Effect of hypoxia on muscle oxygenation and metabolism during arm exercise in humans

Muscle deoxygenation of upper-limb muscles during progressive arm-cranking exercise

The purpose of this study was to determine which upper-limb muscle exhibits the greatest change in muscle deoxygenation during arm-cranking exercise (ACE). We hypothesized that the biceps brachii (BB) would show the greatest change in muscle deoxygenation during progressive ACE to exhaustion relative to triceps brachii (TR), brachioradialis (BR), and anterior deltoid (AD). Healthy young men (n = 11; age = 27 +/- 1 y; mean +/- SEM) performed an incremental ACE test to exhaustion. Near-infrared spectroscopy (NIRS) was used to monitor the relative concentration changes in oxy- (O2Hb), deoxy- (HHb), and total hemoglobin (Hbtot), as well as tissue oxygenation index (TOI) in each of the 4 muscles. During submaximal arm exercise, we found that changes to NIRS-derived measurements were not different between the 4 muscles studied (p > 0.05). At maximal exercise HHb was significantly higher in the BB compared with AD (p < 0.05). Relative to the other 3 muscles, BB exhibited the greatest decrease in O2Hb and TOI (p < 0.05). Our investigation provides two new and important findings: (i) during submaximal ACE the BB, TR, BR, and AD exhibit similar changes in muscle deoxygenation and (ii) during maximal ACE the BB exhibits the greatest change in intramuscular O2 status.

Peripheral circulatory responses in vivo from regional brachial biceps and lumbar muscles in healthy men and women during pushing and pulling exercise

BACKGROUND

Although women have been performing increasingly more manual labor in the workplace in the past 2 decades, their physiological responses and gender-based differences in muscle microvascularity during occupational activities have not yet been extensively documented.

OBJECTIVE

This study assessed gender differences and tissue heterogeneity in peripheral circulatory responses from 2 muscle groups during pushing and pulling exercise until volitional exhaustion.

METHODS

In healthy men and women, near-infrared spectroscopy was used to determine peripheral responses, oxygenation, and blood volume simultaneously from the right biceps brachii and lumbar erector spinae. Pulmonary oxygen uptake was assessed using a metabolic measurement cart.

RESULTS

Although the 11 men who participated in the study demonstrated greater pulmonary oxygen uptake and power output at volitional exhaustion, their peak peripheral responses for both muscles were similar to those of the 11 women participating. In both sexes, oxygenations trends decreased in both muscles with an increase in workload. However, whereas blood volume increased in the biceps, it decreased in the lumbar muscle in both sexes. At 20% to 60% levels of peak pulmonary oxygen uptake, the percent change in peripheral bicep responses was greater for men than for women (P < 0.05). In contrast, women demonstrated greater change in lumbar muscle oxygenation compared with men at 40% to 60% of peak pulmonary oxygen uptake (P < 0.05).

CONCLUSIONS

Similar peripheral responses for biceps and lumbar muscles at the point of volitional exhaustion suggest that gender differences in pulmonary oxygen uptake are independent of oxygen extraction or delivery across the muscle groups monitored. However, at submaximal levels of exercise, the peripheral changes in each muscle were gender dependent. Although biceps and lumbar muscles are 2 discrete muscle groups, based on the heterogeneity found in the blood volume trends it is likely that oxygen supply and demand are regulated by muscle location and muscle fiber characteristics. Overall, gender-based assessment of occupational activities should incorporate both pulmonary and peripheral circulatory responses to understand each sex's performance effectiveness.

Vastus lateralis oxygenation during prolonged cycling in healthy males

This study examined the relationship between acute cardiorespiratory and muscle oxygenation and blood volume changes during prolonged exercise. Eight healthy male volunteers (mean maximum oxygen uptake ([Formula: see text]O2max) = 41.6 ± 2.4 mL/kg/min) performed 60 min submaximal cycling at 50% [Formula: see text]O2max. Oxygen uptake ([Formula: see text]O2) was measured by indirect spirometry, cardiac output (CO) was estimated using a PortapresTM, and right vastus lateralis oxyhemoglobin/ myoglobin (oxyHb/Mb), deoxyhemoglobin/myoglobin (deoxyHb/Mb), and total hemoglobin/myoglobin (total Hb/Mb) were recorded using near-infrared spectroscopy (NIRS). After 40 min of exercise, there was a significant increase in [Formula: see text]O2 due to a significantly higher arteriovenous oxygen difference ((a - v)O2diff). After 30 min of exercise CO remained unchanged, but there was a significant decrease in stroke volume and a proportionate increase in heart rate, thus indicating the occurrence of cardiovascular drift. During the first few minutes of exercise, there was a decline in oxyHb/Mb and total Hb/Mb, whereas deoxyHb/Mb remained unchanged. Thereafter, oxyHb/Mb and total Hb/Mb increased systematically until the termination of exercise while deoxyHb/Mb declined. After 40 min of exercise, these changes were significantly different from the baseline values. There were no significant correlations between the changes in the NIRS variables and systemic [Formula: see text]O2 or mixed (a - v)O2diff during exercise. These results suggest that factors other than localized changes in muscle oxygenation and blood volume account for the increased [Formula: see text]O2 during prolonged submaximal exercise. Key words: near infrared spectroscopy, cardiovascular drift, systemic oxygen consumption.

