Validation of blood pressure monitoring using pulse transit time in heart failure patients with Cheyne-Stokes respiration undergoing adaptive servoventilation therapy.

PURPOSE: Using pulse transit time (PTT) and an ECG appears to be a promising alternative for invasive or noninvasive monitoring of blood pressure (BP). This study assessed the validity of PTT for BP monitoring in clinical practice. METHODS: Twenty-nine patients with chronic heart failure (HF; 27 male, 70.5 ± 9.9 years) and nocturnal Cheyne-Stokes respiration were noninvasively ventilated for one hour using adaptive servoventilation (ASV) therapy (PaceWave, ResMed). BP was measured using two devices (oscillometrically via Task Force Monitor, CNSystems and PTT via SOMNOscreen, Somnomedics) at least every 7 min for 30 min before, during, and after ASV. RESULTS: Mean systolic BP was 118.1 ± 14.4 mmHg vs. 115.9 ± 14.1 mmHg for oscillometric method vs PTT, respectively. Corresponding values for diastolic BP were 72.3 ± 10.3 mmHg and 69.4 ± 11.1 mmHg. While clinically comparable, differences between the two methods were statistically significant (p < 0.05). The difference between the two methods showed an increasing trend over time. A total of 18.5 % of PTT-based measurements could not be analyzed. The direction of a change in BP was opposite for PTT vs oscillometry for 17.0 % and 32.8 % of systolic and diastolic BP measurements, respectively. CONCLUSIONS: When monitoring BP in HF patients, overall BP monitoring using PTT is comparable to oscillometry for a period of 2 h (including a 1-h ASV phase). However, PTT shows a tendency to underestimate BP over time and during ASV.

Comparison of cardiac output estimates obtained from the Antares oscillometric pulse wave analysis algorithm and from Doppler transthoracic echocardiography.

BACKGROUND: In cardiology, cardiac output (CO) is an important parameter for assessing cardiac function. While invasive thermodilution procedures are the gold standard for CO assessment, transthoracic Doppler echocardiography (TTE) has become the established method for routine CO assessment in daily clinical practice. However, a demand persists for non-invasive approaches, including oscillometric pulse wave analysis (PWA), to enhance the accuracy of CO estimation, reduce complications associated with invasive procedures, and facilitate its application in non-intensive care settings. Here, we aimed to compare the TTE and oscillometric PWA algorithm Antares for a non-invasive estimation of CO. METHODS: Non-invasive CO data obtained by two-dimensional TTE were compared with those from an oscillometric blood pressure device (custo med GmbH, Ottobrunn, Germany) using the integrated algorithm Antares (Redwave Medical GmbH, Jena, Germany). In total, 59 patients undergoing elective cardiac catheterization for clinical reasons (71±10 years old, 76% males) were included. Agreement between both CO measures were assessed by Bland-Altman analysis, Student's t-test, and Pearson correlations. RESULTS: The mean difference in CO was 0.04 ± 1.03 l/min (95% confidence interval for the mean difference: -0.23 to 0.30 l/min) for the overall group, with lower and upper limits of agreement at -1.98 and 2.05 l/min, respectively. There was no statistically significant difference in means between both CO measures (P = 0.785). Statistically significant correlations between TTE and Antares CO were observed in the entire cohort (r = 0.705, P<0.001) as well as in female (r = 0.802, P<0.001) and male patients (r = 0.669, P<0.001). CONCLUSIONS: The oscillometric PWA algorithm Antares and established TTE for a non-invasive estimation of CO are highly correlated in male and female patients, with no statistically significant difference between both approaches. Future validation studies of the Antares CO are necessary before a clinical application can be considered.

Meta-analysis of three observational studies of amlodipine/valsartan in hypertensive patients with additional risk factors.

