Baroreflex unloading blunts chemoreceptor sensitivity in Postural Tachycardia Syndrome (POTS)

Abstract

POTS have increased minute ventilation (VE) and decreased end tidal carbon dioxide (ETCO2) compared to healthy subjects. Chemoreceptor sensitivity was measured in 18 POTS (14F, 4M), 10 healthy controls (6F, 4M) 16–35 years old by exposing them to eucapneic hyperoxia‐30%oxygen, eucapneic hypoxia (10%oxygen) and hypercapnia 30%oxygen+5%carbon dioxide) in supine and HUT70 position. We measured heart Rate (HR), mean arterial pressure (MAP) oxygen saturation, ETCO2, mean cerebral blood flow velocity (mCFV) and VE. Chemoreflex sensitivity was ascertained by comparing slopes determined from eucapneic hypoxia‐hyperoxia to measure peripheral chemoreflex sensitivity, and hyperoxic hypercapnia –eucapnia to measure central chemoreflex sensitivity. POTS had significantly higher resting HR, lower MAP, stroke volume (SV) and mCFV as compared to controls (p<0.05). Hypoxia and hypercapnia increased the HR, MAP, CO, mCFV and VE (p<0.05). POTS had increases in VE during supine hypoxia (POTS vs. controls, 3.6± 0.9 vs. 1.6± 0.2, p=0.003) which reversed in HUT70 (1.96± 0.3 vs. 5.4± 1.2). In both POTS and controls, hypercapnia resulted in similar increases in VE when supine but no further increases when HUT70. POTS have higher peripheral chemoreflex sensitivity than controls which attenuates during unloading of baroreflexes.