Relationship of inspiratory flow rate and volume on digit tip skin and ulnar artery vasoconstrictor responses in healthy adults

Reflex vasoconstrictive responses are commonly used to assess sympathetic nerve function of the extremities. A regularly used reflex trigger is deep and rapid inspiration. However, little is known about the relationship between respiratory effort and the magnitude of the resultant vasoconstrictor response. This study investigates the association of inspiratory flow rate and volume to the level of vasoconstrictor reflexes in the 4th digit tip skin and the ulnar artery in 12 healthy volunteers (age range 21-65, mean 38.1 years). The effects of Peak Inspiratory Flow (PIF) and Forced Inspiratory Vital Capacity (FIVC) on blood flow were measured at three levels of respiratory effort: low (PIF < 1.0 l/min; FIVC < 1.0 l), medium (PIF = 1.0-1.5 l/min; FIVC = 1.0-1.5 l), and high (PIF > 1.5 l/min; FIVC > 1.5 l) at two separate occasions. Ulnar vasoconstrictor responses showed good correlation with all levels of respiratory effort. Skin digit tip responses showed good correlation at medium and high levels but not at low respiratory effort. Repeatability of both tests was good. Correlation of inspiratory flow rate to vasoconstriction was consistently better than with inspiratory volume. Both digit tip and ulnar vasoconstrictor responses were maximal with greatest respiratory effort.