Cardiovascular responses to brief static contractions in man with topical nervous blockade

Cardiac acceleration at the onset of exercise: a potential parameter for monitoring progress during physical training in sports and rehabilitation

There is a need for easy-to-use methods to assess training progress in sports and rehabilitation research. The present review investigated whether cardiac acceleration at the onset of physical exercise (HRonset) can be used as a monitoring variable. The digital databases of Scopus and PubMed were searched to retrieve studies investigating HRonset. In total 652 studies were retrieved. These articles were then classified as having emphasis on HRonset in a sports or rehabilitation setting, which resulted in 8 of 112 studies with a sports application and 6 of 68 studies with a rehabilitation application that met inclusion criteria. Two co-existing mechanisms underlie HRonset: feedforward (central command) and feedback (mechanoreflex, metaboreflex, baroreflex) control. A number of studies investigated HRonset during the first few seconds of exercise (HRonsetshort), in which central command and the mechanoreflex determine vagal withdrawal, the major mechanism by which heart rate (HR) increases. In subsequent sports and rehabilitation studies, interest focused on HRonset during dynamic exercise over a longer period of time (HRonsetlong). Central command, mechanoreflexes, baroreflexes, and possibly metaboreflexes contribute to HRonset during the first seconds and minutes of exercise, which in turn leads to further vagal withdrawal and an increase in sympathetic activity. HRonset has been described as the increase in HR compared with resting state (delta HR) or by exponential modeling, with measurement intervals ranging from 0-4 s up to 2 min. Delta HR was used to evaluate HRonsetshort over the first 4 s of exercise, as well as for analyzing HRonsetlong. In exponential modeling, the HR response to dynamic exercise is biphasic, consisting of fast (parasympathetic, 0-10 s) and slow (sympathetic, 1-4 min) components. Although available studies differed largely in measurement protocols, cross-sectional and longitudinal training studies showed that studies analyzing HRonset in relation to physical training primarily incorporated HRonsetlong. HRonsetlong slowed in athletes as well as in patients with a coronary disease, who have a relatively fast HRonsetlong. It is advised to include both HRonsetlong and HRonsetshort in further studies. The findings of this review suggest that HRonset is a potential tool for monitoring and titrating training in sports as well as in rehabilitation settings, particularly in patients with ventricular fibrillation. Monitoring HRonset in the early phase of training can help optimize the effectiveness of training and therapy. More research is needed to gain a better understanding of the mechanisms underlying HRonset in relation to their application in sports and rehabilitation settings.

Mechanical load and physiological responses of four different resistance training methods in bench press exercise

The purpose of the study was to compare the mechanical impact and the corresponding physiological responses of 4 different and often practically applied resistance training methods (RTMs). Ten healthy male subjects (27.3 ± 3.2 years) experienced in resistance training performed 1 exhausting set of bench press exercise until exhaustion for each of the following RTMs: strength endurance (SE), fast force endurance (FFE), hypertrophy (HYP), and maximum strength (MAX). The RTMs were defined by different lifting masses and different temporal distributions of the contraction modes per repetition. Mean concentric power (P), total concentric work (W), and exercise time (EXTIME) were determined. Oxygen uptake (V[Combining Dot Above]O2) was measured during exercise and for 30 minutes postexercise. Mean V[Combining Dot Above]O2, volume of consumed O2, and excess postexercise oxygen consumption (EPOC) were calculated over 30 minutes of recovery. Maximum blood lactate concentration (LAmax) was also determined postexercise. The P was significantly higher (p < 0.01) for FFE and MAX compared with that for SE and HYP. The W was significantly higher for FFE than for all other RTMs (p < 0.01), and it was also lower for SE than for MAX (p < 0.05). EXTIME for SE was significantly higher (p < 0.01) than for all other RTMs, whereas EXTIME for MAX was significantly lower (p < 0.01) than for all other RTMs. Mean V[Combining Dot Above]O2 was significantly higher during FFE than during all other RTMs (p < 0.01). Consumed O2 was significantly higher (p < 0.05) during SE than for HYP and MAX, and it was also significantly higher for FFE and HYP compared with MAX (p < 0.05). The LAmax was significantly higher after FFE than after MAX (p < 0.05). There were no significant differences in EPOC between all RTMs. The results indicate that FFE and MAX are adequate to train muscular power despite the discrepancy in the external load. Because FFE performance achieves the highest amount in mechanical work, it may also elicit the highest total energy expenditure. The FFE challenges aerobic metabolism most and SE enables the longest EXTIME, indicating both are appropriate to enhance aerobic muscular capacities. The EPOC and LA values may indicate that energy needs covered by anaerobic metabolism are not higher during HYP and MAX compared with the RTM of lower external load.

