Effects of Aerobic Exercise Training on the Stiffness of Central and Peripheral Arteries in Middle-Aged Sedentary Men

Aortic pulse wave velocity (PWV) significantly decreased after 16 weeks of moderate-intensity exercise training (walking/jogging) in 17 sedentary middle-aged men, whereas leg PWV did not. These results suggest that in contrast with central arterial stiffness, peripheral arterial stiffness is difficult to change with aerobic exercise training.

Reduction in alpha-adrenergic receptor-mediated vascular tone contributes to improved arterial compliance with endurance training

BACKGROUND

Regular aerobic exercise improves large artery compliance in middle-aged and older humans. However, the underlying mechanisms are unknown. We tested the hypothesis that the improved central arterial compliance with endurance training is mediated by decreased alpha-adrenergic tone and/or increased endothelial function.

METHODS

Seven sedentary healthy adults (60+/-3 years) underwent systemic alpha-adrenergic blockade (phentolamine) and nitric oxide synthase (NOS) inhibition using N(G)-monomethyl-L-arginine in sequence before and after a 3-month moderate endurance training (walk/jog, 4-5 days/week). Phentolamine was given first to isolate the contribution of nitric oxide to arterial compliance by minimizing reflex suppression of sympathetic tone resulting from systemic NOS inhibition as well as to assess the alpha-adrenergic receptor-mediated modulation of arterial compliance.

RESULTS

Baseline arterial compliance (via simultaneous ultrasound and applanation tonometry on the carotid artery) increased 34+/-12% after exercise training (P<0.01). When alpha-adrenergic blockade was performed, arterial compliance increased 37+/-6% (P<0.01) before the exercise training but did not change significantly after the training. Decreases in arterial compliance from the alpha-adrenergic blockade to the subsequent additional NOS blockade were not different before and after exercise training.

CONCLUSION

Our results suggest that the reduction in alpha-adrenergic receptor-mediated vascular tone contributes to the improved central arterial compliance with endurance training.

Relationship between augmentation index obtained from carotid and radial artery pressure waveforms

OBJECTIVE

Increased aortic and carotid arterial augmentation index (AI) has been directly linked with cardiovascular disease risk, mortality and morbidity. The aim of this study was to examine whether AI obtained directly from radial artery pressure waveforms (radial AI) can provide information comparable with carotid arterial AI measurements.

METHODS

In a cross-sectional study of 204 apparently healthy subjects (88 men and 116 women) aged 19-76 years (51 +/- 15 years, mean +/- SD), carotid AI [(second peak carotid systolic pressure - first peak carotid systolic pressure)/carotid pulse pressure*100] and radial AI [(second peak radial systolic pressure - diastolic pressure)/(first peak radial systolic pressure - diastolic pressure)*100] were measured using applanation tonometry.

RESULTS

Radial AI was strongly correlated with carotid AI (r = 0.86, P < 0.0001, SD of difference 10.0%), although radial AI was consistently approximately 66% higher than carotid AI. In 16 apparently healthy young adults (11 men and five women, aged 23 +/- 3 years) handgrip exercise was immediately followed by post-exercise muscle ischaemia (PEMI) to compare changes in carotid and radial AI during increased sympathetic nervous activity. PEMI caused parallel increases in carotid and radial AI (26 and 19%). Accordingly, changes in radial AI with PEMI were strongly correlated with corresponding changes in carotid AI (r = 0.86, P < 0.0001, SD of difference 7.3%).

CONCLUSION

These results suggest that AI obtained directly from radial arterial pressure waveforms could provide equivalent information to carotid arterial AI, and has potential as a surrogate marker of cardiovascular disease.

