Background: Exercise capacity is one of the predictors of morbidity and mortality in patients after the Fontan circulation. The influence of myocardial systolic and diastolic functional reserve on exercise performance has not been well established in this population. This study aimed at studying the myocardial response to exercise in Fontan patients using exercise echocardiography. Methods: Twenty-three Fontan patients with baseline ejection fraction >55% and 23 age and gender matched controls were included. A stepwise exercise stress echocardiography protocol was used. Tissue Doppler imaging (TDI) systolic (s’), and early diastolic (e’) velocities and myocardial acceleration during isovolumic contraction (IVA) were measured in the free wall of the dominant ventricle and interventricular septum and in the left ventricular free wall and septum of controls. Measurement was taken at rest and at incremental heart rate (HR). Changes in tissue Doppler velocities versus heart rate were studies and compared between patients and controls. Results: Resting HR was not significantly different between patients and controls but peak HR was lower in the Fontan group vs controls ( p <0.001). At rest patients had significantly lower lateral and septal e’ and s’ compared to controls (lateral s’: 6.35±1.05 vs. 14.41± 1.88 cm/s; lateral e’: 9.38±1.71 vs.20.66±2.55 cm/s; septal s’: 5.30±2.46 vs. 11.58±2.26 cm/s; septal e’: 10.45±2.46 vs. 17.80±1.58 cm/s P <0.001) except for IVA. At peak exercise, all variables were significantly lower in the patient group. During exercise, the slopes of lateral and septal s’ and IVA were significantly different between patients and controls except for e’. Conclusion: Our data suggest that patients with Fontan physiology have blunted systolic contractile response to exercise. Surprisingly our data suggest that the dynamic early diastolic myocardial reserve is preserved which suggest that early myocardial relaxation is not a limiting factor.
Hot extremes have been shown to be induced by antecedent surface moisture deficits in several regions. While most previous studies on this topic relied on modeling results or precipitation-based surface moisture information (particularly the standardized precipitation index, SPI), we use here a new merged remote sensing soil moisture product that combines active and passive microwave sensors to investigate the relation between the number of hot days (NHD) and preceding soil moisture deficits. Along with analyses of temporal variabilities of surface vs. root-zone soil moisture, this sheds light on the role of different soil depths for soil moisture–temperature coupling. The global patterns of soil moisture–NHD correlations from remote sensing data and from SPI as used in previous studies are comparable. Nonetheless, the strength of the relationship appears underestimated with remote sensing-based soil moisture compared to SPI-based estimates, particularly in regions of strong soil moisture–temperature coupling. This is mainly due to the fact that the temporal hydrological variability is less pronounced in the remote sensing data than in the SPI estimates in these regions, and large dry/wet anomalies appear underestimated. Comparing temporal variabilities of surface and root-zone soil moisture in in-situ observations reveals a drop of surface-layer variability below that of root-zone when dry conditions are considered. This feature is a plausible explanation for the observed weaker relationship of remote sensing-based soil moisture (representing the surface layer) with NHD as it leads to a gradual decoupling of the surface layer from temperature under dry conditions, while root-zone soil moisture sustains more of its temporal variability.
Global warming increases the occurrence probability of hot extremes, and improving the predictability of such events is thus becoming of critical importance. Hot extremes have been shown to be induced by surface moisture deficits in some regions. In this study, we assess whether such a relationship holds at the global scale. We find that wide areas of the world display a strong relationship between the number of hot days in the regions’ hottest month and preceding precipitation deficits. The occurrence probability of an above-average number of hot days is over 70% after precipitation deficits in most parts of South America as well as the Iberian Peninsula and Eastern Australia, and over 60% in most of North America and Eastern Europe, while it is below 30–40% after wet conditions in these regions. Using quantile regression analyses, we show that the impact of precipitation deficits on the number of hot days is asymmetric, i.e. extreme high numbers of hot days are most strongly influenced. This relationship also applies to the 2011 extreme event in Texas. These findings suggest that effects of soil moisture-temperature coupling are geographically more widespread than commonly assumed.
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