Search PubMed⌕ Search

Biomedical subjects

M T Allen

Publications and source records attributed to M T Allen.

35 records · Page 2Linked to original sources
PubMed1989

Patterns of autonomic response during laboratory stressors.

The present study was designed to include an index reflecting the influence of parasympathetic nervous system activity on the heart, respiratory sinus arrhythmia, in addition to measures reflecting primarily sympathetic nervous system activity. The inclusion of the parasympathetic index was considered important for two reasons:(a) Past studies have suggested different patterns of autonomic response to qualitatively different laboratory stressors but have had to infer parasympathetic influences more indirectly, and (b) there is evidence that borderline hypertensives may have reduced vagal tone at rest when compared to normotensives. This last point is important for the study of individual differences in cardiovascular reactivity because excessive responsiveness in young normotensives (beta-adrenergic reactors) has been suggested as a model for studying the precursors of some types of hypertension. Fifty-one male college students were given a reaction time task, a mental arithmetic task, a cold pressor task, and graded bicycle exercise. A variety of cardiovascular and respiratory measures were collected on each subject. Results indicated significant differences in levels of respiratory sinus arrhythmia during the three tasks and the rest period, giving additional evidence for parasympathetic differences (along with sympathetic differences) in these conditions. Additionally, high beta-adrenergic reactors did not differ in mean level of respiratory sinus arrhythmia from low reactors either at rest or during the task periods. These results are discussed in the context of previous research.

Adult↗
PubMed1988

Motor preparation aspects of cardiovascular reactivity to psychological challenge.

Neural control of the circulation has evolved in such a way that behavioral responses to psychological stress may be accompanied by a dramatic activation of the cardiovascular system. This study was designed to address the hypothesis that such instances of cardiovascular mobilization reflect a functional motor preparation response. Twenty-four healthy young men participated in reaction time (RT) tasks which involved responding by squeezing a handgrip dynamometer. Motor preparation demands were manipulated by varying the temporal predictability of response requirements as well as the physical effort involved in responding, while controlling for other factors previously established to influence cardiovascular reactivity to psychologically challenging tasks. Physiological response measurements included heart rate, blood pressure and oxygen consumption. Increases in heart rate and systolic blood pressure during the RT tasks showed a general pattern which was consistent with the predictions of the motor preparation hypothesis, with the greatest elevations occurring in association with low temporal predictability and high physical effort. The possibility is discussed that factors such as incentives and elements of uncertainty may influence cardiovascular reactivity by accentuating behavioral arousal, of which motor preparation may be an inextricable component.

Adaptation, Psychological↗
PubMed1987

Stability of cardiovascular reactivity to laboratory stressors: a 2 1/2 yr follow-up.

The temporal stability of cardiovascular reactivity to laboratory stressors over a 2 1/2 yr period was studied. Subjects who had earlier received a cold pressor and a shock avoidance reaction time task were brought back for retesting using almost identical tasks. Cardiovascular variables that were common to both sessions included heart rate, systolic and diastolic blood pressure, and pre-ejection period. Correlations were computed to examine the association of responses across both sessions for the four cardiovascular variables during rest and the two tasks. Correlations of both heart rate and systolic blood pressure were high for all tasks and rest, whereas inconsistent correlations were found for diastolic pressure and pre-ejection period. Inconsistencies in diastolic pressure are speculated to be due to individual differences in beta-adrenergic response, whereas lack of consistent pre-ejection period associations may be due to differences in methodology. The results generally support the assumption of stability of cardiovascular reactivity.

Adult↗
PubMed1987

Type A behavior pattern, parental history of hypertension, and cardiovascular reactivity in college males.

