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PubMed2004

Changes in arterial stiffness and wave reflection with advancing age in healthy men and women: the Framingham Heart Study.

With advancing age, arterial stiffness and wave reflections increase and elevate systolic and pulse pressures. An elevated central pulse pressure is generally ascribed to increased wave reflection and portends an unfavorable prognosis. Using arterial tonometry, we evaluated central (carotid-femoral) and peripheral (carotid-brachial) pulse wave velocity, amplitudes of forward and reflected pressure waves, and augmentation index in 188 men and 333 women in the Framingham Heart Study offspring cohort who were free of clinical cardiovascular disease, hypertension, diabetes, smoking within the past 12 months, dyslipidemia, and obesity. In multivariable linear regression models, advancing age was the predominant correlate of higher carotid-femoral pulse wave velocity; other correlates were higher mean arterial pressure, heart rate, and triglycerides and walk test before tonometry (model R2=0.512, P<0.001). A similar model was obtained for carotid-brachial pulse wave velocity (model R2=0.227, P<0.001), although the increase with advancing age was smaller. Owing to different relations of age to central and peripheral stiffness measures, carotid-femoral pulse wave velocity was lower than carotid-brachial pulse wave velocity before age 50 years but exceeded it thereafter, leading to reversal of the normal central-to-peripheral arterial stiffness gradient. In this healthy cohort with a minimal burden of cardiovascular disease risk factors, an age-related increase in aortic stiffness, as compared with peripheral arterial stiffness, was associated with increasing forward wave amplitude and pulse pressure and reversal of the arterial stiffness gradient. This phenomenon may facilitate forward transmission of potentially deleterious pressure pulsations into the periphery.

Adult↗

PubMed1989

Arterial dilation and reduced wave reflection. Benefit of dilevalol in hypertension.

We compared dilevalol (an isomer of labetalol), 200-400 mg daily, against atenolol, 50-100 mg daily, in a double-blind, crossover, placebo-controlled trial with respect to effects on arterial distensibility (measured as pulse wave velocity [PWV]) and wave reflection (assessed from carotid pressure wave contour). Twelve patients of mean age 58 years (range 44-73 years) with essential hypertension (supine diastolic blood pressure 95-114 mm Hg) took active therapy for 12 weeks, separated by a 2-4 week placebo period. Carotid pressure waveforms were recorded noninvasively by applanation tonometry with a Millar micromanometer-tipped probe. PWV was measured between carotid and femoral arteries (aortic PWV), carotid and radial arteries (arm PWV), and femoral and pedal arteries (leg PWV). Early wave reflection was calculated from the ratio of the height of the peak of the carotid wave above its shoulder to the pulse pressure and was expressed as an augmentation index. Both drugs were equally effective in reducing brachial sphygmomanometric pressure and PWV in all three regions (active vs. placebo, p less than 0.001), but there was no significant difference between the two active therapies. However, the augmentation index (averaged during the treatment period) was significantly lower with dilevalol (19%) than with atenolol (28%, p less than 0.01), corresponding to a greater decrease of 5-8 mm Hg in carotid systolic pressure compared with the brachial artery. Although both drugs were equally effective in reducing arterial distensibility, the vasodilating action of dilevalol gave added benefit in reducing wave reflection, presumably through its vasodilatory effect on peripheral conduit arteries.

Adult↗

PubMed1995

Short- and long-term effects of antihypertensive drugs on arterial reflections, compliance, and impedance.

