Effect of hematocrit on systemic O2 transport in hypoxic and normoxic exercise in rats

1994 ◽  
Vol 77 (3) ◽  
pp. 1341-1348 ◽  
Author(s):  
N. C. Gonzalez ◽  
L. P. Erwig ◽  
C. F. Painter ◽  
R. L. Clancy ◽  
P. D. Wagner
Keyword(s):  
Exchange Transfusion ◽  
Maximal Exercise ◽  
Systemic Arterial Pressure ◽  
Diffusing Capacity ◽  
O2 Uptake ◽  
Vo2 Max ◽  
O2 Transport ◽  
Maximal Cardiac Output ◽  
O2 Concentration ◽  
Mixed Venous

The effect of hematocrit (Hct) on O2 transport in hypoxic [inspired PO2 (PIO2) approximately 70 Torr] and normoxic (PIO2 approximately 145 Torr) exercise was studied in rats acclimatized to 3 wk of PIO2 at approximately 70 Torr (A rats) and in nonacclimatized littermates (NA rats). Isovolumic exchange transfusion of plasma or red blood cells was used to lower Hct in A rats from approximately 60 to 45% and to raise Hct of NA rats from 45 to 60%: Controls were A and NA rats exchange transfused with whole blood at constant Hct. Lowering Hct of A rats lowered the arterial O2 concentration (CaO2) and the arterial-mixed venous O2 difference and increased the maximal cardiac output (Qmax) without changes in maximal O2 uptake (VO2 max) or in the product of Qmax x CaO2, circulatory O2 convection at maximal exercise (TO2 max). Raising Hct in NA rats produced the opposite changes in CaO2, arterial-mixed venous O2 difference, and Qmax, but VO2 max and TO2 max increased significantly, both in hypoxia and normoxia, because of relatively small changes in Qmax. In NA rats, a steeper slope of the line relating VO2 max to calculated mean capillary PO2 at high Hct suggested a higher tissue O2 diffusing capacity with high Hct. For a given Hct and Qmax, systemic arterial pressure was higher in A rats. The data suggest that 1) the effect of Hct on systemic hemodynamics is different in A and NA rats, resulting in different effects on VO2 max; 2) factors in addition to Hct contribute to the high systemic vascular resistance of A rats; and 3) increased diffusive conductance for O2, as well as increased TO2 max, could be responsible for the effect of Hct on VO2 max of NA rats.

Effects of training on muscle O2 transport at VO2max

1992 ◽  
Vol 73 (3) ◽  
pp. 1067-1076 ◽  
Author(s):  
J. Roca ◽  
A. G. Agusti ◽  
A. Alonso ◽  
D. C. Poole ◽  
C. Viegas ◽  
...  
Keyword(s):  
Blood Flow ◽  
Diffusing Capacity ◽  
O2 Uptake ◽  
O2 Transport ◽  
Straight Line ◽  
O2 Extraction ◽  
O2 Concentration ◽  
Individual Effects ◽  
O2 Supply ◽  
Sedentary Subjects

To quantify the relative contributions of convective and peripheral diffusive components of O2 transport to the increase in leg O2 uptake (VO2leg) at maximum O2 uptake (VO2max) after 9 wk of endurance training, 12 sedentary subjects (age 21.8 +/- 3.4 yr, VO2max 36.9 +/- 5.9 ml.min-1.kg-1) were studied. VO2max, leg blood flow (Qleg), and arterial and femoral venous PO2, and thus VO2leg, were measured while the subjects breathed room air, 15% O2, and 12% O2. The sequence of the three inspirates was balanced. After training, VO2max and VO2leg increased at each inspired O2 concentration [FIO2; mean over the 3 FIO2 values 25.2 +/- 17.8 and 36.5 +/- 33% (SD), respectively]. Before training, VO2leg and mean capillary PO2 were linearly related through the origin during hypoxia but not during room air breathing, suggesting that, at 21% O2, VO2max was not limited by O2 supply. After training, VO2leg and mean capillary PO2 at each FIO2 fell along a straight line with zero intercept, just as in athletes (Roca et al. J. Appl. Physiol. 67: 291–299, 1989). Calculated muscle O2 diffusing capacity (DO2) rose 34% while Qleg increased 19%. The relatively greater rise in DO2 increased the DO2/Qleg, which led to 9.9% greater O2 extraction. By numerical analysis, the increase in Qleg alone (constant DO2) would have raised VO2leg by 35 ml/min (mean), but that of DO2 (constant Qleg) would have increased VO2leg by 85 ml/min, more than twice as much. The sum of these individual effects (120 ml/min) was less (P = 0.013) than the observed rise of 164 ml/min (mean). This synergism (explained by the increase in DO2/Qleg) seems to be an important contribution to increases in VO2max with training.

