Cardiovascular circadian rhythms in normotensive and hypertensive adolescents
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With the improvement in automatic instruments for obtaining cardiovascular measurements, the ability to identify circadian (24-hour) rhythmic patterns in normotensive/hypertensive adolescents is now greatly enhanced. The study's purposes were to: (a) quantify adolescent blood pressure and heart rate as reflected in circadian rhythmic patterning; (b) establish a scientific basis for continued nursing research in circadian rhythmicity; and (c) validate the SpaceLabs 90202 Ambulatory Blood Pressure Monitor. High school students participated in a blood pressure screening program conducted by the investigator. After meeting specific delimitations, ten hypertensive students were matched for age, sex, and ethnicity with a stratified random normotensive group who had no family history of hypertension. Each student wore a SpaceLabs unit for 24 or 48 hours programmed to inflate the blood pressure cuff at specific intervals. An Activity Diary facilitated data interpretation. Cosinor analysis was employed on edited blood pressure and heart rate measurements. The mesor systolic blood pressure was significantly lower (p $\leq$.010 to.001) in the normotensive adolescent. A t-test revealed a significant difference in this parameter between the two groups (p =.0005, df = 13). A t-test also indicated a significant difference in systolic blood pressure amplitude between the normotensive/hypertensive students (p =.023, df = 13). The SpaceLabs 90202 Monitor Validation Study revealed no significant differences in blood pressure readings when the unit's measurements were compared with either auscultatory (p =.001 and.05 for systolic and diastolic blood pressures respectively) or direct arterial measurements (p =.001 and.02 for systolic and diastolic blood pressures respectively). While the findings reflect anticipated greater systolic blood pressure mesors and amplitudes in the hypertensive adolescent, such hypertensive/normotensive categories may be a misnomer since all individuals have a certain percentage of elevated pressures over a 24-hour period. It is recommended that the study be repeated to: (a) further validate the SpaceLabs monitor; (b) collect data for a minimum of 48 hours with specific documentation as to why three or more monitor error codes were being consecutively generated; and (c) further contribute to a circadian cardiovascular data base which may yield additional information about the complex factors modulating adolescent blood pressure.