Blood flow in exercising muscles.
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Animals↗
Biomedical subjects
D Pendergast
Publications and source records attributed to D Pendergast.
Continuous ambulatory venous pressure for diagnosis of venous insufficiency. Preliminary report.
We have found that the venous pressure slope during minimal exercise is a sensitive measurement of venous disease. This parameter differed greatly in our two study populations. Due to increased venous pressure, venous insufficiency syndrome patients have a greater volume of pooled blood, which results in smaller pressure changes with each muscle contraction. In patients with incompetent valves, blood flows in a retrograde fashion in the vein, which leads to a higher steady state minimal pressure and notably to a decreased venous pressure slope. Venous pressure slope is a particularly sensitive measurement and a good prognosticator of venous insufficiency syndrome before symptoms become disabling to the patient. Our data indicate a strong correlation between venous pressure slope and venographic results. In fact, patients with abnormal venographic results invariably have demonstrated venous pressure slopes in the abnormal range.
Ambulatory Care↗
Blood flow in exercising muscles by xenon clearance and by microsphere trapping.
The accuracy of muscle blood flow measurement by the 133Xe clearance method (QXe) was assessed against direct venous outflow (Qv) and microsphere trapping flow (Q mu) determinations in isolated perfused dog gastrocnemius both at rest and during graded stimulation [O2 consumption (VO2) up to 12 ml X 100 g-1 X min-1] and in the gastrocnemius, vastus lateralis, and triceps of intact dogs at rest and while running on a treadmill at varied speeds up to maximum VO2. In 29 measurements performed in 11 isolated muscles, Q mu was in good agreement with Qv at rest and at all stimulation levels (Q mu/Qv = 1.0; r = 0.98). 133Xe clearance yielded much lower blood flows than the venous outflow and the microsphere trapping methods. In 43 measurements in 11 muscles, the mean QXe/Qv ratio was 0.57 +/- 0.03 (SE), independent of blood flow. Similarly, in 65 measurements in 2 intact dogs, the mean QXe/Q mu ratio in all tested muscles was 0.49 +/- 0.02 (SE), independent of blood flow. These results show that the 133Xe clearance method considerably underestimates blood flow in dog muscles.
Animals↗
The effect of preceding anaerobic exercise on aerobic and anaerobic work.
The effects of exercise-induced elevation of lactic acid concentration in blood [Lab] up to 12-14 mM on the subsequent aerobic (less than or equal to VO2 max) and anaerobic (supramaximal) performance was investigated in a group of trained non-athletic subjects. For submaximal loads ranging from 0.6 VO2 max to VO2 max the VO2 max/external work load (Wext) ratio was unaffected by preceding anaerobic exercise, VO2 max was not significantly different, whereas the maximal performance time of a standard exercise was reduced. The kinetics of the VO2 on- adjustment at the onset of 0.9 VO2 max rectangular loads carried out by the arms and/or by the legs was significantly increased by a preceding supramaximal anaerobic load carried out by the same as well as by the non-exercised limbs. It is concluded that in the presence of high [Lab] (1) the maximal aerobic power (VO2 max) is unchanged; (2) the efficiency of aerobic work is unaffected, which implies that during active recovery most La is used as substrate, provided the metabolic level during the latter exceeds 0.6 VO2 max; (3) the endurance for anaerobic as well as for aerobic exercise is reduced; (4) the kinetics of the VO2 adjustment at the onset of submaximal rectangular loads is faster, both in primed and in non-exercised muscles.
Adult↗
Dynamic and steady-state metabolic changes in running dogs.
Dynamic and steady-state changes of VO2, VE, VCO2, PaO2 and blood lactate concentration (Lab) were studied in 4 intact (I) and in the same tracheostomized (T) dogs walking or running uphill (+ 10%) on a treadmill at speeds up to 12 km X h-1. A) Non-steady state results: The half times of the VO2 on-response (t1/2 VO2 on-) to rectangular work loads were 18.9 sec +/- 1.2 (SE) in I and 15.6 sec +/- 1.0 in T dogs (P less than 0.05), independent of work intensity and similar to those found for isolated perfused dog gastrocnemii (15-17 sec). Lab during the rest to work transient was almost unchanged. B) Steady-state results: VO2 and VE increased with increasing speed up to 8 km X h-1 (+ 10%) then levelled off both in I and T. Asymptotic VO2, and VE values were higher for I than for T (VO2 = 93 and 83 ml X kg-1 X min-1; VE = 2.6 and 1.75 l X kg-1 X min-1, respectively). Calculated delta VO2/delta VE ratios for equal external work loads indicate that the energy cost of breathing was about 12 ml O2 per liter VE. From (A) it is concluded that the adjustment of oxidative reactions upon work onset is as fast for the whole animal as for isolated gastrocnemius and can be assessed from gas exchange in the upper airways. From (B) it appears that, in the absence of glycolysis, the cost of running per unit distance decreases with increasing speed while the cost of VE becomes a sizeable part of the overall energy expenditure.
Animals↗
Aerobic and glycolytic metabolism in arm exercise.
Eight kayakers (K) and 3 sedentary subjects (S) performed arm cranking and pedaling while erect or supine at each of several work loads from submaximal to the highest they could sustain for 2 min and for intervals varying from 10 s to 5 min. From measurements of VO2 and blood lactate concentration, the aerobic and glycolytic energy release in arm work was assessed. For steady-state aerobic work all subjects had a mechanical efficiency averaging 0.24 independent of posture or exercise mode. Per unit fat-free limb volume, arm VO2max of group K was 1.5-fold that of group S, whereas leg VO2max was the same in each group. Compared to group S, glycolytic arm work in group K was characterized by: 1) higher thresholds for release of lactate at the onset of submaximal work, 2) lower blood lactate concentrations during comparable absolute or relative submaximal work, 3) higher conventional anaerobic thresholds for absolute, but not relative work loads, 4) higher maximal rates of lactate release, and 5) the same maximal blood lactate concentrations. Measurement of the early lactate threshold, which occurred at considerably lower arm work loads than did anaerobic threshold, but which was greatly increased by specific muscle training, may provide a simple, sensitive, and nontraumatic evaluation of muscle training.
Adult↗
Effects of specific muscle training on VO2 on-response and early blood lactate.
The relationship between half time of the O2 uptake on-response (t1/2 VO2on, seconds) and early blood lactate accumulation (delta Lab, mmol.1(-1) at the onset of submaximal arm and/or leg exercise was the object of a cross-sectional study of sedentary subjects (S,n = 3), and kayakers (K, n = 8), and of a longitudinal study on 11 untrained subjects of specific arm vs. leg training. In supine arm cranking (W = 125 watts) S had an average t1/2 VO2on of 82 s and a delta Aab of 9.2 mmol.1(-1) compared to 47 +/- 7 s and 4 +/- 1.4 mmol.1(-1), respectively, for K. In longitudinal trainees shorter t1/2 VO2on was accompanied by lower Lab for the trained limbs. Specific limb conditioning in swimmers and runners resulted in shorter t1/2 VO2on. A linear relationship was observed between delta Lab and t1/2 VO2on having an intercept on the time axis at congruent to 20 s and a slope proportional to muscle mass. Trained muscles were grouped closest to the intercept indicating local acceleration of the rate of O2 transfer approaching the t1/2 VO2on for isolated perfused muscle at the onset of work. Since t1/2 VO2on, we conclude that factors distal to the capillary are specifically involved in the local training response.
Adenosine Triphosphate↗