Time-Frequency Analysis of Cardiovascular and Cardiorespiratory Interactions During Orthostatic Stress by Extended Partial Directed Coherence.

In this study, the linear method of extended partial directed coherence (ePDC) was applied to establish the temporal dynamic behavior of cardiovascular and cardiorespiratory interactions during orthostatic stress at a 70° head-up tilt (HUT) test on young age-matched healthy subjects and patients with orthostatic intolerance (OI), both male and female. Twenty 5-min windows were used to analyze the minute-wise progression of interactions from 5 min in a supine position (baseline, BL) until 18 min of the orthostatic phase (OP) without including pre-syncopal phases. Gender differences in controls were present in cardiorespiratory interactions during OP without compromised autonomic regulation. However in patients, analysis by ePDC revealed considerable dynamic alterations within cardiovascular and cardiorespiratory interactions over the temporal course during the HUT test. Considering the young female patients with OI, the information flow from heart rate to systolic blood pressure (mechanical modulation) was already increased before the tilt-up, the information flow from systolic blood pressure to heart rate (neural baroreflex) increased during OP, while the information flow from respiration to heart rate (respiratory sinus arrhythmia) decreased during the complete HUT test. Findings revealed impaired cardiovascular interactions in patients with orthostatic intolerance and confirmed the usefulness of ePDC for causality analysis.

[Hemoglobin values for pregnant women residing at middle altitude]. / Valores de hemoglobina en mujeres embarazadas residentes en zonas de altitud media.

OBJECTIVE: To determine maternal hemoglobin behavior during pregnancy for middle altitude residents and to compare it with that reported in other populations with or without iron supplementation. MATERIALS AND METHODS: Hematological values from 227 pregnant women residing at 2 240 m altitude (Mexico City), with low obstetric and perinatal risk, and receiving supplementary iron, were compared with reference values obtained from other populations of pregnant women residing at different altitudes, after correcting for altitude. RESULTS: While the hemoglobin values for the first and second trimester of pregnancy in our studied population were similar to those reported for iron-supplemented populations (p>0.05), the third trimester values were similar to those reported for a population without this supplement (p>0.05). CONCLUSIONS: Despite receiving supplementary iron, hemoglobin values during pregnancy from women residing at middle altitude show similar behavior to that reported for pregnant women without iron supplementation.

Characterization of systolic and diastolic pressure time series in pregnant women with preeclampsia through symbolic dynamics.

Preeclampsia (PE) is one of the leading causes of maternal mortality worldwide. Although clinical strategies to prevent the early onset of PE have been proposed, the ultimate solution is to end the pregnancy. Therefore, patients' identification with major PE risk is important towards the prevention and better management of a severe manifestation of the illness. This study aims to analyze the systolic blood pressure (SBP) and diastolic blood pressure (DBP) time series through a nonlinear perspective using symbolic dynamics and to incorporate a multi-scale assessment in the first trimester of pregnancy, previous to the clinical manifestation of PE. The study group of normotensive women who developed and were diagnosed with PE included 14 pregnant women, a normotensive throughout pregnancy control group (N) consisting of 14 participants, and a group of 14 normotensive women during pregnancy without comorbidities (S) were matched with PE by age, body mass index, gestational age and comorbidities. The preliminary results of this study showed a decreased complexity of SBP, assessed by multiscale symbolic entropy in the first trimester in PE patients, in comparison with normotensive pregnant women.Clinical relevance- This work shows how nonlinear analysis of systolic and diastolic blood pressure time series are useful to detect preeclampsia in the first trimester of pregnancy.

Hemodynamic response to low-flow acute supplemental oxygen in idiopathic pulmonary fibrosis and elderly healthy subjects.

BACKGROUND: Hemodynamic response to supplemental oxygen in idiopathic pulmonary fibrosis (IPF) is still not well known. OBJECTIVE: To determine and compare the effect of low-flow acute supplemental oxygen on the hemodynamics of IPF patients and matched healthy subjects. METHODS: Descriptive and comparative study in 20 IPF-patients and 19 Control-subjects, (60-80 years old) breathing ambient air followed by acute nasal low-flow (3 L/min) supplemental oxygen. Non-invasive methods were used during the supine position to evaluate oxygen saturation, heart rate, stroke volume index, cardiac output index, total peripheral resistance and arterial blood pressure. RESULTS: Breathing ambient air, IPF (vs. Control) presented lower values in stroke volume index (38.7 [29.4-43.2] vs. 45.4 [38.4-50.9] mL•kg-1•m2; p=0.009) and cardiac output index (2.484 [2.268 - 2.946] vs. 2.857 [2.628 - 3.054] L•min-1•m-2; p=0.028), with higher total peripheral resistance (1644 [1559-2076] vs. 1505 [1366-1784] dyne•s•cm-5; p=0.017). During supplemental oxygen (vs. ambient air), both groups increased oxygen saturation above 94% (p<0.001) while heart rate decreased about 6 to 8% (p<0.001); stroke volume index increased around 7% in the Control-group (p=0.004) but only 1% in the IPF-group (p=0.017). In addition, IPF showed increments in total peripheral resistance (1644 [1559-2076] vs. 1706 [1554-2278] dyne•s•cm-5; p=0.017) with subsequent decrements in cardiac output index (2.484 [2.268 - 2.946] vs. 2.362 [2.139 - 2.664] L•min-1•m-2; p<0.001). CONCLUSION: Low-flow acute supplemental oxygen in IPF causes a meaningful decrement in cardiac output due to greater reduction in heart rate and increment in total peripheral resistance than matched healthy subjects. Knowing the hemodynamic profile of IPF patients may be helpful in determining their management with supplemental oxygen.

