Constant infusion transpulmonary thermodilution for the assessment of cardiac output in exercising humans

The Journal of Physiology

Losa‐Reyna

Torres‐Peralta

et al. 2015

Key pointsr Severe acute hypoxia reduces sprint performance. r MuscleV O 2 during sprint exercise in normoxia is not limited by O 2 delivery, O 2 offloading from haemoglobin or structure-dependent diffusion constraints in the skeletal muscle of young healthy men.r A large functional reserve in muscle O 2 diffusing capacity exists and remains available at exhaustion during exercise in normoxia; this functional reserve is recruited during exercise in hypoxia.r During whole-body incremental exercise to exhaustion in severe hypoxia, legV O 2 is primarily dependent on convective O 2 delivery and less limited by diffusion constraints than previously thought.r The kinetics of O 2 offloading from haemoglobin does not limitV O 2 peak in hypoxia. r Our results indicate that the limitation toV O 2 during short sprints resides in mechanisms regulating mitochondrial respiration.Abstract To determine the contribution of convective and diffusive limitations toV O 2 peak during exercise in humans, oxygen transport and haemodynamics were measured in 11 men (22 ± 2 years) during incremental (IE) and 30 s all-out cycling sprints (Wingate test, WgT), in normoxia (Nx, P IO 2 : 143 mmHg) and hypoxia (Hyp, P IO 2 : 73 mmHg). Carboxyhaemoglobin (COHb) was increased to 6-7% before both WgTs to left-shift the oxyhaemoglobin dissociation curve. Leġ V O 2 was measured by the Fick method and leg blood flow (BF) with thermodilution, and muscle O 2 diffusing capacity (D MO 2 ) was calculated. In the WgT mean power output, leg BF, leg O 2 delivery and legV O 2 were 7, 5, 28 and 23% lower in Hyp than Nx (P < 0.05); however, peak WgT D MO 2 was higher in Hyp (51.5 ± 9.7) than Nx (20.5 ± 3.0 ml min −1 mmHg −1 , P < 0.05). Despite a similar P aO 2 (33.3 ± 2.4 and 34.1 ± 3.3 mmHg), mean capillary P O 2 (16.7 ± 1.2 and 17.1 ± 1.6 mmHg), and peak perfusion during IE and WgT in Hyp, D MO 2 and legV O 2 were 12 and 14% higher, respectively, during WgT than IE in Hyp (both P < 0.05). D MO 2 was insensitive to COHb (COHb: 0.7 vs. 7%, in IE Hyp and WgT Hyp). At exhaustion, the Y equilibration index was well above 1.0 in both conditions, reflecting greater convective than diffusive limitation to the O 2 transfer in both Nx and Hyp. In conclusion, muscleV O 2 during sprint exercise is not limited by O 2 delivery, O 2 offloading from haemoglobin or structure-dependent diffusion constraints in

Section: Methodsmentioning

confidence: 97%

Limitations to oxygen transport and utilization during sprint exercise in humans: evidence for a functional reserve in muscle O₂ diffusing capacity

The Journal of Physiology

Losa‐Reyna

Torres‐Peralta

et al. 2015

“…Femoral and subclavian venous blood flow was measured by constant infusion thermodilution, as described elsewhere (Calbet et al., ). Briefly, iced saline was simultaneously infused through the femoral and subclavian vein simultaneously at flow rates sufficient to decrease blood temperature at the thermistor by 0.5–1 °C.…”

Section: Methodsmentioning

confidence: 99%

Central and peripheral hemodynamics in exercising humans: leg vs arm exercise

Scandinavian Med Sci Sports

González‐Alonso

Helge

et al. 2015

Self Cite

In humans, arm exercise is known to elicit larger increases in arterial blood pressure (BP) than leg exercise. However, the precise regulation of regional vascular conductances (VC) for the distribution of cardiac output with exercise intensity remains unknown. Hemodynamic responses were assessed during incremental upright arm cranking (AC) and leg pedalling (LP) to exhaustion (W max ) in nine males. Systemic VC, peak cardiac output (Q peak ) (indocyanine green) and stroke volume (SV) were 18%, 23%, and 20% lower during AC than LP. The mean BP, the rate-pressure product and the associated myocardial oxygen demand were 22%, 12%, and 14% higher, respectively, during maximal AC than LP. Trunk VC was reduced to similar values at W max . At W max , muscle mass-normalized VC and fractional O 2 extraction were lower in the arm than the leg muscles. However, this was compensated for during AC by raising perfusion pressure to increase O 2 delivery, allowing a similar peak VO 2 per kg of muscle mass in both extremities. In summary, despite a lower Q peak during arm cranking the cardiovascular strain is much higher than during leg pedalling. The adjustments of regional conductances during incremental exercise to exhaustion depend mostly on the relative intensity of exercise and are limb-specific.

“…Alonso et al 2000). Infusate temperature was corrected according to the methodology reported inCalbet et al 2015 (study 1) andGonzález-Alonso et al 2000 (study 2).…”

mentioning

confidence: 99%

Blood temperature and perfusion to exercising and non‐exercising human limbs

González‐Alonso

Experimental Physiology

Boushel

et al. 2015

New Findings What is the central question of this study? Temperature‐sensitive mechanisms are thought to contribute to blood‐flow regulation, but the relationship between exercising and non‐exercising limb perfusion and blood temperature is not established. What is the main finding and its importance? The close coupling among perfusion, blood temperature and aerobic metabolism in exercising and non‐exercising extremities across different exercise modalities and activity levels and the tight association between limb vasodilatation and increases in plasma ATP suggest that both temperature‐ and metabolism‐sensitive mechanisms are important for the control of human limb perfusion, possibly by activating ATP release from the erythrocytes. Temperature‐sensitive mechanisms may contribute to blood‐flow regulation, but the influence of temperature on perfusion to exercising and non‐exercising human limbs is not established. Blood temperature (T B), blood flow and oxygen uptake (trueV˙O2) in the legs and arms were measured in 16 healthy humans during 90 min of leg and arm exercise and during exhaustive incremental leg or arm exercise. During prolonged exercise, leg blood flow (LBF) was fourfold higher than arm blood flow (ABF) in association with higher T B and limb trueV˙O2. Leg and arm vascular conductance during exercise compared with rest was related closely to T B (r 2 = 0.91; P < 0.05), plasma ATP (r 2 = 0.94; P < 0.05) and limb V˙normalO2 (r 2 = 0.99; P < 0.05). During incremental leg exercise, LBF increased in association with elevations in T B and limb trueV˙O2, whereas ABF, arm T B and V˙normalO2 remained largely unchanged. During incremental arm exercise, both ABF and LBF increased in relationship to similar increases in trueV˙O2. In 12 trained males, increases in femoral T B and LBF during incremental leg exercise were mirrored by similar pulmonary artery T B and cardiac output dynamics, suggesting that processes in active limbs dominate central temperature and perfusion responses. The present data reveal a close coupling among perfusion, T B and aerobic metabolism in exercising and non‐exercising extremities and a tight association between limb vasodilatation and increases in plasma ATP. These findings suggest that temperature and V˙normalO2 contribute to the regulation of limb perfusion through control of intravascular ATP.