Direct measurement of cardiac sympathetic efferent nerve activity during dynamic exercise

The assumption that tachycardia during light to moderate exercise was predominantly controlled by withdrawal of cardiac parasympathetic nerve activity but not by augmentation of cardiac sympathetic nerve activity (CSNA) was challenged by measuring CSNA during treadmill exercise (speed, 10-60 m/min) for 1 min in five conscious cats. As soon as exercise started, CSNA and heart rate (HR) increased and mean arterial pressure (MAP) decreased; their time courses at the initial 12-s period of exercise were irrespective of the running speed. CSNA increased 168-297% at 7.1 +/- 0.4 s from the exercise onset, and MAP decreased 8-13 mmHg at 6.0 +/- 0.3 s, preceding the increase of 40-53 beats/min in HR at 10.5 +/- 0.4 s. CSNA remained elevated during the later period of exercise, whereas HR and MAP gradually increased until the end of exercise. After the cessation of exercise, CSNA returned quickly to the control, whereas HR was slowly restored. In conclusion, cardiac sympathetic outflow augments at the onset of and during dynamic exercise even though the exercise intensity is low to moderate, which may contribute to acceleration of cardiac pacemaker rhythm.

Non-invasive assessment of arterial stiffness using oscillometric blood pressure measurement

Background

Arterial stiffness is a major contributor to cardiovascular diseases. Because current methods of measuring arterial stiffness are technically demanding, the purpose of this study was to develop a simple method of evaluating arterial stiffness using oscillometric blood pressure measurement.

Methods

Blood pressure was conventionally measured in the left upper arm of 173 individuals using an inflatable cuff. Using the time series of occlusive cuff pressure and the amplitudes of pulse oscillations, we calculated local slopes of the curve between the decreasing cuff pressure and corresponding arterial volume. Whole pressure-volume curve was derived from numerical integration of the local slopes. The curve was fitted using an equation and we identified a numerical coefficient of the equation as an index of arterial stiffness (Arterial Pressure-volume Index, API). We also measured brachial-ankle (baPWV) PWV and carotid-femoral (cfPWV) PWV using a vascular testing device and compared the values with API. Furthermore, we assessed carotid arterial compliance using ultrasound images to compare with API.

Results

The slope of the calculated pressure-volume curve was steeper for compliant (low baPWV or cfPWV) than stiff (high baPWV or cfPWV) arteries. API was related to baPWV (r = -0.53, P < 0.05), cfPWV (r = -0.49, P < 0.05), and carotid arterial compliance (r = 0.32, P < 0.05). A stepwise multiple regression analysis demonstrated that baPWV and carotid arterial compliance were the independent determinants of API, and that API was the independent determinant of baPWV and carotid arterial compliance.

Conclusions

These results suggest that our method can simply and simultaneously evaluate arterial stiffness and blood pressure based on oscillometric measurements of blood pressure.

Effect of systemic nitric oxide synthase inhibition on arterial stiffness in humans

Stiffening of large elastic arteries impairs the buffering function of the arterial system and contributes to cardiovascular disease. The aim of this study was to determine whether endothelium-derived nitric oxide (NO) modulates the stiffness of large elastic arteries in humans. Seven apparently healthy adults (60+/-3 years, 2 males and 5 females) underwent systemic alpha-adrenergic blockade (phentolamine) and systemic NO synthase inhibition using NG-monomethyl-L-arginine (L-NMMA) in sequence. Phentolamine was given first to isolate contribution of NO to arterial stiffness by preventing reflex changes in sympathetic tone that result from systemic NO synthase inhibition, and also to compare arterial stiffness at a similar mean arterial pressure. Mean arterial blood pressure decreased (p<0.05) after phentolamine infusion but returned to baseline levels after L-NMMA infusion. The carotid beta-stiffness index (via simultaneous ultrasound and applanation tonometry on the common carotid artery) did not change after the restraint of systemic alpha-adrenergic nerve activity (9.8+/-1.2 vs. 9.1+/-1.1 U) but increased (p<0.05) after NO synthase inhibition (12.6+/-2.0 U). These results suggest that NO appears to modulate central arterial stiffness in humans.