Temporal Analysis of Cardiovascular and Respiratory Complexity by Multiscale Entropy Based on Symbolic Dynamics.

The effect of an orthostatic stress on cardiovascular and respiratory complexity was investigated to detect impaired autonomic regulation in patients with vasovagal syncope (VVS). A total of 16 female patients and 12 age-matched healthy female subjects were enrolled in a passive 70° head-up tilt test. Also, 12 age-matched healthy male subjects were enrolled to study gender differences. Analysis was performed dynamically using various short-term (5 min) windows shifted by 1 min as well as by 20 min of orthostatic phase (OP) to evaluate local and global complexity. Complexity was determined over multiple time scales by the established method of refined composite multiscale entropy (RCMSE) and by a new proposed method of multiscale entropy based on symbolic dynamics (MSE-SD). Concerning heart rate variability (HRV) during OP, both methods revealed the highest complexity for female controls followed by lower complexity in male controls (p < 0.01) and by the lowest complexity in female patients (p < 0.01). For blood pressure variability (BPV), no gender differences in controls were shown by any method. However, MSE-SD demonstrated highly significantly increased BPV complexity in patients during OP (p < 0.01 on 4 time-scales after 7 min, p < 0.001 on 5 time-scales after 11 min) while RCMSE did not reveal considerable differences (p < 0.05 on 2 time scales after 7 min). Respiratory complexity was further increased in patients primary shown by MSE-SD. Findings indicated impaired autonomic regulation in VVS patients characterized by predominantly increased BPV complexity accompanied with decreased HRV complexity. In addition, results suggested extending the concept of complexity loss with disease.

Dynamics of the cardiovascular autonomic regulation during orthostatic challenge is more relaxed in women.

Linear dynamic analysis of cardiovascular and respiratory time series was performed in healthy subjects with respect to gender by shifted short-term segments throughout a head-up tilt (HUT) test. Beat-to-beat intervals (BBI), systolic (SYS) and diastolic (DIA) blood pressure and respiratory interval (RESP) time series were acquired in 14 men and 15 women. In time domain (TD), the descending slope of the auto-correlation function (ACF) (BBI_a31cor) was more pronounced in women than in men (p<0.05) during the HUT test and considerably steeper (p<0.01) at the end of orthostatic phase (OP). The index SYS_meanNN was slightly but significantly lower (p<0.05) in women during the complete test, while higher respiratory frequency and variability (RESP_sdNN) were found in women (p<0.05), during 10-20 min after tilt-up. In frequency domain (FD), during baseline (BL), BBI-normalized low frequency (BBI_LFN) and BBI_LF/HF were slightly but significantly lower (p<0.05), while normalized high frequency (BBI_HFN) was significantly higher in women. These differences were highly significant from the first 5 min after tilt-up (p<0.01) and highly significant (p<0.001) during 10-14 min of OP. Findings revealed that men showed instantaneously a pronounced and sustained increase in sympathetic activity to compensate orthostatism. In women, sympathetic activity was just increased slightly with delayed onset without considerably affecting sympatho-vagal balance.

Valores de hemoglobina en mujeres embarazadas residentes en zonas de altitud media / Hemoglobin values for pregnant women residing at middle altitude

Objetivo. Determinar el comportamiento de la concentración de hemoglobina materna durante el embarazo en mujeres que residen en zonas de altitud media y compararlo con el reportado para poblaciones con y sin suplemento de hierro. Material y métodos. Valores hematológicos de 227 mujeres embarazadas, residentes a 2 240 metros de altitud (Ciudad de México), sin complicaciones obstétricas ni perinatales y recibiendo suplemento de hierro, fueron comparados con valores de referencia para mujeres embarazadas de otras altitudes. Resultados. Durante el primer y segundo trimestre, los valores de hemoglobina en nuestra población fueron similares a los observados en poblaciones con y sin suplemento de hierro (p>0.05). Durante el tercer trimestre, los valores fueron similares únicamente a los de poblaciones sin suplemento de hierro (p>0.05). Conclusiones. No obstante recibir hierro suplementario, el comportamiento de la concentración de hemoglobina durante el embarazo en mujeres residentes de la altitud media es similar al reportado para poblaciones sin hierro suplementario.

Objective. To determine maternal hemoglobin behavior during pregnancy for middle altitude residents and to compare it with that reported in other populations with or without iron supplementation. Materials and methods. Hematological values from 227 pregnant women residing at 2 240 m altitude (Mexico City), with low obstetric and perinatal risk, and receiving supplementary iron, were compared with reference values obtained from other populations of pregnant women residing at different altitudes, after correcting for altitude. Results. While the hemoglobin values for the first and second trimester of pregnancy in our studied population were similar to those reported for iron-supplemented populations (p>0.05), the third trimester values were similar to those reported for a population without this supplement (p>0.05). Conclusions. Despite receiving supplementary iron, hemoglobin values during pregnancy from women residing at middle altitude show similar behavior to that reported for pregnant women without iron supplementation.

Effect of considering constant variance time-frequency autoregressive models for HRV analysis.

Time-varying autoregressive modeling may consider the driving noise variance as a constant. In this work, the properties of the autoregressive driving noise variance of heart rate variability, with different stationary physiological conditions (resting in supine and sitting; exercise) are obtained. The effect of constant variance consideration for ramp exercise and recovery (a nonstationary condition) is also evaluated by the comparison of the time-varying absolute spectral parameters obtained by parametric estimation, allowing or not the modeling of time-varying noise variance, and a non-parametric time-frequency analysis. The driving noise variance presented a direct non-linear relationship with the heart period for the stationary maneuvers (r=0.91), while for the nonstationary condition, the use of a constant driving noise resulted in bias for the estimation of heart rate variability spectral parameters. A time-varying driving noise variance should be considered.