24-h ambulatory recording of aortic pulse wave velocity and central systolic augmentation: a feasibility study.

Hypertens Res. 2012 Oct;35(10):980-7.

Leonella Luzardo, Inés Lujambio, Mariana Sottolano, Alicia da Rosa, Lutgarde Thijs, Oscar Noboa, Jan A. Staessen, José Boggia

Unidad de Hipertensión Arterial and Centro de Nefrología, Hospital de Clínicas, Universidad de la República, Montevideo, Uruguay.

Abstract

We assessed the feasibility of ambulatory pulse wave analysis by comparing this approach with an established tonometric technique.

We investigated 35 volunteers (45.6 years; 51.0% women) exclusively at rest (R study) and 83 volunteers (49.9 years; 61.4%women) at rest and during daytime (10:00 h – 20:00 h) ambulatory monitoring (R+A study).  We recorded central systolic (cSP), diastolic (cDP) and pulse (cPP) pressures, augmentation index (cAI) and pulse wave velocity (PWV) by brachial oscillometry (Mobil-O-Graph 24h PWA Monitor) and radial tonometry (SphygmoCor).  We applied Bland and Altman’s statistics.

In the R study, tonometric and oscillometric estimates of cSP (105.6 vs. 106.9 mmHg), cDP (74.6 vs. 74.7 mmHg), cPP (31.0 vs. 32.1 mmHg), cAI (21.1 vs. 20.6%) and PWV (7.3 vs. 7.0 m/s) were similar (P≥0.11).  In the R+A study, tonometric vs. oscillometric assessment yielded similar values for cSP (115.4 vs. 113.9 mmHg; P=0.19) and cAI (26.5 vs. 25.3%; P=0.54), but lower cDP (77.8 vs. 81.9 mmHg; P<0.0001), so that cPP was higher (37.6 vs. 32.1 mmHg; P<0.0001).  PWV (7.9 vs.7.4 m/s) was higher (P=0.0002) on tonometric assessment.  The differences between tonometric and oscillometric estimates increased (P≤0.004) with level for cSP (r=0.37), cAI (r=0.39) and PWV (r=0.39), but not (P≥0.17) for cDP (r=0.15), cPP (r=0.13).

Irrespective of measurement conditions, brachial oscillometry compared with an established tonometric method provided similar estimates for central systolic pressure and systolic augmentation, but slightly underestimated pulse wave velocity.  Pending further validation, ambulatory assessment of central hemodynamic variables is feasible.

PMID: 22622282

 

Supplement:

On each  beat, the heart generates a wave that travels along the arterial vessels. Arterial aging is associated with a progressive increase in aortic stiffening  and the velocity of this pulse wave is related to the stiffness of the arteries; it travels faster if the arteries are stiffer. Arterial stiffness predicts cardiovascular complications not only in patients with hypertension, diabetes mellitus or previous cardiovascular disease, but in subjects randomly recruited from populations as well.1 Aortic pulse wave velocity (PWV) has been recommended as the gold-standard measure of arterial stiffness.2 O´Rourke and colleagues developed a simple tonometric method to asses various indexes of arterial stiffness.3  A validated algorithm permits transformation of peripheral arterial to central aortic waveforms.3-5  Analysis of the shape and timing of these waveforms provides information on central pulse pressure (cPP) and augmentation.

A common characteristic of these measurements is that they can only be done with the subjects resting in the supine position and that they require observer training.

The oscillometric Mobil-O-Graph 24h PWA Monitor (I.E.M. GmbH, Stolberg, Germany) is a validated monitor for 24‑hour blood pressure monitoring.6;7  It includes the ARCSolver application,8 which allows pulse wave analysis of the central blood pressure and measuring aortic PWV.  We conducted a study in Uruguayan volunteers to compare central haemodynamic measurements obtained by the Mobil-O-Graph at rest and under ambulatory conditions with those obtained by the SphygmoCor (AtCor Medical Pty. Ltd., West Ryde, New South Wales, Australia) at rest.

We programmed oscillometric Mobil-O-Graph monitors to obtain readings with an interval of 20 minutes from 7:00 h until 23:00 h and every 30 minutes from 23:00 h until 07:00 h.

We performed two different protocols (Figure 1). On the ‘Rest’ protocol we compared the new oscillometric method with the established tonometric technique, under laboratory controlled conditions. On the ‘Rest and Ambulatory’ protocol, we compared the central hemodynamic variables measured by the Mobil-O-Graph 24h PWA Monitor under real life ambulatory conditions with those obtained by the SphygmoCor at rest.

