Occasional cigarette smoking chronically affects arterial function

Kinetic differences between macro- and microvascular measures of reactive hyperemia

Postischemia reperfusion kinetics are markedly dissociated when comparing the macro- versus microvasculature. We used Doppler ultrasound and near-infrared diffuse correlation spectroscopy (NIR-DCS), an emerging technique for continuously and noninvasively quantifying relative changes in skeletal muscle microvascular perfusion (i.e., blood flow index or BFI), to measure macro- and microvascular reactive hyperemia (RH) in the nondominant arm of 16 healthy young adults. First, we manipulated the duration of limb ischemia (3 vs. 6 min) with the limb at heart level (neutral, -N). Then, we reduced/increased forearm perfusion pressure (PP) by positioning the arm above (3 min-A, 60°) or below (3 min-B, 30°) the heart. The major novel findings were twofold: first, changes in the ischemic stimulus similarly affected peak macrovascular (i.e., conduit, mL/min) and microvascular (i.e., peak NIR-DCS-derived BFI) reperfusion during reactive hyperemia (6 min-N > 3 min-N, P < 0.05, both) but did not affect the rate at which microvascular reperfusion occurs (i.e., BFI slope). Second, changing forearm PP predictably affected both peak macro- and microvascular reperfusion during RH (3 min-B > N > A, P < 0.05, all), as well as the rate at which microvascular reperfusion occurred (BFI slope; 3 min-B >N > A, P < 0.05). Together, the data suggest that kinetic differences between macro- and microvascular reperfusion are largely determined by differences in fluid mechanical energy (i.e., pressure, gravitational, and kinetic energies) between the two compartments that work in tandem to restore pressure across the arterial tree following a period of tissue ischemia.NEW & NOTEWORTHY We extend our understanding of macro- versus microvascular hemodynamics in humans, by using near-infrared diffuse correlation spectroscopy (micro-) and Doppler ultrasound (macro-) to characterize reperfusion hemodynamics following experimental manipulation of the ischemic stimulus and tissue perfusion pressure. Our results suggest kinetic differences between macro- and microvascular reperfusion are largely determined by differences in fluid mechanical energy (i.e., pressure, gravitational, and kinetic energies) between the two compartments, rather than inherent differences between the macro- and microvasculature.

Tobacco and bone fractures: A review of the facts and issues that every orthopaedic surgeon should know

Objectives

The aim of this study was to review the impact of smoking tobacco on the musculoskeletal system, and on bone fractures in particular.

Methods

English-language publications of human and animal studies categorizing subjects into smokers and nonsmokers were sourced from MEDLINE, The Cochrane Library, and SCOPUS. This review specifically focused on the risk, surgical treatment, and prevention of fracture complications in smokers.

Results

Smokers have an increased risk of fracture and experience more complications with delayed bone healing, even if they have already stopped smoking, because some adverse effects persist for a prolonged period. Some risks can be reduced during and after surgery by local and general prevention, and smoking cessation is an important factor in lessening this risk. However, if a patient wants to stop smoking at the time of a fracture, the cessation strategies in reducing tobacco use are not easy to implement. The patient should also be warned that using e-cigarettes or other tobaccos does not appear to reduce adverse effects on health.

Conclusion

The evidence reviewed in this study shows that smoking has a negative effect in terms of the risk and treatment of fractures.

Cite this article: J. Hernigou, F. Schuind. Tobacco and bone fractures: A review of the facts and issues that every orthopaedic surgeon should know. Bone Joint Res 2019;8:255–265. DOI: 10.1302/2046-3758.86.BJR-2018-0344.R1.

Effect of passive heat stress on arterial stiffness in smokers versus non-smokers

