A study was carried out on the effects of decreasing mean arterial pressure on the statistical structure of 1st-, 2nd-and 3rd-order pressure waves in various large vessels of anaesthtized, artificially respirated dogs. Mean pressure was lowered by controlled bleeding producing 20 mmHg pressure steps with 30 min duration, or a hemorrhagic shock-model. It was found that decreases in mean pressure elicited profound changes in wave structure. Relative magnitude of stochastic 1st-order (pulsatile) wave components and amplitude of 1st Fourier-harmonics exhibited a U-shape dependence on mean pressure in the 160-90 mmHg range with minimum values at around 100-110 mmHg mean pressure. Changes in thes components became unpredictable after prolonged hypotension. Stochastic pulse pressure components were relatively larger in iliac artery than in ascending aorta or caval vein. In the case of 2nd-order (respiratory) waves the power-density of central venous pressure was most dependent on mean arterial pressure. 3rd-order waves predominantly consisted of random-like components. Their dominant frequency, as well as periodicity decreased when mean pressure was lowered, but as circulatory shock-state became more and more grave the dominant frequency usually disappeared, the spectrum became steady noise-like.
|Number of pages||12|
|Publication status||Published - Jan 1 1978|
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