Lower body negative pressure consistently increased the number of sympathetic bursts in healthy subjects, an effect significantly greater than expected from blood pressure changes alone.
Does lower body negative pressure affect human muscle nerve sympathetic activity in healthy subjects?
Lower body negative pressure increases muscle nerve sympathetic activity in healthy subjects, likely mediated by intrathoracic volume receptors rather than arterial baroreceptors.
Recordings of multi-unit sympathetic activity were made from muscle branches of the median nerve in five healthy subjects during application of lower body negative pressure (l.b.n.p.). Simultaneous recordings of arterial blood pressure were made in four subjects. The strength of the neural activity was quantitated by counting the number of pulse synchronous sympathetic bursts and their amplitudes in the mean voltage neurogram.2. The general appearance of the sympathetic activity in pulse synchronous bursts was similar during control periods and during l.b.n.p., but during l.b.n.p. there was always an increase in the number of sympathetic bursts and usually also in the mean voltage amplitude of the bursts.3. The probability of occurrence of a burst was correlated to different blood pressure parameters of individual heart beats and both during control periods and during l.b.n.p. there was regularly a close negative correlation to diastolic, a low correlation to systolic, an intermediate negative correlation to mean and a positive correlation to pulse pressures.4. The changes in arterial blood pressure during l.b.n.p. were small and in most cases statistically insignificant. The observed increases in the number of sympathetic bursts during l.b.n.p. were significantly greater than what could be expected on the basis of the blood pressure changes.5. The findings suggest that the reflex control from the arterial baroreceptors is maintained during l.b.n.p. but, since the increase of sympathetic activity during l.b.n.p. could not be explained by a change in stimulation of the arterial baroreceptors, influence from other receptor groups (presumably intrathoracic volume receptors) must also have occurred.
Sundlöf et al. (1978) studied Healthy (n=5). Lower body negative pressure (l.b.n.p.) vs. Control periods was evaluated on Muscle nerve sympathetic activity (number and amplitude of pulse synchronous sympathetic bursts). Lower body negative pressure consistently increased the number of sympathetic bursts in healthy subjects, an effect significantly greater than expected from blood pressure changes alone.