Blood pressure and heart rate response to isometric exercise: the effect of spinal cord injury in humans

The systolic (SP) and diastolic (DP) blood pressure and heart rate (HR) responses during a fatiguing isometric contraction of either the handgrip or quadriceps muscles was measured in 139 paraplegic patients divided into five groups (having injuries at T4, T12 and L1-L3 and suffering complete paraplegia and having injuries at T4 but showing incomplete hemiplegia or paraplegia) and 25 controls. While all handgrip exercise was maintained by voluntary effort, only the controls were able to make a voluntary contraction of their quadriceps muscles; the paraplegics had isometric contractions of their quadriceps muscles elicited by functional electrical stimulation (FES). The endurance of the handgrip exercise was not significantly different among the controls and any one of the five experimental groups (control group endurance = 151 s, average paraplegic group endurance = 141 s) while it was higher in the leg muscles (P < 0.05 controls 133 s, paraplegics 111 s). All subjects showed a linear increase in SP and DP throughout the duration of the handgrip exercise, pressure increasing from rest to fatigue by 55-56 mmHg. The controls, subjects with a complete and incomplete spinal cord injuries at T4 showed similar SP and DP increases during leg exercise, both the SP and DP response was eliminated in the T12 and L1-L3 injury groups. The HR increased during fatiguing isometric handgrip contractions from an average resting value of 82 to a maximum of 121 beats x min(-1) in both the controls and paraplegic subjects. However, while the HR increased to a slightly higher level of 127 beats x min(-1) at the end of the contraction of the leg muscles in the controls, the increase in HR during FES exercise was modest, increasing by an average of only 6 beats x min(-1) in the paraplegic group.