Sandra L Poliachik | PubMed Health

PubMed2004

The relation between cavitation and platelet aggregation during exposure to high-intensity focused ultrasound.

Our previous study showed that high-intensity focused ultrasound (HIFU) is capable of producing "primary acoustic hemostasis" in the form of ultrasound (US)-induced platelet activation, aggregation and adhesion to a collagen-coated surface. In the current study, 1.1 MHz continuous-wave HIFU was used to investigate the role of cavitation as a mechanism for platelet aggregation in samples of platelet-rich plasma. A 5 MHz passive cavitation detector was used to monitor cavitation activity and laser aggregometry was used to measure platelet aggregation. Using spatial average intensities from 0 to 3350 W/cm2, the effects of HIFU-induced cavitation on platelet aggregation were investigated by enhancing cavitation activity through use of US contrast agents and by limiting cavitation activity through use of an overpressure system. Our results show that increased cavitation activity lowers the intensity threshold to produce platelet aggregation and decreased cavitation activity in the overpressure system raises the intensity threshold for platelet aggregation.

Albumins↗

PubMed2004

Why rest stimulates bone formation: a hypothesis based on complex adaptive phenomenon.

Moderate exercise is an ineffective strategy to build bone mass. The authors present data demonstrating that allowing bone to rest between each load cycle transforms low- and moderate-magnitude mechanical loading into a signal that potently induces bone accretion. They hypothesize that the osteogenic nature of rest-inserted loading arises by enabling osteocytes to communicate as a small world network.

Adaptation, Physiological↗

PubMed2003

Enabling bone formation in the aged skeleton via rest-inserted mechanical loading.

The mild and moderate physical activity most successfully implemented in the elderly has proven ineffective in augmenting bone mass. We have recently reported that inserting 10 s of unloaded rest between load cycles transformed low-magnitude loading into a potent osteogenic regimen for both adolescent and adult animals. Here, we extended our observations and hypothesized that inserting rest between load cycles will initiate and enhance bone formation in the aged skeleton. Aged female C57BL/6 mice (21.5 months) were subject to 2-week mechanical loading protocols utilizing the noninvasive murine tibia loading device. We tested our hypothesis by examining whether (a) inserting 10 s of rest between low-magnitude load cycles can initiate bone formation in aged mice and (b) whether bone formation response in aged animals can be further enhanced by doubling strain magnitudes, inserting rest between these load cycles, and increasing the number of high-magnitude rest-inserted load cycles. We found that 50 cycles/day of low-magnitude cyclic loading (1200 microepsilon peak strain) did not influence bone formation rates in aged animals. In contrast, inserting 10 s of rest between each of these low-magnitude load cycles was sufficient to initiate and significantly increase periosteal bone formation (fivefold versus intact controls and twofold versus low-magnitude loading). However, otherwise potent strategies of doubling induced strain magnitude (to 2400 microepsilon) and inserting rest (10 s, 20 s) and, lastly, utilizing fivefold the number of high-magnitude rest-inserted load cycles (2400 microepsilon, 250 cycles/day) were not effective in enhancing bone formation beyond that initiated via low-magnitude rest-inserted loading. We conclude that while rest-inserted loading was significantly more osteogenic in aged animals than the corresponding low-magnitude cyclic loading regimen, age-related osteoblastic deficits most likely diminished the ability to optimize this stimulus.

Age Factors↗