In studies at rest recumbent, we examined 35 volunteers after they had rested for 15 minutes in the supine position.  We averaged measurements of the brachial blood pressure and the central haemodynamic variables at baseline and after 15, 30 and 45 minutes by means of the Mobil-O-Graph. We also measured the central haemodynamic variables by means of the SphygmoCor device between the first and second and between the third and fourth Mobil-O-Graph reading.  We calibrated the SphygmoCor using the brachial blood pressure as reported by the Mobil-O-Graph at baseline and at 30 minutes.  For analysis, we averaged the 2 SphygmoCor measurements.

For the second protocol, we enrolled 83 volunteers. The SphygmoCor measurements were done at the right radial artery after the participants had rested 15 minutes in the recumbent position and were calibrated against the brachial blood pressure as measured by the OMROM 705IT at the same arm.9  After that, the Mobil-O-Graph recordings were initiated and ran over at least 24 hours.  When the participants came back the next day to return the Mobil-O-Graph monitors, the SphygmoCor measurements were repeated.  For comparison of the techniques, we averaged the SphygmoCor measurements obtained at the initiation and termination of the ambulatory recordings and we used the daytime ambulatory measurements.

At rest conditions, the tonometric and oscillometric estimates of central systolic pressure (105.6 vs. 106.9 mmHg), diastolic pressure (74.6 vs. 74.7 mmHg) and pulse pressure (31.0 vs. 32.1 mmHg) were similar (P≥0.12).  The crude augmentation index (21.1 vs. 20.6%; P=0.65), the augmentation index standardised to a heart rate of 75 beats per minute (15.1 vs. 14.0%; P=0.57) and PWV (7.3 vs. 7.0; P=0.11) also were similar.

Under ambulatory conditions, in the 83 volunteers, tonometric compared with oscillometric estimates of central haemodynamic variables, provided similar estimates for systolic pressure (115.4 vs. 113.9 mmHg; P=0.19), but central diastolic blood pressure was lower on tonometric assessment (77.8 vs. 81.9 mmHg; P<0.0001), so that central pulse pressure was higher (37.6 vs. 32.1 mmHg; P<0.0001).  Furthermore, the crude augmentation index (26.5 vs. 25.3%; P=0.54) was similar irrespective of the measurement technique, but the augmentation index standardized to a heart rate of 75 beats per minute (22.2 vs. 26.8%; P<0.0001) was lower on tonometric than oscillometric assessment, whereas the opposite was true for PWV (7.9 vs. 7.4 m/s; P=0.0002).

The key finding of our study was that irrespective of measurement conditions, brachial oscillometry by the Mobil-O-Graph, compared with the established radial tonometric method provided comparable estimates of central systolic pressure and systolic augmentation uncorrected for heart rate. Central PWV was slightly lower on oscillometric than tonometric assessment.

Pulse wave analysis derives the central from the peripheral blood pressure waves and is calibrated based on brachial blood pressure.  As observed in the current study, it therefore follows that the central blood pressure must follow a diurnal course similar to that of the peripheral brachial blood pressure (Figure 2). In conclusion, our study suggests that the ambulatory non-invasive assessment of central haemodynamic variables is feasible.  The ARCSolver algorithm underwent preliminary validation in terms of a composite cardiovascular outcome in patients with suspected coronary heart disease undergoing coronarography.10  However, further observations in diverse populations are required before ambulatory assessment of the central haemodynamic variables can make it to clinical practice.  In particular, clinicians need to know the distribution of these measurements in women and men across different age groups.  Prospective studies must generate the outcome data that the diurnal profile of the central haemodynamic measurements provided by the Mobil-O-Graph 24h PWA Monitor adds to risk stratification.

Leonella Luzardo-1

Figure 1.

Description of the two protocols.  R refers to studies exclusively in the office at rest in 35 participants (Panel A).  R+A refers to the studies at the office at rest and in ambulatory conditions in 83 participants (Panel B).  Tonometry (TM) was done at the radial artery by means of the SphygmoCor and oscillometry (OM) at the brachial by means of the Mobil-O-Graph.  The SphygmoCor was calibrated by the brachial blood pressure obtained by the Mobil-O-Graph in study R and by the OMRON 705IT in study R+A. (Reprinted from Hypertens Res. 2012 Oct;35(10):980-7.doi:10.1038/hr .2012.78)

Leonella Luzardo-2

Figure 2.

Central systolic (A), diastolic (B) and pulse (C) pressures, the crude (D) and standardised (E) augmentation indexes and for aortic pulse wave velocity (F) in 83 volunteers enrolled in study R+A.  Plotted values are 2‑hourly mean with 95% confidence interval.  P‑values are for the comparison of the daytime (10:00 h – 20:00 h) and nighttime (00:00 h – 06:00 h) means. (Reprinted from Hypertens Res. 2012 Oct;35(10):980-7.doi:10.1038/hr .2012.78)

 

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