Summary
Background
The finger-toe pathway could be a good alternative for assessing arterial stiffness conveniently.
Aim
To evaluate the accuracy of the pOpmètre ® – a new device that measures finger-toe pulse wave velocity (ft-PWV).
Methods
The pOpmètre has two photodiode sensors, positioned on the finger and the toe. Pulse waves are recorded continuously for 20 seconds, and the difference in pulse wave transit time between toe and finger (ft-TT) is calculated. The travelled distance is estimated using subject height. Study 1 compared ft-PWV with carotid-femoral PWV (cf-PWV) obtained by the reference method (SphygmoCor ® ) in 86 subjects (mean age 53 ± 20 years), including 69 patients with various pathologies and 17 healthy normotensives. Study 2 compared changes in ft-PWV and cf-PWV during a cold pressor test in 10 healthy subjects. Study 3 assessed repeatability in 45 patients.
Results
ft-PWV correlated significantly with cf-PWV ( R 2 = 0.43; P < 0.0001). A better correlation was found in terms of transit time ( R 2 = 0.61; P < 0.0001). The discrepancy between transit times was related to age. The cold pressor test induced parallel changes in cf-PWV and ft-PWV, with increased aortic stiffness that was reversible during recovery. Intra-session repeatability was very good, with a coefficient of variation of 4.52%.
Conclusion
The pOpmètre ® allows measurement of arterial stiffness in routine clinical practice. The greatest advantages of ft-PWV are simplicity, rapidity, feasibility, acceptability by patients and correct agreement with the reference technique. Further studies are needed to adjust for bias and to validate the pOpmètre in larger populations.
Résumé
Contexte
La voie doigt-orteil pourrait représenter une bonne alternative pour évaluer facilement la rigidité artérielle. Le but de cette étude était d’évaluer l’exactitude de pOpmètre (Axelife sas – France) un nouveau dispositif de mesure de la vitesse de l’onde de pouls doigt-orteil (ft-VOP).
Méthodes
pOpmètre ® dispose de 2 capteurs photodiodes, placés sur le doigt et sur l’orteil. La différence (DOD) entre le pied de l’onde de l’orteil et celle du doigt est mesurée pendant 20 s. La distance de parcours est estimée d’après la taille des patients. L’Étude 1 a comparé la ft-VOP à la VOP carotidefémorale (cf-VOP) obtenu par la méthode de référence SphygmoCor ® dans 86 sujets (53 ± 20 ans), dont 69 patients atteints de diverses pathologies et 17 normotendus sains. L’Étude 2 a comparé les changements de ft-VOP et cf-VOP lors d’un stress test à froid dans 10 sujets sains. L’Étude 3 a évalué la répétabilité chez 45 patients.
Résultats
ft-VOP était significativement corrélé avec cf-VOP (r 2 = 0,43, p < 0,0001). Une meilleure corrélation a été trouvée en termes de temps de transit (r 2 = 0,61, p < 0,0001). La différence entre les temps de transit a été liée à l’âge. Le stress test a induit des changements comparables pour la cf-VOP et la ft-VOP: une augmentation de la rigidité aortique réversible lors de la récupération. La répétabilité intra-session a été très bonne avec un coefficient de variation de 4,52 %.
Conclusion
pOpmètre ® permet de mesurer la rigidité artérielle dans la pratique clinique. Les plus grands avantages de ft-VOP sont la facilité, la rapidité, la faisabilité et l’acceptabilité par les patients, avec un agrément correct avec la technique de référence. D’autres études sont nécessaires pour tenir compte des biais afin de valider le pOpmètre dans des populations plus importantes.
Background
Aortic pulse wave velocity (PWV) is the ‘gold standard’ of large artery stiffness. It is one of the best predictors of cardiovascular morbidity and mortality, independent of traditional risk factors, in a large number of populations ; this has been established with carotid-femoral PWV (cf-PWV), a direct measurement of aortic stiffness .
Although cf-PWV is robust, reproducible and relatively simple to use, it may be inconvenient for routine use in clinics because the measurement requires time and training. Additionally, access to the femoral artery might be difficult for cultural or clinical reasons. Other pathways have therefore been investigated, such as brachial-ankle PWV, which provides interesting prognostic data . The pOpmètre ® (Axelife SAS, Saint Nicolas de Redon, France) is an original methodology, taking advantage of easy recording of the pulse wave at the finger and the toe using two photodiodes sensors, and deriving finger-toe PWV (ft-PWV). This very simple technique may be a good alternative for the measurement of arterial stiffness evaluation in outpatient and epidemiological settings. The pOpmètre has already been studied in the general population: ft-PWV correlates with ageing and is linked with carotid plaques in metabolic syndrome . However, ft-PWV has not yet been validated against reference techniques. Moreover, the extent to which ft-PWV reflects central or peripheral arterial stiffness is unknown.
Accordingly, the aims of the present study were: to compare ft-PWV obtained with the pOpmètre with the gold standard cf-PWV (Study 1); then to determine whether ft-PWV is altered similarly to cf-PWV during acute sympathetic stimulation (Study 2); and, finally, to study the repeatability of the pOpmètre PWV measurement (Study 3).
Methods
Study 1
A total of 86 subjects were included: 69 patients and 17 healthy normotensives (42 men; mean age 53 ± 20 years; mean systolic blood pressure 130 ± 18 mmHg) from Georges Pompidou European Hospital and Broca Hospital. Patients were either well-controlled hypertensive patients ( n = 49) or patients with cognitive impairment ( n = 20). In each subject, ft-PWV and cf-PWV were measured in a random order with the pOpmètre and the SphygmoCor ® (AtCor Medical, Sydney, Australia). Measurements were performed according to the recent expert consensus .
