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Alterations of circulatory responses to upright tilt in cardiac patients
Insights
Cardiac patients exhibit blunted circulatory responses to upright tilt compared to healthy individuals. Reduced cardiac output and stroke volume changes suggest altered autonomic function in heart disease.
Area of Science:
- Cardiology
- Physiology
- Hemodynamics
Background:
- The autonomic nervous system regulates circulatory responses to postural changes.
- Cardiac diseases, such as ischemic heart disease and cardiomyopathy, can impair these regulatory mechanisms.
Purpose of the Study:
- To investigate and compare the circulatory responses to upright tilt in normal subjects and cardiac patients.
- To explore potential explanations for altered hemodynamic responses in patients with heart disease.
Main Methods:
- 20 healthy subjects and 27 cardiac patients underwent standardized upright tilt testing.
- Hemodynamic parameters including heart rate, blood pressure, cardiac output, and stroke volume were monitored.
- Systolic time intervals (PEP/LVET) were measured and correlated with circulatory changes.
Main Results:
- Normal subjects showed expected increases in heart rate and diastolic pressure, with decreases in cardiac output and stroke volume during tilt.
- Cardiac patients displayed attenuated circulatory responses, with significantly diminished reductions in cardiac output and stroke volume.
- A paradoxical increase in cardiac output was observed in some patients with low baseline cardiac index.
Conclusions:
- Cardiac patients exhibit blunted hemodynamic adjustments to upright tilt, indicating impaired autonomic cardiovascular regulation.
- Preload reduction may improve cardiac function in diseased hearts, explaining diminished responses.
- Systolic time intervals during tilt may serve as a valuable tool for assessing hemodynamic dysfunction severity in cardiac patients.
Abstract:
Circulatory responses to the upright tilt were studied in 20 normal subjects and 27 cardiac patients with ischemic heart disease or idiopathic cardiomyopathy. In normal subjects, the upright tilt caused obvious increases in heart rate and diastolic pressure, a slight decrease in systolic pressure and marked decreases in cardiac output and stroke volume. The circulatory changes during the tilt were less pronounced in the cardiac patients as compared with the normal subjects. The reductions of cardiac output and stroke volume and the increase in total peripheral resistance were all significantly diminished. A paradoxical increase in cardiac output during the tilt, an observation hitherto not well recognized, was observed in 5 cases with low cardiac index during the control period. Although several possibilities can be considered for the explanation of the diminished, sometimes paradoxical, circulatory responses to the tilt in cardiac patients, the improvement of the function of the diseased heart by preload reduction was proposed as an important factor. There was a significant negative correlation between the per cent changes of cardiac output and the per cent changes of PEP/LVET. It was suggested that the measurements of systolic time intervals during the tilt might be useful for evaluating the severity of the hemodynamic derangement in cardiac patients.