Biomedical subjects

R Callister

Publications and source records attributed to R Callister.

At least 19 recordsLinked to original sources

PubMed2006

Reversal in fatigued athletes of a defect in interferon gamma secretion after administration of Lactobacillus acidophilus.

BACKGROUND: Fatigue and impaired performance in athletes is well recognised and has been loosely linked to "overtraining". Reduced concentration of IgA in the saliva and increased shedding of Epstein Barr virus (EBV) have been associated with intense training in elite athletes. OBJECTIVE: To determine whether athletes presenting with fatigue and impaired performance had an immune defect relevant to defective containment of EBV infection, and whether a probiotic preparation (Lactobacillus acidophilus) shown to enhance mucosal immunity in animal models could reverse any detected abnormality. RESULTS: The fatigued athletes had clinical characteristics consistent with re-activation of EBV infection and significantly (p = 0.02) less secretion of interferon (IFN) gamma from blood CD4 positive T cells. After one month of daily capsules containing 2 x 10(10) colony forming units of L acidophilus, secretion of IFNgamma from T cells had increased significantly (p = 0.01) to levels found in healthy control athletes. A significant (p = 0.03) increase in salivary IFNgamma concentrations in healthy control athletes after the one month course of L acidophilus demonstrated in man the capacity for this probiotic to enhance the mucosal IFNgamma concentration. CONCLUSION: This is the first evidence of a T cell defect in fatigued athletes, and of its reversal following probiotic therapy.

Adolescent↗

PubMed2005

Epidemlology of exercise-related transient abdominal pain at the Sydney City to Surf community run.

A questionnaire was administered to 848 participants (76% runners, 24% walkers) at the conclusion of the 14 km City to Surf community run in order to investigate their experience of exercise-related transient abdominal pain (ETAP). Twenty-seven percent of respondents reported experiencing ETAP during the event, with the condition reported more frequently (p< 0.01) by runners (30%) than walkers (16%). ETAP was mostly described as well-localised (88%) and of an aching (25%), sharp (22%) or cramping (22%) sensation. The most commonly-reported sites of the pain were the right (46%) and left lumbar (23%) regions of the abdomen. Forty-two percent of the respondents who experienced ETAP reported that the pain was detrimental to their performance. Reports of ETAP decreased with age (r= -0.23, p< 0.01) but were unrelated to gender, body mass index or the time taken to complete the event. Among respondents who ran, those who consumed a large mass of food relative to body weight in the time interval 1-2 hr before the event were more likely to develop symptoms of ETAP (p < 0.05). The nutritional content of the pre-event meal did not influence the experience of ETAP. Sufferers of ETAP were more likely to experience nausea (r = 0.12, p< 0.01) and report shoulder tip pain (r= 0.14, p< 0.01). The results indicate that ETAP is a commonly experienced problem and provide insights into the cause of the complaint.

Abdominal Pain↗

PubMed2000

Characteristics and etiology of exercise-related transient abdominal pain.

PURPOSE AND METHODS: In order to investigate the characteristics of the exercise-related transient abdominal pain (ETAP) commonly referred to as "stitch," a questionnaire was administered to a total of 965 regular sporting participants involved in six sports. RESULTS: The percentage of respondents claiming to have experienced ETAP within the past year for the respective sports were: running (69%, N = 439), swimming (75%, N = 103), cycling (32%, N = 76), aerobics (52%, N = 126), basketball (47%, N = 121), and horse riding (62%, N = 100). ETAP appears to be most prevalent in activities that involve repetitive torso movement, either vertical translation or longitudinal rotation. ETAP appears to be a single condition, common in its manifestation to most sufferers, and was described by respondents as a well-localized pain (79%), mostly experienced in the right or left lumbar regions of the abdomen (78%). The sensation of ETAP may be related to the severity of pain with less intense ETAP being described as cramping, aching, or pulling, and greater severity ETAP as sharp or stabbing in nature. Fourteen percent of respondents indicated that they experience shoulder tip pain (STP), which being the diaphragmatic-referred site could suggest irritation of the diaphragm. Respondents claiming to have experienced ETAP were more likely to report STP (r = 0.14, P < 0.01). CONCLUSIONS: The findings of the present study provide perspective on previously suggested etiologies of ETAP, which include diaphragmatic ischemia and stress on the visceral "ligaments," and form the basis for examining alternative etiologies such as cramp of the musculature and irritation of the parietal peritoneum.