This article reviews our work on the effects of different classes of antihypertensive agents on the hemodynamic alterations in essential human hypertension. Short-term studies were done during cardiac catheterization in young normotensive subjects (mean age, 33 years; range, 19 to 40) and several different age-matched (range, 25 to 53 years) groups of patients with essential hypertension. Aortic impedance, resistance, wave reflections, and compliance were calculated from high-fidelity recordings of ascending aortic pressure and flow signals during baseline and after nitroprusside, propranolol followed by phentolamine, phentolamine, captopril, and nifedipine, respectively, at doses sufficient to normalize blood pressure in each hypertensive group. Propranolol exacerbated all the hemodynamic parameters; these effects were only partially overcome by phentolamine. Among the other agents only phentolamine did not completely normalize compliance, and only captopril did not completely normalize wave reflections. The long-term study was a randomized, double-blind comparison of fosinopril and atenolol in 79 normotensive subjects and 79 essential hypertensive patients. Baseline 24-hour ambulatory blood pressures and carotid artery tonometry to index wave reflections were performed in all subjects and in hypertensive patients after 8 weeks of therapy. Both fosinopril and atenolol normalized blood pressure and lowered the elevated augmentation index, but fosinopril had a significantly larger effect than atenolol. Both short- and long-term beta-blockade did not have as beneficial an effect as the other agents. Thus, the differing hemodynamic effects of the various classes of antihypertensive agents might be a consideration in the choice of therapy.

Adult↗

PubMed2001

Arterial wave reflections and survival in end-stage renal failure.

The increased effect of arterial wave reflections on central arteries like the common carotid artery seen in end-stage renal failure (ESRF) patients favors myocardial hypertrophy and oxygen consumption and alters coronary blood flow distribution. Nevertheless, the impact of wave reflection on the outcome and end points such as mortality remains to be demonstrated. One hundred eighty ESRF patients (age, 54+/-16 years) were monitored for 52+/-36 months (mean+/-SD). Seventy deaths, including 40 cardiovascular (CV) and 30 non-CV events, occurred. At entry, patients, in addition to standard clinical and biochemical analyses, underwent aortic pulse wave velocity measurement and determination of arterial wave reflexion by applanation tonometry on the common carotid artery that was expressed as augmentation index. Cox analyses demonstrated that predictors of all-cause and CV mortality were age, aortic pulse wave velocity, low diastolic blood pressure, preexisting CV disease, and increased augmentation index, whereas the prescription of an ACE inhibitor had a favorable effect on survival. After adjustment for all confounding factors, the risk ratio for each 10% increase in augmentation index was 1.51 (95% confidence interval, 1.23 to 1.86; P<0.0001) for all-cause mortality and 1.48 (95% confidence interval, 1.16 to 1.90; P<0.0001) for CV mortality. These results provide the first direct evidence that in ESRF patients increased effect of arterial wave reflections is an independent predictor of all-cause and CV mortality.

Adolescent↗

PubMed1981

Excitation, conduction, and reflection of impulses in isolated bovine and serum cardiac purkinje fibers.

When an impulse arrives at an area of impaired conductivity, a slowly rising electrotonic potential may bring the distal tissue to threshold after a delay imposed by the passive electrical properties of the system and by the time-dependent changes of these properties during diastole. This phenomenon can be demonstrated in Purkinje strands in which an area of depressed conductivity has been induced by the impedance of a sucrose gap and can be mimicked by the application of relatively long current pulses of low amplitude. The functional refractory period, defined as the shortest interval between two distal responses both propagated across the gap, was determined by the application of premature stimuli at progressively earlier intervals. The time course of the recovery of excitability as well as the conduction intervals could be varied almost at will by manipulating the electric impedance between proximal and distal ends of the fiber. When the time of activation of the distal end across the gap exceeded the absolute refractory period of the proximal segment, the impulse reflected back as a closely coupled premature beat. Time-dependent changes in the passive electrical properties of the depressed segment may set the conditions for reflection. The results suggest the possibility of reflection as a mechanism for premature beats and demonstrate obligatory shifts in the patterns of premature reentrant activity accompanying changes in basic cycle length. These experiments provide important clues for the distinction between reentrant and parasystolic mechanisms.

Action Potentials↗

PubMed1997

Increased common carotid intima-media thickness. Adaptive response or a reflection of atherosclerosis? Findings from the Rotterdam Study.