Rapid cardiac adaptation to exercise demand signal and execution of maximal leg muscle contraction

We investigated the neural regulation of the cardiac interval to an exercise demand signal and to a repeated exercise in 20 healthy human subjects. Electrocardiogram (ECG), muscle torque, and electromyogram (EMG) were simultaneously measured and their time relationships compared before and during the exercise. The R-R interval of ECG was directly increased by the exercise demand signal itself before the onset of EMG but not reflexly by muscle contraction. The cardiac interval decreased at the onset of exercise. Under the condition of repeated maximum eccentric training, the resting cardiac interval decreased prior to the exercise, whereas the brief increase in cardiac interval to the exercise demand signal remained unchanged. These results suggested that when autonomic nerve activity to the pacemaker is activated by the exercise demand signal, an initial effect of vagal nerve activity appears, and an effect of vagal nerve withdrawal and/or sympathetic nerve activity then appears. The responses of the heart and leg skeletal muscle at the onset of exercise are not synchronized, and the cardiac interval is controlled by vagal and sympathetic nerve activities to effect a transition to a high heart rate as quickly and smoothly as possible.

Neural blockade during exercise augments central command's contribution to carotid baroreflex resetting

This investigation was designed to determine central command's role on carotid baroreflex (CBR) resetting during exercise. Nine volunteer subjects performed static and rhythmic handgrip exercise at 30 and 40% maximal voluntary contraction (MVC), respectively, before and after partial axillary neural blockade. Stimulus-response curves were developed using the neck pressure-neck suction technique and a rapid pulse train protocol (+40 to -80 Torr). Regional anesthesia resulted in a significant reduction in MVC. Heart rate (HR) and ratings of perceived exertion (RPE) were used as indexes of central command and were elevated during exercise at control force intensity after induced muscle weakness. The CBR function curves were reset vertically with a minimal lateral shift during control exercise and exhibited a further parallel resetting during exercise with neural blockade. The operating point was progressively reset to coincide with the centering point of the CBR curve. These data suggest that central command was a primary mechanism in the resetting of the CBR during exercise. However, it appeared that central command modulated the carotid-cardiac reflex proportionately more than the carotid-vasomotor reflex.

Effect of muscle mass and intensity of isometric contraction on heart rate

The purpose of this study was to determine the effect of muscle mass and the level of force on the contraction-induced rise in heart rate. We conducted an experimental study in a sample of 28 healthy men between 20 and 30 yr of age (power: 95%, alpha: 5%). Smokers, obese subjects, and those who performed regular physical activity over a certain amount of energetic expenditure were excluded from the study. The participants exerted two types of isometric contractions: handgrip and turning a 40-cm-diameter wheel. Both were sustained to exhaustion at 20 and 50% of maximal force. Twenty-five subjects finished the experiment. Heart rate increased a mean of 15.1 beats/min [95% confidence interval (CI): 5.5-24.6] from 20 to 50% handgrip contractions, and 20.7 beats/min (95% CI: 11.9-29.5) from 20 to 50% wheel-turn contractions. Heart rate also increased a mean of 13.3 beats/min (95% CI: 10.4-16.1) from handgrip to wheel-turn contractions at 20% maximal force, and 18.9 beats/min (95% CI: 9. 8-28.0) from handgrip to wheel-turn contractions at 50% maximal force. We conclude that the magnitude of the heart rate increase during isometric exercise is related to the intensity of the contraction and the mass of the contracted muscle.

