Nicotine increases chemoreflex sensitivity to hypoxia in non-smokers

Epigenetic upregulation of carotid body angiotensin signaling increases blood pressure

Epigenetic changes can be shaped by a wide array of environmental cues as well as maternal health and behaviors. One of the most detrimental behaviors to the developing fetus is nicotine exposure. Perinatal nicotine exposure remains a significant risk factor for cardiovascular health and in particular, hypertension. Increased basal carotid body activity and excitation are significant contributors to hypertension. This study investigated the epigenetic changes to carotid body activity induced by perinatal nicotine exposure resulting in carotid body-mediated hypertension. Using a rodent model of perinatal nicotine exposure, we show that angiotensin II type 1 receptor signaling is upregulated in the carotid bodies of nicotine-exposed offspring. These changes were attributed to an upregulation of genetic promotion as DNA methylation of AT1r and PKC occurred within intron regions, exemplifying an upregulation of genetic transcription for these genes. Nicotine increased angiotensin signaling in vitro . Carotid body reactivity to angiotensin was increased in perinatal nicotine-exposed offspring compared to control offspring. Further, carotid body denervation reduced arterial pressure as a result of suppressed efferent sympathetic activity in perinatal nicotine-exposed offspring. Our data demonstrate that perinatal nicotine exposure adversely affects carotid body afferent sensing, which augments efferent sympathetic activity to increase vasoconstrictor signaling and induce hypertension. Targeting angiotensin signaling in the carotid bodies may provide a way to alleviate hypertension acquired by adverse maternal uterine environments in general and perinatal nicotine exposure in particular.

The effect of hypoxemia on muscle sympathetic nerve activity and cardiovascular function: a systematic review and meta-analysis

We conducted a systematic review and meta-analysis to determine the effect of acute poikilocapnic, high-altitude, and acute isocapnia hypoxemia on muscle sympathetic nerve activity (MSNA) and cardiovascular function. A comprehensive search across electronic databases was performed until June 2021. All observational designs were included: population (healthy individuals); exposures (MSNA during hypoxemia); comparators (hypoxemia severity and duration); outcomes (MSNA; heart rate, HR; and mean arterial pressure, MAP). Sixty-one studies were included in the meta-analysis. MSNA burst frequency increased by a greater extent during high-altitude hypoxemia [P < 0.001; mean difference (MD), +22.5 bursts/min; confidence interval (CI) = -19.20 to 25.84] compared with acute poikilocapnic hypoxemia (P < 0.001; MD, +5.63 bursts/min; CI = -4.09 to 7.17) and isocapnic hypoxemia (P < 0.001; MD, +4.72 bursts/min; CI = -3.37 to 6.07). MSNA burst amplitude was only elevated during acute isocapnic hypoxemia (P = 0.03; standard MD, +0.46 au; CI = -0.03 to 0.90), and MSNA burst incidence was only elevated during high-altitude hypoxemia [P < 0.001; MD, 33.05 bursts/100 heartbeats; CI = -28.59 to 37.51]. Meta-regression analysis indicated a strong relationship between MSNA burst frequency and hypoxemia severity for acute isocapnic studies (P < 0.001) but not acute poikilocapnia (P = 0.098). HR increased by the same extent across each type of hypoxemia [P < 0.001; MD +13.81 heartbeats/min; 95% CI = 12.59-15.03]. MAP increased during high-altitude hypoxemia (P < 0.001; MD, +5.06 mmHg; CI = 3.14-6.99), and acute isocapnic hypoxemia (P < 0.001; MD, +1.91 mmHg; CI = 0.84-2.97), but not during acute poikilocapnic hypoxemia (P = 0.95). Both hypoxemia type and severity influenced sympathetic nerve and cardiovascular function. These data are important for the better understanding of healthy human adaptation to hypoxemia.

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.