Abdominal Pain↗

PubMed2000

The effect of baroreflex adaptation on the dynamic cardiovascular response to head-up tilt.

BACKGROUND: Baroreflex adaptation to repetitive +Gz has been reported previously. The underlying mechanism may involve different responses of stroke volume (SV) and total peripheral resistance (TPR) to +Gz. HYPOTHESIS: The previously observed enhanced mean arterial pressure (MAP) regulation in fighter pilots (FP) is mediated by increases in SV and/or TPR. METHODS: There were 8 pilots and 12 non-pilots who underwent head-up tilt. SV was determined using impedance cardiography. RESULTS: MAP increased significantly in FP, due to heart rate (HR) and TPR increasing more and SV decreasing less. CONCLUSION: Baroreflex adaptation results in better performance of HR, SV and TPR in response to +Gz.

Adaptation, Physiological↗

PubMed1999

Analysis of the Gz environment during air combat maneuvering in the F/A-18 fighter aircraft.

BACKGROUND: The F/A-18 Hornet is a high performance fighter aircraft that equips four squadrons of the Royal Australian Air Force (RAAF). The F/A-18 pilot is regularly subjected to high accelerative forces, particularly during air combat maneuvering (ACM). Anecdotal and experimental evidence suggests that cardiovascular adaptation to repetitive Gz can occur. HYPOTHESIS: The purpose of this study was to document the nature and characteristics of the Gz environment to which the pilot is exposed during air combat maneuvering in the F/A-18 fighter aircraft, in terms of its potential to act as a baroreflex training stimulus. The study also aimed to show that onboard data acquisition systems can provide physiologically useful information. METHODS: Two air combat maneuvering sorties were flown. Gz data were downloaded from the F/A-18's onboard computer system for analysis. RESULTS: ACM engagements in the F/A-18 consist of multiple, frequently repetitive excursions to high +Gz levels. Both sorties involved high peak +Gz levels (+7.21 and +7.09), with many excursions (37 and 61) through a +2 Gz threshold. Approximately 20% of each sortie was spent at or above +2 Gz. CONCLUSIONS: This study confirms the physiologically challenging nature of ACM, involving force environment changes of high intensity and frequency. In addition, it indicates the general nature of the training stimulus applied to the arterial baroreflexes which is responsible for the development of cardiovascular adaptation to +Gz seen in previous studies. It also shows that onboard data acquisition systems can provide physiologically useful information, but are limited by low sampling rates.

Adaptation, Physiological↗

PubMed1999

Patterns of physical conditioning in Royal Australian Air Force F/A-18 pilots and the implications for +Gz tolerance.

BACKGROUND: The role of physical conditioning in tolerance to +Gz remains the subject of debate, particularly in relation to the relative merits of aerobic vs. anaerobic conditioning. The purpose of this study was to document the patterns of physical conditioning in Royal Australian Air Force (RAAF) fighter pilots and to relate these findings to the question of +Gz tolerance. METHODS: A questionnaire was used to determine the physical conditioning activities of RAAF F/A-18 pilots. Aerobic fitness levels (VO2max) were determined in a sample of eight pilots using a progressive cycle ergometer protocol. RESULTS: Of the 42 F/A-18 pilots who completed the questionnaire, 86% reported regular physical conditioning, mostly three times per week. Aerobic activities were the most common (83%), with running the most popular activity (55%). Anaerobic activities were reported by 26% of respondents. Most respondents reported doing more than one activity, with an average weekly training volume of 129+/-77 min. The ergometer test results revealed a mean VO2max of 50+/-6 ml O2 x kg x min(-1). CONCLUSION: The high rates of participation in regular physical activity suggest that physical fitness is perceived as important by the fighter pilot operating in the high +Gz environment. The fighter pilots in this study participated in aerobic activities at a much higher rate than anaerobic activities. The aerobic fitness levels measured suggest that the pilots have good but not exceptionally high levels of aerobic power that are unlikely to influence +Gz tolerance.

