Exercise-induced hypoxemia in athletes: role of inadequate hyperventilation

Wearable and telemedicine innovations for Olympic events and elite sport

Rapid advances in wearable technologies and real-time monitoring have resulted in major inroads in the world of recreational and elite sport. One such innovation is the application of real-time monitoring, which comprises a smartwatch application and ecosystem, designed to collect, process and transmit a wide range of physiological, biomechanical, bioenergetic and environmental data using cloud-based services. We plan to assess the impact of this wireless technology during Tokyo 2020, where this technology could help characterize the physiological and thermal strain experienced by an athlete, as well as determine future management of athletes during a medical emergency as a result of a more timely and accurate diagnosis. Here we describe some of the innovative technologies developed for numerous sports at Tokyo 2020 ranging from race walking (20 km and 50 km events), marathon, triathlon, road cycling (including the time trial event), mountain biking, to potentially team sports played outdoors. A more symbiotic relationship between sport, health and technology needs to be encouraged that harnesses the unique demands of elite sport (e.g., the need for unobtrusive devices that provide real-time feedback) and serves as medical and preventive support for the athlete's care. The implementation of such applications would be particularly welcome in the field of medicine (i.e., telemedicine applications) and the workplace (with particular relevance to emergency services, the military and generally workers under extreme environmental conditions). Laboratory and field-based studies are required in simulated scenarios to validate such emerging technologies, with the field of sport serving as an excellent model to understand and impact disease.

Alveolar to arterial gas exchange during constant-load exercise in healthy active men and women

Inadequate hyperventilation and inefficient alveolar to arterial gas exchange are gas exchange challenges that can limit capacity and cause exercise-induced arterial hypoxaemia (EIAH). This work evaluated if the prevalence of gas exchange inefficiencies, defined as AaDO₂>25 mmHg, PaCO₂>38 mmHg, and/or ΔPaO₂>-10 mmHg at any point during constant-load exercise in healthy, active, but not highly trained, individuals suggested an innate sex difference that would make females more susceptible to EIAH. Sixty-four healthy, active males and females completed 18-min of cycling exercise (moderate and vigorous intensity, 9 min/stage). Arterial blood gases were measured at rest and every 3-min during exercise, while constantly assessing gas exchange. Both sexes demonstrated similar levels of AaDO₂ widening until the final 3 min of vigorous exercise, where females demonstrated a trend for greater widening than males (16.3±6.2 mmHg vs. 19.1±6.0 mmHg, p=0.07). Males demonstrated a blunted ventilatory response to moderate exercise with higher PaCO₂ (38.5±2.6 vs. 36.5±2.4, p=0.002) and a lower ventilation when corrected for workload (0.42±0.1 vs. 0.48±0.1, p=0.002). No significant arterial hypoxaemia occurred, but in 6 M and 5 F SaO₂ dropped by ≥2%. There was no difference in prevalence of pulmonary gas exchange inefficiencies between sexes, but the type of inefficiency was influenced by sex.Abbreviations: AaDO₂: alveolar-arterial oxygen difference; BP: blood pressure; EIAH: exercise-induced arterial hypoxaemia; F: females; HR: heart rate; M: males; Q: cardiac output; PaCO₂: arterial partial pressure of carbon dioxide; PaO₂: arterial partial pressure of oxygen; ΔPaO₂: change in arterial partial pressure of oxygen; PAO₂: alveolar partial pressure of oxygen; RPE: rating of perceived exertion; SaO₂: arterial oxygen saturation; V_E: ventilation; V_E/VCO₂: ventilatory equivalent for carbon dioxide; VO_2PEAK: peak oxygen consumption; W_MAX: workload maximum.

Peripheral chemoresponsiveness during exercise in male athletes with exercise-induced arterial hypoxaemia

NEW FINDINGS

What is the central question of this study? Do highly trained male endurance athletes who develop exercise-induced arterial hypoxaemia (EIAH) demonstrate reduced peripheral chemoresponsiveness during exercise? What is the main finding and its importance? Those with the lowest arterial saturation during exercise have a smaller ventilatory response to hypercapnia during exercise. There was no significant relationship between the hyperoxic ventilatory response and EIAH. The findings suggest that peripheral chemoresponsiveness to hypercapnia during exercise could play a role in the development of EIAH. The findings improve our understanding of the mechanisms that contribute to EIAH.

