Effect of beta-adrenergic blockade on respiratory and metabolic responses to exercise

1981 ◽  
Vol 51 (4) ◽  
pp. 788-793 ◽  
Author(s):  
O. P. Twentyman ◽  
A. Disley ◽  
H. R. Gribbin ◽  
K. G. Alberti ◽  
A. E. Tattersfield
Keyword(s):  
Venous Blood ◽  
Normal Subjects ◽  
Cycle Ergometer ◽  
Work Rate ◽  
Adrenergic Blockade ◽  
Early Exercise ◽  
Co2 Output ◽  
Initial Reduction ◽  
Progressive Exercise ◽  
Constant Work Rate

The responses to oral propranolol (80 mg) and placebo were compared in normal subjects during three studies on a cycle ergometer (progressive exercise and two 5-min constant work rate studies at 50 and 70% maximum). Heart rate (HR), ventilation (VE), CO2 output (VCO2) and O2 uptake (VO2) were measured in each study and metabolites in venous blood in the 70% study. Propranolol reduced HR in all studies and endurance time during progressive exercise. During constant-work-rate exercise the changes with propranolol depended on time and work rate. At 50% max, VO2, VCO2, and VE were reduced in early exercise but were similar by min 5. At 70% max, VO2 and VCO2 were again lower initially with propranolol but then rose more rapidly. By min 5 VE was greater with propranolol, coinciding with a rapidly rising venous lactate. We interpret the initial reduction in VO2 and VCO2 to reduced cardiac output and muscle perfusion with propranolol. The resulting increase in anaerobic metabolism during heavy exercise would explain the increased VE at min 5. The metabolic data are compatible with glycogen being the predominant muscle fuel.

Effects of separate rib cage and abdominal restriction on exercise performance in normal humans

1985 ◽  
Vol 58 (6) ◽  
pp. 2020-2026 ◽  
Author(s):  
S. N. Hussain ◽  
B. Rabinovitch ◽  
P. T. Macklem ◽  
R. L. Pardy
Keyword(s):  
Minute Ventilation ◽  
Normal Subjects ◽  
Cycle Ergometer ◽  
Abdominal Muscle ◽  
Work Rate ◽  
Abdominal Pressure ◽  
Transdiaphragmatic Pressure ◽  
Rib Cage ◽  
Constant Work Rate ◽  
And Control

We assessed the effects of selective restriction of movements of the rib cage (Res,rc) and abdomen (Res,ab) on ventilatory pattern, transdiaphragmatic pressure (Pdi), and electrical activity of the diaphragm (Edi) in five normal subjects exercising at a constant work rate (80% of maximum power output) on a cycle ergometer till exhaustion. Restriction of movements was achieved by an inelastic corset applied tightly around the rib cage or abdomen. Edi was recorded by an esophageal electrode, rectified, and then integrated, and peak values during inspiration were measured. Each subject exercised at the same work rate on 3 days: with Res,rc, with Res,ab, and without restriction (control). Res,rc but not Res,ab reduced exercise time (tlim). Up to tlim, minute ventilation (VE) was similar in all three conditions. At any level of VE, however, Res,rc decreased tidal volume and inspiratory and expiratory time, whereas Res,ab had no effect on the pattern of breathing. Res,ab was associated with higher inspiratory Pdi swings at any level of VE, whereas peak Edi was similar to control. Inspiratory Pdi swings were the same with Res,rc as control, but the peak Edi for a given Pdi was greater with Res,rc (P less than 0.05). During Res,rc the abdominal pressure swings in expiration were greater than with Res,ab and control. We conclude that Res,rc altered the pattern of breathing in normal subjects in high-intensity exercise, decreased diaphragmatic contractility, increased abdominal muscle recruitment in expiration, and reduced tlim. On the other hand, Res,ab had no effect on breathing pattern or tlim but was associated with increased diaphragmatic contractility.

