In a sub-study from J-HOP data, Wanthong et al, reported that the hourly blood pressure (BP) surge (HBPS) at around 6 am from a nighttime trough was associated with left ventricular mass index (LVMI) independent of covariates, including clinic and 24 hour BPs. 1 In this study, about half of the patients were awake at 6 am and HBPS at 6 am is characterized with steepest slope of HBPS as shown in fig 1. This finding is partly consistent with the previous study showing that the rate of rise in morning BP is highest when the BP curve is aligned to the midpoint of the morning rise according to waking time. 2 Considering that most of the subjects were in a pre-awakening state at 5 am, the study finding supports that the HBPS in this study is more closely related to a BP rise in the post-wakening period than in the pre-awakening period. 3,4 So, the BP surge at around 6 am shown in this study can be an awakening-specific phenomenon on one hand or might be a circadian rhythm-specific phenomenon on the other hand. In terms of the HBPS being a dynamic parameter of BP rise in the morning, the steepest HBPS rise might not always be observed at around 6 am because the mean awake times could be different among populations.So whether the correlation to HBPS observed at 6 am is incidental to the mean waking time or instead due to the intrinsic circadian rhythm is not known and warrants further studies.Resultantly, this study shows that the level of HBPS is highest at 9 am. It has also been reported that the human endogenous circadian rhythm also shows the greatest platelet activity at around 9 am. 5 Interestingly, also in this study by Scheer et al, the maximal slope of increasing platelet activity or epinephrine level could be observed around 6 am. The most interesting finding of the study by Wanthong et al, is not that the highest level of HBPS at 9 am but that the most dynamic time interval of HBPS at 6 am is independently associated with target organ damage. As for circadian rhythmometry, this result shifts our attention from the acrophase to the tangent or gamma representing the slope of BP rise. And because the steepest slope fits best for 6 hour earlier to the acrophase in the 24-hour single-component cosinor-based model, the result of the study fits better for 12-hour cosinor or two component models. 6 In general, the morning BP surge (MBPS) in a population is defined by the amount of rise during the 2 hour period after the diary based awakening time. Compared to the earlier hour of MBPS, the slope of the BP surge seems to be blunted in the latter hour as shown in fig 1. Even though there are few studies concerning the dynamics of HBPS in the morning and its related factors, many factors are known to be associated with the amount of MBPS. 7,8For example, with a simple calculation, higher nocturnal BP related to salt sensitivity could mean a lower HBPS by simple subtraction from a higher trough BP level. Alternatively, considering physiologic explanations, a BP surge could be even more exaggerated or steeper in response to...