Measurement and Analysis of Cardiac Output in Patients with Orthostatic Hypotension
Date Issued
2008
Date
2008
Author(s)
Lin, Chen-Ying
Abstract
With the advanced medical instrument technology, invasive stroke volume (SV) and cardiac output (CO) assessment technique was widely applied in recent year. The primary research purpose of this study is to investigate the physiological responses of the recruited samples during head-upright tilt test. The impedance cardiography technique and the Kubicek and Sramek-Bernstein equations were used to model the SV and CO of the test subjects. This work studied 12 subjects, 5 subjects among them (5 males: 24.6 ± 2.41 years) have no previous history of either cardiovascular or hypertension diseases, 5 patients (5 males: 51.4 ± 11.2 years) with spinal cord injury (SCI) diseases, and 2 patients (2 males: 67.5 ± 8.5 years) with Parkinson’s disease (PD). The head-upright tilt test was conducted on all subjects for 15 minutes. All subjects lie down flat on a test bed in the first 5 minutes. Then, the tilt test bed increased its angle such that the head-up tilt of test subject reaches to 60° with a tilt speed of 2.5°/sec at the 6th minute, and no further angle changing on the head-up tilt in the following 10 minutes. All of test subjects’ blood pressure (BP), heart rate (HR), SV and CO were recorded and analyzed. This study used Butterworth filter to smooth the signals obtained from electrocardiogram and impedance cardiography. Also, a Sliding Window method was developed to detect the R peaks in electrocardiogram and the specified peaks in impedance cardiography. The successive rate of peak detection achieved is high up to 97%. The results of this study suggest that the systolic or diastolic pressures in the test group of normal subjects have a pressure gradient of more than 10 mmHg, heart rate increase of more 10 beats per minute, and stroke volume drops significantly. For the 40% of SCI patients and PD patients, their systolic or diastolic pressure decreases for more than 20mmHg during head-upright tilt test and this fact implies that these patients were with orthostatic hypotension (OH). Four groups (group A: normal subjects; group B: SCI with orthostatic hypotension; group C: SCI not with orthostatic hypotension; group D: PD with orthostatic hypotension) were included in the statistical test. The repeated measurement of ANOVA was used for inter-group comparisons of patient’s blood pressure. It was found that blood pressures in the test groups of A, B, and D have significant statistical difference (p < 0.05) at the first stage (i.e., during experimental course from 6 to 10 minutes) after head-up tilt to 60° already. Then, the differences of HR, SV, and CO between groups B or D and other groups are of interest. The Post Hoc test with one way repeated measures of ANOVA was used for inter-group comparisons. This study found that heart rate, stroke volume and cardiac output have significant changes (p < 0.05) between groups B and C, and groups B and D at the last stage (i.e., during experimental course from 11 to 15 minutes) after head-up tilt to 60° already, respectively. The statistical analysis also demonstrated that cardiac output in group D significantly changed when different stroke volume equations were used.
Subjects
Stroke volume
Cardiac output
Spinal cord injury
Type
thesis
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