Cerebral desaturation during exercise reversed by O2 supplementation

The combined effects of hyperventilation and arterial desaturation on cerebral oxygenation (ScO2) were determined using near-infrared spectroscopy. Eleven competitive oarsmen were evaluated during a 6-min maximal ergometer row. The study was randomized in a double-blind fashion with an inspired O2 fraction of 0.21 or 0.30 in a crossover design. During exercise with an inspired O2 fraction of 0.21, the arterial CO2 pressure (35 +/- 1 mmHg; mean +/- SE) and O2 pressure (77 +/- 2 mmHg) as well as the hemoglobin saturation (91.9 +/- 0.7%) were reduced (P < 0.05). ScO2 was reduced from 80 +/- 2 to 63 +/- 2% (P < 0.05), and the near-infrared spectroscopy-determined concentration changes in deoxy- (DeltaHb) and oxyhemoglobin (DeltaHbO2) of the vastus lateralis muscle increased 22 +/- 3 microM and decreased 14 +/- 3 microM, respectively (P < 0.05). Increasing the inspired O2 fraction to 0.30 did not affect ventilation (174 +/- 4 l/min), but arterial CO2 pressure (37 +/- 2 mmHg), O2 pressure (165 +/- 5 mmHg), and hemoglobin O2 saturation (99 +/- 0.1%) increased (P < 0. 05). ScO2 remained close to the resting level during exercise (79 +/- 2 vs. 81 +/- 2%), and although the muscle DeltaHb (18 +/- 2 microM) and DeltaHbO2 (-12 +/- 3 microM) were similar to those established without O2 supplementation, work capacity increased from 389 +/- 11 to 413 +/- 10 W (P < 0.05). These results indicate that an elevated inspiratory O2 fraction increases exercise performance related to maintained cerebral oxygenation rather than to an effect on the working muscles.

Reduced arterial diameter during static exercise in humans

In eight subjects luminal diameter of the resting limb radial and dorsalis pedis arteries was determined by high-resolution ultrasound (20 MHz). This measurement was followed during rest and during 2 min of static handgrip or of one-leg knee extension at 30% of maximal voluntary contraction of another limb. Static exercise increased heart rate and mean arterial pressure, which were largest during one-leg knee extension. After exercise heart rate and mean arterial pressure returned to the resting level. No changes were recorded in arterial carbon dioxide tension, and the rate of perceived exertion was approximately 15 units after both types of exercise. The dorsalis pedis arterial diameter was 1.50 +/- 0.20 mm (mean and SE) and the radial AD 2.45 +/- 0.12 mm. During both types of contractions the luminal diameters decreased approximately 3.5% within the first 30 s (P < 0.05), and during one-leg knee extension they continued to decrease to a final exercise value 7.6 +/- 1.1% lower than at rest (P < 0.05). Thus, they became smaller than during the handgrip. After exercise resting values were reestablished. When the arterial diameter was expressed in relation to mean arterial pressure for the radial and dorsalis pedis artery was 22 +/- 3 and 28 +/- 3% lower during handgrip than the relation during rest, respectively. After one-leg knee extension both arteries reached 30 +/- 4% lower values. This study demonstrated arterial constriction in the resting limbs within the first 30 s of static exercise, and continued constriction during one-leg knee extension.(ABSTRACT TRUNCATED AT 250 WORDS)

Central command increases muscle sympathetic nerve activity during intense intermittent isometric exercise in humans

During sustained isometric exercise, central command has very little effect on muscle sympathetic nerve activity (MSNA). To determine if central command has a greater effect on MSNA during intermittent than during sustained contractions, MSNA was recorded with microelectrodes (peroneal nerve) during intermittent isometric handgrip at 25%, 50%, and 75% maximum voluntary contraction (MVC) in 9 human subjects with paced breathing. Similar experiments were performed in 11 additional subjects before and after partial neuromuscular blockade (intravenous curare) to isolate the influence of central command while minimizing force output and thus muscle afferent feedback. Before curare, handgrip at 25% and 50% MVC had no effect on MSNA, whereas handgrip at 75% MVC synchronized the MSNA to the handgrip such that MSNA was 5.7 +/- 1.3 times higher (mean +/- SEM, P < .001) during the contraction periods than during the relaxation periods. After curare, this synchronization of MSNA persisted without attenuation, even though force output fell to < 25% of the initial MVC. From these observations, we conclude that central command causes synchronization of motor activity and muscle sympathetic activity during intense intermittent isometric exercise.

