Experimental and Mathematical Analyses Relating Circadian Period and Phase of Entrainment in Neurospora crassa.

Circadian rhythms are observed in most organisms on earth and are known to play a major role in successful adaptation to the 24-h cycling environment. Circadian phenotypes are characterized by a free-running period that is observed in constant conditions and an entrained phase that is observed in cyclic conditions. Thus, the relationship between the free-running period and phase of entrainment is of interest. A popular simple rule has been that the entrained phase is the expression of the period in a cycling environment (i.e., that a short period causes an advanced phase and a long period causes a delayed phase). However, there are experimental data that are not explained by this simple relationship, and no systematic study has been done to explore all possible period-phase relationships. Here, we show the existence of stable period-phase relationships that are exceptions to this rule. First, we analyzed period-phase relationships using populations with different degrees of genome complexity. Second, we generated isogenic F1 populations by crossing 14 classical period mutants to the same female and analyzed 2 populations with a short period/delayed phase and a long period/advanced phase. Third, we generated a mathematical model to account for such variable relationships between period and phase. Our analyses support the view that the circadian period of an organism is not the only predictor of the entrained phase.

Isosorbide Dinitrate, With or Without Hydralazine, Does Not Reduce Wave Reflections, Left Ventricular Hypertrophy, or Myocardial Fibrosis in Patients With Heart Failure With Preserved Ejection Fraction.

BACKGROUND: Wave reflections, which are increased in patients with heart failure with preserved ejection fraction, impair diastolic function and promote pathologic myocardial remodeling. Organic nitrates reduce wave reflections acutely, but whether this is sustained chronically or affected by hydralazine coadministration is unknown. METHODS AND RESULTS: We randomized 44 patients with heart failure with preserved ejection fraction in a double-blinded fashion to isosorbide dinitrate (ISDN; n=13), ISDN+hydralazine (ISDN+hydral; n=15), or placebo (n=16) for 6 months. The primary end point was the change in reflection magnitude (RM; assessed with arterial tonometry and Doppler echocardiography). Secondary end points included change in left ventricular mass and fibrosis, measured with cardiac magnetic resonance imaging, and the 6-minute walk distance. ISDN reduced aortic characteristic impedance (mean baseline=0.15 [95% CI, 0.14-0.17], 3 months=0.11 [95% CI, 0.10-0.13], 6 months=0.10 [95% CI, 0.08-0.12] mm Hg/mL per second; P=0.003) and forward wave amplitude (Pf, mean baseline=54.8 [95% CI, 47.6-62.0], 3 months=42.2 [95% CI, 33.2-51.3]; 6 months=37.0 [95% CI, 27.2-46.8] mm Hg, P=0.04), but had no effect on RM (P=0.64), left ventricular mass (P=0.33), or fibrosis (P=0.63). ISDN+hydral increased RM (mean baseline=0.39 [95% CI, 0.35-0.43]; 3 months=0.31 [95% CI, 0.25-0.36]; 6 months=0.44 [95% CI, 0.37-0.51], P=0.03), reduced 6-minute walk distance (mean baseline=343.3 [95% CI, 319.2-367.4]; 6 months=277.0 [95% CI, 242.7-311.4] meters, P=0.022), and increased native myocardial T1 (mean baseline=1016.2 [95% CI, 1002.7-1029.7]; 6 months=1054.5 [95% CI, 1036.5-1072.3], P=0.021). A high proportion of patients experienced adverse events with active therapy (ISDN=61.5%, ISDN+hydral=60.0%; placebo=12.5%; P=0.007). CONCLUSIONS: ISDN, with or without hydralazine, does not exert beneficial effects on RM, left ventricular remodeling, or submaximal exercise and is poorly tolerated. ISDN+hydral appears to have deleterious effects on RM, myocardial remodeling, and submaximal exercise. Our findings do not support the routine use of these vasodilators in patients with heart failure with preserved ejection fraction. CLINICAL TRIAL REGISTRATION: URL: www.clinicaltrials.gov. Unique identifier: NCT01516346.

Effect of inorganic nitrate on exercise capacity in heart failure with preserved ejection fraction.

