Principles of Physiology for the Anaesthetist

Peter Kam, Ian Power

• Editore: CRC Press
• Anno: 2020
• ISBN:
  9781000061680
• Edizione: 4
• Argomento: Medicina
• Categoria: Teoría, práctica y referencia médicas

This book provides readers with an anaesthesia-focused alternative to general physiology textbooks. The new edition has been reorganised with the trainee anaesthesist in mind, into shorter bite-sized chapters ideal for exam revision. The content includes the physiology of all major organ systems, with specific emphasis on the nervous, respiratory, and cardiovascular systems as well as special sections on pain, aging, specific environments and obesity. Alongside the learning objectives, reflection points and a handy summary of physiological equations and tables, there is greater emphasis on clinical application in this fourth edition, with applied physiology included in almost every section.

Section Sixteen

Special Environments

Chapter 77

Physiology Related to Special Environments

Physiology of Diving

Life under water exposes the diver to a major rise in ambient pressure of the environment, with physiological changes and problems from the direct effects of pressure on the body. In addition, the diver must be supplied with a mixture of gases to breathe at a pressure equal to ambient pressure, and this can also give rise to other problems.

Physical laws

As the SI unit for pressure (N/m2 [pascals]) is small, the ‘bar’ has been used for ambient pressures. One bar is equal to 105 N/m2, 750 mmHg and approximately 1 atmosphere (atm). However, in the diving industry, pressure is described in terms of depth in sea water, metres of sea water (msw). For every 10 m under sea water (density, 1.025), there is an increase in ambient pressure of about 1 bar. Thus, assuming that normal atmospheric pressure is 1 bar, at a depth of 50 msw the ambient pressure is 6 bar.

Three physical principles must be used to understand the physiological as well as the pathophysiological effects of life under water. Gases are compressible and follow Boyle’s law. During a breath-hold dive, as the volume of a gas is inversely related to its pressure for a given mass of gas at constant temperature, the volume of air in the lungs decreases with increasing depth and ambient pressure.

As the pressure of the gas increases, its density (mass per unit volume) increases. According to Dalton’s law, an increase in the total gas pressure is ...