BACKGROUND AND PURPOSE: Carotid intima-media thickness (IMT) measurements are used widely to study atherosclerosis. Some have suggested that an increased IMT reflects a nonatherosclerotic adaptive response to changes in shear stress and tensile stress. This stems from the hypothesis that changes in shear stress and subsequently in lumen diameter are followed by changes in IMT to keep tensile stress constant. We studied the relation of common carotid IMT to common carotid end-diastolic lumen diameter and tensile stress, as approximated by mean arterial pressure (lumen diameter/IMT)]. METHODS: A cross-sectional analysis was performed with data obtained from the first 1715 participants in the Rotterdam Study, a population-based cohort study among 7983 subjects aged 55 years and over who underwent ultrasonographic examination of the carotid arteries. End-diastolic lumen diameter and IMT of the common carotid arteries were evaluated and quantified. RESULTS: With increasing IMT, inner and outer lumen diameters increased gradually, and beyond an IMT of 1.10 mm, the inner lumen diameter decreased. Tensile stress increased with increasing lumen diameter instead of being constant. The lumen-to-IMT ratio was constant across levels of mean arterial pressure. CONCLUSIONS: Our findings are compatible with the view that at lower degrees of IMT, the thickening appears to reflect an equilibrium state in which the effects of pressure and flow on the arteries are in balance, given a characteristic relation between shear stress and local transmural pressure. Beyond a certain level, IMT more likely may represent atherosclerosis. Regardless of whether common carotid IMT reflects local atherosclerosis, it may still serve as a graded marker for cardiovascular risk.

Adaptation, Physiological↗

PubMed2005

Heritability and a genome-wide linkage scan for arterial stiffness, wave reflection, and mean arterial pressure: the Framingham Heart Study.

BACKGROUND: Arterial stiffness and mean arterial pressure variably contribute to systolic hypertension and increased cardiovascular risk. However, few prior community-based studies have evaluated the genetics of arterial stiffness and separate mean and pulsatile components of blood pressure. METHODS AND RESULTS: Using arterial tonometry, we evaluated heritability and linkage of forward and reflected wave amplitude, mean arterial pressure, and carotid-femoral pulse wave velocity (CFPWV) in 1480 participants representing 817 pedigrees in the Framingham Study offspring cohort. In 204 families with tonometry data, a genome-wide scan was performed with microsatellite markers that covered the genome at 10-cM intervals. Heritability estimates were moderate for reflected wave amplitude (h2=0.48), forward wave amplitude (h2=0.21), CFPWV (h2=0.40), and mean arterial pressure (h2=0.33). Variance components linkage analysis identified 2 regions of linkage for reflected wave amplitude: chromosome 4 at 181 cM (logarithm of odds [LOD]=4.93, permuted P=0.002) and chromosome 8 at 33 cM (LOD=3.27, permuted P=0.058). There was 1 region of linkage for forward wave amplitude on chromosome 7 at 174 cM (LOD=2.88, permuted P=0.017). There were several regions of suggestive linkage for CFPWV: chromosome 2 at 94 cM (LOD=2.46), chromosome 7 at 29 cM (LOD=2.50), chromosome 13 at 108 cm (LOD=2.10), and chromosome 15 at 108 cM (LOD=2.48). There was 1 region of suggestive linkage for mean arterial pressure on chromosome 1 at 192 cM (LOD=2.18). CONCLUSIONS: Arterial stiffness measures and mean and pulsatile components of blood pressure are heritable and appear to have genetic determinants that may be linked to separate genetic loci in humans.

Aged↗

PubMed2001

Noninvasive determination of spatially resolved and time-resolved tissue perfusion in humans during nitric oxide inhibition and inhalation by use of a visible-reflectance hyperspectral imaging technique.

