The relationship between trait hostility and cardiovascular reactivity: A quantitative review and analysis

Results of a series of meta-analyses indicated that high and low scorers on most trait hostility measures do not consistently differ in blood pressure or heart rate reactivity to traditional laboratory stressors. The few significant effects were modest in size, and instances of hyporeactivity were found. When stressors were classified as provocative versus nonprovocative, in accord with Trait x Situation approaches, however, Potential for Hostility-Interpersonal Style was predictive of exaggerated systolic and diastolic blood pressure responses and the Cook–Medley Hostility Inventory was predictive of diastolic blood pressure responses to provocative stressors. Hence, the next generation of studies of the hostility–reactivity hypothesis should emphasize interpersonal stressors. Alternative mechanisms for the disease consequences of hostility should also be examined, however, because the available evidence indicates that the hyperreactivity hypothesis is unlikely to furnish a complete explanation for the association between hostility and heart disease.     

A Miniaturized Carbon Dioxide Gas Sensor Based on Sensing of pH-Sensitive Hydrogel Swelling with a Pressure Sensor

A measurement concept has been realized for the detection of carbon dioxide, where the CO₂ induced pressure generation by an enclosed pH-sensitive hydrogel is measured with a micro pressure sensor. The application of the sensor is the quantification of the partial pressure of CO₂ (Pco₂) in the stomach as diagnosis for gastrointestinal ischemia. The principle is put to the proof by examining the sensor response to changes in Pco₂. Furthermore, the response time, temperature-sensitivity and resolution are determined. The sensor responds well to changes in Pco₂ with a maximum pressure generation of 0.29× 10⁵ Pa at 20 kPa CO₂. The 90% response time varies between 1.5 and 4.5 minutes at 37^∘C. The sensor shows a linear temperature-sensitivity which can easily be compensated for, and enables detection of Pco₂ changes as small as 0.5 kPa CO₂.     

The relationships of impulsivity and cardiovascular responses: The role of gender and task type

The present study was conducted to assess the relationships of impulsivity with both baseline cardiovascular levels and reactivity during two laboratory stressors in both female and male young adults. Heart rate (HR), blood pressure (BP), and heart rate variability (HRV) were measured at rest and during a reaction time and speech task in one hundred and one undergraduate students. Impulsivity was measured using the Barratt Impulsiveness Scale-11 and Block's Ego-Undercontrol Scale. Males and females responded similarly to both laboratory tasks and also did not differ on the impulsivity scales. For males, higher scores on impulsivity were associated with higher systolic BP levels at rest but decreased systolic BP and HR reactivity during the preparation of the speech task; females showed no relationships of resting cardiovascular levels with impulsivity, but more impulsive females did show decreased HR response during speech preparation. No significant relationships were found between impulsivity and either HRV levels or reactivity. It is speculated that tasks involving a degree of planning may be important to find relationships between impulsivity and cardiovascular reactivity, especially in males.     

Carbon dioxide sensitivity of the central chemosensitive mechanisms

Summary In urethane-anaesthetised adult albino rats ventral surface of the brainstem was stimulated chemically by increasing the local CO₂ concentration and electrically. Two areas were demarcated on the ventral surface of the brainstem, one which showed an increase in pulmonary ventilation on chemical and electrical stimulation, and another which showed a decrease in pulmonary ventilation and sometimes even respiratory arrest. EEG activity recorded from the area from where increased pulmonary ventilation was obtained showed a synchronous slow wave activity during chemical stimulation and inhalation of a CO₂-air mixture. This area is situated 0.5–1 mm lateral to the mid-line extending up to the rootlets of the VIIth to IXth cranial nerves. The response increased proportionately on increasing the strength of the chemical stimulus, till it reached a plateau. In carotid body denervated and chronic hypoxic animals, the magnitude of the responses was shown to be increased, probably due to increased sensitivity of the central chemosensitive mechanisms.     

