Optimal fiducial points for pulse rate variability analysis from forehead and finger photoplethysmographic signals.

OBJECTIVE: The aim of this work is to evaluate and compare five fiducial points for the temporal location of each pulse wave from forehead and finger photoplethysmographic (PPG) pulse wave signals to perform pulse rate variability (PRV) analysis as a surrogate for heart rate variability (HRV) analysis. APPROACH: Forehead and finger PPG signals were recorded during a tilt-table test simultaneously with the electrocardiogram (ECG). Artefacts were detected and removed and five fiducial points were computed: apex, middle-amplitude and foot points of the PPG signal, apex point of the first derivative signal and the intersection point of the tangent to the PPG waveform at the apex of the derivative PPG signal and the tangent to the foot of the PPG pulse, defined as the intersecting tangents method. Pulse period (PP) time interval series were obtained from both PPG signals and compared with the RR intervals obtained from the ECG. HRV and PRV signals were estimated and classical time and frequency domain indices were computed. MAIN RESULTS: The middle-amplitude point of the PPG signal (n M ), the apex point of the first derivative ([Formula: see text]), and the tangent intersection point (n T ) are the most suitable fiducial points for PRV analysis, resulting in the lowest relative errors estimated between PRV and HRV indices and higher correlation coefficients and reliability indices. Statistically significant differences according to the Wilcoxon test between PRV and HRV signals were found for the apex and foot fiducial points of the PPG, as well as the lowest agreement between RR and PP series according to Bland-Altman analysis. Hence, these signals have been considered less accurate for variability analysis. In addition, the relative errors are significantly lower for n M and [Formula: see text] using Friedman statistics with a Bonferroni multiple-comparison test, and we propose that n M is the most accurate fiducial point. Based on our results, forehead PPG seems to provide more reliable information for a PRV assessment than finger PPG. SIGNIFICANCE: The accuracy of the pulse wave detection depends on the morphology of the PPG. There is therefore a need to widely define the most accurate fiducial point for performing a PRV analysis under non-stationary conditions based on different PPG sensor locations and signal acquisition techniques.

How Well Are Pulses Measured? Practice-Based Evidence from an Observational Study of Acutely Ill Medical Patients During Hospital Admission.

BACKGROUND: Although taking a radial pulse is considered to be an essential clinical skill, there have been few reports on how well it is measured in clinical practice, and how its accuracy and precision are influenced by rate, rhythm, and blood pressure. METHODS: This study is a retrospective quality audit carried out as part of a larger ongoing prospective observational trial. The radial pulse rates recorded by 2 research nurses were compared with the electrocardiogram (ECG) heart rates measured on acutely ill medical patients during their admission to a resource-poor hospital in sub-Saharan Africa. RESULTS: There were 619 ECGs performed on 231 patients while they were in the hospital. The median interval between measuring the vital signs and obtaining an ECG was 12.6 minutes (mean 62.3, SD 104.3 minutes). The correlation coefficient between the pulse rate recorded and ECG heart rate was 0.54. The bias between the pulse rate and the ECG heart rate was 1.34, SD 13.51 beats per minute (ie, limits of agreement 26.5 beats per minute). Bias and variance were not influenced by blood and pulse pressure. However, tachycardia increased the variance and was the only independent predictor of a pulse deficit (odds ratio 2.32; 95% confidence interval, 1.53-3.51; chi-squared 17.21; P < .0001). CONCLUSION: Practice-based evidence shows that in acutely ill patients, there is a poor correlation between the radial pulse and the ECG heart rate, and that tachycardia increases the variance and is the only independent predictor of a pulse deficit.

Predictors of the accuracy of pulse-contour cardiac index and suggestion of a calibration-index: a prospective evaluation and validation study.

