Effect of acute intermittent hypoxia on baroreflex sensitivity to decreasing and increasing blood pressures

Abstract

ObjectivePatients with sleep apnea exhibit impairments in reflex responses to decreasing, but not increasing, arterial blood pressures (BP). Attenuated BP control may contribute to the increased risk of developing hypertension observed in patients with sleep apnea; however the mechanisms involved are not completely understood. Therefore, we aimed to examine the differential effect of acute intermittent hypoxia (IH) on baroreflex sensitivity during decreasing compared to increasing BP. We hypothesized acute IH would attenuate baroreflex sensitivity to decreasing, but not increasing, BP.MethodsHeart rate (HR, electrocardiography), BP (brachial arterial catheter), and muscle sympathetic nerve activity (MSNA, microneurography of the peroneal nerve) were assessed in 14 healthy adults (8M/6F; 32±1 yrs, 26±1 kg/m2). Baroreflex sensitivity was evaluated during decreasing and increasing BP using the modified Oxford technique before and after 30‐min of IH [25‐s hypoxic (0.10 FiO2) exposures alternating with 120‐s room air breathing]. Data were analyzed from the depressor (nitroprusside) and pressor (phenylephrine) phases of the modified Oxford for measures of cardiovagal and sympathetic baroreflex sensitivity, as well as the T50 (diastolic BP with a 50% likelihood of an MSNA burst).ResultsIH resulted in 15 events where oxygen saturation was reduced (SpO2: 98±1% vs 92±2%, p<0.01). Resting normoxic ventilation, carotid chemosensitivity to hypoxia, and MSNA were increased following IH (all p<0.05). HR, systolic BP, diastolic BP, and the T50 were not altered following 30‐min of IH (p‐value range 0.08 to 0.90). Diastolic BP was greater than T50 at baseline (Decreasing BP: p=0.046); however, after IH, diastolic BP was no longer significantly different than the T50 (p=0.52). Cardiovagal baroreflex sensitivity to decreasing and increasing BP differed at baseline (14.0±1.7 vs 22.0±3.3 ms/mmHg, p=0.02) and following IH (11.3±1.1 vs 19.1±2.0 ms/mmHg, p<0.01). Cardiovagal baroreflex sensitivity to decreasing BP tended to be lower following IH (p=0.09). Sympathetic baroreflex sensitivity to decreasing and increasing BP did not differ at baseline (−2.1±0.3 vs −2.5±0.3 %/mmHg; p=0.28) or following IH (−2.6±0.6 vs −3.0±0.4 %/mmHg, p=0.55) and was unaffected by IH (p‐value range 0.20–0.40).ConclusionsAcute IH has a differential effect on baroreflex sensitivity. Specifically, cardiovagal baroreflex sensitivity to decreasing, but not increasing, BP tends to be lower following IH. In contrast, sympathetic baroreflex sensitivity is unaffected by IH. Prior to IH, diastolic BP is greater than the T50, thus promoting lower MSNA. Despite no change in baroreflex sensitivity after IH, diastolic BP is no longer significantly different than the T50 – consistent with higher MSNA following IH.Support or Funding InformationNIH HL130339, Mayo Clinic Center for Biomedical DiscoveryThis abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.