Is there a disassociation of maximal oxygen consumption and maximal cardiac output?

PURPOSE: The purpose of the present study was to determine whether maximal cardiac output (Q) is affected by the duration of the maximal exercise test. METHODS: Nine healthy men (N = 6) and women (N = 3) performed three separate maximal treadmill exercise tests, separated by at least 24 h, and underwent a body composition assessment by hydrostatic weighing, all within a 2-wk period. A baseline maximal exercise test was performed to establish VO(2max). The second and third tests, assigned randomly, were designed to elicit the subjects' predetermined VO(2max) in either 6 or 12 min. Heart rate (HR), blood pressure (BP), minutes of ventilation, and oxygen consumption (VO(2)) were measured during all tests. At the end of the 6- and 12-min tests, Q was measured using an acetylene rebreathing technique. Stroke volume (SV), mean arterial pressure (MAP), total peripheral resistance (TPR), and arteriovenous O(2) difference were calculated using standard equations. RESULTS: Repeated-measures ANOVA indicated that there were no significant differences in HR and VO(2max) between the baseline, 6-min, and 12-min tests. Paired t-tests revealed significantly greater Q (25.1 +/- 5.6 vs 23.7 +/- 5.2 L.min-1) and SV (138.3 +/- 31.5 vs 130.5 +/- 31.2 mL) in the 6- versus 12-min tests, respectively. There were no significant differences in systolic BP, diastolic BP, MAP, TPR, or arteriovenous O(2) difference. CONCLUSIONS: Despite there being no difference in VO(2max) between the two tests, the 6-min maximal exercise test resulted in a significantly greater Q than the 12-min test, because of a significantly greater SV. Thus, there was a disassociation between VO(2) and Q during maximal exercise.     

Exercise cardiac function in young through elderly endurance trained women.

PURPOSE: To clarify the physiological reasons for the decline in aerobic power of endurance trained (ET) women with aging. METHODS: Blood volume, VO2max, and exercise cardiac function were examined in 23 ET women; six age 20-29 yr, six age 40-45 yr, six age 49-54 yr, and five age 58-63 yr. RESULTS: Blood volume was unchanged with aging. VO2max declined progressively at a rate of 0.51 mL x kg(-1) x min(-1) x yr(-1). During maximal exercise, there was an increase in total peripheral resistance (TPR) and a decrease in heart rate, stroke volume, and cardiac output with increasing age. At all ages, cardiac filling (diastole) was significantly faster than cardiac emptying (systole). Stroke volume did not plateau at a submaximal work rate but increased progressively to maximum. CONCLUSIONS: The decline in VO2max with age in ET women is due to decreases in maximal heart rate, stroke volume and cardiac output, and the primary advantage in the exercise cardiac performance of ET women of all ages is diastolic rather than systolic function.     

Effect of exercise intensity on relationship between VO2max and cardiac output

PURPOSE: The purpose of this study was to determine whether the maximal oxygen uptake (VO2max) is attained with the same central and peripheral factors according to the exercise intensity. METHODS: Nine well-trained males performed an incremental exercise test on a cycle ergometer to determine the maximal power associated with VO2max (pVO2max) and maximal cardiac output (Qmax). Two days later, they performed two continuous cycling exercises at 100% (tlim100 = 5 min 12 s +/- 2 min 25 s) and at an intermediate work rate between the lactate threshold and pVO2max (tlimDelta50 +/- 12 min 6 s +/- 3 min 5 s). Heart rate and stroke volume (SV) were measured (by impedance) continuously during all tests. Cardiac output (Q) and arterial-venous O2 difference (a-vO2 diff) were calculated using standard equations. RESULTS: Repeated measures ANOVA indicated that: 1) maximal heart rate, VE, blood lactate, and VO2 (VO2max) were not different between the three exercises but Q was lower in tlimDelta50 than in the incremental test (24.4 +/- 3.6 L x min(-1) vs 28.4 +/- 4.1 L x min(-1); P < 0.05) due to a lower SV (143 +/- 27 mL x beat(-1) vs 179 +/- 34 mL x beat(-1); P < 0.05), and 2) maximal values of a-vO2 diff were not significantly different between all the exercise protocols but reduced later in tlimDelta50 compared with tlim100 (6 min 58 s +/- 4 min 29 s vs 3 min 6 s +/- 1 min 3 s, P = 0.05). This reduction in a-vO2 diff was correlated with the arterial oxygen desaturation (SaO2 = -15.3 +/- 3.9%) in tlimDelta50 (r = -0.74, P = 0.05). CONCLUSION: VO2max was not attained with the same central and peripheral factors in exhaustive exercises, and tlimDelta50 did not elicit the maximal Q. This might be taken into account if the training aim is to enhance the central factors of VO2max using exercise intensities eliciting VO2max but not necessarily Qmax.     

