Key Points
- To compare the effects of sympathetic nerve stimulation and blood-borne norepinephrine infusions on the dynamic elastic properties and structural mechanics of the main pulmonary artery.
- Measured dynamic pulmonary arterial pressure-diameter relationships at pressures of 5 to 45 mm Hg and heart rates of 40 to 200 beats/min in 20 anesthetized, open-chest dogs.
- Tested responses to sympathetic nerve stimulation, systemic norepinephrine infusion (0.25 µg/kg/min), topical norepinephrine, and topical elastase application.
- Conducted histological examinations of smooth muscle cell orientation and elastic fiber continuity across the outer and inner layers of the arterial media.
- Sympathetic nerve stimulation increased pulmonary arterial stiffness (pressure-diameter slope) by +35% with unchanged diameter intercepts, whereas norepinephrine infusion increased stiffness by +14% and significantly decreased diameter intercepts.
- Local wall application of norepinephrine replicated the effects of sympathetic nerve stimulation, whereas outer wall elastase application abolished stiffness increases for both nerve stimulation and norepinephrine infusions.
- Histology confirmed smooth muscle in the outer media is linked to continuous elastic fibers near nerve endings, whereas inner media smooth muscle connects intercellularly among discontinuous elastic fibers.
Structured PICO
PPopulation20 anesthetized, open-chest dogs
IInterventionSympathetic nerve stimulation and local application of norepinephrine
CComparatorInfusion of norepinephrine (0.25 µg/kg/min)
OOutcomeDynamic elastic properties (stiffness/pressure-diameter slope) of the main pulmonary arterysurrogate
Neuronally released norepinephrine stiffens the pulmonary artery via outer media smooth muscle contraction, whereas blood-borne norepinephrine predominantly stimulates inner layers.