Exercise recovery above and below anaerobic threshold following maximal work

1981 ◽  
Vol 51 (4) ◽  
pp. 840-844 ◽  
Author(s):  
B. A. Stamford ◽  
A. Weltman ◽  
R. Moffatt ◽  
S. Sady
Keyword(s):  
Blood Lactate ◽  
Anaerobic Threshold ◽  
Maximal Exercise ◽  
Lactate Concentration ◽  
Blood Lactate Concentration ◽  
Base Line ◽  
Exercise Recovery ◽  
O2 Uptake ◽  
Vo2 Max ◽  
Individual Subject

The purpose of this study was to determine the effects of resting and exercise recovery above [70% of maximum O2 uptake (VO2 max)] and below [40% of VO2 max] anaerobic threshold (AT) on blood lactate disappearance following maximal exercise. Blood lactate concentrations at rest (0.9 mM) and during exercise at 40% (1.3 mM) and 70% (3.5 mM) of VO2 max without preceding maximal exercise were determined on separate occasions and represented base lines for each condition. The rate of blood lactate disappearance from peak values was ascertained from single-component exponential curves fit for each individual subject for each condition using both the determined and resting base lines. When determined base lines were utilized, there were no significant differences in curve parameters between the 40 and 70% of VO2 max recoveries, and both were significantly different from the resting recovery. When a resting base line (0.9 mM) was utilized for all conditions, 40% of VO2 max demonstrated a significantly faster half time than either 70% of VO2 max or resting recovery. No differences were found between 70% of VO2 max and resting recovery. It was concluded that interpretation of the effectiveness of exercise recovery above and below AT with respect to blood lactate disappearance is influenced by the base-line blood lactate concentration utilized in the calculation of exponential half times.

Influence of age and physical activity on central hemodynamics and lung function in active adults

1978 ◽  
Vol 45 (5) ◽  
pp. 709-717 ◽  
Author(s):  
I. L. Kanstrup ◽  
B. Ekblom
Keyword(s):  
Physical Activity ◽  
Maximal Exercise ◽  
Individual State ◽  
Vo2 Max ◽  
Physically Active ◽  
Circulatory Response ◽  
The Individual ◽  
Active Adults ◽  
Mixed Venous ◽  
Peak Value

Five female and seven male physically active adults were studied twice within a 13-yr interval. The individual state of physical activity was mainly unchanged. Maximal oxygen uptake (VO2 max) was reduced in all subjects except one female, in whom it remained unchanged. During maximal exercise, cardiac output (Q) in males was unchanged. In females, Q was significantly increased due to increased stroke volume (SV). In both sexes, the reduced VO2 max was explained by a smaller arteriovenous O2 difference (mixed venous O2 content (C-VO2) significantly increased). For a given submaximal VO2, Q was increased in both sexes and heart rate was unchanged. Thus, SV was increased and arteriovenous O2 difference was reduced due to increased C-VO2. Another four males were studied several times in various states of physical fitness during an 11-yr period. The reduced VO2 max from peak value was due to a reduced Qmax (SV smaller), whereas the arteriovenous O2 difference and C-VO2 were unchanged. Our results indicate that the observed changes in circulatory response to submaximal and maximal exercise in physically active adults may to a large extent be due to an effect of “detraining.”

Effect of hematocrit on cerebral blood flow with induced polycythemia

1987 ◽  
Vol 62 (3) ◽  
pp. 1090-1096 ◽  
Author(s):  
J. Massik ◽  
Y. L. Tang ◽  
M. L. Hudak ◽  
R. C. Koehler ◽  
R. J. Traystman ◽  
...  
Keyword(s):  
Blood Flow ◽  
Cerebral Blood Flow ◽  
Exchange Transfusion ◽  
Cell Concentration ◽  
Red Cell ◽  
O2 Uptake ◽  
Experimental Animals ◽  
O2 Transport ◽  
Before And After ◽  
Independent Effects

