Haemolysis of Red Blood Cells In Vitro and In Vivo Induced by Ultrasound at 0.75 MHz and at Therapeutic Intensity Levels

Abstract

The physical mechanisms by which ultrasound can modify or damage biological materials has been comprehensively discussed by Nyborg(1). These include microstreaming, thermal effects and a range of cavitation type phenomena. It is well known that an acoustically excited bubble can cause haemolysis of red cells(2). The shearing stresses on the red cells caused by associated microstreaming is sufficient to damage cell membranes. Release of haemoglobin causes changes in optical absorbance when the treated samples are subsequently measured by spectrophotometry. Nyborg(1) and others have remarked that there is little information on cavitation in bulk animal tissues which are characteristically opaque. The objective of the work described here was to direct ultrasound from an unmodified therapeutic generator (Sonacel, Rank Stanley, Cox, Ware, Hertfordshire, England) at the hearts of small animals in an attempt to detect or exclude haemolysis in vivo. The need for this investigation arises from the now widespread use of ultrasound as a therapeutic agent to treat a variety of conditions(3). Furthermore, there is considerable interest in the possibility of treating malignant tumors with focussed or overlapping ultrasound fields(4) with a view to producing local hyperthermia. Clearly it is vital to know if there are likely to be any untoward side-effects arising from such treatment.