OBJECTIVES: In this study, the effectiveness of amlodipine/valsartan single-pill combination was assessed in hypertensive patients with diabetes, metabolic risk or overweight. METHODS: Data from 12,265 patients treated with amlodipine/valsartan from three studies were analyzed in a meta-analysis. These studies focused on (i) non-diabetic hypertensive patients suffering from abdominal obesity; (ii) hypertensive patients with at least one metabolic risk factor; and (iii) hypertensive patients with type 2 diabetes mellitus. The observation periods were 16 weeks for the first two and 24 weeks for the latter cohort. RESULTS: At start of observation, the mean blood pressure was 162.3 mmHg (systolic) and 93.5 mmHg (diastolic). A total of 7.4% of patients were aged ≥ 80 years. At end of the observation, a normalized blood pressure was present in 38.8% of patients. No appreciable differences in blood pressure reduction were evident between the study groups. In both age subgroups (< 80 years and ≥ 80 years) blood pressure reduction was comparable. Tolerability was assessed by treating physicians as "very good" (69.3%) and "good" (27.3%). CONCLUSIONS: In daily practice, treatment of hypertensive patients with additional risk factors with amlodipine/valsartan single-pill combinations is well tolerated and associated with effective reduction of blood pressure.

Invasive validation of the Antares algorithm for determining central blood pressure based on upper arm oscillometric pulse waves in patients with type 2 diabetes.

INTRODUCTION: Antares is a pulse wave analysis (PWA) algorithm designed to allow a non-invasive estimation of central (aortic) blood pressure (cBP) using automated oscillometric blood pressure (BP) devices. Diabetes may affect elastic and muscular arteries differently, resulting in disparate pulse wave characteristics in central and peripheral arteries, which may limit the accuracy of PWA devices. The aim of our study was to evaluate the accuracy of Antares for estimating cBP as compared with invasively measured cBP in patients with type 2 diabetes. RESEARCH DESIGN AND METHODS: In this study, consecutive patients undergoing elective coronary angiography were recruited between November 2017 and September 2020. In 119 patients with type 2 diabetes, cBP was measured invasively and simultaneously determined non-invasively using the custo screen 400 device with the integrated Antares algorithm. RESULTS: The mean difference between the estimated and invasively measured cBP was 1.2±6.3 mmHg for central systolic BP (cSBP), 1.0±4.3 mmHg for central mean arterial pressure (cMAP) and 3.6±5.7 mmHg for central diastolic BP (cDBP). High correlations were found between estimated cBP and invasively measured cBP (cSBP: r=0.916; cMAP: r=0.882; cDBP: r=0.791; all p<0.001). CONCLUSIONS: The present study suggests that the Antares algorithm incorporated into the custo screen 400 device can estimate cBP with high accuracy turning a conventional oscillometric BP device into a type II device for the non-invasive estimation of cBP, which is applicable in patients with type 2 diabetes. Integration of Antares into commercially available BP devices could facilitate the introduction of cBP into routine clinical practice as a part of disease and risk management.

How to find and use validated blood pressure measuring devices.

Clinically validated, automated arm-cuff blood pressure measuring devices (BPMDs) are recommended for BP measurement. However, most BPMDs available for purchase by consumers globally are not properly validated. This is a problem because non-validated BPMDs are less accurate and precise than validated ones, and therefore if used clinically could lead to misdiagnosis and mismanagement of BP. In response to this problem, several validated device lists have been developed, which can be used by clinicians and consumers to identify devices that have passed clinical validation testing. The purpose of this review is to describe the resources that are available for finding validated BPMDs in different world regions, to identify the differences between validated device lists, and describe current gaps and challenges. How to use validated BPMDs properly is also summarised.

Invasively measured and estimated central blood pressure using the oscillometric algorithm Antares in patients with and without obesity.

BACKGROUND: Obesity is a global health concern and risk factor for cardiovascular disease. The assessment of central blood pressure (cBP) has been shown to improve prediction of cardiovascular events. However, few studies have investigated the impact of obesity on cBP in adults, and invasive data on this issue are lacking. This study aimed to evaluate cBP differences between patients with and without obesity, identify cBP determinants, and evaluate the accuracy of the algorithm Antares for non-invasive cBP estimation. METHODS: A total of 190 patients (25% female; 39% with BMI ≥30kg/m2; age: 67±12 years) undergoing elective cardiac catheterization were included. cBP was measured invasively and simultaneously estimated non-invasively using the custo screen 400 device with integrated Antares algorithm. RESULTS: No significant cBP differences were found between obese and non-obese patients. However, females, especially those with obesity, had higher systolic cBP compared to males (P<0.05). Multiple regression analysis showed that brachial mean arterial pressure, pulse pressure, BMI, and heart rate predicted cBP significantly (adjusted R2 = 0.82, P<0.001). Estimated cBP correlated strongly with invasive cBP for systolic, mean arterial, and diastolic cBP (r = 0.74-0.93, P<0.001) and demonstrated excellent accuracy (mean difference <5 and SD <8 mmHg). CONCLUSIONS: This study discovered no significant difference in cBP between obese and non-obese patients. However, it revealed higher cBP values in women, especially those with obesity, which requires further investigation. Additionally, the study highlights Antares' effectiveness in non-invasively determining cBP in obese individuals. This could improve the diagnosis and treatment of hypertension in this special patient population.

