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Related Concept Videos

Requirements for Human Life01:26

Requirements for Human Life

The Earth and its atmosphere have provided humans with air, water, and food, but these are not the only requirements for survival. Humans also require a specific range of temperature and pressure that the Earth and its atmosphere provides.
Oxygen
Atmospheric air is only about 20 percent oxygen, but that oxygen is a key component of the chemical reactions that keep the body alive, including the reactions that produce ATP. Brain cells are susceptible to a lack of oxygen because they require a...
Hyperpnea and Hyperventilation01:25

Hyperpnea and Hyperventilation

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...
Acute Respiratory Failure-II01:21

Acute Respiratory Failure-II

Type I Respiratory Failure, or hypoxemic respiratory failure, occurs when the partial pressure of oxygen (PaO2) in arterial blood falls below 60 mmHg while breathing room air without a corresponding increase in arterial carbon dioxide levels (PaCO2). This condition highlights a significant impairment in the lungs' capacity to oxygenate the blood.
The underlying physiological abnormalities that contribute to hypoxemic respiratory failure include:
Acute Respiratory Failure-III01:30

Acute Respiratory Failure-III

Hypercapnic respiratory failure, also known as Type 2 or ventilatory respiratory failure, is a severe condition characterized by the body's inability to effectively remove carbon dioxide (CO2) from the bloodstream. It leads to an arterial CO2 pressure (PaCO2) exceeding 45 mmHg and a blood pH above 7.35. This situation indicates that the body's ventilatory demand, or the ventilation needed to maintain normal PaCO2 levels, surpasses its supply or the maximum gas flow achievable without causing...
Acute Respiratory Failure-IV01:23

Acute Respiratory Failure-IV

Respiratory failure can manifest suddenly or gradually, characterized by a rapid decline in PaO2 and a rapid rise in PaCO2. This situation indicates a severe respiratory problem that may quickly become a life-threatening emergency. One of the early signs of hypoxemic Acute Respiratory Failure (ARF) is a change in mental status due to the brain's sensitivity to oxygen levels and changes in acid-base balance. Symptoms such as restlessness, confusion, and agitation suggest inadequate oxygen...
Pneumothorax-I01:26

Pneumothorax-I

A pneumothorax is a condition where air builds up in the space between the lung and the chest wall, causing the lung to collapse. This condition arises when air enters the space between the parietal and visceral pleura, disrupting the negative pressure essential for lung inflation. This can lead to a partial or complete collapse of the lung.
Pneumothorax can be even further classified as spontaneous, traumatic, and tension pneumothorax.

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Related Experiment Video

Updated: Jul 13, 2026

A Model to Simulate Clinically Relevant Hypoxia in Humans
09:54

A Model to Simulate Clinically Relevant Hypoxia in Humans

Published on: December 22, 2016

An abrupt zero-preoxygenation altitude threshold for decompression sickness symptoms

J T Webb1, A A Pilmanis, R B O'Connor

  • 1KRUG Life Sciences Inc., San Antonio, TX 78214, USA.

Aviation, Space, and Environmental Medicine
|April 30, 1998
PubMed
Summary

This study determined the altitude threshold for decompression sickness (DCS) symptoms, finding a 5% incidence at 20,500 ft. This suggests current aerospace altitude exposure guidelines may need revision for enhanced safety.

Keywords:
NASA Discipline Environmental HealthNon-NASA Center

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Preoxygenation Techniques for Tracheal Intubation in Critically Ill Adults Utilizing Oxygen Mask and Noninvasive Ventilation
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Area of Science:

  • Aerospace Medicine
  • Physiology
  • Environmental Health

Background:

  • Decompression sickness (DCS) symptom thresholds vary widely, from 18,000 to over 25,000 ft.
  • Precise DCS threshold determination is crucial for aerospace operational safety and efficiency.

Purpose of the Study:

  • To establish a more accurate altitude threshold for the onset of DCS symptoms.
  • To evaluate the relationship between simulated altitude exposure and DCS incidence.

Main Methods:

  • 124 male subjects were exposed to simulated altitudes ranging from 11,500 ft to 25,000 ft for 4-8 hours, breathing 100% oxygen.
  • Monitoring included precordial venous gas emboli (VGE) and DCS symptoms.
  • Probit analysis was used to estimate the risk of DCS and VGE at different altitudes.

Main Results:

  • Venous gas emboli (VGE) were detected starting at 15,000 ft, with incidence increasing significantly at higher altitudes.
  • A 5% incidence of DCS symptoms was observed at 21,200 ft.
  • DCS incidence sharply rose to 55% at 22,500 ft.

Conclusions:

  • The study concluded a 5% DCS symptom threshold at 20,500 ft under the tested conditions.
  • The rapid increase in DCS symptoms above 21,200 ft necessitates a review of current USAF and FAA altitude exposure guidelines.