Value and Variability of Pulse Shape Indicator for Estimating Mean Arterial Pressure in the Radial and Femoral Arteries.

BACKGROUND: The form factor (FF) is a pulse shape indicator that corresponds to the fraction of pulse pressure added to diastolic blood pressure to estimate the time-averaged mean arterial pressure (MAP). Our invasive study assessed the FF value and variability at the radial and femoral artery levels and evaluated the recommended fixed FF value of 0.33. METHODS AND RESULTS: Hemodynamically stable patients were prospectively included in 2 intensive care units. FF was documented at baseline and during dynamic maneuvers. A total of 632 patients (64±16 years of age, 66% men, MAP=81±14 mm Hg) were included. Among them, 355 (56%) had a radial catheter and 277 (44%) had a femoral catheter. The FF was 0.34±0.06. In multiple linear regression, FF was influenced by biological sex (P<0.0001) and heart rate (P=0.04) but not by height, weight, or catheter location. The radial FF was 0.35±0.06, whereas the femoral FF was 0.34±0.05 (P=0.08). Both radial and femoral FF were higher in women than in men (P<0.05). When using the 0.33 FF value to estimate MAP, the error was -0.4±4.0 mm Hg and -0.1±2.9 mm Hg at the radial and femoral level, respectively, and the MAP estimate still demonstrated high accuracy and good precision even after changes in norepinephrine dose, increase in positive end-expiratory pressure level, fluid administration, or prone positioning (n=218). CONCLUSIONS: Despite higher FF in women and despite interindividual variability in FF, using a fixed FF value of 0.33 yielded accurate and precise estimations of MAP. This finding has potential implications for blood pressure monitoring devices and the study of pulse wave amplification.

Non-Invasive Estimation of Central Systolic Blood Pressure by Radial Tonometry: A Simplified Approach.

BACKROUND: Central systolic blood pressure (cSBP) provides valuable clinical and physiological information. A recent invasive study showed that cSBP can be reliably estimated from mean (MBP) and diastolic (DBP) blood pressure. In this non-invasive study, we compared cSBP calculated using a Direct Central Blood Pressure estimation (DCBP = MBP2/DBP) with cSBP estimated by radial tonometry. METHODS: Consecutive patients referred for cardiovascular assessment and prevention were prospectively included. Using applanation tonometry with SphygmoCor device, cSBP was estimated using an inbuilt generalized transfer function derived from radial pressure waveform, which was calibrated to oscillometric brachial SBP and DBP. The time-averaged MBP was calculated from the radial pulse waveform. The minimum acceptable error (DCBP-cSBP) was set at ≤5 (mean) and ≤8 mmHg (SD). RESULTS: We included 160 patients (58 years, 54%men). The cSBP was 123.1 ± 18.3 mmHg (range 86-181 mmHg). The (DCBP-cSBP) error was -1.4 ± 4.9 mmHg. There was a linear relationship between cSBP and DCBP (R2 = 0.93). Forty-seven patients (29%) had cSBP values ≥ 130 mmHg, and a DCBP value > 126 mmHg exhibited a sensitivity of 91.5% and specificity of 94.7% in discriminating this threshold (Youden index = 0.86; AUC = 0.965). CONCLUSIONS: Using the DCBP formula, radial tonometry allows for the robust estimation of cSBP without the need for a generalized transfer function. This finding may have implications for risk stratification.

Velocity-pressure loops can estimate intrinsic and pharmacologically induced changes in cardiac afterload during non-cardiac surgery. An observational study.