ABSTRACT

Exercise-induced arterial hypoxaemia (EIAH) is characterized by a decrease in arterial oxygen tension and/or saturation during whole-body exercise, which may in part result from inadequate alveolar ventilation. However, the role of peripheral chemoresponsiveness in the development of EIAH is not well established. We hypothesized that those with the most severe EIAH would have an attenuated ventilatory response to hyperoxia and hypercapnia during exercise. To evaluate this, on separate days, we measured ventilatory sensitivity to hyperoxia and separately hypercapnia at rest and during three different exercise intensities (25, 50% of V ̇ O 2 max and ventilatory threshold (∼67% of V ̇ O 2 max )) in 12 males cyclists ( V ̇ O 2 max  = 66.6 ± 4.7 ml kg^-1  min^-1 ). Subjects were divided into two groups based on their end-exercise arterial oxygen saturation (ear oximetry, S p O 2 ): a normal oxyhaemoglobin saturation group (NOS, S p O 2  = 93.4 ± 0.4%, n = 5) and a low oxyhaemoglobin saturation group (LOS, S p O 2  = 89.9 ± 0.9%, n = 7). There was no difference in V ̇ O 2 max (66.4 ± 2.9 vs. 66.8 ± 6.0 ml kg^-1  min^-1 , respectively, P = 0.9), peak ventilation during maximal exercise (182 ± 15 vs. 197 ± 32 l min^-1 , respectively, P = 0.36) or ventilatory response to hyperoxia (P = 0.98) at any exercise intensity between NOS and LOS groups. However, those in the LOS group had a significantly lower ventilatory response to hypercapnia (P = 0.004, (η²  = 0.18). There was also a significant relationship between the mean hypercapnic response and end-exercise S p O 2 (r = 0.75, P = 0.009) but not between the mean hyperoxic response and end-exercise S p O 2 (r = 0.21, P = 0.51). A blunted hypercapnic ventilatory response may contribute to EIAH in highly trained men due to a failure to increase ventilation sufficiently to offset exercise-induced gas exchange impairments.

Exercise-induced arterial hypoxemia; some answers, more questions

Exercise-induced arterial hypoxemia (EIAH) is characterized by the decrease in arterial oxygen tension and oxyhemoglobin saturation during dynamic aerobic exercise. Since the time of the initial observations, our knowledge and understanding of EIAH has grown, but many unknowns remain. The purpose of this review is to provide an update on recent findings, highlight areas of disagreement, and identify where information is lacking. Specifically, this review will place emphasis on (i) the occurrence of EIAH during submaximal exercise, (ii) whether there are sex differences in the development and severity of EIAH, and (iii) unresolved questions and future directions.

Alveolar Air and O2 Uptake During Exercise in Patients With Heart Failure

BACKGROUND

Peak exercise pulmonary oxygen uptake (V̇O₂) is a primary marker of prognosis in heart failure (HF). The pathophysiology of impaired peak V̇O₂ is unclear in patients. To what extent alveolar airway function affects V̇O₂ during cardiopulmonary exercise testing (CPET) has not been fully elucidated. This study aimed to describe how changes in alveolar ventilation (V̇_A), volume (V_A), and related parameters couple with exercise V̇O₂ in HF.

METHODS AND RESULTS

A total of 35 patients with HF (left ventricular ejection fraction 20 ± 6%, age 53 ± 7 y) participated in CPET with breath-to-breath measurements of ventilation and gas exchange. At rest, 20 W, and peak exercise, arterial CO₂ tension was measured via radial arterial catheterization and used in alveolar equations to derive V̇_A and V_A. Resting lung diffusion capacity for carbon monoxide (DL_CO) was assessed and indexed to V_A for each time point. Resting R² between V̇O₂ and V̇_A, V_A, DL_CO, and DL_CO/V_A was 0.68, 0.18, 0.20, and 0.07, respectively (all P < .05 except DL_CO/V_A). 20 W R² between V̇O₂ and V̇_A, V_A, DL_CO, and DL_CO/V_A was 0.64, 0.32, 0.07, and 0.18 (all P < .05 except DL_CO). Peak exercise R² between V̇O₂ and V̇_A, V_A, DL_CO, and DL_CO/V_A was 0.55, 0.31, 0.34, and 0.06 (all P < .05 except DL_CO/V_A).