Adult↗

PubMed1999

The non-invasive assessment of stroke volume and cardiac output by impedance cardiography: a review.

Impedance cardiography (IC) is an inexpensive, reliable and noninvasive technique for determining stroke volume (SV) and cardiac output (CO). It relies on the measurement of phasic changes in transthoracic electrical resistivity, related to ejection of blood into the ascending aorta with each heart beat. Because of its non-invasive nature, IC is becoming increasingly used in clinical settings, as well as in many areas of physiological research. This paper discusses IC in terms of its theoretical basis, the components of the impedance signal and how impedance data is mathematically processed. One of the major controversies surrounding IC concerns how well it compares with conventional methods of determining SV and CO, such as thermodilution. A literature review of such comparative studies demonstrated that the controversy is far from settled, but that IC is generally agreed to be capable of accurately monitoring trends in cardiovascular dynamics. The question of accuracy of IC in terms of absolute values of SV and CO remains to be determined. The methodological limitations, accuracy, reliability and reproducibility of IC are examined, as are some of the methods developed to improve these aspects of the technique. The application and utility of IC in aerospace medicine research is also addressed.

Aerospace Medicine↗

PubMed1998

Evidence of baroreflex adaptation to repetitive +Gz in fighter pilots.

BACKGROUND: The arterial baroreflex acts to maintain arterial pressure in the face of an orthostatic challenge. The high +Gz loads experienced by fighter pilots represent an extreme form of orthostatic challenge. G-induced loss of consciousness (G-LOC) represents a failure of the baroreflex system to maintain the appropriate level of cerebral perfusion. The anecdotal experience of fighter pilots is that their cardiovascular systems adapt to frequent exposure to high +Gz levels. HYPOTHESIS: The purpose of this study was to demonstrate that the baroreflex-mediated cardiovascular response of a group of 8 fighter pilots to a mild accelerative stimulus differs from that of a group of 12 non-pilots. METHODS: Arterial pressures and heart rate responses to rapid head-up tilting to +75 degrees were compared between the two groups. Five variables were examined: systolic, diastolic, mean arterial and pulse pressures, and heart rate. RESULTS: The cardiovascular responses of the groups were fundamentally different. In response to tilt, the non-pilots showed little change in systolic and mean arterial pressures, diastolic pressure increased slightly and pulse pressure decreased significantly. In the pilot group, however, significant increases were observed in systolic, diastolic and mean arterial pressures (p < 0.05), whereas pulse pressure did not change. Between groups there were significant differences observed in terms of arterial pressures (p < 0.05), but not heart rate. CONCLUSION: The baroreflex of a fighter pilot is capable of adapting to +Gz, becoming a more sensitive and effective BP control system as a result. This adaptation affords the pilot greater protection against G-LOC.

Adult↗

PubMed1995

Muscle sympathetic nerve activity during postural change in healthy young and older adults.

