Biomedical subjects
Publications and source records attributed to I Wahlberg.
A new diterpenoid containing a rare carbobicyclic cembrane-derived skeleton, the capnosane skeleton, has been isolated from flowers of Greek tobacco. It has been identified as (1S*,3R*,4S*,6R*,7R*,8R*,11Z)-4,6,8-trihydroxy-11-capnosene- 2,10-dione by spectral methods and X-ray analysis of the corresponding benzoate. A full account of the X-ray work is given.
Three different types of unipolar endocardial electrodes--47 in all--were compared in regard to power consumption at stimulation threshold with six different output capacitors and seven pulse widths. Fifteen were conventional large surface electrodes (area 47 mm2); 18 were conventional small surface electrodes (area 6 mm2), and 14 had a specially designed tip with a large area but small active surface of 8 mm2. Pulse widths ranged from 0.15 to 2.0 msec and output capacitors from 1.0 to 22.0 microFarads. All in all about 2,000 measurements were performed. The average current drain to the pacemaker output stage was measured and power consumption was calculated for each electrode--pulse width--output capacitor combination. In all combinations, the two small surface electrodes consumed approximately the same amount of power and, in both cases, significantly less than the larger one. With regard to power economy at stimulation threshold, the pulse width of choice was about 0.5 msec and, furthermore, power consumption decreased with increasing capacitor size. The optimal combination was a small surface electrode, an output capacitor of 22 microF and a pulse width of 0.5 msec.
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Three different electrodes, i.e. conventional large and small surface endocardial electrodes and a new large contact area-small active surface electrode, have been compared with respect to their stimulation thresholds for cardiac pacing in 94 patients with 96 electrodes. Both capacitor discharge and constant current pulses were used for the measurements. The average 2 msec impulse threshold for the 47 mm(2) electrode reached its maximum on the 14th postoperative day and was 3.6+/-1.4 V and 4.4+/-1.8 mA. One month after insertion, the threshold was 3.2+/-1.4 V and 3.9+/-1.7 mA. Corresponding values after one month for the 6 mm(2) electrode were 2.0+/-1.0 V and 1.7+/-0.9 mA and for the new electrode 1.7+/-0.9 V and 1.4+/-0.8 mA. Thresholds increased by about 20% when the impulse duration was diminished from 2 to 0.5 msec. The new large area-small active surface electrode offers advantages of significantly smaller increases in stimulation thresholds during the first month after insertion and good attachment to the endocardium.
The ST segment in a single right-sided chest lead, CR4R, has been studied in 92 consecutive patients with acute inferior transmural left ventricular myocardial infarction. A transient ST- segment rise of more than 1 mm. was recorded in 35 patients, and strongly indicated a significant extension of the infarction to the posterior free right ventricular wall according to autopsy findings. This ECG pattern was furthermore associated with right-sided heart failure, hypotension and oliguria. Left heart failure was also common. The short-term prognosis of patients with ST-segment elevation in CR4R was poor.
Threshold curves with large and small surface intracardiac pacemaker electrodes are compared. The 2 msec. impulse threshold with a 47 sq. mm. electrode was 3.6 v. (4.3 mA.) on the fourteenth postoperative day, when it reached its maximum, and 2.8 v. (3.1 mA.) one month after the operation. These values were 45 and 30 per cent lower with a 6 sq. mm. electrode. Thresholds increased by about 20 per cent when the impulse duration was shortened from 2 to 0.5 msec. The small surface electrode consumed about 35 per cent less current than the 47 sq. mm. one. A newly designed large area-small surface electrode with the shape of an open cage, seems to have the advantages of less increase in postoperative thresholds and good attachment to the endocardial wall.
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Changes in physical and mental work capacity during the menstrual cycle were studied in 12 healthy woemen with severe menstrual distress. Physiological and psychological tests were performed before, during, and after menstruation. Heart rate, pulmonary ventilation, oxygen uptake, blood lactate concentration, and perceived exertion were measured during work on a bicycle ergometer ar two submaximal work loads corresponding to 40 and 70 %, respectively, of individual maximal oxygen uptake. Mental work capacity was studied with the aid of performance tests of psychological functions such as attention, short-term memory, perceptual speed, perception of time, and reaction time. No change in heart rate or oxygen uptake could be observed over the three phases of the menstrual cycle. However, pulmonary ventilation during work varied significantly. It was highest in the menstrual phase. At the same heart rate exercise on the bicycle ergometer was perceived as more exerting in the menstrual phase than in either the premenstrual or postmenstrual phase. Among the performance tests significant results were obtained only in a test of reaction time, which was slightly impaired during the menstrual phase. The results of the performance tests do not however support the assumption that menstruation affects a woman's mental work capacity.
Right heart and pulmonary artery pressures were measured in 28 patients with inferior acute myocardial infarction, 12 of whom also had ECG evidence of right ventricular involvement (RVI). Those with RVI had significantly higher mean right-sided filling pressures 9.3 mm Hg, SD +/- 4.5 than those without RVI, 4.3 mm Hg, SD +/- 1.9. A steeper relationship between right ventricular enddiastolic and mean pulmonary artery pressures was seen in patients with RVI in contrast to those without, where no marked rise in right-sided filling pressures with increasing mean pulmonary artery pressures was seen.