Central Hemodynamic Responses to Loaded and Unloaded ES-Induced and Voluntary Contractions of the Lower Leg

Central hemodynamic responses to Electrical Stimulation (ES)-induced contractions were compared with voluntary contractions of the lower limb muscles in twenty subjects (legs). All subjects were healthy volunteers with normal venous capacitance and no reflux. Exercise protocols consisted of static and continuous loaded and unloaded lower leg muscle contractions produced by: 1) voluntary contraction (VOL), 2) ES-induced contractions of the gastrocnemius and tibialis anterior muscles (ES), and 3) combination of ES and VOL. A computerized impedance cardiograph measured Stroke Volume (SV), Cardiac output (CO), Cardiac Index (CI), Heart rate (HR), Mean Arterial Blood Pressure (MAP), and Total Peripheral Resistance (TPR). Changes in the above variables were statistically analyzed pre and post each exercise protocol. Both static and continuous ES-induced contractions caused increases in SV, CO, and CI in comparison to preexercise values. However, these increases were significantly higher after continuous ES contractions when compared with VOL. TPR increased with static contractions and decreased with continuous contractions in all of the three treatment groups. The decrease in TPR could be secondary to vasodilatation produced by continuous ES. The increases in central hemodynamics were considered to be secondary to a decrease in blood pooling which in turn was secondary to the external stimulus of ES. The reduction in peripheral blood pooling, caused by increased blood flow via ES application, could be due to a mechanical “milking “ effect on the lower limb venous bed during active contraction/exercise of the calf muscles. An increase in the pre-load of the heart may cause an increase in myocardial O2 uptake, and thus improved efficiency of the cardiovascular system. This system (ES) may be used efficiently to reduce blood pooling in paralyzed individuals.