Recent evidence suggests that during orthostatic stress the reflex increase in muscle sympathetic nerve activity may be diminished in older adults. To test this hypothesis, we measured muscle sympathetic nerve activity, plasma noradrenaline concentrations, heart rate, and arterial blood pressure in twelve young (mean, 25 years; range, 19-29 years) adults and 14 older (mean 64 years; range, 60-74 years) healthy adults, while supine and during upright sitting. Supine control levels of muscle sympathetic nerve activity were higher in the older subjects (35 +/- 1 vs. 25 +/- 1 bursts/min, p < 0.05), but there were no differences in plasma noradrenaline concentrations, heart rate or arterial pressure. Despite higher supine control levels in the older group, the absolute unit increases in muscle sympathetic nerve activity in response to upright sitting (p < 0.05 vs. control) were not different in the two groups (7 +/- 1 vs. 7 +/- 1 bursts/min), nor were the increases in plasma noradrenaline concentrations. Heart rate did not increase above supine control in response to sitting in either group. Arterial pressure increased slightly (p < 0.05, supine vs. control), but there were no age-related differences. These results indicate that, contrary to recent findings, the reflex increases in muscle sympathetic nerve activity and plasma noradrenaline concentrations and regulation of arterial pressure during this natural orthostatic stress are well preserved in older healthy men and women.

Adult↗

PubMed1994

Active forearm blood flow adjustments to handgrip exercise in young and older healthy men.

1. Our purpose was to test the hypothesis that ageing impairs the active muscle hyperaemia consequent to dynamic exercise in humans. 2. Eleven young (19-29 years) and eleven older (60-74 years) healthy, non-obese men with similar chronic physical activity levels and forearm size performed two protocols of dynamic handgrip exercise: (a) brief (1 min), incremental loads to exhaustion, and (b) sustained (8 min), submaximal loads. Active forearm blood flow (FBF) was measured at rest and during a brief period of relaxation at the end of each minute of exercise. Arterial blood pressure was recorded to calculate active forearm vascular conductance (FVC). Sustained forearm ischaemia plus handgrip was used to elicit a peak forearm vasodilatatory response. 3. There were no differences in pre-exercise levels of any variable between the young and older men. During exercise, ratings of perceived effort, the peak workload attained, and the ability to sustain submaximal workloads were all similar for the two groups. 4. During brief exercise, both submaximal and peak levels of FBF were similar in the two groups; however, the peak increases in FVC were greater in the older men. During sustained exercise, FBF and FVC were not different in the two groups at the lowest loads, but the increases became relatively greater in the older men with increasing workloads. 5. Peak levels of FBF and FVC in response to the peak vasodilatatory stimulus were similar in the young and older men. 6. These findings fail to support the postulate that ageing results in impaired active muscle hyperaemia and vasodilatation during small-muscle dynamic exercise.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1994

Sympathetic neural reactivity to stress does not increase with age in healthy humans.

Sympathetic nervous system reactivity to stress is though to increase with age in humans. We tested this hypothesis by recording postganglionic sympathetic nerve activity to skeletal muscle (MSNA) (peroneal microneurography) and by measuring plasma norepinephrine concentrations (PNE), heart rate, and arterial pressure before (prestress control) and during cognitive challenge (mental arithmetic and colored word test), thermal stress (i.e., the cold pressor test), and exhaustive isometric handgrip exercise (40% of maximum voluntary force)/postexercise ischemia in 15 older (60-74 yr, mean +/- SE = 64 +/- 1) and 15 young (19-30 yr, mean +/- SE = 25 +/- 1) healthy men and women (8 males, 7 females each). The initial prestress control level of MSNA was higher in the older subjects (P < 0.01 vs. young), but there were no significant differences for PNE, heart rate, or arterial pressure. The MSNA and PNE responses to mental stress were small and not different in the two groups. MSNA and PNE increased markedly in response to the cold pressor test and isometric handgrip exercise/post exercise ischemia in both groups. The absolute unit increases in MSNA were similar in the two groups, but the relative (percentage) increases were actually smaller in the older subjects (P < 0.05 vs. young) due to their elevated baseline levels. The stress-evoked increases in arterial pressure were similar in the groups, but the older subjects tended to demonstrate smaller increases in heart rate. In general, no gender differences were noted in either age group. These findings fail to support the long-held concept that stress-induced sympathetic nervous system stimulation becomes exaggerated with age. Thus, sympathetic neural hyperreactivity does not appear to be a fundamental property of the aging process in humans.

