An investigation of underlying biophysical mechanisms in the use of pulse wave velocity for cuffless measurement of blood pressure
Background: Blood pressure (BP) is a health-based risk factor predictive of cardiovascular complications. Conventional cuff-based techniques measuring BP are limited by being discontinuous and inconvenient. This thesis investigates the underlying components of an alternative cuffless approach, utilising a subject-specific calibration method. This approach aims to minimise the use of a cuff, therefore, addressing these limitations by estimating BP through its relationship with arterial pulse wave velocity (PWV), a measure of arterial stiffness. Methods: Carotid-femoral PWV measurements were taken under baseline conditions and following two interventions; a postural change and a cold pressor test. The postural change generated a calibration factor that was investigated for repeatability. Consecutive PWV measurements assessed reliability and measurement variability. A cross-sectional multivariate statistical analysis was performed to determine possible predictors of the calibration factor. The cold pressor test investigated potential PWV differences in different arterial segments in response to a BP change.Results: The mean calibration factor was 18.78±7.39 mmHg/m/s with good repeatability (difference: 1.40±9.76 mmHg/m/s, p=0.48). This factor correlated with weight (standardised β=0.247, p=0.003) and diastolic BP (β=0.244, p=0.004). The cross-sectional stepwise linear regression model predicted 15% of the calibration factor variability (p<0.05, R2=0.146). Wave-form quality and distance were a source of potential variability. There were significant differences in regional PWV following a change in BP (p<0.05).Conclusions: These findings demonstrate the capacity of the subject-specific calibration factor to estimate BP. Variability present was primarily associated with the PWV measurement. Pulse transit time was significantly affected by changes in BP. As this thesis has only articulated the potential of the calibration approach and factors contributing towards its variability, future research is still required to validate BP estimation incorporating the calibration factor.