Pulse transit time: validation of blood pressure measurement under positive airway pressure ventilation.

PURPOSE: The objective of the present study was to validate noninvasive, continuous blood pressure (BP) measurement using pulse transit time (PTT) to represent absolute values and detect BP changes under continuous positive airway pressure (CPAP) treatment. METHODS: We applied CPAP to 78 patients of a cardiological sleep lab using 0 (baseline), 4, 8, and 12 cmH(2)O for 10 min at every level and measured BP simultaneous via PTT-based method and standard oscillometric method (OM). RESULTS: Quality of signal perception was acceptable to convert PTT into BP values in 64 patients (82%). When comparing both methods, we found a strong linear correlation of systolic and diastolic BP (baseline, r = 0.94 for systolic BP; r = 0.95 for diastolic BP, p < 0.001) while no significant differences between absolute values obtained with OM and PTT measurement. Mean bias at baseline was 4.1 ± 3.2 mmHg for systolic BP and 2.3 ± 2.2 mmHg for diastolic BP. With increasing CPAP levels, PTT and OM measurements differed continuously up to a systolic difference of 6.6 ± 4.9 mmHg and a diastolic difference of 4.4 ± 3.5 mmHg. There was no definite trend of PTT method to either over- or underestimate BP. CONCLUSIONS: We found that PTT- and OM-based BP results are closely correlated while applying CPAP over a period of 40 min. With higher CPAP level, bias between both methods increased.

Study Evaluating the Use of RenalGuard to Protect Patients at High Risk of AKI.

BACKGROUND: Contrast-induced nephropathy (CIN) can occur after cardiovascular procedures using contrast media, which is associated with increased morbidity and mortality. RenalGuard is a closed-loop system designed to match intravenous hydration with diuretic-induced diuresis that has shown mixed results in the prevention of CIN in previous randomized controlled trials. OBJECTIVES: The STRENGTH (Study Evaluating the Use of RenalGuard to Protect Patients at High Risk of AKI) study assessed whether RenalGuard (PLC Medical Systems) is superior to standard intravenous hydration for CIN prevention in patients with chronic kidney disease undergoing complex cardiovascular procedures. METHODS: STRENGTH is a multicenter, international, open-label, postmarket, prospective, randomized (1:1) study monitored by the Cardiovascular European Research Center (Massy, France) that included a total of 259 patients with moderate to severe chronic kidney disease (estimated glomerular filtration 15-40 mL/min/m2) requiring a complex coronary, structural, or peripheral procedure with an expected contrast injection of at least 3 times the estimated glomerular filtration rate. Patients were randomized to either RenalGuard or intravenous saline hydration according to current guidelines. RESULTS: The primary endpoint, the incidence of CIN at day 3 after the procedure, was similar between the 2 groups (17/107 [15.9%] in the RG group vs 15/110 [13.9%] in the control group; P = 0.62). In addition, none of the secondary endpoints differed between the 2 groups. CONCLUSIONS: In high-risk patients undergoing complex cardiovascular interventions in experienced centers, furosemide-induced high urine output with matched hydration using the RenalGuard system did not reduce the risk of CIN and adverse outcomes at 12 months compared with conventional intravenous hydration.

Angiographic assessment of cardiac allograft vasculopathy: results of a Consensus Conference of the Task Force for Thoracic Organ Transplantation of the German Cardiac Society.

