Cardiovascular responses to light isometric and aerobic exercise in 21- and 59-year-old males

The effects of aging on the cardiovascular response to continuous light isometric and aerobic exercise remains to be determined. Thus, the purpose of this study was to compare the cardiovascular response of young and older males during light handgrip and cycle ergometry exercise. Blood pressure, heart rate, rate pressure product, as well as pre-ejection period (derived from impedance cardiography) were obtained for 15 young [mean (SE) age: 21 (0.7) years] and 15 older males [59 (0.8) years] during and after light handgrip exercise and cycle ergometry. The parasympathetic influence on the heart was also assessed through a time-series analysis of heart period variability (HPVts). Both during and when recovering from the handgrip exercise and cycle ergometry, the older subjects exhibited a significantly higher absolute systolic and diastolic blood pressure, and rate pressure product, and a lower HRVts than the young subjects. Relative to baseline, the change in pre-ejection period was lower for the young subjects during the handgrip and cycle ergometry, tasks. These results indicate that although the sympathetic influence on both the myocardium and the vasculature was less pronounced in the older males, the aging cardiovasculature was under greater hemodynamic stress both during rest and during exposure to light isometric and aerobic challenge.     

Core temperature regulation of heart rate during exercise in humans

The relationship between two abnormalities of exercise physiology in chronic heart failure patients was investigated: chronotropic incompetence and decrease in core temperature. While at rest, 13 heart failure patients had an average sinus heart rate that was significantly higher than seven normals (92 +/- 13 vs. 82 +/- 10 min-1, P less than 0.05). However, during exercise, the trend of increase in sinus heart rate as a function of work load and O2 uptake was significantly greater in normals compared with heart failure (P less than 0.05), and the absolute increase in heart rate at 50 W of cycle ergometry was larger in normals compared with heart failure (38 +/- 17 vs. 22 +/- 13 min-1, P less than 0.05). Differences in core temperature regulation were also observed. In the normals, core temperature increased from 37.13 +/- 0.33 degrees C at rest to 37.37 +/- 0.31 degrees C at 50 W of exercise (P less than 0.01). In the heart failure patients, core temperature decreased from 36.99 +/- 0.33 degrees C at rest to 36.66 +/- 0.39 degrees C at 50 W of exercise (P less than 0.01). As expected, significant differences in hemodynamic and gas exchange variables were observed between the normals and the heart failure patients both at rest and during exercise. A multiple linear regression analysis was performed of heart rate changes as the dependent variable and thermoregulatory and hemodynamic changes as the independent variables to test for their influence on heart rate.(ABSTRACT TRUNCATED AT 250 WORDS)     

Cardiorespiratory effects of inelastic chest wall restriction.

We examined the effects of chest wall restriction (CWR) on cardiorespiratory function at rest and during exercise in healthy subjects in an attempt to approximate the cardiorespiratory interactions observed in clinical conditions that result in restrictive lung and/or chest wall changes and a reduced intrathoracic space. Canvas straps were applied around the thorax and abdomen so that vital capacity was reduced by >35%. Data were acquired at rest and during cycle ergometry at 25 and 45% of peak workloads. CWR elicited significant increases in the flow-resistive work performed on the lung (160%) and the gastric pressure-time integral (>400%) at the higher workload, but it resulted in a decrease in the elastic work performed on the lung (56%) compared with control conditions. With CWR, heart rate increased and stroke volume (SV) fell, resulting in >10% fall in cardiac output at rest and during exercise at matched workloads (P < 0.05). Blood pressure and catecholamines were significantly elevated during CWR exercise conditions (P < 0.05). We conclude that CWR significantly impairs SV during exercise and that a compensatory increase in heart rate does not prevent a significant reduction in cardiac output. O(2) consumption appears to be maintained via increased extraction and a redistribution of blood flow via sympathetic activation.     

Prolonged head-down tilt exposure reduces maximal cutaneous vasodilator and sweating capacity in humans.

