Bilateral transit time assessment of upper and lower limbs as a surrogate ankle brachial index marker

Increasing accuracy of pulse transit time measurements by automated elimination of distorted photoplethysmography waves

Photoplethysmography (PPG) is a widely available non-invasive optical technique to visualize pressure pulse waves (PWs). Pulse transit time (PTT) is a physiological parameter that is often derived from calculations on ECG and PPG signals and is based on tightly defined characteristics of the PW shape. PPG signals are sensitive to artefacts. Coughing or movement of the subject can affect PW shapes that much that the PWs become unsuitable for further analysis. The aim of this study was to develop an algorithm that automatically and objectively eliminates unsuitable PWs. In order to develop a proper algorithm for eliminating unsuitable PWs, a literature study was conducted. Next, a '7Step PW-Filter' algorithm was developed that applies seven criteria to determine whether a PW matches the characteristics required to allow PTT calculation. To validate whether the '7Step PW-Filter' eliminates only and all unsuitable PWs, its elimination results were compared to the outcome of manual elimination of unsuitable PWs. The '7Step PW-Filter' had a sensitivity of 96.3% and a specificity of 99.3%. The overall accuracy of the '7Step PW-Filter' for detection of unsuitable PWs was 99.3%. Compared to manual elimination, using the '7Step PW-Filter' reduces PW elimination times from hours to minutes and helps to increase the validity, reliability and reproducibility of PTT data.

Comparison of bilateral pulse arrival time before and after induced vasodilation by axillary block

The propagation time of arterial pulse waves provides information about arterial stiffness. Pulse arrival time (PAT) is calculated as the time between the R-wave (ECG) and three reference points on photoplethysmographic (PPG) pulse waves: foot, first derivative and peak. Because large variation in PAT-values between patients exists, measurements of the contra-lateral arm as reference could be a solution. However, anatomical differences between arteries of the arms could introduce an offset of PAT. Furthermore, when arterial stiffness decreases (e.g. after axillary blockade (AxB)) and pulse wave amplitude increases (vasodilation), the pulse waveform can change. The aim of this study was to investigate whether there is a difference between the PAT of both arms and to evaluate the effect of vasodilation after AxB on PAT. ECG and PPG was measured on both hands in 34 patients, starting 2 min before the injection of local anaesthetic of an AxB and continuing for a period of 30 min after block placement. PAT of the baseline and after AxB were calculated and compared. The mean-PAT of both arms were not significantly different for the three reference points. After AxB, PAT significantly increased for all reference points. PAT can be used for intra-subject comparison.

Measuring pulse wave velocity using ECG and photoplethysmography

Pulse wave velocity (PWV) is a useful method to assess arterial stiffness and predict mortality of atherosclerosis-related diseases. The progression of atherosclerosis is not homogeneous. There must be difference of PWV between sites by site. Therefore we designed a multi-channel instrument to measure PWV at different sites of the body simultaneously. We measured PWV at six different regions simultaneously. Thirty four healthy adults received the measurement. We found that PWVs were higher in the large vessels, by measuring from the heart to toes and heart to fingers as compared with the measurement from the heart to the earlobes (4.76 ± 0.46 m/s; 4.67 ± 0.41 m/s; 1.10 ± 0.16 m/s). The PWV of the left and right sides were the same. Although there were statistically significances, the correlation of PWV between foot and hand is better than those between ear and foot and between ear and hand. Herein we presented a novel and reliable measurement of PWV. The changes of PWV in different regions may be used in predicting disease processes such as stroke, coronary artery diseases and renal diseases, respectively.