Two risk factors for cardiovascular disorders, parental history of hypertension and the Type A behavior pattern, were investigated concurrently with respect to cardiovascular reactivity to challenging situations. Sixty-four college males were given both the Structured Interview (SI) and Jenkins Activity Survey (JAS) for the Type A behavior pattern and a family health questionnaire to determine parental history of hypertension. The students were monitored for blood pressure (BP), heart rate (HR), and pulse transit time (PTT) response to four tasks: cold pressor, isometric handgrip exercise, a reading comprehension task, and backwards digit span. Type As based on SI classification had significantly higher HR levels across all tasks than did Type Bs, as well as higher diastolic BP levels in the cold pressor task. No main effects for Type A-B using JAS classification were found. Positive parental history students had higher HR and shorter PTT levels across all the tasks. Type A and parental history did interact in a limited way on some tasks, but the interactions were also dependent on the Type A classification used.

Adolescent↗
PubMed1981

The relationship of physiological responses to the coronary-prone behavior pattern in children.

Forty-one male and female children were tested for Type A (coronary-prone) behavior using the Bortner test and the MYTH questionnaire. Based on their classification as A or B, three physiological variables were compared: systolic blood pressure (SBP), heart rate (HR) (phasic, tonic, and variability), and skin conductance (SC) (magnitude and latency of responses, number of spontaneous responses) during a 3-min rest period, a 10-min unsignaled reaction time (RT), and a 10-min word task. When using the Bortner to classify groups, Type As showed a tendency toward higher SBP levels and greater SBP reactivity to tasks, and significantly greater HR levels, HR reactivity to tasks, HR variability during rest, and SCR magnitude to RT signals. When using the MYTH, Type A females showed larger increases in SBP and HR to tasks, a lower mean HR, and a faster RT. Type A males showed a higher mean HR. Thus, children classified as Type A resemble Type A adults when compared on physiological responses to stress; however, the results depend on the method used to determine Type A behavior.

Blood Pressure↗
PubMedDate not supplied

Parallel neural systems for classical conditioning: support from computational modeling.

Classical conditioning has been explained by two main types of theories that postulate different learning mechanisms. Rescorla and Wagner (1972) put forth a theory in which conditioning is based on the ability of the US to drive learning through error correction. Alternatively, Mackintosh (1973) put forth a theory in which the ability of the CS to be associated with the unconditioned stimulus is modulated. We have proposed a reconciliation of these two mechanisms as working in parallel within different neural systems: a cerebellar system for US modulation and a hippocampal system for CS modulation. We developed a computational model of cerebellar function in eyeblink conditioning based on the error correction mechanism of the Rescorla-Wagner rule in which learning-related activity from the cerebellum inhibits the inferior olive, which is the US input pathway to the cerebellum (Gluck et al., 1994). We developed a computational model of the hippocampal region that forms altered representations of conditioned stimuli based on their behavioral outcomes (Gluck & Myers, 1993; Myers et al., 1995). Overall, computational modeling and empirical findings support the idea that, at least in the case of eyeblink conditioning, there may be two different neural systems: the cerebellum which mediates US-based error correction and hippocampus which alters representations of CSs.

Animals↗
PubMedDate not supplied

Cluster analyses of cardiovascular responsivity to three laboratory stressors.

Seventy-three young normotensive male subjects were tested with an experimental protocol that included a reaction time, a mental arithmetic, and a cold pressor task. Physiological variables that were recorded included heart rate, stroke volume, pre-ejection period, blood pressure, total peripheral resistance, and respiratory sinus arrhythmia. In order to identify subgroups of subjects who differed in their pattern of autonomic responses to the tasks, the physiological change scores from baseline to the tasks for each subject were entered into a cluster analysis for each task. Ward's method was used as the clustering algorithm. The cluster analyses identified four clusters for the reaction time and mental arithmetic tasks, and five clusters for the cold pressor task. Although there was a wide range of patterns exhibited by cluster subgroups, most subjects who were reactive to the tasks showed response patterns that were qualitatively similar to the pattern of overall mean response by all subjects, albeit varying considerably in terms of quantitative response. Little evidence was generated for the consistency of extreme beta-adrenergic response from one task to another, although significant consistency was noted when milder beta-responders were included in the comparisons. Some consistency of alpha-adrenergic response noted across tasks, as well as significant consistency of being relatively nonreactive to the tasks.