Cutaneous vasodilation and sweat rate are reduced during a thermal challenge after simulated and actual microgravity exposure. The effects of microgravity exposure on cutaneous vasodilator capacity and on sweat gland function are unknown. The purpose of this study was to test the hypothesis that simulated microgravity exposure, using the 6 degrees head-down tilt (HDT) bed rest model, reduces maximal forearm cutaneous vascular conductance (FVC) and sweat gland function and that exercise during HDT preserves these responses. To test these hypotheses, 20 subjects were exposed to 14 days of strict HDT bed rest. Twelve of those subjects exercised (supine cycle ergometry) at 75% of pre-bed rest heart rate maximum for 90 min/day throughout HDT bed rest. Before and after HDT bed rest, maximal FVC was measured, via plethysmography, by heating the entire forearm to 42 degrees C for 45 min. Sweat gland function was assessed by administering 1 x 10(-6) to 2 M acetylcholine (9 doses) via intradermal microdialysis while simultaneously monitoring sweat rate over the microdialysis membranes. In the nonexercise group, maximal FVC and maximal stimulated sweat rate were significantly reduced after HDT bed rest. In contrast, these responses were unchanged in the exercise group. These data suggest that 14 days of simulated microgravity exposure, using the HDT bed rest model, reduces cutaneous vasodilator and sweating capacity, whereas aerobic exercise training during HDT bed rest preserves these responses.     

Heart rate deflection compared to 4 mmol?·?l?1 lactate threshold during incremental exercise and to lactate during steady-state exercise on an arm-cranking ergometer in paraplegic athletes

The deflection point (DP) of the heart rate in relation to the work rate (WR) of 8 male endurance-trained paraplegics and 11 male physically active sports students was investigated during nonsteady-state incremental arm cranking ergometry (IT) and compared to the 4 mmol · l⁻¹ blood lactate concentration threshold and to blood lactate concentration in steady-state exercise (SST). Heart rate, and lactate concentration from capillary blood, were determined at rest, during IT and SST. The DP was calculated by linear regression analysis of the heart rate during IT. The SST consisted of three consecutive exercise intensities over a period of 8 min at exercise intensities of 10 W below, and at 10 W above the work rate at deflection point (WR_DP). No difference was found between the paraplegics and non-handicapped subjects regarding heart rate and blood lactate concentration at rest and during exercise. A DP was established in all the paraplegics and in 72.7% of the non-handicapped subjects, but lactate accumulation was observed in 75% of the paraplegics and in 62.5% of the non-handicapped subjects at the lowest intensity of SST. In summary, endurance-trained paraplegics with an injury level below T₅ showed heart rate and blood lactate concentration values comparable to non-handicapped subjects during IT. A linear increase at moderate exercise intensities and a levelling-off at higher to maximal intensities could be identified in all the paraplegics and in 72.7% of non-handicapped subjects. The determination of the anaerobic threshold by DP should be applied with caution, since no causal relationship of DP and the anaerobic threshold was found and the WR_DP tended to overestimate threshold values. Accepted: 9 February 1998     

Effects of caffeine on blood pressure, heart rate, and forearm blood flow during dynamic leg exercise

This study examined the acute effects of caffeine on thecardiovascular system during dynamic leg exercise. Ten trained,caffeine-naive cyclists (7 women and 3 men) were studied at rest andduring bicycle ergometry before and after the ingestion of 6 mg/kgcaffeine or 6 mg/kg fructose (placebo) with 250 ml of water. Afterconsumption of caffeine or placebo, subjects either rested for 100 min(rest protocol) or rested for 45 min followed by 55 min of cycleergometry at 65% of maximal oxygen consumption (exercise protocol).Measurement of mean arterial pressure (MAP), forearm blood flow (FBF),heart rate, skin temperature, and rectal temperature and calculation offorearm vascular conductance (FVC) were made at baseline and at 20-minintervals. Plasma ANG II was measured at baseline and at 60 minpostingestion in the two exercise protocols. Before exercise, caffeineincreased both systolic blood pressure (17%) and MAP (11%) withoutaffecting FBF or FVC. During dynamic exercise, caffeine attenuated theincrease in FBF (53%) and FVC (50%) and accentuated exercise-inducedincreases in ANG II (44%). Systolic blood pressure and MAP were alsohigher during exercise plus caffeine; however, these increases weresecondary to the effects of caffeine on resting bloodpressure. No significant differences were observed inheart rate, skin temperature, or rectal temperature. These findingsindicate that caffeine can alter the cardiovascular response to dynamicexercise in a manner that may modify regional blood flow andconductance.