In non-smokers, passive heat stress increases shear stress and vasodilation, decreasing arterial stiffness. Smokers, who reportedly have arterial dysfunction, may have similar improvements in arterial stiffness with passive heat stress. Therefore, we examined the effects of an acute bout of whole-body passive heat stress on arterial stiffness in smokers vs. non-smokers. Thirteen smokers (8.8 ± 5.5 [median = 6] cigarettes per day for > 4 years) and 13 non-smokers matched for age, mass, height, and exercise habits (27 ± 8 years; 78.8 ± 15.4 kg; 177.6 ± 6.7 cm) were passively heated to 1.5 °C core temperature (T C) increase. At baseline and each 0.5 °C T C increase, peripheral (pPWV) and central pulse wave velocity (cPWV) were measured via Doppler ultrasound. No differences existed between smokers and non-smokers for any variables (all p >  .05), except cPWV slightly increased from baseline (526.7 ± 81.7 cm · s(-1)) to 1.5 °C ΔT C (579.7 ± 69.8 cm · s(-1); p < 0.005), suggesting heat stress acutely increased central arterial stiffness. pPWV did not change with heating (grand mean: baseline = 691.9 ± 92.9 cm · s(-1); 1.5 °C ΔT C = 691.9 ± 79.5 cm · s(-1); p > 0.05). Changes in cPWV and pPWV during heating correlated (p < 0.05) with baseline PWV in smokers (cPWV: r = -0.59; pPWV: r = -0.62) and non-smokers (cPWV: r = -0.45; pPWV: r = -0.77). Independent of smoking status, baseline stiffness appears to mediate the magnitude of heating-induced changes in arterial stiffness.

The use of shear rate-diameter dose-response curves as an alternative to the flow-mediated dilation test

The brachial artery flow-mediated dilation test (FMD) is the non-invasive gold-standard used to test endothelial function. Reduced FMD precedes the development of atherosclerosis and provides an early marker for predicting future cardiovascular disease events. Although, this test is of high potential, it is somewhat limited by poor reproducibility. By utilizing hand warming and grip exercise combined with hierarchical linear modeling, shear rate-diameter dose-response curves may provide a novel and more accurate way to assess endothelial function in humans. Shear rate-diameter dose-response curves could potentially improve upon the traditional FMD measurement and serve as a superior clinical and research tool for assessing cardiovascular disease risk in a variety of populations. The current paper presents testable hypotheses and methodology for assessing the validity and reliability of an alternative to the current FMD test.

Modifiable cardiovascular disease risk factors among indigenous populations

Objective. To identify modifiable cardio-metabolic and lifestyle risk factors among indigenous populations from Australia (Aboriginal Australians/Torres Strait Islanders), New Zealand (Māori), and the United States (American Indians and Alaska Natives) that contribute to cardiovascular disease (CVD). Methods. National health surveys were identified where available. Electronic databases identified sources for filling missing data. The most relevant data were identified, organized, and synthesized. Results. Compared to their non-indigenous counterparts, indigenous populations exhibit lower life expectancies and a greater prevalence of CVD. All indigenous populations have higher rates of obesity and diabetes, hypertension is greater for Māori and Aboriginal Australians, and high cholesterol is greater only among American Indians/Alaska Natives. In turn, all indigenous groups exhibit higher rates of smoking and dangerous alcohol behaviour as well as consuming less fruits and vegetables. Aboriginal Australians and American Indians/Alaska Natives also exhibit greater rates of sedentary behaviour. Conclusion. Indigenous groups from Australia, New Zealand, and the United States have a lower life expectancy then their respective non-indigenous counterparts. A higher prevalence of CVD is a major driving force behind this discrepancy. A cluster of modifiable cardio-metabolic risk factors precede CVD, which, in turn, is linked to modifiable lifestyle risk factors.

A conceptual framework for managing modifiable risk factors for cardiovascular diseases in Fiji

AIMS

The current review will look at modifiable lifestyle (physical inactivity, poor nutrition, risky alcohol behavior and cigarette smoking) and cardio-metabolic (obesity, diabetes mellitus, high cholesterol and high blood pressure) cardiovascular disease (CVD) risk factors among Indigenous-Fijian and Indo-Fijian subgroups. A framework for monitoring and managing these risk factors will be presented.

METHODS

National health surveys were identified where available. Electronic databases identified sources for filling missing data. The most relevant data were identified, organized and synthesized.

RESULTS

Compared to Indo-Fijians, Indigenous-Fijians have higher rates of obesity (17% vs 11%) and hypertension (21% vs 16%), but lower rates of diabetes mellitus (12% vs 21%) and high cholesterol (33% vs 39%). Indigenous-Fijians report higher rates of prescribed physical activity (25% vs 21%), but poorer recommended vegetable intake (48% vs 56%), greater risky alcohol behavior (17% vs 15%) and a much greater prevalence of cigarette smoking (45% vs 24%). Both Indigenous-Fijians and Indo-Fijians report a low prevalence of recommended fruit intake (17% vs 15%).

CONCLUSIONS

Fiji is progressing through demographic and epidemiological transitions, including a decline in infectious diseases and improved life expectancy. However, in concert with other developing nations, 'modernization' is accompanied by increased mortality from non-communicable diseases, with CVD being the most prevalent. This transition has been associated with changes to socio-cultural aspects of Fiji, including poor lifestyle choices that may contribute to a cluster of cardio-metabolic conditions which precede CVD.

