Levels Of Treadmill Exercise Research Articles

Plasma ATP during exercise: possible role in regulation of coronary blood flow

It was previously shown that red blood cells release ATP when blood oxygen tension decreases. ATP acts on microvascular endothelial cells to produce a retrograde conducted vasodilation (presumably via gap junctions) to the upstream arteriole. These observations form the basis for an ATP hypothesis of local metabolic control of coronary blood flow due to vasodilation in microvascular units where myocardial oxygen extraction is high. Dogs (n = 10) were instrumented with catheters in the aorta and coronary sinus, and a flow transducer was placed around the circumflex coronary artery. Arterial and coronary venous plasma ATP concentrations were measured at rest and during three levels of treadmill exercise by using a luciferin-luciferase assay. During exercise, myocardial oxygen consumption increased approximately 3.2-fold, coronary blood flow increased approximately 2.7-fold, and coronary venous oxygen tension decreased from 19 to 12.9 mmHg. Coronary venous plasma ATP concentration increased significantly from 31.1 to 51.2 nM (P < 0.01) during exercise. Coronary blood flow increased linearly with coronary venous ATP concentration (P < 0.01). Coronary venous-arterial plasma ATP concentration difference increased significantly during exercise (P < 0.05). The data support the hypothesis that ATP is one of the factors controlling coronary blood flow during exercise.

Almost simultaneous measurement of cardiovascular and gas exchange variables during maximal exercise.

We measured gas exchange variables such as oxygen uptake, carbon dioxide output, and lung diffusing capacity using noninvasive techniques almost simultaneous with assessment of cardiovascular variables such as pulmonary blood flow at several levels of treadmill exercise up to and including maximal capacity. We utilized a single breath exhalation technique for measurement of diffusing capacity and cardiac output and breath by breath methodology for evaluating oxygen uptake. The equipment required for these measurements--rapid gas analyzers, oximeters, on-line computation, and pneumatic valves--are well within the capabilities of many exercise laboratories and are not difficult to use with subjects even at the heaviest levels of exercise. The results agreed well with values reported in the literature. From these entirely noninvasive measures, we calculated mixed venous oxygen saturation and maximal tissue oxygen diffusing capacity.

Effect of naltrexone treatment on the treadmill exercise-induced hormone release in amenorrheic women.

The effect of an acute physical stress on hormone secretions before and after a 10-day naltrexone treatment in untrained healthy and amenorrheic women was investigated. Plasma levels of pituitary (LH, FSH, prolactin, GH, ACTH, beta-endorphin) and adrenal (cortisol, androstenedione, testosterone) hormones were measured at rest and in response to 60 min of physical exercise. The test was done both before and after a 10-day naltrexone (50 mg/day) treatment. Graded levels of treadmill exercise (50, 70 and 90% of maximal oxygen uptake (VO2) every 20 min) was used as physical stressor. While mean +/- SE plasma LH levels in control women were higher than in amenorrheic patients and increased following the naltrexone treatment (p < 0.01), no significant differences of basal plasma hormonal levels were observed between amenorrheic and eumenorrheic women, both before and after naltrexone treatment. Physical exercise at 90% VO2 induced a significant increase in plasma GH, ACTH, beta-endorphin, cortisol, androstenedione and testosterone levels in controls before naltrexone treatment (p < 0.01). The mean increase in plasma androstenedione and testosterone levels in control women was significantly higher after naltrexone treatment (p < 0.01). In amenorrheic patients before naltrexone, physical exercise induced an increase in plasma prolactin and GH levels, but not in plasma ACTH, beta-endorphin, cortisol, testosterone and androstenedione. After naltrexone treatment, the exercise induced a significant plasma ACTH, beta-endorphin and cortisol levels, while the increase of plasma prolactin levels was significantly higher than before treatment (p < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Pulmonary angiotensin-converting enzyme substrate hydrolysis during exercise.

We examined exercise-induced changes in indicator-dilution estimates of the angiotensin-converting enzyme first-order kinetic parameter, the ratio of a normalized maximal enzymatic conversion rate to the Michaelis constant (Amax/Km), which, under stable enzymatic conditions, will vary with the pulmonary vascular surface area accessible to vascular substrate, the extravascular lung water (an index of the proportion of lung tissue perfused), and the central blood volume (from pulmonary trunk to aorta). Experiments were performed in 10 mongrel dogs at rest and through two increasing levels of treadmill exercise, with the use of two vascular space tracers (labeled erythrocytes and albumin), a water space tracer ([1,8-14C]-octanediol), and a vascular endothelium surface area marker, benzoyl-Phe-Gly-Pro ([3H]BPGP), which is a pharmacologically inactive angiotensin-converting enzyme substrate. The exercise-induced increase in cardiac output was accompanied by a linear increase in central blood volume, and dilutional extravascular lung water rapidly increased to an asymptotic proportion close to 100% of postmortem vascular lung water. There was an average 55% [3H]BPGP hydrolysis, which did not vary with flow, and the computed Amax/Km increased linearly with exercise. We conclude that exercise results in complete lung tissue recruitment and increases the pulmonary vascular surface area available for BPGP hydrolysis linearly with flow, so that pulmonary vascular recruitment continues after full tissue recruitment.

