Low-grade systemic inflammation and the workplace.

BACKGROUND: Psychosocial and physical stressors can elicit the stress response, co-ordinated by interactions between neuroendocrine and inflammatory processes. The central role of the immune system, specifically low-grade systemic inflammation, is sometimes overlooked in work-related stress research. OBJECTIVE: To review evidence that work-related psychosocial and physical stressors can stimulate a low-grade systemic inflammation which, through interactions with the neurohormonal systems, may impact on the well-being and productivity of workers. METHODS: Literature searches were performed by databases and by hand. Databases used included Interface - EBSCOhost Research Databases; PsycINFO; Academic Search Complete; Africa-Wide Information; CINAHL; E-Journals; MEDLINE and PsycARTICLES. RESULTS: Psychosocial stressors, infections, poor indoor air quality, musculoskeletal injuries and chemicals can stimulate a low-grade systemic inflammation that may adversely affect workers' mental and physical health, as well as productivity. The psychological and physical effects caused by infection-induced inflammation are generally referred to as sickness behaviour and those caused by poor indoor air quality as sick building syndrome. CONCLUSIONS: Stressor-induced low-grade systemic inflammation can be a causal factor in the physical and behavioural symptoms of work-related stress. It is therefore important that those involved with the health of workers be cognisant of inappropriate or chronic low-grade inflammation as a potential health hazard.

Pellagra in South Africa from 1897 to 2019: a scoping review.

OBJECTIVE: Pellagra is a nutritional deficiency disease associated with niacin (vitamin B3) deficiency. The history of pellagra is well documented for Europe and the USA, but less is known about the prevalence in sub-Saharan African countries. This study documents the history of pellagra in South Africa, as diagnosed based on dermatological symptoms. DESIGN: Scoping review of information from scientific databases, library archives, other archives and record services and from Statistics South Africa. SETTING: South Africa, 1897-2019. PARTICIPANTS: South African. RESULTS: Pellagra was first officially recorded in South Africa in 1906, but there are earlier indications of the disease. The prevalence of pellagra peaked after it was all but eradicated in the USA and Europe. Pellagra was never as prevalent in South Africa as in Europe, the USA and Egypt, where special hospitals for pellagrins were established. However, studies on urinary excretion of metabolites conducted in 1960s and 1970s suggested a high prevalence of subclinical (sub-pellagra) niacin deficiency, especially in previously disadvantaged Black populations. As in Europe and the USA, pellagra was associated with poverty and an overdependence on maize as staple food. Malnutrition was the main cause of the disease, but alcohol abuse might have been a contributing factor. In South Africa, reports of pellagra had declined by the late 1980s/early 1990s and hardly any cases were reported by the year 2000. CONCLUSIONS: Although pellagra, diagnosed based on dermatological symptoms, appears to be largely eradicated in South Africa, it does not rule out the potential for subclinical niacin deficiency.

Physical exercise and the patient with schizophrenia.

BACKGROUND: Schizophrenia is a severe mental disorder with profound effects on a person's life. In addition to the psychiatric symptoms, patients with schizophrenia generally have multiple somatic comorbidities, such as cardiovascular and metabolic disorders. The general practitioner (GP) is of key importance for the patient's continuous care and holistic wellbeing. OBJECTIVE: The aim of this article is to emphasise the role of GPs in embracing physical exercise as add-on treatment to antipsychotic medications, and to illustrate the value of exercise for people with schizophrenia by summarising the effects on the psychiatric symptoms, neuroanatomical and neurochemical characteristics, and general physiological and psychological health. DISCUSSION: Physical exercise can lead to improvements in positive, negative and cognitive symptoms, as well as in somatic comorbidities, global functioning and quality of life. Physical exercise can be a valuable add-on intervention for people with schizophrenia. The GP is essential for prescribing and following up on exercise tailored for the individual.

Heart Rate Variability and Academic Performance of First-Year University Students.

BACKGROUND: Heart rate variability (HRV) measures have been shown to be positively associated with cognitive processing, while a positive association between cognitive processing and academic performance has been demonstrated. OBJECTIVES: To determine whether resting HRV or HRV marker response to either a cognitive or an orthostatic challenge is significantly associated with a first-year university student's academic performance. METHOD: HRV markers used in the study included total power (TP) as a measure of overall HRV and the root mean square of successive differences (RMSSD) as a measure of parasympathetic influence on the heart. Academic performance was determined by standardized general mean scores. RESULTS: Greater supine overall HRV (TP) was significantly associated with greater academic performance predominantly in females. Vagal (RMSSD) measures were not shown to be associated with academic performance. CONCLUSIONS: This, to our knowledge, is the first study to show that overall HRV has a significant positive association with academic performance of a first-year university student.

