Optimum waveform envelopes and amplitude ratios in oscillometric blood pressure estimation.

OBJECTIVE: To determine if, when using the oscillometric method, there is a specific range of amplitude ratios in the fixed-ratio algorithm that will result in blood pressure estimates that consistently fall within a mean error ≤5 mmHg and a SD of the error <8 mmHg. Additionally, to apply different representations of the oscillometric waveform envelope to verify if this will affect the accuracy of the results. METHODS: SBP and DBP were obtained using the fixed-ratios method applied to a dataset of 219 oscillometric measurements obtained from 73 healthy volunteers and compared to their corresponding auscultation values. Ratio and envelope analysis were done on Matlab (The MathWorks, Inc., Natick, Massachusetts, USA). RESULTS: Depending on the envelope representation, ratios between 0.44-0.74 for systolic pressure and 0.51-0.85 for diastolic pressure yield results within the limits mentioned above. When a set of optimum envelope representations and ratios are selected based on population mean, the highest percentage of subjects presenting blood pressure estimates within the limits were 72.6% for systolic and 69.9% for diastolic. CONCLUSION: The range of ratios presenting optimum results appears to be independent of the degree of arterial stiffness given the wide range of ages of the subjects in the study. Different representations of the oscillometric waveform envelope may improve the accuracy of the method. However, there remains a considerable percentage of the population with unreliable results. It is therefore important to only use devices that have been properly validated according to standard protocol.

Comparability of oscillometric to simultaneous auscultatory blood pressure measurement in children.

OBJECTIVE: Uncertainty exists regarding the accuracy of automated blood pressure (BP) measurement in children. We recorded oscillometric waveforms in children, derived oscillometric BPs using two standard algorithms, and compared the results to simultaneous auscultation. PATIENTS AND METHODS: Twenty children aged 2-12 years were recruited from a tertiary-care Pediatric Nephrology Clinic. Sex, height, weight, arm circumference, history of hypertension, and clinic BP were recorded. Two, simultaneously measured, oscillometric and auscultatory BP readings were obtained 30-60 s apart. The first reading was discarded and, the second, used for analyses. Fixed-ratio and slope-based algorithms were used for BP derivation. RESULTS: Mean age was 7.95±2.82 years, 40% were female, mean arm circumference was 21.86±4.06 cm, and 50% had hypertension or a history of hypertension. Mean auscultatory BP for all participants (systolic±SD/diastolic±SD) was 93.40±11.80/50.50±9.04 mmHg, oscillometric fixed-ratio BP was 99.20±11.90/57.35±7.15 mmHg and oscillometric slope-based algorithm was 91.60±13.94/60.65±7.71 mmHg. Compared to auscultation, the fixed-ratio method differed by 5.80±12.72/6.85±7.51 mmHg (P=0.06 and <0.01) and the slope-based method differed by -1.80±13.59/10.15±8.07 mmHg (P=0.56 and <0.01). Differences from auscultation were statistically significant for diastolic BP with both fixed-ratio and slope-based methods for all age categories but of greatest magnitude in the youngest children. CONCLUSION: Oscillometric BP derived using two commonly used algorithms differed by more than 5 mmHg in either systolic BP or diastolic BP from simultaneous auscultatory BP in children aged 2-11. These findings emphasize the need for greater understanding of the functionality and accuracy of oscillometry in children.

Phase of electroencephalography theta oscillation during stimulus encoding affects accuracy of memory recall.

Oscillatory activity is a ubiquitous property of brain signals, and yet relatively few studies have investigated how the phase of such ongoing oscillations affects our cognition. One of the main findings in this field is that the phase of electroencephalography (EEG) in the alpha band can affect perception of milliseconds-long stimuli. However, the importance of the phase of EEG for processing more naturalistic stimuli, which have a much longer duration, is still not clear. To address this question here, we presented word-nonword pairs, each of which was visible for 5 s and measured the effect of EEG phase during stimulus onset on later memory recall. The task consisted of an encoding (learning) phase in which 20 novel word-nonword pairs were presented, followed by a test phase in which participants were shown one of the seen words with four target nonwords to choose from. We found that memory recall performance was higher when the words during encoding were presented at a descending phase of the theta oscillation. This effect was the strongest in the frontal cortex. These results suggest that the phase of ongoing cortical activity can affect memorization of seconds-long stimuli that are an integral part of many daily tasks.

Accuracy of oscillometric blood pressure algorithms in healthy adults and in adults with cardiovascular risk factors.

BACKGROUND: Fixed-ratio and slope-based algorithms are used to derive oscillometric blood pressure (BP). However, a paucity of published data exists assessing the accuracy of these methods. Our objective was to determine the accuracy of fixed-ratio and slope-based algorithms in healthy adults and in adults with cardiovascular risk factors. PATIENTS AND METHODS: Overall, 85 healthy adults (age≥18 years) and 85 adults with cardiovascular risk factors were studied. Three oscillometric and four two-observer mercury-based auscultation measurements were performed in each, according to International Standards Organization 2013 methodology. Two fixed-ratio algorithms and one slope-based algorithm were applied to process oscillometric waveform envelopes and derive oscillometric BP. Paired and unpaired t-tests were used to compare mean oscillometric BP within and between each group, respectively. RESULTS: For healthy adults, mean age was 50.3±17.8 years, mean arm circumference was 30.4±3.8 cm, and 62% were female. In the cardiovascular risk group, mean age was 63.8±12.4 years, mean arm circumference was 31.9±4.2 cm, and 62% were female. For systolic BP, the fixed-ratio algorithms produced the lowest mean error and narrowest SD. For diastolic BP, mean errors were similar for all three algorithms, but the fixed-ratio algorithms had higher precision. The comparison of healthy adults and those with cardiovascular risk factor showed high variability for systolic and diastolic BP (SD: 8.113.9 mmHg). CONCLUSION: In both healthy adults and in those with cardiovascular risk factors, the fixed-ratio technique performed better than the slope-based algorithm. High between-group variability indicates that subject-specific algorithms may be needed.