Biomedical subjects

Jack E James

Publications and source records attributed to Jack E James.

11 recordsLinked to original sources

PubMed2006

Hemodynamic profile, compensation deficit, and ambulatory blood pressure.

This study hypothesized that physiologically grounded patterns of hemodynamic profile and compensation deficit would be superior to traditional blood pressure reactivity in the prediction of daily-life blood pressure. Impedance cardiography-derived measures and beat-to-beat blood pressure were monitored continuously in 45 subjects during baseline and four tasks. Ambulatory blood pressure measures were obtained combining data from one work day and one off day. The mediating effects of gender and family history of hypertension were considered. Only gender was significantly associated with hemodynamic profile. Regression analysis indicated that typical reactivity measures failed to predict everyday life blood pressure. After controlling for gender and baseline blood pressure, hemodynamic patterns during specific tasks proved to be strong predictors, overcoming limitations of previous reactivity models in predicting real-life blood pressure.

Adult↗

PubMed2005

Association between hemodynamic profile during laboratory stress and ambulatory pulse pressure.

Hemodynamic responses underlying blood pressure reactivity to laboratory stress are theoretically linked to cardiovascular pathophysiology. The present study investigated whether a vascular response predicted ambulatory pulse pressure, a known risk factor for cardiovascular disease. A new model of hemodynamic profile, previously developed by the authors, was applied to 24-h ambulatory data from 30 female and 34 male healthy young adults. Of these, 40 were monitored during a naturalistic stressor (university examination). For females, hemodynamic profile significantly predicted nighttime systolic blood pressure, and 24-h, day-, and nighttime diastolic blood pressure, but not ambulatory pulse pressure. A vascular or mixed hemodynamic profile significantly predicted 24-h and daytime ambulatory pulse pressure in males. The findings are consistent with theories of pathogenic mechanisms involving vascular changes and suggest that, for males, a vascular or mixed hemodynamic profile measured during laboratory stress may be a risk marker for cardiovascular disease, by its association with ambulatory pulse pressure.

Adult↗

PubMed2005

Effects of caffeine on performance and mood: withdrawal reversal is the most plausible explanation.

RATIONALE: Although it is widely believed that caffeine can enhance human performance and mood, the validity of this belief has been questioned, giving rise to debate. The central question is whether superior performance and mood after caffeine represent net benefits, or whether differences between caffeine and control conditions are due to reversal of adverse withdrawal effects. OBJECTIVES: To provide a focussed review of relevant experimental studies with the aim of clarifying current understanding regarding the effects of caffeine on human performance and mood. METHODS: To avoid the shortcomings of standard placebo-controlled studies, which are ambiguous due to failure to control for the confounding influence of withdrawal reversal, three main experimental approaches have been employed: studies that compare consumers and low/non-consumers, pre-treatment and ad lib consumption studies, and long-term withdrawal studies. RESULTS: Of the three approaches, only long-term withdrawal studies are capable of unambiguously revealing the net effects of caffeine. Overall, there is little evidence of caffeine having beneficial effects on performance or mood under conditions of long-term caffeine use vs abstinence. Although modest acute effects may occur following initial use, tolerance to these effects appears to develop in the context of habitual use of the drug. CONCLUSIONS: Appropriately controlled studies show that the effects of caffeine on performance and mood, widely perceived to be net beneficial psychostimulant effects, are almost wholly attributable to reversal of adverse withdrawal effects associated with short periods of abstinence from the drug.

Affect↗

PubMed2005

Dietary caffeine, performance and mood: enhancing and restorative effects after controlling for withdrawal reversal.

This study aimed to determine whether sustained (i.e. dietary) use of caffeine has net effects on performance and mood compared with sustained abstinence, and whether dietary caffeine restores performance and mood adversely affected by sleep restriction. Participants (n = 96) alternated weekly between ingesting placebo and caffeine (1.75 mg/kg) three times daily for 4 consecutive weeks, while either rested or sleep restricted. Performance involved either a single task requiring sustained vigilance or a varied battery of brief psychomotor and cognitive tasks, and mood was assessed using the Profile of Mood States. Caffeine had no significant net enhancing effects for either performance or mood when participants were rested, and produced no net restorative effects when performance and mood were degraded by sleep restriction.