Adult↗
PubMedDate not supplied

Do cardiovascular responses to laboratory stress relate to ambulatory blood pressure levels?: Yes, in some of the people, some of the time.

Because the correspondence between laboratory measures of blood pressure and heart rate responses to stress and ambulatory measures is less than optimal, this study tested two hypotheses: Are ambulatory measures of blood pressure elevated during periods of perceived stress, relative to no stress? Are ambulatory blood pressures elevated during perceived stress among those individuals who exhibit elevated blood pressure and heart rate responses to laboratory stress? These questions were addressed in a sample of employed, middle-aged men and premenopausal and postmenopausal women, who vary in reproductive hormone status, and in risk for coronary heart disease. All participants performed a series of laboratory studies while their physiological parameters were monitored and then wore an ambulatory blood pressure monitor for a day and a half. This monitor recorded blood pressure every half hour during the waking hours and at the same time the participants assessed their mood states. After excluding participants who reported no variability in stress levels, those who were cardiovascular reactors to a laboratory speech task exhibited elevated ambulatory blood pressure levels during periods of perceived stress. Furthermore, in general, periods of perceived stress were associated on a within subject basis with elevated ambulatory blood pressure. These results suggest that the correspondence between laboratory and field measures of blood pressure would be improved by taking into account the environmental circumstances during the ambulatory assessments and the person characteristics of reactor-nonreactor to laboratory stress.

Adult↗
PubMedDate not supplied

Hemodynamic adjustments to laboratory stress: the influence of gender and personality.

Exaggerated cardiovascular reactivity to psychological stress is a potential pathophysiological mechanism linking behavior and cardiovascular disease. Because of the recognized gender differences in incidence of cardiovascular disease, potential gender differences in cardiovascular reactivity to laboratory stressors have been evaluated. The current study examined the cardiovascular responses of a total of 42 young women (N = 22) and men (N = 20) undergoing a laboratory protocol including the following: a nonverbal math task, a mirror tracing task, the Stroop Color-Word interference task, and an isometric handgrip task. In addition to the assessment of heart rate and blood pressure, cardiac output, stroke volume, total peripheral resistance and preejection period were assessed by impedance cardiography. A number of personality characteristics that vary in prevalence by gender were also measured to evaluate their ability to explain potential gender differences in cardiovascular responses. Results indicated that men responded with greater total peripheral resistance and systolic and diastolic blood pressure responses than did women on a subset of tasks, whereas women exhibited larger increases in heart rate on a subset of tasks. Thus, men were more likely to be "vascular" reactors, with women being more likely to be "cardiac" reactors. Personality characteristics did differ between men and women, but did not explain significant variance in the gender differences in cardiovascular responses. We conclude that additional studies should focus on experimental manipulations of potential physiological mechanisms responsible for these differences, such as reproductive hormones.

Arousal↗
PubMedDate not supplied

Does background stress heighten or dampen children's cardiovascular responses to acute stress?

OBJECTIVE: Does background stress heighten or dampen children's cardiovascular responses to acute stress? METHOD: To address this question, the cardiovascular responses to four acute laboratory stressors of 150 children and adolescents were evaluated according to their self-reported background stress level. Background stress was determined during a standardized interview and was a priori classified according to its importance, frequency, and whether it was ongoing or resolved. RESULTS: Results showed that children and adolescents who reported important stressors or stressors that were ongoing and frequent exhibited a larger increase in diastolic blood pressure and total peripheral resistance during all four laboratory stressors than their low stress counterparts. Additional analysis showed that the results could not be accounted for by sociodemographic variables or by the personality traits measured in this study. CONCLUSIONS: Results suggest the importance of measuring background stress in understanding an individual's acute stress response.

Adolescent↗