BACKGROUND: Inorganic nitrate (NO3(-)), abundant in certain vegetables, is converted to nitrite by bacteria in the oral cavity. Nitrite can be converted to nitric oxide in the setting of hypoxia. We tested the hypothesis that NO3(-) supplementation improves exercise capacity in heart failure with preserved ejection fraction via specific adaptations to exercise. METHODS AND RESULTS: Seventeen subjects participated in this randomized, double-blind, crossover study comparing a single dose of NO3-rich beetroot juice (NO3(-), 12.9 mmol) with an identical nitrate-depleted placebo. Subjects performed supine-cycle maximal-effort cardiopulmonary exercise tests, with measurements of cardiac output and skeletal muscle oxygenation. We also assessed skeletal muscle oxidative function. Study end points included exercise efficiency (total work/total oxygen consumed), peak VO2, total work performed, vasodilatory reserve, forearm mitochondrial oxidative function, and augmentation index (a marker of arterial wave reflections, measured via radial arterial tonometry). Supplementation increased plasma nitric oxide metabolites (median, 326 versus 10 µmol/L; P=0.0003), peak VO2 (12.6±3.7 versus 11.6±3.1 mL O2·min(-1)·kg(-1); P=0.005), and total work performed (55.6±35.3 versus 49.2±28.9 kJ; P=0.04). However, efficiency was unchanged. NO3(-) led to greater reductions in systemic vascular resistance (-42.4±16.6% versus -31.8±20.3%; P=0.03) and increases in cardiac output (121.2±59.9% versus 88.7±53.3%; P=0.006) with exercise. NO3(-) reduced aortic augmentation index (132.2±16.7% versus 141.4±21.9%; P=0.03) and tended to improve mitochondrial oxidative function. CONCLUSIONS: NO3(-) increased exercise capacity in heart failure with preserved ejection fraction by targeting peripheral abnormalities. Efficiency did not change as a result of parallel increases in total work and VO2. NO3(-) increased exercise vasodilatory and cardiac output reserves. NO3(-) also reduced arterial wave reflections, which are linked to left ventricular diastolic dysfunction and remodeling. CLINICAL TRIAL REGISTRATION URL: www.clinicaltrials.gov. Unique identifier: NCT01919177.

Prospective risk factors for increased central augmentation index in men and women.

BACKGROUND: Arterial wave reflections are important determinants of central pressure pulsatility and left ventricular afterload. The augmentation index (AIx) is the most widely used surrogate of arterial wave reflections. Despite multiple cross-sectional studies assessing the correlates of AIx, little prospective data exist regarding changes in AIx over time. We aimed to assess the predictors of changes in AIx over time in adults from the general population. METHODS: We performed radial arterial tonometry assessments a median of 3.18 ± 0.4 years apart on 143 nondiabetic adult participants in the population-based PREVENCION study. Central AIx was obtained using the generalized transfer function of the Sphygmocor device. RESULTS: Predictors of the change in AIx over time were investigated. Among men (n = 67), the change in AIx was predicted by abdominal obesity (standardized ß for waist circumference = 0.34; P = 0.002), impaired fasting glucose (standardized ß = 0.24; P = 0.009), and the change in heart rate (standardized ß = -0.78; P < 0.001). Among women (n = 76), the change in AIx was predicted by non-high-density lipoprotein cholesterol (standardized ß = 0.33; P = 0.001), C-reactive protein levels (standardized ß = 0.24; P = 0.02), change in mean arterial pressure (standardized ß = 0.33; P = 0.001), and change in heart rate (standardized ß = -0.52; P < 0.001). CONCLUSIONS: Metabolic and inflammatory factors predicted changes in AIx over time, with important sex differences. Metabolic factors, such as abdominal obesity and impaired fasting glucose, predicted changes in AIx in men, whereas C-reactive protein and non-high-density lipoprotein cholesterol levels predicted changes in women. Our findings highlight the impact of sex on arterial properties and may guide the design of interventions to favorably impact changes in late systolic pressure augmentation.

Effective arterial elastance is insensitive to pulsatile arterial load.

Effective arterial elastance (E(A)) was proposed as a lumped parameter that incorporates pulsatile and resistive afterload and is increasingly being used in clinical studies. Theoretical modeling studies suggest that E(A) is minimally affected by pulsatile load, but little human data are available. We assessed the relationship between E(A) and arterial load determined noninvasively from central pressure-flow analyses among middle-aged adults in the general population (n=2367) and a diverse clinical population of older adults (n=193). In a separate study, we investigated the sensitivity of E(A) to changes in pulsatile load induced by isometric exercise (n=73). The combination of systemic vascular resistance and heart rate predicted 95.6% and 97.8% of the variability in E(A) among middle-aged and older adults, respectively. E(A) demonstrated a quasi-perfect linear relationship with the ratio of systemic vascular resistance/heart period (middle-aged adults, R=0.972; older adults, R=0.99; P<0.0001). Aortic characteristic impedance, total arterial compliance, reflection magnitude, and timing accounted together for <1% of the variability in E(A) in either middle-aged or older adults. Despite pronounced changes in pulsatile load induced by isometric exercise, changes in E(A) were not independently associated with changes pulsatile load but were rather a nearly perfect linear function of the ratio of systemic vascular resistance/heart period (R=0.99; P<0.0001). Our findings demonstrate that E(A) is simply a function of systemic vascular resistance and heart rate and is negligibly influenced by (and insensitive to) changes in pulsatile afterload in humans. Its current interpretation as a lumped parameter of pulsatile and resistive afterload should thus be reassessed.