PURPOSE: Continuous measurement of aortic pressure and aortic flow velocity signals in the operating theatre allows us to draw velocity-pressure (Vel-Pre) loops. The global afterload angle (GALA), derived from the Vel-Pre loops, has been linked to cardiac afterload indicators. As age is the major determinant of constitutive arterial stiffness, we aimed to describe (1) the evolution of the GALA according to age in a large cohort of anesthetized patients and (2) GALA variations induced by haemodynamic interventions. METHODS: We included patients for whom continuous monitoring of arterial pressure and cardiac output were indicated. Fluid challenges or vasopressors were administered to treat intra-operative hypotension. The primary endpoint was the comparison of the GALA values between young and old patients. The secondary endpoint was the difference in the GALA values before and after haemodynamic interventions. RESULTS: We included 133 anaesthetized patients: 66 old and 67 young patients. At baseline, the GALA was higher in the old patients than in young patients (38 ± 6 vs. 25 ± 4 degrees; p < 0.001). The GALA was positively associated with age (p < 0.001), but the mean arterial pressure (MAP) and cardiac output were not. The GALA did not change after volume expansion, regardless of the fluid response, but it did increase after vasopressor administration. Furthermore, while a vasopressor bolus led to a similar increase in MAP, phenylephrine induced a more substantial increase in the GALA than noradrenaline (+ 12 ± 5° vs. + 8 ± 5°; p = 0.01). CONCLUSION: In non-cardiac surgery, the GALA seems to be associated with both intrinsic rigidity (reflected by age) and pharmacologically induced vasoconstriction changes (by vasopressors). In addition, the GALA can discriminate the differential effects of phenylephrine and noradrenaline. These results should be confirmed in a prospective, ideally randomized, trial.

Real-time estimation of mean arterial blood pressure based on photoplethysmography dicrotic notch and perfusion index. A pilot study.

Hypotension during general anesthesia is associated with poor outcome. Continuous monitoring of mean blood pressure (MAP) during anesthesia is useful and needs to be reliable and minimally invasive. Conventional cuff measurements can lead to delays due to its discontinuous nature. It has been shown that there is a relationship between MAP and photoplethysmography (PPG) parameters like the dicrotic notch and perfusion index (PI). The objective of the study was to continuously estimate MAP from PPG. Pulse wave analysis based on PPG was implemented using either notch relative amplitude (MAPNRA), notch absolute amplitude (MAPNAA) or PI (MAPPI) to estimate MAP from PPG waveform features during general anesthesia. Estimated MAP values were compared to brachial cuff MAP (MAPcuff) and to radial invasive MAP (MAPinv). Forty-six patients were analyzed for a total of 235 h. Compared to MAPcuff, mean bias and limits of agreement were 1 mmHg (- 26 to +29), - 1 mmHg (- 10 to +8) and - 3 mmHg (- 21 to +13) for MAPNRA, MAPNAA and MAPPI respectively. Compared to MAPinv, mean absolute error (MAE) was 20 mmHg [10 to 39], 11 mmHg [5 to 18] and 16 mmHg [9 to 24] for MAP derived from MAPNRA, MAPNAA and MAPPI respectively. When calibrated every 5 min, MAPNAA showed a MAE of 6 mmHg [5 to 9]. MAPNAA provides the best estimates with respect to brachial cuff MAP and invasive MAP. Regular calibration allows to reduce drift over time. Beat to beat estimation of MAP during general anesthesia from the PPG appears possible with an acceptable average error.

New Method to Estimate Central Systolic Blood Pressure From Peripheral Pressure: A Proof of Concept and Validation Study.

Objective: The non-invasive estimation of central systolic blood pressure (cSBP) is increasingly performed using new devices based on various pulse acquisition techniques and mathematical analyses. These devices are most often calibrated assuming that mean (MBP) and diastolic (DBP) BP are essentially unchanged when pressure wave travels from aorta to peripheral artery, an assumption which is evidence-based. We tested a new empirical formula for the direct central blood pressure estimation of cSBP using MBP and DBP only (DCBP = MBP2/DBP). Methods and Results: First, we performed a post-hoc analysis of our prospective invasive high-fidelity aortic pressure database (n = 139, age 49 ± 12 years, 78% men). The cSBP was 146.0 ± 31.1 mmHg. The error between aortic DCBP and cSBP was -0.9 ± 7.4 mmHg, and there was no bias across the cSBP range (82.5-204.0 mmHg). Second, we analyzed 64 patients from two studies of the literature in whom invasive high-fidelity pressures were simultaneously obtained in the aorta and brachial artery. The weighed mean error between brachial DCBP and cSBP was 1.1 mmHg. Finally, 30 intensive care unit patients equipped with fluid-filled catheter in the radial artery were prospectively studied. The cSBP (115.7 ± 18.2 mmHg) was estimated by carotid tonometry. The error between radial DCBP and cSBP was -0.4 ± 5.8 mmHg, and there was no bias across the range. Conclusion: Our study shows that cSBP could be reliably estimated from MBP and DBP only, provided BP measurement errors are minimized. DCBP may have implications for assessing cardiovascular risk associated with cSBP on large BP databases, a point that deserves further studies.

