Reliability of forearm oxygen uptake during handgrip exercise: assessment by ultrasonography and venous blood gas

Abstract

Assessment of forearm oxygen uptake (V˙O₂ ) during handgrip exercise is a keenly investigated concept for observing small muscle mass metabolism. Although a combination of Doppler ultrasound measurements of brachial artery blood flow (Q˙) and blood gas drawn from a deep forearm vein has been utilized to calculate forearm V˙O₂ for more than two decades, the applicability of this experimental design may benefit from a thorough evaluation of its reliability during graded exercise. Therefore, we evaluated the reliability of this technique during incremental handgrip exercise in ten healthy young (24 ± 3(SD) years.) males. V˙O₂ and work rate (WR) exhibited a linear relationship (1.0 W: 43.8 ± 10.1 mL·min^-1 ; 1.5 W: 53.8 ± 14.1 mL·min^-1 ; 2.0 W: 63.4 ± 16.3 mL·min^-1 ; 2.5 W: 72.2 ± 17.6 mL·min^-1 ; 3.0 W: 79.2 ± 18.6 mL·min^-1 ; r = 0.65, P < 0.01). In turn, V˙O₂ was strongly associated with Q˙ (1.0 W: 359 ± 86 mL·min^-1 ; 1.5 W: 431 ± 112 mL·min^-1 ; 2.0 W: 490 ± 123 mL·min^-1 ; 2.5 W: 556 ± 112 mL·min^-1 ; 3.0 W: 622 ± 131 mL·min^-1 ; r = 0.96; P < 0.01), whereas arteriovenous oxygen difference (a-vO_2diff ) remained constant following all WRs (123 ± 11-130 ± 10 mL·L^-1 ). Average V˙O₂ test-retest difference was -0.4 mL·min^-1 with ±2SD limits of agreement (LOA) of 8.4 and -9.2 mL·min^-1 , respectively, whereas coefficients of variation (CVs) ranged from 4-7%. Accordingly, test-retest Q˙ difference was 11.9 mL·min^-1 (LOA: 84.1 mL·min^-1 ; -60.4 mL·min^-1 ) with CVs between 4 and 7%. Test-retest difference for a-vO_2diff was -0.28 mL·dL^-1 (LOA: 1.26mL·dL^-1 ; -1.82 mL·dL^-1 ) with 3-5% CVs. In conclusion, our results revealed that forearm V˙O₂ determination by Doppler ultrasound and direct venous sampling is linearly related to WR, and a reliable experimental design across a range of exercise intensities.

Keywords: Blood flow; V˙O2; oxygen extraction; small muscle mass; test-retest.

Figure 1

Custom‐made cable pulley with handgrip used for testing of forearm oxygen consumption ($\dot{V}$O₂) during the incremental exercise protocol.

Figure 2

Descriptive values for (A) Forearm oxygen uptake ($\dot{V}$O₂), (B) Brachial artery blood flow ($\dot{Q}$), (C) Arteriovenous oxygen difference (a‐vO_2diff), (D) Brachial artery mean blood velocity, (E) Brachial artery diameter, and (F) Forearm venous lactate concentration following 3 min incremental steps of exercise intensity. * Denotes significant (P < 0.05) increase from previous condition. Boxes represent mean values from test and retest, with standard error of the mean (SEM).

Figure 3

Descriptive values for (A) Forearm vascular conductance and (B) Mean arterial pressure (MAP) following 3 min incremental steps of exercise intensity. *Denotes significant (P < 0.05) increase from previous condition. Boxes represent mean values from test and retest, with standard error of the mean (SEM).

Figure 4

Linear relationship between brachial artery blood flow ($\dot{Q}$) and forearm oxygen uptake ($\dot{V}$O₂) following dynamic handgrip exercise with 3 min (0.5 W) increments.

Figure 5

Bland–Altman analysis test–retest variability of (A) Forearm oxygen consumption ($\dot{V}$O₂), (B) Brachial artery blood flow ($\dot{Q}$), and (C) Arteriovenous oxygen difference (a‐vO_2diff). Mean test–retest differences are marked with dashed lines (···). Upper and lower 2SD limits of are marked with solid lines (―).