Correlation between Very Short and Short-Term Blood Pressure Variability in Diabetic-Hypertensive and Healthy Subjects (2024)

Background

Blood pressure (BP) variability can be evaluated by 24-hour ambulatory BPmonitoring (24h-ABPM), but its concordance with results from finger BPmeasurement (FBPM) has not been established yet.

Objective

The aim of this study was to compare parameters of short-term (24h-ABPM) withvery short-term BP variability (FBPM) in healthy (C) anddiabetic-hypertensive (DH) subjects.

Methods

Cross-sectional study with 51 DH subjects and 12 C subjects who underwent24h-ABPM [extracting time-rate, standard deviation (SD), coefficient ofvariation (CV)] and short-term beat-to-beat recording at rest and afterstanding-up maneuvers [FBPM, extracting BP and heart rate (HR) variabilityparameters in the frequency domain, autoregressive spectral analysis].Spearman correlation coefficient was used to correlate BP and HR variabilityparameters obtained from both FBPM and 24h-ABPM (divided into daytime,nighttime, and total). Statistical significance was set at p < 0.05.

Results

There was a circadian variation of BP levels in C and DH groups; systolic BPand time-rate were higher in DH subjects in all periods evaluated. In Csubjects, high positive correlations were shown between time-rate index(24h-ABPM) and LF component of short-term variability (FBPM, total, R =0.591, p = 0.043); standard deviation (24h-ABPM) with LF component BPV(FBPM, total, R = 0.608, p = 0.036), coefficient of variation (24h-ABPM)with total BPV (FBPM, daytime, -0.585, p = 0.046) and alpha index (FBPM,daytime, -0.592, p = 0.043), time rate (24h-ABPM) and delta LF/HF (FBPM,total, R = 0.636, p = 0.026; daytime R = 0,857, p < 0.001). Recordsobtained from DH showed weak positive correlations.

Conclusions

Indices obtained from 24h-ABPM (total, daytime) reflect BP and HRvariability evaluated by FBPM in healthy individuals. This does not applyfor DH subjects.

Keywords: Hypertension; Diabetes Mellitus, Type 2; Autonomic Nervous System; Blood Pressure Monitoring, Ambulatory

Study design and population

This cross-sectional study was conducted at the outpatient clinic of the Hospitalde Clínicas de Porto Alegre (Porto Alegre, RS, Brazil), a tertiaryteaching hospital, and Instituto de Cardiologia do Rio Grande do Sul,Fundação Universitária de Cardiologia, from January 2009 toDecember 2012. The study was approved by the Ethics Committee of bothInstitutions (nº 0469.0.001.000-08 and 4313/09, respectively), which isaccredited by the Office of Human Research Protections as an InstitutionalReview Board, in agreement with the principles outlined in the Declaration ofHelsinki. After protocol approval, all subjects signed a written informedconsent for participation. Adult patients of both genders, aged 18-65 years, andwith hypertension and type 2 diabetes mellitus were invited to participate (DHgroup). Control group (C) consisted of healthy subjects, that is, withoutdiagnosis or medication for hypertension and diabetes.

Clinical evaluation

Patients underwent demographic and clinical baseline data collection. Diabetesmellitus was defined by two fasting plasma glucose ≥ 126 mg/dl or use ofantidiabetic agents or personal history of diabetes. Blood pressure was measuredwith an office aneroid sphygmomanometer and the mean values were estimated afteran two measures on average. The cuff size was selected according to armcircumference. Hypertension was defined by mean blood pressure ≥ 140/90mmHg or use of antihypertensive medication. After baseline data collection,subjects were randomly assigned to evaluations, being first submitted to24h-ABPM or to FBPM. The interval between the two examinations was of no morethan 15 days.

Short-term blood pressure variability evaluation (24h-ABPM)

All individuals were submitted to a 24h-ABPM in a usual working day, using amonitor (Spacelabs 90207, Spacelabs, Redmond, WA). Measurements were obtainedevery 15 minutes from 7 a.m. to 11 p.m., and every 20 minutes from 11 p.m. to 7a.m. to complete 24 hours of the period studied. Cuff size was selectedaccording to subjects' arm circumference.¹⁴

Based on the results of 24h-ABPM, the mean 24-hour systolic (SBP) and diastolic(DBP) blood pressures were calculated for each patient. Three differentparameters of SBP variability were calculated: 1) time-rate index (rate ofchange in SBP over time in mmHg/min, defined as the first derivative values ofSBP by time); 2) coefficient of variation of systolic BP within 24 hours(SD/mean pressure x 100%); and 3) mean of standard deviation of 24-hour systolicBP. The time-rate index allows the calculation of angular coefficients' sum andaims to measure how fast or slow and in which direction SBP values change. Themeasure was calculated using the following formula, where r is the rate of BPvariability over time (considering the differences between BP measurements ateach time interval) and N is the number of recordings:¹⁵

$$\mathit{R}=\left|\overline{\mathit{r}}\right|=\frac{{\sum }_{\mathit{i}=1}^{\mathit{N}-1}\left|\mathit{ri}\right|}{\mathit{N}-1}$$

In addition, considering circadian variations of BP and possible differencesbetween daytime and nighttime 24h-ABPM parameters, data were divided intodaytime and nighttime according to patients' reports and were also analyzedseparately, considering both periods. Circadian behavior differences werecalculated by subtracting nighttime from daytime values for each parameter.