A systematic review of invasive, high-fidelity pressure studies documenting the amplification of blood pressure from the aorta to the brachial and radial arteries.

It is commonly accepted that systolic blood pressure (SBP) is significantly higher in the brachial/radial artery than in the aorta while mean (MBP) and diastolic (DBP) pressures remain unchanged. This may have implications for outcome studies and for non-invasive devices calibration. We performed a systematic review of invasive high-fidelity pressure studies documenting BP in the aorta and brachial/radial artery. We selected articles published prior to July 2015. Pressure amplification (Amp = peripheral minus central pressure) was calculated (weighted mean). The six studies retained (n = 294, 76.5% male, mean age 63.5 years) mainly involved patients with suspected coronary artery disease (CAD). In two studies at the aortic/brachial level (n = 64), MBP and DBP were unchanged (MPAmp = 0.1 mmHg, DPAmp = -1.3 mmHg), while SBP increased (SPAmp = 4.2 mmHg; relative amplification = 3.1%). In four studies in which MBP was not documented (n = 230), brachial DBP remained unchanged and SBP increased (SPAmp = 6.6 mmHg; 4.9%). One of these four studies also reported radial SBP and DBP, not MBP (n = 12). Few high-fidelity pressure studies were found, and they have been performed mainly in elderly male patients with suspected CAD. Counter to expectations, the mean amplification of SBP from the aorta to brachial artery was < 5%. Further studies on SPAmp phenotypes (positive, null, negative) are advocated. Non-invasive device calibration assumptions were confirmed, namely unchanged MBP and DBP from the aorta to the brachial artery. Data did not allow for firm conclusions on the amount of BP changes from the aorta to the radial artery, and from the aorta to the brachial/radial arteries in other populations.

Influence of noninvasive central blood pressure devices for afterload monitoring with aortic velocity-pressure Loop in anesthetized patients.

BACKGROUND: Global afterload angle (GALA) is a parameter derived from velocity-pressure loop (VP Loop), for continuous assessment of cardiac afterload in the operating room. It has been validated with invasive measure of central pressure. The aim of this study was to evaluate the feasibility of noninvasive VP Loop obtained with central pressure measured with two different noninvasive tonometers. METHODS: A prospective, observational, monocentric study was conducted in 51 patients under general anesthesia. Invasive central pressure (cPINV) was measured with a fulfilled intravascular catheter, and noninvasive central pressure signals were obtained with two applanation tonometry devices: radial artery tonometry (cPSHYG: Sphygmocor tonometer) and carotid tonometry (cPCOMP: Complior tonometer). Three VP Loops were built: VP LoopINV, VP LoopSPHYG and VP LoopCOMP. Patients were separated according to cardiovascular risk factors. RESULTS: In the 51 patients under general anesthesia, cPSHYG was adequately obtained in 48 patients (89%) but, compared to cPINV, SBP was underestimated (-4 ± 6 mmHg, P < 0.0001), augmentation index (AIXSPHYG) and a GALASPHYG were overestimated (+13 ± 19%, P = 0.0077 and +4 ± 8°, P = 0.0024, respectively) with large limit of agreement (LOA) (-21 to 47% and -13 to 21° for AIXSPHYG and GALASPHYG, respectively). With the Complior, the failure rate of measurement for cPCOMP was 41%. SBP was similar (3 ± 17 mmHg, P = 0.32), AIXCOMP was underestimated (-11 ± 19%, P = 0.0046) and GALACOMP was similar but with large LOA (-50 to 26% and -20 to 18° for AIXCOMP and GALACOMP, respectively). CONCLUSION: In anesthetized patient, the reliability of noninvasive central pressure monitoring by tonometry seems too limited to monitor cardiac afterload with VP Loop.

Impact of simultaneous measurement of central blood pressure with the SphygmoCor Xcel during MRI acquisition to better estimate aortic distensibility.