Validity of Commonly Used Heart Rate Variability Markers of Autonomic Nervous System Function.

BACKGROUND: Despite strong reservations regarding the validity of a number of heart rate variability (HRV) measures, these are still being used in recent studies. AIMS: We aimed to compare the reactivity of ostensible sympathetic HRV markers (low and very low frequency [LF and VLF]) to that of electrodermal activity (EDA), an exclusively sympathetic marker, in response to cognitive and orthostatic stress, investigate the possibility of LF as a vagal-mediated marker of baroreflex modulation, and compare the ability of HRV markers of parasympathetic function (root mean square of successive differences [RMSSD] and high frequency [HF]) to quantify vagal reactivity to cognitive and orthostatic stress. RESULTS: None of the purported sympathetic HRV markers displayed a reactivity that correlated with electrodermal reactivity. LF (ms2) reactivity correlated with the reactivity of both RMSSD and HF during baroreflex modulation. RMSSD and HF indexed the reactivity of the parasympathetic nervous system under conditions of normal breathing; however, RMSSD performed better as a marker of vagal activity when the task required breathing changes. CONCLUSIONS: Neither LF (in ms2 or normalized units [nu]) nor VLF represent cardiac sympathetic modulation of the heart. LF (ms2) may reflect vagally mediated baroreflex cardiac effects. HRV linear analysis therefore appears to be restricted to the determination of vagal influences on heart rate. With regard to HRV parasympathetic markers, this study supports the suggestion that HRV frequency domain analyses, such as HF, should not be used as an index of vagal activity in study tasks where verbal responses are required, as these responses may induce respiratory changes great enough to distort HF power.

Comparison between plasma neopterin and the urine neopterin:creatinine ratio as inflammatory biomarkers.

BACKGROUND: Neopterin, a product of cell-mediated immunity, is a non-specific biomarker of inflammation. Plasma/serum is generally the body fluid of choice for neopterin assessment, but urine is often used as it does away with venepuncture. Analysis of urine neopterin is based on collection of a single urine sample and expressed as µmol neopterin/mol creatinine. OBJECTIVES: To examine published correlations between plasma neopterin levels and urine neopterin:creatinine ratios and to determine whether they are in diagnostic agreement. METHODS: Literature search was performed by databases and by hand. Databases included Academic Search Complete; Africa-Wide Information; AHFS Consumer Medication Information; eBook Collection (EBSCOhost); Family & Society Studies Worldwide; MasterFILE Premier; MEDLINE; TOC Premier. RESULTS: Positive correlations of varying statistical significance generally exist between plasma neopterin and urine neopterin: creatinine ratios. With a decline in renal clearance, plasma neopterin over-estimates inflammatory activity. With immune-complex renal disease, urine neopterin:creatinine ratios over-estimate systemic inflammation. The two biomarkers can differ in diagnostic validity. CONCLUSION: Correlations between plasma neopterin and urine neopterin:creatinine ratios suggest both as suitable biomarkers. However, since correlations reflect equality of means and not individual values, significant correlations, do not necessarily imply diagnostic agreement. Therefore, plasma and urine cannot summarily be assumed interchangeable for diagnostic/prognostic purposes.

A case study of two adolescent-parent pairs describing the association between vagal tone and social-emotional adjustment during a Positive Cognitive Behaviour Therapy Programme.