Heart rate and blood pressure responses at the onset of dynamic exercise: effect of Valsalva manoeuvre

The influence of respiration on the mean blood pressure (Pa) and R-R interval responses at the onset of dynamic exercise was studied in 15 healthy subjects who performed 4 s of unloaded cycling at 1.5-2.0 Hz, 4 s of Valsalva manoeuvre at 5.3 kPa, and a combination of both, each during a 12-s long apnoea at total lung capacity. The R-R intervals were obtained from the electrocardiogram, Pa was measured continuously by finger plethysmography, and intra-oral pressure was used to estimate the changes in intrapleural pressure. There was an immediate and significant shortening of the R-R intervals during exercise [mean (SE): 790 (20) to 642 (20) ms] that was not modified when Valsalva manoeuvre was added [783 (28) to 654 (21) ms]. Although 4 s of exercise alone did not alter Pa [13.8 (0.5) to 13.7 (0.7) kPa], this may indicate a pressor response, since Pa decreased during apnoea alone. When exercise was performed simultaneously with Valsalva manoeuvre, Pa increased significantly [13.6 (0.4) to 15.8 (0.5) kPa] and of similar magnitude during Valsalva alone [13.2 (0.4) to 15.3 (0.7) kPa]. In conclusion, 4 s of unloaded cycling elicited a fast R-R shortening with no change in Pa from rest. A concomitant Valsalva manoeuvre had no effect on the R-R interval response but caused a marked increase in Pa. From these findings, it is suggested that respiratory influences should be controlled in studies concerned with the cardiovascular responses at the onset of dynamic exercise.

Physiological and biomechanical aspects of rowing. Implications for training

The drag force on a racing shell increases with the square of velocity corresponding to a 3.2 power increase in energy expenditure. However, the metabolic cost increases with only an approximately 2.4 power function of shell velocity. During international races the metabolic cost corresponds to an oxygen uptake of 6.7 to 7.0 L/min over 6.5 min. The relative anaerobic contribution to 6.5 min of 'all-out' rowing has not been determined but is estimated to range from 21 to 30%. Because of the large muscle mass involved in rowing, blood variables reach extreme values: adrenaline 19 nmol/L; noradrenaline 74 nmol/L; pH 7.1; and bicarbonate 9.8 mmol/L. Because of the static component of the rowing stroke at the catch, blood pressure increases to near 200mm Hg, and the heart of oarsmen has adapted to this load by increasing wall thickness and internal diameters. The maximal oxygen uptake of oarsmen may reach 6.6 L/min and ventilation 243 L/min. Arterial oxygen tension decreases by 20mm Hg during 'all-out' rowing corresponding to a decrease in pulmonary diffusion capacity. A force of approximately 800 to 900N is developed on the oar. Force generation during rowing is relatively slow, 0.3 to 0.4 sec. Oarsmen are strongest in low velocity movement with 70 to 75% slow twitch fibres in skeletal muscle. Data indicate that rowing technique and training may improve explaining why results become approximately 0.7 sec faster per year.

