A "Small Vessel Wire Myograph" was introduced by Professor M. J. Mulvany and Professor W. Halpern in 1976. The Wire Myograph allows examination of small vessels (internal diameter 100µm - 3 mm.) in terms of morphology and responsiveness to hormones and other agonists.

The small vessels are mounted as ring preparations by threading them onto two steel wires and securing the wires to two supports. One support is then attached to a micrometer, allowing control of vessel circumference. The other support is attached to a force transducer for measurements of tension development. The whole preparation is kept in a chamber with physiological salt solution at 37°C, bubbled with oxygen. In the chamber the vessels are viable for more than 12 hours.

Following mounting and equilibration, the passive length-tension relationships of the vessels are determined, a so-called normalization. During the actual experiments, the circumference of the vessels are kept constant, i.e. the vessels are examined under isometric conditions. Compounds are added directly to the chamber and vessel tension is monitored for possible contractile or relaxant effects of the compound. Furthermore it is possible to compare vessels from patients with those of control, not only in terms of vessel reactivity to various compounds, but also in terms of morphology. In a Dual Wire Myograph System two vessels can be mounted in one chamber, e.g. allowing comparative studies of vessels from patients with those of control exposing the vessels to identical concentrations of various compounds. It is thus possible to examine whether a given pathological state is associated with altered morphology or reactivity to endogenous compounds. It is also possible to examine whether drugs are able to normalize vessel reactivity. The Myograph is well-suited for investigations of effects of new drugs on vessel reactivity.

The Multi Myograph System

For work requiring a higher throughput, such as drug screening, or in experiments where separation of vessels in separate baths are necessary, the Multi Myograph has been developed. It consists of four simple, single vessel myographs in a compact rack, and has a separate electronic unit. Two kinds of supports are available, for either small or large vessels. With this equipment, myograph work can be performed in a manner equivalent to that of traditional organ-bath experiments.

The Pressure Myograph System

The range of Myographs is complemented by the Pressure Myograph System, where vessels are cannulated at both ends and examined under true distending pressure. Diameter is measured continuously by a PC workstation connected to a microscope. The intravascular pressure and the pressure gradient along the vessel can be controlled precisely, and longitudinal force in the segment is measured continuously. For experiments with high demands on physiological conditions, this set-up allows detailed examination of the influence of transmural pressure and luminal flow on vascular reactivity.