Cardiac responses to exercise in competitive child cyclists

PURPOSE: Cardiovascular responses to exercise in highly trained child endurance athletes have not been well-defined. This study compared hemodynamic responses with progressive cycle exercise in seven competitive child cyclists (mean age 11.9 yr) compared with 39 age-matched untrained boys. METHODS: Doppler echocardiography and gas exchange variables were utilized to assess cardiovascular changes during submaximal and maximal exercise. RESULTS: Mean VO2max was 60.0 (+/-6.0) and 47.0 (+/-5.8) mL x kg(-1) x min(-1) in the cyclists and nonathletes, respectively. At rest and maximal exercise, the cyclists demonstrated greater stroke index than the untrained subjects (resting mean 59 (+/-6) vs 44 (+/-9) mL x m(-2); maximal mean 76 (+/-6) vs 60 (+/-11) mL x m(-2)), but the ratio of maximal:rest stroke index was similar in both groups (1.31 for cyclists, 1.41 for nonathletes). Both groups showed a plateau in stroke volume beyond low-intensity work levels. No significant difference was observed in maximal arteriovenous oxygen difference. CONCLUSIONS: These findings indicate that 1) maximal stroke volume is the critical determinant of the high VO2max in child cyclists and 2) factors that influence resting stroke volume are important in defining VO2max differences between child endurance athletes and untrained boys.     

Enhanced cardiovascular hemodynamics in endurance-trained postmenopausal women athletes

PURPOSE: We sought to determine whether older women athletes who had habitually performed vigorous endurance exercise training had higher stroke volumes and cardiac outputs than sedentary postmenopausal women during maximal exercise. METHODS: Seventeen endurance-trained, postmenopausal women athletes (age 65 +/- 4 yr; VO2max 2.11 +/- 0.31 L x min(-1), 38.3 mL x kg(-1) x min(-1)) and 14 sedentary, postmenopausal women (age 63 +/- 5 yr; VO2max 1.41 +/- 0.22 L x min(-1), 23.7 +/- 3.5 mL x kg(-1) x min(-1)) performed maximal treadmill exercise while cardiac output (via acetylene rebreathing) and other cardiovascular hemodynamics were measured. Approximately half of the subjects in each group were on hormone replacement therapy (HRT). RESULTS: The greater VO2max of the athletes was the result of a greater cardiac output (12.8 +/- 1.6 vs. 9.3 +/- 1.4 L x min(-1)) resulting from their significantly larger stroke volume (80 +/- 10 vs 57 +/- 10 mL) at maximal exercise. There were no significant differences in maximal cardiac output or maximal stroke volume related to HRT status in the sedentary women or athletes. CONCLUSIONS: These data indicate that endurance-trained, competitive, postmenopausal women have higher stroke volumes and cardiac outputs during maximal exercise, than their sedentary peers. However, these data suggest that HRT may not affect maximal CV function in sedentary or endurance-trained postmenopausal women.     

