Non-invasive carotid pressure measurements Sample Clauses

Non-invasive carotid pressure measurements. Since, invasive measurements of aortic pressure can only be obtained at the time of cardiac catheterisation, non-invasive measures of carotid pressure were used as a surrogate for aortic pressure in subjects for whom cardiac catheterisation was not clinically indicated. Although the carotid and aortic pressure waveforms are not identical they resemble each other closely both at rest and during dynamic testing with physiological manoeuvres and drugs.168 Correct calibration of the carotid pulse is important due to pulse pressure amplification and the most widely used method is to calibrate carotid pressure from brachial mean and diastolic blood pressure on the assumption of equality of these pressures at central and peripheral sites.20 Apart from the same variation in waveform morphology other drawbacks of using the carotid pulse as a surrogate for the aortic pulse include the difficulty in obtaining a stable pressure tracing with applanation tonometry, the potential activation of baroreceptors and theoretical adverse effects on undiagnosed carotid plaques. However, the carotid pressure waveform has been widely used as a surrogate for the aortic pressure pulse in epidemiological studies, clinical trials and mechanistic haemodynamic studies.24, 54, 60, 169-171 Measurements were performed in a quiet temperature controlled (24-26 ⁰C) room. Subjects were asked to avoid caffeine and alcohol on the day of the study. All pressure measurements were taken supine following 20-30 minutes resting. Radial and carotid pressure waveforms were obtained by applanation tonometry using the SphygmoCor system (AtCor, Australia). Approximately 10 cardiac cycles were obtained and ensemble averaged. Waveforms that did not meet the in-built quality control criteria in the SphygmoCor system were rejected. Brachial blood pressure was measured in triplicate by a validated oscillometric method (Omron 705CP, Omron Health Care, Japan) and used to calibrate radial waveforms to obtain MAP. Carotid waveforms were calibrated from MAP and diastolic brachial blood pressure on the assumption of equality of these pressures at central and peripheral sites. Carotid pressure and aortic Doppler flow velocity (see below) were measured under the same condition less than 5 minutes apart.