OBJECTIVE: A case study describing the association between vagal tone and social-emotional adaptation in two distressed adolescent-parent (A-P) pairs during a Positive Cognitive Behaviour Therapy Programme (P-CBTP). METHODS: Two A-P pairs completed a P-CBTP with pre- and post-intervention biosocial-emotional assessments; weekly training sessions over 7 weeks to develop individual strengths, new adaptive cognitions, positive discipline skills, optimism and knowledge on age-appropriate developmental expressions; augmented by moderate physical activity. Resting vagal tone and vagal reactivity were assessed by time-domain measures of vagal activity (RMSSD). RESULTS: Social-emotional adjustment improved in all A-P pairs. Resting vagal tone increased over the intervention period, from low-to-low-normal towards average-for-normal in three subjects. The fourth individual had excessive pre-intervention resting vagal tone that declined in the direction of normal over the intervention period. Vagal reactivity in response to orthostatic stress remained the same pre- to post-intervention. CONCLUSIONS: Changes in resting vagal tone demonstrated improvements in psychological functioning in all four subjects over the period of intervention. Results supported the view of the association between vagal tone and mental health not being an absolute positive relationship, but that low, as well as excessive, vagal tone may be maladaptive. Indications are that the same may apply to vagal reactivity to psychological stress. More studies need to examine the association between resting vagal tone and emotion regulation in A-P relationships during P-CBTP, keeping in mind that a linear relationship cannot summarily be expected in population studies.

Allostatic load and heart rate variability as health risk indicators.

BACKGROUND: Uncertainty often exists about the comparability of results obtained by different health risk indicator systems. OBJECTIVES: To compare two health risk indicator systems, i.e, allostatic load and heart rate variability (HRV). Additionally, to investigate the feasibility of inclusion of HRV indicators into allostatic load assessments and which HRV indicators are best to introduce. METHODS: Allostatic loads were calculated based on blood pressure, waist-to-hip ratio, BMI, cholesterol, HDL-C, LDL-C, CRP, albumin, glycosylated haemoglobin, blood glucose and cortisol excretion. Allostatic load scores were compared to HRV results obtained by frequency domain, time domain and Poincaré analyses. RESULTS: Negative correlations were found between allostatic loads and total HRV, for all periods and all HRV analytical techniques (r=-0.67, p=0.0001 to r=-0.435, p=0.035), and between allostatic loads and vagal measures of HRV for supine (r=-0.592, p=0.001 to r=-0.584, p=0.001) and the first 5 minutes standing (r=-0.443, p=0.021 to r=-0.407, p=0.035), with all HRV techniques. Heart rate responses declined with increases in allostatic loads. CONCLUSION: HRV and allostatic load scores give comparable results as health risk indicators. Baseline total HRV and vagal, rather than sympathetic, measures of HRV should be introduced into allostatic load assessments. Results are in line with the concept of vagal tone as a regulator of allostatic systems. Inclusion of heart rate responses to orthostatic stress, into allostatic load assessments, warrants further investigation.

Cynicism as subscale of burnout.

BACKGROUND: Cynicism, as a personality trait, has adverse effects on health. The question was asked whether cynical attitudes that develop due to work-related stress correlate with stress levels and whether it has a negative influence on health. OBJECTIVES: To investigate associations of the cynicism subscale scores of the Maslach Burnout Inventory-General Survey (MBI-GS) with levels of stress, anxiety, questionnaire-based physical health and with a number of physiological health risk indicators. METHODS: Cynicism, anxiety, questionnaire-based physical health scores, as well as allostatic load, heart rate variability and C-reactive protein, were assessed in 27 males working between 40 and 80 irregular hours per week. RESULTS: Cynicism scores related to stress levels (r = 0.411, p = 0.030). Effects of work-related cynicism on physical health were suggested by negative associations with questionnaire-based scores on physical health (r = -0.383, p = 0.044) and heart rate variability indicators (r = -0.379, p = 0.047 to r = -0.496, p = 0.007), and by positive associations with anxiety levels (r = 0.408, p = 0.031), heart rate (r = 0.449, p = 0.017), BMI (r = 0.426, p = 0.024) allostatic load (r = 0.360, p = 0.065) and levels of the inflammatory marker C-reactive protein (r = 0.407, p = 0.035). CONCLUSIONS: Cynicism, as reflected by the MBI-GS, increases with increased stress levels and could contribute to the decline in the health reported for burnout.

Tryptophan depletion in context of the inflammatory and general nutritional status of a low-income South African HIV-infected population.

