Smoking impairs baroreflex sensitivity in humans

Repeated warm water baths decrease sympathetic activity in humans

Acute whole-body heat stress evokes sympathetic activation. However, the chronic effects of repeated moderate heat exposure (RMHE) on muscle sympathetic nerve activity (MSNA) in healthy individuals remains unclear. We performed RMHE with 4 weeks (5 days/week) warm baths (~40 °C, for 30 min) in 9 healthy older (59 ± 2 yrs) volunteers. Hemodynamic variables and MSNA were examined prior, 1 day after and 1 week following 4 weeks of RMHE in a laboratory at ~23 °C. Cold pressor test and handgrip exercise were performed during the tests. Under normothermic condition, the resting MSNA burst rate (prior, post, post 1-wk: 31.6 ± 2.0, 25.2 ± 2.0, 27.7 ± 1.7 bursts/min; P < 0.001) and burst incidence (P < 0.001) significantly decreased after RMHE. Moreover, the resting heart rate significantly decreased after RMHE (62.3 ± 1.6, 59.5 ± 2.0, 58.2 ± 1.6 beats/min, P = 0.031). The low frequency to high frequency ratio of heart rate variability, an index of sympathovagal balance, also decreased after RMHE. The sensitivity of baroreflex control of MSNA and heart rate were not altered by RMHE, although the operating points were reset. The MSNA and hemodynamic responses (i.e. changes) to handgrip exercise or cold pressor test were not significantly altered. These data suggest that the RMHE evoked by warm baths decreases resting sympathetic activity and HR, which can be considered beneficial effects. The mechanism(s) should be examined in future studies.

Balloon Dilation Strategy Does Not Affect Outcomes for Transcarotid Artery Revascularization (TCAR) in Prospective Trials

OBJECTIVES

Strategies of balloon dilation during trans-femoral carotid artery stenting (TFCAS) include pre-stent dilation only (PRE), post-stent dilation only (POST), or both pre- and post- dilation (PRE+POST). Concerns over higher neurological risk have been raised with POST and PRE+POST during TFCAS. Whether these concerns are applicable to Transcarotid Artery Revascularization (TCAR) which utilizes proximal clamping and cerebral blood flow reversal during stent deployment and balloon angioplasty remains unknown. Our aim is to analyze outcomes of PRE, POST or PRE+POST balloon dilation strategies during TCAR.

METHODS

We analyzed the prospectively collected data from the ROADSTER1 (pivotal), ROADSTER2 (FDA indicated post-market), and Roadster Extended Access TCAR trials. All trial patients had high risk anatomic or clinical factors for carotid endarterectomy and were included unless they did not undergo stent deployment nor balloon dilation. For trial inclusion, asymptomatic patients had >80% carotid stenosis, and symptomatic patients had >50% stenosis. Primary outcome measures were stroke, death, and myocardial infarction (MI) at 30 days. Data were statistically analyzed with chi-square, ANOVA, and multivariable analysis as appropriate.

RESULTS

There were 851 patients (566 male) who underwent dilation by PRE (N=216), POST (N=249), or PRE+POST (N=386). Patients had carotid stenosis >70% (N=828, 97%), and 207 (24%) were symptomatic. Flow reversal times were longer in the PRE+POST group (PRE 10.2mins, POST 9.8mins, PRE+ POST 13.3mins, P<.001). The 30-day stroke rate for the whole cohort was 1.9%, mortality was 0.5%, and MI rate was 0.94%. Stroke rates for the PRE cohort (1.9%), POST cohort (2.0%), and PRE+POST cohort (1.8%, P=.98) were similar. Also, death rates at 30 days, and composite stroke/death/myocardial infarction rates were similar in the three cohorts. No significant differences in adverse outcomes were noted among the various dilation strategies for both symptomatic and asymptomatic patients.

CONCLUSION

Based on these prospective trial data, there is no difference in neurological complications due to balloon dilation strategy during TCAR. Balloon dilation technique best suited to the patient's specific lesion morphology should be utilized. Further studies are needed to evaluate the relationship of these dilation strategies to long term outcomes including stent patency, restenosis and reintervention.

Tobacco Use and Risk Factors for Hypertensive Individuals in Kenya

This study aimed to examine the association between hypertension and tobacco use as well as other known hypertensive risk factors (BMI, waist–hip ratio, alcohol consumption, physical activity, and socio-economic factors among adults) in Kenya. The study utilized the 2015 Kenya STEPs survey (adults aged 18–69) and investigated the association between tobacco use and hypertension. Descriptive statistics, correlation, frequencies, and regression (linear and logistic) analyses were used to execute the statistical analysis. The study results indicate a high prevalence of hypertension in association with certain risk factors—body mass index (BMI), alcohol, waist–hip ratio (WHR), and tobacco use—that were higher in males than females among the hypertensive group. Moreover, the findings noted an exceptionally low awareness level of hypertension in the general population. BMI, age, WHR, and alcohol use were prevalent risks of all three outcomes: hypertension, systolic blood pressure, and diastolic blood pressure. Healthcare authorities and policymakers can employ these findings to lower the burden of hypertension by developing health promotion and intervention policies.

Cigarette smoke exposure causes systemic and autonomic cardiocirculatory changes in rats depending on the daily exposure dose

AIMS

To evaluate the systemic changes and autonomic cardiocirculatory control of awaken rats chronically exposed to the cigarette smoke (CS) of 1 or 2 cigarettes/day.

MAIN METHODS

Rats were exposed to clean air (control) or cigarette smoke of 1 (CS1) or 2 (CS2) cigarettes/animal/day for 30 days. Then, arterial pressure (AP) and heart rate (HR) were recorded in conscious rats to assess spontaneous baroreflex sensitivity and HR and AP variabilities. Evoked baroreflex and cardiac autonomic tone were evaluated by vasoactive drugs and autonomic blockers, respectively. In another group, ventilatory and cardiovascular parameters were recorded under hypoxia and hypercapnia stimulus. At the end of protocols, heart, lung, kidneys and liver were collected for histological analysis.

KEY FINDINGS

Rats exposed to CS showed morphological changes, being more evident in the CS2 group. Also, less weight gain and cardiac hypertrophy were prominent in CS2 rats. Basal AP and HR, spontaneous baroreflex sensitivity and cardiovascular variabilities were similar among groups. CS exposure progressively blunted the bradycardia response to phenylephrine (-2.2 ± 0.1 vs. -1.7 ± 0.2 vs. -1.5 ± 0.2) while the tachycardia response to sodium nitroprusside was slightly increased compared to control. Vagal tone was not affected by CS, but CS2 rats exhibited higher sympathetic tone (-25 ± 4 vs. -28 ± 4 vs. -56 ± 9) and lower intrinsic HR (411 ± 4 vs. 420 ± 8 vs. 390 ± 6). Exposure to CS of 2 cigarettes also exacerbated the reflex cardiovascular and ventilatory responses to hypoxia and hypercapnia.

