Cuff Under Pressure for Greater Accuracy

Direct estimation of central aortic pressure from measured or quantified mean and diastolic brachial blood pressure: agreement with invasive records

Background

Recently it has been proposed a new approach to estimate aortic systolic blood pressure (aoSBP) without the need for specific devices, operator-dependent techniques and/or complex wave propagation models/algorithms. The approach proposes aoSBP can be quantified from brachial diastolic and mean blood pressure (bDBP, bMBP) as: aoSBP = bMBP2/bDBP. It remains to be assessed to what extent the method and/or equation used to obtain the bMBP levels considered in aoSBP calculation may affect the estimated aoSBP, and consequently the agreement with aoSBP invasively recorded.

Methods

Brachial and aortic pressure were simultaneously obtained invasively (catheterization) and non-invasively (brachial oscillometry) in 89 subjects. aoSBP was quantified in seven different ways, using measured (oscillometry-derived) and calculated (six equations) mean blood pressure (MBP) levels. The agreement between invasive and estimated aoSBP was analyzed (Concordance correlation coefficient; Bland-Altman Test).

Conclusions

The ability of the equation "aoSBP = MBP2/DBP" to (accurately) estimate (error <5 mmHg) invasive aoSBP depends on the method and equation considered to determine bMBP, and on the aoSBP levels (proportional error). Oscillometric bMBP and/or approaches that consider adjustments for heart rate or a form factor ∼40% (instead of the usual 33%) would be the best way to obtain the bMBP levels to be used to calculate aoSBP.

The Effect of Three Different Cuff/Arm Circumference Ratios Ranging over 80% on Cuff Blood Pressure Measurements

We aimed to explore whether the cuff/arm (C/A) circumference ratio within the suggested range (> 80%) affects the accuracy of mercury cuff blood pressure (BP) measurement (cuff BP) using intrabrachial BP (IABP) as a reference.A total of 253 patients aged 62.42 ± 9.70 years were included. After coronary angiography, the catheter in the right arm was gradually withdrawn toward the cubital fossa, and the IABP was continuously recorded. The cuff BP of the right arm was measured based on the artery blood flow using a special method similar to the traditional mercury method. The cuff was replaced using another C/A ratio after one minute, and the test was performed again. We used three different cuffs for each participant to meet the C/A ratios of 80%-84%, 85%-89%, and 90%-100%. We calculated the percentage deviation degree (DD) between the cuff BP and IABP values: DD = difference/IABP × 100%. The agreement between the values was evaluated using the Bland-Altman method.The IABP values were 138.52 ± 16.89/79.67 ± 9.81 mmHg. The DD of the systolic BP (SBP), with a ratio of 80%-84% (3.06%), was the smallest. The DD of the diastolic BP (DBP) was lowest at a ratio of 85%-89% (2.47%). Men and women had the lowest DD of the SBP at a C/A ratio of 80%-84% and the lowest DD of the DBP at a C/A ratio of 85%-89%. Regardless of whether the participants had coronary heart disease, the DD of the SBP at a C/A ratio of 80%-84% was the lowest, and the DD of the DBP at a C/A ratio of 85%-89% was the lowest.Even in the suggested range of > 80%, when the C/A ratio was 80%-84%, the difference in the SBP between the cuff and IABP was the lowest, but when the C/A ratio was 85%-89%, the difference in the DBP was the lowest.

Comparison between cuff-based and invasive systolic blood pressure amplification

OBJECTIVE

Accurate measurement of central blood pressure (BP) using upper arm cuff-based methods is associated with several factors, including determining the level of systolic BP (SBP) amplification. This study aimed to determine the agreement between cuff-based and invasively measured SBP amplification.

METHODS

Patients undergoing coronary angiography had invasive SBP amplification (brachial SBP - central SBP) measured simultaneously with cuff-based SBP amplification using a commercially available central BP device (device 1: Sphygmocor Xcel; n = 171, 70% men, 60 ± 10 years) and a now superseded model of a central BP device (device 2: Uscom BP+; n = 52, 83% men, 62 ± 10 years).

RESULTS

Mean difference (±2SD, limits of agreement) between cuff-based and invasive SBP amplification was 4 mmHg (-12, +20 mmHg, P < 0.001) for device 1 and -2 mmHg (-14, +10 mmHg, P = 0.10) for device 2. Both devices systematically overestimated SBP amplification at lower levels and underestimated at higher levels of invasive SBP amplification, but with stronger bias for device 1 (r = -0.68 vs. r = -0.52; Z = 2.72; P = 0.008). Concordance of cuff-based and invasive SBP amplification across quartiles of invasive SBP amplification was low, particularly in the lowest and highest quartiles. The root mean square errors from regression between cuff-based central SBP and brachial SBP were significantly lower (indicating less variability) than from invasive regression models (P < 0.001).

CONCLUSIONS

Irrespective of the difference from invasive measurements, cuff-based estimates of SBP amplification showed evidence of proportional systematic bias and had less individual variability. These observations could provide insights on how to improve the performance of cuff-based central BP.