Carbon dioxide,extracellular pH and fibre water in frog skeletal muscle

The fibre water of frog skeletal muscle was increased by exposure of the muscle to CO₂. Exposure to acid at constant PCO₂ caused no change in fibre water although muscle weight decreased, whereas exposure to alkali increased fibre water.Supported by the Schweizerische Stiftung für Midizinisch-Biologische Stipendien     

Difference in human cardiovascular response between upright and supine recovery from upright cycle exercise

Cardiovascular responses were examined in seven healthy male subjects during 10 min of recovery in the upright or supine position following 5 min of upright cycle exercise at 80% peak oxygen uptake. An initial rapid decrease in heart rate (f _c) during the early phase of recovery followed by much slower decrease was observed for both the upright and supine positions. The average f _c at the 10th min of recovery was significantly lower (P < 0.05) in the supine position than in the upright position, while they were both significantly greater than the corresponding pre-exercise levels (each P < 0.05). Accordingly, the amplitude of the high frequency (HF) component of R-R interval variability (by spectrum analysis) in both positions was reduced with a decrease in mean R-R interval, the relationship being expressed by a regression line – mean R-R interval = 0.006 × HF amplitude + 0.570 (r = 0.905, n = 28, P < 0.001). These results would suggest that the slower reduction in f _c following the initial rapid reduction in both positions is partly attributable to a retardation in the restoration of the activity of the cardiac parasympathetic nervous system. Post-exercise upright stroke volume (SV, by impedance cardiography) decreased gradually to just below the pre-exercise level, whereas post-exercise supine SV increased markedly to a level similar to that at rest before exercise. The resultant cardiac output (Q˙ _c) and the total peripheral vascular resistance (TPR) in the upright and supine positions returned gradually to their respective pre-exercise levels in the corresponding positions. At the 10th min of recovery, both average SV and Q˙ _c were significantly greater (each P < 0.005) in the supine than in the upright position, while average TPR was significantly lower (P < 0.05) in the supine than in the upright position. In contrast, immediately after exercise, mean blood pressure dropped markedly in both the supine and upright positions, and their levels at the 10th min of recovery were similar. Therefore we concluded that arterial blood pressure is maintained relatively constant through various compensatory mechanisms associated with f _c, SV, Q˙ _c, and TPR during rest and recovery in different body positions. Accepted: 4 September 1999     

The effects of ventilation pattern on carbon dioxide transfer in three computer models of the airways

We investigate the effects on arterial P(CO(2)) and on arterial-end tidal P(CO(2)) difference of six different ventilation patterns of equal tidal volume, and also of various combinations of tidal volume and respiratory rate that maintain a constant alveolar ventilation. We use predictions from three different mathematical models. Models 1 (distributed) and 2 (compartmental) include combined convection and diffusion effects. Model 3 incorporates a single well-mixed alveolar compartment and an anatomical dead-space in which plug flow occurs. We found that: (i) breathing patterns with longer inspiratory times yield lower arterial P(CO(2)); (ii) varying tidal volume and respiratory rate so that alveolar ventilation is kept constant may change both PA(CO(2)) and the PA(CO(2))-PET(CO(2)) difference; (iii) the distributed model predicts higher end-tidal and arterial P(CO(2)) than the compartmental models under similar conditions; and (iv) P(CO(2)) capnograms predicted by the distributed model exhibit longer phase I and steeper phase II than other models.     

