Biorhythmic patterns of blood pressure in non-surgical patients in an intensive care unit
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Blood pressure is a biorhythm that is primarily exogenous, responds to cues, and has a diurnal pattern characterized by a daytime peak and a nighttime trough. The effect of changing environmental cues such as light-dark cycles on blood pressure is not well documented. This exploratory studied identified the patterns of blood pressure in nonsurgical patients in an intensive care unit. The following research questions were addressed: (1) Does the diurnal pattern of blood pressure synchronize with the environment in nonsurgical patients who are in an intensive care unit environment? and (2) Does the diurnal pattern of blood pressure phase shift in nonsurgical patients who are in an intensive care unit environment? The study was conducted in a 10 bed medical surgical intensive care unit (ICU). Ten subjects, 3 females (30%) and 7 males (70%) who did not have congestive heart failure or recent surgery comprised the sample. Ages ranged from 30 to 77 years with a mean age of 54.9 (±15.23). Blood pressure readings were monitored with a printout and collected every 24 hours by the researcher along with information about the environment using the “Patient Activity” form. The blood pressure printout and the “Patient Activity” form were coded to ensure patient confidentiality. Data were collected for no less than 48 hours and no more than 72 hours. Blood pressure data were analyzed using cosinor rhythmometry, cosinor analysis, autocorrelation and percentage rhythmicity. Environmental information was related anecdotally to each subject. Results from the analyses indicated that although significant circadian rhythms were present in the majority of the subjects, the usual diurnal period was altered by being either lengthened or attenuated. Percentage rhythmicity indicated no synchrony with the environment. Phase shifts were noted in the majority of the subjects indicating that the time of the peak blood pressure was altered from the expected time (12 noon–6 PM). It was concluded that non surgical patients in an ICU experienced not only disruption of the diurnal cycle length but also had phase shifts in both systolic and diastolic blood pressure related to sleep disruptions and a constant lighted environment.