Blood flow, PO2, PCO2 and pH during progressive working contractions in a whole muscle group.

Alterations in blood flow during progressive working contractions were examined to elucidate their relation to work rate in a predominantly glycolytic muscle group, i.e., m. gastrocnemius and m. plantaris, in rabbits anesthetized with urethane and chloralose. In one series of animals, the sciatic nerve was stimulated to induce plantar flexions of constant length at 2, 5 and 8% of an afterload at which only isometric tension could be developed. Another series was exercised at 30 and 50% of this value, and a third group served as non-exercised controls. Each experimental session consisted of a series of 5 min non-exercise periods followed by 6 min exercise periods, and a 10 min post-exercise period. Femoral venous blood was obtained just before the first exercise period, during the final minute of each exercise period, and 10 min after the final exercise period. The composition of venous blood samples from control animals did not change during the experimental session. Blood flow in the exercising limb increased at the lowest workload, and attained a maximum flow rate at the 5% workload. Blood gases were altered to a similar extent at all afterloads, averaging: PO2 = 4.0 +/- 0.2 kPa and PCO2 = 7.5 +/- 0.3 kPa. pH, in contrast, was lower at the heaviest afterloads (X = 7.144 +/- 0.03) compared to the lighter afterloads (X = 7.245 +/- 0.03). The blood flow and pH patterns are consistent with the glycolytic fiber type composition of this muscle group. Venous PO2 indicates that O2 delivery was adequate, even at the highest afterload.(ABSTRACT TRUNCATED AT 250 WORDS)

Changes in blood pressure, heart rate and blood constituents during heat exposure in men with elevated blood pressure.

Although the vascular volume response of hypertensive men during exercise has been rather well characterized, the effect of resting heat exposure in this patient population has not been examined. This was done in the present report in seven men with high blood pressure (BP) (i.e., diastolic pressure greater than 12 kPa (90 mmHg) upon initial interview) and 5 normotensive control subjects. 50 min after each subject had consumed an amount of water equal to 1% of his body weight, he reclined on a cot. 10 min later the subject was carried into an environmental chamber equilibrated at Tdb = 45 degrees C, Twb = 28 degrees C. Free-flowing venous blood samples were obtained from a cubital vein, and BP and heart rate were measured, before the heat exposure and at 15 min intervals during the experiment. Within 30 min systolic, diastolic and mean BP of the high BP subjects had decreased to normal levels; no BP changes were detected in normotensive subjects. Accompanying this depressor response was an exaggerated elevation in plasma glucose concentration. No alterations were found with haematocrit, plasma osmolality or electrolytes, or total protein and albumin. The data suggest that heat exposure may have been more stressful for the subjects with high BP than for their controls. This finding implies that phasic depressor responses may be as important as phasic pressor episodes in the aetiology of established essential hypertension.

Changes in venous blood content from active and inactive hindlimb during isotonic exercise.

Venous blood samples were obtained from either exercising (n = 9) or nonexercising (n = 8) hindlimb during a progressive isotonic exercise in rabbits anesthetized with urethane and chloralose. Each experimental session consisted of 5-min nonexercise periods alternated with 6-min exercise periods, followed by a 10-min postexercise period. During each exercise period, stimulation of the distal stump of the right sciatic nerve at 1 Hz induced plantar flexions which lifted loads comparable to 2, 5, 8, 30, or 50% of an afterload at which only an isometric tension developed. Free-flowing venous blood samples were obtained before the first exercise period, during the last minute of each exercise period, and 10 min following the last exercise session. Increases in [Na+], [K+] and lactate concentration were obtained in blood from active limbs. Only lactate concentration increased in blood from nonexercising limbs, while [K+] decreased slightly. Inferences concerning the vascular volume response to this protocol would be quite different depending on the blood sampling site. Changes in blood from inactive tissue, further, may indicate only saturation of homeostatic mechanisms which normally compensate for vascular volume alterations initiated in active tissue.

Vascular volume changes during cycling and stepping in women at two hydration levels.

Five female Caucasians were studied in a hot, wet environment (32.2 degrees C dry bulb, 30 degrees C wet bulb) during both cycle ergometer exercise and block stepping at exercise intensities (30-40% of the subjects's VO2 max) which produced similar heart rates. During each type of exercise, the women were studied once following 24 h water deprivation and once 60 min after ingestion of an amount of water equal to 1% of their body weight. Venous blood samples were obtained before, and at 10 min intervals during each of the four 60-min exercise session. Hemoconcentration and osmoconcentration were observed during both types of exercise, with more rapid increases in these variables occurring during ergometer exercise compared to block stepping. While the fluid status manipulation was effective in altering the pre-exercise osmolalities by an average of 9 mosmol . kg-1, it had little effect on vascular volume dynamics during either type of exercise. Similarly, increases in heart rate and body temperature during exercise were not altered by the water balance of the subject. The pattern of vascular volume changes during exercise in women, therefore, seems more sensitive to exercise mode than to pre-exercise water balance.