Angiograms of cardiac transplant (HTx) recipients were to be evaluated in a ring experiment and a joint consensus on criteria of angiographic evaluation of coronary arteries of HTx patients was to be reached. Twenty-four coronary angiograms from 11 hospitals were circulated. One hundred eighty-eight blinded evaluations were returned. A joint evaluation by six experienced cardiologists was used as reference standard and a consensus evaluation form was developed. Significant lesions (stenosis 75%, 50% in the left main coronary artery) were diagnosed in 10/23 abnormal coronary angiograms (41.7%). Interventional revascularization was recommended in 8/10 (80%). In 21 coronary angiograms distal pruning was found and in 11/21 (52.4%) cases with distal pruning occlusion of at least one peripheral vessel was detected. The best kappa value (0.7) was found for the presence of at least one clinically significant stenosis. Agreement on the site and grade of local stenosis was much less. Some agreement on remodeling was found in assessing diffuse narrowing in the LCA (kappa=0.371, P<0.001). The kappa value for peripheral obliteration was 0.331 (P=0.001). Angiographic evaluation of cardiac allograft vasculopathy, particularly of diffuse and peripheral disease and remodeling, needs standardization. This should be performed in a downward compatible improvement process.

Efficacy of Electrical Baroreflex Activation Is Independent of Peripheral Chemoreceptor Modulation.

Arterial baroreflex activation through electrical carotid sinus stimulation has been developed for the treatment of resistant hypertension. Previous studies suggested that the peripheral chemoreflex is tonically active in hypertensive patients and may inhibit baroreflex responses. We hypothesized that peripheral chemoreflex activation attenuates baroreflex efficacy evoked by electrical carotid sinus stimulation. We screened 35 patients with an implanted electrical carotid sinus stimulator. Of those, 11 patients with consistent acute depressor response were selected (7 men/4 women, age: 67±8 years, body mass index: 31.6±5.2 kg/m2, 6±2 antihypertensive drug classes). We assessed responses to electrical baroreflex stimulation during normoxia, isocapnic hypoxia (SpO2: 79.0±1.5%), and hyperoxia (40% end-tidal O2 fraction) by measuring heart rate, blood pressure, ventilation, oxygen saturation, end-tidal CO2 and O2 fractions, and muscle sympathetic nerve activity. During normoxia, baroreflex activation reduced systolic blood pressure from 164±27 to 151±25 mm Hg (mean±SD, P<0.001), heart rate from 64±13 to 61±13 bpm (P=0.002), and muscle sympathetic nerve activity from 42±12 to 36±12 bursts/min (P=0.004). Hypoxia increased systolic blood pressure 8±12 mm Hg (P=0.057), heart rate 10±6 bpm (P<0.001), muscle sympathetic nerve activity 7±7 bursts/min (P=0.031), and ventilation 10±7 L/min (P=0.002). However, responses to electrical carotid sinus stimulation did not differ between hypoxic and hyperoxic conditions: systolic blood pressure: -15±7 versus -14±8 mm Hg (P=0.938), heart rate: -2±3 versus -2±2 bpm (P=0.701), and muscle sympathetic nerve activity: -6±4 versus -4±3 bursts/min (P=0.531). We conclude that moderate peripheral chemoreflex activation does not attenuate acute responses to electrical baroreflex activation therapy in patients with resistant hypertension. These patients provided insight into human baroreflex-chemoreflex interactions that could not be gained otherwise.

Management of angina pectoris: the role of spinal cord stimulation.

Progress in prevention as well as drug and interventional therapy has improved the prognosis of patients with cardiovascular disorders. Many patients at risk have advanced coronary artery disease (CAD), have had multiple coronary interventions, and present with significant co-morbidity. Despite adequate risk factor modulation and often several revascularization procedures, some of these patients still have refractory angina pectoris. Apart from advanced CAD and insufficient collateralization, the cause is often endothelial dysfunction. For this situation, one treatment option is neuromodulation. Controlled studies suggest that, in patients with chronic refractory angina pectoris, spinal cord stimulation (SCS) provides a relief from symptoms equivalent to that provided by surgical therapy, but with fewer complications and lower rehospitalization rates. SCS may result in significant long-term pain relief with improved quality of life. In patients with refractory angina undergoing SCS, some studies have shown not only a symptomatic improvement, but also a decrease in myocardial ischemia and an increase in coronary blood flow. Discussion is ongoing as to whether this is a direct effect on parasympathetic vascodilation or merely a secondary phenomenon resulting from increased physical activity following an improvement in clinical symptoms. Results from nuclear medical studies have sparked discussion about improved endothelial function and increased collateralization. SCS is a safe treatment option for patients with refractory angina pectoris, and its long-term effects are evident. It is a procedure without significant complications that is easy to tolerate. SCS does not interact with pacemakers, provided that strict bipolar right-ventricular sensing is used. Use in patients with implanted cardioverter defibrillators is under discussion. Individual testing is mandatory in order to assess optimal safety in each patient.