     

Metoclopramide decreases baroreflex sensitivity in patients with essential hypertension

The effect of metoclopramide (10 mg, iv.) or physiological saline on the exercise-induced (standardized bicycle ergometry) increase in blood pressure and heart rate of patients with essential hypertension was investigated in a double blind, randomized, self controlled study. Metoclopramide had no effect on the exercise-induced increase in blood pressure but significantly enhanced the tachycardia due to ergometry after 4-6 min exercise. The mean slope of linear regression lines calculated from the systolic blood pressure and the corresponding heart rate measured before and during (at 1,2,3,4,5 min) exercise after metoclopramide was significantly steeper than after physiological saline (1.1 +/- 0.12 vs 0.79 +/- 0.09; mean +/- SEM), indicating the decrease in baroreflex sensitivity after metoclopramide. On the basis of results the possible role of endogenous dopaminergic mechanisms in suppressing some components of pressor effect of physical exercise can be hypothesized.     

The entrainment of ventilation frequency to exercise rhythm

To investigate whether ventilation frequency could be entrained to a sub-harmonic of the exercise rhythm, 19 experimentally naive male volunteers were tested during steady state bicycle ergometry and arm cranking under conditions of constant applied workload. Each exercise was performed at two separate ventilatory loads, one within the linear range and the other in the curvilinear range of ventilatory response to exercise. A preferred exercise rhythm was initially adopted (4 min.) followed by forced incremented and decremented rhythm changes each lasting 3 min during a 12 min exercise period. Ventilation, pedal pulse train and heart rate were sampled at 17 Hz on a PDP 11/23 computer. Ratios of limb frequency to dominant respiratory frequency were determined following Fourier analysis of these signals. Data that lay within +/- 0.05 of an integer and half-integer ratio were accepted as indices of entrainment, provided that the observed entrained scores were statistically significant. Ventilation frequency showed a clear, but intermittent tendency to entrain with limb frequency. This tendency was greater during bicycle ergometry, possibly as a consequence of task familiarisation, although both exercise entrainments were independent of workload. No difference between preferred versus varied exercise rhythm was evident, but more entrainment (p less than 0.01) was observed during a decremental change in exercise rhythm. These responses do not appear to support an appreciable role for limb-based afferents in the control of entrainment. The results of this study provide evidence that exercise rhythm has some regulatory role in the control of breathing during moderate rhythmical laboratory-based exercise ergometry.     

Effects of exercise on mitogen- and stress-activated kinase signal transduction in human skeletal muscle

Exercise/contraction is a powerful stimulator of mitogen-activated protein (MAP) kinase cascades in skeletal muscle. Little is known regarding the physiological activation of enzymes downstream of MAP kinase. We investigated whether acute exercise results in activation of mitogen- and stress-activated kinases (MSK) 1 and 2, p90 ribosomal S6 kinase (p90rsk), and MAP kinase-activated protein kinase 2 (MAPKAPK2). Muscle biopsies were obtained from healthy volunteers before, during, and after 60 min one-leg cycle ergometry, from exercising and resting legs. MSK1 and MSK2 activities were increased 400-500% and 200-300%, respectively, in exercised muscle (P < 0.05 vs. rest). A dramatic increase in activity of p90rsk (MAPKAPK1) (>2,500%), and to a lesser extent MAPKAP2 (300%), was noted with exercise (P < 0.05 vs. rest). MSK1, MSK2, p90rsk, and MAPKAP2 activities were sustained throughout exercise. Exercise-induced activation of these enzymes was limited to working muscle, indicating that local rather than systemic factors activate these signaling cascades. Thus physical exercise leads to activation of multiple enzymes downstream of MAP kinase.     

Interrelationships between left ventricular volume and output during exercise in healthy subjects.

To better characterize the relationship between left ventricular volume response and improved ventricular ejection and output during supine exercise in normal subjects, 36 healthy asymptomatic volunteers (age 39 +/- 17 yr) were studied with radionuclide ventriculography during recumbent bicycle ergometry. Relative changes in left ventricular end-diastolic and end-systolic volume were measured at rest and during exercise by a modification of the radionuclide counts-based method that accounted for variability in stress blood pool counts. A biphasic response was noted in left ventricular end-diastolic volume with an initial increase in early exercise (8.5 +/- 11% at 200 kpm/min and 11 +/- 12% at 300 kpm/min) followed by a progressive and significant decline at peak exercise (-3.3 +/- 18% at 547 +/- 140 kpm/min; P < 0.05). There was substantial variation in end-diastolic volume response at peak exercise in the group as a whole, which could be more closely related to changes in end-systolic volume (r = 0.84, P < 0.0001) than in heart rate (r = -0.57, P < 0.01) or age (r = 0.36, P < 0.05) of the study subjects. Despite the decline in ventricular filling, systolic function appeared to improve dramatically at peak exercise (change in left ventricular ejection fraction 15.5 +/- 6.4, P < 0.0001). Although not directly related to increasing systolic ejection, end-diastolic volume was directly related to the percent change in stroke volume at peak exercise among the study subjects (r = 0.88, P < 0.0001).(ABSTRACT TRUNCATED AT 250 WORDS)     

Role of skin blood flow and sweating rate in exercise thermoregulation after bed rest.