Relation between coffee consumption and risk of seizure-related respiratory dysfunction in patients with drug-resistant focal epilepsy

OBJECTIVE

Caffeine is an antagonist of the adenosine pathway, which is involved in regulation of breathing. Extracellular concentrations of adenosine are increased in the immediate aftermath of a seizure. Seizure-related overstimulation of adenosine receptors might promote peri-ictal apnea. However, the relation between caffeine consumption and risk of seizure-related respiratory dysfunction in patients with drug-resistant focal epilepsy remains unknown.

METHODS

We performed a cross-sectional analysis of data collected in patients included in the SAVE study in Lyon's epilepsy monitoring unit at the Adult Epilepsy Department of the Lyon University Hospital between February 2016 and October 2018. The video-electroencephalographic recordings of 156 patients with drug-resistant focal epilepsy included in the study were reviewed to identify those with ≥1 focal seizure (FS), valid pulse oximetry (SpO₂ ) measurement, and information about usual coffee consumption. This latter was collected at inclusion using a standardized self-questionnaire and further classified into four groups: none, rare (≤3 cups/week), moderate (4 cups/week to 3 cups/day), and high (≥4 cups/day). Peri-ictal hypoxemia (PIH) was defined as SpO₂ < 90% for at least 5 s occurring during the ictal period, the post-ictal period, or both.

RESULTS

Ninety patients fulfilled inclusion criteria, and 323 seizures were analyzed. Both the level of usual coffee consumption (p = .033) and the level of antiepileptic drug withdrawal (p = .004) were independent risk factors for occurrence of PIH. In comparison with FS in patients with no coffee consumption, risk of PIH was four times lower in FS in patients with moderate consumption (odds ratio [OR] = .25, 95% confidence interval [CI] = .07-.91, p = .036) and six times lower in FS in patients with high coffee consumption (OR = .16, 95% CI = .04-.66, p = .011). However, when PIH occurred, its duration was longer in patients with moderate or high consumption than in those with no coffee consumption (p = .042).

SIGNIFICANCE

Coffee consumption may be a protective factor for seizure-related respiratory dysfunction, with a dose-dependent effect.

Effect of continuous positive airway pressure on respiratory drive in patients with obstructive sleep apnea

OBJECTIVE

Patients with obstructive sleep apnea (OSA) have an altered control of breathing during wakefulness. Thus far, whether and how treatment with continuous positive airway pressure (CPAP) may restore these abnormalities has been poorly understood. The aim of this study was to investigate the long-term effects of CPAP on the breathing pattern, ventilatory drive (VDr), and chemoreceptor sensitivity in OSA patients.

PATIENTS AND METHODS

This was a prospective, observational study, carried out in an academic sleep outpatient clinic. A total of 62 patients with OSA (mean age [SD], 51 [11] years) underwent polysomnography (PSG), breathing pattern assessment, mouth occlusion pressure, ventilatory response to hypoxemia (V_e/SaO₂), and hypercapnia (V_e/PETCO₂) before and after CPAP titration and during 12-month follow-up. A total of 48 age-matched healthy subjects served as controls. Patients with good (≥6 h/night) and poor (<6 h/night) compliance with CPAP were also compared.

RESULTS

At baseline, VDr as well as thoracic and inspiratory impedances were greater in patients with OSA compared with controls and were reduced by CPAP treatment, starting from the night of titration (P < 0.01), especially in patients with good compliance with CPAP. Baseline V_e/SaO₂ was higher in OSA patients (P < 0.05) and was progressively normalized during CPAP treatment (P < 0.001). The pathophysiological changes were mainly due to a reduction in tidal volume. The remaining breathing pattern parameters were unaltered by CPAP treatment and were similar between groups.

CONCLUSION

In OSA patients, the mechanics of breathing are inefficient because of an imbalance of the VDr. Regular CPAP treatment improves the efficiency of the respiratory system and normalizes the hypoxemic stimulus.