SIGNIFICANCE

CS exposure for 30 days promoted systemic changes and autonomic cardiocirculatory dysfunction in rats depending on the daily exposure dose.

Poststent ballooning during transcarotid artery revascularization

BACKGROUND

Poststent ballooning/angioplasty (post-SB) have been shown to increase the risk of stroke risk after transfemoral carotid artery stenting. With the advancement of transcarotid artery revascularization (TCAR) with dynamic cerebral blood flow reversal, we aimed to study the impact of post-SB during TCAR.

METHODS

Patients undergoing TCAR in the Vascular Quality Initiative between September 2016 and May 2019 were included and were divided into three groups: those who received prestent deployment angioplasty only (pre-SB, reference group), those who received poststent deployment ballooning only (post-SB), and those who received both prestent and poststent deployment ballooning (prepost-SB). Patients who did not receive any angioplasty during their procedure (n = 367 [6.7%]) were excluded because these represent a different group of patients with less complex lesions than those requiring angioplasty. Primary outcome was in-hospital stroke or death. Analysis was performed using univariable and multivariable logistic regression models.

RESULTS

Of 5161 patients undergoing TCAR, 34.7% had pre-SB only, 25% had post-SB only, and 40.3% had both (prepost-SB). No differences in the rates of in-hospital and 30-day stroke, death, and stroke/death were observed among the three groups; in-hospital stroke/death in the pre-SB group was 1.4% (n = 25), post-SB 1.2% (n = 16), and prepost-SB 1.4% (n = 29; P = .92). However, patients undergoing post-SB and prepost-SB had higher rates of in-hospital transient ischemic attacks (TIA) (post-SB, 0.9%; prepost-SB, 1% vs pre-SB, 0.2%, P < .01) and postprocedural hypotension (16.6% and 16.8% vs 13.1%, respectively; P < .001). Post-SB also had longer operative times, as well as flow reversal and fluoroscopy times. On multivariable analysis, no association was seen between post-SB and the primary outcome of in-hospital stroke/death (post-SB odds ratio [OR], 0.88; 95% confidence interval [CI], 0.44-1.73; prepost-SB OR, 0.98; 95% CI, 0.57-1.70). Similarly, no significant differences were noted in terms of postprocedural hemodynamic instability and 30-day outcomes. However, post-SB and prepost-SB were associated with four times the odds of in-hospital TIA compared with pre-SB alone (post-SB OR, 4.24 [95% CI, 1.51-11.8]; prepost-SB OR, 4.76 [95% CI, 1.53-14.79]; P = .01). Symptomatic patients had higher rates of in-hospital stroke/death compared with their asymptomatic counterparts; however, there was no significant interaction between symptomatic status and ballooning in predicting the primary outcome.

CONCLUSIONS

Post-SB was used in 65.3% of TCAR patients. This maneuver seems to be safe without an increase in the odds of postoperative in-hospital stroke/death. However, the increased rates of TIA associated with post-SB requires further investigation.

Acute effects of electronic cigarettes on arterial pressure and peripheral sympathetic activity in young nonsmokers

Electronic cigarettes (e-cigarettes) are marketed as an alternative to smoking for those who want to decrease the health risks of tobacco. Tobacco cigarettes increase heart rate (HR) and arterial pressure, while reducing muscle sympathetic nerve activity (MSNA) through sympathetic baroreflex inhibition. The acute effects of e-cigarettes on arterial pressure and MSNA have not been reported: our purpose was to clarify this issue. Using a randomized crossover design, participants inhaled on a JUUL e-cigarette containing nicotine (59 mg/mL) and a similar placebo e-cigarette (0 mg/mL). Experiments were separated by ∼1 mo. We recorded baseline ECG, finger arterial pressure (n = 15), and MSNA (n = 10). Subjects rested for 10 min (BASE) and then inhaled once every 30 s on an e-cigarette that contained nicotine or placebo (VAPE) for 10 min followed by a 10-min recovery (REC). Data were expressed as Δ means ± SE from BASE. Heart rate increased in the nicotine condition during VAPE and returned to BASE values in REC (5.0 ± 1.3 beats/min nicotine vs. 0.1 ± 0.8 beats/min placebo, during VAPE; P < 0.01). Mean arterial pressure increased in the nicotine condition during VAPE and remained elevated during REC (6.5 ± 1.6 mmHg nicotine vs. 2.6 ± 1 mmHg placebo, during VAPE and 4.6.0 ± 1.7 mmHg nicotine vs. 1.4 ± 1.4 mmHg placebo, during REC; P < 0.05). MSNA decreased from BASE to VAPE and did not restore during REC (-7.1 ± 1.6 bursts/min nicotine vs. 2.6 ± 2 bursts/min placebo, during VAPE and -5.8 ± 1.7 bursts/min nicotine vs. 0.5 ± 1.4 bursts/min placebo, during REC; P < 0.05). Our results show that acute e-cigarette usage increases mean arterial pressure leading to a baroreflex-mediated inhibition of MSNA.NEW & NOTEWORTHY The JUUL e-cigarette is the most popular e-cigarette in the market. In the present study, inhaling on a JUUL e-cigarette increased mean arterial pressure and heart rate, and decreased muscle sympathetic nerve activity (MSNA). In contrast, inhaling on a placebo e-cigarette without nicotine elicited no sympathomimetic effects. Although previous tobacco cigarette studies have demonstrated increased mean arterial pressure and MSNA inhibition, ours is the first study to report similar responses while inhaling on an e-cigarette. Listen to this article's corresponding podcast at @ https://ajpheart.podbean.com/e/aerosolized-nicotine-and-cardiovascular-control/.

ACTH Infusion Impairs Baroreflex Sensitivity-Implications for Cardiovascular Hypoglycemia-Associated Autonomic Failure

CONTEXT

Hypoglycemia attenuates cardiovascular homeostatic autonomic control. This attenuation, known as the cardiovascular component of hypoglycemia-associated autonomic failure (HAAF), is characterized most notably by decreased baroreflex sensitivity (BRS) that begins during hypoglycemia and persists until at least the next day, despite return to euglycemia. Understanding the mechanisms underlying this reduction in BRS is important because BRS attenuation is associated with increased morbidity and mortality.

OBJECTIVE

The objective of this work is to investigate the role of the adrenocorticotropin (ACTH)-adrenal axis in decreasing BRS. We tested the hypothesis that infusion of ACTH 1-24 (cosyntropin), as compared to placebo, would acutely suppress BRS, and that this decrease in BRS would be present the next day.

DESIGN

A double-blind, placebo-controlled, random-order, cross-over study was conducted.

SETTING

This study took place in a clinical research center.

PARTICIPANTS

Participants included healthy men and women.

INTERVENTIONS

Interventions included an intravenous infusion of cosyntropin (70 μg/hour for 2.5 hours in the morning and again in the early afternoon) vs normal saline placebo.

MAIN OUTCOME MEASURES

Outcome measures included BRS during and 16 hours after cosyntropin vs placebo infusions.