Two potential mechanisms, reduced skin blood flow (SBF) and sweating rate (SR), may be responsible for elevated intestinal temperature (T(in)) during exercise after bed rest and spaceflight. Seven men underwent 13 days of 6 degrees head-down bed rest. Pre- and post-bed rest, subjects completed supine submaximal cycle ergometry (20 min at 40% and 20 min at 65% of pre-bed rest supine peak exercise capacity) in a thermoneutral room. After bed rest, T(in) was elevated at rest (+0.31 +/- 0.12 degrees C) and at the end of exercise (+0.33 +/- 0.07 degrees C). Percent increase in SBF during exercise was less after bed rest (211 +/- 53 vs. 96 +/- 31%; P < or = 0.05), SBF/T(in) threshold was greater (37.09 +/- 0.16 vs. 37.33 +/- 0.13 degrees C; P < or = 0.05), and slope of SBF/T(in) tended to be reduced (536 +/- 184 vs. 201 +/- 46%/ degrees C; P = 0.08). SR/T(in) threshold was delayed (37.06 +/- 0.11 vs. 37.34 +/- 0.06 degrees C; P < or = 0.05), but the slope of SR/T(in) (3.45 +/- 1.22 vs. 2.58 +/- 0.71 mg x min-1 x cm-2 x degrees C-1) and total sweat loss (0.42 +/- 0.06 vs. 0.44 +/- 0.08 kg) were not changed. The higher resting and exercise T(in) and delayed onset of SBF and SR suggest a centrally mediated elevation in the thermoregulatory set point during bed rest exposure.     

Effects of Biofeedback Training on Voluntary Heart Rate Control During Dynamic Exercise

The aims of this study were to (1) compare the effect of biofeedback with that of verbal instructions on the control of heart rate during exercise on a treadmill, (2) test the possible effect of workload on this control, and (3) examine the effect of workload on baseline heart rate at rest and during exercise. The study involved 35 participants who were randomly assigned to each of 4 experimental conditions generated by combining the 2 independent variables: training strategy for heart rate control (heart rate biofeedback or verbal control instructions) and work level (30 or 50% of maximal heart rate). By the end of 5 experimental sessions, participants trained with heart rate biofeedback showed a greater attenuation of the increase in heart rate produced by exercise than participants trained with verbal control instructions. The workload did not influence the voluntary control of heart rate, nor did it affect resting baseline heart rate, but it did affect exercise baseline heart rate.     

The effects of arm crank training on the physiological responses to submaximal wheelchair ergometry

The purpose of this investigation was to examine the cardiovascular and metabolic effects of a 5 wk arm crank (AC) training program on submaximal wheelchair (WC) ergometry in able-bodied women. The 6 subjects in the training group (TG) and 4 in the control group (CG) performed a 10 min WC exercise prior to and following the training period at a power output (PO) that elicited 70% of the pre-training peak oxygen uptake (VO2). Steady state VO2, heart rate (HR), cardiac output (Qc) and stroke volume (Vs) were measured. Resting and post-exercise blood lactate concentrations (LA) were measured, the difference was recorded as net LA. The TG exercised on the AC 3 d.wk-1 at a PO that elicited 85% of each subject's recorded peak HR. Each session consisted of four 4 min exercise bouts preceded by a 2 min warm-up and interspersed with 2 min rest periods. After training, the TG had a significantly (p less than 0.05) lower HR, larger Vs and lower LA in response to the WC exercise. Qc and VO2 were not significantly altered. The results demonstrate that the AC exercise program used in this study produced a physiological training effect which was observed during submaximal WC exercise of an intensity frequently encountered during daily WC ambulation. It appears that short-term, moderate intensity AC training offers an adequate stimulus to reduce the stress imposed by wheelchair locomotion.     

