About 7-day (circaseptan) and circadian changes in cold pressor test (CPT).

ABSTRACT

We assess circadian (CD) and circaseptan (CS) changes in the blood pressure (BP) response to a 1-min immersion of the hand into ice water, the cold pressor test (CPT). An about 8 mmHg BP increase in the CPT reported by others for health and an elevation >25 mmHg for patients with "hypertension" have been viewed as predisease, but variables related to the vascular system exhibit prominent CD, CS and circannuals, among other components of their genetically anchored time structure or chronome, and may also have to be considered. Hence, a 16-year-old adolescent (ML) immersed her hand into ice water every 2-4 h for 2 days and once daily in the morning thereafter for 1 week (N = 25), as did, only for <2 days (> or =24 h), four adults 20-66 years of age. BP and heart rate (HR) were monitored automatically around the clock at 15-min intervals and at 1-min intervals before and immediately after the CPT. Data were analyzed by cosinor. The difference between the first post-CPT BP value and the mean of the last seven values prior to the CPT was a measure of CPT response (at 1-min). Overall, ML's systolic (S) BP increased by 8.2 +/- 1.4 mmHg and her diastolic (D) BP by 6.2 +/- 0.9 mmHg (P < 0.001). Increases were found in 96% of the tests for SBP, 92% for DBP and 20% for HR. There was only one tie for HR (4%), resulting in a HR decrease in 76% of CPTs. The BP response to CPT at 1 min was CS-dependent. The CS double amplitudes are 12.5 +/- 4.1 for SBP (P = 0.019) and 7.8 +/- 2.8 mmHg for DBP (P = 0.030), with acrophases occurring on late Sunday, early Monday (at -50 degrees and -67 degrees from 0000 h from Saturday to Sunday for SBP and DBP, respectively, with 360 degrees identical with 1 week). The response of HR did not allow the detection of a CS rhythm (P = 0.969). The CD response peaked in the early morning hours; with 24 h identical with 360 degrees and 0 degrees = local midnight, the acrophase (phi) for SBP is at -80 degrees and for DBP at -113 degrees, in keeping with earlier results from four adult subjects (SBP -37 degrees; DBP -42 degrees ), individual differences notwithstanding. The average timing of the largest overall response of BP to CPT coincides with the timing of the response to other stimuli. The CS acrophases coincide with the times of increased morbidity/mortality from vascular diseases. Chronomes, time structures broader than circadian, notably their about-weekly components, should be considered, not only at the extremes of life when the CS and about-half-weekly rhythms are particularly prominent in BP and HR but also in interpreting BP responses as a gauge of vascular disease status in adolescents.