OBJECTIVES: Aortic distensibility estimation of local aortic stiffness is based on local aortic strains and central pulse pressure (cPP) measurements. Most MRI studies used either brachial PP (bPP) despite differences with cPP, or direct cPP estimates obtained after MRI examination, assuming no major pressure variations. We evaluated the feasibility of assessment of cPP with a specific device fitted with a 6 m long hose (study1) and looked at the influence of using such cPP within the magnet instead of bPP on aortic distensibility in a control population (study 2). METHODS: Brachial and central pressures values were recorded with the SphygmoCor XCEL system fitted with 2 and 6 m long tubing randomly assigned on arms. A 6 m long tubing was used in the second study to measure aortic distensibility with MRI. Aortic distensibility was calculated using either bPP (bAD) or cPP (cAD). RESULTS: Study1, performed on 38 patients (mean age: 43 ±â€Š17 years), showed no statistical difference between bPP and cPP measured with 2 or 6 m long tubing (0.41 ±â€Š4.45 and 0.78 ±â€Š3.18 mmHg, respectively, both P = ns). In study 2, cAD provided statistically higher values than bAD (1.87 ±â€Š1.43 10 ·â€ŠmmHg, P < 0.001) especially in younger individuals (3.28 ±â€Š0.86 10 ·â€ŠmmHg). The correlation between age and aortic distensibility was stronger with cAD (r = -0.92; P < 0,001) than with bAD (r = -0.88; P < 0.001). CONCLUSION: cPP can be estimated with reasonable accuracy during MRI acquisition using a 6 m long tube. Using either cPP or bPP greatly influences aortic distensibility values, especially in young individuals in whom an accurate detection of early or accelerated vascular aging can be of major importance.

Noninvasive Estimation of Aortic Stiffness Through Different Approaches.

Aortic pulse wave velocity is a worldwide accepted index to evaluate aortic stiffness and can be assessed noninvasively by several methods. This study sought to determine if commonly used noninvasive devices can all accurately estimate aortic pulse wave velocity. Pulse wave velocity was estimated in 102 patients (aged 65±13 years) undergoing diagnostic coronary angiography with 7 noninvasive devices and compared with invasive aortic pulse wave velocity. Devices evaluating carotid-femoral pulse wave velocity (Complior Analyse, PulsePen ET, PulsePen ETT, and SphygmoCor) showed a strong agreement between each other ( r>0.83) and with invasive aortic pulse wave velocity. The mean difference ±SD with the invasive pulse wave velocity was -0.73±2.83 m/s ( r=0.64) for Complior-Analyse: 0.20±2.54 m/s ( r=0.71) for PulsePen-ETT: -0.04±2.33 m/s ( r=0.78) for PulsePen ET; and -0.61±2.57 m/s ( r=0.70) for SphygmoCor. The finger-toe pulse wave velocity, evaluated by pOpmètre, showed only a weak relationship with invasive aortic recording (mean difference ±SD =-0.44±4.44 m/s; r=0.41), and with noninvasive carotid-femoral pulse wave velocity measurements ( r<0.33). Pulse wave velocity estimated through a proprietary algorithm by BPLab (v.5.03 and v.6.02) and Mobil-O-Graph showed a weaker agreement with invasive pulse wave velocity compared with carotid-femoral pulse wave velocity (mean difference ±SD =-0.71±3.55 m/s, r=0.23; 1.04±2.27 m/s, r=0.77; and -1.01±2.54 m/s, r=0.71, respectively), revealing a negative proportional bias at Bland-Altman plot. Aortic pulse wave velocity values provided by BPLab and Mobil-O-Graph were entirely dependent on age-squared and peripheral systolic blood pressure (cumulative r2=0.98 and 0.99, respectively). Thus, among the methods evaluated, only those assessing carotid-femoral pulse wave velocity (Complior Analyse, PulsePen ETT, PulsePen ET, and SphygmoCor) appear to be reliable approaches for estimation of aortic stiffness.

Noninvasive continuous detection of arterial hypotension during induction of anaesthesia using a photoplethysmographic signal: proof of concept.

