Cardiovascular Diseases Poster Session
Materials and Methods
Subjects The study involved eight male volunteers (mean 22.5 years, range 21-26), who were asked to abstain from alcohol, caffeine and cigarettes in the 24 hour period prior to the study, and to fast on the morning of the study.
Finger Blood Pressure Monitor Non-invasive continuous measurement of cardiac function was performed using the Portapres (TNO-TPD Biomedical Instrumentation, Amsterdam) which gives an indirect measure of blood pressure in a finger based on an arterial volume clamp method. The waveform is displayed on an external monitor which details heart rate (HR), systolic, diastolic and mean arterial pressure (MAP). An outline of the methods and equipment has been described previously (Imholz et al., 1993). Calculation of cardiac output (CO) and systemic vascular resistance (SVR) is performed by the accompanying BEATFAST software.
Impedance cardiography (ICG) Impedance measurements of stroke volume were made using the non-invasive computer cardiac output monitor (NCCOM) impedance cardiograph (BoMed, Biomed Medical Manufacturing, Irving, California). The method is described in detail elsewhere (Bernstein, 1986).
Sphygmomanometer Measures of systolic and diastolic blood pressure were obtained using a semi-automated oscillometric technique (Takeda UA 751 sphygmomanometer; Tokyo, Japan).
Subjects were supine during all measurements in a quiet room maintained at a constant temperature of 22-25 °C. A 30 minute rest period preceded the exercise protocol, during which baseline measurements were taken at -30, -20, -10 and 0 minutes. The Bruce protocol consists of seven stages of exercise, increasing in terms of energy expenditure, through changes in both treadmill gradient and speed. Each stage lasted three minutes after which the subject immediately returned to the supine position for measurement as before. Measurements were made in quadruplicate at each time point to allow determination of the coefficient of variation.
Data analysis and statistical methods
Measurements were recorded as both absolute values and percentage change from baseline. The strength of relationship between the two methods was initially assessed by calculation of Pearsons product-moment correlation coefficient (r), with significance accepted at p < .05. Agreement between the Portapres and ICG was assessed by calculating the mean difference (d), its standard deviation (s) and the 95% limits of agreement as suggested by Bland and Altman, 1986. One way analysis of variance of baseline measurements at -20, -10 and 0 minutes was used in the quantification of measurement error, which was reported as the within-subjects coefficient of variation and expressed as a percentage.
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|Mills, NL; Spratt, PL; Padfield, DJ; Webb, DJ; (1998). The PORTAPRES In The Non-invasive Assessment Of Dynamic Cardiovascular Function. Presented at INABIS '98 - 5th Internet World Congress on Biomedical Sciences at McMaster University, Canada, Dec 7-16th. Available at URL http://www.mcmaster.ca/inabis98/cvdisease/mills0906/index.html|
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