RESULTS

Cosyntropin infusion attenuated BRS (mm Hg/ms) as compared to placebo (baseline 17.8 ± 1.38 vs 17.0 ± 2.07; during 14.4 ± 1.43 vs 17.3 ± 1.65; and next day 14.8 ± 1.42 vs 18.9 ± 2.04; P < .05, time by treatment, analysis of variance). BRS was decreased during the final 30 minutes of the morning cosyntropin infusion as compared to baseline (P < .01) and remained suppressed the next day (16 hours after afternoon infusion) (P < .025). Placebo infusion did not significantly change BRS. Corrected QT interval was not affected.

CONCLUSIONS

ACTH attenuates BRS, raising the possibility that hypoglycemia-induced increases in ACTH may contribute to the cardiovascular component of HAAF.

Central autonomic network functional connectivity: correlation with baroreflex function and cardiovascular variability in older adults

Baroreflex regulates short-term cardiovascular variability via the autonomic neural system. The contributions of the central autonomic system to the baroreflex regulations of arterial blood pressure (BP) and heart rate have been reported in young healthy adults, but not in older adults. Therefore, we investigated the association between the high-level central autonomic network (CAN) connectivity and baroreflex sensitivity (BRS) under a resting condition in a healthy older population. Twenty-two older adults (68 ± 8 years old) underwent BRS assessment using the modified Oxford and transfer function methods. Resting-state brain functional MRI was performed to assess the CAN functional connectivity at rest. We found that the functional connectivity (FC) between the left amygdala and left medial frontal gyrus (MeFG), bilateral postcentral gyri and bilateral paracentral lobules (PCL) is associated with BRS and R-R interval (RRI) variability in the low-frequency (LF) range. Compared to the left amygdala, the FC map of the right amygdala only showed significant associations with BRS in the anterior cingulate cortex (ACC) and with RRI variability in the left occipital region. In addition, post hoc analysis of the functionally defined left insula sub-region confirmed the association between CAN and BRS. Overall, our study demonstrates that CAN and its related brain regions may be involved, likely in a left-lateral manner, in peripheral cardiac autonomic regulation at rest. The results highlight the potential importance of brain neural network function in maintaining cardiovascular homeostasis in older adults.

Habitual cigarette smoking raises pressor responses to spontaneous bursts of muscle sympathetic nerve activity

Smoking is a risk factor for cardiovascular diseases. Prior reports showed a transient increase in blood pressure (BP) following a spontaneous burst of muscle sympathetic nerve activity (MSNA). We hypothesized that this pressor response would be accentuated in smokers. Using signal-averaging techniques, we examined the BP (Finometer) response to MSNA in 18 otherwise healthy smokers and 42 healthy nonsmokers during resting conditions. The sensitivities of baroreflex control of MSNA and heart rate were also assessed. The mean resting MSNA, heart rate, and mean arterial pressure (MAP) were higher in smokers than nonsmokers. The MAP increase following a burst of MSNA was significantly greater in smokers than nonsmokers (Δ3.4 ± 0.3 vs. Δ1.6 ± 0.1 mmHg, P < 0.001). The baroreflex sensitivity (BRS) of burst incidence, burst area, or total activity was not different between the two groups. However, cardiac BRS was lower in smokers than nonsmokers (14.6 ± 1.7 vs. 24.6 ± 1.5 ms/mmHg, P < 0.001). Moreover, the MAP increase following a burst was negatively correlated with the cardiac BRS. These observations suggest that habitual smoking in otherwise healthy individuals raises the MAP increase following spontaneous MSNA and that the attenuated cardiac BRS in the smokers was a contributing factor. We speculate that the accentuated pressor increase in response to spontaneous MSNA may contribute to the elevated resting BP in the smokers.

Long-term caregiving is associated with impaired cardiovagal baroreflex

OBJECTIVE

Caregiving stress is associated with increased risk of cardiovascular disease (CVD). Inability to adequately regulate blood pressure is a possible underlying mechanism explaining this risk. We examined the relationship between length of caregiving and cardiovagal baroreflex sensitivity (cBRS) to better understand the link between caregiving and CVD risk.

METHODS

A total of 146 elderly individuals (≥55years) participated in this study, of whom 96 were providing in-home care to a spouse with dementia and 50 were healthy controls married to a non-demented spouse (i.e., non-caregivers). Among the caregivers, 56 were short-term caregivers (caring<4years) and 40 were long-term caregivers (caring≥4years). A multiple linear regression model, with contrast codes comparing short and long-term caregivers with non-caregivers was used to understand relationships between chronic caregiving and cBRS.

RESULTS

After controlling for relevant demographic and health characteristics, mean±SE log transformed cBRS for non-caregivers was 0.971±0.029. Relative to non-caregivers, the long-term caregivers had significantly impaired cBRS (0.860±0.033; p=0.013). However, mean cBRS for short-term caregivers did not significant differ from non-caregivers (0.911±0.028; p=0.144).

CONCLUSION

These results suggest that long-term caregiving stress is associated with an impaired cBRS. Accumulation of stress from years of caregiving could result in worse cBRS function, which could be a mechanistic explanation for the correlation between caregiving stress and the increased risk of CVD.

Dynamics of the RR-interval versus blood pressure relationship at exercise onset in humans

PURPOSE

The dynamics of the postulated phenomenon of exercise baroreflex resetting is poorly understood, but can be investigated using closed-loop procedures. To shed light on some mechanisms and temporal relationships participating in the resetting process, we studied the time course of the relationship between the R-R interval (RRi) and arterial pressure with a closed-loop approach.

METHODS

On ten young volunteers at rest and during light exercise in supine and upright position, we continuously determined, on single-beat basis, RRi (electrocardiography), and arterial pressure (non-invasive finger pressure cuff). From pulse pressure profiles, we determined cardiac output (CO) by Modelflow, computed mean arterial pressure (MAP), and calculated total peripheral resistance (TPR).

RESULTS

At exercise start, RRi was lower than in quiet rest. As exercise started, MAP fell to a minimum (MAP_m) of 72.8 ± 9.6 mmHg upright and 73.9 ± 6.2 supine, while RRi dropped. The initial RRi versus MAP relationship was linear, with flatter slope than resting baroreflex sensitivity, in both postures. TPR fell and CO increased. After MAP_m, RRi and MAP varied in opposite direction toward exercise steady state, with further CO increase.

CONCLUSION

These results suggest that, initially, the MAP fall was corrected by a RRi reduction along a baroreflex curve, with lower sensitivity than at rest, but eventually in the same pressure range as at rest. After attainment of MAP_m, a second phase started, where the postulated baroreflex resetting might have occurred. In conclusion, the change in baroreflex sensitivity and the resetting process are distinct phenomena, under different control systems.