Effects of dichloroacetate on hemodynamic responses to dynamic exercise in dogs.

To determine whether lactic acid production contributes significantly to the cardiac responses to muscular dynamic exercise, we administered intravenous sodium dichloroacetate (32 mumol.kg-1.min-1), a pyruvate dehydrogenase activator that facilitates lactate metabolism via the tricarboxylic cycle, in 12 dogs during two graded levels of treadmill exercise. Similar exercise was carried out in nine normal dogs receiving equimolar doses of NaCl. In the latter group, arterial lactate increased progressively from 0.80 +/- 0.11 (SE) mmol/l at rest to 2.13 +/- 0.28 mmol/l by the end of exercise. In contrast, arterial lactate did not change significantly (0.98 +/- 0.12 to 0.95 +/- 0.11 mmol/l) during exercise in dogs receiving dichloroacetate infusion. Dichloroacetate infusion also reduced the increases in plasma norepinephrine, heart rate, and left ventricular contractile indexes that occurred during exercise, suggesting that the sympathetic cardiac stimulation occurring during exercise may be related to the production of lactic acid. However, dichloroacetate affected neither the net increase in cardiac output nor the relationship between total body oxygen consumption and cardiac output that occurred during exercise. Thus we conclude that lactic acid production is not essential to the increase in cardiac output that occurs during mild-to-moderate exercise.

Effect of alpha 1-adrenergic blockade on myocardial blood flow during exercise after myocardial infarction

The effect of alpha 1-adrenergic blockade with prazosin on myocardial blood flow at rest and during two levels of treadmill exercise was assessed in 16 chronically instrumented dogs 9-14 days after myocardial infarction had been produced by occlusion of the left circumflex coronary artery. During resting conditions prazosin did not alter mean myocardial blood flow or the subendocardial-to-subepicardial flow ratio in either normally perfused or collateral-dependent myocardium. However, during exercise at comparable external work loads and comparable rate-pressure products, prazosin significantly increased blood flow to normally perfused (27% increase at the second level of exercise, P less than 0.001) and collateral-dependent myocardium (35% increase at the second level of exercise, P less than 0.001) compared with control. In addition, prazosin caused a small but significant decrease in the subendocardial-to-subepicardial flow ratio in both normal (1.27 +/- 0.04 to 1.19 +/- 0.04; P less than 0.01) and collateral-dependent myocardium (0.57 +/- 0.11 to 0.52 +/- 0.11; P less than 0.01) compared with control, reflecting a disproportionally greater increase in subepicardial flow in response to alpha 1-adrenergic blockade. These data demonstrate that alpha 1-adrenergic vasoconstriction inhibits coronary vasodilation during exercise, even in areas of collateral-dependent myocardium relatively early after coronary artery occlusion.

Baroreflex-induced vasoconstriction in active skeletal muscle of conscious dogs

We investigated the magnitude of baroreflex-mediated vasoconstriction in the hindlimbs of six conscious dogs at rest and during four levels of treadmill exercise ranging in intensity from mild (2 mph, 0% grade) to heavy (6 mph, 10% grade). Dogs were instrumented with vascular occluders on both common carotid arteries, an electromagnetic flow probe and vascular occluder on the terminal aorta, and a catheter in a branch of the femoral artery; aortic baroreceptors were intact. The responses to a 2-min carotid occlusion were observed at rest and after 3-5 min of exercise at each work rate. The increases in mean arterial pressure during carotid occlusion were similar at rest and at each level of exercise (26 +/- 4 to 35 +/- 3 mmHg; no significant difference). At rest, carotid occlusion caused only a small but significant decrease in terminal aortic vascular conductance (TAC) (-0.89 +/- 0.21 ml.min-1.mmHg-1, P less than 0.05). During mild exercise, baseline terminal aortic blood flow (TAQ) and TAC increased, and the reduction in TAC during carotid occlusion exceeded that observed at rest (-1.85 +/- 0.42 ml.min-1.mmHg-1, P less than 0.05). As exercise intensity increased, the magnitude of the reduction in TAC during carotid occlusion increased linearly with the baseline TAQ. At the highest work rate, approximately 59% of the increase in mean arterial pressure during carotid occlusion was due to the large decrease in TAC (-6.35 +/- 0.50 ml.min-1.mmHg-1). We conclude that the vasoconstriction of active skeletal muscle during the pressor response to bilateral carotid occlusion increased with exercise intensity.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of the Frank-Starling Mechanism in Maintaining Cardiac Output During Increasing Levels of Treadmill Exercise in Beta-Blocked Normal Men