Adolescent↗

PubMed2004

Effects of dietary caffeine on mood when rested and sleep restricted.

Prolonged use of caffeine can lead to physical dependence evidenced by characteristic withdrawal symptoms during abstinence. Debate exists as to whether mood enhancement by caffeine represents a net effect or merely the restoration of abstinence-induced mood decrements. One aim of this study was to determine the net effects on mood of dietary caffeine compared with prolonged abstinence. In addition, the study aimed to determine whether caffeine restores mood degraded by a non-caffeine source, namely, sleep restriction. A double-blind placebo-controlled cross-over design was employed in which 48 male and female volunteers alternated weekly between ingesting placebo and caffeine (1.75 mg/kg) three times daily for 4 consecutive weeks, while being either rested or sleep restricted. Mood was assessed using a computerized version of the profile of mood states (POMS), giving scores for overall mood and six mood dimensions. Gender had small effects on mood, whereas all mood dimensions were markedly adversely affected by sleep restriction. Caffeine had no significant net enhancing effects on mood when participants were rested, and produced no net restorative effects when mood was degraded by sleep restriction. On the contrary, caffeine-induced decrements in mood were observed during both conditions of rest and sleep restriction.

Adolescent↗

PubMed2004

Hemodynamic effects of dietary caffeine, sleep restriction, and laboratory stress.

This study examined the separate and interactive effects of caffeine, sleep restriction, and task-induced laboratory stress in 96 healthy male and female volunteers. Participants alternated weekly between ingesting placebo and caffeine (1.75 mg/kg) three times daily for 4 consecutive weeks, while being either rested or sleep restricted. Finapres measurements of blood pressure, cardiac output, and total peripheral resistance showed that caffeine produced persistent blood pressure increases with a vascular hemodynamic profile. Sleep restriction produced a pronounced vascular response not associated with appreciable changes in blood pressure, whereas blood pressure increases induced by cognitive activity showed mixed cardiac and vascular responses. The findings suggest that life-long dietary caffeine may contribute significantly to the development of cardiovascular disease.

Adult↗

PubMed2004

The relation between stimulus function and equivalence class formation.

Fifty participants were exposed to a simple discrimination-training procedure during which six S+ functions were established for six arbitrary stimuli, and S- functions were established for a further six stimuli. Following this training, each participant was exposed to one of five conditions. In the S+ condition, participants were exposed to a stimulus equivalence training and testing procedure using only the six S+ stimuli as samples and comparisons. In the S+/S- condition, participants were exposed to the same training and testing sequence as in the S+ condition, the difference being that three S+ and three S- stimuli were used as sample and comparison stimuli, with each set of three corresponding to the trained equivalence relations. In the S+/S- mixed condition, the S+ and S- stimuli were assigned to their roles as samples and comparisons in a quasi-random order. In the S- condition, all six S- stimuli were used. The no-function condition served as a control condition and employed stimuli for which no stimulus-control functions had been established. The results showed that, on average, participants required more testing trials to form equivalence relations when the stimuli involved were functionally similar rather than functionally different. Moreover, participants required more test trials to form equivalence relations when novel arbitrary stimuli, rather than functionally distinct stimuli, were used as samples and comparisons. The speed of acquisition of stimulus equivalence was also related to the number of functionally similar stimuli established before training. These findings indicate a variety of ways in which the emergence of equivalence relations is affected by the functional classes in which the relevant stimuli participate.

Adolescent↗

PubMed2002

A new model of individual differences in hemodynamic profile and blood pressure reactivity.

