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Hyperpnea and Hyperventilation

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Hyperventilation refers to a higher-than-normal rate and depth of breathing, often associated with anxiety attacks. This excessive breathing surpasses the body's need to expel CO2, leading to a condition known as hypocapnia - an unusually low level of carbon dioxide in the blood. Hypocapnia can constrict cerebral blood vessels, reducing blood flow to the brain, which may result in dizziness or fainting. Early signs include tingling and muscle spasms in the hands and face, caused by falling...

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Updated: Jun 18, 2026

Standardized Hemorrhagic Shock Induction Guided by Cerebral Oximetry and Extended Hemodynamic Monitoring in Pigs

Standardized Hemorrhagic Shock Induction Guided by Cerebral Oximetry and Extended Hemodynamic Monitoring in Pigs

Published on: May 21, 2019

Fainting in animals.

J Gert van Dijk¹

¹Department of Neurology & Clinical Neurophysiology, Leiden University Medical Centre, PO Box 9600, 2300 RC, Leiden, The Netherlands. j.g.van_dijk.neur@lumc.nl

Clinical Autonomic Research : Official Journal of the Clinical Autonomic Research Society

|September 5, 2003

Summary

This summary is machine-generated.

Human fainting, or syncope, is linked to circulatory issues. Comparative animal physiology suggests evolutionary factors, not just posture, contribute to human fainting, with emotional triggers potentially unique to humans.

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Area of Science:

Comparative physiology
Human physiology
Animal physiology

Background:

Syncope (fainting) is unconsciousness from temporary systemic circulation failure impacting cerebral blood flow.
Understanding human syncope can be enhanced by examining animal physiology and fainting mechanisms.

Purpose of the Study:

To discuss fainting in animals.
To explore animal physiology to broaden the understanding of human fainting.

Main Methods:

Comparative analysis of syncope types (cardiac, orthostatic, reflex) across species.
Evaluation of physiological challenges related to posture and circulation in humans and animals.
Investigation of evolutionary factors potentially contributing to human fainting tendencies.

Main Results:

Only cardiac syncope occurs in both animals and humans, stemming from arrhythmia or output failure.
Animals with significant gravitational circulatory challenges (e.g., giraffes) do not appear to faint, challenging posture-based explanations for human syncope.
Human fainting may be influenced by a larger proportion of cardiac output directed to the brain and venous pooling in legs, alongside emotional factors.

Conclusions:

Human fainting is not solely explained by upright posture; evolutionary adaptations are likely significant.
Emotional fainting might be a uniquely human phenomenon requiring further investigation into the mind-circulation connection.
Further research into how mental processes affect circulation is crucial for syncope prevention strategies.