Maximal oxygen uptake as a parametric measure of cardiorespiratory capacity

INTRODUCTION: Maximal oxygen uptake (.VO2max) was defined by Hill and Lupton in 1923 as the oxygen uptake attained during maximal exercise intensity that could not be increased despite further increases in exercise workload, thereby defining the limits of the cardiorespiratory system. This concept has recently been disputed because of the lack of published data reporting an unequivocal plateau in .VO2 during incremental exercise. PURPOSE: The purpose of this investigation was to test the hypothesis that there is no significant difference between the .VO2max obtained during incremental exercise and a subsequent supramaximal exercise test in competitive middle-distance runners. We sought to determine conclusively whether .VO2 attains a maximal value that subsequently plateaus or decreases with further increases in exercise intensity. METHODS: Fifty-two subjects (36 men, 16 women) performed three series of incremental exercise tests while measuring .VO2 using the Douglas bag method. On the day after each incremental test, the subjects returned for a supramaximal test, during which they ran at 8% grade with the speed chosen individually to exhaust the subject between 2 and 4 min. .VO2 at supramaximal exercise intensities (30% above incremental .VO2max) was measured continuously. RESULTS: .VO2max measured during the incremental test (63.3 +/- 6.3 mL.kg(-1).min(-1); mean +/- SD) was indistinguishable from the .VO2max during the supramaximal test (62.9 +/- 6.2, N = 156; P = 0.77) despite a sufficient duration of exercise to demonstrate a plateau in .VO2 during continuous supramaximal exercise. These data provide strong support for the hypothesis that there is indeed a peak and subsequent plateau in .VO2 during maximal exercise intensity. CONCLUSIONS: .VO2max is a valid index measuring the limits of the cardiorespiratory systems' ability to transport oxygen from the air to the tissues at a given level of physical conditioning and oxygen availability.     

No association between ACE I/D polymorphism and cardiovascular hemodynamics during exercise in young women

The ACE I/D polymorphism has been shown to interact with habitual physical activity levels in postmenopausal women to associate with submaximal and with maximal exercise hemodynamics. This investigation was designed to assess the potential relationships between ACE genotype and oxygen consumption (VO2), cardiac output (Q), stroke volume (SV), heart rate (HR), blood pressure (BP), total peripheral resistance (TPR), and arteriovenous oxygen difference ([a-v]O2 diff) during submaximal and maximal exercise in young sedentary and endurance-trained women. Seventy-seven 18-35-yr-old women underwent a maximal exercise test and a number of cardiac output tests on a treadmill using the acetylene rebreathing technique. ACE genotype was not significantly associated with VO2max (II 41.4+/-1.2, ID 39.8+/-0.9, DD 39.8+/-1.1 ml/kg/min, p=ns) or maximal HR (II 191+/-2, ID 191+/-1, DD 193+/-2 bpm, p=ns). In addition, systolic and diastolic BP, (a-v)O2 diff, TPR, SV, and Q during maximal exercise were not significantly associated with ACE genotype. During submaximal exercise, SBP, Q, SV, HR, TPR, and (a-v)O2 diff were not significantly associated with ACE genotype. However, the association between diastolic BP during submaximal exercise and ACE genotype approached significance (p=0.08). In addition, there were no statistically significant interactions between ACE genotype and habitual physical activity (PA) levels for any of the submaximal or the maximal exercise hemodynamic variables. We conclude that the ACE I/D polymorphism was not associated, independently or interacting with habitual PA levels, submaximal, or maximal cardiovascular hemodynamics in young women.     

Stroke volume does not plateau during graded exercise in elite male distance runners.