Peak and time-integrated shear rates independently predict flow-mediated dilation

BACKGROUND

To determine whether peak and time-integrated shear rates independently predict flow-mediated dilation (FMD).

METHODS

Eleven physically active (25 ± 5 years old) male subjects were tested. FMD was defined as the shear rate-diameter relationship. Hierarchical linear modeling was used to estimate brachial artery diameter change with repeated measures of shear rate nested within each subject. Two models were tested: 1) FMD was induced using ischemia-induced hyperemia (2, 4, 6, and 10 minutes); and 2) FMD was induced following transient (ischemia) and steady-state (forearm heating and handgrip exercise) increases in shear rate. For both models we determined whether peak, in addition to time-integrated shear rates, explained a significant portion of variation for diameter change.

RESULTS

Model 1: Time integrated shear rates explained most of the variation for diameter change. However, peak shear rate explained an additional significant portion of variation. Model 2: The transient condition resulted in significantly (p = 0.012) smaller diameter change per shear rate change than the steady-state condition. However, when specifying peak shear rate as a covariate, the difference between conditions became nonsignificant (p = 0.138).

CONCLUSIONS

Peak and time-integrated shear rates independently predict FMD. Future studies using the FMD test should consider both parameters.

Velocity acceleration as a determinant of flow-mediated dilation

Shear stress is the established stimulus for flow-mediated dilation (FMD). In vivo, shear stress is typically estimated using mean blood velocity. However, mean blood velocity may not adequately characterize the shear stimulus. Pulsatile flow results in large shear gradients (velocity acceleration) at the onset of flow. The purpose of this study was to determine the importance of velocity acceleration to FMD. We define FMD as the brachial artery shear rate-diameter slope. Fourteen physically active, young (26 ± 5 years), male subjects were tested. Progressive forearm heating and handgrip exercise elicited steady-state increases in shear rate. FMD was measured prior to and following induced increases in velocity acceleration. Velocity acceleration was increased by inflating a tourniquet around the forearm to 40 mm Hg. Hierarchical linear modeling was used to estimate change in diameter with repeated measures of shear stress nested within each subject. Averaged across conditions, the 40 mm Hg cuff resulted in a 14% increase in velocity acceleration (p = 0.001). FMD was attenuated by 11.0% (p = 0.015) for the acceleration vs. control condition. However, after specifying velocity acceleration as a covariate, FMD was no longer significantly (p = 0.619) different between acceleration and control conditions. This finding suggests that mean blood velocity alone may not adequately characterize the shear stimulus.

Use of ultrasound for non-invasive assessment of flow-mediated dilation

The pathological complications of atherosclerosis, namely heart attacks and strokes, remain the leading cause of mortality in the Western world. Preceding atherosclerosis is endothelial dysfunction. There is therefore interest in the application of non-invasive clinical tools to assess endothelial function. The flow-mediated dilation (FMD) test is the standard tool used to assess endothelial function. Reduced FMD is an early marker of atherosclerosis and has been noted for its capacity to predict future cardiovascular disease events. This review discusses the measurement of endothelial function using ultrasound, with a focus on the FMD technique.

The importance of velocity acceleration to flow-mediated dilation

The validity of the flow-mediated dilation test has been questioned due to the lack of normalization to the primary stimulus, shear stress. Shear stress can be calculated using Poiseuille's law. However, little attention has been given to the most appropriate blood velocity parameter(s) for calculating shear stress. The pulsatile nature of blood flow exposes the endothelial cells to two distinct shear stimuli during the cardiac cycle: a large rate of change in shear at the onset of flow (velocity acceleration), followed by a steady component. The parameter typically entered into the Poiseuille's law equation to determine shear stress is time-averaged blood velocity, with no regard for flow pulsatility. This paper will discuss (1) the limitations of using Posieuille's law to estimate shear stress and (2) the importance of the velocity profile-with emphasis on velocity acceleration-to endothelial function and vascular tone.

Occasional smoking in college: who, what, when and why?

INTRODUCTION

The majority of college students who smoke do so on an occasional basis and generally do not define themselves as smokers. This represents a considerable challenge for public health efforts to prevent escalation of use and to promote cessation. Strengthening such efforts will require further examination of the motivations behind occasional smoking within this vulnerable group.

METHODS

Based within a priori identified content areas, we conducted eight focus groups of occasional smokers (N=53) at two demographically diverse colleges in the southeastern U.S.

