Effects of ß-Blockers on Maximal Heart Rate Prediction Equations in a Cardiac Population.

PURPOSE: To derive specific maximal heart rate (HRmax) prediction equations for a coronary artery disease (CAD) population based upon status of ß-blocker (BB) therapy and to compare these to prior HRmax equations (Fox and Brawner-specific for CAD). METHODS: We retrospectively reviewed stress echocardiogram treadmill tests in patients with CAD, dividing subjects into 3 groups based upon BB use on test day: not prescribed BB therapy (no BB group; n = 110); held for 12 to 24 hr prior (held BB group; n = 155); and continued taking (took BB group; n = 72). RESULTS: Derived HRmax equations for our CAD population were no BB = 200 - 0.79 × age; held BB = 193 - 0.71 × age; and took BB = 168 - 0.51 × age. Achieved HRmax mean was not significantly different between held BB and no BB groups; however, HRmax in the took BB group was significantly lower. Fox and Brawner (no BB)-HRmax equations significantly overestimated (+6 and +9 mean bias) and underestimated (-8 and -6 mean bias) achieved HRmax in no BB and held BB groups, respectively. The Brawner (no BB) equation intercept and slope were not significantly different from our CAD-held BB and no BB equations. The Brawner (on BB) equation intercept and slope were similar to our took BB equation, but greatly underestimated achieved HRmax (-17 mean bias). CONCLUSION: For patients holding BB therapy on test day, a similar CAD HRmax estimation equation to those patients never on BB can be used, comparable to the Brawner (no BB) equation. Further research is needed to determine when patients should take their BB therapy in conjunction with exercise testing.

Controls on the discharge of Chalk streams of the Berkshire Downs, UK.

The water quality and biological functioning of major UK rivers draining permeable basins cannot be fully understood without knowledge of the spatial and temporal controls on the aquifer-river system. In this paper, hydrogeological features of Chalk streams feeding the Thames, the focus of this special issue, are described. Large-scale features, such as line sinks along the Thames and major tributaries such as the Kennet, tend to determine the regional groundwater flow patterns in the Chalk aquifer, whereas the complex characteristics of the Chalk dominate the local spatial and temporal patterns of groundwater discharge to the tributaries draining the dip slopes. These different controls are described and illustrated by particular reference to the Lambourn (a sub-catchment of the Kennet) and Pang catchments. Various issues requiring further investigation are also highlighted.