BACKGROUND: Cardiac Index (CI) is a key-parameter of hemodynamic monitoring. Indicator-dilution is considered as gold standard and can be obtained by pulmonary arterial catheter or transpulmonary thermodilution (TPTD; CItd). Furthermore, CI can be estimated by Pulse-Contour-Analysis (PCA) using arterial wave-form analysis (CIpc). Obviously, adjustment of CIpc to CItd initially improves the accuracy of CIpc. Despite uncertainty after which time accuracy of CIpc might be inappropriate, recalibration by TPTD is suggested after a maximum of 8 h. We hypothesized that accuracy of CIpc might not only depend on time to last TPTD, but also on changes of the arterial wave curve detectable by PCA itself. Therefore, we tried to prospectively characterize predictors of accuracy and precision of CIpc (primary outcome). In addition to "time to last TPTD" we evaluated potential predictors detectable solely by pulse-contour-analysis. Finally, the study aimed to develop a pulse-contour-derived "calibration-index" suggesting recalibration and to validate these results in an independent collective. METHODS: In 28 intensive-care-patients with PiCCO-monitoring (Pulsion Medical-Systems, Germany) 56 datasets were recorded. CIpc-values at baseline and after intervals of 1 h, 2 h, 4 h, 6 h and 8 h were compared to CItd derived from immediately subsequent TPTD. Results from this evaluation-collective were validated in an independent validation-collective (49 patients, 67 datasets). RESULTS: Mean bias values CItd-CIpc after different intervals ranged between -0.248 and 0.112 L/min/m(2). Percentage-error after different intervals to last TPTD ranged between 18.6% (evaluation, 2 h-interval) and 40.3% (validation, 6 h-interval). In the merged data, percentage-error was below 30% after 1 h, 2 h, 4 h and 8 h, and exceeded 30% only after 6 h. "Time to last calibration" was neither associated to accuracy nor to precision of CIpc in any uni- or multivariate analysis. By contrast, the height of CIpc and particularly changes in CIpc compared to last thermodilution-derived CItd(base) univariately and independently predicted the bias CItd-CIpc in both collectives. Relative changes of CIpc compared to CItd(base) exceeding thresholds derived from the evaluation-collective (-11.6% < CIpc-CItd(base)/CItd(base) < 7.4%) were confirmed as significant predictors of a bias |CItd-CIpc| ≥ 20% in the validation-collective. CONCLUSION: Recalibration triggered by changes of CIpc compared to CItd(base) derived from last calibration should be preferred to fixed intervals.

How accurate is pulse rate variability as an estimate of heart rate variability? A review on studies comparing photoplethysmographic technology with an electrocardiogram.

BACKGROUND: The usefulness of heart rate variability (HRV) as a clinical research and diagnostic tool has been verified in numerous studies. The gold standard technique comprises analyzing time series of RR intervals from an electrocardiographic signal. However, some authors have used pulse cycle intervals instead of RR intervals, as they can be determined from a pulse wave (e.g. a photoplethysmographic) signal. This option is often called pulse rate variability (PRV), and utilizing it could expand the serviceability of pulse oximeters or simplify ambulatory monitoring of HRV. METHODS: We review studies investigating the accuracy of PRV as an estimate of HRV, regardless of the underlying technology (photoplethysmography, continuous blood pressure monitoring or Finapresi, impedance plethysmography). RESULTS/CONCLUSIONS: Results speak in favor of sufficient accuracy when subjects are at rest, although many studies suggest that short-term variability is somewhat overestimated by PRV, which reflects coupling effects between respiration and the cardiovascular system. Physical activity and some mental stressors seem to impair the agreement of PRV and HRV, often to an inacceptable extent. Findings regarding the position of the sensor or the detection algorithm are not conclusive. Generally, quantitative conclusions are impeded by the fact that results of different studies are mostly incommensurable due to diverse experimental settings and/or methods of analysis.

Providing best practice in manual pulse measurement.

This article focuses on the knowledge and pulse measurement skills that healthcare professionals require in order to safely care for patients. This paper will define pulse rate and explain why measuring pulse rate is important. In addition, it provides an overview of the different pulse sites, factors affecting the pulse, the equipment and guidelines used and information on significant groups. It will conclude by highlighting the importance of healthcare professionals acquiring the knowledge and skill of pulse monitoring.

