Effects of Hydrostatic Pressure on the Human Body

Learning Objectives

1. To understand what hydrostatic pressure is.
2. To understand how hydrostatic pressure affects the human body, especially during deep diving.
3. To learn about the various equipment and measures that can be taken to prevent or cure the effects to the body caused by hydrostatic pressure.

What is Hydrostatic Pressure

Hydrostatic refers to the pressure exerted by a fluid at equilibrium due to gravity.

The most noticeable effect on a diver is the ability for his lungs to deflate. As the rest of the body is composed of solids and liquids which are relatively incompressible, the changes to the lung capacity when the diver is under pressure is the most obvious. The pressure acting on the diver's body is equal to the weight of the air in the atmosphere in a vertical column above the diver, and the weight of the seawater in the vertical column above the diver. This can be determined by multiplying the density of the water by the height of the fluid above the diver's body to the surface, and the gravitational field strength.

How to determine how long and at what depth to stay under water without making any decompression stops?
X + Y less than 50
X – depth (meters), Y – time (minutes)
Examples: 15 meters – up to 35 minutes (15+35=50), 20 meters – 30 minutes, 35 meters – 15 minutes.
WARNING: This concerns measures in meters and minutes only!

Remember: Up to 13 meters of depth, no-decompression dives are unrestricted in terms of time

Below are some of the diseases that can be acquired when diving
Lack of oxygen; the partial pressure of oxygen falls below 120 mm Hg
Improper handling of pure-oxygen apparatus; If oxygen is not 100 % pure because of a mistake, nitrogen will remain after the consumption of O2. The diver cannot realize the difference and loses consciousness.
Good mood, jauntiness without reason;
Later – dizziness, suffocation, blackout
The patient should be given pure oxygen to breathe; artificial respiration, outer irritation (slaps, amonia under the nose)
Oxygen excess;
partial pressure of oxygen exceeds 360 mm Hg
7 m – the process of receiving O2 and releasing CO2 is hindered;
13 m – this process stops so that cells cannot accept oxygen despite of its abundance;
at first – discomfort, nausea, spasms of lips and eyelids, disturbances in eyesight, sleepiness;
later – stiffness of muscles, convulsions (similar to the epileptic ones), blackout, death
The diver should be taken out to breathe fresh air.
CO2 toxicity - the partial pressure of CO2 is higher than normal;
Improper use of pure-oxygen-apparatus; not working absorber
Rapid pulse rate, shortness of breath and rapid heart beat, rapid respiration, headache, blackout
Artificial respiration;
Access to fresh air;

High pressure nervous syndrome;
This is due to overexcitement of the central nervous system caused by the increased water pressure. It occurs at depths exceeding 350 meters.
Dizziness, nausea, tremors, loss of dexterity and memory
Prevention is the best treatment.
Stage compression with long pauses;
Add N to the breathing mixture to become trimix (He, O2, N)
Decompression Sickness
The formation of gas bubbles in the organism during ascent is called decompression sickness, known also as “the bends”.

They occur 5 minutes to 1 hour after the ascent, sometimes after 2-4 hours. Symptoms range cough, itching, reddened skin or pains in the joints to serious respiratory, cardiac and mental damage (such as rapid pulse and heart beat, shortness of breath, pains in the chest and stomach, paralysis of limbs)

The only remedy to do away with decompression sickness is the chamber for recompression. The diver is exposed to the same pressure (at which he was before the beginning of bubbles’ formation), necessary to dissolve the bubbles. Afterwards, the pressure decreases on stages to avoid decompression sickness.

Energetic movements, vigorous massages and hot baths (38 C) are recommended to the patient.