Role of the Frank-Starling Mechanism in Maintaining Cardiac Output During Increasing Levels of Treadmill Exercise in Beta-Blocked Normal Men

Oxygen deficit-oxygen debt relationships in ponies during submaximal treadmill exercise

The O 2 deficit-O 2 debt relationship in ponies was examined at two levels of treadmill exercise. Five healthy ponies exercised for 8 min at two work rates (WR): (1) 50 m/min at 6% grade and (2) 70 m/min at 12% grade. The O 2 deficit and O 2 debt were calculated using open-circuit measurement of pulmonary gas exchange during the transition from rest to steady-state exercise and during recovery from exercise. The O 2 deficit was significantly ( P < 0.05) than the O 2 debt at each of the two work rates. The means (± SEM) for the deficit and the O 2 debt, respectively, in liters were: (1) low WR = 0.45 ± 0.12; 0.92 ± 0.13high WR = 1.03 ± 0.20; 1.62 ± 0.12. Given the observation that the O 2 deficit and the O 2 debt are generally equal in humans during exercise below the anaerobic threshold, these findings suggest a species difference in the O 2 deficit-O 2 debt relationship. It is hypothesized that the difference in O 2 deficit between man and pony is related to faster V̇ O 2 kinetics fort he on-transient of exercise in which involves a more rapid increase in cardiac output coupled with a release of splenic stored erythrocytes.

Oxygen deficit-oxygen debt relationships in ponies during submaximal treadmill exercise

The O 2 deficit-O 2 debt relationship in ponies was examined at two levels of treadmill exercise. Five healthy ponies exercised for 8 min at two work rates (WR): (1) 50 m/min at 6% grade and (2) 70 m/min at 12% grade. The O 2 deficit and O 2 debt were calculated using open-circuit measurement of pulmonary gas exchange during the transition from rest to steady-state exercise and during recovery from exercise. The O 2 deficit was significantly lower ( P < 0.05) than the O 2 debt at each of the two work rates. The means (± SEM) for the deficit and the O 2 debt, respectively, in liters were: (1) low WR = 0.45 ± 0.12; 0.92 ± 0.13; high WR = 1.03 ± 0.20; 1.62 ± 0.12. Given the observation that the O 2 deficit and the O 2 debt are generally equal in humans during exercise below the anaerobic threshold, these findings suggest a species difference in the O 2 deficit-O 2 debt relationship. It is hypothesized that the difference in O 2 deficit between man and pony is related to faster V̇ O 2 kinetics for the on-transient of exercise which involves a more rapid increase in cardiac output coupled with a release of splenic stored erythrocytes.

Cardiac output monitoring by impedance cardiography during treadmill exercise.

We have modified impedance cardiography for monitoring cardiac output during stress tests. We adapted an ensemble-averaging technique for eliminating motion artifacts. We applied an array consisting of four spot ECG electrodes for impedance cardiogram (ICG) monitoring and compared it to conventional encircling band electrodes. We tested ten normal adults, compared the cardiac output obtained by our ICG monitoring system to that simultaneously obtained by the carbon dioxide (CO2) rebreathing method at rest and during three levels of treadmill exercise. The results show that the correlation coefficient between the spot electrode ICG and the CO2 rebreathing method is r = 0.90, and between the band electrode ICG and the CO2 rebreathing method is r = 0.96. If we use the peak-to-valley height of dz/dt instead of the peak height of dZ/dt in computing cardiac output, the correlation coefficient between the spot electrode ICG and the CO2 rebreathing method can be improved to r = 0.95.

Regional blood flows in running normotensive and renal hypertensive dogs.