BACKGROUND: The essential amino acid tryptophan cannot be synthesised in the body and must be acquired through dietary intake. Oxidation of tryptophan, due to immune induction of the enzyme indoleamine 2,3-dioxygenase (IDO), is considered to be the main cause of tryptophan depletion in HIV infection and AIDS. We examined plasma tryptophan levels in a low-income sub-Saharan HIV-infected population and compared it to that of developed countries. Tryptophan levels were further examined in context of the general nutritional and inflammatory status. METHODS: This cross-sectional study included 105 HIV-positive patients recruited from the Kalafong Hospital in Pretoria, South Africa, and 60 HIV-negative controls. RESULTS: Patient tryptophan levels were in general markedly lower than those reported for developed countries. In contrast to reports from developed countries that showed tryptophan levels on average to be 18.8 % lower than their control values, tryptophan levels in our study were 44.1 % lower than our controls (24.4 ± 4.1 vs. 43.6 ± 11.9 µmol/l; p < 0.001). Tryptophan levels correlated with both CD4 counts (r = 0.341; p = 0.004) and with pro-inflammatory activity as indicated by neopterin levels (r = -0.399; p = 0.0001). Nutritional indicators such as albumin and haemoglobin correlated positively with tryptophan and negatively with the pro-inflammatory indicators neopterin, interleukin 6 and C-reactive protein. The most probable causes of the lower tryptophan levels seen in our population are food insecurity and higher levels of inflammatory activity. CONCLUSIONS: We contend that inflammation-induced tryptophan depletion forms part of a much wider effect of pro-inflammatory activity on the nutritional profile of HIV-infected patients.

EEG Brain Wave Activity at Rest and during Evoked Attention in Children with Attention-Deficit/Hyperactivity Disorder and Effects of Methylphenidate.

OBJECTIVE: The aim of this study was to assess baseline EEG brain wave activity in children with attention-deficit/hyperactivity disorder (ADHD) and to examine the effects of evoked attention and methylphenidate on this activity. METHOD: Children with ADHD (n = 19) were tested while they were stimulant free and during a period in which they were on stimulant (methylphenidate) medication. Control subjects (n = 18) were tested once. EEG brain wave activity was tested both at baseline and during focussed attention. Attention was evoked and EEG brain wave activity was determined by means of the BioGraph Infiniti biofeedback apparatus. RESULTS: The main finding of this study was that control subjects and stimulant-free children with ADHD exhibited the expected reactivity in high alpha-wave activity (11-12 Hz) from baseline to focussed attention; however, methylphenidate appeared to abolish this reactivity. CONCLUSION: Methylphenidate attenuates the normal cortical response to a cognitive challenge.

The kynurenine pathway activities in a sub-Saharan HIV/AIDS population.

BACKGROUND: Tryptophan is an essential amino acid for the synthesis of proteins and important metabolites such as serotonin, melatonin, tryptamine and niacin. After protein synthesis, more than 90 % of tryptophan catabolism occurs along the kynurenine pathway. The inflammation-inducible enzyme indoleamine 2,3 dioxygenase (IDO) is responsible for the first rate-limiting step in the kynurenine pathway, i.e., oxidation of tryptophan to kynurenine. Excessive IDO activity in conditions such as HIV/AIDS may lead to tryptophan depletion and accumulation of metabolites downstream from kynurenine. Little is known about the kynurenine pathway of HIV/AIDS patients in sub-Saharan regions. This study, in a low income sub-Saharan HIV/AIDS population, examined the effects of activities in the kynurenine pathway on plasma levels of tryptophan, kynurenine and the neurotoxin quinolinic acid, and on de novo synthesis of nicotinamide. METHODS: Plasma samples were obtained from a cohort of 105 HIV patients and 60 controls. Kynurenine pathway metabolites were analysed using gas chromatography - mass spectrometry. ELISA and flow cytometry were used to assess plasma inflammatory markers. RESULTS: IDO activity, depletion of tryptophan, as well as accumulation of kynurenine and the neurotoxin quinolinic acid, were not only significantly greater in the patients than in the controls, but also markedly greater than in HIV/AIDS patients from developed countries. Tryptophan levels were 12.3 % higher, kynurenine levels 16.2 % lower, quinolinic acid levels 43.2 % lower and nicotinamide levels 27,2 % lower in patients on antiretroviral treatment than in antiretroviral-naïve patients. Patients' kynurenine pathway metabolites correlated with the levels of inflammatory markers, including that of the major IDO-inducer, interferon-gamma. Indications are that the rate of de novo synthesis of nicotinamide in the kynurenine pathway correlates with increases in quinolinic acid levels up to a point where saturation of the enzyme quinolinate phosphoribosyl transferase occurs. CONCLUSIONS: Higher levels of inflammatory activity in this low income sub-Saharan HIV/AIDS population than in patients from developed countries lead to greater tryptophan depletion and greater accumulation of metabolites downstream from tryptophan with quinolinic acid levels often reaching levels associated with the development of HIV/AIDS-associated neurocognitive dysfunction. De novo synthesis of nicotinamide from quinolinic acid contributes to the maintenance of nicotinamide, and by implication NAD levels, in HIV/AIDS patients from low income populations. Antiretroviral treatment partially corrects disturbances in the kynurenine pathway.