Evidence that the metabolic acidosis threshold is the anaerobic threshold

1990 ◽  
Vol 68 (6) ◽  
pp. 2521-2526 ◽  
Author(s):  
A. Koike ◽  
D. Weiler-Ravell ◽  
D. K. McKenzie ◽  
S. Zanconato ◽  
K. Wasserman
Keyword(s):  
Metabolic Acidosis ◽  
Anaerobic Threshold ◽  
Normal Subjects ◽  
Cycle Ergometer ◽  
Work Rate ◽  
Exercise Tests ◽  
Slope Analysis ◽  
O2 Transport ◽  
Co2 Output ◽  
Upper Slope

We evaluated maximal O2 uptake (VO2max), the metabolic acidosis threshold determined by the V-slope analysis [plot of CO2 output (VCO2) as a function of oxygen uptake (VO2)], the ratio of increase in VO2 to work rate increment (delta VO2/delta WR), the upper slope (S2) of the V-slope analysis, and the VO2 for work below and above the metabolic acidosis threshold to determine whether the changes in O2 transport caused by increased carboxyhemoglobin (HbCO) affected these parameters and variables. Ten normal subjects (aged 32.8 +/- 7.1 yr) performed symptom-limited incremental exercise tests in a ramp pattern on a cycle ergometer while breathing air and air with added carbon monoxide to cause HbCO to be approximately 11% and 20%. VO2max decreased by 11.6 and 19.3%, the metabolic acidosis threshold decreased by 11.9 and 19.6%, delta VO2/delta WR decreased by 8.9 and 14.0%, and S2 increased by 13.6 and 21.8% when HbCO was increased to 11 and 20%, respectively. Most importantly, VO2 was unchanged related to work rate below the metabolic acidosis threshold during the tests with increased HbCO but was reduced at the work rates above the metabolic acidosis threshold. These findings are consistent with the concept that the metabolic acidosis threshold is synonymous with an anaerobic threshold, i.e., the latter demarcating the VO2 above which the contracting muscles are not adequately supplied with O2 but below which they are.

Mediation of reduced ventilatory response to exercise after endurance training

1987 ◽  
Vol 63 (4) ◽  
pp. 1533-1538 ◽  
Author(s):  
R. Casaburi ◽  
T. W. Storer ◽  
K. Wasserman
Keyword(s):  
Endurance Training ◽  
Venous Blood ◽  
Normal Subjects ◽  
Cycle Ergometer ◽  
Work Rate ◽  
Exercise Tests ◽  
Average Decrease ◽  
Cycle Ergometer Exercise ◽  
Ergometer Exercise ◽  
The Difference

To investigate the mechanism by which ventilatory (VE) demand is modulated by endurance training, 10 normal subjects performed cycle ergometer exercise of 15 min duration at each of four constant work rates. These work rates represented 90% of the anaerobic threshold (AT) work rate and 25, 50, and 75% of the difference between maximum O2 consumption and AT work rates for that subject (as determined from previous incremental exercise tests). Subjects then underwent 8 wk of strenuous cycle ergometer exercise for 45 min/day. They then repeated the four constant work rate tests at work rates identical to those used before training. During tests before and after training, VE and gas exchange were measured breath by breath and rectal temperature (Tre) was measured continuously. A venous blood sample was drawn at the end of each test and assayed for lactate (La), epinephrine (EPI), and norepinephrine (NE). We found that the VE for below AT work was reduced minimally by training (averaging 3 l/min). For the above AT tests, however, training reduced VE markedly, by an average of 7, 23, and 37 l/min for progressively higher work rates. End-exercise La, NE, EPI, and Tre were all lower for identical work rates after training. Importantly, the magnitude of the reduction in VE was well correlated with the reduction in end-exercise La (r = 0.69) with an average decrease of 5.8 l/min of VE per milliequivalent per liter decrease in La. Correlations of VE with NE, EPI, and Tre were much less strong (r = 0.49, 0.43, and 0.15, respectively).