Very short-term blood pressure variability evaluation (FBPM)

Blood pressure was recorded continuously, on a beat-to-beat basis, using theFINAPRES system (Ohmeda 2300, Monitoring Systems, Englewood, CO, USA).¹⁶ In this method, the pressurewave can be continuously monitored by a sensor placed on the patient'snon-dominant middle finger, detecting small oscillations only. The experimentalprotocol had measurements at two different stages: ten minutes at rest in asitting position and ten minutes after standing-up maneuver (sympatheticactivation).

The BP signal was digitized by the CODAS system (Computer Operated DataAcquisition Software; DATAQ, Instruments, AKRON, OH, USA), sampling at 1 kHz andanalyzed for each condition. Pulse interval (PI) tachogram and systolic arterial(SA) systogram series were constructed through the algorithm of Windaq/DATAQ,which identifies systolic peaks from BP waves. Systogram and tachogram serieswere analyzed by spectral analysis (frequency domain analysis) using anautoregressive model, applied to stationary intervals, which were selected ineach segment condition. The stationarity of each time series was tested aspreviously reported.¹⁷Short-term BP and HR variabilities were evaluated based on systogram andtachogram analyses, respectively.

In humans, the frequency domain analysis considers three distinct bands: highfrequency (HF), which includes the interval between 0.15 and 0.4 Hz; lowfrequency (LF) between 0.04 and 0.15 Hz; and very low frequency (VLF), lowerthan 0.04 Hz.^18,19 The same analysis was appliedto tachogram series. Among parameters obtained by frequency domain analysis, LFand HF components are distinguished by physiological significance. They aremainly related to sympathetic and parasympathetic cardiac modulations,respectively; the relation between them-LF/HF index-is related tosympathetic-vagal balance;²⁰and the absolute powers of LF and VLF components are predominantly related tovascular sympathetic modulation and to renin-angiotensin system modulation onSBP, respectively.¹ The alphaindex was obtained from the square root of the ratio between the LF component oftachogram and systogram when coherence, assessed by cross-spectral analysis,exceeded 0.5 in these bands²¹and expressed spontaneous baroreflex sensitivity. All series were analyzed by atrained researcher who was also blinded to conditions and subjects.

Delta indices were calculated for HR variability (HRV), LF/HF index and LFcomponent of BPV, using variable values before (rest) and after standing-upmaneuver (sympathetic activation, SA) for normalization, as follows:

$$\mathrm{Delta}=\frac{\mathrm{SA}-\mathrm{REST}}{\mathrm{REST}}$$

These indices had been previously proposed in order to quantify autonomicresponses to standing-up maneuver.^22,23

Biochemical measurements

Venous blood samples for biochemical measurements were drawn after 12-hourfasting. Plasma glucose was determined by the glucose oxidase method, serumcreatinine by Jaffé's reaction, and glycated hemoglobin (HbA1c) byion-exchange HPLC (Merck-Hitachi L-9100 HbA_1c analyzer; Merck,Darmstadt, Germany). Serum cholesterol and triglycerides were measured byenzymatic-colorimetric methods (Merck Diagnostica, Darmstadt, Germany;Boehringer Mannheim, Buenos Aires, Argentina), and HDL cholesterol by ahomogeneous direct method (autoanalyzer, ADVIA 1650). Low-density lipoprotein(LDL) cholesterol was calculated using Friedewald's formula.²⁴

Statistical analyses

Data are expressed as mean ± standard deviation (SD) or medians andinterquartile intervals, according to normality plots with tests andpercentages. Pearson's chi-square, unpaired Student's t-test, Mann-Whitney ranksum test, two-way repeated measures ANOVA or Friedman repeated measures analysisof variance on rank, post hoc Student-Newman-Keuls were usedwhen variables were compared between groups, as indicated. The correlationbetween the different indices obtained by 24h-ABPM and by FBPM were analyzed bythe Spearman's correlation coefficient. Correlations were considered fordiscussion only if they were statistically significant and representedlarge-effect sizes, as defined by a correlation coefficient of 0.50 orhigher.²⁵ Allstatistical analyses were performed using the SPSS statistical software packageversion 17.0 for Windows (SPSS Inc., Chicago, IL, USA). Statistical significancewas set at p < 0.05.

Table 1.

Clinical characteristics of controls (C) and diabetic-hypertensive (DH)subjects.

Table 2.

Very short-term blood pressure variability and heart rate variability (FBPM)at rest and after standing-up maneuver.

Table 3.

Correlation between very short- (FBPM) and short-term (24h-ABPM) BPvariability parameters - Control group.

Table 4.

Correlation between very short- (FBPM) and short-term (24h-ABPM) BPvariability parameters - DH group.

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