Reports of research work funded by grants prior to 2014
University of Otago Wellington
Reproducibility of the Sit-to-stand Manoeuvre to assess Baroreflex Function
End of study report
KC Peebles, HM Horsman, DG Galletly and Y-C (Shieak) Tzeng
Cardiovascular Systems Laboratory, Department of Surgery and Anaesthesia
Introduction: The repeated sit-to stand method (SSM), which induces bi-directional changes in blood pressure (BP) at a desired frequency, is suitable for assessing dynamic baroreflex sensitivity (BRS). However, its use in the research environments is hampered by the lack of knowledge about its test re-test reliability and ability to detect hysteresis. Hence, this study sought to: i) evaluate and compare the reliability of the SSM for assessing BRS against that of two established methods (Oxford method [OM] and Valsalva manoeuvre [VM]); and ii) examine if the frequency of the SSM influences hysteresis.
Methods: Sixteen healthy participants undertook this study. Throughout the study we recorded BP (finger photoplethysmography), heart rate (electrocardiogram) and end-tidal carbon dioxide levels (capnography) using established methodologies. Each participant underwent three trials of each method in random order. For the SSM, which was performed at 0.1 and 0.05 Hz, we calculated: i) the integrated BRS (BRSINT), which was a composite of response to falling and rising BP; ii) the BRS in response to a fall in BP (BRSDOWN); and iii) the BRS in response to a rise in BP (BRSUP). For the OM and VM, we quantified BRSDOWN and BRSUP as per convention i.e. BRSINT was not calculated. Test-retest reliability was assessed using the intraclass correlation coefficient (ICC), the standard error of measurement (SEM), and Pearson’s product-moment correlation coefficients. Between- and within- method statistical comparisons were performed using two-way repeated measures ANOVA, with post hoc analysis (paired t-tests), as required.
Summary of main findings: Irrespective of frequency, the ICC for BRSINT, BRSUP and BRSDOWN during the SSM was ≥0.88. Whilst the ICC for BRSUP in the OM was 0.78, it was ≤0.5 for the remaining measures. Compared to the OM and VM, the SSM showed the lowest SEM and highest correlation coefficients. Irrespective of the direction of BP changes, the OM and VM showed high SEM values and low correlation values indicating poor reliability.
During the SSM, hysteresis was apparent in all participants at 0.1 Hz, but was absent at 0.05 Hz, suggesting the baroreflex is frequency dependent.
Implications: This study has shown the sit-to-stand method to be a reliable method suitable for use in the research setting that is able to distinguish between individual results with clinically appropriate sensitivity. Therefore we suggest that using the sit-to-stand method at 0.1 Hz and 0.05 Hz to calculate BRSINT, BRSDOWN and BRSUP would provide a reliable, simple and non-invasive method for complementary assessment of the baroreflex. Furthermore, using the sit-to-stand method we have shown that baroreflex hysteresis is dependent on the frequency of BP oscillation, which highlights the importance of controlling the rate of BP change.
Progress to date: We are in the final stages of drafting a manuscript, which we intend to submit in early 2014. This data is currently being prepared for an oral presentation to an internal audience (Wellington Health and Biomedical Research Society New Investigator meeting on 25 November, 2013). Also, an abstract is under review for a poster at Experimental Biology (San Diego, USA in April, 2014).