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Recently, a novel method to estimate wedge pressure (P w )-corrected minimal microvascular resistance (MR) was introduced. However, this method has not been validated since, and there are some theoretical concerns regarding the impact of different physiological conditions on the derivation of P w measurements. This study sought to validate the recently introduced method to estimate P w -corrected MR in a Doppler-derived study population and to evaluate the impact of different physiological conditions on the P w measurements and the derivation of P w -corrected MR. The method to derive "estimated" hyperemic microvascular resistance (HMR) without the need for P w measurements was validated by estimating the coronary fractional flow reserve (FFR cor ) from myocardial fractional flow reserve (FFR myo ) in a Doppler-derived study population ( N = 53). From these patients, 24 had hyperemic P w measurements available for the evaluation of hyperemic conditions on the derivation of P w and its effect on the derivation of both "true" (with measured P w ) and "estimated" P w -corrected HMR. Nonhyperemic P w differed significantly from P w measured in hyperemic conditions (26 ± 14 vs. 35 ± 14 mmHg, respectively, P < 0.005). Nevertheless, there was a strong linear relationship between FFR cor and FFR myo in nonhyperemic conditions ( R 2 = 0.91, P < 0.005), as well as in hyperemic conditions ( R 2 = 0.87, P < 0.005). There was a strong linear relationship between "true" HMR and "estimated" HMR using either nonhyperemic ( R 2 = 0.86, P < 0.005) or hyperemic conditions ( R 2 = 0.85, P < 0.005) for correction. In contrast to a modest agreement between nonhyperemic P w -corrected HMR and apparent HMR ( R 2 = 0.67, P < 0.005), hyperemic P w -corrected HMR showed a strong agreement with apparent HMR ( R 2 = 0.88, P < 0.005). We validated the calculation method for P w -corrected MR in a Doppler velocity-derived population. In addition, we found a significant impact of hyperemic conditions on the measurement of P w and the derivation of P w -corrected HMR. NEW & NOTEWORTHY The following are what is known: 1 ) wedge-pressure correction is often considered for the derivation of indices of minimal microvascular resistance, and 2 ) the Yong method for calculating wedge pressure-corrected index of microvascular resistance (IMR) without balloon inflation has never been validated in a Doppler-derived population and has not been tested under different physiological conditions. This study 1 ) adds validation for the Yong method for calculated wedge-pressure correction in a Doppler-derived study population and 2 ) shows significant influence of the physiological conditions on the derivation of coronary wedge pressure.

Renal sympathetic innervation is important in the control of renal and systemic hemodynamics and is a target for pharmacological and catheter-based therapies. The effect of a physiological sympathetic stimulus using static handgrip exercise on renal hemodynamics and intraglomerular pressure in humans is unknown. We recorded renal arterial pressure and flow velocity in patients with a clinical indication for coronary or peripheral angiography using a sensor-equipped guidewire during baseline, handgrip, rest, and hyperemia following intrarenal dopamine (30 μg/kg). Changes in perfusion pressure were expressed as the change in mean arterial pressure, and changes in flow were expressed as a percentage with respect to baseline. Intraglomerular pressure was estimated using a Windkessel model. A total of 18 patients (61% male and 39% female) with a median age of 57 yr (range: 27-85 yr) with successful measurements were included. During static handgrip, renal arterial pressure increased by 15.2 mmHg (range: 4.2-53.0 mmHg), whereas flow decreased by 11.2%, but with a large variation between individuals (range: -13.4 to 49.8). Intraglomerular pressure increased by 4.2 mmHg (range: -3.9 to 22.1 mmHg). Flow velocity under resting conditions remained stable, with a median of 100.6% (range: 82.3%-114.6%) compared with baseline. During hyperemia, maximal flow was 180% (range: 111%-281%), whereas intraglomerular pressure decreased by 9.6 mmHg (interquartile range: 4.8 to 13.9 mmHg). Changes in renal pressure and flow during handgrip exercise were significantly correlated (ρ = -0.68, P = 0.002). Measurement of renal arterial pressure and flow velocity during handgrip exercise allows the identification of patients with higher and lower sympathetic control of renal perfusion. This suggests that hemodynamic measurements may be useful to assess the response to therapeutic interventions aimed at altering renal sympathetic control. NEW & NOTEWORTHY Renal sympathetic innervation is important in the homeostasis of systemic and renal hemodynamics. We showed that renal arterial pressure significantly increased and that flow decreased during static handgrip exercise using direct renal arterial pressure and flow measurements in humans, but with a large difference between individuals. These findings may be useful for future studies aimed to assess the effect of interventions that influence renal sympathetic control.