RESULTS

Few participants self-identified as a smoker and few had immediate desire to quit. Most identified extrinsic motivations for future quitting, including college graduation and parenthood. Although participants acknowledged smoking-related health risks, they minimized them as being personally irrelevant. Participants highlighted social (i.e., alcohol and other smokers) and stress-related smoking triggers. They also described how they carefully managed the situations in which they would, and would not smoke in order to preserve their identity.

CONCLUSIONS

College students who smoke occasionally appear to engage in impression management, taking effort to shape their personal image to not appear as a smoker. They use smoking mainly as a social engagement tool, but also to alleviate negative emotions. They express minimal desire to quit and believe they are immune to the health risks of smoking. Public health messages should address this common pattern of smoking among young adults differently than regular smoking patterns by highlighting the social, emotional, and health consequences of occasional smoking before nicotine dependence has fully developed.

Evaluation of cuff-induced ischemia in the lower extremity by magnetic resonance oximetry

OBJECTIVES

The aim of this study was to evaluate vascular function in the lower extremities by making direct time-course measurement of oxygen saturation in the femoral/popliteal arteries and veins during cuff-induced reactive hyperemia with magnetic resonance imaging-based oximetry.

BACKGROUND

Magnetic resonance imaging-based oximetry is a new calibration-free technique taking advantage of the paramagnetic nature of blood that depends on the volume fraction of deoxyhemoglobin in red blood cells.

METHODS

We compared post-occlusive blood oxygenation time-course of femoral/popliteal vessels in: 1) young healthy subjects (YH) (n = 10; mean ankle-brachial index [ABI] 1.0 +/- 0.1, mean age 30 +/- 7 years); 2) peripheral arterial disease (PAD) patients (n = 12; mean ABI 0.6 +/- 0.1, mean age 71 +/- 9 years); and 3) age-matched healthy control subjects (AHC) (n = 8; mean ABI 1.1 +/- 0.1, mean age 68 +/- 9 years). Blood oxygenation was quantified at 3.0-T field strength with a field mapping pulse sequence yielding the magnetic susceptibility difference between blood in the vessels and surrounding muscle tissue from which the intravascular blood oxygen saturation is computed as %HbO(2).

RESULTS

Significantly longer washout time (42 +/- 16 s vs. 14 +/- 4 s; p < 0.0001) and lower upslope (0.60 +/- 0.20 %HbO(2)/s vs. 1.32 +/- 0.41 %HbO(2)/s; p = 0.0008) were observed for PAD patients compared with healthy subjects (YH and AHC combined). Furthermore, greater overshoot was observed in YH than in AHC (21 +/- 8 %HbO(2) vs. 10 +/- 5 %HbO(2); p = 0.0116).

CONCLUSIONS

Post-occlusive transient changes in venous blood oxygenation might provide a new measure of vascular competence, which was found to be reduced in subjects with abnormal ABI, manifesting in prolonged recovery during the early phase of hyperemia.

Light and intermittent cigarette smokers: a review (1989-2009)

RATIONALE

Growing proportions of smokers in the USA do not smoke everyday and can be referred to as light and intermittent smokers (LITS). Despite a current prevalence of LITS in the USA estimated at 25-33% of all smokers, a systematic review of the literature on this group of smokers has yet to be written.

OBJECTIVES

The aim of this paper is to review and evaluate research on LITS and to identify, describe and discuss commonalities and differences between LITS and daily smokers.

METHODS

The primary databases used to search for publications were Pub Med (National Library of Medicine) and SCOPUS (Elsevier).

RESULTS

LITS inhale smoke and have post-smoking blood nicotine concentrations that are broadly equivalent to those found in daily smokers. However, LITS differ from daily smokers with regard to cigarette consumption and frequency of cigarette use, sociodemographic and socioeconomic characteristics, motives, personality traits, dependence, withdrawal and craving, response to smoking-related cues, quitting perception, past-smoking status, and initiation.

CONCLUSIONS

In contrast to daily smokers, LITS show few or no signs of dependence as currently defined by DSM-IV criteria, appear to exercise more self-control, seem to be less impulsive, and their smoking experience is primarily associated with positive rather than negative reinforcement. Conclusions drawn from the reviewed literature highlight the multivariate factors that must be taken into account when defining LITS and emphasize the importance of further research on this increasing fraction of smokers. The potential implications of increased LITS prevalence on smoking-related disease risks remain to be thoroughly investigated.