Effect of injury on the reflex control of pulse rate in man.

The changes in pulse rate elicited by a Valsalva maneuver, a maximal inspiration and a passive head-up tilt, have been measured in patients within a few hours of limb injury before definitive treatment and in control subjects. The injuries were of minor or moderate severity. In all those tested in the Valsalva maneuver, the pulse rate increased during phase 2 and decreased during phase 4 of the response, and both changes were directly related to the initial pulse rate. In controls the increase in pulse rate during phase 2 was greater when the maneuver was performed at 40 mm Hg than at 20 mm Hg, but after injury this difference was not seen and the increases at 20 mmHg and at 40 mm Hg were the same as in controls at 20 mm Hg. The bradycardia during phase 4 was less in injured patients than in controls. The responses returned to normal during recovery. The increase in pulse rate during a maximal inspiration was not affected by injury. When the controls were given a head-up tilt the pulse rate increased, the rise depending on the angle of the tilt. A proportion of the injured patients, which increased with the severity of the injury, did not show this response, for the pulse rate decreased at the higher angles of tilt.