The impact of preload reduction with head-up tilt testing on longitudinal and transverse left ventricular mechanics.

BACKGROUND: Left ventricular (LV) function is dependent on load, intrinsic contractility and relaxation with a variable impact on specific mechanics. Strain (ε) imaging allows the assessment of cardiac function however the direct relationship between volume and strain is currently unknown. The aim of this study was to establish the impact of preload reduction through head-up tilt (HUT) testing on simultaneous left ventricular (LV) longitudinal and transverse function and their respective contribution to volume change. METHODS: A focused transthoracic echocardiogram was performed on 10 healthy male participants (23 ± 3 years,) in the supine position and following 1 min and 5 min of HUT testing. Raw temporal longitudinal ε (Ls) and transverse ε (Ts) values were exported and divided into 5% increments across the cardiac cycle and corresponding LV volumes were traced at each 5% increment. This provided simultaneous LV longitudinal and transverse ε and volume-loops (deformation-volume analysis - DVA). RESULTS: There was a leftward- shift of the ε -volume loop from supine to 1 min and 5 min of HUT, p<0.001). Moreover, longitudinal shortening was reduced (p<0.001) with a concomitant increase in transverse thickening from supine to 1min, which was further augmented at 5min (p=0.018). CONCLUSIONS: Preload reduction occurs within 1 minute of HUT but does not further reduce at 5 minutes. This decline is associated with a decrease in longitudinal ε and concomitant increase in transverse ε. Consequently, augmented transverse relaxation appears to be an important factor in the maintenance of LV filling in the setting of reduced preload. DVA provides information on the relative contribution of mechanics to a change in LV volume and may have a role in the assessment of clinical populations

Influence of different dynamic sporting disciplines on right ventricular Structure and function in elite male athletes.

Our objective was to assess the influence of different levels of exposure to dynamic training on right ventricular (RV) structure, function and mechanics in elite male athletes. We recruited 492 male elite athletes aged between 18 and 30 years old. Athletes were grouped according to their sporting discipline using the Mitchell Classification as Low Dynamic (LD), Moderate Dynamic (MD) or High Dynamic (HD). All participants underwent 2D, Doppler, tissue Doppler and strain (ε) echocardiography with a focused and comprehensive assessment of the right heart. Athletes involved in MD sports had the largest absolute RV chamber size and when scaled to body size RVOT PLAX, RVOT2, RVD1 and RVD3 were larger in HD compared to MD and LD athletes. There were no between group differences in conventional RV functional indices as well as global RV ε (LD: - 23.4 ± 3.1 vs. MD: - 22.7 ± 2.7 vs. HD: - 23.5 ± 2.6, %) and strain rate (P > 0.01). The base to apex ε gradient in the RV septum was lower in the MD athletes compared to HD and LD due to a lower apical septal ε which significantly correlated with absolute RV chamber size. After scaling for body size there was evidence of larger RV cavities in both MD and HD athletes compared to LD athletes. Global RV function, ε and strain rate were not different between groups. MD athletes had lower apical septal ε that contributed to a smaller base-to-apex ε gradient that is partially associated with larger absolute RV chamber dimensions

Dynamic variability of the phytoplankton electron requirement for carbon fixation in eastern Australian waters

© 2019 Elsevier B.V. Fast Repetition Rate fluorometry (FRRf) generates high-resolution measures of phytoplankton primary productivity as electron transport rates (ETRs). How ETRs scale to corresponding inorganic carbon (C) uptake rates (the so-called electron requirement for carbon fixation, Φe,C), inherently describes the extent and effectiveness with which absorbed light energy drives C-fixation. However, it remains unclear whether and how Φe,C follows predictable patterns for oceanographic datasets spanning physically dynamic, and complex, environmental gradients. We utilise a unique high-throughput approach, coupling ETRs and 14C-incubations to produce a semi-continuous dataset of Φe,C (n = 80), predominantly from surface waters, along the Australian coast (Brisbane to the Tasman Sea), including the East Australian Current (EAC). Environmental conditions along this transect could be generally grouped into cooler, more nutrient-rich waters dominated by larger size-fractionated Chl-a (>10 μm) versus warmer nutrient-poorer waters dominated by smaller size-fractionated Chl-a (<2 μm). Whilst Φe,C was higher for warmer water samples, environmental conditions alone explained <20% variance of Φe,C, and changes in predominant size-fraction(s) distributions of Chl-a (biomass) failed to explain variance of Φe,C. Instead, normalised Stern-Volmer non-photochemical quenching (NPQNSV = F0′/Fv′) was a better predictor of Φe,C, explaining ~55% of observed variability. NPQNSV is a physiological descriptor that accounts for changes in both long-term driven acclimation in non-radiative decay, and quasi-instantaneous PSII downregulation, and thus may prove a useful predictor of Φe,C across physically-dynamic regimes, provided the slope describing their relationship is predictable. We also consider recent advances in fluorescence-based corrections to evaluate the potential role of baseline fluorescence (Fb) in contributing to overestimation of Φe,C and the correlation between Φe,C and NPQNSV – in doing so, we highlight the need for Fb corrections for future field-based assessments of Φe,C