A non-specific biomarker of disease activity in HIV/AIDS patients from resource-limited environments.

BACKGROUND: A general non-specific marker of disease activity that could alert the clinician and prompt further investigation would be of value in patients with HIV/AIDS, especially in resource limited environments. OBJECTIVE: To investigate the potential of neopterin as non-specific biomarker in patients with advanced HIV/AIDS. METHODS: Cross-sectional study in 105 HIV positive patients (75 on highly active antiretroviral treatment (HAART). Neopterin was assessed by enzyme linked immune-absorbent assay and cytokines by flow cytometry. RESULTS: Neopterin levels were significantly higher (p<0.001) for the total patient than for the control group. Significant correlations between neopterin and plasma indicators of inflammation showed neopterin to be a good indicator of active inflammatory status and of the effect of HAART on the immune system. Neopterin was superior to C-reactive protein and to individual cytokines as indicator of immune deficiency. Increased neopterin levels were associated with a decline in albumin, haemoglobin and the albumin/globulin ratio, and with increases in red cell distribution width. CONCLUSIONS: Plasma neopterin is a good non-specific biomarker of disease activity in HIV/AIDS patients. It is a good indicator of inflammatory activity, perpetuation of inflammation-associated co-morbidities, degree of immune deficiency and has predictive value for underlying disease, and for monitoring the HAART response.

Antidepressants may lead to a decrease in niacin and NAD in patients with poor dietary intake.

The term niacin is the generic name for the two compounds nicotinic acid and nicotinamide, the major dietary precursors for two important coenzymes, nicotinamide adenine dinucleotide (NAD) and its phosphorylated form, NADP. Niacin is important for the maintenance of cellular integrity and energy production and is involved in more than 500 intracellular reactions. Deficiencies of niacin may contribute to neuropsychiatric and neurodegenerative disorders. Patients who develop nutritional deficiencies as a result of poor dietary intake, especially inadequate intake of proteins and vitamins, could potentially suffer from niacin deficiency and NAD depletion. However, de novo synthesis of niacin and NAD in the kynurenine pathway of tryptophan metabolism may compensate for impaired dietary intake. The rate of synthesis of NAD and niacin from tryptophan oxidation depends on the induction of the enzyme indoleamine 2,3-dioxygenase (IDO) by pro-inflammatory cytokines such as interferon-gamma. Niacin synthesis is not limited by a decrease in tryptophan and excessive IDO activity may therefore lead to a decline in tryptophan levels. Antidepressants have an anti-inflammatory effect, including reduction of interferon-gamma and therefore inhibition of IDO, the rate-limiting enzyme of the kynurenine pathway. In theory, this could account for increased serotonin as more tryptophan becomes available for serotonin synthesis. However, the downside may be that less NAD and niacin are synthesised downstream, which could exacerbate common psychiatric problems. It is our hypothesis that patients with poor dietary intake, who are treated with antidepressants, are at risk of developing niacin/NAD deficiency with possible development of associated neuropsychiatric symptoms. We therefore propose that niacin supplementation be considered in patients with inadequate diets who are treated with antidepressants. We believe that if this does not happen, a subclinical niacin deficiency may result, which would be difficult to detect as it would cause the same symptoms of the original illness (e.g. depression). Niacin deficiency should be considered and ruled out in all patients with treatment-resistant depression, who have a poor response to antidepressants. This is potentially a cost-effective and easy intervention, which could be examined in a randomized controlled trial.

Heart rate variability assessment of the effect of physical training on autonomic cardiac control.