Stroke volume (SV) responses during graded treadmill exercise were studied in 1) elite male distance runners (N = 5), 2) male university distance runners (N = 10), and 3) male untrained university students (N = 10). METHODS: Cardiac output (Q) and SV were determined by a modified acetylene rebreathing procedure. RESULTS: There were no differences in SV responses among the three groups during the transition from rest to light exercise (P > 0.05). However, the rates of change of SV during light to maximal exercise in untrained subjects (slope = -0.1544 mL x beat(-1)) and university distance runners (slope = 0.1041) did not change, whereas it dramatically increased (P < 0.001) in elite distant runners (slope = 0.6734). Moreover, the elite distance runners showed a further slope increase in SV when heart rate was above 160 bpm, which resulted in an average maximal SV of 187 +/- 14 mL x beat(-1) compared with 145 +/- 8 and 128 +/- 14 mL x beat(-1) in the university runners and untrained students, respectively (P < 0.001). Similarly, max Q reached 33.8 +/- 2.3, 26.3 +/- 1.7, and 21.3 +/- 1.5 L x min(-1) in the three groups, respectively (P < 0.001). On the other hand, there was a nonsignificant tendency for maximal arteriovenous oxygen content difference to be lower in the elite athletes compared with the other groups. CONCLUSION: Results from university distance runners and untrained university students support the classic observation that SV plateaus at about 40% of maximal oxygen consumption despite increasing intensity of exercise. In contrast, stroke volume in the elite athletes does not plateau but increases continuously with increasing intensity of exercise over the full range of the incremental exercise test.     

Frequency of the VO2max plateau phenomenon in world-class cyclists

We aimed to determine the frequency of the VO2max plateau phenomenon in top-level male professional road cyclists (n = 38; VO2max [mean +/- SD]: 73.5 +/- 5.5 ml.kg(-1).min(-1)) and in healthy, sedentary male controls (n = 37; VO2max: 42.7 +/- 5.6 ml.kg(-1).min(-1)). All subjects performed a continuous incremental cycle-ergometer test of 1-min workloads until exhaustion. Power output was increased from a starting value of 25 W (cyclists) or 20 W (controls) at the rate of 25 W.min(-1) (cyclists) or 20 W.min(-1) (controls) until volitional exhaustion. We measured gas-exchange and heart rate (HR) throughout the test. Blood concentrations of lactate (BLa) were measured at end-exercise in both groups. We defined maximal exercise exertion as the attainment of a respiratory exchange rate (RER) >or= 1.1; HR > 95 % age-predicted maximum; and BLa > 8 mmo.l(-1). The VO2max plateau phenomenon was defined as an increase in two or more consecutive 1-min mean VO2 values of less than 1.5 ml.kg(-1).min(-1). Most cyclists met our criteria for maximal exercise effort (RER > 1.1, 100 %; 95 % predicted maximal HR [HRmax], 82 %; BLa > 8 mmol.l(-1), 84 %). However, the proportion of cyclists attaining a V.O (2max) plateau was considerably lower, i.e., 47 %. The majority of controls met the criteria for maximal exercise effort (RER > 1.1, 100 %; predicted HRmax, 68 %; BLa > 8 mmol. l(-1), 73 %), but the proportion of these subjects with a VO2max plateau was only 24 % (significantly lower proportion than in cyclists [p < 0.05]). Scientists should consider 1) if typical criteria of attainment of maximal effort are sufficiently stringent, especially in elite endurance athletes; and 2) whether those humans exhibiting the VO2max plateau phenomenon are those who perform an absolute maximum effort or there are additional distinctive features associated with this phenomenon.     

Cardiovascular and metabolic responses during 30 minutes of treadmill exercise shortly after consuming a small, high-carbohydrate meal.

Fourteen male endurance runners (VO2peak = 64.8 +/- 8.7 ml x kg(-1) x min(-1)) participated in this study to determine the cardiovascular and metabolic responses during 30 minutes of treadmill running at a moderate intensity soon after consuming a small, high-carbohydrate meal (CHO-M). In randomized order on separate days, subjects either consumed the CHO-M (2088 kJ; 77% carbohydrate) 15 minutes prior to running or they fasted (FAST). Data were collected for 5 minutes beginning at 5, 15, and 25 minutes of the 30-minute run. Heart rate (HR) was determined, a metabolic measurement cart was used to determine VO2 and respiratory exchange ratio (RER), and the CO2 rebreathing procedure (Collier plateau method) was used to determine cardiac output (Q). Statistical analyses indicated that the CHO-M did not affect HR, stroke volume, Q, VO2, or RER compared to FAST. However, all grouped CHO-M and FAST variables, except VO2, changed significantly across the 30-minute exercise session. These data suggest that a small, high-carbohydrate meal does not alter cardiovascular and metabolic function during moderate-intensity exercise in endurance-trained subjects.     

