Spleen Contraction During Sudden Eupneic Hypoxia Elevates Hemoglobin Concentration

Abstract

The spleen contracts progressively during moderate normobaric hypoxia exposure of 20 min, which elevates hemoglobin concentration (Hb). However, acute hypoxia exposure could be shorter and more severe when oxygen systems fail during, e.g., high-altitude sky diving, aircraft cabin pressure drop, balloon flights, extreme altitude climbing, and in some maladies. We aimed to evaluate the speed and magnitude of spleen contraction during short exposure to extreme eupneic hypoxia and its subsequent recovery on oxygen. Eight female and seven male volunteers were exposed to normobaric hypoxia (10% oxygen) for 10 min during sitting rest, followed by 10 min on 100% oxygen. Heart rate (HR), arterial oxygen saturation (SpO2), and mean arterial blood pressure (MAP) were measured continuously. The spleen was measured via ultrasonic imaging every minute for volume calculations, and venous blood samples were drawn before and after exposure for hemoglobin concentration (Hb). Mean (SD) spleen volume was 279 (115) mL before exposure, 219 (75) mL (21% reduction; P = 0.005) at 3 min of exposure, and 201 (93) mL after 10 min exposure to hypoxia (28% reduction; P < 0.001). Hb was 138.8 (7.6) g·L−1 before and 142.9 (8.1) g·L−1 after 10 min of exposure (2.9% increase; P < 0.001). SpO2 was 96.4 (1.7)% before exposure and 74.7 (8.4)% during the last minute of exposure (22.5% reduction; P < 0.001). HR increased from 80 (14) to 90 (17) bpm during exposure (12% increase, P < 0.05). MAP remained unchanged. After 10 min recovery on oxygen, values had been restored for spleen volume and Hb, while SpO2 was higher and HR lower compared with before hypoxia exposure. We concluded that acute normobaric hypoxia of only 10 min caused significant spleen volume contraction with Hb increase. This rapid spleen response, evident already after 3 min of exposure, could have a protective effect during sudden exposure to severe hypoxia.

Chemoreflex Control as the Cornerstone in Immersion Water Sports: Possible Role on Breath-Hold

“…Additionally, the aforementioned studies have mostly focused on autonomic and cardiovascular responses, thus excluding other organs that could contribute to the maintenance of oxygen saturation despite not experiencing ventilation. One of these organs could be the spleen, which has been shown to play an important role in the responses and adaptations to hypoxic training; however, studies of this organ in voluntary apnea conditions are extremely limited ( Engan et al, 2013 ; Pernett et al, 2021 ).…”

“…This reservoir of blood, which is delivered into the systemic circulation, is capable of contributing to maintaining oxygen saturation for a long time period, despite not experiencing pulmonary ventilation ( Bakovic et al, 2003 ; Richardson et al, 2008 ). Additionally, it can maintain hemoglobin levels during prolonged voluntary apnea or short-term exposure to eupneic normobaric hypoxia ( Bakovic et al, 2003 ; Richardson et al, 2008 ; Lodin-Sundström and Schagatay, 2010 ; Pernett et al, 2021 ). The blood contained in the spleen is released into the systemic circulation via splenic contraction, which is dependent on sympathetic activity ( Bakovic et al, 2013 ).…”

Splenic contraction and cardiovascular responses are augmented during apnea compared to rebreathing in humans

“…Previous studies have found effects from chemoreceptor stimulation on splenic contraction and associated hematological changes ( Pernett et al, 2021 ). Lodin-Sundström and Schagatay (2010) showed that apnea induced a significantly more pronounced splenic contraction than normobaric hypoxic breathing, at similar hypoxic stress, and suggested that hypercapnia or a faster development of hypoxia during apnea might explain the difference.…”

“…The splenic contraction is most likely related to an increase in sympathetic nervous activity, with the splenic nerve containing approximately 98% sympathetic nerve fibers ( Felten et al, 1985 ; Mignini et al, 2003 ). Splenic contraction can also be initiated by various other stressors associated with an increase in sympathetic activity ( Shephard, 2016 ), such as exercise ( Laub et al, 1993 ; Engan et al, 2014 ), normobaric hypoxic breathing ( Richardson et al, 2008 ; Pernett et al, 2021 ), and high-altitude exposure ( Schagatay et al, 2020 ; Holmström et al, 2021 ). The observations with normobaric hypoxic breathing and high-altitude exposure suggest that hypoxia could be a key stimulus for splenic contraction.…”

Eight weeks of dry dynamic breath-hold training results in larger spleen volume but does not increase haemoglobin concentration

“…Extensive studies of splenic and haematological reactions after apnoea have already been performed in the literature (Shephard et al, 2016;Elia et al, 2021;Pernett et al, 2021;Nordine et al, 2022). It has been proven that long-term static apnoea training increases both spleen volume and HGB (Bouten et al, 2019).…”