Sleep Duration and Quality in Pregnant Women: A Cross-Sectional Survey in China

Objectives: Good maternal health and fetal development require sufficient and good quality of sleep during pregnancy. This study investigated sleep duration and quality in pregnant women, assessing factors with possibly influence on sleep. Method: A cross-sectional survey was conducted on pregnant women between June and August in 2015 in 16 hospitals in five provinces in China. A total of 2345 pregnant women aged 18 years and older were surveyed. Insufficient sleeping duration was defined as sleeping of less than 7 h per day. Excessive sleep duration was defined as sleeping of more than 9 h per day. Results: A total of 561 (23.9%) participants reported insufficient sleeping duration, whereas 485 (20.9%) claimed excessive sleep duration. A total of 358 (15.2%) of pregnant women reported problems regarding sleep quality. Compared to pregnant women with sufficient sleeping duration, those with insufficient sleeping duration were prone to have poor sleep quality, whereas those with excessive sleeping duration featured low possibility of poor sleep quality. High-risk groups of insufficient sleep duration include women of Han nationality, with siblings, in their first trimester of pregnancy, receiving care in low-capacity/quality hospital settings, and with daily or 1-3 days of secondhand smoke exposure. High-risk groups of excessive sleep duration include women living in rural areas, unemployed, in their third trimester of pregnancy, and receiving care in medium-capacity/quality hospital settings. High-risk groups of poor sleep quality include women of non-Han nationality, low income level, in their third trimester of pregnancy, and with insufficient sleep duration. Conclusions: Insufficient/excessive sleep duration and poor sleep quality commonly occur during pregnancy in China. Findings provide a better understanding of the influencing factors of insufficient/excessive sleep duration and poor quality of sleep. These findings have some implications for future interventions on sleep among pregnant women.

Lower hypoxic ventilatory response in smokers compared to non-smokers during abstinence from cigarettes

BACKGROUND

Carotid body O₂-chemosensitivity determines the hypoxic ventilatory response (HVR) as part of crucial regulatory reflex within oxygen homeostasis. Nicotine has been suggested to attenuate HVR in neonates of smoking mothers. However, whether smoking affects HVR in adulthood has remained unclear and probably blurred by acute ventilatory stimulation through cigarette smoke. We hypothesized that HVR is substantially reduced in smokers when studied after an overnight abstinence from cigarettes i.e. after nicotine elimination.

METHODS

We therefore determined the isocapnic HVR of 23 healthy male smokers (age 33.9 ± 2.0 years, BMI 24.2 ± 0.5 kg m^-2, mean ± SEM) with a smoking history of >8 years after 12 h of abstinence and compared it to that of 23 healthy male non-smokers matched for age and BMI.

RESULTS

Smokers and non-smokers were comparable with regard to factors known to affect isocapnic HVR such as plasma levels of glucose and thiols as well as intracellular levels of glutathione in blood mononuclear cells. As a new finding, abstinent smokers had a significantly lower isocapnic HVR (0.024 ± 0.002 vs. 0.037 ± 0.003 l min^-1 %^-1BMI^-1, P = 0.002) compared to non-smokers. However, upon re-exposure to cigarettes the smokers' HVR increased immediately to the non-smokers' level.

CONCLUSIONS

This is the first report of a substantial HVR reduction in abstinent adult smokers which appears to be masked by daily smoking routine and may therefore have been previously overlooked. A low HVR may be suggested as a novel link between smoking and aggravated hypoxemia during sleep especially in relevant clinical conditions such as COPD.

Association between smoking and the risk of acute mountain sickness: a meta-analysis of observational studies

BACKGROUND

People rapidly ascending to high altitudes (>2500 m) may suffer from acute mountain sickness (AMS). The association between smoking and AMS risk remains unclear. Therefore, we performed a meta-analysis to evaluate the association between smoking and AMS risk.

