The Mayo Clinic records linkage facility for residents of Rochester, Minnesota, Yielded 102 cases of ankylosing spondylitis (AS) diagnosed from 1935 through 1973. The incidence did not change significantly over the 39 years. Three times as many males as females were affected. In contrast to another recent report, survivorship of males with AS was not different from that of the general population, whereas survivorship of females with AS was reduced. The overall prevalence was 129/100,000.

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In an effort to define a simple, precise measure of cardiovascular response to exercise, a test devised by Bruno Balke was studied. The test involves walking at constant speed on a treadmill, the slope of which is periodically increased, while heart rate is measured accurately each minute. Balke had noted that physiologic alterations indicative of impending exhaustion occurred at or near the time the heart rate reached 180/min.; he used the time at which the rate was attained as an end point. Our studies suggested that a single temporal measurement was insufficiently sensitive as an estimate of cardiovascular response to the procedure. Another scoring method was derived, involving the integration of heart rates with respect to time. A strong positive correlation was found between the described score and the work done during each of 133 test runs. Additionally, evidence was obtained which suggests that it may not be necessary to force subjects to an end point near exhaustion in order to estimate their ability to tolerate exercise of this type. Submitted on March 14, 1960