BACKGROUND: The effect of exercise interventions on autonomic nervous system (ANS) control of the heart by heart rate variability (HRV) is often investigated in just one position. It was hypothesized that results of exercise-induced changes on ANS are dependent on body position and that it is possible to distinguish between exercise induced changes in vagal and sympathetic influence by taking measurements in different body positions. METHODS: One hundred eighty-three (male = 100, female = 83) healthy volunteers, between 18 and 22 years, participated in a prospective twelve week medium to high intensity exercise intervention study with a self-control design. The influence of the exercise intervention was investigated on supine, rising, and standing as well as on the orthostatic response. Time domain, frequency domain and nonlinear (Poincaré) HRV analysis were performed. RESULTS: The exercise intervention lead to a significant increase (P < 0.05) in vagal influence during supine, rising, and standing. Sympathetic control in the supine position was decreased and increased during rising and standing. In the initial orthostatic response to rising from the supine position, the exercise intervention lead to increased (P < 0.05) vagal withdrawal as well as increased sympathetic control. The orthostatic response measured as the difference between standing and supine indicated only an exercise induced increase in sympathetic control. CONCLUSIONS: Exercise-induced changes in sympathetic and parasympathetic ANS control differ, depending on posture and period of measurement. Exercise induced changes in parasympathetic and sympathetic outflow, respectively, can be extracted from measurements from supine, through the orthostatic response, to standing, thereby detecting changes in ANS that are otherwise obscured.

Expression of the H- and L-subunits of ferritin in bone marrow macrophages of patients with osteoarthritis.

Osteoarthritis is a disease characterized by an increase in the production of reactive oxygen species (ROS) in afflicted joints. Excess iron, due to its role in the production of ROS and crystal deposition in the joints, is implicated in the disease progression of osteoarthritis. Ferritin is a major regulator of the bioavailability of iron, and its functions are determined largely by the combination of H- and L-subunits present in its outer protein shell. The purpose of the study was to investigate the expression of the H- and L-subunits of ferritin in bone marrow macrophages of osteoarthritis patients. The cytokine profiles were assessed as cytokines play an important role in the expression of the ferritin subunits. The H-subunit of ferritin in the bone marrow macrophages was significantly higher (P value = 0.035) in the osteoarthritis patients compared with the controls (107.84; 69.25-167.94 counts/µm(2); n = 7 versus 71.07; 58.56-86.26 counts/µm(2); n = 19). A marginally significant increase (P value = 0.059) was shown for the expression of the L-subunit in the osteoarthritis patients compared with the controls (133.03; 104.04-170.10 counts/µm(2); n = 7 versus 104.23; 91.53-118.70 counts/µm(2); n = 19). The osteoarthritis and control groups had comparable C-reactive protein, as well as proinflammatory and anti-inflammatory cytokine concentrations. The major exception was for transforming growth factor-ß (TGF-ß), which was higher (P value = 0.014) in the plasma of the osteoarthritis patients (16.69; 13.09-21.28 ng/mL; n = 7 versus 8.60; 6.34-11.67 ng/mL; n = 19). Up-regulation of the ferritin subunits decreases the levels of bioavailable iron and provides protection against the unwarranted production of ROS and crystal deposition. A role for TGF-ß in the up-regulation of the expression of the H-subunit, and possibly the L-subunit, of ferritin is postulated in osteoarthritis.

Importance of tachogram length and period of recording during noninvasive investigation of the autonomic nervous system.

BACKGROUND: Various disciplines use quantification of heart rate variability (HRV) as an indicator of autonomic function without recognizing the importance of using standardized methodologies. The aim of this study was to assess the influence of tachogram length and period of recording on HRV indicator values. METHODS: To test the influence of the length of the recording time, HRV indicator values calculated from 180, 300, 420, and 600 seconds recording periods (supine and standing) were compared. Also individual 3- minute periods (0-180 seconds, 180-360 seconds, 360-540 seconds) from 10-minute (supine and standing) tachograms were compared. RESULTS: In the supine position, vagal-efferent HRV indicators were not influenced by tachogram length varying between 3 and 10 minutes (P > 0.05). Supine HRV indicator values representing combined sympathetic and parasympathetic influences were tachogram length-dependent (P < 0.05). During orthostatic stress all HRV indicators were tachogram length-dependent (P < 0.05). Upon standing up marked vagal withdrawal and sympathetic activation occurred. Vagal withdrawal tapered off during the 3-6-minute period after rising while indicators representing combined vagal and sympathetic activation were totally reversed. CONCLUSIONS: During application of orthostatic stress the exact starting point of recording, as well as the length of recording, is critical due to the activation and normalization of homeostatic mechanisms. Starting the tachogram recording too late will miss out on part of the initial response to change in body position. Longer recording times will give a combination of values recorded during the stress response and values obtained after stabilization in the standing position.