Systemic alpha-adrenergic and nitric oxide inhibition on basal limb blood flow: effects of endurance training in middle-aged and older adults

Endurance training improves endothelium-dependent vasodilation, yet it does not increase basal blood flow in the legs. We determined the effects of a 3-mo aerobic exercise intervention on basal leg blood flow and alpha-adrenergic vasoconstriction and nitric oxide (NO) release in seven apparently healthy middle-aged and older adults (60 +/- 3 yr). Basal femoral artery blood flow (via Doppler ultrasound) (pretraining: 354 +/- 29; posttraining: 335 +/- 34 ml/min) and vascular conductance did not change significantly with the exercise training. Before the exercise intervention, femoral artery blood flow increased 32 +/- 16% with systemic alpha-adrenergic blockade (with phentolamine) (P < 0.05), and the addition of nitric oxide synthase (NOS) inhibition using N(G)-monomethyl-L-arginine (L-NMMA) did not affect femoral artery blood flow. After training was completed, femoral artery blood flow increased 47 +/- 7% with alpha-adrenergic blockade (P < 0.01) and then decreased 18 +/- 7% with the subsequent administration of L-NMMA (P < 0.05). Leg vascular conductance showed a greater alpha-adrenergic blockade-induced vasodilation (+1.7 +/- 0.5 to +3.0 +/- 0.5 units, P < 0.05) as well as NOS inhibition-induced vasoconstriction (-0.8 +/- 0.4 to -2.7 +/- 0.7 units, P < 0.05) after the exercise intervention. Resting plasma norepinephrine concentration significantly increased after the training. These results suggest that regular aerobic exercise training enhances NO bioavailability in middle-aged and older adults and that basal limb blood flow does not change with exercise training because of the contrasting influences of sympathetic nervous system activity and endothelium-derived vasodilation on the vasculature.

Central command blunts the baroreflex bradycardia to aortic nerve stimulation at the onset of voluntary static exercise in cats

To examine whether the central characteristics of the aortic baroreflex alter from moment to moment during static exercise, we identified the dynamic changes in the sizes of the bradycardia and depressor response evoked by stimulation of the aortic depressor nerve (ADN). Three conscious cats were trained to voluntarily extend the right forelimb and press a bar for 31 +/- 1 s with a peak force of 337 +/- 22 g while maintaining a sitting posture. The ADN stimulation-induced bradycardia was attenuated at the initial period of exercise (up to 8 s from the exercise onset) to 62 +/- 5% of the preexercise bradycardia and remained blunted until the end of exercise. The most blunted bradycardia was observed immediately before or when the forelimb was extended before force development. The baroreflex-induced bradycardia was suppressed again at cessation of exercise when the forelimb was retracted and recovered within a few seconds. In contrast, static exercise did not affect the ADN stimulation-induced depressor response. The ADN stimulation-induced bradycardia was also blunted at the beginning of naturally occurring body movement such as spontaneous postural change or grooming behavior. Thus it is likely that the central characteristics of the aortic baroreflex dynamically change from moment to moment during voluntary static exercise and during natural body movement and that particularly a central inhibition of the cardiac component of the aortic baroreflex is induced by central command at the onset of static exercise, whereas the central property of the vasomotor component of the baroreflex is preserved.

Noninvasive evaluation of cardiac output during postural change and exercise in humans: comparison between the modelflow and pulse dye-densitometry

To investigate whether the Model-flow method, by simulating the aortic input impedance model from a noninvasive monitoring of arterial blood pressure, reflected a reliable measure of cardiac output (CO) during postural change and whole-body exercise occurring in daily life, we compared the Modelflow-estimated CO with a simultaneous reference determined by the pulse dye-densitometry. Nine healthy volunteers performed postural change from supine to upright and dynamic stepping exercise. The Modelflow-estimated CO decreased to 4.8 +/- 0.5 l/min, from 5.8 +/- 0.6 l/min, during the postural change and increased to 12.8 +/- 1.3 l/min during a stepping exercise, returning to 5.1 +/- 0.4 l/min at 5 min after exercise. When comparing the pooled data of CO during resting and following exercise between the Modelflow and pulse dye-densitometry, we found that the average CO did not differ between the two estimates and that there was a significant correlation between them; the slope of the linear regression line corresponded to approximately 1.0. Although such linear relationship was also observed in an individual subject, the slope of the regression line varied from 0.737 to 1.588 among the subjects. The calibration of the Modelflow-estimated CO with the dye-densitometry value at supine or upright improved a correlation between the two estimates. Thus it is likely that the noninvasive Modelflow simulation from arterial blood pressure can provide a reliable estimation of group-average cardiac output during postural change and stepping exercise occurring in daily life. It will be recommended for a more accurate estimation of cardiac output in a given subject to calibrate the Modelflow data with an independent measure.