BACKGROUND: During general anaesthesia, intraoperative hypotension (IOH), defined as a mean arterial pressure (MAP) reduction of > 20%, is frequent and may lead to complications. Pulse oximetry is mandatory in the operating room, making the photoplethysmographic signal and parameters, such as relative dicrotic notch height (Dicpleth) or perfusion index (PI), readily available. The purpose of this study was to investigate whether relative variations of Dicpleth and PI could detect IOH during anaesthesia induction, and to follow their variations during vasopressor boluses. METHODS: MAP, Dicpleth, and PI were monitored at 1-min intervals during target control induction of anaesthesia with propofol and remifentanil in 61 subjects. Vasopressor infusion (norepinephrine or phenylephrine) was performed when hypotension occurred according to the decision of the physician. RESULTS: The delta in Dicpleth and PI accurately detected IOH, with areas under the receiver operating characteristic curves (AUC) of 0.86 and 0.83, respectively. The optimal thresholds were -19% (sensitivity 79%; specificity 84%) and 51% (sensitivity 82%; specificity 74%) for ΔDicpleth and ΔPI, respectively. There was no difference between the ROC of ΔDicpleth and ΔPI (P=0.22). Combining both ΔDicpleth and ΔPI further improved the hypotension detection power (AUC=0.91) with a sensitivity and specificity of 84%. MAP variations were correlated with ΔDicpleth and ΔPI during vasopressor infusion (r=0.73 and -0.62, respectively; P<0.001). CONCLUSIONS: The relative variation in Dicpleth and PI derived from the photoplethysmographic signal can be used as a non invasive, continuous, and simple tool to detect intraoperative hypotension, and to track the vascular response to vasoconstrictor drugs during induction of general anaesthesia. CLINICAL TRIAL REGISTRATION: NCT03756935.

Validation and Critical Evaluation of the Effective Arterial Elastance in Critically Ill Patients.

OBJECTIVES: First, to validate bedside estimates of effective arterial elastance = end-systolic pressure/stroke volume in critically ill patients. Second, to document the added value of effective arterial elastance, which is increasingly used as an index of left ventricular afterload. DESIGN: Prospective study. SETTING: Medical ICU. PATIENTS: Fifty hemodynamically stable and spontaneously breathing patients equipped with a femoral (n = 21) or radial (n = 29) catheter were entered in a "comparison" study. Thirty ventilated patients with invasive hemodynamic monitoring (PiCCO-2; Pulsion Medical Systems, Feldkirchen, Germany), in whom fluid administration was planned were entered in a " dynamic" study. INTERVENTIONS: In the "dynamic" study, data were obtained before/after a 500 mL saline administration. MEASUREMENTS AND MAIN RESULTS: According to the "cardiocentric" view, end-systolic pressure was considered the classic index of left ventricular afterload. End-systolic pressure was calculated as 0.9 × systolic arterial pressure at the carotid, femoral, and radial artery level. In the "comparison" study, carotid tonometry allowed the calculation of the reference effective arterial elastance value (1.73 ± 0.62 mm Hg/mL). The femoral estimate of effective arterial elastance was more accurate and precise than the radial estimate. In the "dynamic" study, fluid administration increased stroke volume and end-systolic pressure, whereas effective arterial elastance (femoral estimate) and systemic vascular resistance did not change. Effective arterial elastance was related to systemic vascular resistance at baseline (r = 0.89) and fluid-induced changes in effective arterial elastance and systemic vascular resistance were correlated (r = 0.88). In the 15 fluid responders (cardiac index increases ≥ 15%), fluid administration increased end-systolic pressure and decreased effective arterial elastance and systemic vascular resistance (each p < 0.05). In the 15 fluid nonresponders, end-systolic pressure increased (p < 0.05), whereas effective arterial elastance and systemic vascular resistance remained unchanged. CONCLUSIONS: In critically ill patients, effective arterial elastance may be reliably estimated at bedside (0.9 × systolic femoral pressure/stroke volume). We support the use of this validated estimate of effective arterial elastance when coupled with an index of left ventricular contractility for studying the ventricular-arterial coupling. Conversely, effective arterial elastance should not be used in isolation as an index of left ventricular afterload.