Reduced leg blood flow during submaximal exercise in type 2 diabetes

It is unclear whether impaired cardiac and/or vascular function contribute to exercise intolerance in patients with type 2 diabetes. PURPOSE: Magnetic resonance imaging (MRI) was used to determine whether reductions in cardiac output and/or femoral arterial blood flow contribute to reduced aerobic capacity in patients with type 2 diabetes. METHODS: Cardiac and femoral arterial blood flow MRI scans were performed at rest and during low-intensity leg exercise in eight patients with type 2 diabetes and 11 healthy individuals. Maximal aerobic capacity VO(2 max) and maximal oxygen pulse were also determined in all participants. RESULTS: V O(2 max) was 20% lower and maximal oxygen pulse was 16% lower in patients with type 2 diabetes (P < 0.05), whereas maximal heart rate was the same between groups. Low-intensity exercise induced a 20% increase in heart rate and cardiac output as well as a 60-70% increase in femoral blood flow in both groups (P < 0.05). Femoral arterial blood flow indexed to thigh lean mass was reduced during exercise in patients with type 2 diabetes compared with healthy individuals. Stroke volume indexed to fat-free mass was lower in patients with type 2 diabetes, but greater heart rate allowed cardiac output to be maintained during submaximal exercise. CONCLUSIONS: These findings suggest that impaired femoral arterial blood flow, an indirect marker of muscle perfusion, affects low-intensity exercise performance in patients with type 2 diabetes. However, because of lower exercising stroke volume, we propose that femoral arterial blood flow and, possibly, cardiac output, limit V O(2 max) in patients with type 2 diabetes.     

Incremental test protocol, recovery mode and the individual anaerobic threshold

The individual anaerobic threshold (IAT) is defined as the highest metabolic rate at which blood lactate (LA) concentrations are maintained at a steady-state during prolonged exercise. The purpose of this study was to compare the effects of active and passive recovery on the determination of IAT following both a submaximal or maximal incremental exercise test. Seven males (VO2max = 57.6 +/- 5.8 ml.kg-1.min -1) did two submaximal, incremental cycle exercise tests (30 W and 4 min per step) and two maximal incremental tests. Blood was sampled repeatedly during exercise and for 12 min during the subsequent recovery period, which was passive for one submaximal and one maximal test and active (approximately 35% VO2max) during the other tests. An IAT metabolic rate and power output were calculated for the submax-passive (IATsp, LA = 1.85 +/- 0.42 mmol.l-1), max-passive (IATmp, LA = 3.41 +/- 1.14 mmol.l-1), submax-active (IATsa, LA = 2.13 +/- 0.45 mmol.l-1) and max-active (IATma, LA = 3.44 +/- 0.73 mmol.l-1) protocols. At weekly intervals, the subjects exercised for 30 min at one of the four IAT metabolic rates. Active recovery did not affect the calculation of IAT, but following the maximal incremental tests, IAT occurred at a higher (p less than 0.05) power output, absolute VO2 and %VO2max (71% VO2max) compared with the IAT determined with the submaximal incremental tests (61% VO2max).(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of short-term training on cardiac function during prolonged exercise

