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Biomedical subjects

R L Powis

Publications and source records attributed to R L Powis.

7 recordsLinked to original sources
PubMed1994

Color flow imaging.

The most recent technology change in diagnostic ultrasound is color flow imaging (CFI), which is a merging of gray-scale and motion-detection processing to produce an image that depicts soft tissue in gray scale and blood flow in color. Currently, CFI comes in three forms: synchronous signal processing, asynchronous signal processing, and time domain analysis. The first two employ Doppler-based principles, and the third uses direct measurements of blood flow displacement in the image. All three forms of CFI break the image into multiple sampling segments and process amplitude and motion information. A functional understanding of these technologies helps define and extend their roles in radiology as imaging tools.

Blood Flow Velocity↗
PubMed1986

Recent advances in imaging and evaluation of blood flow using ultrasound.

Use of ultrasound for noninvasive evaluation of the vascular system is now commonplace. A new imager has been developed that depicts Doppler images (moving structures) and B-mode images (nonmoving structures) on the same image screen. The new instrument and its potential for clinical use are described.

Blood Circulation↗
PubMed1986

Ultrasound science for the veterinarian.

In order to successfully sort out the information, both real and bogus, in an ultrasonic image, one must have a fundamental understanding of the physical and electronic events that produced the image. We have looked at the basic science, signal processing, some case examples of ultrasound science in practice, and some popular illusions. It is a good starting place for the newcomer to ultrasonic imaging.

Animals↗
PubMed1975

Growth hormone in cardiac hypertrophy induced by nephrogenous hypertension.

Current evidence about the role of growth hormone in cardiac hypertrophy is ambiguous. The purpose of this investigation was to determine whether growth hormone was an important element in the cardiac hypertrophy induced by systemic hypertension. Male rats with either an intact hypophysis or a hypophysectomy were bilaterally adrenalectomized, and corticoids were replaced with exogenous deoxycorticosterone and hydrocortosone. Hypophysectomized rats were further treated with thyroxine, testosterone, and, where appropriate, bovine growth hormone. Selected groups of rats were made hypertensive by means of a surgical compression of the renal capsule which produced systemic hypertension. The magnitude of the hypertension was measured in awake rats by means of a tail plethysmograph and compressing tail-cuff. The hormone replacement program re-established systolic blood pressures in sham-operated, hypophysectomized rats to levels observed in intact-hypophysis, sham-operated rats. Thus, hypertensive, hypophysectomized rats obtained pressures above both hypophysectomized and intact-hypophysis, sham-operated rats. Hypertensive rats with an intact hypophysis and hypophysectomized rats with growth hormone developed cardiac hypertrophy. In spite of the hormone therapy, the above normal systemic blood pressures, and low mortality hopophysectomized rats without growth hormone did not develop cardiac hypertrophy.

Animals↗
PubMed1975

The influence of growth hormone on myocardial weight and water fraction in rats.

While conducting experiments on the role of growth hormone in cardiac hypertrophy, data were also gathered on the influence of growth hormone on myocardial wet and dry weight in relation to body weight and myocardial water fraction. Male rats with either in intact hypophysis or a hypophysectomy were bilaterally adrenalectomized, and corticoids were replaced with deoxycorticosterone and hydrocortisone therapy. Hypophysectomized rats were further treated with thyroxine, testosterone, and, where appropriate, bovine growth hormone. The hormone replacement program re-established systolic blood pressure in hypophysectomized rats to levels observed in intact-hypophysis rats. The left ventricle weight (wet and dry)/body weight ratio was used as an indication of relative myocardial weight. Hypophysectomized rats without growth hormone were observed to have higher left ventricle weight/body ratios than both hypophysectomized rats with growth hormone and intact-hypophysis rats. Further, rats without growth hormone were determined to have a lower myocardial water content than rats with growth hormone. Mathematical analysis established that the relationship between myocardial water fraction and ventricular wet weight is nonlinear. This relationship shows that small changes in water fraction can produce large changes in ventricular wet weight. The reasons for the different water content in the myocardium were not further investigated.

Animals↗