Kim H. Parker

Background: Physiology‐guided coronary revascularization using fractional flow reserve (FFR) and/or instantaneous wave‐free ratio (iFR) improves outcomes compared with angiography alone. However, when FFR and iFR are measured simultaneously, discordance occurs in 15%–20% of lesions and is associated with heterogeneous clinical outcomes, while the underlying hemodynamic mechanisms are not fully captured by conventional pressure tracings. Reservoir–excess pressure analysis (REPA), which decomposes arterial pressure into reservoir pressure (Pr) and excess pressure (Pxs), and quantifies the diastolic rate constant (DRC), may offer additional pathophysiological insight into these differences. Elevated DRC and Pxs with reduced Pr may indicate systemic hyperperfusion accompanied by lower aortic compliance. Aims: The objective of this study was to characterize pressure‐derived hemodynamics (i.e., REPA) and identify mechanisms related to FFR/iFR discordance in coronary arteries with angiographically intermediate stenoses. Methods: This secondary analysis included 249 unique lesions with intermediate coronary artery stenoses (visually estimated diameter stenosis of 40%–70%) from 223 patients in the international, multicenter DEFINE‐FLOW study. FFR was defined as hyperemic Pd/Pa and iFR as resting Pd/Pa during the wave‐free period. Established thresholds (FFR ≤ 0.80 and iFR ≤ 0.89) were used to define concordant and discordant stenoses. REPA was performed on ensemble‐averaged proximal aortic pressure waveforms at rest to derive Pr, Pxs, and related parameters (Figure 2). Results: REPA parameters demonstrated distinct hemodynamic profiles across groups. FFR−/iFR+ cases showed significantly higher Pxs (7.53 [4.97, 10.12] mmHg) and DRC (3.00 [2.06, 3.52]) and lower IntPr/IntPxs (11.73 [9.57, 17.00]) compared with FFR+/iFR− (Pxs: 5.19 [4.21, 6.89] mmHg, DRC: 2.28 [1.69, 2.51], IntPr/IntPxs: 17.90 [14.23, 19.87]) and FFR−/iFR− (Pxs: 5.38 [4.03, 7.17] mmHg, DRC: 2.20 [1.67, 2.91], IntPr/IntPxs: 17.03 [12.76, 21.21]) cases. Notably, both Pxs and DRC values were highest and IntPr/IntPxs was lowest in FFR−/iFR+ cases. Pxs was an independent predictor of FFR−/iFR+ discordance among cases with FFR > 0.80; higher aortic Pxs was associated with lower iFR values and a greater likelihood of an abnormal iFR classification (OR: 1.230; 95% CI: 1.026–1.473; p = 0.025). In contrast, higher hAPV (OR: 1.187; 95% CI: 1.100–1.281; p < 0.001) and lower bAPV (OR: 0.751; 95% CI: 0.644–0.875; p < 0.001), which together reflect a higher CFR, were independent predictors of FFR+/iFR− discordance. Conclusions: Weaker proximal aortic reservoir function and higher aortic Pxs are associated with abnormal iFR in lesions with normal FFR, whereas higher CFR is associated with normal iFR in lesions with abnormal FFR. Systemic hemodynamics, including proximal aortic reservoir behavior, may provide additional mechanistic insight into altered coronary pressure hemodynamics and improve the pathophysiological understanding of FFR–iFR discordance that may affect revascularization decisions in chronic coronary syndromes.

Spinal surgery procedure is often necessary to remove cancerous tissue within or surrounding the spinal cord and spinal column. This procedure, however, is restricted by the incapability of rigid hand-held drills and cutting tools to reach the target tissue in complex anatomical pathways. Previously, we introduced the surgical robotic platform with a novel concentric connector joint and developed a haptic control system that integrates an active constraint controller into a surgical robot platform. This study introduces the design and experimental testing of a new articulated surgical tool that can navigate around the spinal column using a water jet cutting system for safer removal of tumorous tissue. This innovative approach allows the removal of cancerous tissue on both the anterior and posterior sides of the spinal column without high-speed rotating equipment. A water jet cutting system integrated with an articulated distal tip (ADT) has been developed and successfully tested. A mock surgical procedure on the lower lumbar vertebrae has been used to test the accuracy and performance of the prototype. Results show promise for combining waterjet cutting and an ADT for surgical spinal procedures. The articulated surgical water jet tool removed 82% of mock cancerous tissue compared to 16% of tissue removed by the rigid tool.