Impact of prolonged walking exercise on cardiac structure and function in cardiac patients versus healthy controls.

BACKGROUND AND DESIGN: Previous studies have demonstrated that endurance exercise can cause an acute transient decrease in cardiac function in healthy subjects. Whether this also occurs in cardiac patients is unknown. We investigated the impact of prolonged single day and three-day walking exercise on cardiac function and cardiac biomarkers between cardiac patients and healthy controls in an observational study. METHODS: We recruited 10 cardiac patients (nine males, one female, 68 ± 5 years) and 10 age- and sex-matched healthy control subjects (nine males, one female, 68 ± 4 years) to perform 30 or 40 km of walking exercise per day for three consecutive days. Cardiac function was examined using echocardiography and cardiac biomarkers (cardiac troponin and B-type natriuretic peptide) with blood samples. Data were collected before walking and directly after walking on day 1 and day 3. RESULTS: Post-exercise early systolic tissue contraction velocity of the left ventricle (p = 0.005) and global longitudinal left ventricle strain (P = 0.026) were increased in both groups compared with baseline. Post-exercise right ventricle peak early diastolic tissue filling velocity and systolic blood pressure/left ventricle end-systolic volume ratio decreased in both groups (p = 0.043 and p = 0.028, respectively). Post-exercise cardiac troponin levels increased (p = 0.045) but did not differ across groups (p = 0.60), whereas B-type natriuretic peptide levels did not change (p = 0.43). CONCLUSION: This study suggests that stable cardiac patients are capable of performing three days of prolonged walking exercise without clinically significant acute overall deterioration in cardiac function or more pronounced increase in cardiac biomarkers compared with healthy controls

Acute response and chronic stimulus for cardiac structural and functional adaptation in a professional boxer.

The individual response to acute and chronic changes in cardiac structure and function to intense exercise training is not fully understood and therefore evidence in this setting may help to improve the timing and interpretation of pre-participation cardiac screening. The following case report highlights an acute increase in right ventricular (RV) size and a reduction in left ventricular (LV) basal radial function with concomitant increase at the mid-level in response to a week's increase in training volume in a professional boxer. These adaptations settle by the second week; however, chronic physiological adaptation occurs over a 12-week period. Electrocardiographic findings demonstrate an acute lateral T-wave inversion at 1 week, which revert to baseline for the duration of training. It appears that a change in training intensity and volume generates an acute response within the RV that acts as a stimulus for chronic adaptation in this professional boxer

Myocardial Strain Imaging in Resistant Hypertension.

PURPOSE OF REVIEW: Resistant hypertension (RH) is a major contributor to cardiovascular diseases and is associated with increased all-cause and cardiovascular mortality. Cardiac changes such as impaired left ventricular (LV) function, left ventricular hypertrophy (LVH), myocardial fibrosis, and enlarged left atrium (LA) are consequences of chronic exposure to an elevated blood pressure. The purpose of this review article is to demonstrate the potential benefits of using STE as a non-invasive imaging technique in the assessment of cardiac remodeling in patients with hypertension and specifically in uncontrolled and RH population. RECENT FINDINGS: It is well-recognized that conventional transthoracic echocardiography is a useful analytic imaging modality to evaluate hypertension-mediated organ damage (HMOD) and in a resistant hypertensive population. More recently two-dimensional speckle tracking echocardiography (STE) has been utilized to provide further risk assessment to this population. Recent data has shown that STE is a new promising echocardiographic marker to evaluate early stage LV dysfunction and myocardial fibrosis over conventional 2D parameters in patients with cardiovascular diseases

Alterations in Cardiac Mechanics Following Ultra-Endurance Exercise: Insights from Left and Right Ventricular Area-Deformation Loops.

