CARDIOVASCULAR MEASUREMENTS IN ANIMALS IN THE MILLIGRAM RANGE

The study of microscopic animals should be intensified because: most o f the world's animal biomass consists of very small animals; life as a small animal is both qualitatively and quantitatively very different from that of a large animal; and almost all animals are very small as they begin their development. Fortunately, developing technology now a llows us to make quantitative measurements in microscopic animals. Thi s paper describes new techniques for measuring cardiovascular variable s such as blood pressure, stroke volume, heart rate and cardiac output in animals weighing as little as a few mg, Non-invasive techniques su ch as videomicroscopy can be used for determining heart stroke volume in small animals. Impedance measurement is another non-invasive or min or invasive technique for determining rates of heart beat, gill or lun g ventilation and limb movement as well as giving qualitative informat ion on changes in blood flow. Pulsed Doppler technology can be used to obtain blood flow velocity in small vessels, Invasive techniques depe nd on servo-null micropressure systems that record pressure through gl ass microelectrodes that are implanted into the vessel or heart lumen. This allows stable pressure recordings for up to 5-6 h in animals wei ghing as little as a few mg, Microinjectors can be used for intravascu lar injections of vasoactive drugs (or blood withdrawals). Newly emerg ing techniques for in vivo cardiovascular measurements allow us to und erstand the function of the cardiovascular system in a larger portion of the world's animal biomass, as well as in the immature and as yet p oorly understood early developmental stages of animals.