To determine the relationship between the training-induced increases in plasma volume (PV) and alterations in cardiac performance during prolonged submaximal cycle exercise, seven male subjects were studied prior to and following a short-term (3 d) training period (2 h.d-1 at 65% VO2max). Mean (range) VO2max was 3.42 l.min-1 (2.96-3.87). Training resulted in a 20% increase (P less than 0.05) in plasma volume (PV) and a 12% increase (P less than 0.05) in total blood volume (TBV). In contrast, training had no effect (P greater than 0.05) in altering exercise VO2, VCO2, VE BTPS, or RER. Cardiac output (Q) was higher (P less than 0.05) posttraining at all exercise sampling times (30, 60, 90, and 120 min). The elevations in Q were accompanied by an average decrease (P less than 0.05) in stroke volume (SV) of 22 ml. Arteriovenous O2 (a-v O2) difference was depressed (P less than 0.05) during exercise following the training. Although elevations (P less than 0.05) in core temperature (degrees C) occurred during the exercise, the training-induced PV increases did not affect thermoregulatory behavior. These results indicate that an early adaptive response to exercise training is an elevation in Q, an increase in SV, and a reduction in HR. These effects persist during prolonged exercise in spite of the progressive increase in body heat content. It is proposed that the increase in Q serves primarily to increase muscle blood flow and maintain arterial O2 delivery, while the altered cardiodynamic behavior serves to increase cardiac reserve, providing a greater tolerance to prolonged heavy exercise.     

Central and peripheral cardiovascular adaptations during a maximal cycle exercise in boys and men

PURPOSE: Stroke volume response to exercise depends on changes in cardiac filling, intrinsic myocardial contractility, and left ventricular afterload. The purpose of this study was to compare these responses during an upright cycle test performed until exhaustion in children and adults. METHODS: Stroke volume, cardiac output (Doppler echocardiography), left ventricular dimensions (two-dimensional and time-movement echocardiography), as well as arterial pressure and systemic vascular resistance (SVR) were assessed in 17 boys (mean age, 11.7 +/- 0.6 yr) and 23 young adult men (mean age, 21.2 +/- 2.7 yr) having a similar aerobic potential. All variables were measured at the end of the resting period, during the final minute of each workload, and during the last minute of the test. RESULTS: No significant differences were obtained for stroke volume, cardiac output, and left ventricular dimensions when they were scaled to body surface area at rest and whatever the exercise intensity. However, arteriovenous oxygen uptake was higher and the SVR lower in the adults than in the children. CONCLUSION: The patterns of stroke volume, as well as its underlying mechanisms, were not age-related during an upright maximal exercise test. However, other studies are required to understand further the effect of pubertal status on the peripheral cardiovascular system.     

The effect of detraining and reduced training on the physiological adaptations to aerobic exercise training

In previously sedentary individuals, regularly performed aerobic exercise results in significant improvements in exercise capacity. The development of peak exercise performance, as typified by competitive endurance athletes, is dependent upon several months to years of aerobic training. The physiological adaptations associated with these improvements in both maximal exercise performance, as reflected by increases in maximal oxygen uptake (VO2max), and submaximal exercise endurance include increases in both cardiovascular function and skeletal muscle oxidative capacity. Despite prolonged periods of aerobic training, reductions in maximal and submaximal exercise performance occur within weeks after the cessation of training. These losses in exercise performance coincide with declines in cardiovascular function and muscle metabolic potential. Significant reductions in VO2max have been reported to occur within 2 to 4 weeks of detraining. This initial rapid decline in VO2max is likely related to a corresponding fall in maximal cardiac output which, in turn, appears to be mediated by a reduced stroke volume with little or no change in maximal heart rate. A loss in blood volume appears to, at least partially, account for the decline in stroke volume and VO2max during the initial weeks of detraining, although changes in cardiac hypertrophy, total haemoglobin content, skeletal muscle capillarisation and temperature regulation have been suggested as possible mediating factors. When detraining continues beyond 2 to 4 weeks, further declines in VO2max appear to be a function of corresponding reductions in maximal arterial-venous (mixed) oxygen difference. Whether reductions in oxygen delivery to and/or extraction by working muscle regulates this progressive decline is not readily apparent. Changes in maximal oxygen delivery may result from decreases in total haemoglobin content and/or maximal muscle blood flow and vascular conductance. The declines in skeletal muscle oxidative enzyme activity observed with detraining are not causally linked to changes in VO2max but appear to be functionally related to the accelerated carbohydrate oxidation and lactate production observed during exercise at a given intensity. Alternatively, reductions in submaximal exercise performance may be related to changes in the mean transit time of blood flow through the active muscle and/or the thermoregulatory response (i.e. degree of thermal strain) to exercise. In contrast to the responses observed with detraining, currently available research indicates that the adaptations to aerobic training may be retained for at least several months when training is maintained at a reduced level. Reductions of one- to two-thirds in training frequency and/or duration do not significantly alter VO2max or submaximal endurance time provided the intensity of each exercise session is maintained.(ABSTRACT TRUNCATED AT 400 WORDS)     

Are the arms and legs in competition for cardiac output?