Myocardial perfusion after one year of spinal cord stimulation in patients with refractory angina.

AIM: Spinal cord stimulation (SCS) is recommended for patients with coronary artery disease (CAD) and refractory angina. We used positron emission tomography (PET) to investigate the long-term effect of SCS on regional myocardial perfusion in patients suffering from angina pectoris refractory to medical treatment and without option for coronary intervention. PATIENTS, METHODS: We analyzed data of 44 patients with stable CAD (91% three vessel disease). At baseline, we determined coronary flow reserve (CFR) using 13N-ammonia-PET and myocardial viability with 18F-FDG. SCS was performed for one year (Medtronic Itrell III or Synergy, Düsseldorf, Germany). During follow-up, no cardiac interventions were necessary and no myocardial infarctions occurred. At one year follow-up, CFR was measured again. RESULTS: In the majority of patients (77%), SCS led to an improvement of clinical symptoms. CFR did not change significantly during follow-up. Subjective improvement did not correlate with an increase of CFR. CONCLUSIONS: Despite its clinical effect, SCS does not have a direct impact on CFR in patients with stable CAD. According to our results, the pain relief is not due to an improvement of the myocardial blood supply.

[Actual Standard of Blood Pressure Measurement - Statement of the German High Blood Pressure League]. / Aktueller Standard der Blutdruckmessung ­ Stellungnahme der Deutschen Hochdruckliga e. V. DHL® ­ Deutsche Gesellschaft für Hypertonie und Prävention.

Arterial hypertension is one of the most prevalent chronic diseases, and a major risk factor for cardiovascular diseases. It is essential to perform the blood pressure measurement under standardized conditions in the office/clinical setting, otherwise inaccuracy of blood pressure values may lead to poor blood pressure control or misdiagnosis. Compliance with these standards by a trained observer is of crucial importance for a reliable and accurate blood pressure measurement in clinical practice. Regardless of the standardized assessment, it has to be kept in mind that available devices on the market may not measure blood pressure accurate enough. Therefore, a validated (e. g. German Hypertension League Quality Seal) blood pressure monitor should be used. Out-of-office (home and ambulatory) blood pressure measurements provide important information beyond determining resting office/clinical BP.

Invasive Validation of Antares, a New Algorithm to Calculate Central Blood Pressure from Oscillometric Upper Arm Pulse Waves.

Background: Antares is an algorithm for pulse wave analysis (PWA) by oscillometric blood pressure (BP) monitors in order to estimate central (aortic) blood pressure (cBP). Antares aims to enable brachial cuff-based BP monitors to be type II-devices, determining absolute cBP values independently of potential peripheral BP inaccuracies. The present study is an invasive validation of the Antares algorithm in the custo screen 400. Methods: We followed entirely the 2017 ARTERY protocol for validation of non-invasive cBP devices, the 2013 American National Standards Institute, Inc./Association for the Advancement of Medical Instrumentation/International Organization for Standardization (ANSI/AAMI/ISO) 81060-2 and 2018 AAMI/European Society of Hypertension (ESH)/ISO validation standard protocols. In total, 191 patients undergoing cardiac catheterization were included, of which 145 patients entered analysis. Invasive cBP recordings were compared to simultaneous non-invasive cBP estimations using the Antares algorithm, integrated into an oscillometric BP monitor. Results: Mean difference between invasive and non-invasively estimated systolic cBP was 0.71 mmHg with standard deviation of 5.95 mmHg, fulfilling highest validation criteria. Conclusion: Antares is the first algorithm for estimation of cBP that entirely fulfills the 2017 ARTERY and AAMI/ESH/ISO validation protocols. The Antares algorithm turns the custo screen 400 BP monitor into a type II-device. Integration of Antares into commercially available BP monitors could make it possible to measure PWA parameters in virtually every practice in future.

Myocardial sympathetic innervation in patients with symptomatic coronary artery disease: follow-up after 1 year with neurostimulation.

