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Biomedical subjects

B J Freund

Publications and source records attributed to B J Freund.

32 records · Page 2Linked to original sources
PubMed1988

Effect of beta-blockade on the drift in O2 consumption during prolonged exercise.

The effect of beta-adrenergic blockade on the drift in O2 consumption (VO2 drift) typically observed during prolonged constant-rate exercise was studied in 14 healthy males in moderate heat at 40% of maximal O2 consumption (VO2max). After an initial maximum cycle ergometer test to determine the subjects' control VO2max, subjects were administered each of three medications: placebo, atenolol (100 mg once daily), and propranolol (80 mg twice daily), in a randomized double-blind fashion. Each medication period was 5 days in length and was followed by a 4-day washout period. On the 3rd day of each medication period, subjects performed a maximal cycle ergometer test. On the final day of each medication period, subjects exercised at 40% of their control VO2max for 90 min on a cycle ergometer in a warm (31.7 +/- 0.3 degrees C) moderately humid (44.7 +/- 4.7%) environment. beta-Blockade caused significant (P less than 0.05) reductions in VO2max, maximal minute ventilation (VEmax), maximal heart rate (HRmax), and maximal exercise time. Significantly greater decreases in VO2max, VEmax, and HRmax were associated with the propranolol compared with the atenolol treatment. During the 90-min submaximal rides, beta-blockade significantly reduced heart rate. Substantially lower values for O2 consumption (VO2) and minute ventilation (VE) were observed with propranolol compared with atenolol or placebo. Furthermore, VO2 drift and HR drift were observed under atenolol and placebo conditions but not with propranolol. Respiratory exchange ratio decreased significantly over time during the placebo and atenolol trials but did not change during the propranolol trial.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1988

Effects of exercise on atrial natriuretic factor. Release mechanisms and implications for fluid homeostasis.

Atrial natriuretic factor is reported to be elevated during and immediately following exercise and is thought to play a role in fluid homeostasis and cardiovascular regulation. The predominant stimuli for atrial natriuretic factor release during exercise appear to be increases in atrial pressures or atrial distension, both of which are reported to increase with exercise. The intensity and perhaps duration of exercise also influence the magnitude of the atrial natriuretic factor response. It is not clear if the rise in plasma atrial natriuretic factor during exercise plays any role in altering renal function since high intensity exercise is typically associated with an antidiuresis. However, elevations in plasma atrial natriuretic factor may in part be responsible for the increase in urine flow reported when exercise is performed at low or moderate intensities. Atrial natriuretic factor also has vascular effects which may be important in buffering or moderating the blood pressure response to exercise. The atrial natriuretic factor response to exercise and basal levels of the hormone are greatly elevated in patients who suffer from a variety of cardiovascular and pulmonary disease conditions. These elevated plasma atrial natriuretic factor values are associated with increases in atrial pressure and appear to be related to the severity of disease. Although much controversy exists regarding the renal and vascular effects of atrial natriuretic factor, the measurement of this hormone, particularly during exercise, may be of clinical value by providing an additional tool to evaluate patients and determine the effectiveness of various treatment regimens.

Atrial Natriuretic Factor↗
PubMed1987

Hormonal and vascular fluid responses to maximal exercise in trained and untrained males.

The trained condition is associated with alterations in fluid regulation. In attempt to elucidate mechanisms responsible for these differences, resting, postexercise (maximal treadmill exercise of 8-13 min duration), and recovery measurements were made in seven trained (mean peak O2 consumption was 60.5 +/- 1.6 ml.kg-1.min-1) and seven untrained (mean peak O2 consumption was 40.7 +/- 1.7 ml.kg-1.min-1) male subjects. Samples were obtained by venipuncture with subjects seated. No significant differences in resting plasma osmolality (Osm), sodium, potassium, antidiuretic hormone (ADH), aldosterone, renin activity, or atrial natriuretic factor were found between groups. Maximal exercise produced significant increases in all of the above variables. Values immediately postexercise were similar between groups except for plasma Osm and sodium, which were significantly higher in the untrained group. Despite a reduction in plasma volume of equal magnitude in both groups, trained subjects demonstrated an increase in vascular proteins and mean corpuscular volume during exercise. This increase in plasma protein may be an important initiating factor responsible for the elevated plasma volume after 1-h recovery from exercise in the trained group. Lastly, similar ADH responses despite lower Osm in trained subjects may indicate that training increases the sensitivity of ADH to osmotic stimulation.

