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.     

Renal and intrarenal blood flow distribution in swine during severe exercise

It is known that a compensatory reduction and diversion of renal flow occurs in severe exercise in humans but not in dogs. We investigated this in miniature swine by measuring changes in total renal blood flow (TRF) and intra-renal blood flow (IRBF) distribution with tracer microspheres (15 +/- 5 mum) at rest and during steady-state exercise at 4.8-7.2 kph and 0% grade, and during severe exercise at 4.8-7.2 kph and 10% grade. We measured heart rate and cardiac output (Q) via implanted probes. TRF was determined as a percent of Q and as ml/100 g per min. IRBF was determined for the outer cortex, inner cortex, outer medulla, and inner medulla. Our results show that renal blood flow is significantly (P less than 0.05) reduced in pigs with exercise. Steady-state exercise reduced flow to about 66% of control and severe exercise reduced renal flow to 30% of control. IRBF was unchanged throughout. These results show that the exercising pig augments blood flow to skeletal muscle by reducing blood flow to kidneys, a response known to occur in man.     

Solute distribution during steady-state cellular growth

A theoretical model is developed to compute solute distribution in the liquid region and interface position in unidirectional solidification of cylindrical cells using Galerkin's method.^{[13, 14, 15]} The model is based on satisfaction of mass conservation and the Gibbs-Thomson shift of the melting point at the interface. Cell shapes and solute composition profiles measured on directionally solidified Sn-0.9 wt pct Pb are in good agreement with the predictions of this analysis. The model confirms that the cellular mode of solidification in an alloy is feasible or preferred only over a limited range of growth conditions. It appears that with decreasing temperature gradient, regular cylindrical cell growth may not commence immediately after the breakdown of planar front. P.S. BASAK, formerly Research-Scholar, Department of Metallurgical Engineering, Indian Institute of Technology-Kharagpur     

Age alters regional distribution of blood flow during moderate-intensity exercise

During dynamic exercise in warm environments, requisite increases in skin and active muscle blood flows are supported by increasing cardiac output (Qc) and redistributing flow away from splanchnic and renal circulations. To examine the effect of age on these responses, six young (Y; 26 +/- 2 yr) and six older (O; 64 +/- 2 yr) men performed upright cycle exercise at 35 and 60% of peak O2 consumption (VO2peak) in 22 and 36 degrees C environments. To further isolate age, the two age groups were closely matched for VO2peak, weight, surface area, and body composition. Measurements included heart rate, Qc (CO2 rebreathing), skin blood flow (from increases in forearm blood flow (venous occlusion plethysmography), splanchnic blood flow (indocyanine green dilution), renal blood flow (p-amino-hippurate clearance), and plasma norepinephrine concentration. There were no significant age differences in Qc; however, in both environments the O group maintained Qc at a higher stroke volume and lower heart rate. At 60% VO2peak, forearm blood flow was significantly lower in the O subjects in each environment. Splanchnic blood flow fell (by 12-14% in both groups) at the lower intensity, then decreased to a greater extent at 60% VO2peak in Y than in O subjects (e.g., -45 +/- 2 vs. -33 +/- 3% for the hot environment, P < 0.01). Renal blood flow was lower at rest in the O group, remained relatively constant at 35% VO2peak, then decreased by 20-25% in both groups at 60% VO2peak. At 60% VO2peak, 27 and 37% more total blood flow was redistributed away from these two circulations in the Y than in the O group at 22 and 36 degrees, respectively. It was concluded that the greater increase in skin blood flow in Y subjects is partially supported by a greater redistribution of blood flow away from splanchnic and renal vascular beds.     

Acadesine increases blood flow in the collateralized heart during exercise

Acadesine, an adenosine-regulating agent, has been shown to increase coronary flow and exert cardioprotective effects in acutely ischemic myocardium, but a beneficial effect on coronary collateral flow during exercise has not been demonstrated. We examined the effect of acadesine, 100 micromol/min, i.v., on myocardial blood flow during treadmill exercise in six normal dogs and seven dogs with moderately well-developed coronary collateral vessels. Collateral vessel growth was produced with 2-min intermittent occlusions of the left circumflex coronary artery followed by permanent occlusion. During resting conditions, myocardial blood flow in the collateral zone was not significantly less than in the normal zone, but during exercise, blood flow increased by only 79 +/- 21% (from 0.98 +/- 0.29 ml/min/g to 1.64 +/- 0.19 ml/min/g; p < 0.05) in the collateral zone as compared with 118 +/- 32% (from 1.09 +/- 0.28 ml/min/g to 2.14 +/- 0.2 ml/min/g; p < 0.01) in the normal zone. During exercise, acadesine further increased mean blood flow in the collateral-dependent region by 24 +/- 5% (to 2.04 +/- 0.26 ml/min/g; p < 0.05) with no change in the transmural distribution of perfusion. The increase in collateral zone blood flow in response to acadesine resulted from a decrease in both transcollateral resistance from 25.1 +/- 2.7 mm Hg/min/g/ml to 18.8 +/- 8 mm Hg/min/g/ml (p < 0.05) and small-vessel resistance in the collateral-dependent myocardium from 45.3 +/- 6.6 mm Hg/min/g/ml to 36.4 +/- 5.8 mm Hg/min/g/ml (p < 0.05). Acadesine also significantly increased normal-zone flow in the collateralized dogs (to 2.62 +/- 0.33 ml/min/g; p < 0.05). In contrast, acadesine had no effect on coronary blood flow in normal dogs. In dogs with moderately well-developed collateral vessels, acadesine increased blood flow in both the collateral-dependent and normal myocardial zones during exercise. In contrast, acadesine did not increase blood flow in normal dogs. These findings suggest that adenosine metabolism is altered not only in the collateral-dependent region but also in the normal region of hearts with a coronary artery occlusion.     

