Cardiac baroreflex hysteresis is one of the determinants of the heart period variability asymmetry.

In heart period (HP) variability (HPV) recordings the percentage of negative HP variations tends to be greater than that of positive ones and this pattern is referred to as HPV asymmetry (HPVA). HPVA has been studied in several experimental conditions in healthy and pathological populations, but its origin is unclear. The baroreflex (BR) exhibits an asymmetric behavior as well given that it reacts more importantly to positive than negative arterial pressure (AP) variations. We tested the hypothesis that the BR asymmetry (BRA) is a HPVA determinant over spontaneous fluctuations of HP and systolic AP (SAP). We studied 100 healthy subjects (age from 21 to 70 yr, 54 men) comprising 20 subjects in each age decade. Electrocardiogram and noninvasive AP were recorded for 15 min at rest in supine position (REST) and during active standing (STAND). The HPVA was evaluated via Porta's index and Guzik's index, while the BRA was assessed as the difference, and normalized difference, between BR sensitivities computed over positive and negative SAP variations via the sequence method applied to HP and SAP variability. HPVA significantly increased during STAND and decreased progressively with age. BRA was not significantly detected both at REST and during STAND. However, we found a significant positive association between BRA and HPVA markers during STAND persisting even within the age groups. This study supports the use of HPVA indexes as descriptors of BRA and identified a challenge soliciting the BR response like STAND to maximize the association between HPVA and BRA markers.

Maximal expiratory pressure and Valsalva manoeuvre do not produce similar cardiovascular responses in healthy men.

NEW FINDINGS: What is the central question of this study? This is the first study to evaluate and describe the cardiovascular responses during maximal expiratory pressure compared with the Valsalva manoeuvre, and whether those responses are similar. What is the main finding and its importance? This study showed that the duration of the manoeuvres appears to be responsible for the different physiological mechanisms involved in the cardiovascular responses to each manoeuvre and that the intensity of expiratory effort was related to the response in maximal expiratory pressure. These results are important to identify the risks to which subjects are exposed when performing these manoeuvres. The main purpose of this study was to compare the cardiovascular responses between the Valsalva manoeuvre (VM) and maximal expiratory pressure (MEP) and to evaluate the effect of age on these responses. Twenty-eight healthy men were evaluated and divided into two groups, younger (n = 15, 25 ± 5 years) and middle aged (n = 13, 50 ± 5 years), and they performed the VM and MEP measurement. The VM consisted of an expiratory effort (40 mmHg) against a manometer for 15 s, and the MEP was performed according to American Thoracic Society guidelines. The cardiovascular responses were analysed at rest, isotime (3 s), peak, nadir and recovery, and the cardiovascular variations (Δ) were calculated as peak or isotime minus resting values. For the statistical analysis, we used two-way ANOVA (P < 0.05). We observed that MEP and the VM generate similar changes in cardiac output (P > 0.05), but MEP presents higher values for mean arterial pressure (MAPPeak , MAPIsotime , ΔMAP and ΔMAPIsotime ) than those observed in the VM (P < 0.05). The execution time of the manoeuvres (VM ∼15 s and MEP ∼5 s) appears to be largely responsible for the activation of different physiological mechanisms involved in the cardiovascular control for each manoeuvre, and the intensity of expiratory effort is related to the higher response of MAP and peripheral vascular resistance (PVRIsotime and ΔPVRIsotime ) during MEP (P < 0.05). Moreover, it appears that age affects only the heart rate and PVR responses (P < 0.05), which were higher in the young and middle-aged group, respectively. Based on these findings, we can conclude that MEP and the VM do not generate similar cardiovascular responses, except for cardiac output.

Circulatory and Ventilatory Power: Characterization in Patients with Coronary Artery Disease.