Neural influence on cardiovascular and endocrine responses to static exercise in humans

At the onset of exercise, signals from the central nervous system result in immediate vagal withdrawal and resulting increases in heart rate and arterial blood pressure. From the second heart beat peripheral nerve (reflex) influence from exercising muscle can be detected. With continued exertion, especially with large muscle groups, this influence becomes increasingly important. Sympathetic nerve signals to resting muscle can be influenced by the central nervous system, but are dominated by influence from 'metaboreceptors' in exercising muscle, while sympathetic nerve signals to skin are more influenced by the central nervous system. Cardiovascular responses to static contractions increase with the percentage of maximum contraction intensity as well as with the muscle mass involved. Plasma catecholamines rise in proportion to increases in cardiovascular variables and are influenced by a central nervous mechanism early in the contraction. Furthermore, during static contractions the increase in plasma adrenaline (epinephrine) is larger relative to that of noradrenaline than during dynamic exercise. Both catecholamine responses and the responses of pituitary hormones depend on the active muscle mass, but are small compared to those established during dynamic exercise. Experiments designed to enhance central command, resulting in increased cardiovascular and endocrine responses compared to control experiments and experiments in which an attenuation of peripheral nerve influence resulted in reduced changes in these variables during exercise, contrast with the notion that the 2 neural control mechanisms are redundant. Rather, the 2 neural influences on the autonomic nervous system work in concert in eliciting the responses manifest during static exercise.

Central command influences cardiorespiratory response to dynamic exercise in humans with unilateral weakness

1. Changes in ventilation and cardiovascular variables which occur during exercise may be partly due to 'radiation' of activity in central neurones innervating exercising muscles to the respiratory and cardiovascular control areas. To test this hypothesis, we compared ventilatory and cardiovascular responses to two levels of steady-state exercise with each leg separately, in subjects with painless unilateral leg weakness. We assumed that exercise with a weak leg would require more central neural drive than the same level of exercise with the normal leg. 2. Ventilation during exercise with the weak leg was greater than with the normal leg (P less than 0.02). This was a result of greater tidal volume (Vt; P less than 0.005). There was a greater increase in heart rate (P less than 0.005), and systolic (P = 0.001) and diastolic (P less than 0.02) blood pressures during exercise with the weak leg compared to exercise with the normal leg. The increases in stroke volume and cardiac output during exercise were not different with the two legs. 3. These results support the hypothesis that ventilation, blood pressure and heart rate are influenced by the central neural drive to exercise.

Changes in R-R interval at the start of muscle contraction in the decerebrate cat

1. The effect on R-R interval of a brief hindlimb contraction, elicited by electrical stimulation of L7 ventral roots, was investigated in decerebrate cats. The first series of experiments was performed at both low and high carotid sinus pressure to vary the level of vagal tone. When carotid sinus pressure was elevated to increase vagal tone, contraction commenced 1 s later. 2. The change in R-R interval at low carotid sinus pressure was expressed as the difference between the mean of the five R-R intervals immediately preceding contraction and the mean of the last five R-R intervals at the end of a 5 s contraction. At high carotid sinus pressure, the change was expressed as the difference between the mean of the last five R-R intervals at the end of a 5 s contraction and the mean of five R-R intervals at an equivalent time after raising pressure alone. 3. Hindlimb contraction at low carotid sinus pressure produced a significant reduction in R-R interval from 359 +/- 25 (mean +/- S.E.M. n = 8) to 336 +/- 24 ms (P less than 0.005). At high carotid sinus pressure the response was enhanced with contraction producing a reduction in R-R interval from 474 +/- 45 to 419 +/- 47 ms (P less than 0.001). 4. The shortening of R-R interval produced by hindlimb contraction at high carotid sinus pressure, 55 +/- 8 ms, was significantly greater than that observed at low sinus pressure, 23 +/- 5 ms (P less than 0.001, n = 8, paired t test). This pattern of response was also seen at stimulation frequencies as low as 10 Hz. 5. In a second series of experiments, designed to determine the latency of the cardiac acceleration, the minimum latency between the onset of L7 ventral root stimulation and the end of the first shortened R-R interval was 687 +/- 29 ms (n = 5). 6. Atropine (0.4 mg kg-1, I.V.) prevented a 5 s contraction from producing any change in R-R interval. 7. These results indicate that afferent information originating from receptors in contracting muscles is responsible for producing an immediate shortening of R-R interval, which is mediated by vagal withdrawal. The possibility that the shortening of R-R interval at the start of contraction is linked to a reduction in arterial baroreceptor reflex sensitivity, possibly via inhibitory effects on neurones forming the central pathway of the baroreceptor reflex, is discussed.