CONCLUSIONS

These data suggest that alveolar airway function that is not exclusively related to effects caused by localized lung diffusivity affects exercise V̇O₂ in moderate-to-severe HF.

Prevalence of Exercise-Induced Arterial Hypoxemia in Distance Runners at Sea Level

PURPOSE

It has been reported that ~50% of endurance-trained men demonstrate exercise-induced arterial hypoxemia (EIAH) during heavy exercise. However, this often-cited prevalence rate comes from a single study using a cohort of 25 highly trained men who completed maximal cycle ergometry. As arterial oxyhemoglobin saturation (SpO2) during maximal exercise is reported to be significantly lower during treadmill versus cycle ergometry in the same subjects, we hypothesized that the prevalence of EIAH would be greater than previously reported (and commonly referenced) in a larger cohort of highly endurance-trained men during maximal treadmill running.

METHODS

Data from 124 highly trained male distance runners (V˙O2max range = 60.3-84.7 mL·kg·min) were retrospectively examined from previously published studies completed in the Indiana University Human Performance Laboratory. Subjects completed a constant speed, progressive-grade treadmill exercise test to volitional exhaustion, and arterial oxyhemoglobin saturation (SaO2ear) in all subjects was estimated using the same oximeter (Hewlett Packard 47201A).

RESULTS

Using similar inclusion criteria as previously published for highly trained (V˙O2max > 68 mL·kg·min) and for EIAH (SaO2ear ≤ 91%), 55 of 79 subjects (70%) exhibited exercise-induced arterial desaturation. Across all 124 subjects, 104 (84%) demonstrated at least moderate EIAH (SaO2ear ≤ 93%) during maximal treadmill exercise. SaO2ear was significantly yet weakly correlated with V˙E/V˙O2 (P < 0.01, r = 0.28) and V˙E/V˙CO2 (P < 0.001, r = 0.33) but not with V˙O2max.

CONCLUSION

These results indicate that the prevalence of EIAH in highly trained men during maximal treadmill exercise at sea level is greater compared with previously suggested data, with exercise mode perhaps playing a factor in the number of athletes who experience EIAH.

Maximal Oxygen Uptake Is Achieved in Hypoxia but Not Normoxia during an Exhaustive Severe Intensity Run

Highly aerobically trained individuals are unable to achieve maximal oxygen uptake (V˙O2max) during exhaustive running lasting ~2 min, instead V˙O2 plateaus below V˙O2max after ~1 min. Hypoxia offers the opportunity to study the (V˙O2) response to an exhaustive run relative to a hypoxia induced reduction in V˙O2max. The aim of this study was to explore whether there is a difference in the percentage of V˙O2max achieved (during a 2 min exhaustive run) in normoxia and hypoxia. Fourteen competitive middle distance runners (normoxic V˙O2max 67.0 ± 5.2 ml.kg⁻¹.min⁻¹) completed exhaustive treadmill ramp tests and constant work rate (CWR) tests in normoxia and hypoxia (F_iO₂ 0.13). The V˙O2 data from the CWR tests were modeled using a single exponential function. End exercise normoxic CWR V˙O2 was less than normoxic V˙O2max (86 ± 6% ramp, P < 0.001). During the hypoxic CWR test, hypoxic V˙O2max was achieved (102 ± 8% ramp, P = 0.490). The phase II time constant was greater in hypoxia (12.7 ± 2.8 s) relative to normoxia (10.4 ± 2.6 s) (P = 0.029). The results demonstrate that highly aerobically trained individuals cannot achieve V˙O2max during exhaustive severe intensity treadmill running in normoxia, but can achieve the lower V˙O2max in hypoxia despite a slightly slower V˙O2 response.

Regulation of increased blood flow (hyperemia) to muscles during exercise: a hierarchy of competing physiological needs

This review focuses on how blood flow to contracting skeletal muscles is regulated during exercise in humans. The idea is that blood flow to the contracting muscles links oxygen in the atmosphere with the contracting muscles where it is consumed. In this context, we take a top down approach and review the basics of oxygen consumption at rest and during exercise in humans, how these values change with training, and the systemic hemodynamic adaptations that support them. We highlight the very high muscle blood flow responses to exercise discovered in the 1980s. We also discuss the vasodilating factors in the contracting muscles responsible for these very high flows. Finally, the competition between demand for blood flow by contracting muscles and maximum systemic cardiac output is discussed as a potential challenge to blood pressure regulation during heavy large muscle mass or whole body exercise in humans. At this time, no one dominant dilator mechanism accounts for exercise hyperemia. Additionally, complex interactions between the sympathetic nervous system and the microcirculation facilitate high levels of systemic oxygen extraction and permit just enough sympathetic control of blood flow to contracting muscles to regulate blood pressure during large muscle mass exercise in humans.