Sympathetic activity and early mobilization in patients in intensive and intermediate care with severe brain injuries: a preliminary prospective randomized study

Background

Patients who experience severe brain injuries are at risk of secondary brain damage, because of delayed vasospasm and edema. Traditionally, many of these patients are kept on prolonged bed rest in order to maintain adequate cerebral blood flow, especially in the case of subarachnoid hemorrhage. On the other hand, prolonged bed rest carries important morbidity. There may be a clinical benefit in early mobilization and our hypothesis is that early gradual mobilization is safe in these patients. The aim of this study was to observe and quantify the changes in sympathetic activity, mainly related to stress, and blood pressure in gradual postural changes by the verticalization robot (Erigo®) and after training by a lower body ergometer (MOTOmed-letto®), after prolonged bed rest of minimum 7 days.

Methods

Thirty patients with severe neurological injuries were randomized into 3 groups with different protocols of mobilization: Standard, MOTOmed-letto® or Erigo® protocol. We measured plasma catecholamines, metanephrines and blood pressure before, during and after mobilization.

Results

Blood pressure does not show any significant difference between the 3 groups. The analysis of the catecholamines suggests a significant increase in catecholamine production during Standard mobilization with physiotherapists and with MOTOmed-letto® and no changes with Erigo®.

Conclusions

This preliminary prospective randomized study shows that the mobilization of patients with severe brain injuries by means of Erigo® does not increase the production of catecholamines. It means that Erigo® is a well-tolerated method of mobilization and can be considered a safe system of early mobilization of these patients. Further studies are required to validate our conclusions.

Trial registration

The study was registered in the ISRCTN registry with the trial registration number ISRCTN56402432. Date of registration: 08.03.2016. Retrospectively registered.

Young smoker "ABCD" vascular assessment: a four-step ultrasound examination for detecting peripheral, extra and intra-cranial early arterial damage

Background

Cigarette smoking is known as a major risk factor in the pathogenic mechanisms of stroke, coronary and peripheral artery disease (CAD and PAD), even in young subjects. The aim of this study is the creation of a four-step ultrasound examination to evaluate and monitor the peripheral, the extra and the intra-cranial assessment of the arterial early damage in smokers. The evaluations of A, the Ankle-brachial index, ABI, B, the Breath holding index, BHI, C, the Carotid intima media thickness, CIMT, and D, the Diameter of the abdominal aorta represent the “ABCD” assessment.

Methods

Thirty-eight healthy smokers and 43 controls underwent A, calculated for each leg. B was calculated after determination of subjects’ flow velocity of middle cerebral artery (MCA) by trans-cranial colour Doppler (TCCD) before and after 30 s of apnoea at baseline and just after smoking a cigarette, to simulate the chronic and acute effects of smoking. Finally, C and D evaluation were assessed using a high-resolution B-mode ultrasound.

Results

Smokers presented higher values of CIMT (mean and maximal), and lower BHI both at baseline and just after smoking (p < 0.01), though in the normal range. No significant differences were found for A and D between smokers and non- smokers.

Conclusions

Our results underline the importance of the assessment of B and C, that, though in the normal range, present significant differences between smokers and non-smokers. These data could drive the screening between smokers in age-related manner. Moreover, the “ABCD” examination could represent a valid method to detect and then monitor smokers’ vascular damage. Although it is far to be considered a screening and routine tool, it should be contemplated in a wider context of possible not-invasive practical screening and follow-up modalities. This would be designed to implement preventive strategies and tools aimed at discouraging tobacco addiction and monitoring cardiovascular risk patients.

Arterial Compliance and Autonomic Functions in Adult Male Smokers

INTRODUCTION

Smoking is known to augment sympathetic activity and may lead to increased arterial stiffness. Several studies have reported association of increased sympathetic activity and arterial stiffness to cardiovascular risks among smokers. Pulse Wave Velocity (PWV) of peripheral arteries, instead of aorta can be used as a non-invasive indicator of arterial stiffness.

AIM

To measure non-invasively, the autonomic functions and peripheral arterial stiffness in smokers, and to find out whether the aforementioned factors are modified by the level of physical activity in these smokers.

MATERIALS AND METHODS

This cross-sectional analytical study was conducted in the Department of Physiology, HIMS, Dehradun, over a period of 12 months (2013-2014) on 100 adult males (20-40 years); 50 smokers and 50 non-smokers. The parameters analysed include relevant anthropometric and cardiovascular parameters, Pulse Wave Velocity (PWV), sustained Hand Grip Test (HGT) and Heart Rate Variability (HRV) domains. Data interpretation and analysis was carried out using SPSS 17.0. Comparison of the above mentioned parameters amongst groups was done with unpaired t-test. The relationship of pack-years & physical activity with vascular functions was assessed by Pearson's correlation. Interaction of various grades of smoking and physical activity with Cardiovascular System (CVS) parameters was assessed by one-way ANOVA.

RESULTS

Smokers had higher values of PWV (5.7±0.5m/s) as compared to non-smokers (4.8±0.4m/s) (p<0.001). ΔDBP during HGT was lower (7±3.18mmHg) among smokers as compared to non-smokers (19.4±3.5mmHg) (p<0.001). Smoking (pack-years) was positively related to PWV (r= .03) but showed a weak negative relationship with change in Diastolic Blood Pressure (ΔDBP) (r= -0.084, p=0.56) showing that, more the frequency of smoking, the more was arterial stiffening and the lesser was the sympathetic response to the HGT. The smokers had significantly higher sympathetic activity; Low Frequency (LF) & Low Frequency: High Frequency ratio (LF: HF) (p<.001) whereas High Frequency (HF) was significantly lower (p<.001) showing a decline in parasympathetic activity.

CONCLUSION

Smokers demonstrated higher peripheral PWV and higher intrinsic sympathetic activity and this increase in intrinsic sympathetic activity may lead to increased arterial stiffness. Interaction of autonomic function and PWV with levels of physical activity and grades of smoking showed no significant differences, suggesting the fact that increased physical activity or reduced smoking may not have any effect on the endothelial dysfunction or CVS morbidity caused by smoking.

Impairment of nitric oxide synthase but not heme oxygenase accounts for baroreflex dysfunction caused by chronic nicotine in female rats