Pulse contour analysis and transesophageal echocardiography: a comparison of measurements of cardiac output during laparoscopic colon surgery.

BACKGROUND: Pulse wave analysis (PWA) allows cardiac output (CO) measurement after calibration by transpulmonary thermodilution. A PWA system that does not require previous calibration, the FloTrac/Vigileo (FTV), has been recently developed. We compared determinations of CO made with the FTV to simultaneous measurements using transesophageal echocardiography (TEE). METHOD: Ten ASA I-II patients scheduled for laparoscopic colorectal surgery were studied. A radial 20-gauge cannula was inserted and connected to a hemodynamic monitor and a FTV system for PWA and determination of CO (CO(PWA)). TEE CO (CO(TEE)) was determined as previously described. Measurements were made after intubation, 5 min after establishing the lithotomy position, 5 min after establishing pneumoperitoneum, every 30 min, or each time mean arterial blood pressure decreased below basal values. Statistical analysis was made with the Bland and Altman method. RESULTS: Eighty-eight measurements were compared. The CO(TEE) values ranged from 3.23 to 12 Lt/min (mean 6.21 +/- 1.85). Values for CO(PWA) ranged from 2.9 to 8.5 Lt/min (mean 4.84 +/- 1.14). Bias was 1.17 and limits of agreement -2.02 and 4.37. The percentage error between all CO(TEE) and CO(PWA) measurements was 40% (27%-50%) mean (range). CONCLUSION: During laparoscopic colon surgery, clinically important differences were observed between CO determinations made with TEE and FTV.

How to standardize 3 finger positions of examiner for palpating radial pulses at wrist in traditional Chinese medicine.

This study was to provide a standardized definition of the positioning method of finger placement on the radial artery for pulse diagnosis in traditional Chinese medicine (TCM); that is, to define the locations of Cun, Guan and Chi in TCM. A total of 200 subjects (100 males and 100 females, 18-40 years of age) were recruited from the general population. According to ancient TCM records, the "6% of the elbow length" (ELx6%) is used as the standard method of establishing the length of Cun. We hypothesized that the highest point of "prominent bone" (PB) is the lower limit of Cun, so "the distance between the distal wrist crease and the highest point of the PB" (DWP) is considered the length of Cun. If this hypothesis holds, then we can define the locations of Cun, Guan and Chi by using the ratio 6:6:7 from the ancient TCM records. The distribution of relative bias and paired t-test were used to verify the findings. The mean value of relative bias of DWP compared with ELx6% was close to 0% (males = 2.1%, SD = 12.2%; females = 0.2%, SD = 12.6%). The paired t-test confirmed that there was no significant difference (p > 0.05) between the mean values of the DWP and ELx6%. Therefore, it is reasonable to assume that the length of the Cun is equal to the length of the DWP. Our findings confirm that the location of Cun is from the distal wrist crease to the highest point of PB.

The reliability of pulse contour-derived cardiac output during hemorrhage and after vasopressor administration.

BACKGROUND: Reliable measurement of cardiac output (CO) is important in the critically ill. Pulse contour-derived CO (PCCO) has been evaluated during stable hemodynamics, but is sensitive to changes in vascular tone and has not been validated under conditions of changing hemodynamics. Furthermore, PCCO requires calibration for the individual vascular impedance by transpulmonary thermodilution CO (TPCO), and the required frequency of recalibration to maintain accurate measurements, especially during changing conditions, has not been confirmed. We compared PCCO measurements of CO with TPCO and continuous and bolus pulmonary artery CO (CCO and BCO, respectively) during conditions of uncontrolled hemorrhage and resuscitation with norepinephrine. METHODS: Thirteen pigs were anesthetized and instrumented for determination of CO by BCO and CCO, respectively, as well as bolus TPCO and PCCO. Uncontrolled hemorrhage was accomplished by liver incision. When mean arterial blood pressure was <25 mm Hg, or heart rate declined progressively to <20% of its peak value, vasopressor therapy was started. TPCO and BCO were performed after induction of anesthesia and 15 min after start of therapy, and PCCO and CCO were obtained repeatedly. CO measurements were compared using Bland-Altman analysis. RESULTS: Mean arterial blood pressure, CO and systemic vascular resistance decreased after hemorrhage (P < 0.001 and <0.01, respectively). Bias and limits of agreement between CCO and PCCO (0.54 L/min; 1.46 L/min) increased after hemorrhage (-3.49; 6.12) and further deteriorated after norepinephrine administration (-8.01; 9.9). After recalibration, bias and limits of agreement returned to -0.51 and 1.28. CONCLUSIONS: PCCO needs frequent recalibration during hemorrhage and after vasopressor administration.

