Non-invasive assessment of the changes in static and oscillatory components of peripheral pressure/flow relationships produced by moderate exercise in humans

Evaluating the association between cardiac and peripheral resistance arms of the baroreflex

The study proposes an extension of cardiac baroreflex (cBR) sequence analysis, traditionally performed over spontaneous fluctuations of heart period and systolic arterial pressure, to typify peripheral resistance baroreflex (prBR) from spontaneous variations of peripheral resistances and diastolic arterial pressure. The prBR baroreflex sensitivity (BRS_prBR) and percentage of prBR sequences (SEQ%_prBR) were computed along with analogous quantities assessed over cBR (i.e. BRS_cBR and SEQ%_cBR). The cBR and prBR were typified in healthy subjects at rest (REST) and during light bicycle ergometer exercise at 10 percent of the maximal effort (EXE). Both cBR and prBR were affected by EXE: indeed, BRS_cBR and SEQ%_prBR were significantly reduced. Moreover, while BRS_cBR and BRS_prBR were not significantly associated, SEQ%_cBR and SEQ%_prBR were, and the correlation coefficient was positive. This study suggests that prBR can be typified from spontaneous variabilities along with the more traditional cBR, thus enlarging the possibility of monitoring human cardiovascular control mechanisms.

On the Relevance of Computing a Local Version of Sample Entropy in Cardiovascular Control Analysis

OBJECTIVE

Traditional definition of sample entropy (SampEn), here referred to as global SampEn (GSampEn), provides a conditional entropy estimate that blurs the local statistical properties of the time series. We hypothesized that a local version of SampEn (LSampEn) might be more powerful in the presence of determinism than GSampEn.

METHODS

LSampEn was computed by calculating the probability of the current sample conditioned on each reference pattern and averaging it over all reference patterns. The improved ability of LSampEn compared to GSampEn was demonstrated by simulating deterministic periodic, deterministic chaotic, and linear stochastic dynamics corrupted by additive noise and over real cardiovascular variability series recorded from 16 healthy subjects (max-min age range: 22-58 years) during incremental bicycle ergometer exercise.

RESULTS

We found that: i) LSampEn is more robust in describing deterministic periodic or nonlinear features in the presence of additive noise than GSampEn, ii) in association with a surrogate approach, LSampEn is more powerful in detecting nonlinear dynamics than GSampEn, iii) LSampEn and GSampEn are equivalent in the presence of stochastic linear dynamics, and iv) only LSampEn can detect the decrease of complexity of heart period variability during bicycle exercise being a likely hallmark of sympathetic activation.

CONCLUSION

LSampEn preserves the GSampEn capability in characterizing the complexity of short sequences but improves its reliability in the presence of deterministic patterns featuring sharp state transitions and nonlinear dynamics.

SIGNIFICANCE

Variations of complexity can be measured with a greater statistical power over short series using LSampEn, especially when nonlinear features are present.

Peripheral Resistance Baroreflex During Incremental Bicycle Ergometer Exercise: Characterization and Correlation With Cardiac Baroreflex

The arm of the baroreflex (BR) controlling peripheral resistances (PR), labeled as BR of PR (prBR), was characterized through an extension of the cardiac BR (cBR) sequence analysis. The method exploits recordings of skin blood flow (SBF) from the palm of the non-dominant hand via a laser Doppler flowmeter and of arterial pressure (AP) from the middle finger of the same hand via a plethysmographic device. PR was estimated beat-by-beat as the ratio of mean AP to mean SBF computed over the same heart period (HP). Peripheral resistances-diastolic arterial pressure (PR-DAP) sequences featuring simultaneous increases of PR and decreases of diastolic AP (DAP) or vice versa were identified and the slope of the regression line in the (DAP, PR) plane was taken as an estimate of prBR sensitivity (BRS_prBR). The percentage of prBR sequences (SEQ%_prBR) was taken as a measure of prBR involvement and the prBR effectiveness index (EI_prBR) was computed as the fraction of DAP sequences capable to drive antiparallel PR variations. Analogous markers were computed over cBR from HP and systolic AP (SAP) variability [i.e., cBR sensitivity (BRS_cBR), percentage of cBR sequences (SEQ%_cBR)_, and effectiveness index of the cBR (EI_cBR)]. prBR and cBR were typified during incremental light-to-moderate bicycle ergometer exercise at 10, 20, and 30% of the maximum effort in 16 healthy subjects (aged from 22 to 58 years, six males). We found that: (i) BRS_cBR decreased gradually with the challenge, while BRS_prBR declined only at the heaviest workload; (ii) SEQ%_cBR decreased solely at the lightest workload, while the decline of SEQ%_prBR was significant regardless of the intensity of the challenge; (iii) EI_prBR and EI_cBR were not affected by exercise; (iv) after pooling together all the data regardless of the experimental conditions, BRS_prBR and BRS_cBR were uncorrelated, while SEQ%_cBR and SEQ%_prBR as well as EI_cBR and EI_prBR, were significantly and positively correlated; (v) when the correlation between SEQ%_cBR and SEQ%_prBR and between EI_cBR and EI_prBR was assessed separately in each experimental condition, it was not systematically detected. This study suggests that prBR characterization provides information complementary to cBR that might be fruitfully exploited to improve patients' risk stratification.