BACKGROUND: Vascular disease is commonly associated with reduced local synthesis of nitric oxide (NO) and impaired tissue perfusion. We introduce a novel noninvasive, visible-reflectance, hyperspectral imaging technique for quantifying the percentage of hemoglobin existing as oxyhemoglobin (HbO(2)) as an index of skin tissue perfusion. METHODS AND RESULTS: To simulate vascular endothelial dysfunction, N(G)-monomethyl-L-arginine (L-NMMA) was infused into the brachial arteries of 9 healthy subjects for 5 minutes to inhibit forearm NO synthesis, first with the subject breathing room air and subsequently during NO inhalation at 80 ppm for 1 hour. Blood flow was measured by venous occlusion plethysmography, and the percentage of HbO(2) perfusing skin tissue was imaged noninvasively with a visible-reflectance hyperspectral technique. L-NMMA reduced blood flow by 31.7+/-4.9% and percentage of HbO(2) by 6.5+/-0.1 (P=0.002 and P<0.001 versus baseline, respectively). With subjects inhaling NO, blood flow fell during L-NMMA infusion by only 10.9+/-7.3%, and the percentage of HbO(2) decreased by 3.6+/-0.1 (P=0.007 and P<0.001, respectively, versus room air L-NMMA responses). CONCLUSIONS: Visible-reflectance hyperspectral imaging demonstrates (1) a significant decline in the percentage of HbO(2) in skin tissue when blood flow is reduced after inhibition of forearm NO synthesis and (2) restoration of HbO(2) toward basal values with improved blood flow during inhalation of NO. This imaging method may provide an effective approach for time-resolved noninvasive monitoring of skin hemoglobin oxygen saturation and assessment of responses to therapeutic interventions in patients with vascular disease.

Administration, Inhalation↗

PubMed2001

Improvement in blood pressure, arterial stiffness and wave reflections with a very-low-dose perindopril/indapamide combination in hypertensive patient: a comparison with atenolol.

International guidelines recommend that antihypertensive drug therapy should normalize not only diastolic (DBP) but also systolic blood pressure (SBP). Therapeutic trials based on cardiovascular mortality have recently shown that SBP reduction requires normalization of both large artery stiffness and wave reflections. The aim of the present study was to compare the antihypertensive effects of the very-low-dose combination indapamide (0.625 mg) and perindopril (2 mg) (Per/Ind) with the beta-blocking agent atenolol (50 mg) to determine whether Per/Ind decreases SBP and pulse pressure (PP) more than does atenolol and, if so, whether this decrease is predominantly due to reduction of aortic pulse wave velocity (PWV) (automatic measurements) and reduction of wave reflections (pulse wave analysis, applanation tonometry). In a double-blind randomized study, 471 patients with essential hypertension were followed for 12 months. For the same DBP reduction, Per/Ind decreased brachial SBP (-6.02 mm Hg; 95% confidence interval, -8.90 to -3.14) and PP (-5.57; 95% confidence interval, -7.70 to -3.44) significantly more than did atenolol. This difference was significantly more pronounced for the carotid artery than for the brachial artery. Whereas the 2 antihypertensive agents decreased PWV to a similar degree, only Per/Ind significantly attenuated carotid wave reflections, resulting in a selective decrease in SBP and PP. The very-low-dose combination Per/Ind normalizes SBP, PP, and arterial function to a significantly larger extent than does atenolol, a hemodynamic profile that is known to improve survival in hypertensive populations with high cardiovascular risk.

Adolescent↗

PubMed1989

Maximal relaxation rates of esophageal, nose, and mouth pressures during a sniff reflect inspiratory muscle fatigue.

Maximal relaxation rate (MRR, % pressure fall/10 msec) of the inspiratory muscles is reduced with fatigue. We have investigated whether MRR of esophageal pressure (Pes) generated by voluntary sniffs is decreased by fatigue, and whether sniff nasopharyngeal (Pnp) and mouth (Pmo) MRR reflect these changes. In 10 normal subjects, control MRR of sniff Pes correlated closely to Pnp MRR (r = 0.977, p less than 0.001) and Pmo MRR (r = 0.947, p less than 0.001). To produce inspiratory muscle fatigue, four highly motivated subjects breathed to exhaustion (3 to 6 min) through a high inspiratory resistance. MRR was determined from 10 sniffs for Pes, Pnp, and Pmo before fatigue, and at intervals up to 10 min after fatigue. The subjects showed a mean decrease in sniff Pes MRR of 33% (range, 20 to 42) immediately after fatigue, which returned exponentially to control values within 3 to 4 min. The mean changes in Pes MRR were reflected by similar changes in Pnp MRR, 32% (range, 18 to 43) and Pmo MRR, 33% (range, 21 to 42). Studies were repeated in the four subjects with closely similar results. We conclude that fatigue of the inspiratory muscles reduces MRR of sniff Pes, and that this is reflected in Pnp and Pmo. Sniff Pes, Pnp, and Pmo MRR measurements may provide a useful method for detecting and monitoring fatigue; Pnp and Pmo have the advantage of being less invasive.