BACKGROUND: Circulatory power (CP) and ventilatory power (VP) are indices that have been used for the clinical evaluation of patients with heart failure; however, no study has evaluated these indices in patients with coronary artery disease (CAD) without heart failure. OBJECTIVE: To characterize both indices in patients with CAD compared with healthy controls. METHODS: Eighty-seven men [CAD group = 42 subjects and healthy control group (CG) = 45 subjects] aged 40-65 years were included. Cardiopulmonary exercise testing was performed on a treadmill and the following parameters were measured: 1) peak oxygen consumption (VO2), 2) peak heart rate (HR), 3) peak blood pressure (BP), 4) peak rate-pressure product (peak systolic HR x peak BP), 5) peak oxygen pulse (peak VO2/peak HR), 6) oxygen uptake efficiency (OUES), 7) carbon dioxide production efficiency (minute ventilation/carbon dioxide production slope), 8) CP (peak VO2 x peak systolic BP) and 9) VP (peak systolic BP/carbon dioxide production efficiency). RESULTS: The CAD group had significantly lower values for peak VO2 (p < 0.001), peak HR (p < 0.001), peak systolic BP (p < 0.001), peak rate-pressure product (p < 0.001), peak oxygen pulse (p = 0.008), OUES (p < 0.001), CP (p < 0.001), and VP (p < 0.001) and significantly higher values for peak diastolic BP (p = 0.004) and carbon dioxide production efficiency (p < 0.001) compared with CG. Stepwise regression analysis showed that CP was influenced by group (R2 = 0.44, p < 0.001) and VP was influenced by both group and number of vessels with stenosis after treatment (interaction effects: R2 = 0.46, p < 0.001). CONCLUSION: The indices CP and VP were lower in men with CAD than healthy controls.

Circulatory and Ventilatory Power: Characterization in Patients with Coronary Artery Disease / Potência Circulatória e Ventilatória: Caracterização em Pacientes com Doença Arterial Coronariana

Background: Circulatory power (CP) and ventilatory power (VP) are indices that have been used for the clinical evaluation of patients with heart failure; however, no study has evaluated these indices in patients with coronary artery disease (CAD) without heart failure. Objective: To characterize both indices in patients with CAD compared with healthy controls. Methods: Eighty-seven men [CAD group = 42 subjects and healthy control group (CG) = 45 subjects] aged 40–65 years were included. Cardiopulmonary exercise testing was performed on a treadmill and the following parameters were measured: 1) peak oxygen consumption (VO2), 2) peak heart rate (HR), 3) peak blood pressure (BP), 4) peak rate-pressure product (peak systolic HR x peak BP), 5) peak oxygen pulse (peak VO2/peak HR), 6) oxygen uptake efficiency (OUES), 7) carbon dioxide production efficiency (minute ventilation/carbon dioxide production slope), 8) CP (peak VO2 x peak systolic BP) and 9) VP (peak systolic BP/carbon dioxide production efficiency). Results: The CAD group had significantly lower values for peak VO2 (p < 0.001), peak HR (p < 0.001), peak systolic BP (p < 0.001), peak rate-pressure product (p < 0.001), peak oxygen pulse (p = 0.008), OUES (p < 0.001), CP (p < 0.001), and VP (p < 0.001) and significantly higher values for peak diastolic BP (p = 0.004) and carbon dioxide production efficiency (p < 0.001) compared with CG. Stepwise regression analysis showed that CP was influenced by group (R2 = 0.44, p < 0.001) and VP was influenced by both group and number of vessels with stenosis after treatment (interaction effects: R2 = 0.46, p < 0.001). Conclusion: The indices CP and VP were lower in men with CAD than healthy controls. .

Fundamento: Os índices da Potência Circulatória (PC) e Potência Ventilatória (PV) têm sido utilizados para avaliação clínica de pacientes com insuficiência cardíaca, mas nenhum estudo avaliou esses índices em pacientes com Doença Arterial Coronariana (DAC). Objetivo: Caracterizar ambos os índices em pacientes com DAC comparados a indivíduos saudáveis. Métodos: Oitenta e sete homens [grupo DAC = 42 sujeitos e, grupo controle (GC) = 45 sujeitos] com idade entre 45 e 65 anos foram incluídos. Um Teste de Exercício Cardiopulmonar (TECP) foi realizado em esteira e as seguintes variáveis foram obtidas: 1) consumo de oxigênio (VO2) pico; 2) Frequência Cardíaca (FC) pico; 3) Pressão Arterial (PA) pico; 4) duplo produto pico (PA sistólica pico x FC pico); 5) pulso de oxigênio pico (VO2 pico dividido pela FC pico); 6) eficiência ventilatória para o consumo de oxigênio (OUES); 7) eficiência ventilatória para a produção de dióxido de carbono (VE/VCO2 slope); 8) PC (VO2 pico x PA sistólica pico); e 9) PV (PA sistólica pico dividido pelo VE/VCO2 slope). Resultados: O grupo DAC apresentou valores significativamente menores das seguintes variáveis no pico do exercício: VO2 (p < 0,001), FC (p < 0,001), PA sistólica (p < 0,001), duplo produto (p < 0,001), pulso de oxigênio (p = 0,008), OUES (p < 0,001), PC (p < 0,001) e PV (p < 0,001), e valores significativamente maiores de PA diastólica (p = 0,004) e VE/VCO2 slope (p < 0,001) em relação ao GC. Uma análise de regressão pelo método stepwise mostrou que a PC foi influenciada pelo grupo (R2 = 0,44, p < 0,001) e a PV tanto pelo grupo quanto pelo número de vasos com estenose pós tratamento (efeito de interação: R2 = 0,46, p < 0,001). Conclusion: Os índices da PC e PV foram menores em homens com DAC comparados ao GC, podendo dessa forma ser utilizados na caracterização dessa população. .