Additionally, carotid-radial PWV and femoral-post-tibial PWV were obtained in 30 subjects using the SphygmoCor. Blood pressure and heart rate were recorded by an automatic device (Colin BP-880; Colin Medical, TX, USA) every 3 minutes to calculate the mean blood pressure value.
Study 2
The ‘cold pressor test’ was chosen as a sympathetic stimulation ; it was performed by immersing the right hand into an ice water container (4–5 °C) for 1 minute. Ten healthy subjects (4 men; mean age 30 ± 8.5 years; systolic blood pressure 118 ± 14.3 mmHg) were measured, and three sequences of measurements were performed: at baseline (every minute during 4 minutes), during the test (at 0, 30 and 60 seconds) and during recovery (at 30, 60, 90, 120 and 180 seconds). Blood pressures were recorded continuously with the oscillometric device during the test. We used the Complior ® system (Alam Medical, Vincennes, France) for cf-PWV measurement, to obtain simultaneous measurement of cf-PWV and ft-PWV during these dynamic conditions.
Study 3
The ft-PWV was measured in 45 patients in the nephrology clinic of Tours Hospital; 38 patients with various pathologies and 7 healthy subjects were measured according to the guidelines after 10 minutes of supine resting. Measurements were done every 5 minutes. If the two first measures differed by more than 0.5 m/s, then a third was performed and the median retained; the two closest measures were kept and the third discarded. All patients gave informed consent.
The study designs were approved by the ethics committee of the Georges Pompidou European Hospital, Paris, France.
Pulse wave velocity measurements
The pOpmètre was developed based on similar assumptions as those for brachial-ankle devices . The pOpmètre takes advantage of two photodiode sensors, similar to pulse oximeters (see Fig. 1 ). The photodiodes are positioned on the finger and the toe, so that the pulpar arteries are in the scope of the infrared ray. The pOpmètre measures the transit time between the foot of the pulse waves of the finger and the toe, approximating the aortic pulse transit time if the timings in the upper and lower limbs are similar; it measures continuously for 20 seconds and simultaneously on the same pulse wave. Two indices are computed: difference in pulse wave transit time between toe and finger (ft-TT; in ms); and ft-PWV [in m/s; ft-PWV = k × subject’s height/ft-TT], using a chart based on the height of 187 individuals measured in occupational medicine (personal data), where k is dependent on height. The use of the height chart relates to the fact that the aortic valves correspond to an anatomical stable landmark .
For cf-PWV measurements, the SphygmoCor records carotid and femoral pulses successively and then, related to the R wave of the electrocardiogram, calculates the transit time.
The Complior measures the arterial pulse wave at the carotid and femoral sites simultaneously. The travelled distance is the direct distance between the carotid and femoral sites of measurement multiplied by 0.8, according to the consensus for the travelled distance measurement .
Statistical analysis
Data are expressed as means ± standard deviations. A value of P < 0.05 was considered significant. The statistical analysis was performed using NCSS 2007 (NCSS LLC, Kaysville, UT, USA).
The correlation between measurement values was investigated using Pearson regression coefficient. The Bland-Altman plot was used to analyse the agreement between the two methods. The relative differences between each pair of measurements were plotted against their mean. The discrepancy between two methods was studied using multivariable correlation analyses between the relative differences and other variables.
For Study 2, ft-PWV and cf-PWV were analysed by mixed models to demonstrate the evolution of blood pressure, heart rate and PWV in the same time frame. We also determined the correlation between changes in ft-PWV and changes in cf-PWV during the test and recovery period.
In Study 3, we used the Bland-Altman method for graphic representation, and we calculated the coefficient of variation as the standard deviation divided by the mean.
Results
Study 1
Table 1 shows the descriptive variables for the main population of studies 1 and 2, and those of the study 3. As shown in Fig. 2 , ft-PWV correlated with cf-PWV ( R 2 = 0.43; P < 0.0001) and the plot of the transit time of the two methods showed a better correlation ( R 2 = 0.61; P < 0.0001). Table 2 shows the mean values and comparisons of the PWVs, transit times and distances measured by the two methods. Table 3 shows the detailed data for controls and patients.
| Variable | Studies 1 and 2 ( n = 86; 42 men) | Study 3 ( n = 45; 28 men) |
|---|---|---|
| Age (years) | 53.2 ± 20.0 [22.0–87.0] | 49.7 ± 17.5 [19.1–78.9] |
| Height (cm) | 167 ± 11 [147–198] | 168 ± 8 [151–187] |
| Weight (kg) | 66 ± 16 [52–116] | 67 ± 12 [40–103] |
| BMI (kg/m 2 ) | 23.1 ± 5.1 [16.8–32.5] | 23.5 ± 4.1 [17–34.4] |
| SBP (mmHg) | 130 ± 18 [98–192] | 137 ± 8 [96–174] |
| MBP (mmHg) | 92 ± 13 [65–139] | 109 ± 68 [43–100] |
| DBP (mmHg) | 72 ± 12 [52–113] | 79 ± 11 [51–98] |
| PP (mmHg) | 67 ± 12 [45–121] | 58 ± 16 [26–98] |
| cf-PWV (m/s) | 8.74 ± 2.15 [5.52–16.24] | – |
| cf-TT (ms) | 59 ± 14 [32–91] | – |
| ft-PWV (m/s) | 8.52 ± 3.26 [3.58–22.53] | 11.25 ± 3.94 [5.03–28.20] |
| ft-TT (ms) | 76 ± 27 [23–150] | 66 ± 18 [16–127] |
| Normalized ft-PWV | 8.77 ± 2.36 [4.48–14.79] | – |
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