Responses to exercise in normobaric hypoxia: comparison of elite and recreational ski mountaineers

PURPOSE

Hypoxia is known to reduce maximal oxygen uptake (VO(2max)) more in trained than in untrained subjects in several lowland sports. Ski mountaineering is practiced mainly at altitude, so elite ski mountaineers spend significantly longer training duration at altitude than their lower-level counterparts. Since acclimatization in hypobaric hypoxia is effective, the authors hypothesized that elite ski mountaineers would exhibit a VO2max decrement in hypoxia similar to that of recreational ski mountaineers.

METHODS

Eleven elite (E, Swiss national team) and 12 recreational (R) ski mountaineers completed an incremental treadmill test to exhaustion in normobaric hypoxia (H, 3000 m, F(1)O(2) 14.6% ± 0.1%) and in normoxia (N, 485 m, F(1)O(2) 20.9% ± 0.0%). Pulse oxygen saturation in blood (SpO(2)), VO(2max), minute ventilation, and heart rate were recorded.

RESULTS

At rest, hypoxic ventilatory response was higher (P < .05) in E than in R (1.4 ± 1.9 vs 0.3 ± 0.6 L · min⁻¹ · kg⁻¹). At maximal intensity, SpO(2) was significantly lower (P < .01) in E than in R, both in N (91.1% ± 3.3% vs 94.3% ± 2.3%) and in H (76.4% ± 5.4% vs 82.3% ± 3.5%). In both groups, SpO(2) was lower (P < .01) in H. Between N and H, VO(2max) decreased to a greater extent (P < .05) in E than in R (-18% and -12%, P < .01). In E only, the VO(2max) decrement was significantly correlated with the SpO(2) decrement (r = .74, P < .01) but also with VO(2max) measured in N (r = .64, P < .05).

CONCLUSION

Despite a probable better acclimatization to altitude, VO(2max) was more reduced in E than in R ski mountaineers, confirming previous results observed in lowlander E athletes.

Pulmonary gas exchange and acid-base balance during exercise

As the first step in the oxygen-transport chain, the lung has a critical task: optimizing the exchange of respiratory gases to maintain delivery of oxygen and the elimination of carbon dioxide. In healthy subjects, gas exchange, as evaluated by the alveolar-to-arterial PO2 difference (A-aDO2), worsens with incremental exercise, and typically reaches an A-aDO2 of approximately 25 mmHg at peak exercise. While there is great individual variability, A-aDO2 is generally largest at peak exercise in subjects with the highest peak oxygen consumption. Inert gas data has shown that the increase in A-aDO2 is explained by decreased ventilation-perfusion matching, and the development of a diffusion limitation for oxygen. Gas exchange data does not indicate the presence of right-to-left intrapulmonary shunt developing with exercise, despite recent data suggesting that large-diameter arteriovenous shunt vessels may be recruited with exercise. At the same time, multisystem mechanisms regulate systemic acid-base balance in integrative processes that involve gas exchange between tissues and the environment and simultaneous net changes in the concentrations of strong and weak ions within, and transfer between, extracellular and intracellular fluids. The physicochemical approach to acid-base balance is used to understand the contributions from independent acid-base variables to measured acid-base disturbances within contracting skeletal muscle, erythrocytes and noncontracting tissues. In muscle, the magnitude of the disturbance is proportional to the concentrations of dissociated weak acids, the rate at which acid equivalents (strong acid) accumulate and the rate at which strong base cations are added to or removed from muscle.

Analysis of physiological variables during acute hypoxia and maximal stress test in adolescents clinically diagnosed with mild intermittent or mild persistent asthma

OBJECTIVE

To analyze adolescents clinically diagnosed with asthma, in terms of the physiological changes occurring during acute hypoxia and during a maximal stress test.