Adult↗

PubMed1994

Endurance exercise training is associated with elevated basal sympathetic nerve activity in healthy older humans.

We tested the hypothesis that endurance training is associated with altered basal levels of muscle sympathetic nerve activity (MSNA) and responses to acute stress in healthy older adults. MSNA (peroneal microneurography) and plasma norepinephrine (NE) concentrations were measured during supine rest, a cold pressor test, and isometric handgrip (40% maximal voluntary force to exhaustion) in 16 older masters endurance athletes [10 men, 6 women; 66 +/- 1 (SE) yr] and 15 healthy normotensive untrained control subjects (9 men, 6 women; 65 +/- 1 yr). The athletes had higher levels of estimated daily energy expenditure and maximal oxygen uptake and lower levels of resting heart rate and body fat than the control subjects (all P < 0.05). MSNA during supine rest was elevated in the athletes whether expressed as burst frequency (43 +/- 2 vs. 32 +/- 3 bursts/min, respectively; P < 0.05) or burst incidence (75 +/- 4 vs. 52 +/- 5 bursts/100 heartbeats, respectively; P < 0.01). These whole group differences were due primarily to markedly higher levels of MSNA in the athletic vs. untrained women (48 +/- 4 vs. 25 +/- 3 bursts/min, 82 +/- 3 vs. 38 +/- 3 bursts/100 heartbeats, respectively, P < 0.001). In contrast, basal plasma NE concentrations were not significantly different in the athletes vs. control subjects. The MSNA and plasma NE responses to acute stress tended to be greater in the athletes. These findings indicate that vigorous regular aerobic exercise is associated with an elevated level of MSNA at rest and a tendency for an enhanced response to acute stress in healthy normotensive older humans.

Aged↗

PubMed1994

Arm muscle sympathetic nerve activity during preparation for and initiation of leg-cycling exercise in humans.

We tested the hypothesis that sympathetic vasoconstrictor nerve activity to nonactive skeletal muscle (MSNA) decreases immediately before and remains suppressed during initiation of conventional large muscle upright dynamic exercise in humans. In 11 healthy young subjects, adequate recordings of MSNA from the radial nerve in the arm were obtained during upright seated rest (control) and throughout 1 min of leg-cycling exercise at one or more submaximal workloads (range 33-266 W; approximately 10-80% of peak power output). MSNA was analyzed during four consecutive time intervals; control, preparation for cycling (end of control to onset of pedal movement), initiation of cycling (onset of pedal movement to attainment of target power output), and the initial 60 s of cycling at target power output. MSNA decreased (P < 0.05) abruptly and markedly in all subjects [to 19 +/- 4% (SE) of control levels] during the preparation period before the 33-W load and remained suppressed throughout the period of initiation of cycling in 8 of 11 subjects; MSNA increased during the initiation period in three subjects in whom diastolic arterial pressure fell below control levels. This general pattern was observed at all loads. MSNA remained at or below control levels throughout the 1 min of cycling exercise at 33-166 W. MSNA increased above control levels during the latter portion of the 1 min of cycling only at loads > or = 60% of peak power output.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1993

Induction and prevention of low-T3 syndrome in exercising women.

To investigate the influence of exercise on thyroid metabolism, 46 healthy young regularly menstruating sedentary women were randomly assigned to a 3 x 2 experimental design of aerobic exercise and energy availability treatments. Energy availability was defined as dietary energy intake minus energy expenditure during exercise. After 4 days of treatments, low energy availability (8 vs. 30 kcal.kg body wt-1.day-1) had reduced 3,5,3'-triiodothyronine (T3) by 15% and free T3 (fT3) by 18% and had increased thyroxine (T4) by 7% and reverse T3 (rT3) by 24% (all P < 0.01), whereas free T4 (fT4) was unchanged (P = 0.08). Exercise quantity (0 vs. 1,300 kcal/day) and intensity (40 vs. 70% of aerobic capacity) did not affect any thyroid hormone (all P > 0.10). That is, low-T3 syndrome was induced by the energy cost of exercise and was prevented in exercising women by increasing dietary energy intake. Selective observation of low-T3 syndrome in amenorrheic and not in regularly menstruating athletes suggests that exercise may compromise the availability of energy for reproductive function in humans. If so, athletic amenorrhea might be prevented or reversed through dietary reform without reducing exercise quantity or intensity.

