Dynamic cerebral autoregulation after confinement in an isolated environment for 14 days

BACKGROUND@#To develop human space exploration, it is necessary to study the effects of an isolated and confined environment, as well as a microgravity environment, on cerebral circulation. However, no studies on cerebral circulation in an isolated and confined environment have been reported. Therefore, we investigated the effects of a 14-day period of confinement in an isolated environment on dynamic cerebral autoregulation.@*METHODS@#We participated in an isolation and confinement experiment conducted by the Japan Aerospace Exploration Agency in 2016. Eight healthy males were isolated and confined in a facility for 14 days. Data were collected on the days immediately before and after confinement. Arterial blood pressure waveforms were obtained using a finger blood pressure monitor, and cerebral blood flow velocity waveforms in the middle cerebral artery were obtained using transcranial Doppler ultrasonography for 6 min during quiet rest in a supine position. Dynamic cerebral autoregulation was evaluated by transfer function analysis between spontaneous variability of beat-to-beat mean arterial blood pressure and mean cerebral blood flow velocity.@*RESULTS@#Transfer function gain in the low- and high-frequency ranges increased significantly (0.54 ± 0.07 to 0.69 ± 0.09 cm/s/mmHg and 0.80 ± 0.05 to 0.92 ± 0.09 cm/s/mmHg, respectively) after the confinement.@*CONCLUSION@#The increases observed in transfer function gain may be interpreted as indicating less suppressive capability against transmission from arterial blood pressure oscillation to cerebral blood flow velocity fluctuation. These results suggest that confinement in an isolated environment for 14 days may impair dynamic cerebral autoregulation.@*TRIAL REGISTRATION@#UMIN000020703 , Registered 2016/01/22.

The Influence of Sevoflurane Anesthesia on Various Kinds of Spontaneous Baroreflex Sensitivities / 대한마취과학회지

BACKGROUND: In contrast to classic drug injection method, various types of noninvasive spontaneous baroreflex sensitivity (SBRS) methods have been developed using the computer analysis of the spontaneous fluctuation of heart rate and arterial blood pressure for baroreflex evaluation. In this study, we evaluated the effects of sevoflurane anesthesia on SBRS by comparing various SBRS estimates and their correlations before and after sevoflurane anesthesia. METHODS: Radial arterial pressure and electrocardiography were recorded in 50 patients before and after sevoflurane anesthesia. We derived six SBRS indices from the methods including sequence, alpha-index, transfer function analysis and impulse response function. The sequence method measured an average of baroreflex sequences. The alpha-index used the average of the square roots of the ratios between the RRI and SBP spectral power. The transfer function index used RRI and SBP cross-spectral magnitude for this index. The impulse response function method employed an inverse Fourier transform. RESULTS: All SBRS and accompanying correlations were reduced after sevoflurane anesthesia. Low (44%) and high (4%) frequency transfer function gain and sequence SBRS (4%) failed to be computed out of some patients after sevoflurane anesthesia due to poor coherence and absence of a valid sequence. CONCLUSIONS: Sevoflurane anesthesia caused marked depression of SBRS and weakened their correlations. Therefore, it is necessary to understand the characteristics of each SBRS method for selecting an appropriate method during anesthesia.

Comparison of METHODS Assessing Spontaneous Baroreflex Sensitivity during Sevoflurane Anesthesia: Sequence versus Transfer Function Analysis / 대한마취과학회지

BACKGROUND: The arterial baroreflex is a key mechanism involved in blood pressure (BP) homeostasis and serves as a pressure buffer system against increase and decrease in BP. In contrast to awake patients, little has been known about correlations among METHODS assessing spontaneous baroreflex sensitivity (SBRS) during general anesthesia. The aim of present study was to compare SBRS obtained from sequence method and transfer function analysis (TFA), and examined their relationship to vagal cardiac function in patients during sevoflurane general anesthesia. METHODS: 20 patients were anesthetized with 1 MAC sevoflurane with 50% N2O and mechanically ventilated at 0.25 Hz. 5 min beat-to-beat BP and electrocardiogram were recorded to assess sequence BRS and TFA BRS from spontaneous RR interval and systolic BP fluctuation. We derived 4 proposed indices (Sequence BRS, low frequency (LF) BRS, high frequency (HF) BRS, and average BRS). RESULTS: The indices were correlated with each other significantly and the Bland-Altman method demonstrated that sequence BRS was in close agreement with each other except LF BRS. The indices were also correlated highly with HF heart rate variability representing vagal cardiac function. CONCLUSIONS: SBRS was related to vagal cardic function. Because of the correlations and agreements between these two METHODS, it may employ them except for LF BRS during sevoflurane general anesthesia.