The effect of training on endurance and the cardiovascular responses of individuals with paraplegia during dynamic exercise induced by functional electrical stimulation

Endurance for dynamic exercise, cardiac output, blood pressure, heart rate, ventilation, and oxygen consumption was measured in eight individuals with paraplegia at the end of 4-min bouts of exercise on a friction braked cycle ergometer. Movement of the subjects' legs was induced by electrically stimulating the quadriceps, gluteus maximus and hamstring muscles with a computer-controlled biphasic square--wave current at a frequency of 30 Hz. The friction braked cycle ergometer was pedalled at work rates which varied between 0 and 40 W. Measurements were repeated after 3 and 6 months to assess the affect of training. After 3 months of training it was found that endurance increased from 8 min at a work rate of 0 W to 30 min at a work rate of 40 W. Compared to the cardiovascular responses in non-paralyzed subjects, computerized cycle ergometry was found to be associated with higher relative stresses for a given level of absolute work. Mean blood pressure, for example, increased by over 30% during maximal work in individuals with paralysis compared to the typical response obtained for able-bodied subjects. Analysis of the data showed that instead of the 20-30% metabolic efficiency commonly reported for cycle ergometry, the calculated metabolic efficiency during computer-controlled cycle ergometry was only 3.6%.     

Carotid baroreflex sensitivity at rest and during exercise is not influenced by opioid receptor antagonism

Physical effort involves, along with an increase in the plasma concentration of beta-endorphin, profound cardiovascular adaptations. The aim of the present study was to investigate with the use of the variable neck chamber technique, the influence of the endogenous opioids on the carotid baroreflex control of blood pressure and heart rate at rest as well as during exercise. Ten normal volunteers exercised in the supine position up to 33% and 66% of their maximal exercise capacity and received, in a randomized double-blind cross-over protocol, either saline or naloxone (10 mg intravenously, followed by a continuous infusion of 10 mg.h-1). During exercise a progressive attenuation of the carotid baroreceptor reflex control of blood pressure and heart rate was noted. However, neither at rest nor during exercise, did opioid antagonism influence the carotid baroreceptor control of blood pressure and heart rate. Intra-arterial pressure and heart rate also remained unaffected. In contrast, both at rest and during exercise, naloxone administration produced a significant increase in the plasma concentration of cortisol. The latter suggests that in vivo the opioid receptors were effectively antagonized. In conclusion the present study confirms that opioids play only a minor role in cardiovascular homeostasis at rest. In addition, this study demonstrates that they are not involved in the cardiovascular adaptation to exercise, nor in the exercise-related attenuation of the carotid baroreceptor control of pressure and heart rate.     

Energy substrate partitioning and efficiency in individuals with atherogenic lipoprotein phenotype

Individuals with an atherogenic lipoprotein phenotype (ALP) characterized by increased levels of small dense low-density lipoprotein (LDL) particles tend to have greater adiposity compared to unaffected subjects. We sought to determine whether this may be related to alterations in energy substrate partitioning or efficiency. These were assessed by indirect calorimetry in men with ALP (ALP(+), n = 7) and unaffected controls (ALP(-), n = 8) during rest (30 min) and exercise (10 min). Gross, net and delta efficiencies were calculated during graded leg-cycle ergometry at workloads of 10 and 50 W. Respiratory exchange ratios (RER) were significantly (P < 0.05) higher in ALP(+) vs. ALP(-) during rest (0.86 ± 0.01 vs. 0.83 ± 0.02) and exercise at 10 W (0.88 ± 0.02 vs. 0.84 ± 0.02) and 50 W (0.92 ± 0.01 vs. 0.87 ± 0.01, respectively) (P < 0.05). Lipid oxidation (kcal/min) was lower in ALP(+) vs. ALP(-) during rest (0.56 ± 0.02 vs. 0.71 ± 0.07) and exercise at 10 W (1.52 ± 0.25 vs. 2.00 ± 0.20) and 50 W (1.28 ± 0.10 vs. 2.32 ± 0.22, respectively) (P < 0.05). Gross and net efficiencies were significantly increased (P = 0.005) in ALP(+) vs. ALP(-) at 10 W. RER was correlated positively with plasma triglyceride during exercise and inversely with high-density lipoprotein (HDL) cholesterol and LDL peak particle diameter during rest and exercise (P < 0.05). These findings suggest that increased muscular efficiency at low exercise intensity and reduced lipid oxidation during rest and exercise may contribute to both dyslipidemia and increased adiposity in individuals with ALP.     

Measurement of gluconeogenesis in exercising men by mass isotopomer distribution analysis.