Whereas studying the aortic valve in isolation has facilitated the development of life-saving procedures and technologies, the dynamic interplay of the aortic valve and its surrounding structures is vital to preserving their function across the wide range of conditions encountered in an active lifestyle. Our view is that these structures should be viewed as an integrated functional unit, here referred to as the aortic valve apparatus (AVA). The coupling of the aortic valve and root, left ventricular outflow tract, and blood circulation is crucial for AVA’s functions: unidirectional flow out of the left ventricle, coronary perfusion, reservoir function, and support of left ventricular function. In this review, we explore the multiscale biological and physical phenomena that underlie the simultaneous fulfillment of these functions. A brief overview of the tools used to investigate the AVA, such as medical imaging modalities, experimental methods, and computational modeling, specifically fluid-structure interaction (FSI) simulations, is included. Some pathologies affecting the AVA are explored, and insights are provided on treatments and interventions that aim to maintain quality of life. The concepts explained in this article support the idea of AVA being an integrated functional unit and help identify unanswered research questions. Incorporating phenomena through the molecular, micro, meso, and whole tissue scales is crucial for understanding the sophisticated normal functions and diseases of the AVA.

Robotic minimally invasive surgery (MIS) has changed numerous surgical techniques in the past few years and enhanced their results. Haptic feedback is integrated into robotic surgical systems to restore the surgeon's perception of forces in response to interaction with objects in the surgical environment. The ideal exact emulation of the robot's interaction with its physical environment in free space is a very challenging problem to solve completely. Previously, we introduced the surgical robotic platform (SRP) with a novel concentric connector joint (CCJ). This study aims to develop a haptic control system that integrates an active constraint controller into a surgical robot platform. We have successfully established haptic feedback control for the surgical robot using constraint control and inverse kinematic relationships integrated into the overall positioning structure. A preliminary feasibility study, modelling, and simulation were presented.

The separation of measured arterial pressure into a reservoir pressure and an excess pressure was introduced nearly 20 years ago as an heuristic hypothesis. We demonstrate that a two-time asymptotic analysis of the 1-D conservation equations in each artery coupled with the separation of the smaller arteries into inviscid and resistance arteries, based on their resistance coefficients, results, for the first time, in a formal derivation of the reservoir pressure. The key to the two-time analysis is the existence of a fast time associated with the propagation of waves through the arteries and a slow time associated with the convective velocity of the blood. The ratio between these two time scales is given by the Mach number; the ratio of a characteristic convective velocity to a characteristic wave speed. If the Mach number is small, a formal asymptotic analysis can be carried out which is accurate to the order of the square of the Mach number. The slow-time conservation equations involve a resistance coefficient that models the effect of viscosity on the convective velocity. On the basis of this resistance coefficient, we separate the arteries into the larger inviscid arteries where the coefficient is negligible and the smaller resistance arteries where it it is not negligible. The slow time pressure in the inviscid arteries is shown to be spatially uniform but varying in time. We define this pressure as the reservoir pressure. Dynamic analysis using mass conservation in the inviscid arteries shows that the reservoir pressure accounts for the storage of potential energy by the distension of the elastic inviscid arteries during early systole and its release during late systole and diastole. This analysis thus provides a formal derivation of the reservoir pressure and its physical meaning.

Wave intensity analysis (WIA) uses simultaneous changes in pressure and flow velocity to determine wave energy, type, and timing of traveling waves in the circulation. In this study, we characterized wave propagation in the pulmonary artery in patients with pulmonary hypertension associated with left‐sided heart disease (PHLHD) and the effects of dobutamine. During right heart catheterization, pressure and velocity data were acquired using a dual‐tipped pressure and Doppler flow sensor wire (Combowire; Phillips Volcano), and processed offline using customized Matlab software (MathWorks). Patients with low cardiac output underwent dobutamine challenge. Twenty patients with PHLHD (all heart failure with reduced left ventricular ejection fraction) were studied. Right ventricular systole produced a forward compression wave (FCW), followed by a forward decompression wave (FDW) during diastole. Wave reflection manifesting as backward compression wave (BCW) following the FCW was observed in 14 patients. Compared to patients without BCW, patients with BCW had higher mean pulmonary artery pressure (28.7 ± 6.12 vs. 38.6 ± 6.5 mmHg, p = 0.005), and lower pulmonary arterial capacitance (PAC: 2.88 ± 1.75 vs. 1.73 ± 1.16, p = 0.002). Pulmonary vascular resistance was comparable. Mean pulmonary artery pressure of 34.5 mmHg (area under the curve [AUC]: 0.881) and PAC of 2.29 mL/mmHg (AUC: 0.833) predicted BCW. The magnitude of the FCW increased with dobutamine (n = 11) and correlated with pulmonary artery wedge pressure. Wave reflection in PHLHD is more likely at higher pulmonary artery pressures and lower PAC and the magnitude of reflected waves correlated with pulmonary artery wedge pressure. Dobutamine increased FCW but did not affect wave reflection.