Oxygen transport to working skeletal muscles is challenged during whole-body exercise. In general, arm-cranking exercise elicits a maximal oxygen uptake (VO2max) corresponding to approximately 70% of the value reached during leg exercise. However, in arm-trained subjects such as rowers, cross-country skiers, and swimmers, the arm VO2max approaches or surpasses the leg value. Despite this similarity between arm and leg VO2max, when arm exercise is added to leg exercise, VO2max is not markedly elevated, which suggests a central or cardiac limitation. In fact, when intense arm exercise is added to leg exercise, leg blood flow at a given work rate is approximately 10% less than during leg exercise alone. Similarly, when intense leg exercise is added to arm exercise, arm blood flow and muscle oxygenation are reduced by approximately 10%. Such reductions in regional blood flow are mainly attributed to peripheral vasoconstriction induced by the arterial baroreflex to support the prevailing blood pressure. This putative mechanism is also demonstrated when the ability to increase cardiac output is compromised; during exercise, the prevailing blood pressure is established primarily by an increase in cardiac output, but if the contribution of the cardiac output is not sufficient to maintain the preset blood pressure, the arterial baroreflex increases peripheral resistance by augmenting sympathetic activity and restricting blood flow to working skeletal muscles.     

NOS3 gene polymorphisms and exercise hemodynamics in postmenopausal women

We tested whether the G894T and T-786C NOS3 polymorphisms were associated with exercise cardiovascular (CV) hemodynamics in sedentary, physically active, and endurance-trained postmenopausal women. CV hemodynamic parameters including heart rate (HR), systolic (SBP) and diastolic (DBP) blood pressures and cardiac output (Q), as determined by acetylene rebreathing, stroke volume (SV), arteriovenous oxygen difference (a-vO2 diff), and total peripheral resistance (TPR) were measured during submaximal (40, 60, 80 %) and maximal (approximately 100 % VO2max) exercise. NOS3 G894T genotype was not significantly associated, either independently or interactively with habitual physical activity (PA) level, with SBP, Q, TPR, or a-vO2 diff during submaximal or maximal exercise. However, NOS3 894T non-carriers had a higher submaximal exercise HR than NOS3 894T allele carriers (120 +/- 2 vs. 112 +/- 2 beats/min, p = 0.007). NOS3 894T allele carriers had a higher SV than 894T non-carriers (78 +/- 2 vs. 72 +/- 2 ml/beat, p = 0.03) during submaximal exercise. NOS3 894T non-carriers also had a higher maximal exercise HR averaged across habitual PA groups than T allele carrier women (165 +/- 2 vs. 158 +/- 2 beats/min, p = 0.04). NOS3 894T allele carriers also tended to have a higher SV during maximal exercise than 894T non-carriers (70 +/- 2 vs. 64 +/- 2 ml/beat, p = 0.08). NOS3 T-786C genotype was not significantly associated, either independently or interactively, with any of the CV hemodynamic measures during submaximal or maximal exercise. These results suggest an association of NOS3 G894T genotype with submaximal and maximal exercise CV hemodynamic responses, especially HR, in postmenopausal women.     