Capillary blood lactate concentrations during intermittent all-out exercise

Struma has called for treatment very early in medical history due to its appearance. At the beginning of our calendar, the physicians dealt with this problem already. This paper gives a historical review about the surgical treatment of struma.     

Hepatic blood flow in horses during the recuperative period from maximal exercise

OBJECTIVE: To determine effects of walking or standing on hepatic blood flow of horses after brief, intense exercise. ANIMALS: 6 adult Thoroughbreds (4 mares, 2 geldings). PROCEDURE: Horses were preconditioned on a treadmill to establish uniform level of fitness. Once fit, treadmill speed causing each horse to exercise at 120% of maximal oxygen consumption was determined and used in simulated races at 14-day intervals. In a three-way crossover study, horses were exercised at a speed inducing 120% of maximal oxygen consumption until fatigued or for a maximum of 2 minutes. Three interventions were studied: resting on the treadmill (REST), exercised then standing on the treadmill for 30 minutes (MS), and exercised then walking at 2 m/s for 30 minutes (MW). At 60 seconds after completion of exercise, bromsulphalein (BSP) was infused IV, and blood samples were collected every 2 minutes for 30 minutes for analysis of BSP concentration. Hematocrit and plasma total solids concentration were measured. Pharmacokinetic parameters were derived, using nonlinear regression, and were compared, using Friedman's repeated measures analysis on ranks. RESULTS: Plasma BSP concentration was higher after exercise. Median hepatic blood flow (BSP clearance) decreased significantly from 23.8 (REST) to 20.7 (MS) and 18.7 (MW) ml/min/kg. Median steady-state volume of distribution of BSP decreased from 47.6 (REST) to 42.7 (MW) and 40.2 (MS) ml/kg. Differences among trials were not significant when horses walked or stood after exercise. CONCLUSIONS: Hepatic blood flow and pharmacokinetics of BSP are markedly altered immediately after exercise. Limiting movement of horses during this period did not affect hepatic blood flow.     

Changes in muscle blood flow distribution during hyperthermia

Blood flow is a critical parameter for obtaining satisfactory temperature distributions during clinical hyperthermia. This study examines the changes in blood flow distribution in normal porcine skeletal muscle before, during and after a period of regional microwave hyperthermia. The baseline blood flow distribution during general anaesthesia and after the insertion of the thermal probes was established independently in order to isolate the changes due to hyperthermia. General anaesthesia alone and thermocouple insertion during anesthesia had no significant effect on the muscle blood flow distribution. Regional microwave heating generated a non-uniform blood flow distribution which was a function of the tissue temperature distribution. Blood flow was greater in those tissues samples in which higher temperatures were recorded and less in those sampled further from the applicators peak SAR (Specific Absorption Rate). The increase in blood flow appears to be primarily a local phenomenon. Although muscle blood flow may be considered to be uniform prior to heating, this does not hold during hyperthermia treatment. Therefore, the non-uniform nature of the blood distribution during heating should be incorporated into any practical bioheat transfer model.     

Effects of emphysema on diaphragm blood flow during exercise

Pseudomonas flavescens strain B62 (NCPPB 3063) is a recently described bacterium isolated from walnut blight cankers. This strain has been designated as the type strain of a Pseudomonas rRNA group-I species. Strain B62 produced a mixture of two exopolysaccharides, differing in weight average relative molecular mass and composition. Only the most abundant exopolysaccharide (90% by mass), corresponding to the one with the lower molecular mass, was investigated by use of methylation analysis, partial acid hydrolysis, and NMR spectroscopy. The polysaccharide was depolymerised by the action of the cellulase produced by Penicillum funiculosum and the oligosaccharide obtained, corresponding to the repeating unit, was characterised by NMR spectroscopy and ion-spray mass spectrometry. The repeating unit of the B62 exopolysaccharide is [structure in text] where X is glucose (75%) or mannose (25%), and Lac is lactate. The O-acetyl groups are present only on 75% of the repeating units, and they are linked to the C6 of the hexose residues in non-stoichiometric amounts.     