Fixed acid and carbon dioxide bohr effects as functions of hemoglobin-oxygen saturation and erythrocyte pH in the blood of the frog,Rana temporaria

Using a thin film, dynamic recording technique, the pH sensitivity of the oxygen equilibrium (Bohr effect) of whole blood in the frogRana temporaria, and its dependence on CO₂ and fixed acids and on plasma and erythrocyte pH values were measured. Under standard conditions (20°C,P _{CO 2}=14.7 mm Hg, pH=7.65) the oxygen equilibrium could be described by a P₅₀ value of 38 mm Hg andn ₅₀ of 1.8. Hill plots of the oxygen equilibria showed increased cooperativity in oxygen binding with increasing saturation (n ₂₀ 1.2,n ₈₀ 4.0). Values of the fixed acid and CO₂ Bohr factors ({ie7-1} and {ie7-2}, respectively) were similar at specific saturations (S_{20, 50, 80}) but showed saturation dependence with high values occurring at high saturation. The same statements also hold for the intracellular Bohr factors (derived from the relation between blood P₅₀ and erythrocyte pH) although the values of both {ie7-3} and {ie7-4} now were greater than those related to blood pH.     

Symptoms of depression and cardiovascular reactions to acute psychological stress: evidence from a population study

Depression and exaggerated cardiovascular reactivity are considered risk factors for cardiovascular disease, possibly as a result of common antecedents, such as altered autonomic nervous system function. We examined the association between depressive symptomatology and cardiovascular reactions to psychological stress in 1608 adults (875 women) comprising 3 distinct age cohorts: 24-, 44-, and 63-year olds. Depression was assessed using the Hospital Anxiety and Depression Scale. Blood pressure and heart rate were measured at baseline and during the paced auditory serial arithmetic test. Depression scores were negatively associated with systolic blood pressure and heart rate reactions, after adjustment for likely confounders such as sex, cohort, occupational status, body mass index, stress task performance score, baseline cardiovascular activity, antidepressant, and antihypertensive medication. The direction of association was opposite to that which would be expected if excessive reactivity were to mediate the association between depression and cardiovascular disease outcomes or if they shared common antecedents.     

Differential cardiovascular changes as a function of stimulation electrode site in rabbit hypothalamus

Twenty chronically prepared, unanesthetized rabbits received both high-frequency (200 pulse/sec), short pulse-train (1.0 sec) and relatively low-frequency (25 pulse-sec), long pulse-train (10 sec) electrical stimulation of the hypothalamus. High-frequency, short pulse-train stimulation elicited a pressor response and bradycardia at all 27 electrode sites. In contrast, three other cardiovascular response patterns were obtained following low-frequency, long pulse-train stimulation. These latter patterns reflected a medial-lateral organization of autonomic function within the hypothalamus. Whereas all 15 lateral hypothalamic placements yielded depressor responses, 7 of 12 medial hypothalamic placements yielded pressor responses and tachycardia. Cardiovascular changes following administration of selective autonomic blocking agents (e.g., phentolamine, propranolol, methylatropine) suggest that high-frequency, short pulse-train stimulation elicited a pressor response followed by a reflexive bradycardia essentially mediated by an increase in vagal restraint. In contrast, the heart rate changes observed to low-frequency, long pulse-train stimulation all appear to have been importantly influenced by changes at the heart in beta-adrenergic activity.     

The Relationship between the Type A Behavior Pattern and Physiological Responsivity: A Quantitative Review

Researchers have attempted to specify the process linking Type A behavior to coronary artery disease. Increased cardiovascular and neuroendocrine reactivity in Type A individuals has been proposed as the intervening mechanism. There have been several previous reviews of the research relating Type A behavior to physiological reactivity. The authors' conclusions have been equivocal; some assert that Type A persons are more reactive, whereas others find no evidence for such a conclusion. In this report, meta-analysis, an alternative to the traditional narrative review, was employed to provide a quantitative evaluation of the relationship between Type A behavior and physiological reactivity. Results indicated that: 1) Type As respond to cognitive and psychomotor stimulus situations with greater heart rate and systolic blood pressure responses, 2) this relationship is not evident in females, 3) the relationship is more evident for some cognitive tasks than for others, and 4) the strength of the relationship depends upon the instrument used to assess Type A behavior.     