Effect of age on complexity and causality of the cardiovascular control: comparison between model-based and model-free approaches.

The proposed approach evaluates complexity of the cardiovascular control and causality among cardiovascular regulatory mechanisms from spontaneous variability of heart period (HP), systolic arterial pressure (SAP) and respiration (RESP). It relies on construction of a multivariate embedding space, optimization of the embedding dimension and a procedure allowing the selection of the components most suitable to form the multivariate embedding space. Moreover, it allows the comparison between linear model-based (MB) and nonlinear model-free (MF) techniques and between MF approaches exploiting local predictability (LP) and conditional entropy (CE). The framework was applied to study age-related modifications of complexity and causality in healthy humans in supine resting (REST) and during standing (STAND). We found that: 1) MF approaches are more efficient than the MB method when nonlinear components are present, while the reverse situation holds in presence of high dimensional embedding spaces; 2) the CE method is the least powerful in detecting age-related trends; 3) the association of HP complexity on age suggests an impairment of cardiac regulation and response to STAND; 4) the relation of SAP complexity on age indicates a gradual increase of sympathetic activity and a reduced responsiveness of vasomotor control to STAND; 5) the association from SAP to HP on age during STAND reveals a progressive inefficiency of baroreflex; 6) the reduced connection from HP to SAP with age might be linked to the progressive exploitation of Frank-Starling mechanism at REST and to the progressive increase of peripheral resistances during STAND; 7) at REST the diminished association from RESP to HP with age suggests a vagal withdrawal and a gradual uncoupling between respiratory activity and heart; 8) the weakened connection from RESP to SAP with age might be related to the progressive increase of left ventricular thickness and vascular stiffness and to the gradual decrease of respiratory sinus arrhythmia.

Effect of hormone replacement therapy on cardiac autonomic modulation.

OBJECTIVE: To investigate the effects of hormone replacement therapy (HRT) on heart rate variability (HRV) in healthy postmenopausal women. METHODS: Two groups were evaluated: group 1 (G1): 20 women not undergoing HRT (60 ± 5.89 years), group 2 (G2): 20 women undergoing HRT (59 ± 5.70 years). The HRTs involved were either conjugated equine estrogen with or without medroxyprogesterone, synthetic estrogen hormone, estradiol associated with norethisterone acetate or isoflavonoids. Electrocardiogram was recorded in the supine position for 10 min. Spectral analysis included low and high frequencies in absolute (LF and HF) and normalized units (LFnu and HFnu), which are predominantly cardiac sympathetic modulation (CSM) and cardiac vagal modulation (CVM) indicators, respectively. The LF/HF ratio was also calculated. Symbolic analysis involved the following indexes: 0V % (CSM indicator), 1V % (CSM and CVM indicators), 2LV % (predominantly CVM indicator) and 2UV % (CVM indicator). Shannon and conditional entropies were also calculated. RESULTS: Spectral analysis demonstrated that HRT affected HRV. LF, LFnu and LF/HF ratio were higher (showing increased CSM), while HFnu was lower (representing decreased CVM) in G2 than in G1. Correlations between complexity indices and HFnu were significant and positive only in G1. INTERPRETATION: Women undergoing HRT presented higher CSM and lower CVM than those who were not. Moreover, the expected positive relationship between CVM and complexity of HRV was found only in control group, thus indicating that CVM in women under therapy drop below a minimal value necessary to the association to become apparent, suggesting an unfavorable cardiac autonomic modulation in spite of HRT.