Adult↗
PubMed1987

Thermoregulation during prolonged exercise in heat: alterations with beta-adrenergic blockade.

Thermoregulation and cardiovascular drift were studied under conditions of prolonged exercise in a warm environment (dry bulb temperature 31.7 +/- 0.3 degrees C, rh 44.7 +/- 4.7%) during beta-adrenergic blockade. Fourteen subjects performed 90-min rides on a cycle ergometer at a work rate equivalent to 40% of their control maximal O2 uptake under each of three treatments provided in a randomized double-blind manner: atenolol (100 mg/day), propranolol (160 mg/day), and a placebo. Exercise during the propranolol trial resulted in significantly higher forearm vascular resistance values and significantly lower forearm blood flows (FBF) compared with the placebo trial. However, the significantly lower FBF during propranolol did not significantly alter the rectal temperature (Tre) response to prolonged exercise. In addition, both beta-blockers produced lower FBF for any given Tre, suggesting that beta-adrenergic blockade affects FBF through nonthermal factors. The slight differences in Tre, despite the large differences in FBF between the various treatments, are apparently the result of an enhanced sweat loss and a lower mean skin temperature during exercise with beta-blockade. The uncoupling of FBF and sweat loss provides evidence of independent regulation. The reduction in FBF at any given Tre was concomitant to lower blood pressure values during beta-blockade and suggests that baroreflexes provide significant input to the control of skin blood flow when both pressure and temperature maintenance are simultaneously challenged.

Adult↗
PubMed1986

Effects of aerobic training on exercise tolerance and echocardiographic dimensions in untrained postmenopausal women.

The cardiovascular effects of physical training were evaluated in a controlled trial involving 32 healthy, untrained, postmenopausal women. The subjects were randomly assigned to an aerobic exercise training program or a control group. The exercise group participated in at least three 40-minute supervised sessions per week for 8 months. Twenty-five subjects completed the study: eight in the control group and 17 in the training group. The training group had a significant increase over the training period in maximal oxygen consumption (27.3 +/- 4.6 ml/kg/min vs 30.8 +/- 5.4 ml/kg/min, p less than 0.05) and maximal treadmill exercise duration (9.8 +/- 2.6 minutes vs 11.3 +/- 2.2 minutes; p less than 0.05). The control group had no significant change in maximal treadmill exercise duration (9.0 +/- 1.2 minutes vs 9.2 +/- 1.4 minutes) but had a slight increase in maximal oxygen consumption (23.7 +/- 3.4 ml/kg/min vs 24.4 +/- 4.1 ml/kg/min, p less than 0.05). The training group had significant increases in M-mode echocardiographic left ventricular end-diastolic dimension (4.6 +/- 0.6 cm vs 4.8 +/- 0.4 cm, p less than 0.05) and calculated left ventricular ejection fraction (0.66 +/- 0.14 vs 0.74 +/- 0.12, p less than 0.05). M-mode echocardiograms demonstrated no significant change in left ventricular dimensions or wall thickness in the control group. In this group of untrained postmenopausal women, a training effect was associated with enhanced resting left ventricular ejection fraction and increased resting left ventricular end-diastolic dimension.

Adaptation, Physiological↗
PubMed1986

Effects of beta-blockade on exercise capacity of trained and untrained men: a hemodynamic comparison.

To study the effects of cardiovascular fitness on hemodynamic responses to exercise during beta-adrenergic blockade (BAB), submaximal [60% of maximum O2 uptake (VO2max)] and maximal treadmill exercise data were collected in 11 trained (T, VO2max 63.3 ml X kg-1 X min-1, 26.8 yr) and 11 untrained (UT, VO2max 44.5 ml X kg-1 X min-1, 25.0 yr) male subjects. Subjects completed two maximal control tests followed by a randomized, double-blind series of maximal tests after 1-wk treatments with placebo (PLAC), propranolol (PROP, 160 mg/day, beta 1- and beta 2-blockade), and atenolol (ATEN, 100 mg/day, beta 1-blockade). Treatments were separated by 1-wk washout periods. At 60% of control VO2max T and UT subjects experienced no reductions in O2 uptake (VO2) with either drug. Submaximal heart rate (HR, beats/min) was 134.8 PLAC, 107.0 PROP, 107.9 ATEN (P less than 0.05 both drugs vs. PLAC) in T subjects and 141.1 PLAC, 106.1 PROP, and 105.0 ATEN (P less than 0.05 both drugs vs. PLAC) in UT subjects. Cardiac output (1/min) for T was 17.3 PLAC, 16.9 PROP, 16.5 ATEN (P less than 0.05 ATEN vs. PLAC in T only) and for UT it was 12.2 (PLAC), 11.7 (PROP), 11.5 (ATEN) (P less than 0.05 both drugs vs. PLAC in UT). Stroke volume increased from 129.8 ml (PLAC) to 158.6 (PROP) and 156.2 (ATEN) in T (P less than 0.05 both drugs vs. PLAC) and from 86.8 (PLAC) to 110.0 (PROP) and 109.8 (ATEN) (P less than 0.05 both drugs vs. PLAC) in UT. The increases in stroke volume (SV) were similar in both groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1986