Muscle Oxygenation Trends During Dynamic Exercise Measured by Near Infrared Spectroscopy

During the last decade, NIRS has been used extensively to evaluate the changes in muscle oxygenation and blood volume during a variety of exercise modes. The important findings from this research are as follows: (a) There is a strong correlation between the lactate (ventilatory) threshold during incremental cycle exercise and the exaggerated reduction in muscle oxygenation measured by NIRS. (b) The delay in steady-state oxygen uptake during constant work rate exercise at intensities above the lactate/ventilatory threshold is closely related to changes in muscle oxygenation measured by NIRS. (c) The degree of muscle deoxygenation at the same absolute oxygen uptake is significantly lower in older persons compared younger persons; however, these changes are negated when muscle oxygenation is expressed relative to maximal oxygen uptake values. (d) There is no significant difference between the rate of biceps brachii and vastus lateralis deoxygenation during arm cranking and leg cycling exercise, respectively, in males and females. (e) Muscle deoxygenation trends recorded during short duration, high-intensity exercise such as the Wingate test indicate that there is a substantial degree of aerobic metabolism during such exercise. Recent studies that have used NIRS at multiple sites, such as brain and muscle tissue, provide useful information pertaining to the regional changes in oxygen availability in these tissues during dynamic exercise. Key words: blood volume, noninvasive measurement

The effect of varied fractional inspired oxygen on arm exercise performance in spinal cord injury and able-bodied persons

OBJECTIVE

To examine the effect of different levels of fractional inspired oxygen (FiO(2)) (15%, 21%, 50%) on peak oxygen consumption (VO(2)peak) during arm exercise in persons with spinal cord injury and in able-bodied controls.

DESIGN

Case-control study.

SETTING

University medical center in the Netherlands.

PARTICIPANTS

Ten able-bodied controls, 6 persons with paraplegia, and 6 persons with tetraplegia.

INTERVENTIONS

Inspiration of 15%, 21%, and 50% oxygen during a 15-minute period before and during arm exercise.

MAIN OUTCOME MEASURES

Oxygen uptake (VO(2)peak, VO(2)peak/kg), power output, ventilation, and base excess.

RESULTS

In the able-bodied controls, significant FiO(2) dependency was seen in power output, VO(2)peak, and VO(2)peak/kg. Persons with paraplegia showed significant FiO(2) dependency in VO(2) and VO(2)/kg. In persons with tetraplegia, no FiO(2) dependency was observed; however, VO(2) and VO(2)/kg were significantly higher at 50% than at 15% FiO(2). Ventilation and base excess did not change in able-bodied controls or in persons with paraplegia with different levels of FiO(2). In persons with tetraplegia, ventilation was significantly higher at 15% than at 50% FiO(2), and base excess did not change. No significant interactions between groups and FiO(2) were observed.

CONCLUSIONS

Oxygen consumption during peak arm-cranking exercise is enhanced with an increased inspiratory oxygen fraction in able-bodied controls as well as in persons with paraplegia and to a lesser extent in persons with tetraplegia, indicating that peak oxygen consumption during arm exercise is limited by oxygen supply rather than by the small muscle mass and related biochemical limitations.

The effect of inspired oxygen fraction on peak oxygen uptake during arm exercise

It has been shown that peak oxygen uptake (O(2)peak) during leg exercise is enhanced by an increased inspiratory oxygen fraction ( FiO(2)), indicating that oxygen supply is the limiting factor. Whether oxygen supply is a limiting factor in arm exercise performance is unknown. The purpose of this study, therefore, was to examine the effect of different levels of FiO(2 )on O(2)peak during arm exercise in healthy individuals. Nine men successfully performed three incremental arm-cranking exercise tests with FiO(2)15%, FiO(2)21% and FiO(2)50% applied in counterbalanced order. A significant FiO(2 )dependency was observed for O(2)peak ( p=0.02) and power output ( p=0.03) and post hoc tests revealed a significant difference in O(2)peak between 15 and 50% FiO(2 )( p=0.02), but not between 15 and 21% FiO(2), and 21 and 50% FiO(2). The results of this study show that O(2)peak is enhanced with increasing FiO(2), and suggest that O(2)peak during arm exercise is limited by oxygen supply rather than by the metabolic machinery within the muscle itself.

