Measurement of cardiac output using Transonic® flow probes
Measurements of cardiac output in animal models is often overlooked, but vital in determining if a treatment has lowered blood pressure because of vasodilation, or if it is simply a consequence of throwing the subject into heart failure.
As anesthesias, virtually ALL of them, promote a dramatic reduction in cardiac output, it is optimal to measure the cardiac output in awake chronically instrumented models.
Major Disadvantages of other techniques
1. Electromagnetic flow probes can accurately measure flow, but they are bulky and unsuitable for use small animals.
2. Doppler probes are flexible and easier to implant, but they still require substantial surgical skills to implant and are limited to measuring velocity. Consequently they are of limited use for long-term monitoring of flow, or for use in models which display impairments in healing or immunosuppression.
3. Transonic® flow probes are small, they can be used to precisely measure true flow, and they quite suitable for chronic implants. However, one should bear in mind that they are still invasive and may be unsuitable in certain models of compromised healing.
The basic placement of the probe is illustrated at the top. The thin flexible cables are then tunneled subcutaneously and exit at the nape of the neck via a needle wound. The animals are given at least four days before beginning measurements.
The resulting traces are SPECTACULAR, and exceptionally accurate.
The additional fitting with a chronic aortic catheter (as above) will allow the silmutaneous measurements of arterial pressure, cardiac output and heart rate in the awake animal so that one can use the well established equation:
arterial pressure = cardiac output x total peripheral resistance
stroke volume = cardiac output / heart rate
...to calculate all parameters, stroke volume, total peripheral resistance, cardiac output and mean arterial pressure in an awake model.