Pet _CO2 inversely affects MSNA response to orthostatic stress

Abstract

Arterial hypocapnia has been associated with orthostatic intolerance. Therefore, we tested the hypothesis that hypocapnia may be detrimental to increases in muscle sympathetic nerve activity (MSNA) and total peripheral resistance (TPR) during head-up tilt (HUT). Ventilation was increased approximately 1.5 times above baseline for each of three conditions, whereas end-tidal PCO(2) (PET(CO(2))) was clamped at normocapnic (Normo), hypercapnic (Hyper; +5 mmHg relative to Normo), and hypocapnic (Hypo; -5 mmHg relative to Normo) conditions. MSNA (microneurography), heart rate, blood pressure (BP, Finapres), and cardiac output (Q, Doppler) were measured continuously during supine rest and 45 degrees HUT. The increase in heart rate when changing from supine to HUT (P < 0.001) was not different across PET(CO(2)) conditions. MSNA burst frequency increased similarly with HUT in all conditions (P < 0.05). However, total MSNA and the increase in total amplitude relative to baseline (%DeltaMSNA) increased more when changing to HUT during Hypo compared with Hyper (P < 0.05). Both BP and Q were higher during Hyper than both Normo and Hypo (main effect; P < 0.05). Therefore, the MSNA response to HUT varied inversely with levels of PET(CO(2)). The combined data suggest that augmented cardiac output with hypercapnia sustained blood pressure during HUT leading to a diminished sympathetic response.

Postural hypocapnic hyperventilation is associated with enhanced peripheral vasoconstriction in postural tachycardia syndrome with normal supine blood flow

“…This same group demonstrated a close relation between increased peroneal muscle sympathetic nerve activity and experimentally controlled PET CO 2 in another group of healthy subjects (31).…”

Lateralization of expression of neural sympathetic activity to the vessels and effects of carotid baroreceptor stimulation

“…Because of the normalization procedure, this might be reflected in all the other experimental settings of the present study, including the supine spontaneous respiration condition characterized by the right MSNA laterality. However, a previous investigation suggested that hypocapnia does not affect either rate or strength burst parameters at rest (26). Indeed, subjects either on spontaneous breathing or controlled respiration at 0.25 Hz showed similar values in MSNA burst rate and total amplitude, both during hypocapnia and normocapnia (26).…”

“…However, a previous investigation suggested that hypocapnia does not affect either rate or strength burst parameters at rest (26). Indeed, subjects either on spontaneous breathing or controlled respiration at 0.25 Hz showed similar values in MSNA burst rate and total amplitude, both during hypocapnia and normocapnia (26).…”

Hormonal and autonomic responses to autonomic stimulation are altered in young men with Down syndrome

“…HRV utilization responds to both criteria: it is a pertinent tool to better understand responses of participants with DS when they undergo stimulation tests, and it allows to identify possible cardiovascular limits to exercise or other stress. In addition, head-up tilt test is widely used in physiology to describe neurovegetative and cardiovascular reflex thanks to its simplicity, reproducibility and the availability of numerous results concerning these adaptations [39][40][41][42][43]. The crossing of the three test results allowed to get an accurate diagnosis respecting Ewing et al [44] classifications.…”