[Note: POTS is a dysregulation of ‘automatic’ heart rate/blood pressure adjustments that support changes in the body’s requirements – e.g., in POTS heart rate is exaggerated (tachycardia) on rising from prone to upright position. ME/CFS and POTS are often associated and “may share a common pathophysiology.”]
Patients with Postural Tachycardia Syndrome (POTS) have excessive orthostatic tachycardia (<30 bpm) when standing from a supine position [lying on the back].
Heart rate (HR) and blood pressure (BP) are known to exhibit diurnal variability [variation depending on time of day], but the role of diurnal variability in orthostatic changes of HR & BP is not known.
In this study, we tested the hypothesis that there is diurnal variation of orthostatic HR & BP in patients with POTS and healthy controls. Patients with POTS (n=54) and healthy volunteers (n=26) were admitted to the Clinical Research Center.
Supine and standing (5 min) HR & BP were obtained on the evening on the day of admission and in the following morning. Overall, standing HR was significantly higher in the morning than the evening (102±3 bpm [AM] vs. 93±2 bpm [PM]; P<0.001).
Standing HR was higher in the morning in both POTS patients (108±4 bpm [AM] vs. 100±3 bpm [PM]; P=0.012) and controls (89±3 bpm [AM] vs. 80±2 bpm [PM]; P=0.005), when analyzed separately.
There was no diurnal variability in orthostatic BP in POTS.
More subjects met the POTS HR criterion in the morning compared with the evening (P=0.008).[bolding added]
There was significant diurnal variability in orthostatic tachycardia, with a great orthostatic tachycardia in the morning compared to the evening in both patients with POTS and healthy subjects.
Given the importance of orthostatic tachycardia in diagnosing POTS, this diurnal variability should be considered in the clinic as it may affect the diagnosis of POTS.
Source: Clinical Science, Jul 14, 2011. Brewster JA, Garland EM, Biaggioni I, Black BK, Ling JF, Shibao CA, Robertson D, Raj SR.Vanderbilt University School of Medicine, Nashville, Tennessee, USA. [Email: firstname.lastname@example.org]