UNLABELLED: In both diabetic and nondiabetic patients, there is a loose correlation between coronary flow reserve (CFR) and sympathetic innervation in viable myocardial segments. The loose correlation implies that sympathetic innervation may be preserved even with major impairment of myocardial blood supply. In some patients, denervation is due to repetitive episodes of ischemia in areas with severely reduced CFR. We investigated the long-term effect of reduced CFR on myocardial sympathetic innervation in diabetic and nondiabetic patients with spinal cord stimulation. METHODS: We analyzed 23 patients (10 diabetic and 13 nondiabetic) with coronary artery disease and without known cardiac autonomic neuropathy. At baseline, we determined quantitative myocardial blood flow using (13)N-ammonia PET, myocardial viability using (18)F-FDG PET, and cardiac innervation using (11)C-hydroxyephedrine (HED) PET. At the 1-y follow-up we measured CFR and (11)C-HED retention. During follow-up, no cardiac intervention was performed and no myocardial infarction occurred. In all patients, spinal cord stimulation was performed for relief of angina. RESULTS: There was no significant difference in segmental (11)C-HED retention between baseline and follow-up in the whole patient group. In diabetic patients, as well as in segments with severely reduced CFR (<1.5), (11)C-HED retention showed a small but significant decrease (P<0.05). Linear regression of segmental (11)C-HED retention between baseline and follow-up was high (r(2)=0.81), confirming good reproducibility of the investigation on the one hand and little change in regional sympathetic innervation on the other hand. CONCLUSION: In patients with stable chronic coronary artery disease, sympathetic innervation of the myocardium is almost unchanged in both diabetic and nondiabetic patients in a 1-y follow-up. In myocardial segments with severely altered blood supply, a small but significant decrease in (11)C-HED retention most probably reflects ischemic neuronal damage. The prognostic relevance of sympathetic denervation in viable myocardium still has to be determined.

A Universal Standard for the Validation of Blood Pressure Measuring Devices: Association for the Advancement of Medical Instrumentation/European Society of Hypertension/International Organization for Standardization (AAMI/ESH/ISO) Collaboration Statement.

In the past 30 years, several organizations, such as the US Association for the Advancement of Medical Instrumentation (AAMI), the British Hypertension Society, the European Society of Hypertension (ESH) Working Group on Blood Pressure (BP) Monitoring, and the International Organization for Standardization (ISO), have developed protocols for clinical validation of BP measuring devices. However, it is recognized that science, as well as patients, consumers, and manufacturers, would be best served if all BP measuring devices were assessed for accuracy according to an agreed single validation protocol that had global acceptance. Therefore, an international initiative was taken by the AAMI, ESH, and ISO experts who agreed to develop a universal standard for device validation. This statement presents the key aspects of a validation procedure, which were agreed by the AAMI, ESH, and ISO representatives as the basis for a single universal validation protocol. As soon as the AAMI/ESH/ISO standard is fully developed, this will be regarded as the single universal standard and will replace all other previous standards/protocols.

A universal standard for the validation of blood pressure measuring devices: Association for the Advancement of Medical Instrumentation/European Society of Hypertension/International Organization for Standardization (AAMI/ESH/ISO) Collaboration Statement.

: In the last 30 years, several organizations, such as the US Association for the Advancement of Medical Instrumentation (AAMI), the British Hypertension Society, the European Society of Hypertension (ESH) Working Group on Blood Pressure (BP) Monitoring and the International Organization for Standardization (ISO) have developed protocols for clinical validation of BP measuring devices. However, it is recognized that science, as well as patients, consumers and manufacturers would be best served if all BP measuring devices were assessed for accuracy according to an agreed single validation protocol that had global acceptance. Therefore, an international initiative was taken by AAMI, ESH and ISO experts who agreed to develop a universal standard for device validation. This statement presents the key aspects of a validation procedure, which were agreed by the AAMI, ESH and ISO representatives as the basis for a single universal validation protocol. As soon as the AAMI/ESH/ISO standard is fully developed, this will be regarded as the single universal standard and will replace all other previous standards/protocols.

[Taking blood pressure in the presence of atrial fibrillation]. / Blutdruckmessung bei Vorhofflimmern. 17 Minuten für einen zuverlässigen Wert.

Measuring the blood pressure of patients with atrial fibrillation is difficult due to the high variability of the blood pressure. To obtain a representative average, the blood pressure should be measured as often as possible. Each blood pressure measurement should be repeated at least three times in succession.