Hormonal, metabolic, and cardiovascular responses to static exercise in humans: influence of epidural anesthesia

To determine the role of reflex neural mechanisms for hormonal, metabolic, heart rate (HR), and blood pressure (MABP) changes during static exercise, seven health young males performed 10-min periods of two-legged static knee extension both during control and during epidural anesthesia. Comparisons were made at identical absolute (29 Nm) and relative [15% maximal voluntary contraction (MVC)] force. Afferent nerve blockade was verified by hypesthesia below T10-T12 and attenuated postexercise ischemic pressor response. Leg strength was reduced to 67 +/- 5% of control. At same relative force, increases in MABP and HR occurred more rapidly without than with epidural anesthesia (P less than 0.05). This difference was diminished during identical absolute force. Changes in plasma concentrations of catecholamines followed the pattern of HR and MABP responses, with differences between epidural and control experiments being most pronounced early in the work period. Plasma beta-endorphin was elevated only after control exercise. No response at 15% MVC was found for growth hormone, adrenocorticotropic hormone, insulin, glucagon, cortisol, glycerol, free fatty acids, or glucose (P greater than 0.05). In conclusion, during static exercise with large muscle groups and moderate relative force, modest changes in plasma hormones and metabolites take place. Furthermore, afferent nervous feedback from contracting muscles is important in regulation of blood pressure, heart rate, and catecholamine responses during static exercise in humans.

Central command increases sympathetic nerve activity during spontaneous locomotion in cats

A controversial issue in exercise physiology is the relative contribution of central command versus afferent input from contracting muscles and baroreceptors in the regulation of sympathetic nerve activity (SNA) during exercise. Recent studies of exercising humans have suggested that central command increases cutaneous sympathetic sudomotor nerve activity but have challenged the concept that central command contributes importantly to increases in sympathetic vasoconstrictor nerve activity to skin and skeletal muscle. The purpose of this study was to examine the influence of central command on renal SNA and lumbar SNA during spontaneous locomotion in decorticate cats. Unanesthetized decorticate cats that developed locomotion spontaneously or during electrical stimulation of the subthalamic locomotor region were studied in the presence and absence of input from skeletal muscle and baroreceptor afferents. Spontaneous rhythmic locomotion in the unparalyzed state was associated with significant increases in mean arterial pressure (MAP) from 106 +/- 10 to 133 +/- 11 mm Hg (p less than 0.05) and increases in renal SNA of 301 +/- 100% (p less than 0.05). During spontaneous fictive rhythmic locomotion in paralyzed cats, there were also significant (p less than 0.05) increases in MAP (43 +/- 6%), renal SNA (183 +/- 32%), and lumbar SNA (223 +/- 83%). Baroreceptor denervation did not attenuate increases in MAP, renal SNA, and lumbar SNA during locomotion. During electrical stimulation of the subthalamic locomotor region in paralyzed cats, MAP increased by 43 +/- 17% (p less than 0.05), and renal SNA increased by 175 +/- 47% (p less than 0.05). These findings indicate that central command is capable of increasing sympathetic neural drive in unanesthetized decorticate cats. This increase in sympathetic drive occurs even in the absence of feedback from contracting muscles or from arterial and cardiopulmonary baroreceptors.

Changes in the baroreceptor reflex at the start of muscle contraction in the decerebrate cat

1. The action of muscle contraction on the sensitivity of the cardiac vagal component of the baroreceptor reflex was examined in decerebrate cats. 2. The sensitivity of the baroreceptor reflex was expressed as the difference between the maximum prolongation of the R-R interval in response to carotid sinus baroreceptor stimulation and the mean of ten R-R intervals immediately before carotid sinus pressure elevation. 3. Muscle contraction elicited by electrical stimulation of L7 ventral roots (50 Hz) significantly reduced the sensitivity of the baroreceptor reflex by reducing the prolongation of the R-R interval from 269 +/- 31 to 159 +/- 22 ms. 4. Inhibition of the cardiac vagal component of the baroreceptor reflex was seen just 1 s after the onset of contraction and with stimulation frequencies as low as 10 Hz. 5. These results show for the first time that changes in the sensitivity of the baroreceptor reflex during exercise result in part from afferent information originating in the contracting muscles.

