Pressure Threshold for Shock Wave Induced Renal Hemorrhage

Abstract

Studies were performed with an interest in determining a pressure threshold for extracorporeal shock wave induced renal damage. Histological evidence of intraparenchymal hemorrhage was used as an indicator of tissue trauma. Depilated C3H mice were anesthetized and placed on a special frame to enhance visualization and treatment of the kidneys in situ. A Wolf electrohydraulic generator and 9 French probe designed for endoscopic use were utilized to expose the kidneys to 10 double spherically divergent shock waves. Measurements of the shock waves revealed two positive pressure peaks of similar magnitude for each spark discharge. The kidneys were exposed to different peak pressures by choice of distance from the spark source and were removed immediately after treatment for histologic processing. A dose response was noted with severe corticomedullary damage apparent following 15 to 20 MPa shocks. Hemorrhage was more apparent in the medulla where evidence of damage could be seen following pressures as low as three to five MPa. When a latex membrane was interposed to prevent possible collapse of the initial bubble from the spark source against the skin surface, histological evaluation revealed substantial reduction of severe tissue damage associated with the highest pressures tested, 20 MPa. However, the threshold level for evidence of hemorrhage remained about three to five MPa. Hydrophonic measurements indicated that the membrane allowed transmission of the acoustic shock waves and suggested that collapse of the bubble generated by electrohydraulic probes may have local effects due to a cavitation-like mechanism.

Shear strain from irrotational tissue displacements near bubbles

“…Consider the following: (1) Exposure of mouse kidney to 200, 40 MPa, piezoelectric lithotripter shock waves caused only barely detectable superficial petechiae (Raeman et al, 1994). (2) Exposure of mouse kidney to ten, spherically diverging, 3 MPa shocks from a spark-generated bubble produced significant hemorrhage throughout both cortex and medulla (Mayer et al, 1990). In each example, peak positive pressures are cited.…”

Section 8--clinical relevance. American Institute of Ultrasound in Medicine.

“…This is true after birth only because in the human fetal state (as is true for all mammals), the lung and intestine are both fluid filled. Although to date, there are no clinical or experimental mechanical bioeffects data available for human lung or intestine (exclusive of incidental extracorporeal shockwave lithotripsy anecdotal data), a number of investigators have clearly demonstrated the occurrence of lung hemorrhage in a variety of mammalian models, as well as hemorrhage in mouse intestine from diagnostic ultrasound (Child et al, 1990;Zachary and O'Brien, 1995;Holland et al, 1996). Bioeffects in tissues with naturally occurring gas bodies are extensively reviewed in Section 4 together with a discussion of the theoretical basis for their occurrence and available experimental proof.…”

“…Incidental or deliberate exposure of the human lung occurs during a variety of specific ultrasound examinations, including routine and transesophageal echocardiography and chest wall, pleural space, diaphragm, and lung parenchymal evaluations; the intestine, however, is always exposed whenever an abdominal organ is examined and during most obstetrical and gynecologic studies. Using a variety of experimental models, a number of investigators have shown that the threshold acoustic pressure for lung hemorrhage across species is 1 MPa (Mechanical Index [MI] 0.5) with a weak correlation with frequency, pulse length, and total exposure time (Section 4) (Child et al, 1990;Raeman et al, 1996). At the present time, data are inconsistent as to whether there are age or species differences in the thresholds for lung hemorrhage, although animals may be grouped into those species with "thin" visceral pleura (mice, rats, rabbit, cats, dogs, and monkeys), which are more susceptible to lung hemorrhage, versus species with "thick" visceral pleura (sheep, pigs, humans, cattle, and horses) who may be relatively protected from mechanical bioeffects, as discussed in Section 3 (Frizzell et al, 1994;Zachary and O'Brien, 1995; Baggs et al, 1996;O'Brien and Zachary, 1996; Dalecki et al, 1997b Dalecki et al, , 1997a.…”

“…In many cases, these experimental ultrasound field conditions would be expected to enhance any bubble activity. For example, many bioeffects, including kidney tissue damage (Delius et al, 1988b(Delius et al, , 1988cMayer et al, 1990;Weber et al, 1992) and effects on or near bone (Delius et al, 1995;Dalecki et al, 1997b), have been reported following exposure to extracorporeal shock wave lithotripsy sources. These studies provide information under extreme ultrasound field conditions that have been used to guide research for bioeffects under ultrasound field conditions typically used in diagnostic applications.…”

Shock wave therapy of ischemic heart disease in the light of general pathology

“…1) is 100 bar (10 MPa). For comparison, cytoskeletal damage in vitro was demonstrated after the impact of 16 MPa [8]; peak pressure of 3-5 MPa was reported as a threshold for renal hemorrhage in mice whereas severe corticomedullary damage was seen after 15-20 MPa [9]; 10 MPa caused pulmonary bleedings in beagle dogs [10]. Moreover, hemodynamic forces (blood flow turbulence, hypertension) are known to cause endothelial dysfunction and to accelerate atherosclerosis [11].…”