Cardiovascular control during voluntary static exercise in humans with tetraplegia

The purpose of the present study was 1) to investigate whether an increase in heart rate (HR) at the onset of voluntary static arm exercise in tetraplegic subjects was similar to that of normal subjects and 2) to identify how the cardiovascular adaptation during static exercise was disturbed by sympathetic decentralization. Mean arterial blood pressure (MAP) and HR were noninvasively recorded during static arm exercise at 35% of maximal voluntary contraction in six tetraplegic subjects who had complete cervical spinal cord injury (C(6)-C(7)). Stroke volume (SV), cardiac output (CO), and total peripheral resistance (TPR) were estimated by using a Modelflow method simulating aortic input impedance from arterial blood pressure waveform. In tetraplegic subjects, the increase in HR at the onset of static exercise was blunted compared with age-matched control subjects, whereas the peak increase in HR at the end of exercise was similar between the two groups. CO increased during exercise with no or slight decrease in SV. MAP increased approximately one-third above the control pressor response but TPR did not rise at all throughout static exercise, indicating that the slight pressor response is determined by the increase in CO. We conclude that the cardiovascular adaptation during voluntary static arm exercise in tetraplegic subjects is mainly accomplished by increasing cardiac pump output according to the tachycardia, which is controlled by cardiac vagal outflow, and that sympathetic decentralization causes both absent peripheral vasoconstriction and a decreased capacity to increase HR, especially at the onset of exercise.

Central inhibition of the aortic baroreceptors-heart rate reflex at the onset of spontaneous muscle contraction

Animals decerebrated at the precollicular-premammillary body level exhibit spontaneous locomotion without any artificial stimulation. Our laboratory reported that the cardiovascular and autonomic responses at the onset of spontaneous locomotor events are evoked by central command, generated from the caudal diencephalon and the brain stem (Matsukawa K, Murata J, and Wada T. Am J Physiol Heart Circ Physiol 275: H1115–H1121, 1998). In this study, we examined whether central command and/or a reflex resulting from muscle afferents modulates arterial baroreflex function using a decerebrate cat model. The baroreflex was evoked by stimulating the aortic depressor nerve (ADN) at the onset of spontaneous muscle contraction (to test the possible influence of central command) and during electrically evoked contraction or passive stretch (to test the possible influence of the muscle reflex). When the ADN was stimulated at rest, heart rate and arterial blood pressure decreased by 40 ± 2 beats/min and 11 ± 1 mmHg, respectively. The baroreflex bradycardia was attenuated to 55 ± 4% at the onset of spontaneous contraction. The attenuating effect on the baroreflex bradycardia was not observed at the onset and middle of electrically evoked contraction or passive stretch. The depressor response to ADN stimulation was identical among resting and any muscle interventions. The inhibition of the baroreflex bradycardia during spontaneous contraction was seen after β-adrenergic blockade but abolished by muscarinic blockade, suggesting that the bradycardia is mainly evoked through cardiac vagal outflow. We conclude that central command, produced within the caudal diencephalon and the brain stem, selectively inhibits the cardiac component, but not the vasomotor component, of the aortic baroreflex at the onset of spontaneous exercise.

Regular endurance exercise in young men increases arterial baroreflex sensitivity through neural alteration of baroreflex arc

Endurance exercise training increases arterial baroreflex sensitivity that corresponds to alteration in vessel wall compliance of the carotid artery in elderly men. Here, we examined whether regular endurance exercise increases arterial baroreflex sensitivity through neural alteration of the baroreflex arc in young men. We assessed arterial baroreflex sensitivity in eight sedentary men (age 24 ± 1 yr) and nine men trained in endurance exercise (age 23 ± 1 yr) during phase IV of the Valsalva maneuver [systolic arterial blood pressure (SAP)–R-R interval relationship]. Arterial baroreflex sensitivity was further analyzed by dividing the mechanical component [SAP–end-systolic carotid lumen diameter relationship (ultrasonography)] and the neural component (end-systolic carotid lumen diameter–R-R interval relationship). Carotid arterial compliance was determined using B-mode ultrasound and arterial applanation tonometry on the common carotid artery. Arterial baroreflex sensitivity and its neural component were greater in the exercise-trained group ( P < 0.05). In contrast, carotid arterial compliance and the mechanical component of arterial baroreflex sensitivity did not differ between groups. These results suggest that regular endurance exercise in young men increases arterial baroreflex sensitivity through changes in the neural component of the baroreflex arc and not through alterations in vessel wall compliance of the carotid artery.