BACKGROUND: The aim of this study was to use novel area-deformation (ε) loops to interrogate the interaction between the right ventricular (RV) and left ventricular (LV) mechanics following a 100-mile endurance run. METHODS: Fifteen participants (mean body mass, 70.1 ± 8.8 kg; mean age, 40 ± 8 years) were recruited for the study. Echocardiography was performed before the race, after the race, and 6 hours into recovery. RV and LV area and longitudinal ε were assessed using standard and speckle-tracking echocardiography. Following cubic spline interpolation, these variables were obtained across the same cardiac cycle and used to derive area-ε loops. RESULTS: The RV area-ε loop demonstrated a rightward shift after the race, with increased RV area (from 26.0 to 27.1 cm(2)) and reduced peak RV ε (from -28.6% to -25.8%). The recovery RV area-ε loop was similar to the postrace loop. A leftward shift was observed in the LV area-ε loop after the race, secondary to reduced LV area (from 35.8 to 32.5 cm(2)) and reduced peak ε (from -18.3% to -16.6%). In recovery, LV ε values returned toward baseline. CONCLUSIONS: A 100-mile ultramarathon resulted in a rightward shift in the RV area-ε loop as a result of RV dilatation. There was a concomitant leftward shift in the LV area-ε loop as a result of underfilling of the left ventricle. At 6 hours after exercise, there was a partial recovery of the left ventricle, while RV function remained depressed. It appears that changes in RV function do not have a serial impact on the left ventricle during recovery from ultra-endurance activity

Practical tips and tricks in measuring strain, strain rate and twist for the left and right ventricles.

Strain imaging provides an accessible, feasible and non-invasive technique to assess cardiac mechanics. Speckle tracking echocardiography (STE) is the primary modality with the utility for detection of subclinical ventricular dysfunction. Investigation and adoption of this technique has increased significantly in both the research and clinical environment. It is therefore important to provide information to guide the sonographer on the production of valid and reproducible data. The focus of this review is to (1) describe cardiac physiology and mechanics relevant to strain imaging, (2) discuss the concepts of strain imaging and STE and (3) provide a practical guide for the investigation and interpretation of cardiac mechanics using STE

Reduced left ventricular filling following blood volume extraction does not result in compensatory augmentation of cardiac mechanics.

An acute non-invasive reduction in preload has been shown to augment cardiac mechanics to maintain stroke volume and cardiac output. Such interventions induce concomitant changes in heart rate (HR), whereas blood volume extraction reduces preload without HR changes. Therefore, the purpose of this study was to determine whether a preload reduction in isolation resulted in augmented stroke volume achieved via enhanced cardiac mechanics. Nine healthy volunteers (4 female, age 29 ± 11 years) underwent echocardiography for the assessment of left ventricular (LV) volumes and mechanics in a supine position at baseline and end-extraction following the controlled removal of 25% of total blood volume (1062 ± 342 ml). Arterial blood pressure was monitored continuously by a pressure transducer attached to an indwelling radial artery catheter. HR and total peripheral resistance were unchanged from baseline to end extraction, but systolic blood pressure was reduced (148 to 127 mmHg). LV end diastolic volume (89 to 71 ml) and stroke volume (56 to 37 ml) were significantly reduced from baseline to end extraction; however, there was no change in LV twist, basal or apical rotation. In contrast, LV longitudinal strain (-20 to -17%) and basal circumferential strain (-22 to -19%) were significantly reduced from baseline to end extraction. In conclusion, a preload reduction during blood volume extraction does not result in compensatory changes in stroke volume or cardiac mechanics. Our data suggest that LV strain is dependent on LV filling and consequent geometry whereas LV twist could be mediated by heart rate. This article is protected by copyright. All rights reserved