This protocol describes a method to standardize the measurements of carotid-femoral pulse wave velocity to evaluate arterial stiffness.
For the elderly, arterial stiffening is a good marker for aging evaluation and it is recommended that the arterial stiffness be determined noninvasively by the measurement of carotid to femoral pulse wave velocity (cf-PWV) (Class I; Level of Evidence A). In literature, numerous community-based or disease-specific studies have reported that higher cf-PWV is associated with increased cardiovascular risk. Here, we discuss strategies to evaluate arterial stiffness with cf-PWV. Following the well-defined steps detailed here, e.g., proper position operator, distance measurement, and tonometer position, we will obtain a standard cf-PWV value to evaluate arterial stiffness. In this paper, a detailed stepwise method to record a good quality PWV and pulse wave analysis (PWA) using a non-invasive tonometry-based device will be discussed.
Arterial stiffening is a good marker for vascular aging evaluation1,2. The measurement of arterial stiffening is traditionally conducted using a pulse wave velocity (PWV) methodology that is an important and reliable measure of arterial stiffness1,3,4,5. Specifically, PWV represents the stiffness of a specific arterial segment. The pulse wave is transmitted through the arterial vessels in a specific segment, and its speed is inversely related to the viscoelastic properties of the wall itself6. PWV value increases with arterial stiffening.
Carotid-femoral PWV (cf-PWV) and brachial-ankle PWV (ba-PWV) are the 2 most frequently applied PWV measurements. They are widely used in clinical practice, where cf-PWV is popular in western countries and ba-PWV is popular in Asian countries.7,8. In fact, cf-PWV has been considered as the 'gold-standard' measurement of arterial stiffness1. For cf-PWV, it is taken as representative of the PWV for the entire aorta. Besides, for ba- PWV, there is no true arterial pathway linking the measurement sites (brachial to ankle). The estimated ba-PWV represents the PWV for the entirety of the central and peripheral arterial system9. A previous study has reported that cf-PWV is superior to ba-PWV in associations with asymptomatic hypertensive target organ damage (TOD)10 (Figure 1).
Non-invasive devices for regional stiffness equipped with a specific tonometer are increasingly being used to measure the stiffness of the carotid to femoral segment1. In cf-PWV measurements, this device and a handheld tonometer create a steady waveform on the computer that can record high resolution digital waveform images and the specific PWV values (Figure 2). All these measurements need to be standardized. Here, we show how to record a good quality cf-PWV with this non-invasive tonometry-based device in a real-world setting.
Some established cardiovascular risk prediction models such as the Framingham risk score and the SCORE Risk Charts are mainly calculated and sorted by conventional risk factors11,12. However, some novel biomarkers should be added into the risk assessment model to improve the risk stratification13. In literature, arterial stiffening is considered as an intermediate state between conventional risk factors and clinical cardiovascular events14. Thus, adding cf-PWV into the risk assessment model may be a tool for risk stratification15,16.
Here, we generate a methodology plan to assess participants' cf-PWV, together with PWA, to establish a standard protocol for arterial stiffening assessment.
This protocol was approved by the Ethics Committee of Shanghai Tenth People's Hospital.
1. Recruitment of Participants
2. Measurements of Vascular TOD
NOTE: cf-PWV and PWA measurements, like conventional four-limb blood pressure measurements, are performed through a non-invasive evaluating method. A standard protocol is crucial to obtain an accurate value, especially when there are multiple operators. Make sure to practice the method before the actual operation. The participant's cooperation is key for the measurement of cf-PWV.
Cf-PWV (with this method) and ba-PWV (with other method10) were conducted in all of the 2098 participants from Northern Shanghai Study19. Both cf-PWV and ba-PWV were used in the same logistic regression model. In this model, age and gender were adjusted. The results showed that only cf-PWV, but not ba-PWV, was significantly associated with increased IMT and arterial plaque, which indicates the superiority of cf-PWV over ba-PWV in the association with vascular abnormalities in the elderly (Figure 1).
Figure 1: The cf-PWV and ba-PWV in association with other hypertensive target organ damage in 2098 participants from Northern Shanghai Study. Odds ratios of cf-PWV and ba-PWV were presented using logistic regressions when cf-PWV and ba-PWV were both put into the same full-mode model. This data has been recalculated with the current 2098 participants. The figure was modified from a previous publication10.
