function in Sherpa Living High, Sherpa Living Low and Nepalese Lowlanders

Spleen Size and Function in Sherpa Living High, Sherpa Living Low and Nepalese Lowlanders

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

Larger spleens and greater splenic contraction during exercise may be an adaptive characteristic of Nepali Sherpa at high‐altitude

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