The aortic root (AR) performs sophisticated functions regulating the blood dynamics during the cardiac cycle. Such complex function depends on the nature of flow in the AR. Here, we investigate the potential of new quantitative parameters of flow asymmetry that could have clinical implications. We developed a MATLAB program to study the AR hemodynamics in each sinus of Valsalva using two-dimensional (2-D) cardiac magnetic resonance imaging during systole and particularly at peak systolic flow in 13 healthy volunteers and compared with 10 patients with hypertrophic obstructive cardiomyopathy (HOCM). We show that the effective area of the aortic jet in healthy volunteers is significantly higher at peak systolic flow and on average during systole. The flow asymmetry index, indicating how the jet is skewed away from the left coronary sinus (LCS), is small in healthy volunteers and much larger in HOCM at peak systole. The average of this index over systole is significantly more different between cohorts. Looking in more detail at the flow in the sinuses during systole, we show that the AR jet in healthy volunteers is more symmetrical, affecting the three sinuses almost equally, unlike the asymmetric AR jet in patients with HOCM that has decreased flow rate in the LCS and increased fractional area of backward flow in the LCS. The percentage of backward flow in the sinuses of Valsalva calculated over systole is a potential indicator of perturbed AR hemodynamics and the distribution of vortical flow and could be used as a measure of flow asymmetry. NEW & NOTEWORTHY The aortic root is a vital organ responsible for performing sophisticated functions to regulate the blood flow dynamics during the cardiac cycle. Such synchronized complex performance affects and is affected by the flow symmetry and type of flow reaching the aorta. Here, we report flow asymmetry in the aortic root which could have clinical implications, and we investigate the potential of various quantitative parameters as measures of flow asymmetry in hypertrophic obstructive cardiomyopathy.

This memorial remembers the lives of two distinguished researchers who made major contributions to cardiovascular physiology; NicoWesterhof (1937-2022) and John Tyberg (1938-2022). It is a joint memorial not because they collaborated closely but because they held very different views about the nature of waves in the arteries. Their papers and particularly their lively discussions at many scientific meetings stimulated interest in the subject. Both were thoughtful and articulate about their views, and the debates were polite and dignified. They never resolved their differences and, after outlining what these differences were, we will suggest that perhaps there is no resolution. The authors of this memorial were close to one or the other protagonist; a son, a son-in-law and two close collaborators. We all have different views about the nature of waves in the arteries, but we all share great respect for both men and felt that a joint memorial was a fitting way to remember them and their many contributions. All of the authors knew the subjects of this memorial as 'Nico' and 'John', and we will use these informal names throughout.

Objective: The association between high salt intake and blood pressure is well-recognised. In overweight/obese individuals, obesity-associated hyperinsulinaemia augments renal sodium reabsorption and in combination with high salt intake this may alter blood pressure and arterial haemodynamics. We determined whether short-term high salt intake altered reservoir-excess pressure and central artery haemodynamic parameters in overweight/obese individuals. Design and method: We studied 15 middle-aged and older adults (59.3 ± 6.4 yrs, 5F) who were overweight/obese with elevated systolic blood pressure (130 < SBP < 159 mmHg). In a double-blind cross-over design, they were randomly assigned to seven days of low salt diet (LSD: 50 mmol/day) or high salt intake (HIS: LSD with 200 mmol/day of sodium tablets) separated by a two-week washout period. The parameters derived from reservoir-excess pressure analysis including reservoir pressure integral, peak reservoir pressure (MAXPR), excess pressure integral (INTXSP), peak excess pressure (MAXXSP), systolic rate constant and diastolic rate constant (DRC) were obtained by radial artery tonometry. Additionally central artery haemodynamic parameters including aortic systolic pressure (aSBP), diastolic pressure (aDBP), pulse pressure (aPP) and subendocardial viability index (SVI) were derived from ensemble-averaged radial pulse waveform using generalised transfer function. Aortic pulse wave velocity (aPWV) was estimated as proposed by Hughes et al (Front Physiol. 2020). Results: MAXPR (111.0 ± 10.9 vs 105.4 ± 10.4 mmHg), MAXXSP (41.7 ± 12.0 vs 36.6 ± 5.7 mmHg) and DRC (2.0 ± 0.4 vs 1.8 ± 0.3 s-1) were higher following HIS compared to LSD (p < 0.05). There was no convincing evidence that INTXSP was greater following HIS than LSD (6.9 ± 3.2 vs 5.8 ± 1.6 mmHg s, p = 0.055). aSBP (126.3 ± 15.4 vs 117.6 ± 10.1 mmHg), aDBP (76.3 ± 6.2 vs 73.1 ± 6.3 mmHg) and aPP (50.0 ± 17.4 vs 44.5 ± 10.8 mmHg) were also higher following HIS compared to LSD (p < 0.05). SVI was similar between HIS and LSD (162.7 ± 29.6 vs 171.6 ± 25.0 %, p = 0.143). A greater aPWV was observed following HIS compared to LSD (5.6 ± 1.6 vs 4.9 ± 0.8 m/s, p = 0.034). Conclusions: Short-term HIS adversely alters reservoir function and central artery haemodynamics in overweight/obese adults. These observations suggest a potential mechanism that may increase cardiovascular disease risk associated with HIS in this population.