METHODS

This was a descriptive, cross-sectional study involving 48 adolescents (12-14 years of age) who were divided into three groups: mild intermittent asthma (MIA, n = 12); mild persistent asthma (MPA, n = 12); and control (n = 24). All subjects were induced to acute hypoxia and were submitted to maximal stress testing. Anthropometric data were collected, and functional variables were assessed before and after the maximal stress test. During acute hypoxia, the time to a decrease in SpO2 and the time to recovery of SpO2 (at rest) were determined.

RESULTS

No significant differences were found among the groups regarding the anthropometric variables or regarding the ventilatory variables during the stress test. Significant differences were found in oxygen half-saturation pressure of hemoglobin prior to the test and in PaO2 prior to the test between the MPA and control groups (p = 0.0279 and p = 0.0116, respectively), as was in the oxygen extraction tension prior to the test between the MIA and MPA groups (p = 0.0419). There were no significant differences in terms of the SpO2 times under any of the conditions studied. Oxygen consumption and respiratory efficiency were similar among the groups. The use of a bronchodilator provided no significant benefit during the hypoxia test. No correlations were found between the hypoxia test results and the physiological variables.

CONCLUSIONS

Our findings suggest that adolescents with mild persistent asthma have a greater capacity to adapt to hypoxia than do those with other types of asthma.

Impairment of 3000-m run time at altitude is influenced by arterial oxyhemoglobin saturation

The decline in maximal oxygen uptake (ΔVO(2)max) with acute exposure to moderate altitude is dependent on the ability to maintain arterial oxyhemoglobin saturation (SaO2).

PURPOSE

This study examined if factors related to ΔVO(2)max at altitude are also related to the decline in race performance of elite athletes at altitude.

METHODS

Twenty-seven elite distance runners (18 men and 9 women, VO(2)max = 71.8 ± 7.2 mL·kg(-1)·min(-1)) performed a treadmill exercise at a constant speed that simulated their 3000-m race pace, both in normoxia and in 16.3% O2 (∼2100 m). Separate 3000-m time trials were completed at sea level (18 h before altitude exposure) and at 2100 m (48 h after arrival at altitude). Statistical significance was set at P ≤ 0.05.

RESULTS

Group 3000-m performance was significantly slower at altitude versus sea level (48.5 ± 12.7 s), and the declines were significant in men (48.4 ± 14.6 s) and women (48.6 ± 8.9 s). Athletes grouped by low SaO2 during race pace in normoxia (SaO2 < 91%, n = 7) had a significantly larger ΔVO(2) in hypoxia (-9.2 ± 2.1 mL·kg(-1)·min(-1)) and Δ3000-m time at altitude (54.0 ± 13.7 s) compared with athletes with high SaO2 in normoxia (SaO2 > 93%, n = 7, ΔVO(2) = -3.5 ± 2.0 mL·kg(-1)·min(-1), Δ3000-m time = 38.9 ± 9.7 s). For all athletes, SaO2 during normoxic race pace running was significantly correlated with both ΔVO(2) (r = -0.68) and Δ3000-m time (r = -0.38).

CONCLUSIONS

These results indicate that the degree of arterial oxyhemoglobin desaturation, already known to influence ΔVO(2)max at altitude, also contributes to the magnitude of decline in race performance at altitude.

Exercise-induced hypoxemia: fact or fallacy?

Whereas the prevalence of exercise-induced hypoxemia (EIH) in endurance athletes is commonly reported as approximately 50%, most previous studies have not corrected PaO2 for exercise-induced hyperthermia. Furthermore, although a detrimental effect on aerobic performance has been assumed, no study has measured arterial oxygen content (CaO2) in this context.

PURPOSE

To determine the effect of temperature-correcting PaO2 values for rectal, arterial blood, esophageal, and exercising muscle temperatures during exercise on CaO2 and the prevalence of EIH.

METHODS

Twenty-three trained males (age 26 +/- 5 yr; VO2peak 65.2 +/- 1.6 mL x kg-1 x min-1) performed incremental treadmill exercise to exhaustion with PaO2 corrected for simultaneous temperature measurements at all four sites. EIH was defined as DeltaPaO2 >or= 10 mm Hg.