Adipose tissue blood flow during prolonged, heavy exercise

Subcutaneous adipose tissue blood flow (ATBF) was examined in 8 subjects during 6 h exercise on a bicycle ergometer. The initial work load was 118 W corresponding to about 50% of maximal work capacity. The oxygen uptake increased from 0.261 - min-1 at rest to about 1.61-min-1 during work. In 7 subjects ATBF increased, in 1 it remained constant. After 3 h exercise ATBF at an average reached values 3--4 times the control value. This increase was maintained for the remaining work periods. The increase was significant at the 5% level. Plasma free fatty acids increased 7-, plasma glycerol 10-fold during work.     

Skeletal muscle blood flow in humans and its regulation during exercise

Regional limb blood flow has been measured with dilution techniques (cardio-green or thermodilution) and ultrasound Doppler. When applied to the femoral artery and vein at rest and during dynamical exercise these methods give similar reproducible results. The blood flow in the femoral artery is approximately 0.3 L min(-1) at rest and increases linearly with dynamical knee-extensor exercise as a function of the power output to 6-10 L min[-1] (Q= 1.94 + 0.07 load). Considering the size of the knee-extensor muscles, perfusion during peak effort may amount to 2-3 L kg(-1) min(-1), i.e. approximately 100-fold elevation from rest. The onset of hyperaemia is very fast at the start of exercise with T 1/2 of 2-10 s related to the power output with the muscle pump bringing about the very first increase in blood flow. A steady level is reached within approximately 10-150 s of exercise. At all exercise intensities the blood flow fluctuates primarily due to the variation in intramuscular pressure, resulting in a phase shift with the pulse pressure as a superimposed minor influence. Among the many vasoactive compounds likely to contribute to the vasodilation after the first contraction adenosine is a primary candidate as it can be demonstrated to (1) cause a change in limb blood flow when infused i.a., that is similar in time and magnitude as observed in exercise, and (2) become elevated in the interstitial space (microdialysis technique) during exercise to levels inducing vasodilation. NO appears less likely since NOS blockade with L-NMMA causing a reduced blood flow at rest and during recovery, it has no effect during exercise. Muscle contraction causes with some delay (60 s) an elevation in muscle sympathetic nerve activity (MSNA), related to the exercise intensity. The compounds produced in the contracting muscle activating the group IIl-IV sensory nerves (the muscle reflex) are unknown. In small muscle group exercise an elevation in MSNA may not cause vasoconstriction (functional sympatholysis). The mechanism for functional sympatholysis is still unknown. However, when engaging a large fraction of the muscle mass more intensely during exercise, the MSNA has an important functional role in maintaining blood pressure by limiting blood flow also to exercising muscles.     

Comparison of left ventricular function during interval versus steady-state exercise training in patients with chronic congestive heart failure

This study sought to assess the safety of interval exercise training in patients with chronic congestive heart failure (CHF) with respect to left ventricular (LV) function. For effective rehabilitation in CHF, both aerobic capacity and muscle strength need to be improved. We have previously demonstrated in both coronary artery bypass surgery and patients with CHF that interval exercise training (IET) offers advantages over steady-state exercise training (SSET). However, because LV function during IET has not yet been studied, the safety of this method in CHF remains unclear. To assess LV function during IET and SSET, at the same average power output, 11 patients with stable CHF were compared with 9 stable coronary patients with minimal LV dysfunction (control group). Using first-pass radionuclide ventriculography, changes in LV function were assessed during work versus recovery phases, at temporally matched times between the fifth and sixteenth minute of IET and SSET. In CHF during IET, there were no significant variations in the parameters measured during work and/or recovery phases. During the course of both IET and SSET, there was a significant increase in LV ejection fraction (5 vs 4 U; p <0.05 each), accompanied by increased heart rate (6 vs 8 beats/min; p <0.05 each) and cardiac output (2.4 vs 1.8 L/min; p <0.01 and p <0.05). In CHF, the magnitude of change in LV ejection fraction during IET was similar to that seen in controls. Both LV ejection fraction and the clinical status in patients with CHF remained stable during IET. Because IET appears to be as safe as SSET with respect to LV function, IET can be recommended for exercise training in CHF to apply higher peripheral exercise stimuli and with no greater LV stress than during SSET.     

