Protection against orthostatic hypotension by means of isometric muscle contraction of lower extremities

Abstract

Isometric muscle contraction of lower extremities was evaluated to elucidate its preventive effect on orthostatic hypotension. Eight college students including 5 males and 3 females were volunteered to be the subjects. After resting period of a half hour the subjects seated on a chair for 10 minutes and followed by standing for 18 minutes. During the initial 10 minutes of standing period the subjects were asked to stand still. In the following 5 minutes the subjects repeated muscle contraction and relaxation of the both lower extremities with such a pattern as: contraction of anterior tibial muscle by extending fingers dorsally for one second followed by isometric contraction of femoral quadriceps muscle for one second. This combined muscle contractions were repeated for 5 minutes once in 10 seconds, once in 5 seconds or once every 2 seconds. During sitting; quiet standing, muscle contraction, and 3 minutes after contraction period, blood pressure was measured and ECG, phonocardiogram, and carotid pulse wave were recorded to determine heart fate, pre-ejection period index (PEPi), and ejection time index (LVETi). During quiet standing systolic blood pressure fell and diastolic blood pressure and heart rate increased. PEPi was lengthend and LVETi was shortened. These findings were completely compensated by muscle contraction, and blood pressure was kept above the control value through the period of muscle contraction. The results led us to a conclusion that isometric muscle contraction of lower extremities during standing affords a powerful protection against orthostatic hypotension. And the frequency of one contraction in 10 seconds is verified to be enough for this purpose.