Influence of exercise type, hydration, and heat on plasma volume shifts in men.

Four male Caucasians were studied during cycle ergometer exercise and stair stepping in a hot wet environment (32 degrees C db, 30 degrees C wb) after exertion was equated by matching heart rates during training. With each exercise, one session was conducted after 24 h of water deprivation, the other 50 min after ingestion of an amount of water equal to 1% body weight. Venous blood samples were obtained 24 h before each exercise and before and at 10-min intervals during each exercise. No changes in osmolality were found during stair stepping. A progressive osmoconcentration, however, occurred during cycling after dehydration and an initial osmoconcentration with little subsequent change accompanied ergometer exercise after hydration. This latter effect was due to a consistent osmodilution in all subjects, but occurring at different times during the session in each. All attained an osmolality of 290 mosmol/kg before dilution. Because this value is above the threshold of arginine vasopressin release, this hormone may have been responsible for the osmodilution. Therefore, the preexercise osmolality and the rate at which the threshold for vasopressin release is attained may determine whether osmodilution, osmoconcentration, or both occur during exercise.

Blood pressure and cardiac changes during signalled and unsignalled avoidance in dogs.

Alterations in blood pressure (BP) during two aversive behavioral tasks were studied in five chronically-prepared dogs. During a signalled-avoidance task, BP levels were not altered, although heart rate (HR) increased. While propranolol (0.3 mg/kg, IA) led to slight increases in resting pressure, and phenoxybenzamine (1.0 mg/kg) reductions, the tachycardia at avoidance onset was not affected. Exposure to an unsignalled-avoidance task led to elevated diastolic BP levels during a preavoidance period and to increases in systolic BP, HR and aortic dP/dt at the inception of the avoidance session. Again, neither drug affected the tachycardia during avoidance, but both agents precluded BP and aortic dP/dt increases. Patterns of intercorrelations among cardiovascular variables were similar for both tasks, and suggested that the basis of the BP maintenance shifted from vasomotor to cardiac control during the avoidance periods. The differential cardiovascular adjustments during these tasks could not be accounted for in terms of differences in response rate. Rather, the critical variable seemed to be the amount of feedback the animal received for responding.

Classical aversive conditioning of heart rate in curarized rats at different blood gas levels.

In an effort to examine whether normal blood gas tensions were essential for conditioning, paralyzed rats received a classical aversive heart rate (HR) conditioning session while respirated at different peak expired CO2 values. After the session, arterial blood was drawn for analysis. That peak expired CO2 was effective in manipulating PCO2 was indicated by a significant correlation (r=0.594, df=17, P less than 0.05). In addition, only rats with blood gas values similar to those of anesthetized controls displayed a discriminated HR CR. These animals also had lower baseline HRs and greater HR variability. Further, 7 of the 9 rats with normal blood gas values were respirated at peak expired CO2 values from 5.0-5.1 per cent, and no animal ventilated within this range displayed abnormal values. These findings suggest that previous difficulties in obtaining calssical and operant conditioning in paralyzed animals may, in part, be attributable to inadequate ventilation.

Neuromuscular blocking drugs and heart rate changes after direct nerve stimulation and during classical conditioning in cats.

Two experiments investigated cardiovascular responses to several common neuromuscular blocking compounds. Experiment 1, employing 16 cats, assessed ganglionic transmission in sympathetic and parasympathetic systems controlling heart rate and blood pressure after d-tubocurarine chloride (d-T.C.), dimethyl d-tubocurarine iodide (D. d-T.I.), succinylcholine chloride (SC), or saline. Cardiovascular responses to sympathetic stimulation were essentially unaffected at drug levels that blocked evoked electromyograms; however, vagally evoked bradycardia and corresponding blood pressure decrease were blocked by d-T.C. and redduced by D. d-T.I. and SC. Experiment 2 compared heart responses of 12 cats under the same blocking compounds during differential classical aversive conditioning. Differential conditioned responses and unconditioned responses occurred under D. d-T.I., less under SC, but not under d-T.C. However, animals trained under d-T.C. and tested under D. D-T.I. showed differential conditioned responses.