Adult↗

PubMed1993

Age and gender influence muscle sympathetic nerve activity at rest in healthy humans.

Muscle sympathetic nerve activity at rest increases with age in humans. The respective influences of the aging process per se and gender on this increase and whether age and gender effects on muscle sympathetic nerve activity can be identified with plasma norepinephrine concentrations, however, have not been established. To examine these issues, nine young women (aged 24 +/- 1 years; mean +/- SEM), eight young men (aged 26 +/- 1 years), seven older women (aged 63 +/- 1 years), and eight older men (aged 66 +/- 1 years) were studied. All were healthy, normotensive (blood pressure < 140/90 mm Hg), nonobese (< 20% above ideal weight), unmedicated, nonsmokers engaged in minimal to recreational levels of chronic physical activity. Arterial blood pressure (manual sphygmomanometry, brachial artery), heart rate, muscle sympathetic nerve activity (peroneal microneurography), and antecubital venous plasma norepinephrine concentrations (radioenzymatic assay) were determined during quiet supine resting conditions. Body weight was higher in men, but there were no age-related differences, whereas estimated body fat (sum of skinfolds) was higher in women and in the older groups (p < 0.05). Estimated daily energy expenditure, arterial blood pressure, and heart rate were not different among the groups. Both muscle sympathetic nerve activity burst frequency and burst incidence at rest were progressively higher in the young women, young men, older women, and older men (10 +/- 1 versus 18 +/- 2 versus 25 +/- 3 versus 39 +/- 5 bursts/min and 16 +/- 1 versus 30 +/- 4 versus 40 +/- 3 versus 61 +/- 6 bursts/100 heartbeats, respectively; all p < 0.05 versus each other).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1992

Design and control of the head retractor muscle in a turtle, Pseudemys (Trachemys) scripta: I. Architecture and histochemistry of single muscle fibers.

We are using the head retractor muscle (RCCQ) of a turtle, Pseudemys scripta, to analyze the neuromuscular mechanisms by which organisms vary the force and timing of muscle contraction. Previously we demonstrated that RCCQ comprises three histochemically defined fiber types: fast glycolytic (Fg), fast oxidative glycolytic (FOG), and slow oxidative (SO). In the present paper we report the 1) architectural features of single muscle fibers in RCCQ, including their lengths, diameters, and taper characteristics, 2) histochemical profiles of single muscle fibers, and 3) quantitative relations between our architectural and histochemical variables. Single fibers in RCCQ exhibit an order of magnitude variation in length (4-60 mm). Approximately 40% span the full muscle. The remaining fibers generally attach to bone or tendon at one end, and the other end tapers intramuscularly; rarely a fiber may taper at both ends. The maximum (untapering) diameters of single fibers are bimodally distributed, forming two diameter classes. Fibers also vary in the percentage of their total length that tapers and in the shape of the tapering region. Large diameter muscle fibers generally are longer and have shorter, more blunted tapers than small diameter fibers. The large diameter fibers are almost all Fg types; these fibers have a median diameter of 59.3 microns, and they account for approximately 60% of total fibers in RCCQ. FOG and SO fibers generally have small diameters (median: 32.5 microns and 35.8 microns), and they typically account for 30% and 10% of total fibers. We use these relations to draw inferences about the attachments and architecture of glycolytic (Fg) and oxidative (FOG, SO) fiber types. Taken together, our data suggest that single muscle fibers in RCCQ may be architecturally as well as histochemically specialized to perform different roles in head retraction. In the accompanying paper we report the efferent innervation of these fibers and consider some of the neural control problems posed by these diverse fiber types.