Adult↗

PubMed2003

Retinal spectral sensitivity, fur coloration, and urine reflectance in the genus octodon (rodentia): implications for visual ecology.

PURPOSE: To determine the eye's spectral sensitivity in three species of the genus Octodon (order Rodentia; infraorder Caviomorpha), O. degus, O. bridgesi, and O. lunatus, as well as the spectral properties of the animals' fur and urine and of objects in their habitat. The genus is endemic in Chile and contains species with different habitats and circadian patterns (diurnal versus nocturnal). METHODS: The electroretinogram (ERG) was used to record scotopic and photopic spectral sensitivity. The reflectance of ventral and dorsal body parts, urine, and other objects from the natural microhabitat were measured with a fiber-optic spectrometer. RESULTS: In scotopic conditions, the maxima of sensitivity (lambda(max)) were at 505.7 +/- 7.7 nm in O. degus, 501 +/- 7.4 nm in O. bridgesi, and 510.1 +/- 7.4 nm in O. lunatus, representing the rod mechanism. In photopic conditions, only the diurnal species O. degus (common degu) was studied. The degu's photopic sensitivity had a lambda(max) at 500.6 +/- 1.2 nm and contained two cone mechanisms with lambda(max) at 500 nm (green, medium-wavelength-sensitive [M] cones) and approximately 360 nm (ultraviolet, short-wavelength-sensitive [S] cones). In all three Octodon species, dorsal body parts were more cryptically colored than ventral ones, and ventral body parts had a significant UV reflectance. The fresh urine of O. degus, used for scent marking in various behavioral patterns, was also high in UV reflectance. CONCLUSIONS: It is suggested that territorial urine marks are visual as well as pheromone cues for UV-sensitive species and hence may have favored the evolution of UV-cones in rodents.

Animal Communication↗

PubMed1988

Study on reaction of subpapillary venous plexus in patients with arterial occlusive diseases of lower extremity by reflective spectrophotometry.

The reactions of the subpapillary venous plexus were observed by analyzed fractional blood volume of tissue (Vb) in patients with arterial occlusive diseases, Fontaine's stage I-II, using the reflective spectrophotometer. The sole skin of 11 normal subjects, 17 patients with arteriosclerosis obliterans (ASO), and 14 patients with thromboangiitis obliterans (TAO) were scanned by the light reflectance of four specially selected wavelengths, including isobestic points (586 and 569 nm) and peaks in the spectra of oxyhemoglobin and deoxyhemoglobin (577 and 560 nm) in referring to time. Sampling area was the subpapillary venous plexus histologically because the depth for receiving reflectance is about 1.0 mm from the sole skin surface. One series observations was divided into five steps depending on the modes of combination of the applied pressure to ankle cuff and tilting. The Kubelka-Munk equation was utilized to calculate blood volume (Vb). It is concluded that the patients with ASO might have a dysfunction, not of the subpapillary venous plexus, but of the venular valve, whereas patients with TAO might have a dysfunction of both the subpapillary venous plexus and venular valve.

Adult↗

PubMed2003

Reflections on power and justice in enabling occupation.

BACKGROUND: This descriptive paper offers reflections on power and justice associated with occupational therapy's client-centred practice, now described as the practice of enabling occupation. Framed as a contribution to the sociology of professions, the questions addressed are: How do power and justice work in occupational therapy today? What vision of power and justice guides the profession in implementing the client-centred practice of enabling occupation? METHOD: The paper opens with an overview of the analytic framework for reflections. Two sources for reflections are highlighted: the development of the Canadian guidelines and, client/consumer and occupational therapy perspectives. To illustrate the discussion of power and justice, two contrasting diagrams are presented, one on late 20th century power relations and the other on potential power relations. RESULTS: Recommendations for research, education, practice, and guidelines development are offered prior to a conclusion that acknowledges the dissonance facing occupational therapists who struggle to focus on occupations in client-centred practice. PRACTICE IMPLICATIONS: The paper offers insights and strategies for addressing power and justice as issues in implementing the client-centred practice of enabling occupation. The analysis may be used in raising awareness and guiding the strategic development of institutional change toward social inclusion and enabling occupation.

