Nevertheless dobutamine infusion should not be considered equivalent to physical exercise. The increase in heart rate is usually lower than with exercise and useful clinical information such as duration of exercise, exercise capacity, and reproduction of clinical signs may not be obtained. 15 Measurements of different neuroendocrine factors is still involves many methodological problems. The method most commonly used to determine factor concentrations in plasma and tissue is radioimmunoassay. This method is very tedious to perform, especially for measurements of tissue levels, and is not suitable for routine clinical practice.
Much work remains for developing more rapid and simpler methods.
Furthermore, there are often special requirements concerning sample collection and storage. This reaction may continue in the tubes after the samples have been collected. The trend is that new substances are often considered to be very unstable. With time, the assays become more robust and more knowledge about that specific factor is available. This leads to that the requirements for sample collection and sample storage tend to become less strict.