SUMMARY Pacific bluefin tuna inhabit a wide range of thermal environments across the Pacific ocean. To examine how metabolism varies across this thermal range,we studied the effect of ambient water temperature on metabolic rate of juvenile Pacific bluefin tuna, Thunnus thynnus, swimming in a swim tunnel. Rate of oxygen consumption(ṀO2) was measured at ambient temperatures of 8–25°C and swimming speeds of 0.75–1.75 body lengths (BL) s–1. Pacific bluefin swimming at 1 BL s–1 per second exhibited a U-shaped curve of metabolic rate vs ambient temperature, with a thermal minimum zone between 15°C to 20°C. Minimum ṀO2 of 175±29 mg kg–1 h–1 was recorded at 15°C, while both cold and warm temperatures resulted in increased metabolic rates of 331±62 mg kg–1 h–1at 8°C and 256±19 mg kg–1 h–1 at 25°C. Tailbeat frequencies were negatively correlated with ambient temperature. Additional experiments indicated that the increase in ṀO2 at low temperature occurred only at low swimming speeds. Ambient water temperature data from electronic tags implanted in wild fish indicate that Pacific bluefin of similar size to the experimental fish used in the swim tunnel spend most of their time in ambient temperatures in the metabolic thermal minimum zone.
SUMMARY To confirm reports of increased absenteeism after worksite hypertension screening, we performed a three-stage blood pressure screening among 5888 self-selected heterogeneous workers at 11 electronics plants using standardized screening and labeling procedures. A total of 296 subjects with mean systolic blood pressure of 140 mm Hg or greater or diastolic blood pressure of 90 mm Hg or greater on all three occasions were considered to have sustained hypertension. From the untreated normotensive subjects matched for eight sociodemographic and occupational variables, we prospectively selected one to three controls for each sustained hypertensive subject. Uncorrected absenteeism rates for sustained hypertensive subjects increased 22% from baseline in the postscreening year. Correction by logarithmic transformation for skewed distributions and by rates for matched controls for temporal trends reduced these changes to statistical insignificance with high statistical power. Several subgroups exhibited trends to increased absenteeism. At 12-month follow-up, the blood pressure of the sustained hypertensive subjects showed mean decreases of 12.6/6.7 mm Hg (p<0.0001) after the majority had received pharmacological antihypertensive treatment. These results suggest that worksite hypertension screening and labeling produce insignificant absenteeism change overall among self-selected heterogeneous work force populations. (Hypertension 10: 425-436, 1987) KEY WORDS • absenteeism • hypertension screening • labeling H YPERTENSION is the most common principal diagnosis cited by U.S. physicians during office visits, accounting for nearly 24 million visits annually, or 5% of the total.1 Despite substantial improvement in the proportion of Americans newly diagnosed as hypertensive and brought to treatment, major problems remain. By recently revised criteria, about 46% of hypertensive Americans are still undiagnosed, especially younger adults with mild disease. In nearly 21% hypertension is diagnosed but untreated, and in 22% it is treated but still uncon-
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