Biomedical subjects

S L Findley

Publications and source records attributed to S L Findley.

4 recordsLinked to original sources

PubMed1988

The effect of energy window on cardiac ejection fraction.

ECG gated gamma-ray energy spectra from the left ventricle were created each 50 msec during the cardiac cycle. Nine of ten subjects were studied with a nonimaging Nal probe, and the tenth with a high-resolution Germanium detector. Placing multiple energy windows over the energy spectra, EF was found to vary with the energy window selected. Moving a 20% window across the photopeak produced a roughly linear increase in EF with energy (2.3 EF units per 10 keV increase in energy) in eight of the ten subjects. Dividing the photopeak into a low (126-140 keV) and high-energy (140-154 keV) portion gave significantly different EFs (high energy exceeding low energy by 17%). Increasing the width of a narrow window centered about the photopeak produced negligible change in EF. Examining the energy spectra showed that the small-angle scattered radiation (126-139 keV) was proportionately greater at end systole than at end diastole, after normalizing the spectra to the same photopeak area.

Electrocardiography↗

PubMed1984

Scintigraphic quantification of asynchronous myocardial motion during the left ventricular isovolumic relaxation period: a study in the dog during acute ischemia.

Asynchronous motion of left ventricular myocardium during the period of left ventricular isovolumic relaxation has often been observed in patients with coronary artery disease. Detection and quantitation of this abnormality with noninvasive nuclear tracer methods, however, have not yet been reported. Thus, functional images of regional left ventricular time to minimum counts (or volume), computed from gated blood pool image sequences, were analyzed to detect and quantitate myocardial asynchrony during this interval. The method was tested by comparing regional with global time to minimum counts before and after coronary artery occlusion in the awake dog. After occlusion, minimum counts in the ischemic region occurred later in the cardiac cycle than did global minimum counts (average difference 69 +/- 37 ms, p less than 0.001). Before occlusion, however, minimum counts in the same region occurred at the same moment as global minimum counts (average difference 4 +/- 12 ms, NS). Thus, acute ischemia in dogs produces a pronounced asynchrony in myocardial motion during the earliest moments of diastole. The magnitude of this asynchrony (69 ms) probably corresponds to the length of the global isovolumic relaxation period in these animals after occlusion. This method might be useful in detecting and quantitating isovolumic asynchrony in ischemia and changes in this asynchrony with therapy (verapamil therapy, for example).

Animals↗

PubMed1983

Assessment of regional left ventricular function by sector analysis: a method for objective evaluation of radionuclide blood pool studies.

Regional wall motion abnormalities are most often detected visually, and hence subjectively, in gated blood pool studies of the heart. Therefore, an automated method was developed to objectively assess regional left ventricular (LV) function. The method was tested in 26 normal volunteers and 29 patients with angiographically proved coronary artery disease. Fifteen patients with coronary artery disease had a normal LV ejection fraction (EF) at rest, and all had an abnormal EF response with exercise; 23 had visual regional wall motion abnormalities with rest or exercise. The left ventricle was divided into 28 sectors that radiated from the LV center of gravity, with 1 region at the LV center. A time-activity curve was generated for each sector and the EF and Fourier phase were computed from each curve. Rest and exercise sector EF versus sector number plots were superimposed and the area difference between these 2 curves was taken as an index of regional contraction. Similarly, an estimator of sector phase differences, obtained from the plot of phase versus sector number, was taken as an index of wall motion asynchrony. Analysis of the reliability of these 2 indexes suggests that this automated technique has at least the same efficiency as subjective evaluation of gated blood pool studies, but possesses the advantage of objectivity. The technique may also be useful in localizing regional defects and, perhaps, in detecting mild abnormalities not readily perceived visually.

Coronary Disease↗

PubMed1981

Measurement of ventricular function by ECG gating during atrial fibrillation.

The assumptions necessary to perform ECG-gated cardiac studies are seemingly not valid for patients in atrial fibrillation (AF). To evaluate the effect of AF on equilibrium gated scintigraphy, beat-by-beat measurements of left-ventricular function were made on seven subjects in AF (mean heart rate 64 bpm), using a high-efficiency nonimaging detector. The parameters evaluated were ejection fraction (EF), time to end-systole (TES), peak rates of ejection and filling (PER,PFR), and their times of occurrence (TPER,TPFR). By averaging together single-beat values of EF, PER, etc., it was possible to determine the true mean values of these parameters. The single-beat mean values were compared with the corresponding parameters calculated from one ECG-gated time-activity curve (TAC) obtained by superimposing all the single-beat TACs irrespective of their length. For this population with slow heart rates, we find that the values for EF, etc., produced from ECG-gated time-activity curves, are very similar to those obtained from the single-beat data. Thus use of ECG gating at low heart rates may allow reliable estimation of average cardiac function even in subjects with AF.

Atrial Fibrillation↗