Animals↗

PubMed1992

Sympathetic nervous system activity during skin cooling in humans: relationship to stimulus intensity and pain sensation.

1. Our aim was to determine the relationship between efferent sympathetic nervous system activity to skeletal muscle (MSNA) and both the dynamics of the stimulus and pain sensation during localized skin cooling in humans. MSNA in the lower leg (peroneal microneurography), heart rate, arterial blood pressure, hand skin and muscle temperatures and perceptions of pain were recorded in ten healthy subjects before, during and after immersion (3 min) of a hand in water of different temperatures ranging from non-noxious to extremely noxious (28, 21, 14, 7 and 0 degrees C). 2. Immersion produced an abrupt, water temperature-dependent fall in hand skin temperature (initial 30 s) followed by a more gradual decline. In contrast, the fall in hand muscle temperature was almost linear during immersion. Throughout immersions at the 28, 21, and 14 degrees C water temperatures and during the initial phase of the 7 degrees C level, sensations ranged from not painful to somewhat painful; however, the latter phase of the 7 degrees C immersion and the entire 0 degrees C level were perceived as intensely painful. 3. During the initial 15-30 s of immersion at the 21-7 degrees C water temperatures, MSNA decreased from control levels in all subjects (47-58% on average, P < 0.05), whereas mean arterial blood pressure did not change. MSNA then returned to and remained at control levels throughout the 28-14 degrees C immersions, although arterial pressure, primarily systolic, rose slightly. 4. After some delay, MSNA increased during immersion at both the 7 degrees C (P < 0.05 at 90 s) and 0 degrees C (P < 0.05 at 60 s) levels in a progressive, water temperature-dependent manner, achieving peak values of approximately 200 and 300% of control, respectively, by 2.0-2.5 min. These elevations in MSNA were associated with parallel increases in arterial pressure. 5. Heart rate rose during the onset of immersion at all water temperatures (P < 0.05), but fell rapidly to control levels after 60-90 s. The increases were small (approximately 5 beats/min) and similar at the 28-7 degrees C levels, but were twice as great at the coldest water temperature.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗

PubMed1992

Sympathetic activity is influenced by task difficulty and stress perception during mental challenge in humans.

1. Our aim was to determine the influence of the type of task, the absolute and relative difficulty of the task, and the perceived stress associated with performance of the task on sympathetic circulatory regulation during cognitive challenge in humans. 2. Sympathetic nerve activity to skeletal muscle (MSNA) determined from peroneal microneurography, heart rate and arterial blood pressure were recorded continuously in twelve subjects during a modified Stroop colour word test (CWT) and mental arithmetic (MA), each performed over six levels of increasing absolute task difficulty. Performance (percentage correct) on each task was assessed and ratings of perceived stress obtained. Responses to CWT and MA were compared at similar levels of performance and perceived stress. 3. MSNA decreased at task onset, remained below baseline levels at low levels of difficulty which were not perceived as stressful, increased above baseline levels at higher levels of difficulty which were perceived as stressful, and increased further during recovery. Thus, the regulation of MSNA was stress dependent. At similar levels of stress perception there were no differences in MSNA between CWT and MA. Although performance declined as task difficulty increased, there was no particular 'threshold' level of performance associated with the stimulation of MSNA. 4. Arterial pressure and heart rate were elevated above baseline levels throughout the mental tasks. Arterial pressure increased over the first 3-4 levels of each task and then plateaued whereas heart rate did not vary across increasing levels of task difficulty. Heart rate and arterial pressure responses to CWT were higher than those to MA. 5. These data demonstrate that during cognitive challenge the stimulation of MSNA is governed primarily by perceived stress which is dependent, in part, on the absolute level of task difficulty. In contrast, neither performance nor the type of cognitive task appear to be important determinants of MSNA. Arterial pressure is influenced by the task and level of difficulty. Heart rate is independent of task difficulty but may be task dependent.

Adult↗