RESULTS

: With no temperature correction, DeltaPaO2 was -20.8 +/- 5.0 mm Hg and prevalence was 96% (n = 23), but when corrected for rectal temperature, DeltaPaO2 was -14.7 +/- 7.8 mm Hg and prevalence was 73% (n = 20); for arterial blood temperature, DeltaPaO2 was -7.7 +/- 6.5 mm Hg and prevalence was 35% (n = 20); and for esophageal temperature, DeltaPaO2 was -8.1 +/- 7.7 mm Hg and prevalence was 48% (n = 23), although when corrected for active muscle temperature, DeltaPaO2 was +8.2 +/- 7.8 mm Hg and prevalence was 0% (n = 10). There were no significant changes in CaO2 except for uncorrected values, and there was no correlation between DeltaPaO2 and VO2peak.

CONCLUSIONS

Although the prevalence of EIH depends on the temperature correction applied to PaO2 values, in no case is there a significant change in CaO2 or any relationship with maximal aerobic power.

Exercise-induced asthma, respiratory and allergic disorders in elite athletes: epidemiology, mechanisms and diagnosis: part I of the report from the Joint Task Force of the European Respiratory Society (ERS) and the European Academy of Allergy and Clinical Immunology (EAACI) in cooperation with GA2LEN

AIMS

To analyze the changes in the prevalence of asthma, bronchial hyperresponsiveness (BHR) and allergies in elite athletes over the past years, to review the specific pathogenetic features of these conditions and to make recommendations for their diagnosis.

METHODS

The Task Force reviewed present literature by searching Medline up to November 2006 for relevant papers by the search words: asthma, bronchial responsiveness, EIB, athletes and sports. Sign criteria were used to assess level of evidence and grades of recommendation.

RESULTS

The problems of sports-related asthma and allergy are outlined. Epidemiological evidence for an increased prevalence of asthma and BHR among competitive athletes, especially in endurance sports, is provided. The mechanisms for development of asthma and bronchial hyperresponsiveness in athletes are outlined. Criteria are given for the diagnosis of asthma and exercise induced asthma in the athlete.

CONCLUSIONS

The prevalence of asthma and bronchial hyperresponsiveness is markedly increased in athletes, especially within endurance sports. Environmental factors often contribute. Recommendations for the diagnosis of asthma in athletes are outlined.

The effect of acute simulated moderate altitude on power, performance and pacing strategies in well-trained cyclists

Athletes regularly compete at 2,000-3,000 m altitude where peak oxygen consumption (VO2peak) declines approximately 10-20%. Factors other than VO2peak including gross efficiency (GE), power output, and pacing are all important for cycling performance. It is therefore imperative to understand how all these factors and not just VO2peak are affected by acute hypobaric hypoxia to select athletes who can compete successfully at these altitudes. Ten well-trained, non-altitude-acclimatised male cyclists and triathletes completed cycling tests at four simulated altitudes (200, 1,200, 2,200, 3,200 m) in a randomised, counter-balanced order. The exercise protocol comprised 5 x 5-min submaximal efforts (50, 100, 150, 200 and 250 W) to determine submaximal VO2 and GE and, after 10-min rest, a 5-min maximal time-trial (5-minTT) to determine VO2peak and mean power output (5-minTT(power)). VO2peak declined 8.2 +/- 2.0, 13.9 +/- 2.9 and 22.5 +/- 3.8% at 1,200, 2,200 and 3,200 m compared with 200 m, respectively, P < 0.05. The corresponding decreases in 5-minTT(power) were 5.8 +/- 2.9, 10.3 +/- 4.3 and 19.8 +/- 3.5% (P < 0.05). GE during the 5-minTT was not different across the four altitudes. There was no change in submaximal VO2 at any of the simulated altitudes, however, submaximal efficiency decreased at 3,200 m compared with both 200 and 1,200 m. Despite substantially reduced power at simulated altitude, there was no difference in pacing at the four altitudes for athletes whose first trial was at 200 or 1,200 m; whereas athletes whose first trial was at 2,200 or 3,200 m tended to mis-pace that effort. In conclusion, during the 5-minTT there was a dose-response effect of hypoxia on both VO2peak and 5-minTT(power) but no effect on GE.

