Changes In Splanchnic Blood Flow And Blood Pressure During Inspiratory Resistive Breathing

Abstract

PURPOSE: The hyperpnea during whole-body heavy exercise leads to an increase in respiratory muscle work, which is associated with cardiovascular regulations during exercise (i.e., respiratory muscle metaboreflex). In resting condition, blood flow to inactive limbs is reduced with inspiratory resistive breathing. Furthermore, increasing the work of breathing during dynamic exercise influences inactive limb blood flow. Therefore, it is conceivable that the respiratory muscle-induced metaboreflex is associated with blood flow redistribution during exercise. Redistribution of blood flow is also associated with splanchnic blood flow as well as inactive blood flow. However, influence of respiratory muscle metaboreflex on splanchnic blood flow in humans remains unknown. We hypothesized that blood flow to splanchnic organs would reduce via respiratory muscle-induced metaboreflex. METHODS: Ten healthy young men (20.2 ± 0.4 yrs, mean ± SE) performed two voluntary hyperventilation tests (tidal volume of 40% of vital capacity, a breathing frequency of 40 breaths/min and inspiratory duty cycle of 50%). One trial was voluntary hyperventilation with inspiratory resistance (about 40% of maximal inspiratory pressure), and the trial was terminated when the subject could not maintain the target ventilation (the resistance trial), and the other one was voluntary hyperventilation without inspiratory resistance until the same time as the resistance trial (the non-resistance trial). During trials, mean arterial blood pressure (MAP) was measured using finger photoplethysmography, and celiac artery blood flow was recorded by Doppler ultrasonography. RESULTS: MAP increased progressively and was higher (P < 0.05) in the resistance trial (100.5 ± 4.4 mmHg) than in the non-resistance trial (92.8 ± 2.0 mmHg) at the end of trial. Celiac artery blood flow decreased gradually from baseline value in the resistance trial (469.3 ± 47.6 mL/min), whereas did not change in the non-resistance trial (605.7 ± 56.2 mL/min). Celiac artery vascular conductance was lower in the resistance trial (4.8 ± 0.6 mL/min/mmHg) than in the non-resistance trial (6.6 ± 0.6 mL/min/mmHg, P < 0.05). CONCLUSIONS: These results suggest that increasing work of breathing affects the splanchnic circulation, via respiratory muscle-induced metaboreflex.