A quantitative, theory-driven model of hemodynamics was developed, relating reactivity in blood pressure to orthogonal dimensions of "hemodynamic profile" and "compensation deficit," which were derived from the (multiplicative) interaction of cardiac output and total peripheral resistance. A Finapres 2300e was used to estimate blood pressure, cardiac output, and total peripheral resistance in 100 healthy men and women during mental arithmetic and cold pressor tasks on two occasions. Results were consistent with model predictions. As predicted, cardiac output and peripheral resistance reactions were curvilinearly related, and blood pressure reactivity was strongly related to compensation deficit (r = .76-.89). Conversely, the orthogonally defined hemodynamic profile remained independent of blood pressure reactivity (r = .11 or less). The data show that the present model overcomes several difficulties and inconsistencies in previous attempts to obtain an independent measure of hemodynamic profile. The new model could help to elucidate sources of cardiovascular pathogenesis not suggested from the study of blood pressure reactivity alone.

Adolescent↗

PubMed2002

Third-party threats to research integrity in public-private partnerships.

This paper examines threats to scientific integrity posed by possible conflicts of interests that can occur when commercial entities participate in publicly funded research partnerships. Particular attention is given to the activities of the International Life Sciences Institute (ILSI), which presents itself as a society of learned individuals and groups working in the public interest. In reality, ILSI's members largely consist of commercial companies and corporate conglomerates involved in the manufacture of foods, beverages, chemicals and pharmaceuticals. The main conclusion is that conflicts of interest arising from third-party involvement in research partnerships are a threat to scientific integrity. Urgent action is needed by the scientific community to find ways to safeguard against threats to scientific integrity due to undeclared involvement of commercial entities in seemingly independent research and scholarship.

Academies and Institutes↗

PubMed2002

Influence of attention focus and trait anxiety on tolerance of acute pain.

OBJECTIVES: In light of inconsistencies in the reported effects of attention and anxiety on pain tolerance, this study examined the separate and combined effects of attention focus and trait anxiety on tolerance of acute experimental pain. DESIGN: Participants with 'high' and 'low' trait anxiety were assigned to three attention-focus conditions: pain-focused attention, 'undirected' (no experimenter-induced attempts to influence attention focus) and distraction. METHODS: Several indices of autonomic arousal (systolic and diastolic blood pressure, heart rate and EMG) were measured before and during, and several self-report inventories were completed before and after, each of two administrations of the cold pressor test. RESULTS: In general, pain tolerance was greater when participants were distracted and in low- rather than high-anxiety participants. However, attention and anxiety interacted such that low-anxiety participants were most pain tolerant, and high-anxiety participants were least pain tolerant, in the undirected condition. CONCLUSION: The results are consistent with the notion that anxiety fosters attentiveness to possible environmental threats, and might have implications for the clinical management of acute pain.

Journal Article↗

PubMedDate not supplied

Critical review of dietary caffeine and blood pressure: a relationship that should be taken more seriously.

OBJECTIVE: This review aims to determine whether, and to what extent, dietary caffeine may be a risk to cardiovascular health. METHODS: A critical review of the relevant experimental and epidemiologic literature was conducted, with particular reference to studies of caffeine and blood pressure (BP). RESULTS: There is extensive evidence that caffeine at dietary doses increases BP. However, concern that the drug may contribute to cardiovascular disease appears to have been dampened by (1) the belief that habitual use leads to the development of tolerance, and (2) confusion regarding relevant epidemiologic findings. When considered comprehensively, findings from experimental and epidemiologic studies converge to show that BP remains reactive to the pressor effects of caffeine in the diet. Overall, the impact of dietary caffeine on population BP levels is likely to be modest, probably in the region of 4/2 mm Hg. At these levels, however, population studies of BP indicate that caffeine use could account for premature deaths in the region of 14% for coronary heart disease and 20% for stroke. CONCLUSIONS: Current evidence supports the conclusion that the BP-elevating effects of dietary caffeine may be contributing appreciably to population levels of cardiovascular mortality and morbidity. Accordingly, strategies for encouraging reduced dietary levels of caffeine deserve serious consideration.

Adenosine↗