Canada↗

PubMed2005

Reflection as a means to foster client-centred practice.

BACKGROUND: Client-centred practice embraces important concepts about partnership and justice that promote client participation in meaningful occupations. It is important to understand how occupational therapists can engage in and continue to develop client-centred practice within the constraints of everyday settings. PURPOSE AND METHODS: An action research study was undertaken by a group of four occupational therapists to describe insights gained, and to show the effectiveness of participation in reflective education to help foster client-centred practice. RESULTS: The six main insights generated by the group involve: congruence, understanding the potential, environmental factors, personal factors, expectations, and lifelong learning. PRACTICE IMPLICATIONS: Although actual change to daily practice was limited, group members felt the reflective group discussion provided them with a launch pad to start a journey toward more client-centred practice. This may be the key to moving beyond simply changing the face and language of occupational therapy practice toward a deeper understanding and implementation of client-centred practice to improve client outcomes. Suggestions are provided for implementing reflection to help continue to develop your own practice.

Biomedical Research↗

PubMed1983

Canadian Journal of Occupational Therapy: a reflection of professional growth.

The Canadian Journal of Occupational therapy (CJOT) is the only Canadian refereed professional publication reflecting the views and professional development of occupational therapists in Canada. A study of all issues of CJOT published during three five-year periods was carried out to see if CJOT could be said to be improving in terms of reflecting professional trends. Some areas examined were quantity of articles, type of articles, references, authors and citations. It was found that although CJOT did reflect professional growth in many areas, there were a number of areas needing improvement before CJOT could be considered to be the primary professional publication for occupational therapists in Canada.

Canada↗

PubMed1999

Accuracy of glucose reflectance testing for detecting hypoglycemia in term newborns.

Glucose concentrations of 248 newborns at 1 and 3 hours of age were determined at the bedside by means of the Accu-Chek III Reflectance meter and in the laboratory by means of the Vitros 750 analyzer. Hypoglycemia being defined as a glucose concentration less than 40 mg/dL, the reflectance meter had a sensitivity of 0.757 and a specificity of 0.876 at 1 hour and 0.975 at 3 hours. The imprecision of the reflectance meter at 1 hour eliminated it as a routine testing method.

Gestational Age↗

PubMed1984

Effects of backing reflectance and mold size on polymerization of photo-activated composite resin.

The in vitro depth of cure of a visible-light-activated microfilled composite, as influenced by backing reflectance and mold size, was investigated using microhardness measurements. More extensive polymerization was obtained with higher values of backing reflectance. Mold size larger than the cross-sectional area of the photo-activating beam also increased the degree of polymerization. Backing reflectance and mold size are influential factors and need to be defined in depth-of-cure evaluations if in vitro measurements are to be valid predictors of clinical performance.

Chemical Phenomena↗

PubMed2000

Do clinical practice guidelines reflect research evidence?

OBJECTIVES: To examine whether existing clinical practice guidelines (CPGs) for cholesterol testing reflect research evidence and hence may control or reduce costs while maintaining or improving the quality of care. METHODS: A systematic search for published and unpublished cholesterol testing CPGs and independent critical appraisal of the CPGs by two researchers using a standard checklist. RESULTS: In four of the five CPGs analysed, the link between the research evidence and the recommendations was not maintained. The appraisal, local experience and the literature all suggest that panel composition is an important explanation, in that the greater the involvement of clinical experts in the development process of the CPGs, the less the recommendations reflected the research evidence. Even though their participation is important for CPG uptake, clinical expert panels appear to have difficulty limiting CPGs to research-based recommendations. CONCLUSIONS: Existing cholesterol testing CPGs are unlikely to improve the quality of care while controlling or reducing costs. The problem lies not with guideline implementation but with the guidelines themselves. It is unclear how best to ensure that recommendations reflect research evidence but this is likely to require significant and progressive changes to the current guideline development process, including a redefinition of the clinical experts' role.

Adult↗