Splenic constriction during isometric handgrip exercise in humans

Abstract

During the first minute of a moderate-intensity isometric handgrip (HG) exercise, there is an increase in stroke volume and cardiac output that occurs without any change in systemic vascular conductance. Although the mechanism of increased venous return is not yet known, current focus has been placed on the constriction of visceral organs. The human spleen represents a compliant organ with high perfusion that constricts during the rather severe stresses of maximal exercise, a diving reflex, or prolonged apnea. This study tested the hypothesis that spleen constriction occurs during isometric HG exercise. Eight participants performed a 1 min isometric HG test at 40% maximum voluntary contraction. Splenic length and width were measured (with ultrasound imaging) after 1 min of exercise, and volume was calculated. To investigate the reflex specificity of this response, spleen dimensions were also measured during 4 min of lower-body negative pressure (LBNP; -20 mm Hg). To test the additional impact of altered breathing and intra-abdominal pressures during the HG, measures were also taken during Valsalva's manoeuvre (VM) at 30 mm Hg. Compared with baseline, both length and width of the spleen were reduced by 0.20 to 0.55 cm (or 4.44%-6.09%; p < 0.05) during each test. This resulted in relative reductions in splenic volume of 13 +/- 1% (HG), 9% +/- 7% (LBNP) and 18% +/- 7% (VM) (p < 0.05; all mean +/- SD). It was concluded that the spleen can constrict during the first minute of isometric HG exercise.

Increased Hematocrit After Applications of Conducted Energy Weapons (Including TASER® Devices) to Sus scrofa*

“…During exhaustive exercise, however, such contraction can account for approximately 25% of any increase in Hct (33). During isometric handgrip exercise in humans, the splenic volume has been reduced as much as 18% during the first minute of exercise (34). …”

Effect of Breath Holding on Spleen Volume Measured by Magnetic Resonance Imaging

“…The volume reduction has been speculatively attributed to spleen contraction via sympathetic activation [19,22–24], and mechanical compression may be also related [22]. Previous studies of spleen response to breath-hold apnea aimed to investigate physiology in diving, and the experimental conditions simulated diving.…”

“…The Valsalva maneuver increases intrathoracic and intra-abdominal pressure, reduces venous return, and stimulates sympathetic activity [25]. An 18% reduction in spleen volume has been demonstrated using ultrasonography during a 20-s Valsalva maneuver, without comparison with ordinary breath holding [24]. In the present study, the degree of reduction in spleen volume did not differ significantly among expiration breath holding, deep-inspiration breath holding, and free breathing, indicating that the type of respiratory manipulation does not substantially affect the estimated spleen volume.…”

“…One slice was acquired for 266 ms at the end of expiration in one respiratory cycle in the present study, and the effect of movement during acquisition should be negligible. Stress-induced reduction in spleen volume has been speculated to be mediated by sympathetic stimulation [19,22–24] and may diminish in patients with impaired sympathetic nerve function. The spleen contains a large amount of blood cells and releases them on contraction.…”

Increased Blood Pressure and Hyperdynamic Cardiovascular Responses in Carriers of a Common Hyperfunctional Variant of Adenylyl Cyclase 6

“…Artery images were recorded on a S-VHS videocassette recorder (SVO-9500 MDP; Sony, Tokyo, Japan). Cardiac output was derived on a beat-bybeat basis from the transfer function of the finger pulsatile pressure wave form, as validated for these maneuvers (Shoemaker et al, 2007;Frances et al, 2008). All analog data were sampled at 1000 Hz by using a data-acquisition system (PowerLab; ADInstruments, Colorado Springs, CO).…”