The effects of ultrasound on the cells of the vascular wall

Investigations into the safety of diagnostic ultrasound and mechanisms of therapeutic ultrasound have provided evidence of a number of cellular responses to ultrasound. These studies have mainly concentrated on cells in culture, while work on intact tissue employed mainly kHz ultrasound fields, although diagnostic and many therapeutic procedures are performed using MHz ultrasound. Vascular tissue is known to respond to a variety of physical and chemical signals, and so arteries were used as a model system in this thesis to study the effects of MHz ultrasound in vitro. Rings of equine carotid and lateral cecal mesenteric artery exhibited reversible, repeatable contraction on exposure to both pulsed and continuous wave 3.2 MHz ultrasound at acoustic powers up to 145 mW. Wall stress increased by up to 1.5% in carotid arteries and up to 2% in mesenteric arteries during exposure, and returned to basal levels after approximately 10 minutes. Contraction was endothelium independent, and was not affected by changes in the pulsing regime. The magnitude of contraction was dependent on the acoustic power, and the change in wall stress increased with increasing acoustic power in a linear fashion. The acoustic power dependence suggested the response was thermally mediated and this was confirmed by investigation of the response of arteries to non ultrasound generated heating, which also induced contraction. The effects of ultrasound and heating were also investigated in 1st order branches of the lateral cecal artery, as a model of a small artery. No response was observed in either case. In order to determine the cellular basis of the response of carotid and mesenteric arteries, the involvement of potassium ion channels in the response was investigated using a potassium channel blocker. The response of arteries to ultrasound was increased by inhibition of inward-rectifier potassium channels, which would otherwise help to return the cell membrane potential to the normal level. The change in wall stress was increased by 42% on average, confirming the involvement of these channels in the response. Contraction of arteries is mediated by an increase in intracellular calcium. The ion channel activity during non ultrasound generated heating was examined further by observation of intracellular calcium concentration using a fluorescent calcium sensitive dye. Increases in intracellular calcium were observed in carotid and large mesenteric arteries, which confirmed the thermal influence on ion channel function in these vessels. No such effect was observed in the smaller vessels.EThOS - Electronic Theses Online ServiceEPSRCGBUnited Kingdo

Broadband measurements of the frequency dependence of attenuation coefficient and velocity in amniotic fluid, urine and human serum albumin solutions

The frequency dependence of attenuation coefficient in amniotic fluid, urine and 4.5% and 20% human serum albumin solutions over the frequency range 5 MHz to 25 MHz was measured at both room temperature and physiological temperature using a variable path length technique. A 15 MHz (13 mm diameter) transducer was used to produce a broadband single-cycle pulse and a 4 mm diameter bilaminar polyvinylidene difluoride membrane hydrophone was used to detect the attenuated pulse. Standard time-of-flight measurement techniques were used to measure the acoustic velocity in the same fluid samples. At physiological temperature, the attenuation coefficients in amniotic fluid, urine and 4.5% and 20% human albumin solution were found to be 0.0053 f(1.65), 0.0047 f(1.67), 0.019 f(1.57) and 0.167 f(1.27) dB cm(-1), respectively, where f is in MHz. The velocities in amniotic fluid, urine and 4.5% human albumin solution at physiological temperature were found to be 1541.1 m s(-1) +/- 1.3 m s(-1), 1551.3 m s(-1) +/- 1.3 ms(-1) and 1547.3 m s(-1) +/- 1.0 m s(-1), respectively. The results provide unique data over the diagnostic and therapeutic ultrasonic frequency range that can be used as input data for theoretical models that attempt to simulate nonlinear pressure fields and temperature rises from medical ultrasonic transducers

Ultrasound-induced heating in a foetal skull bone phantom and its dependence on beam width and perfusion

The cooling effect of single and multiple perfusing channels has been measured in a model of human foetal skull bone heated by wide and narrow beams of simulated pulsed spectral Doppler ultrasound (US). A focussed transducer operating with a centre frequency of 3.5 MHz, that emitted pulses of 5.7 MUs duration with a repetition frequency of 8 kHz, was used. This produced a beam of power 100 ± 2 mW with –6 dB diameters of 3.1 mm and 7.8 mm at 9 cm and 6 cm, respectively, from the transducer face. Arterial perfusion was simulated by allowing distilled water to flow in a large single channel or a grid of fine channels near the heated bone target. This study has established that: 1. perfusion-induced cooling is significantly enhanced when the bone phantom is heated by a wide rather than a narrow beam; 2. irrespective of the US beam width, a grid of small channels is more effective in cooling a heated bone target than a single larger diameter channel with the same volume flow rate; 3. the measured temperature rise and rate of temperature rise support the prediction of inverse proportionality to the US beam width; and 4. the perfusion time constants determined in our phantom model are 2 to 30 times larger than that assumed for the thermal index (TIB) algorithm

An Enhancer Mutant of Arabidopsis salt overly sensitive 3 Mediates both Ion Homeostasis and the Oxidative Stress Response▿

The myristoylated calcium sensor SOS3 and its interacting protein kinase, SOS2, play critical regulatory roles in salt tolerance. Mutations in either of these proteins render Arabidopsis thaliana plants hypersensitive to salt stress. We report here the isolation and characterization of a mutant called enh1-1 that enhances the salt sensitivity of sos3-1 and also causes increased salt sensitivity by itself. ENH1 encodes a chloroplast-localized protein with a PDZ domain at the N-terminal region and a rubredoxin domain in the C-terminal part. Rubredoxins are known to be involved in the reduction of superoxide in some anaerobic bacteria. The enh1-1 mutation causes enhanced accumulation of reactive oxygen species (ROS), particularly under salt stress. ROS also accumulate to higher levels in sos2-1 but not in sos3-1 mutants. The enh1-1 mutation does not enhance sos2-1 phenotypes. Also, enh1-1 and sos2-1 mutants, but not sos3-1 mutants, show increased sensitivity to oxidative stress. These results indicate that ENH1 functions in the detoxification of reactive oxygen species resulting from salt stress by participating in a new salt tolerance pathway that may involve SOS2 but not SOS3