The influence of short-term hypertension on the haemodynamic response to exercise was studied by measuring arterial pressure and regional blood flow (radio-active microspheres) in dogs at two levels of treadmill exercise (5 km/h at 0 degrees and 10 km/h at 4.5 degrees). One group of dogs (n = 5) had one-kidney, one clip hypertension of 1-week duration and was compared to normotensive controls (n = 5). Both groups exhibited similar increases in heart rate, but arterial pressure increased only in the normotensive dogs. Left ventricular myocardial blood flow increased significantly in both groups. However, the increase was more pronounced in the hypertensive dogs. In some groups of active skeletal muscles (biceps brachii, tibialis cranialis), increases in blood flow in excess of 30-fold were observed during exercise in normotensive animals. Several muscles showed exaggerated increases in flow in hypertensive dogs. Perfusion of the brain, the kidneys and the splanchnic area was not compromised in either group of dogs. We conclude that in one-kidney, one clip hypertension of 1-week duration, when structural cardiovascular changes are presumably far from being completely developed, vasodilatation to increased metabolic demands in the myocardium and in most skeletal muscles is not limited in response to mild to moderate levels of exercise, and that perfusion of other vascular beds is not compromised.

Effect of ICI 118,587 on left ventricular function during graded treadmill exercise in conscious dogs

Effect of ICI 118,587 (corwin, ICI), a new cardioselective beta-partial agonist, on left ventricular (LV) function was studied and compared with that of isoproterenol and propranolol in 10 conscious normal dogs, instrumented with a micromanometer and pairs of ultrasonic crystals for analysis of LV wall motion. Heart rate, LV dP/dt and mean circumferential shortening velocity were measured at rest and during 3 levels of treadmill exercise (Ex). Before drug administration (control), the heart rate, dP/dt, percent shortening and mean circumferential shortening velocity were enhanced linearly along with the graded Ex. The Ex response curve shifted upward during isoproterenol infusion and downward after the administration of propranolol. With ICI, hemodynamic and contractile indexes were enhanced at rest as with isoproterenol, while these indexes were depressed during maximal Ex as after propranolol. The Ex response curve after ICI crossed the control response curve at a moderate level of Ex. Thus ICI exerts positive inotropic and chronotropic effects at rest when basal sympathetic tone is low, whereas it exerts negative inotropic and chronotropic properties at maximal Ex when sympathetic tone is high. The inherent dual action of this drug is expected to open a new field of treatment for ischemic heart disease with or without heart failure.

Adenosine and coronary blood flow in conscious dogs during normal physiological stimuli.

The role of adenosine in matching myocardial oxygen supply to demand by regulating coronary blood flow has been the subject of intensive study. The present experiments were designed to determine the relationship among myocardial oxygen consumption, coronary blood flow, and adenosine production as estimated by pericardial adenosine accumulation under several physiological conditions in the same animal. Conscious chronically instrumented dogs were used to measure changes in coronary blood flow, myocardial oxygen consumption, and pericardial adenosine accumulation during two levels of treadmill exercise, excitement caused by loud noises, and feeding (the presentation and consumption of a meal). The results show significant increases in the adenosine production with all experimental procedures and significant linear correlations between myocardial oxygen consumption and coronary blood flow (r = 0.78), myocardial oxygen consumption and adenosine production (r = 0.73), and adenosine production and coronary blood flow (r = 0.88). These data show that increases in adenosine production by the normally oxygenated myocardium can be the physiological mechanism for matching oxygen supply to increased oxygen demand in the conscious dog.

Respiratory disability in coal miners

To the Editor.— My experience with blood gas analysis in evaluating respiratory disability among coal miners differs substantially from that of Morgan et al. The exercise protocol used by my laboratory, which is more suitable for the often sedentary subjects studied, is less abrupt than that of Morgan et al. After a light warm-up, two to five graded levels of tread-mill exercise are given, to a measured oxygen uptake of up to 20 to 25 cc/kg/min, if possible. Increments are based on each patient's tolerance and the examiner's clinical judgment, with 30 to 40 minutes' rest between levels. Determination of arterial blood level is obtained after 5 1/2 minutes of a six-minute exercise and is immediately analyzed simultaneously in three analyzers (Po 2 and Pco 2 electrodes, one model 113 and two model 813 analyzers). Most of the miners referred here by the Department of Labor (DOL) are from southern

Renal prostaglandin E 2 AND F 2α secretion and excretion in exercising conscious dogs

Renal prostaglandin E 2 (PGE 2) and F 2α (PGF 2α) secretion and excretion rates were determined in dogs at rest and during various levels of treadmill exercise. Four animals were chronically instrumented to measure mean arterial pressure (MAP), heart rate (HR), left renal blood flow (RBF), and to sample renal venous (RV) blood. In four additional animals, the bladder was cannulated to enable urine collection prior to and after exercise. When compared to resting values, RV PGE 2 concentrations increased by 99, 119, and 50 percent during light, moderate and heavy exercise workloads, respectively. RBF was constant during exercise and consequently renal PGE 2 secretion increased as a function of RV PGE 2 concentration. Similar changes were observed in PGF 2α in 2 dogs. When compared to resting values, excretion rates of PGE 2 and PGF 2α after exercise increased by 111 and 195 percent, respectively, due to an increase in urine PGE 2 and PGF 2α concentrations. The data demonstrate that renal PG synthesis, as evaluated by PG secretion and excretion, is increased during exercise in the dog.

