science

Intermittent hypoxia

Intermittent hypoxia is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Intermittent hypoxia rather than just read about it. In short: Intermittent hypoxia (also known as episodic hypoxia) is an intervention in which a person or animal undergoes alternating periods of normoxia and hypoxia. Normoxia is defined as exposure to oxygen levels normally found in Earth's atmosphere (~21% O2) and hypoxia as any oxygen levels lower than those of normoxia.

Key takeaways

Intermittent hypoxia belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Intermittent hypoxia to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Intermittent hypoxia from memory before moving on to harder problems.

Reference excerpt

Intermittent hypoxia (also known as episodic hypoxia) is an intervention in which a person or animal undergoes alternating periods of normoxia and hypoxia. Normoxia is defined as exposure to oxygen levels normally found in Earth's atmosphere (~21% O2) and hypoxia as any oxygen levels lower than those of normoxia. Normally, exposure to hypoxia is negatively associated to physiological changes to the body, such as altitude sickness. However, when used in moderation, intermittent hypoxia may be used clinically as a means to alleviate various pathological conditions.

General mechanisms

When used as a rehabilitative intervention, particularly for respiration and walking, intermittent hypoxia typically works by using long-term facilitation (LTF). LTF, which is synonymous to long-term potentiation, occurs when there are long-term increases in synaptic strength due to synaptic plasticity. In the case of intermittent hypoxia, these increases in synaptic strength result in increased motor output. Reduced partial pressures of oxygen in the arteries due to intermittent hypoxia are sensed by and stimulate the carotid body, a chemoafferent receptor. The activated carotid body triggers the release of serotonin that attach to serotonin receptors on the surface of motoneurons, such as the phrenic motoneuron in the case of respiratory recovery. This signal transduction pathway then uses downstream molecules such as TrkB, BDNF, and PKA to increase the synaptic output of the involved motor neuron which in turn increases the motor output of the involved muscles and, thus, decreases functional impairment. As the amount of intermittent hypoxia changes the amount of serotonin release and, as a result, the amount of LTF, this process exhibits metaplasticity. Metaplasticity occurs when the LTF is itself plastic or variable. Intermittent hypoxia-induced LTF has also been demonstrated in carotid denervated rats, suggesting that synaptic plasticity due to intermittent hypoxia also works through other mechanisms outside of carotid chemoafferents. Aside from this, intermittent hypoxia also alters overall nitric oxide production, concentration, and gene expression, which occurs due to cardiovascular adaptations to hypoxia. This mechanism is relevant when used as a means to decrease hypertension or increase bone mineral density

Dosage

An understanding of proper dosage is needed in order to design an effective intermittent hypoxia protocol, particularly due to the comorbidities associated with hypoxia. For example, intermittent hypoxia has been shown to induce LTF in rats while continuous hypoxia does not. And acute IH shows no evidence of the hippocampal cell death found in rats while chronic intermittent hypoxia exposure does Though intermittent hypoxia has been used for various therapeutic applications across a number of physiological system, there is a general consensus in what can be considered a safe and beneficial amount of intermittent hypoxia. Such a protocol would involve a fraction of inspired oxygen (FiO2) ranging between 0.09 – 0.16 with 3 – 15 episodes per day with comorbidities found in the range of a FiO2 of 0.03 – 0.08 and 48 – 2400 episodes per day.

Pathological and beneficial effects

Therapeutic applications

Though intermittent hypoxia is initially involved with only the respiratory system, its downstream effects allow it to also be used as an effective rehabilitative intervention in a number of different biological systems in both animals and humans.

LTF For the respiratory system, the LTF facilitated by intermittent hypoxia aids in increasing phrenic motor nerve output. This has been shown to help people with obstructive sleep apnea and COPD. The ability to increase muscle activity, specifically for walking, has also been demonstrated in both rats and humans after spinal cord injury.

Hippocampal neurogenesis Hippocampal neurogenesis has also been demonstrated in rats subjected to intermittent hypoxia. This neurogenesis has shown related cognitive improvements such as enhanced learning and memory as well as overall increases in spatial cognitive ability. Additionally, antidepressant-like effects are exhibited in rats undergoing such treatment.

Nitric oxide production Nitric oxide level changes due to intermittent hypoxia also provide potential benefits. People with hypertension have shown decreases in blood pressure. Increases in bone mineral density in rats has also been attributed to this process. Such changes to nitric oxide levels also aid in protection from myocardial ischemia and perfusion.

See also Hypoxia (medical) Hypoxia (disambiguation) Intermittent hypoxic training

References

Illustrations

Intermittent hypoxia: COPD vs. healthy lung. — COPD vs. healthy lung.

Worked examples

Example 1 — a first encounter with Intermittent hypoxia

Start with the simplest possible case. Write down what Intermittent hypoxia claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Intermittent hypoxia before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Intermittent hypoxia ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Intermittent hypoxia

In research: Intermittent hypoxia appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Intermittent hypoxia in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Intermittent hypoxia is common in secondary-school and first-year university syllabi. It links to neighbouring topics Medical treatments, so understanding it makes those chapters shorter.
In everyday life: Look for Intermittent hypoxia outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

Affiliate

Preply — study more efficiently by working with a personal tutor. 50% off.

How to study Intermittent hypoxia in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Intermittent hypoxia means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Intermittent hypoxia out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Intermittent hypoxia in simple terms?

Why does Intermittent hypoxia matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Intermittent hypoxia?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Intermittent hypoxia.