Cerebral blood flow (CBF) is lowered during polycythemia. Whether this fall is due to an increase in red blood cell concentration (Hct) or to an increase in arterial O2 content (Cao2) is controversial. We examined the independent effects of Hct and Cao2 on CBF as Hct was raised from 30 to 55% in anesthetized 1- to 7-day-old sheep. CBF was measured by the radiolabeled microsphere technique before and after isovolemic exchange transfusion with either oxyhemoglobin-containing erythrocytes (in 5 control animals) or with methemoglobin-containing erythrocytes (in 9 experimental animals). Following exchange transfusion in the control animals, Hct rose (30 +/- 1 vs. 55 +/- 1%, mean +/- SE), Cao2 increased (15.1 +/- 0.8 vs. 26.7 +/- 0.9 vol%), and CBF fell (66 +/- 9 vs. 35 +/- 5 ml X min-1 X 100 g-1). Because the fall in CBF was proportionate to the rise in Cao2, cerebral O2 transport (CBF X Cao2) was unchanged. Following exchange transfusion in the experimental animals, Hct rose (32 +/- 1 vs. 55 +/- 1%) but Cao2 did not change. Nevertheless, CBF still fell (73 +/- 4 vs. 48 +/- 2 ml X min-1 X 100 g-1) and, as a result, cerebral O2 transport also fell. The latter cannot be attributed to a fall in cerebral O2 uptake, as cerebral O2 uptake was unaffected during each of these conditions. Comparison of the two groups of animals showed that approximately 60% of the fall in CBF may be attributed to the increase in red cell concentration alone. It is probable that this effect is due largely to changes in blood viscosity.

Characteristics of adjustment of lung diffusing capacity to work

1982 ◽  
Vol 52 (5) ◽  
pp. 1124-1127 ◽  
Author(s):  
J. T. Fisher ◽  
F. J. Cerny
Keyword(s):  
Steady State ◽  
Work Load ◽  
Time Interval ◽  
Diffusing Capacity ◽  
O2 Uptake ◽  
Total Response ◽  
Vascular Control ◽  
Vo2 Max ◽  
Single Breath ◽  
Healthy Males

The response of lung diffusing capacity for CO (DLCO) to the onset of exercise or a change in work load was studied in four healthy males. Single-breath DLCO was measured during the transients 1) from rest to 40% of maximum O2 uptake (VO2 max); 2) from rest to 80% VO2 max; and 3) from steady-state exercise at 40 to 80% VO2 max. Protocols 1 and 2 consisted of 8.5 min of exercise while 3 consisted of 10.5 min of exercise at 40% VO2 max followed by 8.5 min at 80% VO2 max. DLCO was measured at 10, 20, 30, 60, 90, 240, and 510 s after onset of change in load. Half times of the responses (1, 39: 2, 43; 3, 56 s) were not statistically different. The percentage of the total response completed at each time interval indicated that 3 was significantly (P less than 0.05) slower than 1 and 2 at 10 and 20 s. The rapid response of DLCO at the onset of exercise may reflect a neural component in pulmonary vascular control during exercise.

Dynamic exercise in senescent beagles: oxygen consumption and hemodynamic responses

1989 ◽  
Vol 257 (5) ◽  
pp. H1428-H1437 ◽  
Author(s):  
G. C. Haidet
Keyword(s):  
Stroke Volume ◽  
Maximal Exercise ◽  
Submaximal Exercise ◽  
Vo2 Max ◽  
Hemodynamic Responses ◽  
Absolute Level ◽  
Relative Level ◽  
Age Related ◽  
Maximal Cardiac Output ◽  
Total Body

