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A total of 220 simultaneous pairs of measurements of cardiac stroke volume were made in twelve women before and during Caesarean section in order to compare impedance cardiography with the thermodilution method. A significantly higher coefficient of correlation was found before (r = 0.77) than during anaesthesia (r = 0.55). Further, there was a significant difference in the slope of the regression lines: before anaesthesia the slope was 1.07 and during anaesthesia with thiopentone, nitrous oxide, oxygen and suxamethonium it was 0.45. Significant changes in the intercept on the Y-axis were found before (-13.9 ml) and during anaesthesia (33.4 ml). When the uterus was displaced upwards and to the left from the 15 degrees tilt position the stroke volume and the cardiac output were increased when measured by both methods to nearly the same values as in the left lateral position. It is concluded that the impedance method is reliable for measuring cardiac stroke volume in late pregnancy under physiological conditions in the conscious patient, but that it cannot replace the thermodilution method in pharmacological studies.

Forty patients who had normal-pressure hydrocephalus were examined neuropsychologically before and 12 months after a ventriculoatrial shunt operation. Comparison of the preoperative and postoperative test results showed that cognitive functions improved in 16 patients, were unchanged in 19, and deteriorated in 5. Moreover, we found that the outcome of the operation depended on patient selection criteria. When three or more of the following preoperative signs were present (known cause, short history, low cerebrospinal fluid outflow, small sulci and/or periventricular hypodensity indicated by computed tomography), an improvement in cognitive function was seen in 80% of the patients after a shunt operation.

One hundred and twenty-nine simultaneous measurements were carried out on seven patients, 67 at rest and 62 during the Valsalva manoeuvre, in order to compare impedance cardiography with the thermodilution method, during rapid changes in cardiac stroke volume and pulmonary blood volume. A coefficient of correlation of 0.86 was found following linear regression analysis of the whole material. Analysis of the individual patient showed that the mean coefficient of correlation was 0.94 (range 0.91-0.97), and that the slope of the regression lines was 0.41 to 1.82, and further that the mean intercept was 0.2 ml. It is concluded that impedance cardiography can be employed for measuring the relative intraindividual changes in cardiac stroke volume during the Valsalva manoeuvre, and it is suggested that it may be of use in other situations, such as during haemorrhage or continuous positive pressure ventilation.

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