Self-reported health and cardiovascular reactions to psychological stress in a large community sample: Cross-sectional and prospective associations

Exaggerated cardiovascular reactions to acute psychological stress have been implicated in a number of adverse health outcomes. This study examined, in a large community sample, the cross-sectional and prospective associations between reactivity and self-reported health. Blood pressure and heart rate were measured at rest and in response to an arithmetic stress task. Self-reported health was assessed concurrently and 5 years later. In cross-sectional analyses, those with excellent/good self-reported health exhibited larger cardiovascular reactions than those with fair/poor subjective health. In prospective analyses, participants who had larger cardiovascular reactions to stress were more likely to report excellent/good health 5 years later, taking into account their reported health status at the earlier assessment. The findings suggest that greater cardiovascular reactivity may not always be associated with negative health outcomes.     

Why savannah monitor lizards hyperventilate during activity: a comparison of model predictions and experimental data

The functional and structural factors that limit maximal oxygen uptake (VO2 max) in lizards are not completely understood. Using an integrative model describing the interactive nature of the individual oxygen transport conductances, we performed an analysis of the oxygen transport system in the highly aerobic lizard Varanus exanthematicus with specific reference to the sensitivity of VO2 max to potential limitations in the ventilatory system. Our analysis predicts that DLO2 must increase more than three-fold at VO2 max and even with this increase in DLO2 , the VO2 max may be sensitive to factors that alter lung ventilation and/or lower lung PO2. To test the predictions of the model analysis, we experimentally determined the effects of reducing inspired O2 on VO2 max during treadmill exercise. We conclude from both our theoretical and experimental analyses that V. exanthematicus operates near the functional limits of its lung.     

The relationship between the neuromodulator adenosine and behavioral symptoms of autism

The neuromodulator adenosine is an endogenous sleep promoter, neuroprotector and anticonvulsant, and people with autism often suffer from sleep disruption and/or seizures. We hypothesized that increasing adenosine can decrease behavioral symptoms of autism spectrum disorders, and, based on published research, specific physiological stimuli are expected to increase brain adenosine. To test the relationship between adenosine and autism, we developed a customized parent-based questionnaire to assess child participation in activities expected to influence adenosine and quantify behavioral changes following these experiences. Parents were naive to study hypotheses and all conditions were pre-assigned. Results demonstrate significantly better behavior associated with events pre-established as predicted to increase rather than decrease or have no influence on adenosine. Understanding the physiological relationship between adenosine and autism could open new therapeutic strategies – potentially preventing seizures, improving sleep, and reducing social and behavioral dysfunction.     

The influence of trait and state rumination on cardiovascular recovery from a negative emotional stressor

The purpose of this study was to evaluate the influence of trait and state rumination on cardiovascular recovery following a negative emotional stressor. Cardiovascular data was collected from 64 undergraduate women during a 10-min baseline period, 5-min emotional recall stress task, and a 15-min recovery period. Trait rumination was assessed using the Stress Reactive Rumination Scale and state rumination was assessed 5 and 10 min after the stressor, using a thought-report technique. Results indicated that trait and state rumination interacted such that low trait ruminators who were ruminating at 10 min after the termination of the stressor had poorer diastolic blood pressure and high-frequency heart rate variability recovery compared to low trait ruminators who were not ruminating. State rumination was not associated with cardiovascular recovery in high trait ruminators. Results suggest that rumination may play a role in the association between stress and hypertension by prolonging cardiovascular activation following stress.     

Post-exercise recovery of autonomic cardiovascular control: a study by spectrum and cross-spectrum analysis in humans

