Cardiovascular responses to two minutes of isometric contractions of the finger flexors in healthy women

The purpose of this study was to investigate the cardiovascular responses to prolonged submaximal (20% MVC) and maximal (100% MVC) isometric contraction of the finger flexors in healthy women between the ages of 20 and 35 years. The cardiovascular variables which were investigated included; heart rate (HR), systolic blood pressure (SBP), diastolic blood pressure (DBP), mean arterial pressure (MAP), pulse pressure (PP), stroke volume (SV) and cardiac output (CO).Doppler echocardiography was used to estimate stroke volume from the measures of aortic diameter, using 2 dimensional echocardiography, and time-velocity integrals, using Doppler ultrasound. Since aortic diameter and Doppler velocities can not be measured simultaneously, this study involved two separate experiments. Experiment I was designed to investigate changes in aortic diameter during two minutes of prolonged maximal (100% MVC) isometric contraction of the finger flexors. Based on the finding that aortic diameter did not change significantly (.05 level) during maximal isometric contractions, Experiment II was designed to investigate HR (EKG), blood pressure (auscultation), stroke volume (resting aortic diameter $\times$ time-velocity integrals) and cardiac output (SV $\times$ HR).During the submaximal isometric contractions (20% MVC), HR, PP, SV and CO did not change significantly from rest during the first 30 seconds of contraction or during the two-minute contraction period. SBP, DBP and MAP increased significantly from resting levels during the two minutes of submaximal isometric contractions.During maximal isometric contraction (100% MVC), HR, SBP, DBP, MAP and CO increased significantly during the first 30 seconds of contraction. HR and CO levelled off during the remainder of the contraction period, whereas SBP, DBP and MAP continued to rise throughout the contraction period. PP and SV remained relatively constant throughout the maximal isometric contraction, with SV increasing significantly during the first 30 seconds of recovery.These data suggest that there is a greater magnitude of cardiovascular response to maximal isometric contractions and that there is a different pattern of response between HR and BP variables. Also, differences in cardiac output are affected more by changes in HR than in SV, as SV remains relatively constant during both submaximal (20% MVC) and maximal (100% MVC) isometric contractions of the finger flexors.U of I OnlyETDs are only available to UIUC Users without author permissio