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Biomedical subjects

D F Ortega

Publications and source records attributed to D F Ortega.

10 recordsLinked to original sources
PubMed1993

Feasibility of measuring relative right ventricular volumes and ejection fraction with implantable rhythm control devices.

Ejection fraction (EF), the ratio between stroke volume (SV) and end-diastolic volume (EDV), is a valuable contractility indicator. Unlike SV, the Frank-Starling effect is automatically compensated in the calculation of EF. It was the aim of this study to evaluate the physiological behavior of impedance derived measurements of relative right ventricular (RV) volumes and EF, obtained with standard pacing leads. Seven patients were evaluated at the time of pacemaker implant or replacement. Since no absolute standard of comparison was available for RV volumes, the value of the measurements was assessed by observing their behavior under cardio-circulatory challenges. A 2.5-kHz carrier was fed to the ring and tip electrodes of standard bipolar pacing leads and the resulting voltage was digitized and stored. The peak-to-peak voltage (PPV) of the carrier at the time of QRS was used as EDV, and the largest PPV as end-systolic volume (ESV). Relative SV was the difference between EDV and ESV, and EF = SV/EDV x 100. Pacing was used to reduce EDV, and the effect of contractility was tested with isometric hand grip, recumbent leg exercise, or isoproterenol drip. Only minimal changes in EF were noted during incremental pacing; relative SV and EDV decreased as expected; and EF increased significantly during contractility challenges. A high correlation coefficient was observed between EDV and SV changes induced by incremental pacing at rest (r values from 0.62 to 0.98, P from < 0.01 to 0.001). The study revealed that impedance volumetry, utilizing conventional bipolar pacing leads, yields useful hemodynamic data related to EDV, ESV, and EF. Given the simplicity of the method, it is reasonable to conclude on the feasibility of using said impedance derived hemodynamic parameters in implantable rhythm control devices.

Adult↗
PubMed1991

Nonphysiological left heart AV intervals as a result of DDD and AAI "physiological" pacing.

DDD and AAI pacemakers are considered physiological, since they preserve atrioventricular (AV) synchrony. Artificial pacing, however, is performed largely from right heart chambers, causing aberrant depolarization pathways. Pacing at the right atrial appendage (RAP) is known to delay left atrial contraction due to interatrial conduction time (IACT), and right ventricular (RV) apical pacing (RVP) delays left ventricular (LV) contraction due to interventricular conduction time (IVCT). These delays may render the left heart AV intervals (LAV) either too short or too long, thus affecting LV systolic function. The purpose of this study was to evaluate the actual LAV intervals during conventional, right heart AAI and DDD pacing. Resulting LAV intervals were compared to programmed AV values during all DDD pacing modalities. Ten patients with DDD and six patients with AAI pacemakers were studied. IACT was measured from the atrial spike to the onset of left P wave, as recorded by an esophageal lead. Systolic time intervals were measured using either a carotid pulse tracing or a densitogram (photoplethysmography). LV function was appraised by measuring rate-corrected LV ejection time (LVETc). IVCT was measured indirectly as the lengthening of LV preejection period (PEP) caused by RV pacing, as compared to normal depolarization pathway. Intrinsic IACT and IVCT were considered zero. Right heart AV intervals (RAV) were measured from surface ECG and LAVs were calculated according to the following equations: Sinus Rhythm: LAV = RAV; Atrial Pace + Ventricular Sense: LAV = RAV - IACT; Atrial Sense + Ventricular Pace: LAV = RAV + IVCT; Sequential AV Pace: LAV = RAV - IACT + IVCT.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1984

Challenge seeking and the type A coronary-prone behavior pattern.

The present investigation sought to further delineate the Type A coronary-prone behavior pattern and to elucidate the psychophysiological process through which this behavioral disposition is translated into heart disease. Type A and Type B male subjects engaged in tasks that required varying degrees of activity before an assessment of challenge-seeking tendencies. Type A participants sought greater degrees of challenge than did their Type B counterparts. In addition, the more active the person with Pattern A had been immediately before the challenge-seeking opportunity, the greater the degree of challenge sought. Precedent activity level did not significantly influence challenge seeking in the Type B population. The Type A subjects also had significantly faster heart rates during performance of a challenging task. Pattern A behavior may be translated into heart disease through the cumulative deleterious effects of chronic and excessive challenge-induced cardiovascular excitation.

Adult↗
PubMed1978

Relaxation exercise with cerebral palsied adults showing spasticity.

A method for improving the muscle incoordination associated with cerebral palsy was empirically tested. Relaxation exercises, involving the successive tensing and relaxing of the major muscle groups of the body, were performed by four adults with spastic quadraplegia. All four subjects were sheltered workshop employees. Their IQs ranged from normal to mentally deficient. Testing consisted of two timed-trials of both the Placing Test and the Turning Test from the Minnesota Rate of Manipulation Tests. These tests measured the amount of time required to complete various manual manipulations involving pegs and pegboard. A multiple baseline across subjects design was employed to provide experimental control. All subjects showed significant improvement over baseline performance on the tests following the relaxation training. Limitations of this preliminary investigation and implications of these results for future research were noted.

Adult↗