METHODS

The association between smoking and AMS risk was determined according to predefined criteria established by our team. Meta-analysis was conducted according to the PRISMA guidelines. We included all relevant studies listed in the PubMed and Embase databases as of September 2015 in this meta-analysis and performed systemic searches using the terms "smoking", "acute mountain sickness" and "risk factor". The included studies were required to provide clear explanations regarding their definitions of smoking, the final altitudes reached by their participants and the diagnostic criteria used to diagnose AMS. Odds ratios (ORs) were used to evaluate the association between smoking and AMS risk across the studies, and the Q statistic was used to test OR heterogeneity, which was considered significant when P < 0.05. We also computed 95% confidence intervals (CIs). Data extracted from the articles were analyzed with Review Manager 5.3 (Cochrane Collaboration, Oxford, UK).

RESULTS

We used seven case-control studies including 694 smoking patients and 1986 non-smoking controls to analyze the association between smoking and AMS risk. We observed a significant association between AMS and smoking (OR = 0.71, 95% CI 0.52-0.96, P = 0.03).

CONCLUSIONS

We determined that smoking may protect against AMS development. However, we do not advise smoking to prevent AMS. More studies are necessary to confirm the role of smoking in AMS risk.

At high cardiac output, diesel exhaust exposure increases pulmonary vascular resistance and decreases distensibility of pulmonary resistive vessels

Air pollution has recently been associated with the development of acute decompensated heart failure, but the underlying biological mechanisms remain unclear. A pulmonary vasoconstrictor effect of air pollution, combined with its systemic effects, may precipitate decompensated heart failure. The aim of the present study was to investigate the effects of acute exposure to diesel exhaust (DE) on pulmonary vascular resistance (PVR) under resting and stress conditions but also to determine whether air pollution may potentiate acquired pulmonary hypertension. Eighteen healthy male volunteers were exposed to ambient air (AA) or dilute DE with a particulate matter of <2.5 μm concentration of 300 μg/m(3) for 2 h in a randomized, crossover study design. The effects of DE on PVR, on the coefficient of distensibilty of pulmonary vessels (α), and on right and left ventricular function were evaluated at rest (n = 18), during dobutamine stress echocardiography (n = 10), and during exercise stress echocardiography performed in hypoxia (n = 8). Serum endothelin-1 and fractional exhaled nitric oxide were also measured. At rest, exposure to DE did not affect PVR. During dobutamine stress, the slope of the mean pulmonary artery pressure-cardiac output relationship increased from 2.8 ± 0.5 mmHg · min · l (-1) in AA to 3.9 ± 0.5 mmHg · min · l (-1) in DE (P < 0.05) and the α coefficient decreased from 0.96 ± 0.15 to 0.64 ± 0.12%/mmHg (P < 0.01). DE did not further enhance the hypoxia-related upper shift of the mean pulmonary artery pressure-cardiac output relationship. Exposure to DE did not affect serum endothelin-1 concentration or fractional exhaled nitric oxide. In conclusion, acute exposure to DE increased pulmonary vasomotor tone by decreasing the distensibility of pulmonary resistive vessels at high cardiac output.

Smoking is associated with the incidence of AMS: a large-sample cohort study

BACKGROUND

In recent years, the number of people visiting high altitudes has increased. After rapidly ascending to a high altitude, some of these individuals, who reside on plains or other areas of low altitude, have suffered from acute mountain sickness (AMS). Smoking interferes with the body's oxygen metabolism, but research about the relationship between smoking and AMS has yielded controversial results.

METHODS

We collected demographic data, conducted a smoking history and performed physical examinations on 2000 potential study participants, at sea level. Blood pressure (BP) and pulse oxygen saturation (SpO2) were measured for only some of the patients due to time and manpower limitations. We ultimately recruited 520 smokers and 450 nonsmokers according to the inclusion and exclusion criteria of our study. Following acute high-altitude exposure, we examined their Lake Louise Symptom (LLS) scores, BP, HR and SpO2; however, cerebral blood flow (CBF) was measured for only some of the subjects due to limited time, manpower and equipment.