Arterial stiffness alteration and obstructive sleep apnea in an elderly cohort free of cardiovascular event history: the PROOF cohort study.

INTRODUCTION: Several studies suggest in middle-aged subjects a relationship between arterial stiffness, a cardiovascular risk marker, and moderate to severe obstructive sleep apnea (OSA). No extensive data are present in older subjects. This study explores this association in a sample of healthy older subjects suffering OSA. METHODS: A total of 101 volunteers aged 75.3 ± 0.7 years were examined at the hospital sleep center. Each subject was assessed for medical history, body mass index and 24-h blood pressure measures, biological blood samples, and home polygraphy in 2002-2003 (P2) as well as in 2009-2010 (P4). Arterial stiffness was also assessed using carotid-femoral and carotid-radial pulse wave velocity (cfPWV and crPWV) during P4 examination. RESULTS: The total group consisted of 59 women and 42 men with a mean apnea-hypopnea index (AHI) of 17.8 ± 12.1 and a mean oxygen desaturation index (ODI) of 9.8 ± 8.9. No-OSA (AHI < 15) represented 50% of the sample, and severe cases (AHI > 30) 17%. No significant differences had been founded between men and women for blood pressure, cfPWV, and crPWV. Considering the severity of the AHI, no significant differences between groups were present for PWV and blood pressure values. No difference for PWV was present for subjects with and without hypertension. No correlation was found between PWV value and AHI and ODI values at P2 or between P2 and P4 visits. cfPWV was higher in patients demonstrating incident hypertension during the follow-up. CONCLUSIONS: In this sample of older subjects, PWV is not affected by AHI and ODI but was associated with incident hypertension. These results may suggest potential protective and adaptive mechanisms in older sleep apnea patients. CLINICAL TRIAL REGISTRATIONS: NCT 00759304 and NCT 00766584 .

Evaluation of cardiac output variations with the peripheral pulse pressure to mean arterial pressure ratio.

Cardiac output (CO) optimisation during surgery reduces post-operative morbidity. Various methods based on pulse pressure analysis have been developed to overcome difficulties to measure accurate CO variations in standard anaesthetic settings. Several of these methods include, among other parameters, the ratio of pulse pressure to mean arterial pressure (PP/MAP). The aim of this study was to evaluate whether the ratio of radial pulse pressure to mean arterial pressure (ΔPPrad/MAP) could track CO variations (ΔCO) induced by various therapeutic interventions such as fluid infusions and vasopressors boluses [phenylephrine (PE), norepinephrine (NA) or ephedrine (EP)] in the operating room. Trans-oesophageal Doppler signal and pressure waveforms were recorded in patients undergoing neurosurgery. CO and PPrad/MAP were recorded before and after fluid challenges, PE, NA and EP bolus infusions as medically required during their anaesthesia. One hundred and three patients (mean age: 52 ± 12 years old, 38 men) have been included with a total of 636 sets of measurement. During fluids challenges (n = 188), a positive correlation was found between ΔPPrad/MAP and ΔCO (r = 0.22, p = 0.003). After PE (n = 256) and NA (n = 121) boluses, ΔPPrad/MAP positively tracked ΔCO (r = 0.53 and 0.41 respectively, p < 0.001). By contrast, there was no relation between ΔPPrad/MAP and ΔCO after EP boluses (r = 0.10, p = 0.39). ΔPPrad/MAP tracked ΔCO variations during PE and NA vasopressor challenges. However, after positive fluid challenge or EP boluses, ΔPPrad/MAP was not as performant to track ΔCO which could make the use of this ratio difficult in current clinical practice.

Contribution of obstructive sleep apnoea to arterial stiffness: a meta-analysis using individual patient data.