We recently reported that chronic nicotine impairs reflex chronotropic activity in female rats. Here, we sought evidence to implicate nitric oxide synthase (NOS) and/or heme oxygenase (HO) in the nicotine-baroreflex interaction. Baroreflex curves relating changes in heart rate to increases (phenylephrine) or decreases (sodium nitroprusside) in blood pressure were generated in conscious female rats treated with nicotine or saline in absence and presence of pharmacological modulators of NOS or HO activity. Compared with saline-treated rats, nicotine (2 mg/kg/day i.p., for 14 days) significantly reduced the slopes of baroreflex curves, a measure of baroreflex sensitivity (BRS). Findings that favor the involvement of NOS inhibition in the nicotine effect were (i) NOS inhibition (Nω-Nitro-L-arginine methyl ester, L-NAME) reduced BRS in control rats but failed to do so in nicotine-treated rats, (ii) L-arginine, NO donor, reversed the BRS inhibitory effect of nicotine. Alternatively, HO inhibition (zinc protoporphyrin IX, ZnPP) had no effect on BRS in nicotine- or control rats and failed to reverse the beneficial effect of L-arginine on nicotine-BRS interaction. Similar to female rats, BRS was reduced by L-NAME, but not ZnPP, in male rats and the L-NAME effect was not accentuated after concomitant administration of nicotine. Baroreflex dysfunction caused by nicotine in female rats was blunted after supplementation with hemin (HO inducer) but not tricarbonyldichlororuthenium(II) dimer (CORM-2), a carbon monoxide (CO) releasing molecule, or bilirubin, the breakdown product of heme catabolism. The facilitatory effect of hemin was abolished upon simultaneous treatment with L-NAME or 1H-[1], [2], [4] oxadiazolo[4,3-a] quinoxalin-1-one (inhibitor of soluble guanylate cyclase, sGC). The activities of HO and NOS in brainstem tissues were also significantly increased by hemin. Thus, the inhibition of NOS, but not HO, accounts for the baroreflex depressant of chronic nicotine. Further, hemin alleviates the nicotine effect through a mechanism that is NOS/sGC but not CO or bilirubin-dependent.

Abnormal sympathetic nerve activity in women exposed to cigarette smoke: a potential mechanism to explain increased cardiac risk

In women, cardiac deaths attributable to tobacco exposure have reached the same high levels as men. Normally, sympathetic nerve activity (SNA) fluctuates according to the menstrual phase, but in habitual smokers, SNA levels remain constant. Our purpose is to extend these observations to other groups of women exposed to tobacco smoke and to explore potential mechanisms. We hypothesize that women exposed to secondhand smoke, but not former smokers, have nonfluctuating SNA compared with never smokers, and that impaired baroreflex suppression of SNA, and/or heightened central SNA responses, underlie this nonfluctuating SNA. We also hypothesize that female smokers have impaired nocturnal blood pressure dipping, normally mediated by modulation of SNA. In 49 females (19 never, 12 current, 9 former, 9 passive smokers), SNA was recorded (microneurography) during high- and low-hormone ovarian phases at rest, during pharmacological baroreflex testing, and during the cold pressor test (CPT). Twenty-four hour blood pressure (BP) monitoring was performed. Current and passive smokers, but not former smokers, had a nonfluctuating pattern of SNA, unlike never smokers in whom SNA varied with the menstrual phase. Baroreflex control of SNA was significantly blunted in current smokers, independent of menstrual phase. In passive smokers, SNA response to CPT was markedly increased. Nondipping was unexpectedly high in all groups. SNA does not vary during the menstrual cycle in active and passive smokers, unlike never and former smokers. Baroreflex control of SNA is blunted in current smokers, whereas SNA response to CPT is heightened in passive smokers. Smoking cessation is associated with return of the altered SNA pattern to normal.

The influence of tobacco smoking on the relationship between pressure and flow in the middle cerebral artery in humans

Background

Cigarette smoking is associated with an increased risk of stroke but the mechanism is unclear. The study examined whether acute and chronic cigarette smoking alters the dynamic relationship between blood pressure and cerebral blood flow. We hypothesised that acute and chronic smoking would result in a cerebral circulation that was less capable of buffering against dynamic fluctuations in blood pressure. Further, these changes would be accompanied by a reduction in baroreflex sensitivity, which is reduced after smoking (acute smoking).

Methods

We recruited 17 non-smokers and 15 habitual smokers (13 ± 5 pack years). Continuous measurements of mean cerebral blood flow velocity (transcranial Doppler ultrasound), blood pressure (finger photoplethysmography) and heart rate enabled transfer function analysis of the dynamic relationship between pressure and flow (gain, normalised gain, phase and coherence) and baroreflex sensitivity during supine rest before and after smoking a single cigarette (acute smoking).

Results

There were no between-group differences in gain, phase or coherence before acute smoking. However, both groups showed a reduction in gain and coherence, associated with a reduction in baroreflex sensitivity, and increase in phase after acute smoking.

Conclusions

Contrary to our hypothesis, these findings suggest that in the face of a reduction in baroreflex sensitivity acute smoking may potentially improve the ability of the cerebral circulation to buffer against changes in blood pressure. However, chronic smoking did not alter the dynamic relationship between blood pressure and cerebral blood flow velocity. These results have implications on understanding mechanisms for attenuating stroke risk.

The effect of smoking on the cardiovascular autonomic functions: a cross sectional study

INTRODUCTION

Smoking is a worldwide major cause of preventable morbidity and mortality. Smoking affects the cardiovascular system by several mechanisms. The present study was planned to study the effect of smoking on the cardiovascular autonomic functions among smokers.

MATERIAL AND METHODS

Hundred male subjects who were in the age group of 25 to 40 years, who included 50 smokers and 50 non - smokers who formed the control group were selected for the present study. The participant subjects were selected from among the staff members, residents and the patients from the routine OPD. Prior informed written consents were obtained from them after explaining to them, the procedure and the purpose of the study tests. The Cardiovascular Autonomic Function Tests were assessed by using a CANWIN AUTONOMIC ANALYSER which was available in the department.

RESULTS AND CONCLUSION

After applying the 'Z'-test for the difference between the two sample means, it was observed that there was a highly significant difference between the mean values of the para-sympathetic function tests among the smokers and the non - smokers (i.e. p<0.01) The Resting Heart Rate had significantly increased and the Expiration: Inspiration Ratio, the 30:15 Ratio (Response to standing) and the Valsalva Ratio had significantly decreased in the smokers as compared to those in the non - smokers. After applying the 'Z'-test for the difference between the two sample means, it was observed that there was no significant difference between the mean values of the Postural hypotension test (i.e. p>0.05) and that there was a highly significant difference between the mean values of the Sustained handgrip test in the smokers and the non - smokers (i.e. p<0.01).

The effects of omega-3 polyunsaturated fatty acids on cardiac rhythm: a critical reassessment

Although epidemiological studies provide strong evidence for an inverse relationship between omega-3 polyunsaturated fatty acids (n-3 PUFAs) and cardiac mortality, inconsistent and often conflicting results have been obtained from both animal studies and clinical prevention trials. Despite these heterogeneous results, some general conclusions can be drawn from these studies: 1) n-PUFAs have potent effects on ion channels and calcium regulatory proteins that vary depending on the route of administration. Circulating (acute administration) n-3 PUFAs affect ion channels directly while incorporation (long-term supplementation) of these lipids into cell membranes indirectly alter cardiac electrical activity via alteration of membrane properties. 2) n-3 PUFAs reduce baseline HR and increase HRV via alterations in intrinsic pacemaker rate rather than from changes in cardiac autonomic neural regulation. 3) n-3 PUFAs may be only effective if given before electrophysiological or structural remodeling has begun and have no efficacy against atrial fibrillation. 5) Despite initial encouraging results, more recent clinical prevention and animal studies have not only failed to reduce sudden cardiac death but actually increased mortality in angina patients and increased rather than decreased malignant arrhythmias in animal models of regional ischemia. 6) Given the inconsistent benefits reported in clinical and experimental studies and the potential adverse actions on cardiac rhythm noted during myocardial ischemia, n-3 PUFA must be prescribed with caution and generalized recommendations to increase fish intake or to take n-3 PUFA supplements need to be reconsidered.