Seven senescent beagles and seven younger mature beagles were studied at rest, as well as during maximal and submaximal exercise on a motor-driven treadmill. Maximal exercise capacity was significantly (P less than 0.05) reduced, and maximal total body O2 consumption (VO2 max) was 31% lower in senescent beagles. VO2 was also significantly reduced in old dogs, when directly compared at the same relative workloads in old and younger mature dogs. However, VO2 was very similar in both groups during each of the absolute levels of directly comparable exercise. The observed age-related reduction in VO2 max was associated with a significant 25% reduction in maximal cardiac output (CO) in senescent beagles, and with an 11% reduction in maximal arteriovenous O2 difference. CO was also significantly reduced in old dogs at the same relative levels of submaximal exercise evaluated. Combined effects of reductions in stroke volume and in heart rate both contributed to the observed reductions in CO observed in senescent dogs during maximal exercise, as well as during relative levels of submaximal exercise. However, CO responses at each absolute level of submaximal exercise were similar in senescent and younger mature beagles, and the relationship between CO and VO2 was also similar in both groups. Increases in stroke volume significantly contributed to observed increases in CO beginning at the same relative level of exercise in both old and young dogs. Results of this study demonstrate that significant age-related changes in VO2max and in other associated hemodynamic parameters occur during maximal exercise. Many of these changes are also apparent when relative levels of submaximal exercise are directly compared in senescent and in younger mature beagles. However, most hemodynamic responses during absolute levels of exercise are similar in both groups, unless these parameters reflect the relative workload performed, indicating that these responses are appropriate for each absolute level of work that can be performed in the senescent dogs.

Critical O2 transport values at lowered body temperatures in rats

1983 ◽  
Vol 55 (6) ◽  
pp. 1713-1717 ◽  
Author(s):  
S. M. Cain ◽  
W. E. Bradley
Keyword(s):  
Cardiac Output ◽  
Body Temperature ◽  
Critical Value ◽  
Whole Body ◽  
Body Temperatures ◽  
O2 Uptake ◽  
O2 Transport ◽  
Normal Ranges ◽  
O2 Concentration ◽  
Lowered Body

Whole-body O2 uptake (VO2) in rats was reported not to increase when total O2 transport (TOT = cardiac output X arterial O2 concentration) was increased above normal ranges when body temperature was kept at 38 degrees C (J. Appl. Physiol.: Respirat. Environ. Exercise Physiol. 53: 660-664, 1982). Similar experiments were performed to see if hypothermic rats at 34 degrees C would increase VO2 with an increased TOT in an effort to generate heat. Anesthetized rats were ventilated with 9 or 12% O2 (hypoxia), room air (normoxia), and O2 (hyperoxia) to vary TOT from 52.6 to 6.6 ml X kg-1 X min-1. VO2 was measured in a closed-circuit, double servospirometer system. Although VO2 was significantly lower at 34 degrees C than the values previously found at 38 degrees C with normoxia and hyperoxia, there was no increase with increasing values of TOT. In spite of a lower plateau value of VO2 at 34 degrees C, the critical value of TOT below which VO2 could not be maintained was nearly the same as at 38 degrees C (22 ml X kg-1 X min-1). The reason for this was that O2 was less completely extracted as TOT was lowered below the critical value in the hypothermic animal. Some of the difficulty in extracting O2 at the tissues was probably due to the decrease in P50 (PO2 at 50% saturation) that occurs with decreased body temperature.

Aging among elite distance runners: a 22-yr longitudinal study

1996 ◽  
Vol 80 (1) ◽  
pp. 285-290 ◽  
Author(s):  
S. W. Trappe ◽  
D. L. Costill ◽  
M. D. Vukovich ◽  
J. Jones ◽  
T. Melham
Keyword(s):  
Maximal Exercise ◽  
Physiological Responses ◽  
Energy Requirements ◽  
Distance Runners ◽  
O2 Uptake ◽  
Vo2 Max ◽  
Cross Sectional ◽  
Perceived Effort ◽  
The Mean ◽  
Level Of Training

The purpose of this study was to assess the physiological responses of former elite distance runners during submaximal and maximal exercise after a mean period of 22 yr. Fifty-three men were initially tested (T1) in the late 1960s and early 1970s when they were all highly trained and competitive. For the current evaluation (T2), these men were classified as highly trained (HT; n = 10), fitness trained (FT; n = 18), untrained (UT; n = 15), and fit older (FO; n = 10), depending on their continued level of training and age. The mean (+/- SE) age for the HT, FT, and UT men during T2 was similar (46.5 +/- 1.6 yr), whereas the FO men were significantly (P < 0.05) older (68.4 +/- 2.7 yr). All groups experienced a significant decrease (P < 0.05) in maximal O2 uptake (VO2 max) from T1 to T2. However, this decrease was related to the amount of training between evaluations. The HT men had the smallest reduction (6% per decade) in VO2 max (from 68.8 to 59.2 ml.g-1.min-1). The FT men's VO2 max was approximately 10% lower per decade (from 64.1 to 48.9 ml.kg-1.min-1), whereas an approximately 15% decrease per decade was observed for the UT (from 70.7 to 46.7 ml.kg-1.min-1) and FO (from 60.3 to 40.7 ml.kg-1.min-1) men, despite the continued training of the FO men. Energy requirements for a standardized run at 12 km/run were similar from T1 to T2 for the HT and FT men, whereas the UT men required an increased (P < 0.05) O2 uptake (40.3-41.8 l/min), ventilation (53.7-72.7 l/min), and heart rate (127-142 beats/min). The perceived effort and %VO2 max for this submaximal run were greater during T2 for all groups, which was related to the decline in VO2 max. These longitudinal data indicate that after more than two decades the physiological capacities of these aging runners are compromised, regardless of training. These data also confirm previous cross-sectional findings that aerobic capacity of highly trained middle-aged men declines approximately 5-7% per decade.

