Peak rapid filling rate (PRFR) is often used clinically as an index of left ventricular relaxation, i.e., of early diastolic function. This study tests the hypothesis that early filling rate is a function of the atrioventricular pressure difference and hence is influenced by the left atrial pressure as well as by the rate of left ventricular relaxation. As indexes, we chose the left atrial pressure at the atrioventricular pressure crossover (PCO), and the time constant (T) of an assumed exponential decline in left ventricular pressure. We accurately determined the magnitude and timing of filling parameters in conscious dogs by direct measurement of phasic mitral flow (electromagnetically) and high-fidelity chamber pressures. To obtain a diverse hemodynamic data base, loading conditions were changed by infusions of volume and angiotensin LI. The latter was administered to produce a change in left ventricular pressure of less than 35% (A-1) or a change in peak left ventricular pressure of greater than 35% (A-2). PRFR increased with volume loading, was unchanged with A-1, and was decreased with A-2; T and PCO increased in all three groups (p < .005 for all changes). PRFR correlated strongly with the diastolic atrioventricular pressure difference at the time of PRFR (r = .899, p < .001) and weakly with both T (r = .369, p < .01) and PCO (r = .601, p < .001). The correlation improved significantly when T and PCO were both included in the multivariate regression (r = .797, p < .0001). PRFR is thus determined by both the left atrial pressure and the left ventricular relaxation rate and should be used with caution as an index of left ventricular diastolic function.Circulation 74, No. 1, 187-196, 1986. RELAXATION ABNORMALITIES are one of the earliest manifestations of cardiac dysfunction and frequently precede systolic dysfunction in many disease states.'' Early filling function has been evaluated in a variety of diseases, e.g., coronary artery disease, hypertrophic cardiomyopathy, hypertensive heart disease, aortic valve disease, and congestive cardiomyop-

Background:American youth football leagues are typically structured using either age-only (AO) or age-and-weight (AW) playing standard conditions. These playing standard conditions group players by age in the former condition and by a combination of age and weight in the latter condition. However, no study has systematically compared injury risk between these 2 playing standards.Purpose:To compare injury rates between youth tackle football players in the AO and AW playing standard conditions.Study Design:Cohort study; Level of evidence, 2.Methods:Athletic trainers evaluated and recorded injuries at each practice and game during the 2012 and 2013 football seasons. Players (age, 5-14 years) were drawn from 13 recreational leagues across 6 states. The sample included 4092 athlete-seasons (AW, 2065; AO, 2027) from 210 teams (AW, 106; O, 104). Injury rate ratios (RRs) with 95% CIs were used to compare the playing standard conditions. Multivariate Poisson regression was used to estimate RRs adjusted for residual effects of age and clustering by team and league. There were 4 endpoints of interest: (1) any injury, (2) non–time loss (NTL) injuries only, (3) time loss (TL) injuries only, and (4) concussions only.Results:Over 2 seasons, the cohort accumulated 1475 injuries and 142,536 athlete-exposures (AEs). The most common injuries were contusions (34.4%), ligament sprains (16.3%), concussions (9.6%), and muscle strains (7.8%). The overall injury rate for both playing standard conditions combined was 10.3 per 1000 AEs (95% CI, 9.8-10.9). The TL injury, NTL injury, and concussion rates in both playing standard conditions combined were 3.1, 7.2, and 1.0 per 1000 AEs, respectively. In multivariate Poisson regression models controlling for age, team, and league, no differences were found between playing standard conditions in the overall injury rate (RRoverall, 1.1; 95% CI, 0.4-2.6). Rates for the other 3 endpoints were also similar (RRNTL, 1.1 [95% CI, 0.4-3.0]; RRTL, 0.9 [95% CI, 0.4-1.9]; RRconcussion, 0.6 [95% CI, 0.3-1.4]).Conclusion:For the injury endpoints examined in this study, the injury rates were similar in the AO and AW playing standards. Future research should examine other policies, rules, and behavioral factors that may affect injury risk within youth football.

Study Design: A repeated-measure crossover design was used. The independent variable was the type of ultrasound (pulsed or continuous) and the dependent variable was intramuscular temperature. Objective: To compare changes in intramuscular temperature resulting from the use of pulsed ultrasound versus continuous ultrasound with an equivalent spatial average temporal average (SATA) intensity. Background: There is a lack of research on the heat-generating capabilities of pulsed ultrasound within human muscle. Methods and Measures:The subjects were 16 healthy volunteers (mean age ± SD, 21.3 ± 2.5 years). Each subject was treated with pulsed ultrasound (3 MHz, 1.0 W/cm 2 , 50% duty cycle, for 10 minutes) and continuous ultrasound (3 MHz, 0.5 W/cm 2 , for 10 minutes) during a single testing session. Tissue temperature returned to baseline and stabilized between treatments and treatment order was randomized. Tissue temperature was measured every 30 seconds using a 26-gauge needle microprobe inserted at a depth of 2 cm in the left medial gastrocnemius muscle. Data were analyzed using a linear mixed model. Results: Treatment with continuous ultrasound produced a mean (±SD) temperature increase of 2.8°C ± 0.8°C above baseline. Treatment with pulsed ultrasound produced a mean (±SD) temperature increase of 2.8°C ± 0.7°C above baseline. Statistical analysis revealed no significant differences in either the extent or rate of temperature increases between the 2 modes of ultrasound application. Conclusion: Pulsed ultrasound (3 MHz, 1.0 W/cm 2 , 50% duty cycle, for 10 minutes) produces similar intramuscular temperature increases as continuous ultrasound (3 MHz, 0.5 W/cm 2 , for 10 minutes) at a 2-cm depth in the human gastrocnemius. Spatial average temporal average intensity is an important consideration when selecting pulsed ultrasound parameters intended to deliver nonthermal effects.

A substantial proportion of mildly hypertensive patients presenting in primary care have LVH determined by ECHO. Our results suggest that this procedure could significantly improve cardiovascular risk stratification in those patients with multiple risk factors, but no evidence of target organ damage by routine investigations.

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