BACKGROUND: Arterial stiffness, measured by pulse wave velocity (PWV), is a strong independent predictor of late cardiovascular events and mortality. It is recognised that obstructive sleep apnoea (OSA) is associated with cardiovascular comorbidities and mortality. Although previous meta-analyses concluded that PWV is elevated in OSA, we feel that an individual patient data analysis from nine relatively homogeneous studies could help answer: to what extent does OSA drive arterial stiffness? METHODS: Individual data from well-characterised patients referred for suspicion of OSA, included in nine studies in which carotid-femoral PWV was measured using a Complior device, were merged for an individual patient data meta-analysis. RESULTS: 893 subjects were included (age: 56±11 (mean±SD), 72% men, 84% with confirmed OSA). Body Mass Index varied from 15 to 81 kg/m2 (30±7 kg/m2). PWV ranged from 5.3 to 20.5 m/s (10.4±2.3 m/s). In univariate analysis, log(PWV) was strongly related to age, gender, systolic blood pressure, presence of type 2 diabetes (all p<0.01) as well as to dyslipidaemia (p=0.03) and an Epworth Sleepiness Scale score ≥9 (p=0.04), whereas it was not related to obesity (p=0.54), a severe Apnoea-Hypopnoea Index (p=0.14), mean nocturnal saturation (p=0.33) or sleep time with oxygen saturation below 90% (p=0.47). In multivariable analysis, PWV was independently associated with age, systolic blood pressure and diabetes (all p<0.01), whereas severe OSA was not significantly associated with PWV. CONCLUSION: Our individual patient meta-analysis showed that elevated arterial stiffness in patients with OSA is driven by conventional cardiovascular risk factors rather than apnoea parameters.

Beat-by-beat assessment of cardiac afterload using descending aortic velocity-pressure loop during general anesthesia: a pilot study.

INTRODUCTION: Continuous cardiac afterload evaluation could represent a useful tool during general anesthesia (GA) to titrate vasopressor effect. Using beat to beat descending aortic pressure(P)/flow velocity(U) loop obtained from esophageal Doppler and femoral pressure signals might allow to track afterload changes. Methods We defined three angles characterizing the PU loop (alpha, beta and Global After-Load Angle (GALA)). Augmentation index (AIx) and total arterial compliance (Ctot) were measured via radial tonometry. Peripheral Vascular Resistances (PVR) were also calculated. Twenty patients were recruited and classified into low and high cardiovascular (CV) risk group. Vasopressors were administered, when baseline mean arterial pressure (MAP) fell by 20%. Results We studied 118 pairs of pre/post bolus measurements. At baseline, patients in the lower CV risk group had higher cardiac output (6.1 ± 1.7 vs 4.2 ± 0.6 L min; p = 0.005), higher Ctot (2.7 ± 1.0 vs 2.0 ± 0.4 ml/mmHg, p = 0.033), lower AIx and PVR (13 ± 10 vs 32 ± 11% and 1011 ± 318 vs 1390 ± 327 dyn s/cm5; p < 0.001 and p = 0.016, respectively) and lower GALA (41 ± 15 vs 68 ± 6°; p < 0.001). GALA was the only PU Loop parameter associated with Ctot, AIx and PVR. After vasopressors, MAP increase was associated with a decrease in Ctot, an increase in AIx and PVR and an increase in alpha, beta and GALA (p < 0.001 for all). Changes in GALA and Ctot after vasopressors were strongly associated (p = 0.004). Conclusions PU Loop assessment from routine invasive hemodynamic optimization management during GA and especially GALA parameter could monitor cardiac afterload continuously in anesthetized patients, and may help clinicians to titrate vasopressor therapy.

Velocity-pressure loops for continuous assessment of ventricular afterload: influence of pressure measurement site.

VPloop, the graphical representation of pressure versus velocity, and its characteristic angles, GALA and ß, can be used to monitor cardiac afterload during anesthesia. Ideally VPloop should be measured from pressure and velocity obtained at the same arterial location but standard of care usually provide either radial or femoral pressure waveforms. The purpose of this study was to look at the influence of arterial sites and the use of a transfer function (TF) on VPloop and its related angles. Invasive pressure signals were recorded in 25 patients undergoing neuroradiology intervention under general anesthesia with transesophageal flow velocity monitoring. Pressures were recorded in the descending thoracic aorta, abdominal aorta, femoral and radial arteries. We compared GALA and ß from VPloops generated from each location and in high and low risk patients. GALA was similar in the central locations (55°[49-63], 52°[47-61] and 54°[45-62] from descending thoracic to femoral artery, median[interquartile], p = 0.10), while there was a difference in ß angle (16°[4-27] to 8°[3-15], p < 0.0001). GALA and ß obtained from radial waveforms were different (39°[31-47] compared to 46°[36-54] and 6°[2-14] compared to 16°[4-27] for GALA and ß angles respectively, p < 0.001) which was corrected by the use of a TF (45°[32-55] and 17°[5-28], p = ns). GALA and ß are underestimated when measured with a radial catheter. Using pressure waveforms from femoral locations alters VPloops, GALA and ß in a smaller extend. The use of a TF on radial pressure allows to correctly plot VPloops and their characteristic angles for routine clinical use.