Myocardial blood flow distribution in miniature pigs during exercise.

Total and regional myocardial blood flow was measured in miniature pigs at rest and during two levels of treadmill exercise, including maximal exercise. Exercise increased the myocardial blood flow in a linear manner with heart rate (r = 0.87). At rest the endocardial/epicardial blood flow ratio was significantly greater than unity with flow favoring the endocardium. Exercise failed to appreciably alter the distribution of coronary blood flow. Thus the myocardium was capable of further dilatation and perfusion of blood without compromising endocardial flow even during the most severe level of exercise when maximal heart rates were attained.

Effect of exercise on perfusion of collateral-dependent myocardium in dogs with chronic coronary artery occlusion.

Since the ability of mature intercoronary collateral channels to increase myocardial blood flow in response to drug-induced coronary vasodilation has been questioned, the present study was undertaken to evaluate the response of coronary collateral circulation to the stress of exercise. Studies were performed at rest and during two levels of treadmill exercise in six dogs a minimum of 6 mo after placement of an Ameroid constrictor on the left circumflex coronary artery. Regional myocardial blood flow was estimated in normally perfused anterior and predominantly collateral-dependent posterior left ventricular wall with left atrial injections of radio-nuclide-labeled microscheres 7-10 mum in diameter. At rest, heart rate was 87 +/- 7 beats/min and mean myocardial blood flow was comparable in control and collateral-dependent regions (0.96 +/- 0.13 and 0.97 +/- 0.14 ml/min-g, respectively). During exercise, heart rates increased to 180 +/- 13 and 228 +/- 14 beats/min and myocardial blood flow (MBF) in the anterior control region increased linearly with heart rate (HR), (MBF = 0.133 HR - 0.202, r = 0.88). MBF to the posterior collateral-dependent region was similarly augmented during exercise (MBF = 0.140 HR - 0.252, r = 0.89), so that the linear correlation between HR and MBF was similar for the control and collateral-dependent regions. In addition, the transmural distribution of MBF was uniform at rest and during exercise in both the anterior control and posterior collateral-dependent regions. Thus, not only could the mature intercoronary collateral vasculature supply adequate flow at rest, but when subjected to the natural stress of exercise, the increase in flow to the predominantly collateral-dependent area was similar to that in the normally perfused area.

Energy Expenditure and [Vdot]O2Max of Female Athletes during Treadmill Exercise

Abstract Several physiological responses, including oxygen uptake, of a group of female athletes (N = 26) were measured during various levels of treadmill exercise. Their aerobic power was also measured and correlated with performance on the Cooper 12-min-run test. The energy requirement during treadmill exercise, expressed as [Vdot]O2/kg · min-1, was very similar to values reported for males. The mean aerobic power was 41 ml/kg · min-1. A statistically significant correlation (r = .70) was found between aerobic power and performance on the Cooper 12-min-run test. This was consistent with previous studies.

Adipose Tissue Cell Size and Lipolysis in the Rat: Response to Exercise Intensity and Food Restriction

This experiment was designed to determine if the adaptive increase in adipose tissue epinephrine-stimulated lipolysis (ESL) observed in exercise trained rats is related to decreased adipocyte size or a direct response to exercise. Two levels of treadmill exercise and three levels of food restriction were imposed on male rats over a 12 week experimental period to create a distribution of adipose tissue cell sizes. Epinephrine-stimulated lipolysis was subsequently measured in the isolated adipocytes from rats trained at two different exercise levels and in untrained rats fed either ad libitum or 16%, 27%, or 35% dietary restriction. Energy restriction was effective in reducing body weight and to some extent epididymal fat pad weight; however, adipocyte size and number were not significantly affected. Exercise in both groups of trained rats was effective in reducing adipocyte size; however, cell size did not differ between training groups. The group receiving the greatest amount of daily exercise had significantly greater ESL indicating that the adaptive increase in lipolytic potential seen in adipose tissue of exercise trained rats is a true metabolic adaptation not secondary to reduced cell size.