Abstract
We wanted to demonstrate the relationship between blood volume, cardiac size, cardiac output and maximum oxygen uptake (O2max) and to quantify blood volume shifts during exercise and their impact on oxygen transport. Twenty-four healthy, non-smoking, heterogeneously trained male participants (27 ± 4.6 years) performed incremental cycle ergometer tests to determine O2max and changes in blood volume and cardiac output. Cardiac output was determined by an inert gas rebreathing procedure. Heart dimensions were determined by 3D echocardiography. Blood volume and hemoglobin mass were determined by using the optimized CO-rebreathing method. The O2max ranged between 47.5 and 74.1 mL⋅kg–1⋅min–1. Heart volume ranged between 7.7 and 17.9 mL⋅kg–1 and maximum cardiac output ranged between 252 and 434 mL⋅kg–1⋅min–1. The mean blood volume decreased by 8% (567 ± 187 mL, p = 0.001) until maximum exercise, leading to an increase in [Hb] by 1.3 ± 0.4 g⋅dL–1 while peripheral oxygen saturation decreased by 6.1 ± 2.4%. There were close correlations between resting blood volume and heart volume (r = 0.73, p = 0.002), maximum blood volume and maximum cardiac output (r = 0.68, p = 0.001), and maximum cardiac output and O2max (r = 0.76, p < 0.001). An increase in maximum blood volume by 1,000 mL was associated with an increase in maximum stroke volume by 25 mL and in maximum cardiac output by 3.5 L⋅min–1. In conclusion, blood volume markedly decreased until maximal exhaustion, potentially affecting the stroke volume response during exercise. Simultaneously, hemoconcentrations maintained the arterial oxygen content and compensated for the potential loss in maximum cardiac output. Therefore, a large blood volume at rest is an important factor for achieving a high cardiac output during exercise and blood volume shifts compensate for the decrease in peripheral oxygen saturation, thereby maintaining a high arteriovenous oxygen difference.
Highlights
Over the years, it has been well established that cardiac output (Q ) is a major limiting factor for the maximum oxygen uptake (V O2max) during exercise (Bassett and Howley, 2000; Stöhr et al, 2011; Lundby et al, 2017)
As blood volume (BV) significantly decreased from rest to maximal exercise by 567 mL (8%), we calculate a possible limitation in Qmax by 1.6 L·min−1, but we demonstrate a consistent oxygen transport capacity due to the increase in hemoconcentration
We found a strong correlation between BVmax and Qmax, suggesting that an increase in BVmax by 1 L is associated with an increase in Qmax by ∼3.5 L·min−1
Summary
It has been well established that cardiac output (Q ) is a major limiting factor for the maximum oxygen uptake (V O2max) during exercise (Bassett and Howley, 2000; Stöhr et al, 2011; Lundby et al, 2017). Qequals the product of heart rate (HR) and stroke volume (SV), and is largely determined by a harmonic structural and functional adaption of the heart, where especially cardiac compliance is a prerequisite for large end-diastolic volumes (Levine, 2008; Magder, 2016). If these prerequisites are given, the heart, e.g., the athletic heart—which is characterized by greater dimensions, harmonically increased leftventricular dimensions (Baggish and Wood, 2011; La Sanz-de Garza et al, 2020)—has a greater ability to use the FrankStarling-mechanism. This effect has been demonstrated in cross-sectional (González-Alonso et al, 2000; Warburton et al, 2002) and longitudinal, i.e., manipulative studies (Wilmore et al, 2001; Daussin et al, 2007; Bonne et al, 2014)
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