RESULTS

Both the incidence of AMS and Lake Louise Symptom (LLS) scores were lower in smokers than in nonsmokers. Comparing AMS-related symptoms between nonsmokers and smokers, the incidence and severity of headaches and the incidence of sleep difficulties were lower in smokers than in nonsmokers. The incidences of both cough and mental status change were higher in smokers than in nonsmokers; blood pressure, HR and cerebral blood flow velocity were lower in smokers than in nonsmokers.

CONCLUSION

Our findings suggest that the incidence of AMS is lower in the smoking group, possibly related to a retardation of cerebral blood flow and a relief of AMS-related symptoms, such as headache.

Secondhand smoke exposure, restless sleep, and sleep duration in adolescents

Purpose. To examine whether secondhand smoke (SHS) exposure is associated with restless sleep and/or nighttime sleep duration among adolescents. Methods. Data were analyzed from 1,592 adolescents who completed an internet-delivered survey as part of the British Columbia Adolescent Substance Use Survey cohort study. Ordinal logistic and linear regression models were used to examine associations between frequency of SHS exposure in the past month and frequency of restless sleep and nighttime sleep duration, respectively. Results. SHS exposure was significantly positively associated with restless sleep and significantly negatively associated with sleep duration. In fully adjusted models, compared with students who reported never being exposed to SHS in the past month, students who reported a low, medium, or high frequency of SHS exposure were 1.53, 1.76, and 2.51 times as likely, respectively, to report more frequent restless sleep (OR = 1.53, 95% CI 1.08-2.16; OR = 1.76, 95% CI 1.22-2.53; OR = 2.51, 95% CI 1.59-3.98). With regard to sleep duration, as frequency of SHS exposure increased by one category, nighttime sleep duration during the week and weekend decreased by 4 minutes (B = -0.06, 95% CI = -0.01- - 0.11) and 6 minutes (B = -0.09, 95% CI = -0.03- - 0.14), respectively. Conclusions. This study suggests that frequency of SHS exposure has a significant dose-response relationship with restless sleep and sleep duration in adolescents.

Clinical Implications of Impaired Sleep

Despite its pervasiveness in primary care, deficient sleep often is underappreciated as a cue to other health risks. Accordingly, this review discusses contemporary evidence-based perspectives on impaired sleep and its associations with other lifestyle medicine concerns, including obesity, cardiovascular conditions, psychological problems, and health-compromising habits. The potential clinical benefits of promoting sleep health also will be considered.

Orexin: a potential role in the process of obstructive sleep apnea

Obstructive sleep apnea (OSA) is a complicated disease with an unrecognized mechanism. Obesity, sex, age, and smoking have been found to be independent correlates of OSA. Orexin (also named hypocretin) mainly secreted by lateral hypothalamus neurons has a wide array of biological functions like regulating sleep, energy levels and breathing. Several clinical studies found ties between orexin and OSA. Because of the close correlation between orexin and obesity, sex, age and smoking (which are the key risk factors for OSA patients), we hypothesize that orexin may play a key role in the pathogenesis of OSA.

Baroreceptor unloading in postural tachycardia syndrome augments peripheral chemoreceptor sensitivity and decreases central chemoreceptor sensitivity