An automatic selections method for cerebral blood flow autoregulation signals from neonates

Interpretation and quantification of cerebral blood flow autoregulation can be carreid out from step responses to arterial blood pressure changes estimated with various identification methods. However estimates usually need to be visually inspected to rejected some that are not physiologically acceptable...

The Effect of Low-dose Atropine on Baroreflex Sensitivity Assessed by Transfer Function Analysis / 대한마취과학회지

BACKGROUND: The arterial baroreflex is a key mechanism for maintaining blood pressure homeostasis. Low-dose atropine (LDA) causes bradycardia, either by acting on the sinoatrial node or due to its effect on central muscarinic receptors, which increases vagal activity. We evaluated the effect of LDA on baroreflex sensitivity (BRS) in healthy awake subjects. METHODS: We assessed changes in RR interval (RRI) and systolic blood pressure (SBP), power spectral densities of heart rate variability (HRV) and systolic blood pressure variability (SBPV), and spontaneous BRS by using transfer function analysis before and after LDA (2microgram/kg) in 17 healthy volunteers. RESULTS: LDA induced not only bradycardia but also increased of the high-frequency (HF) component of HRV, RMSSD (root mean squared successive difference interval), and pNN50 (percentage of sinus cycles differing from the preceding cycle by > 50 ms). The HF and LF components of SBPV remained unchanged. Spontaneous BRS determined by transfer function analysis increased significantly (P < 0.05), and changes in BRS were significantly associated with changes in the HF component of HRV (P < 0.05). CONCLUSIONS: LDA increased vagal cardiac function and arterial baroreflex in awake subjects. This result suggests that increased vagal cardiac function by LDA application is related to baroreflex increase.

Transfer Function Analysis of Doppler Waveforms of Lower Extremity

BACKGROUND: There are two methods to understand a periodic signal. One is describing it in the time domain, and the other is in the frequency domain. Various methods have been described for analysis of Doppler signals in terms of velocities and they need to be further characterized. Frequency domain analysis involves conventional Fourier transformation and analysis by modeling. In 1980's, Skidmore et al. applied Laplace transformation analysis to the femoral and ankle Doppler waveforms and described the waveforms in terms of damping, stiffness and distal impedance. However, few subsequent studies have been reported by other authors. Further, an appealing feature of frequency function analysis is that it can be used for modeling of the resistive and/or storage property of the circuit. PURPOSE: The purpose of study is to analyze the Doppler waveforms of lower extremity in frequency domain and compare the results with the currently known parameters of pusatility in the time domain. METHODS: This study includes 119 Doppler waveforms from 7 non-symptomatic limbs and from 18 limbs with symptoms of chronic low extremity ischemia. Each five representative beats of Doppler waveforms were curve-fitted by third-order AR (auto-regressive) model and z-transformed resulting in three representative roots in the z-plane. Maximum velocity (Max), minimum velocity (Min), maximum excursion of the waveform (Max-Min; MaxE), mean velocity (Avg), pulsatility index (PI) and resistive index (RI) were calculated and compared with the values of the roots. RESULTS: Mostly, the poles of the transfer function were two imaginary and one real poles. Severely diseased waveforms had all three poles in real axis or the imaginary poles approached toward the real axis. The average value of the three poles (Rmean) was 0.5096 ( 0.0967 S.D.) (range: 0.2193~0.7197). The real value of the first pole (R1real) was 0.8957 ( 0.067 S.D.) (range: 0.5964~0.97). The absolute value of imaginary value of the first pole (R1imag) was 0.0998 ( 0.0713 S.D.) (range: 0~0.2336). Significant correlation was observed between 1) Rmean and MaxE (r=0.769), Max (r=0.7498), Avg (r=0.3106), RI (r=0.4378), 2) R1real and MaxE (r=0.5382), Max (r=0.4732), RI (r=0.3629), and 3) R1imag and MaxE (r=0.4785), Max (r=0.3333), Min (r= 0.3703), RI (r=0.5611). CONCLUSIONS: The position of roots of third-order transfer function of Doppler waveforms seems to correlate with the known parameters of velocity. In addition to these parameters of velocity, transfer function analysis appears to be a useful tool to evaluate the Doppler waveforms. Further studies are needed in relation to clinical manifestation.