Physics in anaesthesia

This chapter covers the basic science of physics relevant to anaesthetic practice. Equipment and measurement devices are covered elsewhere. Starting with fundamentals, atomic structure is introduced, followed by dimensions and units as used in science. Basic mechanics are then discussed, focusing on mass and density, force, pressure, energy, and power. The concept of linearity, hysteresis, and frequency response in physical systems is then introduced, using relevant examples, which are easy to understand. Laminar and turbulent fluid flow is then described, using flow measurement devices as applications of this theory. The concept of pressure and its measurement is then discussed in some detail, including partial pressure. Starting with the kinetic theory of gases, heat and temperature are described, along with the gas laws, critical temperature, sublimation, latent heat, vapour pressure and vaporization illustrated by the function of anaesthetic vaporizers, humidity, solubility, diffusion, osmosis, and osmotic pressure. Ultrasound and its medical applications are discussed in some detail, including Doppler and its use to measure flow. This is followed by an introduction to lasers and their medical uses. The final subject covered is electricity, starting with concepts of charge and current, voltage, energy, and power, and the role of magnetism. This is followed by a discussion of electrical circuits and the rules governing them, and bridge circuits used in measurement. The function of capacitors and inductors is then introduced, and alternating current and transformers are described.