Spontaneous oscillation of the systemic arterial pressure during cardiopulmonary bypass in man. The effects of some drugs used during the operation

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Abstract
Despite the fact that the blood flow maintained during cardiopulmonary bypass is rather steady in the extracorporeal pump output, the arterial pressure under high-dose fentanly anaesthesia quite often shows sinusoidal oscillations. In the present study the duration of an oscillatory cycle was on average 17.6±3.6 s, its amplitude 7.3±1.6 mm Hg and mean systemic arterial pressure 75±12 mm Hg. The oscillation is affected by the drugs used under bypass conditions. In our series of clinical observations the blood pressure oscillation disappeared under the influence of chlorpromazine, phentolamine, droperidol, and enflurane, and it disappeared or at least was distinctly attenuated under fentanyl, thiopental, diazepam, sodium nitroprusside, nitroglycerine, acebutolol, and potassium chloride. Pancuronium, atropine and furosemide appeared to be practically incffective. In spite of the fact that the drugs used affected several sites of the sympathetic efferent chain, the disappearance and attenuation of the oscillation were associated with a simultaneous decrease of blood pressure. Hence, it is suggested that the occurrence of the oscillations requires some level of peripheral vascular tone.