Central command blunts sensitivity of arterial baroreceptor-heart rate reflex at onset of voluntary static exercise

We have reported that baroreflex bradycardia by stimulation of the aortic depressor nerve is blunted at the onset of voluntary static exercise in conscious cats. Central command may contribute to the blunted bradycardia, because the most blunted bradycardia occurs immediately before exercise or when a forelimb is extended before force development. However, it remained unknown whether the blunted bradycardia is due to either reduced sensitivity of the baroreflex stimulus-response curve or resetting of the curve toward a higher blood pressure. To determine this, we examined the stimulus-response relationship between systolic (SAP) or mean arterial pressure (MAP) and heart rate (HR) at the onset of and during the later period of static exercise in seven cats ( n = 348 trials) by changing arterial pressure with infusion of nitroprusside and phenylephrine or norepinephrine. The slope of the MAP-HR curve decreased at the onset of exercise to 48% of the preexercise value (2.9 ± 0.4 beats·min−1·mmHg−1); the slope of the SAP-HR curve decreased to 59%. The threshold blood pressures of the stimulus-response curves, at which HR started to fall due to arterial baroreflex, were not affected. In contrast, the slopes of the stimulus-response curves during the later period of exercise returned near the preexercise levels, whereas the threshold blood pressures elevated 6–8 mmHg. The maximal plateau level of HR was not different before and during static exercise, denying an upward shift of the baroreflex stimulus-response curves. Thus central command is likely to attenuate sensitivity of the cardiac component of arterial baroreflex at the onset of voluntary static exercise without shifting the stimulus-response curve.

Increased oxygenation of the cerebral prefrontal cortex prior to the onset of voluntary exercise in humans

To determine whether output from the forebrain (termed central command) may descend early enough to increase cardiac and renal sympathetic outflows at the onset of voluntary exercise, we examined the changes in regional tissue blood flows of bilateral prefrontal cortices with near-infrared spectroscopy, precisely identifying the onset of voluntary ergometer 30-s exercise at 41 ± 2% of the maximal exercise intensity in humans. Prefrontal oxygenated-hemoglobin (Oxy-Hb) concentration was measured as index of regional blood flow unless deoxygenated-hemoglobin concentration remained unchanged. Prefrontal Oxy-Hb concentration increased significantly ( P < 0.05) 5 s prior to the onset of exercise with arbitrary start, whereas such increase in prefrontal Oxy-Hb was absent before exercise abruptly started by a verbal cue. Furthermore, the increase in prefrontal Oxy-Hb observed at the initial 15-s period of exercise was greater with arbitrary start than cued start. The prefrontal Oxy-Hb, thereafter, decreased during the later period of exercise, irrespective of either arbitrary or cued start. The reduction in prefrontal Oxy-Hb had the same time course and response magnitude as that during motor-driven passive exercise. Cardiac output increased at the initial period of exercise, whereas arterial blood pressure and total peripheral resistance decreased. The depressor response was more pronounced ( P < 0.05) with arbitrary start than cued start. Taken together, it is suggested that the increase in prefrontal Oxy-Hb observed prior to the onset of voluntary exercise may be in association with central command, while the later decrease in the Oxy-Hb during exercise may be in association with feedback stimulated by mechanical limb motion.