Short-Term Repeatability of Noninvasive Aortic Pulse Wave Velocity Assessment: Comparison Between Methods and Devices.

BACKGROUND: Aortic pulse wave velocity (PWV) is an indirect index of arterial stiffness and an independent cardiovascular risk factor. Consistency of PWV assessment over time is thus an essential feature for its clinical application. However, studies providing a comparative estimate of the reproducibility of PWV across different noninvasive devices are lacking, especially in the elderly and in individuals at high cardiovascular risk. METHODS: Aimed at filling this gap, short-term repeatability of PWV, estimated with 6 different devices (Complior Analyse, PulsePen-ETT, PulsePen-ET, SphygmoCor Px/Vx, BPLab, and Mobil-O-Graph), was evaluated in 102 high cardiovascular risk patients hospitalized for suspected coronary artery disease (72 males, 65 ± 13 years). PWV was measured in a single session twice, at 15-minute interval, and its reproducibility was assessed though coefficient of variation (CV), coefficient of repeatability, and intraclass correlation coefficient. RESULTS: The CV of PWV, measured with any of these devices, was <10%. Repeatability was higher with cuff-based methods (BPLab: CV = 5.5% and Mobil-O-Graph: CV = 3.4%) than with devices measuring carotid-femoral PWV (Complior: CV = 8.2%; PulsePen-TT: CV = 8.0%; PulsePen-ETT: CV = 5.8%; and SphygmoCor: CV = 9.5%). In the latter group, PWV repeatability was lower in subjects with higher carotid-femoral PWV. The differences in PWV between repeated measurements, except for the Mobil-O-Graph, did not depend on short-term variations of mean blood pressure or heart rate. CONCLUSIONS: Our study shows that the short-term repeatability of PWV measures is good but not homogenous across different devices and at different PWV values. These findings, obtained in patients at high cardiovascular risk, may be relevant when evaluating the prognostic importance of PWV.

Influence of critical closing pressure on systemic vascular resistance and total arterial compliance: A clinical invasive study.

BACKGROUND: Systemic vascular resistance (SVR) and total arterial compliance (TAC) modulate systemic arterial load, and their product is the time constant (Tau) of the Windkessel. Previous studies have assumed that aortic pressure decays towards a pressure asymptote (P∞) close to 0mmHg, as right atrial pressure is considered the outflow pressure. Using these assumptions, aortic Tau values of ∼1.5seconds have been documented. However, a zero P∞ may not be physiological because of the high critical closing pressure previously documented in vivo. AIMS: To calculate precisely the Tau and P∞ of the Windkessel, and to determine the implications for the indices of systemic arterial load. METHODS: Aortic pressure decay was analysed using high-fidelity recordings in 16 subjects. Tau was calculated assuming P∞=0mmHg, and by two methods that make no assumptions regarding P∞ (the derivative and best-fit methods). RESULTS: Assuming P∞=0mmHg, we documented a Tau value of 1372±308ms, with only 29% of Windkessel function manifested by end-diastole. In contrast, Tau values of 306±109 and 353±106ms were found from the derivative and best-fit methods, with P∞ values of 75±12 and 71±12mmHg, and with ∼80% completion of Windkessel function. The "effective" resistance and compliance were ∼70% and ∼40% less than SVR and TAC (area method), respectively. CONCLUSION: We did not challenge the Windkessel model, but rather the estimation technique of model variables (Tau, SVR, TAC) that assumes P∞=0. The study favoured a shorter Tau of the Windkessel and a higher P∞ compared with previous studies. This calls for a reappraisal of the quantification of systemic arterial load.