Three recent research projects have yielded interesting findings about daily (and nightly) cardiovascular function.

One team demonstrated in mice that ACE inhibitors work most effectively at bedtime, when they lower increases in levels of hormones with heart-damaging potential. When given at sleep time, captopril improved cardiac function and significantly decreased other measures of heart trouble (but induced similar drops in BP at sleep or wake time, suggesting that the time-of-day differences were not caused by BP changes). However, when administered during wake time, the drug worked no better than placebo (J Am Coll Cardiol. 2011;57:2020-2028).

Aida Suárez-Barrientos and colleagues reported in Heart that infarct size changed according to the time of day of ST-segment elevation myocardial infarction (STEMI) onset: The field of damage was more likely to be 20% larger when STEMI occurred in the dark-to-light transition period of 6:00 am to 12:00 pm.

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Although increased BP is a major risk factor for adverse cardiovascular events, another set of researchers was surprised to find that the internal BP cycles actually caused the lowest BP measurements in the late morning, with the highest occurring at about 9:00 pm (Circ Res. 2011;108:980-984). This indicates that the circadian rhythm of BP is unlikely to be linked to the well-documented morning peaks in heart events and strokes.