Lactate accumulation during incremental exercise with varied inspired oxygen fractions

1983 ◽  
Vol 55 (4) ◽  
pp. 1134-1140 ◽  
Author(s):  
M. C. Hogan ◽  
R. H. Cox ◽  
H. G. Welch
Keyword(s):  
Cycle Ergometer ◽  
Work Rate ◽  
O2 Uptake ◽  
Lactate Accumulation ◽  
Oxygen Fraction ◽  
Co2 Output ◽  
Break Points ◽  
Expired Gas ◽  
Gas Fractions ◽  
Inspired Oxygen

Six subjects pedaled a stationary cycle ergometer to exhaustion on three separate occasions while breathing gas mixtures of 17, 21, or 60% O2 in N2. Each subject rode for 3 min at work rates of 60, 90, 105 W, followed by 15-W increases every 3 min until exhaustion. Inspired and expired gas fractions, ventilation (V), heart rate, and blood lactate were measured. O2 uptake (VO2) and CO2 output (VCO2) were calculated for the last minute of each work rate; blood samples were drawn during the last 5 s. “Break points” for lactate, V, VCO2, V/VO2, and expired oxygen fraction (FEO2) were mathematically determined. VO2 was not significantly different at any work rate among the three different conditions. Nor did maximal VO2 differ significantly among the three treatments (P greater than 0.05). Lactate concentrations were significantly lower during hyperoxia and significantly higher during hypoxia compared with normoxia. Lactate values at exhaustion were not significantly different among the three treatments. Four subjects were able to work for a longer period of time during hyperoxic breathing. The variations in lactate accumulation as reported in this study cannot be explained on the basis of differences in VO2. The results of this research lend support to the hypothesis that differences in the performance of subjects breathing altered fractions of inspired oxygen may be caused by differences in lactate (or H+) accumulation.

Lactic acidosis as a facilitator of oxyhemoglobin dissociation during exercise

1994 ◽  
Vol 76 (4) ◽  
pp. 1462-1467 ◽  
Author(s):  
W. Stringer ◽  
K. Wasserman ◽  
R. Casaburi ◽  
J. Porszasz ◽  
K. Maehara ◽  
...  
Keyword(s):  
Lactic Acidosis ◽  
Femoral Vein ◽  
Lactate Concentration ◽  
Cycle Ergometer ◽  
Work Rate ◽  
Exercise Tests ◽  
Ergometer Exercise ◽  
Constant Work Rate ◽  
Slow Rise ◽  
Lactic Acidosis Threshold

The slow rise in O2 uptake (VO2), which has been shown to be linearly correlated with the increase in lactate concentration during heavy constant work rate exercise, led us to investigate the role of H+ from lactic acid in facilitating oxyhemoglobin (O2Hb) dissociation. We measured femoral venous PO2, O2Hb saturation, pH, PCO2, lactate, and standard HCO3- during increasing work rate and two constant work rate cycle ergometer exercise tests [below and above the lactic acidosis threshold (LAT)] in two groups of five healthy subjects. Mean end-exercise femoral vein blood and VO2 values for the below- and above-LAT square waves and the increasing work rate protocol were, respectively, PO2 of 19.8 +/- 2.1 (SD), 18.8 +/- 4.7, and 19.8 +/- 3.3 Torr; O2 saturation of 22.5 +/- 4.1, 13.8 +/- 4.2, and 18.5 +/- 6.3%; pH of 7.26 +/- 0.01, 7.02 +/- 0.11, and 7.09 +/- 0.07; lactate of 1.9 +/- 0.9, 11.0 +/- 3.8, and 8.3 +/- 2.9 mmol/l; and VO2 of 1.77 +/- 0.24, 3.36 +/- 0.4, and 3.91 +/- 0.68 l/min. End-exercise femoral vein PO2 did not differ statistically for the three protocols, whereas O2Hb saturation continued to decrease for work rates above LAT. We conclude that decreasing capillary PO2 accounted for most of the O2Hb dissociation during below-LAT exercise and that acidification of muscle capillary blood due to lactic acidosis accounted for virtually all of the O2Hb dissociation above LAT.

Anaerobic threshold alterations caused by endurance training in middle-aged men

1979 ◽  
Vol 46 (6) ◽  
pp. 1039-1046 ◽  
Author(s):  
J. A. Davis ◽  
M. H. Frank ◽  
B. J. Whipp ◽  
K. Wasserman
Keyword(s):  
Endurance Training ◽  
Anaerobic Threshold ◽  
Minute Ventilation ◽  
Correlation Coefficients ◽  
Cycle Ergometer ◽  
Work Rate ◽  
Middle Aged ◽  
Co2 Output ◽  
Before And After ◽  
Cycle Endurance

