Key result
Morning exercise was associated with a significantly lower ischemic threshold compared to the afternoon (115 vs 128 bpm; p<0.04), likely related to higher morning plasma endothelin-1 levels.
Why the study?
Does the time of day (morning vs afternoon) affect the ischemic threshold and plasma ET-1 levels in patients with stable angina?
Observational (n=21)
Does the time of day (morning vs afternoon) affect the ischemic threshold and plasma ET-1 levels in patients with stable angina?
Circadian variation in plasma ET-1 levels is associated with a lower ischemic threshold in the morning hours in patients with stable angina.
Lower morning ischemic threshold may inform exercise counseling in stable angina; leaves open causal ET-1 mechanisms requiring confirmation.
To investigate circadian variation in ischemic threshold in chronic coronary heart disease (CHD) and its relation to plasma endothelin-1 (ET-1), 21 patients with stable angina underwent treadmill exercise tests twice within a day, performed at 8-9 AM for the first test and at 3-4 PM for the second one. Ischemic threshold was defined as the heart rate at the onset of 1 mm ST segment depression during exercise tests. Blood samples were taken at 5 minutes before each exercise test, and plasma ET-1 was measured for determining the possible relation to ischemic threshold in patients with CHD. The results showed that the heart rate-ischemic threshold in individual patients varied by 10 +/- 1% (range, 2-15%) in the morning and 9 +/- 1% (range, 2-14%) in the afternoon, while there was a mean (11.2%) reduction in the ischemic threshold between 2 time points, with the ischemic threshold being significantly lower in the morning compared with that in the afternoon (115 +/- 22 bpm vs 128 +/- 31 bpm p<0.04). ET-1 values were 6.20 +/- 2.44 ng/L in the morning hours and 4.02 +/- 1.61 ng/L in the afternoon hours, with a statistical significant difference (p<0.01). In conclusion, the present study indicated that circadian variation of plasma levels of ET-1 was likely to be one of the most likely mechanisms involved in reduction in the ischemic threshold in the morning hours.
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Li et al. (2002) conducted an observational in chronic coronary heart disease (CHD) with stable angina (n=21). Morning time (8-9 AM) vs. Afternoon time (3-4 PM) was evaluated on Ischemic threshold (heart rate at the onset of 1 mm ST segment depression) (11.2% reduction, p=<0.04). Morning exercise was associated with a significantly lower ischemic threshold compared to the afternoon (115 vs 128 bpm; p<0.04), likely related to higher morning plasma endothelin-1 levels.
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