Multivariate decomposition of arterial blood pressure variability for the assessment of arterial control of circulation

In order to analyze the information carried by arterial blood pressure (ABP) variability, a multivariate parametric model of interactions involving systolic ABP (SAP), diastolic ABP (DAP), pulse pressure (PP), heart period (HP), and respiration is proposed. The model defines SAP as sum of the preceding DAP and PP values; DAP model accounts for arterial baroreflex, diastolic runoff; PP reflects changes in stroke volume related to respiration and HP, afterload; equation residuals reveal other vascular and cardiac output modulations. The model was applied to data from nine young volunteers (aged 29 +/- 6 years) during supine cycling at 10%, 20%, and 30% of their maximum effort. Significant basal values and changes across the epochs of the experiment were found in all hemodynamic parameters describing fast, beat-by-beat responses; in SAP and PP total power, DAP low- and high-frequency power (LF, HF), PP very low frequency (VLF), and LF and HF power. A primary role of vascular control through DAP and PP was emphasized by the considered feedbacks and the model residuals. The model proved to be able to assess beat-by-beat cardiovascular interactions and offer a comprehensive view of arterial tree control.

Cardiac autonomic dysregulation in patients with acute hepatitis

BACKGROUND

Autonomic dysfunction is common in patients with chronic liver disease, but it is still unclear whether acute hepatitis coincides with alterations in autonomic functions.

METHODS

We evaluated the heart rate variability (HRV) of 10 patients with acute hepatitis (6 males, 4 females; mean age, 44.0 y; range, 20-69 y). Frequency-domain analysis of short-term and stationary R-R intervals was performed on the first day of admission to detect low-frequency power (LF; 0.04-0.15 Hz), high-frequency power (HF, 0.15-0.40 Hz), the ratio of LF to HF (LF/HF), and LF in normalized units (LF%). The same measurement was repeated on the 7th day of admission.

RESULTS

We found that there was a significant increase of HF as well as variance of the R-R interval on the 7th day after admission (P < 0.05). There was a significant negative correlation between HF and the change of total bilirubin (P < 0.05).

CONCLUSIONS

The study demonstrates a change in cardiac vagal tone associated with acute hepatitis by analysis of HRV, and such alteration is less pronounced later during the clinical course of acute hepatitis.

Cardiac autonomic regulation differentiates reflux disease with and without erosive esophagitis

OBJECTIVE

Impaired autonomic function has been observed in patients with gastroesophageal reflex disease (GERD), but little is known about autonomic function in patients with non-erosive reflux disease (NERD). The objective of this study was to investigate potential differences in autonomic function by means of heart rate variability in GERD patients with and without erosive esophagitis.

MATERIAL AND METHODS

Thirty-five GERD patients and 20 healthy controls participated in the study. Seventeen subjects with NERD and 18 patients with erosive reflux disease (ERD) were identified based on typical reflux symptoms, endoscopic findings, and 24-h esophageal pH. Spectral analysis of heart rate variability was performed to calculate the low-frequency (LF) band, the high-frequency (HF) band, and the LF/HF ratio.