Nine previously sedentary middle-aged males underwent cycle endurance training 45 min/day for 9 wk with an average attendance of 4.1 days/wk. Seven males served as controls. Before and after the training period, the subjects performed three cycle ergometer tests. Work rate was incremented by 15 W/min, to the limit of the subjects' tolerance, in the first two tests; the third test consisted of contant-load cycling at an O2 uptake (VO2) just below the pretraining anaerobic threshold (AT). After training, the AT increased significantly by 44%, expressed as absolute VO2, and by 15%, expressed relative to VO2 max. Significant increases were also noted in VO2max (25%), maximal minute ventilation (19%), and maximal work rate (28%). The test-retest correlation coefficients for the AT (%VO2max) were 0.91, pre- and posttraining. Training did not alter steady-state VO2 during the submaximal exercise test whereas significant decreases occurred in CO2 output, VE, respiratory quotient, and VE/VO2. No changes occurred in the control subjects during this period. These results demonstrate that the AT is profoundly influenced by endurance training in previously sedentary middle-aged males.

Kinetics of gas exchange and ventilation in transitions from rest or prior exercise

1977 ◽  
Vol 43 (4) ◽  
pp. 704-708 ◽  
Author(s):  
L. B. Diamond ◽  
R. Casaburi ◽  
K. Wasserman ◽  
B. J. Whipp
Keyword(s):  
Normal Subjects ◽  
Cycle Ergometer ◽  
Work Rate ◽  
Prior Exercise ◽  
Exercise Hyperpnea ◽  
The Mean ◽  
Highly Correlated ◽  
Co2 Flow ◽  
Kinetics Of ◽  
High Work

Seven normal subjects each performed three transitions to a subanaerobic threshold work rate on a cycle ergometer: 1) from rest, 2) from a low work rate (both at 60 rpm), and 3) from a low work rate at 40 rpm to the high work rate at 80 rpm. Oxygen uptake (VO2), carbon dioxide output (VCO2), and ventilation (VE) were computed breath-by-breath and response kinetics extracted. The mean half-times of VO2, VCO2, and VE were 32, 44, and 49 s, respectively, and were not appreciably affected by the prior exercise or by variation of pedal rate. The kinetics of VE was highly correlated with VCO2 (r = 0.94), with VCO2 leading VE, providing further description of the relation of the exercise hyperpnea to CO2 flow to the lungs.

O2 uptake kinetics after acetazolamide administration during moderate- and heavy-intensity exercise

1998 ◽  
Vol 85 (4) ◽  
pp. 1384-1393 ◽  
Author(s):  
Barry W. Scheuermann ◽  
John M. Kowalchuk ◽  
Donald H. Paterson ◽  
David A. Cunningham
Keyword(s):  
Energy Demand ◽  
Ventilatory Threshold ◽  
Venous Blood ◽  
Lactate Concentration ◽  
Exponential Model ◽  
Constant Load ◽  
Cycle Ergometer ◽  
Work Rate ◽  
Ergometer Exercise ◽  
Single Response

Inhibition of carbonic anhydrase (CA) is associated with a lower plasma lactate concentration ([La−]pl) during fatiguing exercise. We hypothesized that a lower [La−]plmay be associated with faster O2uptake (V˙o 2) kinetics during constant-load exercise. Seven men performed cycle ergometer exercise during control (Con) and acute CA inhibition with acetazolamide (Acz, 10 mg/kg body wt iv). On 6 separate days, each subject performed 6-min step transitions in work rate from 0 to 100 W (below ventilatory threshold, <V˙eT) or to a V˙o 2 corresponding to ∼50% of the difference between the work rate atV˙eT and peakV˙o 2(>V˙eT). Gas exchange was measured breath by breath. Trials were interpolated at 1-s intervals and ensemble averaged to yield a single response. The mean response time (MRT, i.e., time to 63% of total exponential increase) for on- and off-transients was determined using a two- (<V˙eT) or a three-component exponential model (>V˙eT). Arterialized venous blood was sampled from a dorsal hand vein and analyzed for [La−]pl. MRT was similar during Con (31.2 ± 2.6 and 32.7 ± 1.2 s for on and off, respectively) and Acz (30.9 ± 3.0 and 31.4 ± 1.5 s for on and off, respectively) for work rates <V˙eT. At work rates >V˙eT, MRT was similar between Con (69.1 ± 6.1 and 50.4 ± 3.5 s for on and off, respectively) and Acz (69.7 ± 5.9 and 53.8 ± 3.8 s for on and off, respectively). On- and off-MRTs were slower for >V˙eT than for <V˙eT exercise. [La−]plincreased above 0-W cycling values during <V˙eT and >V˙eT exercise but was lower at the end of the transition during Acz (1.4 ± 0.2 and 7.1 ± 0.5 mmol/l for <V˙eT and >V˙eT, respectively) than during Con (2.0 ± 0.2 and 9.8 ± 0.9 mmol/l for <V˙eT and >V˙eT, respectively). CA inhibition does not affect O2 utilization at the onset of <V˙eT or >V˙eT exercise, suggesting that the contribution of oxidative phosphorylation to the energy demand is not affected by acute CA inhibition with Acz.

