Biomedical subjects

J Holen

Publications and source records attributed to J Holen.

21 records · Page 2Linked to original sources

PubMedDate not supplied

CW and pulsed Doppler echocardiography utilizing a stand-alone system.

An independent directional Doppler system operating in pulsed or continuous-wave mode and a real-time spectral analyzer with a 3 ms temporal resolution have been used to supplement conventional real-time and M-mode echocardiography. Examination techniques as well as findings in normal and abnormal hearts are presented. Continuous-wave Doppler is most useful for detection of peak frequency shifts for calculation of valvular gradients while pulsed Doppler is superior in the detection of small jets of abnormal flow and in display of spectral broadening. Real-time spectral analysis allows interactive selection of peak frequency shifts, can separate coincident flows by signal intensity and depicts high frequency valvular movements to rival the capabilities of M-mode.

Aortic Valve Insufficiency↗

PubMedDate not supplied

Doppler ultrasound in orifice flow. In vitro studies of the relationship between pressure difference and fluid velocity.

The validity of an orifice equation (Torricelli's law) which expresses a simple relationship between the pressure difference across an orifice and the maximum fluid velocity in the orifice was tested in vitro. An aqueous suspension of barium sulfate particles with a polymer added to attain variations in viscosity, was forced through orifices which ranged in diameter from 0.4 to 4.7 mm. The pressure difference across the orifice was determined with a transducer and the maximum fluid velocity in the orifice was determined with Doppler ultrasound. Tests were performed at Reynolds numbers, fluid viscosities, and pressure differences that spanned the following ranges: 400-25,000, 1-5 cP, and 3-100 mmHg, respectively. At pressure differences larger than 3 mmHg and fluid viscosity 3 cP (approximate viscosity of in vivo blood), Torricelli's law was demonstrated to be valid for orifice diameters larger than 1.6 mm. The validity of the law was found to be relatively insensitive to variations in orifice length.

Carotid Artery Diseases↗

PubMedDate not supplied

Representations of rapidly oscillating structures on the Doppler display.

In cardiovascular applications of Doppler ultrasound, oscillating structures are at times within the sample volume of the transducer. When the period of oscillation is shorter than the time window of the Fourier transform, the velocities of the structure are not resolved in time by the frequency analyzer. The resulting display can differ considerably from that obtained from structures with linear velocities. The investigation characterizes this phenomenon with the use of theoretical relations, mechanical model experiments and patient data. The results demonstrate that the representations of rapidly oscillating structures on the Doppler display can be interpreted in terms of frequency of oscillation and also, to some extent, in terms of maximum displacement of the structure.

Carotid Artery Diseases↗