Physiological Responses to Acute and Chronic Hypoxia

The physiological response to reduced oxygen availability unfolds across temporal scales. Acute hypoxia provokes immediate cardio-respiratory adjustments driven by peripheral chemoreceptors in the carotid bodies, resulting in increased ventilation, heart rate and redistribution of blood flow to vital organs. Concurrently, there is a shift towards anaerobic metabolism and early activation of intracellular sensors such as hypoxia-inducible factors, AMP-activated protein kinase and reactive oxygen species signalling, which modulate mitochondrial efficiency and ATP turnover. If hypoxia persists, ventilatory acclimatisation ensues, characterised by sustained hyperventilation and blunted peripheral chemoreceptor sensitivity. Over days to weeks, haematological adaptations such as erythropoiesis enhance oxygen-carrying capacity, while vascular remodelling and angiogenesis improve tissue perfusion. Chronic exposure further triggers metabolic reprogramming in key organs, endocrine adjustments including alterations in thyroid and adrenal hormones, and changes in thermoregulatory set-points. These integrated mechanisms allow organisms from small heterothermic mammals to high-altitude dwellers to tolerate low-oxygen environments, with profound implications for human health, high-altitude physiology, critical care medicine and our understanding of evolutionary adaptations to hypoxia.

Research from Nature Portfolio

Recent studies have shown that highly hypoxia-tolerant mammals can rapidly down-regulate heat production to conserve oxygen. In one investigation, non-shivering thermogenesis in brown adipose tissue was almost completely abolished within hours of exposure to severe hypoxia. This occurred through a marked decrease in UCP1 protein abundance, fragmentation of the mitochondrial network and alterations in respiratory-chain complexes, revealing an evolved strategy to reduce metabolic demand under acute oxygen deprivation.

Physiological Responses to Acute and Chronic Hypoxia publication trend

The graph below shows the total number of articles in physiological responses to acute and chronic hypoxia across all publications each year (not limited to Nature Index journals).

Technical terms

Acute hypoxia: A rapid onset of low oxygen availability, typically initiating immediate respiratory and cardiovascular reflexes.

Chronic hypoxia: Sustained exposure to reduced oxygen levels over days to weeks, leading to long-term haematological and vascular adaptations.

Non-shivering thermogenesis: Heat production by brown adipose tissue via mitochondrial uncoupling, independent of muscle activity.

Hypoxic ventilatory response (HVR): The increase in ventilation triggered by low arterial oxygen sensed primarily by carotid body chemoreceptors.

Metabolic reprogramming: Cellular and systemic shifts in energy substrate use and enzyme activity to optimise ATP production under hypoxia.

References

1. Naked mole-rat brown fat thermogenesis is diminished during hypoxia through a rapid decrease in UCP1. Nature Communications (2021).
2. Metabolomic Analysis of Carbohydrate and Amino Acid Changes Induced by Hypoxia in Naked Mole-Rat Brain and Liver. Metabolites (2022).
3. Physiological responses to hypoxia are constrained by environmental temperature in heterothermic tenrecs. Journal of Experimental Biology (2023).
4. Hypoxia impairs blood glucose homeostasis in naked mole-rat subordinate adults but not queens. Journal of Experimental Biology (2024).