Parents measuring pulses; an observational study.

Parent reported pulse rates could provide important information on a child's clinical condition. The agreement between the parent's measurement of their child's pulse and a pulse oximeter was assessed following a brief educational intervention. Parents can be taught to measure the pulse of school age children, but have difficulty with preschool children.

Cardiopulmonary Resuscitation Guidelines 2000 update: what's happened since?

PURPOSE OF REVIEW: To examine the literature for new resuscitation science since the publication of the Guidelines 2000 for Cardiopulmonary Resuscitation and Emergency Cardiac Care. RECENT FINDINGS: The two and a half years since the publication of the Guidelines 2000 have seen the advent of a number of new and important resuscitation studies. Such studies highlight the importance of simplification of cardiopulmonary resuscitation techniques and guidelines, including the elimination of the layperson pulse check and the need for a simple form of basic life support cardiopulmonary resuscitation that decreases interruptions of chest compressions. Automatic external defibrillators, even in the hands of nontraditional first responders, are effective and safe. A second prospective, randomized clinical trial of amiodarone for refractory ventricular fibrillation has again shown positive results in improving survival to hospital admission. Finally, mild hypothermia appears to be the first effective therapy at decreasing central nervous system injury when administered after resuscitation. SUMMARY: In this report, we review these new studies and discuss how they corroborate or alter the published 2000 guidelines.

Data compression for arterial pulse waveform.

The arterial pulse possesses important clinical information in traditional Chinese medicine. It is usually recorded for a long period of time in the applications of telemedicine and PACS systems. Due to the huge amount of data, by recognizing the strong correlation between successive beat patterns in arterial pulse waveform sequences, a novel and efficient data compression scheme based mainly on pattern matching is introduced. The simulation results show that our coding scheme can achieve a very high compression ratio and low distortion for arterial pulse waveform.

Wave travel and reflection in the arterial system.

Blood pressure indices reveal pertinent information regarding the risk factors associated with certain cardiovascular conditions. In the last decade, research has focused on determining which module of measurement is most relevant as well as exploring new investigative techniques to aid in detection and treatment of cardiovascular disease (CVD). The rates of isolated systolic hypertension, arteriosclerosis and other diseases associated with ageing continue to rise as the elderly population grows. The cuff sphygmomanometer only measures blood pressure in the brachial artery. Pulse wave analysis (PWA) is a noninvasive method of generating the ascending aorta pressure wave from the arterial pressure pulse measured in the carotid or radial artery. Pulse wave analysis identifies the effects of increased pulse wave velocity (PWV), an indicator of arterial stiffness, and an independent measure of cardiovascular risk. As there is a discrepancy between pulse readings at different sites, PWA is invaluable in providing information on the left ventricle and on large arteries. This measurement can reveal the unseen beneficial effects of antihypertensive drugs, as ascending aortic systolic and pulse pressure often decrease more than brachial pressure, and can indicate the presence of spurious systolic hypertension. The technique is not difficult to learn and results have been reproduced in several studies. Continuing research into PWA needs to be done, however, to assure the reliability of the measurements and minimize the possibility of incorrect readings.