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Effects on platelet aggregation and fibrinolytic activity during upright posture and exercise in healthy men
K Winther1, W Hillegass, G H Tofler
1Harvard Medical School, Boston, Massachusetts.
Insights
Daily activities like standing and exercise impact blood clotting. Upright posture increases platelet aggregation, while exercise boosts fibrinolysis, potentially influencing vascular event timing.
Area of Science:
- Cardiovascular Physiology
- Hemostasis and Thrombosis
Background:
- Circadian rhythms influence acute myocardial infarction onset.
- Daily activities may trigger coronary thrombosis by altering blood's prothrombotic and antithrombotic balance.
Purpose of the Study:
- To compare the effects of assuming upright posture and exercise on platelet aggregation and fibrinolytic activity.
- To investigate how common daily activities influence thrombogenic potential.
Main Methods:
- Healthy male subjects were studied.
- Measurements of platelet aggregation and fibrinolytic activity were taken before and after assuming upright posture and during exercise.
- Posture changes (upright vs. supine) were systematically varied.
Main Results:
- Assuming upright posture significantly increased platelet aggregation and moderately increased fibrinolysis within 10 minutes, effects sustained for 90 minutes.
- Return to supine posture normalized these parameters.
- Exercise did not elevate platelet aggregation beyond upright posture but markedly increased fibrinolytic activity.
Conclusions:
- Upright posture and exercise induce distinct changes in blood's thrombogenic potential.
- These physiological responses may play a role in the circadian timing of clinical vascular events.
Abstract:
The circadian variation of acute myocardial infarction suggests that daily activities such as assuming the upright posture and performing different daily activities may trigger the onset of coronary thrombosis. Such triggering may result from unfavorable alterations in the balance between the prothrombotic and antithrombotic properties of the blood. The present study compares the effects of 2 common daily activities, assuming the upright posture and exercise, on platelet aggregation and fibrinolytic activity. In healthy male subjects, assuming the upright posture in the morning significantly increased platelet aggregation and produced only a moderate increase in fibrinolytic activity within 10 minutes. These changes were still present after 90 minutes in the upright posture. Supine posture for 45 minutes resulted in levels of fibrinolytic activity and platelet aggregation comparable to that observed before initially assuming the upright posture in the morning. Return to the supine posture for 45 minutes resulted in levels of fibrinolytic activity and platelet aggregation comparable to that observed before the initial assumption of upright posture. The changes recurred when upright posture was taken later in the day. Exercise did not increase platelet aggregation to levels beyond that produced by the upright posture, but was associated with a marked increase in fibrinolytic activity. Thus, exercise and upright posture produce distinctive alterations in the thrombogenic potential of the blood that may influence the timing of clinical vascular events.