Does passive head-up tilt alter left ventricular systolic time intervals in normal subjects compared to patients with congestive heart failure?
Systolic time intervals respond dynamically to postural circulatory stress in normal subjects, but this response is blunted in congestive heart failure and can be partially restored following diuresis.
The effects of graded increments of passive head-up tilt on the duration of the systolic time intervals corrected for heart rate were investigated in 15 normal subjects. Head-up tilt caused a prolongation of the pre-ejection period and a shortening of the left ventricular ejection time, while total electromechanical systole diminished minimally. The lengthening of the pre-ejection period and abbreviation of the left ventricular ejection time increased progressively with stepwise increments of head-up tilt. The application of venous occlusive tourniquets produced changes in the systolic intervals directionally similar to those observed with head-up tilt. In contrast to the normal subjects, three patients with congestive heart failure demonstrated no change in the systolic time intervals during head-up tilt. After diuresis in two of the patients with heart failure, the responses of their systolic time intervals to head-up tilt returned toward normal.
Stafford et al. (Sun,) studied this question.
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