While orthostatic tachycardia is the hallmark of postural tachycardia syndrome (POTS), orthostasis also initiates increased minute ventilation (Ve) and decreased end-tidal CO(2) in many patients. We hypothesized that chemoreflex sensitivity would be increased in patients with POTS. We therefore measured chemoreceptor sensitivity in 20 POTS (16 women and 4 men) and 14 healthy controls (10 women and 4 men), 16-35 yr old by exposing them to eucapneic hyperoxia (30% O(2)), eucapneic hypoxia (10% O(2)), and hypercapnic hyperoxia (30% O(2) + 5% CO(2)) while supine and during 70° head-upright tilt. Heart rate, mean arterial pressure, O(2) saturation, end-tidal CO(2), and Ve were measured. Peripheral chemoreflex sensitivity was calculated as the difference in Ve during hypoxia compared with room air divided by the change in O(2) saturation. Central chemoreflex sensitivity was determined by the difference in Ve during hypercapnia divided by the change in CO(2). POTS subjects had an increased peripheral chemoreflex sensitivity (in l·min(-1)·%oxygen(-1)) in response to hypoxia (0.42 ± 0.38 vs. 0.19 ± 0.17) but a decreased central chemoreflex sensitivity (l·min(-1)·Torr(-1)) CO(2) response (0.49 ± 0.38 vs. 1.04 ± 0.18) compared with controls. CO(2) sensitivity was also reduced in POTS subjects when supine. POTS patients are markedly sensitized to hypoxia when upright but desensitized to CO(2) while upright or supine. The interactions between orthostatic baroreflex unloading and altered chemoreflex sensitivities may explain the hyperventilation in POTS patients.

The association between active smoking, smokeless tobacco, second-hand smoke exposure and insufficient sleep

BACKGROUND

Studies have shown that cigarette smoking is associated with sleep disorders in the general population. But studies examining the association between smokeless tobacco use, second-hand smoke exposure and insufficient rest/sleep are limited.

METHODS

We examined the association between smoking, smokeless tobacco use (n=83,072), second-hand smoke exposure (n=28,557) and insufficient rest/sleep among adults aged ≥20 years in the state-based 2008 Behavioral Risk Factor Surveillance System. Exposure to second-hand smoke was defined as >1 day of exposure to cigarette smoking either at home or in the workplace in the preceding 7 days. Insufficient rest/sleep was defined as not getting enough rest/sleep everyday in the preceding 30 days.

RESULTS

Compared to never smokeless tobacco users, the odds ratio (OR; 95% confidence interval [CI]) of insufficient rest/sleep was 1.16 (1.00-1.36) and 1.74 (1.37-2.22) among former and current users. Compared to non-smokers/non-smokeless tobacco users, the OR (95% CI) of insufficient rest/sleep for those who were both current smokers and current smokeless tobacco users was 2.21 (1.66-2.94). Regarding second-hand smoke exposure among non-smokers, those with second-hand smoke exposure had higher odds for insufficient rest/sleep than those without. In contrast, the odds of insufficient rest/sleep were similar among current smokers with or without second-hand smoke exposure.

CONCLUSIONS

In a multiethnic sample of US adults, compared to non-smokers/non-smokeless tobacco users, those who were both current smokers and current smokeless tobacco users had twice the odds of insufficient sleep. Second-hand smoke exposure was associated with insufficient rest/sleep among non-smokers.

Smoking is associated with chronic sympathetic activation in hypertension

OBJECTIVE

Previous studies have shown that smoking contributes importantly to short-term modulation of sympathetic nerve traffic. However, effect of smoking status on resting muscle sympathetic nerve activity (MSNA) in hypertension is unknown. Therefore, we tested the hypothesis that smoking is associated with chronic sympathetic activation in patients with essential hypertension.

METHODS

We measured MSNA, heart rate (HR) and blood pressure during undisturbed supine rest and in 30 hypertensive smokers (22 males, age 38+/-4 years, body mass index, BMI 27+/-1 kg/m(2), mean+/-SEM). These measurements were compared with those obtained 38 non-smoking hypertensive patients matched for gender, age and BMI. All hypertensives underwent 24-h ambulatory blood pressure monitoring. Patients were newly diagnosed, never treated for hypertension and were free of any other known diseases.

RESULTS

In comparison with non-smokers, smokers had smaller office-daytime systolic blood pressure difference (6+/-2 vs 15+/-3 mmHg, respectively; p<0.01). Despite similar resting values, HR in smokers was greater than in non-smokers during both daytime (86+/-3 vs 77+/-2 beats/min, respectively; p< 0.001) and night-time (73+/-3 vs 66+/-2 beats/min, respectively; p<0.01). MSNA was elevated in smokers (36+/-3 bursts/min) compared with non-smokers (28+/-3 bursts/min; p<0.01). Similar results were obtained when MSNA was expressed as bursts/100 heart beats. Multiple linear regression analysis revealed that only age and smoking status were linked independently to MSNA (R(2)=0.42, p< 0.001).