Modification of cellular immune functions in humans by endurance exercise training during beta-adrenergic blockade with atenolol or propranolol.

Young, healthy, previously inactive men were trained aerobically 40 to 50 min X d-1, 5 d X wk-1 for 15 wk. They were randomly assigned to one of three medication groups: placebo, propranolol (160 mg X d-1), or atenolol (100 mg X d-1). All subjects lost weight and decreased relative body fat as a result of training. Following training, submaximal steady-state heart rates were reduced in all groups. Maximal oxygen uptake and maximal treadmill times were also increased in all groups. The VO2max of the placebo increased 18.4%. While that of the atenolol group increased 19.4%, the propranolol group went up 17.0%. After training the maximal heart rate did not change in the placebo group, while treatment with propranolol and atenolol reduced at 24.6 and 21.9%, respectively. Training caused a significant decrease in the natural killer cell activity in all three groups. The placebo group had 38.8% +/- 3.8 (SD) before and 29.3 +/- 3.2% lysis of target cells by natural killer cells after physical conditioning, which was significantly lower (P less than 0.01). The groups treated with propranolol and atenolol were also similarly decreased. The use of propranolol or atenolol had no additional significant effect on natural killer cell activity. T-cell mitogenesis stimulated with a mitogen significantly increased with conditioning. The groups given atenolol or propranolol tended to increase somewhat more than the placebo group, although this difference was not statistically significant. There was no significant change in the percentage of total lymphocytes isolated due to training or beta-blockade.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1986

Interaction of test protocol and horizontal run training on maximal oxygen uptake.

Twenty-seven untrained college-age males (mean age = 23.1 yr) volunteered for this 12-wk training study, which investigated potential interactions between training specificity and treadmill protocol specificity. The study was designed to analyze the interaction between a subject's maximal oxygen uptake (VO2max) on an inclined protocol (IP) vs a horizontal protocol (HP) before and after training exclusively on flat terrain. Experimental subjects (E, N = 17) trained by running on flat terrain for 12 wk, 4 d/wk, 37 min/d at an intensity equal to 65 to 85% of their heart rate reserve while control subjects (C, N = 10) remained sedentary. All subjects underwent a minimum of four maximal treadmill tests (two with an IP and two with a HP) prior to training and two maximal treadmill tests (one IP and one HP) post-training. Multivariate analysis of variance and post-hoc t-tests using a pooled variance-covariance matrix were used to analyze the data. Alterations in E, consequent to training, included significant increases in VO2max [mean IP = 53.6 to 58.4 (+8.9%) and mean HP = 51.7 to 56.2 ml. kg-1 . min-1 (+8.7%)]. C showed a significant pre- to post-training decrease on the HP for VO2max [mean HP = 52.4 to 50.7 ml . kg-1 . min-1 (-3.2%)], but showed no significant change on the IP. There was no significant pre- to post-training interaction between protocols for VO2max. It was concluded that the post-training results do not support the concept of protocol specificity when evaluating VO2max in subjects trained exclusively on flat terrain.

Adult↗
PubMed1986

Interaction of test protocol and inclined run training on maximal oxygen uptake.

Twenty-two men, 17 to 27 years of age, volunteered to participate in an inclined terrain running program. Men were randomly assigned to a control (N = 10) or an experimental (N = 12) group. The experimental group ran on inclined terrain 4 times/wk for 35 min a session at an intensity of 65 to 85% of maximal aerobic power for 12 wk. The purpose of this study was to analyze the interaction between a subject's VO2max on an inclined protocol (IP) vs a horizontal protocol (HP) before and after training on incline terrain. VO2max, HRmax, VEmax, Rmax, and maximum treadmill time were evaluated on both treadmill protocols (IP and HP). Prior to training, results indicated no difference in VO2max values between protocols. Following training, VEmax, maximum treadmill time, and VO2max increased 8.7, 9.1, and 8.5%, respectively, on the IP and 5.8, 6.8, and 5.3% on the HP respectively. All increases were statistically significant at the 0.05 level. The post-training VO2max on the IP was significantly greater than the value on the HP. These results support the concept of specificity of training and indicate the importance of careful selection of both the test protocol as well as the test mode.