Comparison of circulatory responses to submaximal exercise in equally trained men and women

In previous studies comparing circulatory responses to exercise in men and women, the habitual physical activity of the groups was not documented. Thus, it is possible that sex differences observed were partly a function of differences in level of physical condition. The purpose of this study was to compare central circulatory responses to submaximal bicycle ergometer exercise in equally trained men and women. Cardiac output (Q), stroke volume (SV), heart rate (HR), and arteriovenous oxygen content difference [(a-v)O2 diff] were determined at approximately 30%, 50%, 70%, and 90% VO2max in 18 male and 18 female trained young adults. Q was determined by the CO2 -rebreathing method. The men and women had similar training backgrounds and nonsignificantly different mean VO2max in ml . kg FFW-1 . min-1 (62.3 and 60.3, respectively). Mean differences between men and women in Q (0.44 l . min-1), HR (23 bts . min-1), and (a-v)O2 diff at 1.5 l . min-1 and in heart rate at various percentages of VO2max (2-4 bts . min-1) were smaller than in previous research. Smaller sex differences in various VO2max expressions in the present study suggest that there was a difference between males and females in habitual physical activity in earlier research. It is concluded that a portion of previously reported sex differences in certain circulatory responses to submaximal exercise was a consequence of different levels of physical condition of the male and female subjects. The magnitude of gender-related differences in circulatory responses to submaximal exercise appears to be smaller than previously thought.     

Hypokinetic circulation in persons with paraplegia

INTRODUCTION: It is well established that hemodynamic dysfunction, resulting in diminished upper-extremity work capacity, occurs in persons with spinal cord injury (SCI) as compared with those who are nondisabled (ND). Although it has been shown that persons with paraplegia display higher values of heart rate (HR) with lower values of stroke volume (SV) during exercise, it is not resolved whether there is adequate compensation to produce similar values of cardiac output (.Q) as in ND. PURPOSE: This study examined central cardiovascular responses (HR, SV, and .Q) of 20 subjects with complete thoracic level SCI (T(4)-T(11)) and 20 sedentary ND subjects during matched levels of arm-crank (AC) exercise. METHODS: All subjects performed an incremental peak AC test to volitional exhaustion with continuous metabolic analysis and HR measurement via open circuit spirometry and 12-lead electrocardiography, respectively. Stroke volume was assessed using transthoracic impedance. RESULTS: Heart rate was higher for SCI (P< 0.05) with significantly lower values for SV and .Q at rest (approximately 25%). Peak responses were significantly higher for ND in all factors except HR. Although subpeak HRs at matched absolute workloads were significantly higher for SCI (12-20 beats.min (-1) ), SV and .Q were significantly lower (P< 0.05). CONCLUSIONS: The results of this study indicate that .Q is significantly lower in SCI than in ND during AC, despite significantly greater values of HR. These findings also suggest that the disparity in exercise values of .Q is related to differences exhibited at rest.     

Effects of breathing a normoxic He-O2 gas mixture on exercise tolerance and VO2 max

The purpose of these experiments was to compare the effects of breathing air (79% N2-21% O2) and a normoxic helium oxygen gas mixture (He-O2) (79% He-21% O2) on maximal oxygen uptake (VO2 max) and work tolerance during both incremental and high-intensity constant load exercise. First, eight subjects underwent two separate short incremental cycle ergometer exercise tests until the subject could not maintain the desired power output. Second, four subjects exercised to exhaustion on two separate occasions at a constant exercise intensity (100% VO2 max). Each exercise protocol required the subject to breathe air on one test and a normoxic He-O2 mixture on an additional occasion. Data analysis revealed higher (P less than 0.05) minute ventilations, an increased time to exhaustion, and a greater VO2 max during He-O2 breathing in both exercise conditions. Small but significant (P less than 0.05) differences existed in the percent hemoglobin saturated with O2 (% SO2) at exercise demands greater than 120 W during the incremental experiment and during each minute of the constant load test with He-O2 giving the higher value. These data support the hypothesis that breathing a normoxic He-O2 gas mixture during exercise elevates VO2 max and increases exercise tolerance. Further, although it appears that breathing a He-O2 mixture results in higher %SO2 during intense exercise, the increase in arterial O2 content is small and probably does not fully account for the higher VO2 max observed under these conditions.