Relationship of inspiratory flow rate and volume on digit tip skin and ulnar artery vasoconstrictor responses in healthy adults Einar Wilder-Smith T , Linda Liu, Khin Thein Ma Ma, Benjamin K.C. Ong Division of Neurology, National University of Singapore, 5 Lower Kent Ridge Road, 119072 Singapore Received 13 October 2004 Abstract 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 b 1.0 l/min; FIVC b 1.0 l), medium (PIF = 1.0–1.5 l/min; FIVC = 1.0–1.5 l), and high (PIF N 1.5 l/min; FIVC N 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. D 2005 Elsevier Inc. All rights reserved. Keywords: Vasomotor reflexes; Vasoconstrictor reflexes; Inspiratory rate; Respiratory effort; Small nerve fiber function; Doppler; Skin blood flow; Ulnar artery Introduction Blood flow to the hand and feet is regulated through sympathetic vasoconstrictor neurons receiving inputs from central and local modulators (Gibbins, 1997). Although the main modulator of sympathetic activity to the vasculature of the extremities is temperature, functional studies have identified separate and distinct innervation of distal arterio- venous anastomosis of the hands and feet primarily driven by bnon-thermalQ stimuli such as mental strain, sudden noises, or touch and rapid inspiration (Gibbins, 1994). Reflex vasoconstriction of the digit tip skin and hand arteries is commonly induced with the help of an inspiratory gasp (Eicke et al., 2004; Khan et al., 1991; Morris, 1997; Wilder-Smith et al., 2000). The exact pathways of this reflex arc are not well understood. There is evidence that bnon- thermalQ afferent stimuli activate structures in the brain stem, which in turn stimulate descending sympathetic preganglionic neurons (SPN) (Gilbey, 1997). The superior cervical ganglion contains the cell bodies of the SPN innervating hand vasculature (Gibbins, 1994). Reflex vaso- constriction of the skin of the digit tip and the forearm arteries is used as an indicator of the hand sympathetic function of the hands and feet (Eicke et al., 2004; Wilder- Smith et al., 2000). Although rapid inspiration is the most commonly employed trigger of the reflex, little is known about the relationship of the respiratory effort on the magnitude of the vasoconstrictor reflex. This study, inves- tigates the relationship of the inspiratory flow rate and the inspiratory volume on the magnitude of the vasoconstrictor reflex over the 4th finger digit tip skin and the ulnar artery. Materials and methods We studied 12 healthy volunteers (age range 21–65 years, mean 38.1 years, 3 males, 9 females) recruited from the staff 0026-2862/$ - see front matter D 2005 Elsevier Inc. All rights reserved. doi:10.1016/j.mvr.2005.01.003 T Corresponding author. Fax: +65 67794112. E-mail address: mdcwse@nus.edu.sg (E. Wilder-Smith). Microvascular Research 69 (2005) 95 – 100 www.elsevier.com/locate/ymvre