Effects of partial neuromuscular blockade on sympathetic nerve responses to static exercise in humans.
Level 3 - non-randomized controlled study
Non-randomized physiological laboratory crossover study in humans
PubMed 2752552 · doi:10.1161/01.res.65.2.468
What was done
In nine healthy conscious subjects, investigators measured arterial pressure, heart rate, and muscle sympathetic nerve activity via peroneal nerve microelectrodes in a resting leg. Measurements were taken during static handgrip (15% and 30% maximal voluntary contraction) and during attempted handgrip under partial neuromuscular blockade induced by intravenous tubocurarine chloride (0.075 mg/kg). In 11 additional subjects, heart rate responses during curare administration were evaluated following atropine or propranolol administration.
What was found
Attempted handgrip with near-maximal effort under partial neuromuscular blockade generated minimal force. Central command alone significantly increased muscle sympathetic nerve activity, arterial pressure, and heart rate (p < 0.05). The increases in muscle sympathetic nerve activity (+56 +/- 16% over control) and mean arterial pressure (+12 +/- 2 mm Hg) during attempted handgrip were significantly smaller (p < 0.05) than during actual static handgrip at 30% maximal voluntary contraction (+217 +/- 37% and +25 +/- 3 mm Hg, respectively). Heart rate increase during attempted contraction (+18 +/- 2 beats/min) was comparable to actual contraction (+16 +/- 4 beats/min). In the 11 additional subjects, the heart rate response during curare was significantly attenuated by atropine (p < 0.05) but not by propranolol.
Why it matters
This study provides direct microneurographic evidence in humans that central command alone can activate sympathetic outflow and raise blood pressure, though peripheral feedback is required to achieve the full pressor and sympathetic response.
Limits
The sample size is small (n = 9 for microneurography, n = 11 for heart rate pharmacology). Participant demographics, randomization of the exercise order, and baseline absolute values are not reported in the abstract.
Cited by
- supports Experiments by Jere Mitchell and Niels Secher using curare nerve blocks demonstrated that attempt to contract paralyzed muscle causes heart rate to rise through Central Command independent of actual muscle contraction.