Sympathetic cholinergic nerve contributes to increased muscle blood flow at the onset of voluntary static exercise in conscious cats

We examined whether a sympathetic cholinergic mechanism contributed to increased blood flow of the exercising muscle at the onset of voluntary static exercise in conscious cats. After six cats were operantly conditioned to perform static bar press exercise with a forelimb while maintaining a sitting posture, a Transonic or pulsed Doppler flow probe was implanted on the brachial artery of the exercising forelimb, and catheters were inserted into the left carotid artery and jugular vein. After the baseline brachial blood flow and vascular conductance decreased and became stable in progress of postoperative recovery, the static exercise experiments were started. Brachial blood flow and vascular conductance began to increase simultaneously with the onset of exercise. Their initial increases reached 52 +/- 8% and 40 +/- 6% at 3 s from the exercise onset, respectively. Both a sympathetic ganglionic blocker (hexamethonium bromide) and atropine sulfate or methyl nitrate blunted the increase in brachial vascular conductance at the onset of static exercise, whereas an inhibitor of nitric oxide synthesis (N(omega)-nitro-l-arginine methyl ester) did not alter the increase in brachial vascular resistance. Brachial blood flow and vascular conductance increased during natural grooming behavior with the forelimb in which the flow probe was implanted, whereas they decreased during grooming with the opposite forelimb and during eating behavior. Thus it is likely that the sympathetic cholinergic mechanism is capable of evoking muscle vasodilatation at the onset of voluntary static exercise in conscious cats.

Reflex responses in plasma catecholamines caused by static contraction of skeletal muscle

To examine a hypothesis of whether static muscle contraction produces a release of catecholamines from the adrenal medulla via reflex stimulation of preganglionic adrenal sympathetic nerve activity induced by receptors in the contracting muscle, we compared the reflex responses in a concentration of epinephrine (Ep) and norepinephrine (NEp) in arterial plasma during static contraction and during a mechanical stretch of the hindlimb triceps surae muscle in anesthetized cats. Static contraction was evoked by electrically stimulating the peripheral ends of the cut L(7) and S(1) ventral roots at 20 or 40 Hz. Mean arterial pressure (MAP) and heart rate (HR) increased 23 +/- 3.1 mmHg and 19 +/- 4.3 beats/min during static contraction. Ep in arterial plasma increased 0.18 +/- 0.072 ng/ml over the control of 0.14 +/- 0.051 ng/ml within 1 min from the onset of static contraction, and NEp increased 0.47 +/- 0.087 ng/ml over the control of 0.71 +/- 0.108 ng/ml. Following a neuromuscular blockade, although the same ventral root stimulation failed to produce the cardiovascular and plasma catecholamine responses, the mechanical stretch of the muscle increased MAP, HR, and plasma Ep, but not plasma NEp. With bilateral adrenalectomy, the baseline Ep became negligible (0.012 +/- 0.001 ng/ml) and the baseline NEp was lowered to 0.52 +/- 0.109 ng/ml. Neither static contraction nor mechanical stretch produced significant responses in plasma Ep and NEp following the adrenalectomy. These results suggest that static muscle contraction augments preganglionic adrenal sympathetic nerve activity, which in turn secretes epinephrine from the adrenal medulla into plasma. A muscle mechanoreflex from the contracting muscle may play a role in stimulation of the adrenal sympathetic nerve activity.

Impact of chronic exercise training on the blood pressure response to orthostatic stimulation

Exercise training elicits morphological adaptations in the left ventricle (LV) and large-conduit arteries that are specific to the type of training performed (i.e., endurance vs. resistance exercise). We investigated whether the mode of chronic exercise training, and the associated cardiovascular adaptations, influence the blood pressure responses to orthostatic stimulation in 30 young healthy men (10 sedentary, 10 endurance trained, and 10 resistance trained). The endurance-trained group had a significantly larger LV end-diastolic volume normalized by body surface area (vs. sedentary and resistance-trained groups), whereas the resistance-trained group had a significantly higher LV wall thickness and aortic pulse wave velocity (PWV) compared with the endurance-trained group. In response to 60° head-up tilt (HUT), mean arterial pressure (MAP) rose in the resistance-trained group (+6.5 ± 1.6 mmHg, P < 0.05) but did not change significantly in sedentary and the endurance-trained groups. Systolic blood pressure (SBP) decreased in endurance-trained group (-8.3 ± 2.4 mmHg, P < 0.05) but did not significantly change in sedentary and resistance-trained groups. A forward stepwise multiple regression analysis revealed that LV wall thickness and aortic PWV were significantly and independently associated with the MAP response to HUT, explaining ∼41% of its variability (R(2) =0.414, P < 0.001). Likewise, aortic PWV and the corresponding HUT-mediated change in stroke volume were significantly and independently associated with the SBP response to HUT, explaining ∼52% of its variability (R(2) = 0.519, P < 0.0001). Furthermore, the change in stroke volume significantly correlated with LV wall thickness (r = 0.39, P < 0.01). These results indicate that chronic resistance and endurance exercise training differentially affect the BP response to HUT, and that this appears to be associated with training-induced morphological adaptations of the LV and large-conduit arteries.