The recovery of the baseline autonomic control of cardiovascular activity after exercise has not been extensively studied. In 12 healthy subjects, we assessed the time-course of recovery by autoregressive spectrum and cross-spectrum analysis of heart period and systolic blood pressure during the 3 h after the end of 20 min of steady-state exercise at 50% (light workload, LW) and 80% (moderate workload, MW) of the individual's anaerobic threshold. The electrocardiogram and non-invasive blood pressure were simultaneously recorded during 10 min periods in the sitting position, at rest before exercise, and at 15, 60 and 180 min of recovery after exercise. At 15 min we observed a persistent tachycardia and relative hypotension; after MW, at 60 min heart rate was still slightly higher. Spectrum and cross-spectrum analysis showed, at 15 min, an increase in the low frequency component of systolic blood pressure, a reduction in the high frequency component of heart rate (larger in MW), and a decrease in baroreceptor sensitivity. After 60 and 180 min none of these parameters was significantly different from those at rest, although, in MW, some subjects still displayed signs of sympathetic activation after 1 h. We concluded that, after 15 min of recovery, the cardiovascular reflexes were blunted, that sympathetic nerve activity was still enhanced, and that the tone in the vagus had not fully recovered. Only the persistent vagal restraint seemed to be exercise intensity-dependent. For complete restoration of autonomic control after LW 1 h of rest was sufficient, and just enough after MW. Accepted: 2 November 2000     

Diagonal band of Broca modulates the cardiac component of the baroreflex in unanesthetized rats

The diagonal band of Broca (DBB) is involved in cardiovascular control in rats. In the present study, we report the effect of acute and reversible neurotransmission inhibition in the DBB by bilateral microinjection of the nonselective neurotransmission blocker CoCl(2) (1mM, 100 nL) on the cardiac baroreflex response in unanesthetized rats. Local DBB neurotransmission inhibition did not affect baseline values of either blood pressure or heart rate, suggesting no tonic DBB influence on cardiovascular system activity. However, CoCl(2) microinjections enhanced both the reflex bradycardia associated with blood pressure increases caused by i.v. infusion of phenylephrine and tachycardiac response evoked by blood pressure decreases caused by i.v. infusion of sodium nitroprusside. An increase in baroreflex gain was also observed. Baroreflex returned to control values 60 min after CoCl(2) microinjections, confirming its reversible effect. In conclusion, our data suggest that synapses within DBB have a tonic inhibitory influence on both the cardiac parasympathetic and sympathetic components of the baroreflex.     

In vivo measurement of carbon dioxide tension with a miniature electrode

A commercially available catheter type electrode with whichP _CO2 can be continuously measured in vivo and in vitro gave progressively less accurate results the longer the measuring period was extended. This proved to be due to temperature effects and a change in sensitivity with time. A correction procedure for these effects was developed which was based on two observations. 1. The relationship between temperature and the logarithm of the sensitivity of the electrodeamplifier combination was linear and virtually identical for 9 electrodes: 8% change in sensitivity for a deviation of 1° C from the temperature during calibration. 2. The change in sensitivity due to drift of the electrode output is approximately a logarithmic function of time: 1 h after calibration all electrodes exhibited a decreased sensitivity, varying between 0.3 and 16.7%. The drift effect can be dealt with by repeated calibrations, preferably at 1^1/2 h intervals.The adequacy of the correction procedure was assessed in in vivo measurements in cats and dogs. The meanP _CO2 difference between the in vivo measurement, corrected for temperature and drift, and samples analyzed with a conventional electrode, was 0.005 kPa (0.04 mm Hg) with a standard deviation of 0.187 kPa (1.39 mm Hg).     

Prospective associations between cardiovascular reactions to acute psychological stress and change in physical disability in a large community sample

Exaggerated haemodynamic reactions to acute psychological stress have been implicated in cardiovascular disease outcomes, while lower reactions have been considered benign. This study examined, in a large cohort, the prospective associations between stress reactivity and physical disability. Blood pressure and pulse rate were measured at rest and in response to a stress task. Physical disability was assessed using the OPCS survey of disability at baseline and five years later. Heart rate reactivity was negatively associated with change in physical disability over time, such that those with lower heart rate reactivity were more likely to deteriorate over the following five years. These effects remained significant following adjustment for a number of confounding variables. These data give further support to the recent argument that for some health outcomes, lower or blunted cardiovascular stress reactivity is not necessarily protective.