Adult↗
PubMed1985

Acute response to submaximal and maximal exercise consequent to beta-adrenergic blockade: implications for the prescription of exercise.

Forty-seven healthy male subjects, 17 to 34 years old, completed a test to exhaustion on a motor-driven treadmill to determine their maximal oxygen uptake. A second test was administered 2 days later during which the subject walked for 20 to 25 minutes at a steady-state level representing 60% of the maximal oxygen uptake as determined in the first test. The grade was then increased every 2 minutes until the subject reached the state of exhaustion. After the second test, the subjects were randomly assigned, in a double-blind manner, to either placebo, propranolol (160 mg/day), or atenolol (100 mg/day) treatment for 7 days. Exactly 1 week from the time of the second test, and 3 hours after the last medication, the subjects completed the final exercise test using the same treadmill protocol administered in the second test. Heart rate and systolic blood pressure at rest and during submaximal steady-state exercise were significantly reduced by both drugs, whereas diastolic pressure was unaffected. During submaximal steady-state exercise, cardiac output was reduced in both the placebo and atenolol groups, stroke volume was increased in both atenolol and propranolol groups, oxygen uptake was reduced in the atenolol group, pulmonary ventilation was reduced in both propranolol and atenolol groups, and the respiratory exchange ratio remained unchanged. With maximal exercise, treadmill time was significantly reduced with propranolol, pulmonary ventilation and heart rate were reduced significantly with both drugs, but maximal oxygen uptake remained unchanged. Thus, beta blockade does not appear to limit ability to exercise. However, there appears to be a significant advantage to using a cardioselective rather than a nonselective beta-blocking agent.

Adolescent↗
PubMed1985

Cardiorespiratory alterations consequent to endurance exercise training during chronic beta-adrenergic blockade with atenolol and propranolol.

A study was undertaken to determine if normal healthy subjects can increase their endurance capacity consequent to endurance training during chronic beta-adrenergic blockade. Forty-seven subjects, 17 to 34 years of age, were randomly assigned to 1 of 3 treatments (placebo, propranolol, 160 mg/day, and atenolol, 100 mg/day) and then completed a 15-week aerobic exercise training program. All groups reduced their submaximal steady-state heart rates consequent to training; submaximal oxygen uptake was slightly reduced; submaximal stroke volume was increased only in the placebo and atenolol groups; submaximal cardiac output was generally lower; and arterial-mixed venous oxygen difference was increased after training in all 3 groups, suggesting decreased muscle blood flow and increased oxidative capacity. Maximal oxygen uptake and maximal treadmill time were increased in all 3 groups after training. However, while still on medication the atenolol group had significantly greater increases in maximal oxygen uptake and maximal treadmill time compared with the propranolol group. Because most patients will remain on medication, these results suggest a distinct advantage for cardioselective blocking agents. It is concluded that beta-adrenergic blockade does not reduce the ability of normal healthy subjects to gain the benefits associated with cardiorespiratory endurance training.

Adolescent↗
PubMed1985

Effects of cardioselective and nonselective beta-adrenergic blockade on the performance of highly trained runners.

Twenty-five highly trained runners with a maximal oxygen uptake (VO2 max) of 64.7 +/- 4.3 ml . kg-1. min-1 were administered clinically equivalent doses of a nonselective (propranolol) and a cardioselective (atenolol) beta-blocking agent as well as a placebo. The subjects performed a horizontal treadmill test on the eighth day and a 10-km track race on the tenth day of each treatment. Beta blockade decreased submaximal heart rate and propranolol caused the largest decrease. Beta blockade caused a decrease in maximal heart rate, VO2 max, maximal ventilation, maximal respiratory exchange ratio and treadmill time. Propranolol caused a greater decrease than atenolol in each of these values. The 10-km race times were significantly slower during beta blockade, and propranolol race times were significantly slower than atenolol race times. It is concluded that the performance of highly trained distance runners is significantly altered by beta-adrenergic blockade and that nonselective agents reduce performance to a greater extent than cardioselective agents.

Adult↗