RESULTS

No significant differences were found in age, gender, body mass index, or current tobacco use among the reflux patients and controls. The Helicobacter pylori status and severity of reflux symptoms were similar between the two groups. The HF band power was significantly lower in patients with ERD than in NERD patients (p < 0.01) and controls (p < 0.05). LF band power (%) and LF/HF ratio were significantly lower in the NERD patients compared with ERD patients (p < 0.05) and controls (p < 0.05). There was no statistically significant correlation between any heart rate variability parameter and symptom severity score in either the ERD or NERD group.

CONCLUSIONS

Patients with ERD and NERD display a similar degree of symptom severity, but the pattern of autonomic function appears to differ between NERD and ERD.

Global versus local linear beat-to-beat analysis of the relationship between arterial pressure and pulse transit time during dynamic exercise

Global linear analysis has been traditionally performed to verify the relationship between pulse transit time (PTT) and systolic arterial pressure (SAP) at the level of their spontaneous beat-to-beat variabilities: PTT and SAP have been plotted in the plane (PTT,SAP) and a significant linear correlation has been found. However, this relationship is weak and in specific individuals cannot be found. This result prevents the utilization of the SAP-PTT relationship to derive arterial pressure changes from PTT measures on an individual basis. We propose a local linear approach to study the SAP-PTT relationship. This approach is based on the definition of short SAP-PTT sequences characterized by SAP increase (decrease) and PTT decrease (increase) and on their search in the SAP and PTT beat-to-beat series. This local approach was applied to PTT and SAP series derived from 13 healthy humans during incremental supine dynamic exercise (at 10, 20 and 30% of the nominal individual maximum effort) and compared to the global approach. While global approach failed in some subjects, local analysis allowed the extraction of the gain of the SAP-PTT relationship in all subjects both at rest and during exercise. When both local and global analyses were successful, the local SAP-PTT gain is more negative than the global one as a likely result of noise reduction.

Contrasting effects of acute and chronic cigarette smoking on skin microcirculation in young healthy subjects

OBJECTIVE

The aim of our study was to assess the effects of acute and chronic smoking on skin microvascular properties of young healthy subjects.

DESIGN

An observational study, using a totally non-invasive approach, employing continuous palmar microvascular flow (laser Doppler) and arterial pressure measurements, to compute estimates of microvascular resistive (Z0) and oscillatory (impedance, i.e. ZC) properties. Measures were obtained at baseline and after iontophoretic administration of acetylcholine (ACh), an endothelium-dependent vasodilator and of sodium nitroprusside (NP), an endothelium-independent vasodilator.

PARTICIPANTS

A total of 20 healthy male subjects (nine habitual smokers and 11 non-smokers; aged 27 +/- 1 and 29 +/- 2 years, respectively) in resting conditions and during administration of ACh and of NP (in two different days), before and after smoking one cigarette were evaluated.

RESULTS

Smokers showed significant lower baseline Z0 and ZC than non-smokers. In non-smokers, ACh and NP iontophoresis induced a significant decrease of both Z0 and ZC, before and after smoking one cigarette (P < 0.02). Conversely, in smokers, both Z0 and ZC were not affected by ACh iontophoresis before acute smoking, while, after smoking, a significant decrease of both Z0 and ZC (P < 0.02) was detected after ACh challenge. In smokers, both Z0 and ZC were not affected by NP iontophoresis, either before or after smoking a cigarette.

CONCLUSIONS

Smokers appeared characterized by a complex disruption of peripheral microcirculatory regulation, including inappropriate resting vasodilation, impaired endothelium-dependent and independent vasodilation, paradoxical recovery of endothelium-dependent vasodilation in response to acute smoking.

Hypertension, stress and erectile dysfunction: potential insights from the analysis of heart rate variability

Increased sympathetic activity and mental stress may affect erectile function. These effects may be acute and/or chronic. Cardiovascular regulation can be assessed non-invasively using a computer-based analysis of suitable haemodynamic signals. This research may provide new insights into the complex pathogenesis of erectile dysfunction (ED). In particular, there is still a largely unexplored area of research that covers the effect of drugs on these regulatory mechanisms. Such research may provide new therapeutic options.