Racial Differences in Relation Between Carotid and Radial Augmentation Index

BACKGROUND: Augmented central artery wave reflection is a cardiovascular disease risk factor. Augmentation index (AI) obtained from peripheral artery waveforms provides qualitatively similar information to AI from central artery waveforms. Little information is available, however, regarding the influence of racial difference in association between central and peripheral AI. METHODS: We studied 47 White adults (45+/-17 yr, 20 women) and 94 age-matched Asian adults (45+/-14 yr, 42 women). RESULTS: The White group was significantly taller than the Asian group, whereas there were no significant group differences in blood pressure and heart rate. Carotid and radial AI tended to be lower in White compared with Asian adults (P<0.10 for both). Such tendency disappeared when the difference in height was taken into account using ANCOVA (P=0.84 and P=0.77, respectively). Radial AI was strongly and positively correlated with carotid AI in White adults (r=0.75, P<0.0001) as well as in Asian adults (r=0.82, P<0.0001). The slope and intercept of linear regression line between radial and carotid AI of White adults were highly comparable with those of Asian adults. CONCLUSION: AI in the conveniently located peripheral vasculature may provide a surrogate measure of central AI irrespective of difference in race (e.g., Asian vs. White populations).

Physiological reaction and manual performance during work in cold storages

Subjects were 10 workers (Group R) working in two cold storages (air temperature was between -20 degrees C and -23.2 degrees C), and eight workers (Group C) working in a general storehouse (air temperature was between 12 degrees C and 15.2 degrees C). They were all male workers operating forklift-trucks. Average (SE) age for Group R was 41.4(1.3) years and for Group C was 47.3(1.6) years. Hand tremor, handgrip strength, pinch strength, counting task, flicker value, peak flow rate and blood pressure were measured five times (before work, at 10 a.m., before lunch, at 3 p.m. and after work) per day. Blood samples were collected before lunch. Free fatty acid (FFA) of Group R was significantly higher than that of Group C. There were no significant differences in handgrip strength, pinch strength, counting task, flicker value and peak flow rate between Group R and Group C. However, changes in hand tremor and diastolic blood pressure for Group R were significantly greater than those for Group C. Only for Group R, there was a significant relationship between FFA and the hand tremor values measured the second time. Work loads of Group R would be increased by not only the extreme coldness but also large temperature difference between the inside and the outside of the cold storages. The actual forklift work in these cold storages did not cause a distinct reduction in manual performance, but caused an increase in stress which would be expressed as an increase in catecholamine excretion.

Forelimb vasodilatation induced by hypothalamic stimulation is greatly mediated with nitric oxide in anesthetized cats

The aim of this study was to examine whether or not stimulation of the hypothalamic defense area is capable of inducing sympathetic vasodilatation of the forelimb vascular bed in anesthetized cats. When the hypothalamic defense area was electrically stimulated, brachial blood flow velocity (brachial BFV) and vascular conductance were increased as well as femoral BFV and vascular conductance. Brachial BFV and vascular conductance increased by 110-139% during hypothalamic stimulation. These increases were blunted to approximately one-fifth of the control responses following i.v. injection of a synthesis inhibitor of nitric oxide, N(omega)-nitro-L-arginine methyl ester (L-NAME). The attenuating effect of L-NAME on forelimb vasodilatation evoked by hypothalamic stimulation was greater than that on hindlimb vasodilatation. The combined administration of L-NAME and atropine sulfate eliminated nearly all of the increases in brachial BFV and vascular conductance during hypothalamic stimulation. From the present results, we conclude that stimulation of the hypothalamic defense area is able to induce neurogenic vasodilatation of the cat forelimb vascular bed, which is greatly mediated with a nitric oxide mechanism. The contribution of nitric oxide to neurogenic vasodilatation seems to be greater in the forelimbs than hindlimbs.