Lactate acidosis and the increase in VE/VO2 during incremental exercise

1987 ◽  
Vol 62 (4) ◽  
pp. 1551-1555 ◽  
Author(s):  
S. W. Farrell ◽  
J. L. Ivy
Keyword(s):  
Blood Lactate ◽  
Venous Blood ◽  
Experimental Treatment ◽  
Cycle Ergometer ◽  
Work Rate ◽  
Incremental Exercise ◽  
Exercise Tests ◽  
Similar Work ◽  
Blood Ph ◽  
Lactate Acidosis

The purpose of this investigation was to determine whether the onset of lactate acidosis is responsible for the increase in ventilatory equivalent (VE/VO2) during exercise of increasing intensity. Eight male subjects performed maximal incremental exercise tests on a cycle ergometer on two separate occasions. For the control (C) treatment, the initial work rates consisted of 4 min of unloaded pedaling (60 rpm) and 1 min of pedaling at a work rate of 30 W. Thereafter, the work rate was increased each minute by 22 W until volitional fatigue. Venous blood samples were taken before the onset of exercise and at the end of each work rate for determination of pH and lactate. Ventilatory parameters at each work rate were also monitored. Before the experimental treatment (E), the subjects performed two 3-min work bouts at high intensity (210–330 W) on the cycle ergometer in order to prematurely raise blood lactate levels and lower blood pH. The same incremental exercise test as C was then performed. The results indicated that the increase in VE/VO2 occurred at similar work rates and %VO2max although the venous H+ and lactate concentrations were significantly elevated during the E treatment. These results suggest that a decrease in the blood pH resulting from blood lactate accumulation is not responsible for the increase in VE/VO2 during incremental exercise.

Effect of beta-adrenergic blockade during exercise on ventilation and gas exchange

1976 ◽  
Vol 41 (6) ◽  
pp. 886-892 ◽  
Author(s):  
H. V. Brown ◽  
K. Wasserman ◽  
B. J. Whipp
Keyword(s):  
Heart Rate ◽  
Cardiac Output ◽  
Steady State ◽  
Minute Ventilation ◽  
Co2 Flux ◽  
Normal Subjects ◽  
Adrenergic Blockade ◽  
Beta Adrenergic ◽  
Co2 Output ◽  
Ventilatory Effects

The ventilatory effects of beta-adrenergic blockade during steady-state exercise were studied in eight normal subjects using intravenous propranolol hydrochloride (0.2 mg/kg). Heart rate decreased in all subjects by an average of 17%. Coincident with the phase of decreasing heart rate was a significant decrease in both minute ventilation (VE) and CO2 output (VCO2), averaging 9.6 and 9.2%, respectively. Both functions returned to prepropranolollevels after heart rate had reached its reduced steady-state value. The change in VE was significantly correlated with the change in VCO2 (r = 0.85, Pless than 0.005), and was associated with negligible changes in endtidal CO2 tensions and ventilatory equivalents for CO2. We interpret these studies as showing that the transient isocapnic hypopnea concomitant with an acute reduction in cardiac output was secondary to a transient decrease in CO2 flux (cardiac output x mixed venous CO2 content). This decrease in VE appearsto be induced by the acute decrease in cardiac output (“cardiodynamic hypopnea”), in fashion similar to the previously described cardiodynamic hyperpnea.

Sign in / Sign up

Export Citation Format

Share Document