Beat:To:Beat Autonomic Cardiovascular Response to Short:Term 100%O2 Breathing: a Time:Frequency Analysis Approach

Abstract

In sixteen healthy volunteers, we assessed the effects produced by short-term 100%O2 breathing on the instantaneous time courses of R-R intervals (RR), arterial pressure (AP), arterial oxygen saturation (SaO2), respiratory volume (Res), and, estimated by a time frequency distribution, the high frequency powers of RR (HFRR) and Res (HFRes), the low frequency powers of RR (LFRR) and systolic pressure (LFSP), the LFRR/HFRR ratio, baroreflex sensitivity (BRS) by alpha index and respiratory sinus arrhythmia sensitivity (RSAS IntroductionDespite the extensive therapeutic use of supplemental oxygen in normoxemic and hypoxemic patients [1], which is not risk-free, the reported autonomiccardiovascular effects of 100%O2 breathing in healthy subjects are not consistent. On the one hand, there is consensus that hyperoxia directly causes vasoconstriction [1], vagal activity increase with heart rate (HR) reduction [2,3] and sympathetic activity decrease [2,4]; but on the other hand, contradictory effects of hyperoxia on pulmonary ventilation (PV) [5], arterial pressure (AP) [3,6] and baroreflex sensitivity (BRS) [2,3,7] have been reported. Apparently, hyperoxia produces various effects on different organs in a parallel manner, directly, and separately [1]. Moreover, the participation of either the baroreflex or the respiratory sinus arrhythmia (RSA) mechanisms in these effects remains unclear. Additionally, spectral analysis of cardiovascular variability under hyperoxemic conditions has only been performed using steady-state techniques [2,3,7,8], so the transient changes of the autonomic-cardiovascular variables in the first minutes of hyperoxemia are still unknown. To clarify these issues, by using a timefrequency spectral analysis approach, we assessed the instantaneous time course of the effects produced by short-term 100%O2 breathing on the spectral measures of heart rate variability (HRV) and systolic pressure variability, BRS, RSA sensitivity (RSAS), R-R intervals (RR), AP and respiratory variables. Methods SubjectsSixteen healthy, normotensive and sedentary subjects, 8 men and 8 women, were studied. Their mean age, height and weight were 22.3±1.7 years, 163.2±6.4 cm and 61.6±9.6 kg respectively. Their written informed consent was requested to participate. The present study was approved by the ethics committee of our university. ProtocolVolunteers visited the laboratory twice. The first time, their health status and anthropometric variables were evaluated, and in the second visit the experimental stage was carried out. It consisted of 1-min control (air breathing), 2-min maneuver during which the subjects, with occluded nose, breathed 100%O2 gas stored in a Douglas bag through a non-rebreathing valve (Hans Rudolph), followed by 1.5-min recovery breathing air.ECG, AP, arterial oxygen saturation (SaO2), expired CO2 concentration, and respiration (Res) were recorded throughout the entire study.