Heart rate and arterial blood pressure at the onset of static exercise in man with complete neural blockade

1. We tested the 'muscle-heart reflex' hypothesis for the immediate increases in heart rate and blood pressure at the onset of static exercise in man by performing complete blockade of afferent nerves from the working muscles. Brief (5 s) maximal static hand-grip contractions were performed without performing a Valsalva-like manoeuvre and with no increase in central venous pressure both before and after combined axillary and radial blockade with lidocaine. Muscle strength was reduced to near zero. The effectiveness of the afferent neural blockade was evaluated by recording the heart rate and blood pressure responses and rating the perceived pain during a cold pressor test of the blocked and contralateral unblocked hand. 2. The cold pressor test increased blood pressure but had no effect on heart rate. Afferent neural blockade eliminated the increase in blood pressure and the perceived pain associated with the cold pressor test. Maximal hand-grip contractions resulted in immediate and similar increases in heart rate and blood pressure before and after afferent neural blockade of the arm. 3. The results of this study suggest that the immediate increases in heart rate and blood pressure at the onset of static exercise in man occur when the 'muscle-heart reflex' is inoperable.

Effects of cuff inflation on self-recorded blood pressure

Changes in continuously recorded 'Finapres' finger blood pressure in ten normotensive and seven hypertensive subjects induced by self-inflation of the cuff or just wearing the inflated cuff were studied. Inflating the cuff caused an instantaneous rise in systolic blood pressure of 13 and 12 mm Hg (hypertensive and normotensive subjects, respectively). Wearing the inflated cuff did not change blood pressure. Thus the rise in pressure was related to the muscular activity required for cuff inflation. Systolic blood pressure took on average 7 s and at most 21 s to return to baseline level after stopping cuff inflation. Since first Korotkoff sounds may already be heard after 10-15 s when following recommended procedures, self-recorded systolic blood pressure may be recorded as too high when subjects inflate their cuff at too low a pressure or deflate it too fast.

Epidural anaesthesia and cardiovascular responses to static exercise in man

1. In human subjects, sustained static contractions of the knee extensors were performed in one leg with the same absolute (10% of the initial maximal voluntary contraction) and relative (30% of the maximal voluntary contraction immediately prior to the static exercise) intensities before and during epidural anaesthesia. Epidural anaesthesia reduced strength to 62 +/- 8% of the control value and partially blocked sensory input from the working muscles. During contractions performed with the same relative force, the increases in mean arterial pressure and heart rate were greater during control contractions than during epidural anaesthesia. During contractions at the same absolute force, there was no significant difference in magnitude of cardiovascular responses between control contractions and contractions performed during epidural anaesthesia. 2. The metabolic role in the exercise pressor reflex was assessed by applying an arterial leg cuff 10 s before cessation of exercise and through the following 3 min of recovery. Although mean arterial pressure and heart rate decreased immediately after cessation of exercise, application of the arterial occlusion cuff resulted in higher post-exercise mean arterial pressure and heart rate values. Control and epidural mean arterial pressures during arterial occlusion were not significantly different. 3. The results of this study suggest that the reflex neural mechanism rather than the intended effort (central command) is important in determining the blood pressure and heart rate responses to static exercise in man. That is, when epidural anaesthesia diminishes sensory feedback and produces muscular weakness, central command does not determine the cardiovascular response. This conclusion, however, is opposite to that derived from experiments with partial neuromuscular blockade which demonstrated the importance of central command in determining the cardiovascular response to static exercise (Leonard, Mitchell, Mizuno, Rube, Saltin & Secher, 1985). Taken together, these two studies are complementary and support the concept that both central and reflex neural mechanisms play roles in regulating arterial blood pressure and heart rate during static exercise in man.