Arm blood flow and oxygenation on the transition from arm to combined arm and leg exercise in humans

The cardiovascular response to exercise with several groups of skeletal muscle implies that work with the legs may reduce arm blood flow. This study followed arm blood flow (Yarm) and oxygenation on the transition from arm cranking (A) to combined arm and leg exercise (A+L). Seven healthy male subjects performed A at approximately 80 % of maximum work rate (Wmax) and A at ~80 % Wmax combined with L at approximately 60 % Wmax. A transition trial to volitional exhaustion was performed where L was added after 2 min of A. The Yarm was determined by constant infusion thermodilution in the axillary vein and changes in biceps muscle oxygenation were measured with near-infrared spectroscopy. During A+L Yarm was lowered by 0.38 +/- 0.06 l min-1 (10.4 +/- 3.3 %, P < 0.05) from 2.96 +/- 1.54 l min-1 during A. Total (HbT) and oxygenated haemoglobin (HbO2) concentrations were also lower. During the transition from A to A+L Yarm decreased by 0.22 +/- 0.03 l min-1 (7.9 +/- 1.8 %, P < 0.05) within 9.6 +/- 0.2 s, while HbT and HbO2 decreased similarly within 30 +/- 2 s. At the same time mean arterial pressure and arm vascular conductance also decreased. The data demonstrate reduction in blood flow to active skeletal muscle during maximal whole body exercise to a degree that arm oxygen uptake and muscle tissue oxygenation are compromised.

Muscle oxygenation trends during constant work rate cycle exercise in men and women

PURPOSE

To examine the relationship between muscle oxygenation and arteriovenous oxygen difference [(a - v)O2diff)] at four constant rate workloads in healthy men and women and to compare these responses between the genders.

METHODS

Nineteen men and 14 women consented to perform an incremental test to identify the lactic acidosis threshold (LAT) and maximal aerobic power (VO2max) and an intermittent constant work rate test at an oxygen uptake corresponding to 40% LAT, 80% LAT, 25% LAT-VO2max, and 50% LAT-VO2max. Each exercise interval was 5 min long followed by 2 min of recovery. Cardiac output was measured by CO2 rebreathing at each workload from which (a - v)O2diff was computed. Tissue absorbency was measured from the vastus lateralis in both the test sessions using near infrared spectroscopy (NIRS). Muscle oxygenation during constant work rate exercise and recovery was expressed as a percentage (%Mox) of the maximum range observed during incremental exercise and recovery.

RESULTS

A systematic decrease was observed in %Mox with increasing intensity, followed by a proportional increase during recovery from each exercise bout. Significant inverse relationships were observed between %Mox and (a - v)O2diff in men (r = -0.34) and women (r = -0.31) across the four intensities. Mean %Mox was significantly higher (P < 0.05) in women compared with men, suggesting lesser deoxygenation at the same relative exercise intensity.

CONCLUSIONS

%Mox was not an accurate predictor of mixed (a - v)O2diff during exercise because of the low common variance between these two variables, and it is unclear whether the gender difference in %Mox is a true physiological phenomenon or whether it is an artifact of the NIRS technique.

Oxidative metabolism in muscle

Oxidative metabolism is the dominant source of energy for skeletal muscle. Near-infrared spectroscopy allows the non-invasive measurement of local oxygenation, blood flow and oxygen consumption. Although several muscle studies have been made using various near-infrared optical techniques, it is still difficult to interpret the local muscle metabolism properly. The main findings of near-infrared spectroscopy muscle studies in human physiology and clinical medicine are summarized. The advantages and problems of near-infrared spectroscopy measurements, in resting and exercising skeletal muscles studies, are discussed through some representative examples.

Brain and muscle oxygen saturation during head-up-tilt-induced central hypovolaemia in humans

Near-infrared spectrophotometry-determined cerebral (ScO2) and muscle oxygen saturations (SmO2) were followed in 15 volunteers during passive 50 degrees head-up-tilt-induced central hypovolaemia, and in nine volunteers during ventilatory manoeuvres affecting arterial carbon dioxide tension. During head-up tilt, mean arterial pressure [MAP, 88 (77-118) to 97 (80-136) mmHg, median and range] and heart rate [HR; 66 (49-77) to 87 (42-132) beats min-1 P < 0.01] increased, but after 22 (1-45) min they declined [to 61 (40-91) mmHg and 69 (38-109) beats min-1, respectively, P = 0.001] and pre-syncopal symptoms developed. Central hypovolaemia was indicated by an increased thoracic electrical impedance, and a decreased cardiac output and central venous oxygen saturation. The arterial oxygen saturation, pulmonal oxygen uptake and skin temperatures remained constant. The ScO2 remained stable at 72 (62-77)% until the pre-syncopal incidence, when it decreased to 62 (31-73)% (P = 0.001), and tilt down made it increase to 75 (36-87)% (P < 0.05) before the recovery value was established. In contrast, SmO2 decreased during tilting [75(70-87) to 65 (53-70)%], and recovered to 70 (53-83)%, P < 0.01) during the hypotensive episode. The end-tidal CO2 tension decreased only during tilt-up. The ScO2 decreased, and SmO2 increased during hyperventilation, and ScO2 increased during breathing of 5% carbon dioxide. Rebreathing from a bag made SmO2 decrease and resulted in a biphasic ScO2 response: it first increased and subsequently decreased. Cardiovascular changes during tilt were not reflected in skin temperature. The ScO2 reflected the maintained autoregulation of cerebral blood flow until the perfusion pressure decreased markedly. In contrast, SmO2 mirrored muscle vasoconstriction early during tilt, and vasodilatation when pre-syncopal symptoms appeared.