Beat-to-Beat Modulation of Atrioventricular Conduction during Dynamic Exercise in Humans

A complex balance between extrinsic neural and intrinsic mechanisms is responsible for regulating atrioventricular (AV) conduction. We hypothesized that atrial excitation interval is shortened during dynamic exercise by extrinsic cardiac autonomic activity and that if AV conduction time responds inversely to fluctuation in atrial rhythm, ventricular excitation interval will be maintained at the predetermined cardiac cycle length. To examine such inverse relationship between PP interval and the subsequent change in PR interval (DeltaPR), we analyzed the beat-to-beat changes in PP, PR, and RR intervals during stair-stepping exercise for 10 min in 11 sedentary and 9 trained subjects. In the sedentary group, the average PR interval significantly shortened during exercise, in parallel with the reduction in the average PP and RR intervals. The variance of PP and RR intervals was also significantly decreased during exercise. The reduction in the variance of RR interval was, however, much greater than that of PP interval, implying that AV conduction time changes inversely to fluctuation in atrial excitation rhythm. Indeed, the variance of PR interval was augmented during exercise and there was a clear inverse relationship between PP and DeltaPR intervals. Although trained subjects were characterized by their lower heart rate response during dynamic exercise, the responses in the variability of PP, PR, and RR intervals were fundamentally identical with those in sedentary subjects. We conclude that the AV nodal mechanism that operates at a higher level of heart rate during dynamic exercise may cancel fluctuation in atrial excitation interval and keep ventricular excitation rhythm at the predetermined cardiac cycle length.

Sympathetic cholinergic vasodilation of skeletal muscle small arteries

Recently we have studied the direct vasomotor response of the hindlimb extramuscular large arteries (internal diameter, 500-1400 microm) and intramuscular small arteries (internal diameter, 50-500 microm) of in vivo thick skeletal muscle during activation of sympathetic cholinergic nerve in anesthetized cats. The hypothalamic defense area was electrically stimulated so as to induce a profound increase in femoral blood flow mediated by sympathetic cholinergic fibers. To visualize the vascular arrangement from the extramuscular large feeding arteries to small arteries in the triceps surae muscle, we developed a new X-ray TV system. The internal diameter, flow velocity, and volume flow of arterial blood vessels were directly measured before and during stimulation of the hypothalamic defense area. The major new finding is that the hypothalamic stimulation causes an intense increase in the internal diameter of small arteries in skeletal muscle, which is abolished either by cholinergic blockade or by the section of the sciatic nerve, but not by combined alpha- and beta-adrenergic blockade. In contrast, the internal diameter of the extramuscular larger arteries does not change during the hypothalamic stimulation, but their flow velocity and volume flow increase. These findings indicate that sympathetic cholinergic vasodilation occurs at intramuscular small arteries with internal diameter of 50-500 microm, which in turn increases flow velocity and volume flow of upstream blood vessels.

Arterial elastic property in young endurance and resistance-trained women

In men, regular aerobic exercise increases central arterial elasticity, but it is decreased by resistance training. We determined the relation between the type of exercise training and arterial elasticity in healthy young women: 26 healthy young women who were sedentary (CO, n = 9), endurance-trained (ET, n = 9), and resistance-trained (RT, n = 8) groups. We determined the carotid arterial compliance and distensibility coefficient (simultaneous ultrasound and applanation tonometry), VO(2max), and 1RM (bench press and leg extension). The VO(2max) in the ET groups was higher than in the CO and RT groups. Both 1RM were higher in the RT groups than in the CO and ET groups. No significant difference was found in the carotid artery compliance and distensibility coefficient among the ET, RT, and CO groups. These results underscore the difficulty in detecting a change in arterial elasticity in young female athletes using the type of exercise training by which it is shown in young men.