We evaluated the hypothesis that coordinated adjustments in absolute rates of gluconeogenesis (GNG(ab)) and hepatic glycogenolysis (Gly) would maintain euglycemia and match glucose production (GP) to peripheral utilization during rest and exercise. Specifically, we evaluated the extent to which gradations in exercise power output would affect the contribution of GNG(ab) to GP. For these purposes, we employed mass isotopomer distribution analysis (MIDA) and isotope-dilution techniques on eight postabsorptive (PA) endurance-trained men during 90 min of leg cycle ergometry at 45 and 65% peak O(2) consumption (VO(2 peak); moderate and hard intensities, respectively) and the preceding rest period. GP was constant in resting subjects, whereas the fraction from GNG (f(GNG)) increased over time during rest (22.3 +/- 0.9% at 11.25 h PA vs. 25.6 +/- 0.9% at 12.0 h PA, P < 0.05). In the transition from rest to exercise, GP increased in an intensity-dependent manner (rest, 2.0 +/- 0.1; 45%, 4.0 +/- 0.4; 65%, 5.84 +/- 0.64 mg. kg(-1). min(-1), P < 0.05), although glucose rate of disappearance exceeded rate of appearance during the last 30 min of exercise at 65% VO(2 peak). Compared with rest, increases in GP were sustained by 92 and 135% increments in GNG(ab) during moderate- and hard-intensity exercises, respectively. Correspondingly, Gly (calculated as the difference between GP and MIDA-measured GNG(ab)) increased 100 and 203% over rest during the two exercise intensities. During moderate-intensity exercise, f(GNG) was the same as at rest; however, during the harder exercise f(GNG) decreased significantly to account for only 21% of GP. The highest sustained GNG(ab) observed in these trials on PA men was 1.24 +/- 0.3 mg. kg(-1). min(-1). We conclude that, after an overnight fast, 1) absolute GNG rates increased with intensity of effort despite a reduced f(GNG) at 65% VO(2 peak), 2) during exercise Gly is more responsible than GNG(ab) for maintaining GP, and 3) in 12-h fasted men, neither increased Gly or GNG(ab) nor was their combination able to maintain euglycemia during prolonged hard (65% VO(2 peak)) exercise.     

Cardiac responses to exercise in the dog before and after destruction of the sinoatrial node

Chronotropic and dromotropic responses to treadmill exercise were compared in conscious dogs prior to and following excision of the sinoatrial node (SAN). The initial junctional rhythm accompanying removal of the SAN region was replaced within hours to days by subsidiary atrial pacemaker (SAP) foci located in the inferior right atrium along the sulcus terminalis. With SAN intact, cardiac acceleration was immediate at onset of exercise and the tachycardia was directly proportional to work intensity. Atrioventricular (AV) conduction concurrently accelerated during exercise as manifest by shortening in P-R and atrioventricular (A-V) intervals. Following SAN excision, subsidiary atrial pacemaker foci likewise demonstrated prompt tachycardias during exercise, although heart rate was significantly reduced at rest and during steady state exercise. In the SAP state, tachycardia during exercise was related to work intensity and was mediated by changes in cardiac autonomic nerve activity. Combined propranolol-atropine blockade increased heart rate at rest in the SAP state, and significantly attenuated the tachycardia accompanying treadmill exercise. Following SAN excision the P-R (A-V) interval was significantly reduced in the resting animal. In response to exercise, AV conduction time decreased in the SAP state, though the absolute levels during steady state exercise were not significantly different from prior control runs with SAN intact. Blood pressure response to exercise was similar during both SAN and SAP states. We conclude that following an initial unstable period, SAP foci maintain adequate heart rate increases in response to dynamic exercise, primarily mediated via autonomic nerve regulation.     

Fibrinolytic activity is not dependent upon exercise mode in post-myocardial infarction patients

In this study we investigated possible differences in fibrinolytic activity in cardiac patients while they performed treadmill and cycle ergometry. Thirteen post-myocardial infarction patients completed two maximal exercise tests on treadmill and cycle ergometers. Blood was collected before and after each exercise test and was analyzed for the fibrinolytic variables, tissue plasminogen activator (t-PA) and plasminogen activator inhibitor-1 (PAI-1) activity, and lactate. Maximal oxygen uptake, heart rate, and ventilation were greater (P < 0.05) on the treadmill than during cycle ergometry, however, blood lactate was similar between modes. t-PA activity significantly increased with exercise (P < 0.05) and there was a trend toward a reduction in PAI-1 activity with exercise, but this did not reach statistical significance. The fibrinolytic responses to maximal exercise did not differ between the two modes of exercise studied. Therefore, exercise intensity, but not the mode of exercise, appeared to be the primary determinant of the fibrinolytic response to acute exercise in these patients. Accepted: 29 January 1998