Blood lactate disappearance at various intensities of recovery exercise

1984 ◽  
Vol 57 (5) ◽  
pp. 1462-1465 ◽  
Author(s):  
S. Dodd ◽  
S. K. Powers ◽  
T. Callender ◽  
E. Brooks
Keyword(s):  
Blood Lactate ◽  
Maximal Exercise ◽  
Exercise Recovery ◽  
Intense Exercise ◽  
O2 Uptake ◽  
Vo2 Max ◽  
Passive Recovery ◽  
Significant Difference ◽  
Recovery Exercise ◽  
Treatment Order

Numerous studies have reported that following intense exercise the rate of blood lactate (La) disappearance is greater during continuous aerobic work than during passive recovery. Recent work indicates that a combination of high- and low-intensity work may be optimal in reducing blood La. We tested this hypothesis by measuring the changes in blood La levels following maximal exercise during four different recovery patterns. Immediately following 50 S of maximal work, subjects (n = 7) performed one of the following recovery treatments for 40 min: 1) passive recovery (PR); 2) cycling at 35% maximal O2 uptake (VO2 max) (35% R); 3) cycling at 65% VO2 max (65% R); 4) cycling at 65% for 7 min followed by cycling at 35% for 33 min (CR). The treatment order was counterbalanced with each subject performing all treatments. Serial blood samples were obtained throughout recovery treatments and analyzed for La. The rate of blood La disappearance was significantly greater (P less than 0.05) in both the 35% R and CR when compared with either the 65% R or PR. No significant difference (P greater than 0.05) existed in the rate of blood La disappearance between the 35% R and CR. These data do not support the hypothesis that exercise recovery at a combination of intensities is superior to a recovery involving continuous submaximal exercise in lowering blood La following maximal work.

Time course of loss of adaptations after stopping prolonged intense endurance training

1984 ◽  
Vol 57 (6) ◽  
pp. 1857-1864 ◽  
Author(s):  
E. F. Coyle ◽  
W. H. Martin ◽  
D. R. Sinacore ◽  
M. J. Joyner ◽  
J. M. Hagberg ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Time Course ◽  
Citrate Synthase ◽  
Half Time ◽  
O2 Uptake ◽  
Sedentary Control ◽  
Vo2 Max ◽  
Trained Subjects ◽  
Experimental Subjects ◽  
Mixed Venous

Seven endurance exercise-trained subjects were studied 12, 21, 56, and 84 days after cessation of training. Maximal O2 uptake (VO2 max) declined 7% (P less than 0.05) during the first 21 days of inactivity and stabilized after 56 days at a level 16% (P less than 0.05) below the initial trained value. After 84 days of detraining the experimental subjects still had a higher VO2 max than did eight sedentary control subjects who had never trained (50.8 vs. 43.3 ml X kg-1 X min-1), due primarily to a larger arterial-mixed venous O2 (a-vO2) difference. Stroke volume (SV) during exercise was high initially and declined during the early detraining period to a level not different from control. Skeletal muscle capillarization did not decline with inactivity and remained 50% above (P less than 0.05) sedentary control. Citrate synthase and succinate dehydrogenase activities in muscle declined with a half-time of 12 days and stabilized at levels 50% above sedentary control (P less than 0.05). The initial decline in VO2 max was related to a reduced SV and the later decline to a reduced a-vO2 difference. Muscle capillarization and oxidative enzyme activity remained above sedentary levels and this may help explain why a-vO2 difference and VO2 max after 84 days of detraining were still higher than in untrained subjects.

Sign in / Sign up

Export Citation Format

Share Document