Heart rate variability - a historical perspective

Heart rate variability (HRV), the beat-to-beat variation in either heart rate or the duration of the R-R interval - the heart period, has become a popular clinical and investigational tool. The temporal fluctuations in heart rate exhibit a marked synchrony with respiration (increasing during inspiration and decreasing during expiration - the so called respiratory sinus arrhythmia, RSA) and are widely believed to reflect changes in cardiac autonomic regulation. Although the exact contributions of the parasympathetic and the sympathetic divisions of the autonomic nervous system to this variability are controversial and remain the subject of active investigation and debate, a number of time and frequency domain techniques have been developed to provide insight into cardiac autonomic regulation in both health and disease. It is the purpose of this essay to provide an historical overview of the evolution in the concept of HRV. Briefly, pulse rate was first measured by ancient Greek physicians and scientists. However, it was not until the invention of the "Physician's Pulse Watch" (a watch with a second hand that could be stopped) in 1707 that changes in pulse rate could be accurately assessed. The Rev. Stephen Hales (1733) was the first to note that pulse varied with respiration and in 1847 Carl Ludwig was the first to record RSA. With the measurement of the ECG (1895) and advent of digital signal processing techniques in the 1960s, investigation of HRV and its relationship to health and disease has exploded. This essay will conclude with a brief description of time domain, frequency domain, and non-linear dynamic analysis techniques (and their limitations) that are commonly used to measure HRV.

The acute effects of smoking on the cyclic variations in blood echogenicity of carotid artery

The objective of this research is to study the cyclic variations in echogenicity (CVE) as an acute response to smoking. CVEs, caused by the aggregation of red blood cells (RBC) were measured from the cross-sectional images of the common carotid artery using coded harmonic imaging of a commercial ultrasound system. The amplitude of the CVE (A(cve)) was analyzed among 28 smokers before and after smoking. A(cve) was increased in 22 smokers and decreased in six smokers after 1-2 cigarettes were smoked. Heart rate (HR) was also estimated from the ultrasonic images before and after smoking. The smokers were optimally divided into two clusters with respect to the change in A(cve) and the intrinsic characteristics of smokers (i.e., daily consumed cigarettes and smoking years) through a two-step cluster analysis (TSCA). The increase in A(cve) after smoking was significantly higher in the heavy smoker cluster compared with the light smoker cluster. The results suggest that the acute changes in A(cve) in response to smoking are different between heavy smokers and light smokers. This preliminary study demonstrates the potential application of coded harmonic ultrasound imaging to detect or characterize RBC aggregation. In addition, the results may be useful for understanding the acute physiologic changes caused by smoking.

Cardiac autonomic neural remodeling and susceptibility to sudden cardiac death: effect of endurance exercise training

Sudden cardiac death resulting from ventricular tachyarrhythmias remains the leading cause of death in industrially developed countries, accounting for between 300,000 and 500,000 deaths each year in the United States. Yet, despite the enormity of this problem, both the identification of factors contributing to ventricular fibrillation as well as the development of safe and effective antiarrhythmic agents remain elusive. Subnormal cardiac parasympathetic regulation coupled with an elevated cardiac sympathetic activation may allow for the formation of malignant ventricular arrhythmias. In particular, myocardial infarction can reduce cardiac parasympathetic regulation and alter beta-adrenoceptor subtype expression enhancing beta(2)-adrenoceptor sensitivity that can lead to intracellular calcium dysregulation and arrhythmias. As such, myocardial infarction can induce a remodeling of cardiac autonomic regulation that may be required to maintain cardiac pump function. If alterations in cardiac autonomic regulation play an important role in the genesis of life-threatening arrhythmias, then one would predict that interventions designed to either augment parasympathetic activity and/or reduce cardiac adrenergic activity would also protect against ventricular fibrillation. Recently, studies using a canine model of sudden death demonstrate that endurance exercise training (treadmill running) enhanced cardiac parasympathetic regulation (increased heart rate variability), restored a more normal beta-adrenoceptor balance (i.e., reduced beta(2)-adrenoceptor sensitivity and expression), and protected against ventricular fibrillation induced by acute myocardial ischemia. Thus exercise training may reverse the autonomic neural remodeling induced by myocardial infarction and thereby enhance the electrical stability of the heart in individuals shown to be at an increased risk for sudden cardiac death.

Cardiovascular variability during treatment with haloperidol, olanzapine or risperidone in recent-onset schizophrenia

This study aimed to investigate the effects of treatment with haloperidol, olanzapine and risperidone on cardiovascular variability in patients with recent-onset schizophrenia by means of spectral analysis. Unmedicated patients (n = 18) had a higher mean heart rate and a tendency for a lower high-frequency power of heart rate variability than healthy control subjects (n = 57), indicating a decreased cardiac vagal control in unmedicated patients with schizophrenia. Patients treated with haloperidol (n = 10) showed significantly lower low-frequency power of heart rate and systolic blood pressure variability compared with olanzapine-treated patients, suggesting that haloperidol attenuated sympathetic functioning. On the contrary, olanzapine-treated patients (n = 10) showed the highest power in the low-frequency range of heart rate and systolic blood pressure variability, suggesting an increased sympathetic cardiac functioning. No significant effects of risperidone (n = 13) were found. None of the antipsychotic agents differed in their parasympathetic cardiovascular effects. We conclude that young, unmedicated patients with schizophrenia differed from controls in their parasympathetic functioning, but the antipsychotic agents haloperidol, risperidone and olanzapine induced only minor cardiovascular side effects.

Prenatal nicotine exposure increases heart susceptibility to ischemia/reperfusion injury in adult offspring

In the present study we tested the hypothesis that prenatal nicotine exposure increases heart susceptibility to ischemia/reperfusion (I/R) injury in adult offspring. Nicotine was administered to pregnant rats via subcutaneous osmotic minipumps throughout gestation. Nicotine treatment resulted in a rapid and transient decrease in food-intake and a moderate decrease in maternal body weight gain. Hearts were isolated from adult male and female offspring and subjected to I/R in a Langendorff preparation. Nicotine significantly attenuated left ventricle (LV) developed pressure, heart rate, and coronary flow rate in female but not male hearts at baseline. Additionally, nicotine significantly increased LV infarct size and attenuated postischemic recovery of LV function in both male and female offspring with more pronounced effects in females. In female but not male hearts, nicotine significantly decreased the postischemic coronary flow rate. However, coronary nitric oxide release was decreased in male but not female hearts. Caspase-3, -8, and -9 levels were not significantly changed in either female or male hearts. However, nicotine caused a significant decrease in protein levels of protein kinase (PK) Cepsilon in both male and female hearts and a decrease in PKCdelta levels in female hearts only. Control studies of maternal food restriction showed that a moderate decrease in maternal body weight gain had no effect on female hearts but significantly improved postischemic recovery of LV function in male hearts. The results suggest that prenatal nicotine exposure causes in utero programming of the PKC isozyme gene expression pattern in the developing heart and increases heart susceptibility to I/R injury in adult offspring.