Stimulants and growth in children with attention-deficit/hyperactivity disorder.

Initial suggestions that suppression of growth may be an intrinsic characteristic of attention-deficit/hyperactivity disorder (ADHD) have now largely been disproven. Although controversy persists regarding the possible negative effect of adrenergic stimulants on growth in children with ADHD, the consensus that appears to be reached in the scientific literature is that stimulant usage may cause a manageable attenuation of growth in these children. Since it is known that stimulants increase the amount of dopamine and noradrenaline in the synapse, this writing suggests that these increases in dopamine and noradrenaline are responsible for the growth attenuation in these children. It appears that increased amounts of dopamine and noradrenaline have the ability to inhibit the secretion of growth hormone and growth-related hormones such as prolactin, thyroid hormones, sex hormones and insulin. Therefore, it would be reasonable to suggest that the increases in dopamine and noradrenaline caused by stimulant usage can disrupt the homeostasis of both growth hormone and growth-related hormones, generating the potential for the suppression of growth.

Autonomic correlates at rest and during evoked attention in children with attention-deficit/hyperactivity disorder and effects of methylphenidate.

OBJECTIVE: The aim of this study was to assess autonomic nervous system functioning in children with attention-deficit/hyperactivity disorder (ADHD) and to examine the effects of methylphenidate and focussed attention. METHOD: Children with ADHD (n = 19) were tested while they were stimulant free and during a period in which they were on stimulants. On both occasions, autonomic nervous system functioning was tested at baseline and during focussed attention. Autonomic nervous system functioning of control subjects was also tested at baseline and during focussed attention. Autonomic nervous system activity was determined by means of heart rate variability (HRV) and skin conductivity analyses. Attention was evoked by means of the BioGraph Infiniti biofeedback apparatus. HRV was determined by time domain, frequency domain and Poincaré analysis of RR interval data. Skin conductivity was determined by the BioGraph Infiniti biofeedback apparatus. RESULTS: The main findings of this study were (a) that stimulant-free children with ADHD showed a sympathetic underarousal and parasympathetic overarousal of the sympathovagal balance relative to control subjects; (b) methylphenidate shifted the autonomic balance of children with ADHD towards normal levels; however, a normal autonomic balance was not reached, and (c) stimulant-free children with ADHD exhibited a shift in the sympathovagal balance towards the sympathetic nervous system from baseline to focussed attention; however, methylphenidate appeared to abolish this shift. CONCLUSIONS: Stimulant-free children with ADHD have a parasympathetic dominance of the autonomic balance, relative to control subjects. Methylphenidate attempts to restore the normal autonomic balance in children with ADHD, but inhibits the normal autonomic nervous system response to a cognitive challenge. CLINICAL APPLICATIONS: These results indicate that methylphenidate may have a suppressive effect on the normal stress response. Although this may be of benefit to those who interact with children who suffer from ADHD, the implications for the physiological and psychological well-being of the children themselves are debatable. Further research is needed. LIMITATIONS OF THE STUDY: Only 19 children with ADHD and 18 control subjects were tested. Further studies should include prior testing in order to exclude children with possible co-existing learning disabilities. Cognitive function and emotional responses of children with ADHD were not tested.

The effect of sympathomimetic medication on cardiovascular functioning of children with attention-deficit/hyperactivity disorder.

OBJECTIVE: The aim of this study was to investigate the effects of sympathomimetic medication on the cardiovascular system of children with attention-deficit/hyperactivity disorder (ADHD). METHODS: Cardiovascular functioning of children with ADHD (n = 19) was tested while the children were stimulant free and during a period in which they were on stimulant medication. Electrocardiograms (ECGs) were obtained by means of a Schiller CardioLaptop AT-110 ECG recorder using the standard 12-lead cable positioning for a resting ECG. Blood pressure was measured by means of a stethoscope and mercury sphygmomanometer. RESULTS: The main findings of this study were that methylphenidate usage is associated with increases in heart rate (HR) and blood pressure (BP), and that it does not adversely affect HR-corrected QT and JT intervals or cardiac dispersion values. CONCLUSION: Methylphenidate causes an increase in HR as well as increases in both systolic and diastolic BP, but no change in cardiac depolarisation and repolarisation duration or homogeneity.