Abbreviations: IMT, carotid intima-media thickness; TOD, target organ damage. Please click here to view a larger version of this figure.
Figure 2: The positions of electrodes and the segments of measured arteries. By recording the ECG and tonometer signal, the device will measure transit time as the time delay between the arrival of the pulse wave at the common carotid artery and the common femoral artery. Carotid-femoral PWV is calculated by dividing traveled distance by transit time (PWV=distance/time)
Abbreviations: RA: right arm; LL: left leg; LA: left arm Please click here to view a larger version of this figure.
Figure 3: Examiners and Patients Positioning for PWV measurement. Measurements should be performed in supine position after at least 5 min of rest. Measurements should preferentially be done at the right common carotid and common femoral arteries. The room should be quiet with stable room temperature.
Figure 4: A normal pulse wave analysis waveform (radial artery) imaged using a non-invasive tonometry-based device. The waveform will be recorded in the device and the operator index is provided directly. An operator index greater than 80% is considered as a reliable measurement. Please click here to view a larger version of this figure.
Figure 5: A normal pulse wave velocity waveform (carotid and femoral arteries) imaged using a non-invasive tonometry-based device. The waveform will be recorded in the device and the PWV value is provided directly. A cf-PWV over 10 m/s is considered as arterial stiffening. Please click here to view a larger version of this figure.
Here, we demonstrate a widely accessible methodology to assess the participants' novel preclinical vascular TOD, arterial stiffness, evaluated by cf-PWV. In order to compare PWs with minimal hemodynamic differences between measurements done prior to devices, only accept data when the brachial systolic and diastolic BP varied by less than 3 mmHg. This reduces the deviation caused by human manipulation. In this protocol, the critical steps are to have standardized patient conditions using 80% of the direct straight distance between the carotid artery and femoral artery sites and using 10 m/s as standard cut-off value for carotid-femoral PWV as arterial stiffening.
With this tonometry-based device, we can non-invasively assess participants' PWV. In fact, among tonometry-based devices, they assess similar cardiovascular risk for individuals. However, they were not consistent in measurements of central BP and wave reflections in clinical practice, with considerable and significant differences among them20. This tonometry-based device is commonly used in the measurement of aortic PWV1.
We can also get the central BP measurements from this device. However, the accuracy of the central BP measurements from non-invasive devices is very much debated and should be improved. To achieve accurate non-invasive assessment of true central BP, more accurate non-invasive estimates of intra-arterial brachial BP are needed21. The data of central BP from this measurement can be further used to make comparisons with other non-invasive devices or invasive intra-arterial standards22.
Arterial stiffening can be considered as an intermediate state between risk factors and clinical CV events, which will affect medical decision making. For instance, long term hypertension may result in severe arterial stiffening. The anti-hypertensive treatment is important for hypertensive participants. However, we prefer to reverse, terminate or at least control the process of arterial stiffening with medications, instead of just focusing on hypertension. Arterial stiffening might better represent exposure to risk factors than hypertension itself. Thus, the arterial stiffening should also be considered into the risk prediction model. It is also important to consider the effect from TOD to make risk stratification strategies. In fact, arterial stiffening which is defined as increased PWV is a composite of aging and micro-changes. An increased PWV should be considered as the phenomenon of accelerated development of cardiovascular diseases in some patients. Researches focusing on PWV and its management may provide a much longer disease-free life span23. In this way, we can make a more accurate CV assessment so as to provide a more effective guidance for management and treatment.
The authors have nothing to disclose.
This work is under the financial support from National key research and development program of China (Grant No. 2017YFC0111800) and the Shanghai municipal government (Grant ID. 2013ZYJB0902 and 15GWZK1002). Dr. Yi Zhang was supported by the National Nature Science Foundation of China (Grant ID. 81300239 and 81670377).
SphygmoCor tonometry-based device | AtCor Medical, Australia | For central blood pressures and cf-PWV | |
Electrodes | AtCor Medical, Australia | To record the ECG | |
Semiautomatic Oscillometric device | OMRON Healthcare, kyoto, Japan | To measure brachial BP |