CONCLUSIONS

In patients with essential hypertension, smoking is independently associated with chronic increase in MSNA. These findings may have implications for our understanding of the mechanisms linking smoking to cardiovascular events.

Facial cooling and peripheral chemoreflex mechanisms in humans

AIM

Reductions in arterial oxygen partial pressure activate the peripheral chemoreceptors which increase ventilation, and, after cessation of breathing, reduce heart rate. We tested the hypothesis that facial cooling facilitates these peripheral chemoreflex mechanisms.

METHODS

Chemoreflex control was assessed by the ventilatory response to hypoxia (10% O2 in N2) and the bradycardic response to voluntary end-expiratory apnoeas of maximal duration in 12 young, healthy subjects. We recorded minute ventilation, haemoglobin O2 saturation, RR interval (the time between two R waves of the QRS complex) and the standard deviation of the RR interval (SDNN), a marker of cardiac vagal activity throughout the study. Measurements were performed with the subject's face exposed to air flow at 23 and 4 degrees C.

RESULTS

Cold air decreased facial temperature by 11 degrees C (P < 0.0001) but did not affect minute ventilation during normoxia. However, facial cooling increased the ventilatory response to hypoxia (P < 0.05). The RR interval increased by 31 +/- 8% of the mean RR preceding the apnoea during the hypoxic apnoeas in the presence of cold air, compared to 17 +/- 5% of the mean RR preceding the apnoea in the absence of facial cooling (P < 0.05). This increase occurred despite identical apnoea durations and reductions in oxygen saturation. Finally, facial cooling increased SDNN during normoxia and hypoxia, as well as during the apnoeas performed in hypoxic conditions (all P < 0.05).

CONCLUSION

The larger ventilatory response to hypoxia suggests that facial cooling facilitates peripheral chemoreflex mechanisms in normal humans. Moreover, simultaneous diving reflex and peripheral chemoreflex activation enhances cardiac vagal activation, and favours further bradycardia upon cessation of breathing.

Acute effect of sidestream cigarette smoke extract on vascular endothelial function

Acute exposure to passive smoking adversely affects vascular function by promoting oxidative stress and endothelial dysfunction. However, it is not known whether tobacco sidestream (SS) smoke has a greater deleterious effect on the endothelium than non-tobacco SS smoke and whether these effects are related to nicotinic endothelial stimulation. To test these hypotheses, endothelial-dependent relaxation and superoxide anion production were assessed in isolated rat aortas incubated with tobacco SS smoke, non-tobacco SS smoke, or pure nicotine. Tobacco SS smoke decreased the maximal relaxation to acetylcholine (Ach) from 79 +/- 6% to 57 +/- 7.3% (% inhibition of phenylephrine-induced plateau, P < 0.001) and increased superoxide anion production from 31 +/- 9.7 to 116 +/- 24 count/10 sec/mg (P < 0.01, lucigenin-enhanced chemiluminescence technique). The non-tobacco SS smoke extract had no significant effect on the response to Ach but increased superoxide anion production in the aortic wall to 133 +/- 2 count/10 sec/mg (P < 0.001). Furthermore, concentration-response curves to Ach and superoxide production remained unaltered with nicotine (0.001, 0.01, or 0.1 mM). In conclusion, despite similar increases in vascular wall superoxide production with tobacco and non-tobacco SS smoke, only the tobacco SS smoke extracts affected endothelium-dependent vasorelaxation. Nicotine alone does not reproduce the effects seen with tobacco SS smoke, suggesting that the acute endothelial toxicity of passive smoking cannot simply be ascribed to a nicotine-dependent mechanism.