Ambient noise interferes with auscultatory blood pressure measurement during exercise

In the past decade, there has been a surge of renewed interest in the study of developmental evolution. One approach that has been taken is to examine the expression patterns of a candidate gene in divergent taxa and to use these results to infer which aspects of a particular genetic pathway are either conserved or altered. Here we consider this approach from the perspective of the neo-Darwinian paradigm for evolutionary change. If adaptations are typically composed of large numbers of gene substitutions that are of small effect individually, then the candidate gene approach is unlikely to bridge the gap between developmental pattern and evolutionary process: changes in gene expression patterns may identify the steps in developmental pathways that have been altered during evolution but fail to identify the actual genetic changes that have occurred. On the other hand, there is growing support for the view that adaptations often involve large-effect genes; fortunately, the candidate gene approach is well suited to this type of genetic architecture.     

Respiratory muscle work compromises leg blood flow during maximal exercise

We hypothesized that during exercise at maximal O2 consumption (VO2max), high demand for respiratory muscle blood flow (Q) would elicit locomotor muscle vasoconstriction and compromise limb Q. Seven male cyclists (VO2max 64 +/- 6 ml.kg-1.min-1) each completed 14 exercise bouts of 2.5-min duration at VO2max on a cycle ergometer during two testing sessions. Inspiratory muscle work was either 1) reduced via a proportional-assist ventilator, 2) increased via graded resistive loads, or 3) was not manipulated (control). Arterial (brachial) and venous (femoral) blood samples, arterial blood pressure, leg Q (Qlegs; thermodilution), esophageal pressure, and O2 consumption (VO2) were measured. Within each subject and across all subjects, at constant maximal work rate, significant correlations existed (r = 0.74-0.90; P < 0.05) between work of breathing (Wb) and Qlegs (inverse), leg vascular resistance (LVR), and leg VO2 (VO2legs; inverse), and between LVR and norepinephrine spillover. Mean arterial pressure did not change with changes in Wb nor did tidal volume or minute ventilation. For a +/-50% change from control in Wb, Qlegs changed 2 l/min or 11% of control, LVR changed 13% of control, and O2 extraction did not change; thus VO2legs changed 0.4 l/min or 10% of control. Total VO2max was unchanged with loading but fell 9.3% with unloading; thus VO2legs as a percentage of total VO2max was 81% in control, increased to 89% with respiratory muscle unloading, and decreased to 71% with respiratory muscle loading. We conclude that Wb normally incurred during maximal exercise causes vasoconstriction in locomotor muscles and compromises locomotor muscle perfusion and VO2.     

Effect of alterations in blood volume on cardiac function during maximal exercise

Recently, we proposed that the higher stroke volume (SV) and cardiac output (Q) of endurance-trained (ETR) versus untrained (UTR) individuals are attributable primarily to the enhanced diastolic filling of ETR consequent to a larger blood volume (BV). To test this hypothesis, we examined the effects of manipulating BV on the cardiac function of six ETR and six UTR males. Both groups were examined in the control BV condition (BVctl), then ETR were examined immediately following a 500 mL reduction in BV (BVred) and UTR were examined immediately following a 500 mL expansion of BV (BVexp). In BVctl, compared with UTR, ETR had significantly greater BV (16%), maximal diastolic filling rate (47.4%), maximal ventricular emptying rate (24.6%), SVmax (31.6%), Qmax (29%) and VO2max (54.5%). Following BVexp in UTR, there were immediate significant increases in maximal diastolic filling rate (22.5%), SVmax (9.1%), Qmax (8.9%), and VO2max (12.7%). Following BVred in ETR there were immediate significant decreases in maximal diastolic filling rate (27%), SVmax (14.3%), Qmax (14.7%), and VO2max (7.0%). Maximal systolic emptying rate did not change significantly following BVred or BVexp. We conclude that changes in SV and Q consequent to alterations in BV are attributable primarily to changes in diastolic function, and the majority of the higher diastolic filling rate of ETR is due to their larger BV.     

Effects of physical training on ventilatory equivalent and respiratory exchange ratio during weight supported, steady-state exercise

Thirty-three college men participated in a 9-week endurance training program. An equal number of subjects served as controls. Pre- and post-test metabolic measurements were made during 10 min of submaximal exercise (1080 kpm/min at 60 rpm) and 15 min of recovery. Measurements included oxygen consumption, CO2 production, ventilatory equivalent (Ve/VO2 ratio) and respiratory exchange ratio (R). A three factor design variance analysis was used to analyze the effects of training on min-by-min exercise and recovery Ve/VO2 ratio and R. For the experimental group training resulted in a significant improvement in ventilatory efficiency during exercise, as well as a significant decrease in R. During recovery, Ve/VO2 and R decreased significantly for both groups although the magnitude of change was greater for the group that trained. Apparently, there was a significant habituation effect due to test procedures for the control group. The results are discussed in terms of lactate production and substrate utilization during exercise.