Contribution of endothelial nitric oxide to blood pressure in humans

Impaired endothelial-derived NO (eNO) is invoked in the development of many pathological conditions. Systemic inhibition of NO synthesis, used to assess the importance of NO to blood pressure (BP) regulation, increases BP by approximately 15 mm Hg. This approach underestimates the importance of eNO, because BP is restrained by baroreflex mechanisms and does not account for a role of neurally derived NO. To overcome these limitations, we induced complete autonomic blockade with trimethaphan in 17 normotensive healthy control subjects to eliminate baroreflex mechanisms and contribution of neurally derived NO. Under these conditions, the increase in BP reflects mostly blockade of tonic eNO. N(G)-Monomethyl-l-arginine (250 microg/kg per minute IV) increased mean BP by 6+/-3.7 mm Hg (from 77 to 82 mm Hg) in intact subjects and by 21+/-8.4 mm Hg (from 75 to 96 mm Hg) during autonomic blockade. We did not find a significant contribution of neurally derived NO to BP regulation after accounting for baroreflex buffering. To further validate this approach, we compared the effect of NOS inhibition during autonomic blockade in 10 normotensive individuals with that of 6 normotensive smokers known to have endothelial dysfunction but who were otherwise normal. As expected, normotensive smokers showed a significantly lower increase in systolic BP during selective eNO blockade (11+/-4.5 versus 30+/-2.3 mm Hg in normotensive individuals; P<0.005). Thus, we report a novel approach to preferentially evaluate the role of eNO on BP control in normal and disease states. Our results suggest that eNO is one of the most potent metabolic determinants of BP in humans, tonically restraining it by approximately 30 mm Hg.

Autonomic cardiovascular function in high-altitude Andean natives with chronic mountain sickness

We evaluated autonomic cardiovascular regulation in subjects with polycythemia and chronic mountain sickness (CMS) and tested the hypothesis that an increase in arterial oxygen saturation has a beneficial effect on arterial baroreflex sensitivity in these subjects. Ten Andean natives with a Hct >65% and 10 natives with a Hct <60%, all living permanently at an altitude of 4,300 m, were included in the study. Cardiovascular autonomic regulation was evaluated by spectral analysis of hemodynamic parameters, while subjects breathed spontaneously or frequency controlled at 0.1 and 0.25 Hz, respectively. The recordings were repeated after a 1-h administration of supplemental oxygen and after frequency-controlled breathing at 6 breaths/min for 1 h, respectively. Subjects with Hct >65% showed an increased incidence of CMS compared with subjects with Hct <60%. Spontaneous baroreflex sensitivity was significantly lower in subjects with high Hct compared with the control group. The effects of supplemental oxygen or modification of the breathing pattern on autonomic function were as follows: 1) heart rate decreased significantly after both maneuvers in both groups, and 2) spontaneous baroreflex sensitivity increased significantly in subjects with high Hct and did not differ from subjects with low Hct. Temporary slow-frequency breathing may provide a beneficial effect on the autonomic cardiovascular function in high-altitude natives with CMS.

Continuous positive airway pressure treatment improves baroreflex control of heart rate during sleep in severe obstructive sleep apnea syndrome

The role of the arterial baroreflex in the cardiovascular changes associated with the obstructive sleep apnea syndrome (OSAS), and the effect of nasal continuous positive airway pressure (CPAP) treatment on baroreflex function during sleep are unknown. Baroreflex control of heart rate was studied in 29 normotensive patients with OSAS under no treatment, in 11 age-matched control subjects, and in 10 patients at CPAP withdrawal after 5.5 +/- 3.7 (range 3-14) months of treatment. Baroreflex control of heart rate was assessed by "sequence method" analysis of continuous blood pressure recordings (Finapres) obtained during nocturnal polysomnography. In untreated OSAS, baroreflex sensitivity (BRS) was low during wakefulness and non-rapid eye movement (REM) stage 2 sleep compared with control subjects, and correlated inversely with mean lowest Sa(O(2)) and the blood pressure increase after apneas. After CPAP treatment, the apnea-hypopnea index was lower, and mean lowest Sa(O(2)) higher than before treatment. After CPAP, patients were more bradycardic, blood pressure and its standard deviation decreased as Sa(O(2)) improved in non-REM stage 2 sleep, and BRS increased (nocturnal wakefulness: +59%; non-REM stage 2 sleep: +68% over pretreatment values). Our data suggest that baroreflex dysfunction in OSAS may be at least partly accounted for by nocturnal intermittent hypoxemia, and can be reversed by long-term CPAP treatment.

Positive and negative feedback mechanisms in the neural regulation of cardiovascular function in healthy and spinal cord-injured humans

BACKGROUND

We tested the hypothesis that in humans, hypertension/tachycardia and hypotension/bradycardia nonbaroreflex sequences that occur within spontaneous arterial pressure (AP) and R-R interval fluctuations are an expression of positive feedback mechanisms neurally regulating the cardiovascular system.

METHODS AND RESULTS

We studied 15 spinal cord-injured (SCI) subjects (8 tetraplegics and 7 paraplegics) and 8 healthy subjects. The occurrence of nonbaroreflex (NBseq) and baroreflex (Bseq) sequences, ie, hypertension-bradycardia and hypotension-tachycardia sequences, was assessed during rest and head-up tilt (HUT). The ratio between Bseq and NBseq (B/NB ratio) was also calculated. In resting conditions, the occurrence of NBseq was significantly lower (P:<0.05) in tetraplegics (7.9+/-1.5) than in paraplegics (16.2+/-3.2) and normal subjects (19.0+/-3.5), whereas the occurrence of Bseq was not significantly different between the 3 groups (38.6+/-11.9 versus 45.4+/-6.0 versus 47.0+/-11.9). In tetraplegics, the B/NB ratio showed a marked, significant decrease (from 8.4+/-4.2 to 1.9+/-0.8, P:<0.05) in response to HUT, whereas in normal subjects, it showed a significant increase (from 3.5+/-0.7 to 9.4+/-2.7, P:<0.05). In paraplegics, the B/NB ratio did not change significantly in response to HUT (from 4.5+/-1.6 to 4.8+/-1.1).

CONCLUSIONS

Our data suggest that nonbaroreflex sequences occur in humans and might represent the expression of an integrated, neurally mediated, feed-forward type of short-term cardiovascular regulation that is able to interact dynamically with feedback mechanisms of baroreflex origin.

