Comparison between central and automated peripheral blood pressure measurement for early detection of kidney dysfunction in hypertensive patients

Hypertension is a common problem among older adults, reaching prevalence as high as 70 to 80%. Untreated hypertension is notorious for increasing the risk of mortality and is often described as a silent killer. It may be associated with a risk of atherosclerotic disease among 30% and organ damage among 50% of people within 8–10 years after its onset. End stage renal disease is one of the main complications of HTN particularly among diabetics patients [17, 18].

The current study enrolled 201 hypertensive patients who were classified into 108 patients with CKD and 93 patients without CKD. We aimed to assess two different methods in BP measurement and test their value in prediction of early renal dysfunction among hypertensive patients.

We noticed that patients with CKD had significantly higher mean age and mean duration of HTN in comparison to those without CKD. Also, there was male predominance among CKD group but of no statistical significance. Our results were consistent with Tannor et al. who stated that patients with CKD had significantly higher mean age and longer duration of HTN. Also, they reported that age was considered a predictor for CKD among patients with HTN and male patients had higher risk to progress to CKD in comparison to females [19]. We noticed that usage of ACEIs or ARBs was significantly higher among patients without CKD. This was in concordance with major guideline recommending the use of ACEIs or ARBs for their benefits in decreasing proteinuria and preventing progression of kidney disease [14]. Most enrolled patients were on low or conventional doses of ACEI or ARBs but high doses had been shown to improve proteinuria and prevent CKD progression [20].

Reliability of brachial BP measurement in the physician’s office has its own limitations that make it less reliable than out-of-office BP measurement, using either home BP monitoring or ambulatory BP monitoring (ABPM) techniques [21]. In recent years, there is increasing evidence that central aortic BP might be superior to peripheral BP in the prediction of cardiovascular events. It was found a close association of central BP with target organ damage and cardiovascular risk [22]. Several issues can complicate the measurement of BP among patients with CKD, including an increased likelihood of arrhythmias, arterial stiffness, and masked hypertension. Accurate BP measurement is particularly important in high cardiovascular disease settings such as those that prevail in patients with CKD [22].

BP is traditionally measured at the brachial arteries, so brachial BP measurement is the gold standard method for diagnosis and management of hypertension. However, in many individuals, there are some discrepancies between central and peripheral BP. These discrepancies have long been a common research aspect, and whether central BP is a better clinical surrogate than brachial BP has also been universally debated [23].

Our study revealed that that automatic peripheral BP measurement slightly overestimated SBP and DBP in comparison to central BP measurement with subsequent overestimation of mean BP either among those with CKD or without CKD in consistent with Drawz et al. who found that peripheral measurement of both SBP and mean BP were overestimated due to the consequence of the calibration method [22].Similarly, in a published meta-analysis about the accuracy of non-invasive measurements of BP concluded that these measures could be used to assess BP and the slightly reported errors in BP estimation by these devices are mostly attributable to the errors introduced during calibration [24]. Moreover, our study revealed a strong degree of agreement between both automatic peripheral and central BP measurements in concordance with Rouxinol-Dias et al. who stated that it might be reasonable to use non-invasive brachial BP as an estimate of central BP [25] and many other authors recommended the use of brachial pressure assessment as an estimate of central BP and the diagnosis of HTN [25, 26].

Till now, the diagnosis of hypertension, according to office, home, or ambulatory BP measurements, is currently based on recordings from the brachial arteries. Because of the phenomenon of PP amplification, brachial BP and PP are usually higher than the corresponding readings in the central aorta [27]. However, either by the auscultatory method or automatic oscillometric sphygmomanometers, the non-invasively measured brachial BP and PP are usually lower than the invasively measured intra-arterial readings. Such variability between central monitoring and cuff measurement of BP may be attributed to number of factors, including age, sex, body height, heart rate, medications, and systemic vascular diseases. Besides, noninvasive brachial SBP as a surrogate for central SBP has been shown to have a large random error [27].

On the other hand, our study demonstrated that diagnostic accuracy of central and automatic peripheral BP measurements had no significant value in the prediction of CKD (P > 0.05). It’s known that central BP may reflect the pulsatile load on the heart and large arteries better than brachial BP and more closely associated with end organ damage [28]. In contrast, the current study disagreed with this concept may be due to relatively small sample size and discordant with a systematic review of 58 studies which revealed that a central BP compared with brachial BP seems to be more strongly associated with most of the investigated indices of preclinical organ damage [28].

Recent technological advances have enabled several non-invasive methods to estimate arterial stiffness. Of these non-invasive measurements; higher PWV and augmentation index as indicators of intra-renal hemodynamics, are known to be associated with worse renal function and further, have a predictive value for renal outcomes among patients with essential HTN [25].

Our study corroborates and extends previous findings that patients with CKD had significantly higher augmentation index (P < 0.001) and PWV (P = 0.004) in comparison to those without CKD. Also, both PWV and augmentation had a negative correlation with eGFR and increased among patients with abnormal ACR. This indicates that PWV and augmentation increases with progression of the renal damage. In concordance with Kusunoki et al. who demonstrated that arterial stiffness indices such as PWV and augmentation index as well renal resistive index (RI) increased with increasing severity of CKD stage among hypertensive patients. They also found that PWV is one of the predictors for advanced renal disease in such patients. This could be explained by excessive pulsatile energy transmission into the susceptible renal microvasculature as an important mechanism of progression of kidney damage and renal resistive index was known to be associated with carotid-femoral PWV and abnormal ACR. So, increased RI was associated with more renal damage [29].

It should be noted that augmentation index at cut-off point 10 had 82% sensitivity (AUC = 0.651) while PWV at cut-off point 7 m/s had 84% sensitivity (AUC = 0.617) for prediction of CKD. Furthermore, combination of augmentation index and PWV improved sensitivity to 94% (AUC = 0.772) for prediction of CKD. Overall, our positive results of the combined augmentation index and PWV agreed with Fouad et al., who revealed that PWV was significantly higher among hypertensive patients compared to normotensive patients which make PWV is a good predictor for end organ damage [21].

It is important to note that, our data indicated that PWV and augmentation index provide complementary information on target organ damage among hypertensive patients, but its predictive role for CKD as organ damage development parameter needs to be assessed in large prospective clinical trials. Also, our data reinforced the concept that automatic peripheral BP measurement may be helpful in diagnosing and monitoring hypertension. But some of the normotensives in the office and some of the controlled hypertensive appeared to show some type of masked hypertension, as well as an increase in central pressure, both of which are associated with the increase in aortic stiffness as measured by PWV and augmentation index.

Finally, it has long been recognized that individual discrepancies between central and peripheral BP may be magnified during hemodynamic changes or after pharmacological interventions. The differential responses of central BP vs. brachial BP to various antihypertensive agents are highly variable among individuals in clinical studies [30].

Study limitations

We acknowledge a few limitations for the present study. First, our study is limited by the enrollment of a relatively small sample included from a single center. However, this was overcome using appropriate statistical tests. The results, therefore, are preliminary and need to be confirmed and extended in larger multicenter studies on a larger number of patients to get more valid and reliable diagnostic impact.

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