Pressor response to intravenous tyramine is a marker of cardiac, but not vascular, adrenergic function.

Intravenous injections of the indirect sympathetic amine, tyramine, are used as a test of peripheral adrenergic function. The authors measured the time course of increases in ejection fraction, heart rate, systolic and diastolic pressure, popliteal artery flow, and greater saphenous vein diameter before and after an injection of 4.0 mg/m(2) body surface area of tyramine in normal human subjects.

Peripheral leukocyte subpopulations and catecholamine levels in astronauts as a function of mission duration.

Objective: The objective of this study was to determine the effects of spaceflight duration on immune cells and their relationship to catecholamine levels.

Methods: Eleven astronauts who flew aboard five different US Space Shuttle flights ranging in duration from 4 to 16 days were studied before launch and after landing.

Results: Consistent with prior studies, spaceflight was associated with a significant increase in the number of circulating white blood cells (p <.

Repetitive high G exposure is associated with increased occurrence of cardiac valvular regurgitation.

Background: Exposure to repeated high +Gz loads and the methods to prevent loss of consciousness cause unique stresses on the cardiovascular system. The purpose of this study was to determine if the +Gz environment is associated with an increased occurrence of valvular regurgitation in pilots of high performance aircraft.

Methods: There were 247 subjects who were divided into pilot (n = 46) and non-pilot (n = 201) groups.

An episode of ventricular tachycardia during long-duration spaceflight.

An episode of nonsustained ventricular tachycardia was recorded from a crew member during the second month aboard the MIR space station. Although asymptomatic, this cardiac event increases the concern that serious cardiac dysrhythmias may be a limiting factor during long-duration spaceflight.