Background: Invasive assessments of microvascular function are rapidly becoming an integral part of physiological assessment in chronic coronary syndromes., Objective: We aimed to establish a reference range for Doppler flow velocity-derived hyperaemic microvascular resistance index (HMR) in a cohort of angina with no significant epicardial coronary obstruction (ANOCA) patients with no structural pathophysiological alterations in the coronary circulation., Methods: The reference population consisted of ANOCA patients undergoing invasive coronary vasomotor function assessment who had a coronary flow reserve (CFR) >2.5, and had either (1) tested negatively for spasm provocation (n = 12) or (2) tested positively with only angina at rest (n = 29). A reference range for HMR was established using a non-parametric method and correlations with clinical characteristics were determined using a spearman rank correlation analysis., Results: In 41 patients median HMR amounted to 1.6 mmHg/cm/s [Q1, Q3: 1.3, 2.2 mmHg/cm/s]. The reference range for HMR that is applicable to 95% of the population was 0.8 mmHg/cm/s (90% CI: 0.8-1.0 mmHg/cm/s) to 2.7 mmHg/cm/s (90% CI: 2.6-2.7 mmHg/cm/s). No significant correlations were found between HMR and clinical characteristics., Conclusion: In this reference population undergoing invasive coronary vasomotor function testing, the 90% confidence interval of the HMR upper limit of normal ranges from 2.6 to 2.7 mmHg/cm/s. A > 2.5 mmHg/cm/s HMR threshold can be used to identify abnormal microvascular resistance in daily clinical practice., Competing Interests: Declaration of Competing Interest None., (Copyright © 2022 The Author(s). Published by Elsevier B.V. All rights reserved.)

Objectives: The aim of this study was to compare Doppler flow velocity and thermodilution-derived indexes and to determine the optimal thermodilution-based diagnostic thresholds for coronary flow reserve (CFR)., Background: The majority of clinical data and diagnostic thresholds for flow-based indexes are derived from Doppler measurements, and correspondence with thermodilution-derived indices remain unclear., Methods: An international multicenter registry was conducted among patients who had coronary flow measurements using both Doppler and thermodilution techniques in the same vessel and during the same procedure., Results: Physiological data from 250 vessels (in 149 patients) were included in the study. A modest correlation was found between thermodilution-derived CFR (CFR thermo ) and Doppler-derived CFR (CFR Doppler ) (r 2  = 0.36; P < 0.0001). CFR thermo overestimated CFR Doppler (mean 2.59 ± 1.46 vs 2.05 ± 0.89; P < 0.0001; mean bias 0.59 ± 1.24 by Bland-Altman analysis), the relationship being described by the equation CFR thermo  = 1.04 × CFR Doppler  + 0.50. The commonly used dichotomous CFR thermo threshold of 2.0 had poor sensitivity at predicting a CFR Doppler value <2.5. The optimal CFR thermo threshold was 2.5 (sensitivity 75.54%, specificity 81.25%). There was only a weak correlation between hyperemic microvascular resistance and index of microvascular resistance (r 2  = 0.19; P < 0.0001), due largely to variation in the measurement of flow by each modality. Forty-four percent of patients were discordantly classified as having abnormal microvascular resistance by hyperemic microvascular resistance (≥2.5 mm Hg · cm -1 · s) and index of microvascular resistance (≥25)., Conclusions: CFR calculated by thermodilution overestimates Doppler-derived CFR, while both parameters show modest correlation. The commonly used CFR thermo threshold of 2.0 has poor sensitivity for identifying vessels with diminished CFR, but using the same binary diagnostic threshold as for Doppler (<2.5) yields reasonable diagnostic accuracy. There was only a weak correlation between microvascular resistance indexes assessed by the 2 modalities., Competing Interests: Funding Support and Author Disclosures This work was supported by the British Heart Foundation (PG/19/9/34228), the National Institute for Health Research via the Biomedical Research Centre award to Guy’s and St Thomas’ Hospital and King’s College London, and the National Institute for Health Research Oxford Biomedical Research Centre. The authors have reported that they have no relationships relevant to the contents of this paper to disclose., (Copyright © 2022 The Authors. Published by Elsevier Inc. All rights reserved.)

Aims: We evaluated the occurrence and physiology of respiration-related beat-to-beat variations in resting Pd/Pa and FFR during intravenous adenosine administration, and its impact on clinical decision-making., Methods and Results: Coronary pressure tracings in rest and at plateau hyperemia were analyzed in a total of 39 stenosis from 37 patients, and respiratory rate was calculated with ECG-derived respiration (EDR) in 26 stenoses from 26 patients. Beat-to-beat variations in FFR occurred in a cyclical fashion and were strongly correlated with respiratory rate (R 2  = 0.757, p < 0.001). There was no correlation between respiratory rate and variations in resting Pd/Pa. When single-beat averages were used to calculate FFR, mean ΔFFR was 0.04 ± 0.02. With averaging of FFR over three or five cardiac cycles, mean ΔFFR decreased to 0.02 ± 0.02, and 0.01 ± 0.01, respectively. Using a FFR ≤ 0.80 threshold, stenosis classification changed in 20.5% (8/39), 12.8% (5/39) and 5.1% (2/39) for single-beat, three-beat and five-beat averaged FFR. The impact of respiration was more pronounced in patients with pulmonary disease (ΔFFR 0.05 ± 0.02 vs 0.03 ± 0.02, p = 0.021)., Conclusion: Beat-to-beat variations in FFR during plateau hyperemia related to respiration are common, of clinically relevant magnitude, and frequently lead FFR to cross treatment thresholds. A five-beat averaged FFR, overcomes clinically relevant impact of FFR variation., (© 2021 The Authors. Catheterization and Cardiovascular Interventions published by Wiley Periodicals LLC.)