Determinants of spontaneous baroreflex sensitivity in a healthy working population

Baroreflex sensitivity (BRS) by the spontaneous sequence technique has been widely used as a cardiac autonomic index for a variety of pathological conditions. However, little information is available on determinants of the variability of spontaneous BRS and on age-related reference values of this measurement in a healthy population. We evaluated BRS as the slope of spontaneous changes in systolic blood pressure (BP) and pulse interval from 10 minutes BP (Finapres) and ECG recordings in 1134 healthy volunteers 18 to 60 years of age. Measurement of BRS could be obtained in 90% of subjects. Those with unmeasurable spontaneous BRS had a slightly lower heart rate but were otherwise not different from the rest of the population. BRS was inversely related to age (lnBRS, 3.24-0.03xage; r(2)=0.23; P:<0.0001) in both genders. In addition, univariate analysis revealed a significant inverse correlation between BRS and heart rate, body mass index, and BP. Sedentary lifestyle and regular alcohol consumption were also associated with lower BRS. However, only age, heart rate, systolic and diastolic BP, body mass index, smoking, and gender were independent predictors of BRS in a multivariate model, accounting for 47% of the variance of BRS. The present study provides reference values for spontaneous BRS in a healthy white population. Only approximately half of the variability of BRS could be explained by anthropometric variables and common risk factors, which suggests that a significant proportion of interindividual differences may reflect genetic heterogeneity.

Dynamic regulation of heart rate during acute hypotension: new insight into baroreflex function

To examine the dynamic properties of baroreflex function, we measured beat-to-beat changes in arterial blood pressure (ABP) and heart rate (HR) during acute hypotension induced by thigh cuff deflation in 10 healthy subjects under supine resting conditions and during progressive lower body negative pressure (LBNP). The quantitative, temporal relationship between ABP and HR was fitted by a second-order autoregressive (AR) model. The frequency response was evaluated by transfer function analysis.

RESULTS

HR changes during acute hypotension appear to be controlled by an ABP error signal between baseline and induced hypotension. The quantitative relationship between changes in ABP and HR is characterized by a second-order AR model with a pure time delay of 0.75 s containing low-pass filter properties. During LBNP, the change in HR/change in ABP during induced hypotension significantly decreased, as did the numerator coefficients of the AR model and transfer function gain.

CONCLUSIONS

1) Beat-to-beat HR responses to dynamic changes in ABP may be controlled by an error signal rather than directional changes in pressure, suggesting a "set point" mechanism in short-term ABP control. 2) The quantitative relationship between dynamic changes in ABP and HR can be described by a second-order AR model with a pure time delay. 3) The ability of the baroreflex to evoke a HR response to transient changes in pressure was reduced during LBNP, which was due primarily to a reduction of the static gain of the baroreflex.

Long-term lifestyle changes maintain the autonomic modulation induced by rehabilitation after myocardial infarction

The altered autonomic balance observed after myocardial infarction is shifted toward a higher parasympathetic tone by rehabilitation. This effect persists after 1 year, however we observed a discrete variability in the long-term sympathovagal balance among patients. We postulated that such variability derives from the disparate adherence of patients to lifestyle prescriptions regarding exercise continuance and smoking avoidance. To test this hypothesis, we reviewed the data of 40 patients, who completed with a favourable autonomic modulation the initial rehabilitation phase after myocardial infarction and underwent the annual follow-up. One year after infarction, 23 patients complied to the advice about regular exercise and smoking avoidance (adherent, Group 1); 17 did not (non-adherent, Group 2). Groups were similar for age, site of infarction, left ventricular function, stress test duration and therapy. The ratio LF/HF, derived from the power spectral density of RR intervals variability, was used as an index of the sympathovagal balance. It was obtained from 15 min of ECG at rest, assessed 1 month after MI (baseline), and repeated 3 months (rehabilitation) and 1 year (follow-up) afterwards. Rehabilitation increased parasympathetic tone in all patients, reducing LF/HF by 33%. At follow-up, this potentially favourable autonomic profile persisted only in Group 1 patients. In conclusion, after a first myocardial infarction, the persistence of the potentially beneficial effect of rehabilitation on the sympathovagal balance depends on the compliance to the lifestyle changes proposed during the initial phase.

Effects of smoking cessation on blood pressure and heart rate variability in habitual smokers

We investigated the effects of 1-week of smoking cessation on ambulatory blood pressure, heart rate, and heart rate variability in 39 normotensive male habitual smokers (mean+/-SEM, 32.5+/-1.0 years). The ambulatory blood pressure, heart rate, and ECG R-R intervals were measured during a 24-hour period with a portable recorder (TM-2425) on the last day of 1-week smoking and nonsmoking periods. The order of the 2 periods was randomized. In the smoking period, the subjects were instructed to smoke cigarettes according to their usual smoking patterns. A power-spectral analysis of R-R intervals was performed to obtain the low-frequency (LF) and high-frequency (HF) components. The percentage of differences between adjacent normal R-R intervals >50 milliseconds (pNN50) was used as a time-domain measure of heart rate variability. The 24-hour ambulatory blood pressure was significantly lower in the nonsmoking period than in the smoking period, by 3.5+/-1.1 mm Hg systole [P<0. 01] and by 1.9+/-0.7 mm Hg diastole [P<0.05], whereas the nighttime blood pressure did not differ significantly between the 2 periods. The 24-hour heart rate was significantly lower in the nonsmoking period than in the smoking period, by 7.3+/-1.0 beats/min (P<0.0001). The pNN50 and the 24-hour HF component were significantly higher in the nonsmoking period than in the smoking period (P<0.0001 for each). The plasma norepinephrine and epinephrine concentrations were significantly lower in the nonsmoking period than in the smoking period (P<0.05 for each). These results demonstrate the substantial and immediate benefits of smoking cessation on these cardiovascular indices.

Cigarette smoking increases sympathetic outflow in humans

BACKGROUND

It is generally accepted that smoking increases blood pressure and inhibits muscle sympathetic nerve activity (SNA). The decrease in muscle SNA with cigarette smoking might be secondary to baroreflex responses to the pressor effect of smoking, thus obscuring a sympathetic excitatory effect of smoking. We tested the hypothesis that smoking increases sympathetic outflow.

METHODS AND RESULTS

We examined the effects of sham smoking, cigarette smoking, and cigarette smoking in combination with nitroprusside on muscle (baroreflex-dependent) SNA in 10 healthy habitual smokers. The 3 sessions were performed in random order, each study on a separate day. In an additional study, we also investigated the effects of sham smoking and cigarette smoking on skin (baroreflex-independent) SNA in 9 subjects. Compared with sham smoking, cigarette smoking alone increased blood pressure and decreased muscle SNA. When the blood pressure increase in response to smoking was blunted by nitroprusside infusion, there was a striking increase in muscle SNA. Muscle SNA increased up to 3-fold the levels seen before smoking (P<0.001), accompanied by an increase in heart rate of up to 37+/-4 bpm. Cigarette smoking also induced a 102+/-22% increase in skin SNA (P=0.03).

CONCLUSIONS

These data provide the first direct evidence that cigarette smoking increases sympathetic outflow.