Pulmonary Oedema following Exercise in Humans

Pulmonary physiologists have documented many transient changes in the lung and the respiratory system during and following exercise, including the incomplete oxygen saturation of arterial blood in some subjects, possibly due to transient pulmonary oedema. The large increase in pulmonary arterial pressure during exercise, leading to either increased pulmonary capillary leakage and/or pulmonary capillary stress failure, is likely to be responsible for any increase in extravascular lung water during exercise. The purpose of this article is to summarise the studies to date that have specifically examined lung water following exercise. A limited number of studies have been completed with the specific purpose of identifying pulmonary oedema following exercise or a similar intervention. Of these, approximately 50% have observed a positive change and the remaining have provided results that are either inconclusive or show no change in extravascular lung water. While it is difficult to draw a firm conclusion from these studies, we believe that pulmonary oedema does occur in some humans following exercise. As such, this is a phenomenon of significance to pulmonary and exercise physiologists. This possibility warrants further study in the area with more precise measurement tools than has previously been undertaken.

Exercise induced arterial hypoxemia: the role of ventilation-perfusion inequality and pulmonary diffusion limitation

Many apparently healthy individuals experience pulmonary gas exchange limitations during exercise, and the term "exercise induced arterial hypoxemia" (EIAH) has been used to describe the increase in alveolar-arterial difference for oxygen (AaDO2), which combined with a minimal alveolar hyperventilatory response, results in a reduction in arterial PO2. Despite more than two decades of research, the mechanisms of pulmonary gas exchange limitations during exercise are still debated. Using data in 166 healthy normal subjects collated from several previously published studies it can be shown that approximately 20% of the variation in PaO2 between individuals can be explained on the basis of variations in alveolar ventilation, whereas variations in AaDO2 explain approximately 80%. Using multiple inert gas data the relative contributions of ventilation-perfusion ("VA/Q") inequality and diffusion limitation to the AaDO2 can be assessed. During maximal exercise, both in individuals with minimal (AaDO2 < 20 Torr, x = 13 +/- 5, means +/- SD, n = 35) and moderate to severe (AaDO2= 25-40 Torr, x = 33 +/- 6, n = 20) gas exchange limitations, VA/Q inequality is an important contributor to the AaDO2. However, in subjects with minimal gas exchange impairment, VA/Q inequality accounts for virtually all of the AaDO2 (12 +/- 6 Torr), whereas in subjects with moderate to severe gas exchange impairment it accounts for less than 50% of the AaDO2 (15 +/- 6 Torr). Using this framework, the difficulties associated with unraveling the mechanisms of pulmonary gas exchange limitations during exercise are explored, and current data discussed.

The lung at maximal exercise: insights from comparative physiology

Horses are bred selectively for aerobic performance and have extraordinarily high maximal oxygen consumption, approximately double the mass-specific value for human athletes. Pulmonary limitations to exercise performance are well described in these animals, including exercise-induced arterial hypoxemia and exercise-induced pulmonary hemorrhage. In human athletes, pulmonary limitations are recognized increasingly as affecting athletic performance. Potential pulmonary limitations during maximal exercise are compared in human and equine athletes.

Effect of hyperoxia on maximal O2 uptake in exercise-induced arterial hypoxaemic subjects

This study focuses on the effect of hyperoxia on maximal oxygen uptake VO2max and maximal power (Pmax) in subjects exhibiting exercise-induced arterial hypoxemia (EIH) at sea level. Sixteen competing male cyclists VO2max > 60 ml.min(-1).kg(-1)) performed exhaustive ramp exercise (cycle-ergometer) under normoxia and moderate hyperoxia (FIO2 = 30%). After the normoxic trial, the subjects were divided into those demonstrating EIH during exercise [arterial O2 desaturation (delta SaO2) >5%; n = 9] and those who did not (n = 7). Under hyperoxia, SaO2 raised and the increase was greater for the EIH than for the non-EIH group (P<0.001). VO2max improved for both groups and to a greater extent for EIH (12.8 +/- 5.7% vs. 4.2 +/- 4.6%, P<0.01; mean+/-SD) and the increase was correlated to the gain in SaO2 for all subjects (r = 0.71, P<0.01). Pmax improved by 3.3 +/- 3.3% (P<0.01) regardless of the group. These data suggest that pulmonary gas exchange contributes to a limitation in VO2max and power for especially EIH subjects.

Rectal temperature correction overestimates the frequency of exercise-induced hypoxemia

INTRODUCTION

Exercise-induced hypoxemia (EIH) occurs in an uncertain proportion of endurance trained athletes. Whereas blood gas measurements must be corrected for core temperature at the time of sampling, the commonly used rectal temperature readings may not be the most appropriate.

METHODS

Ten males [mean peak oxygen uptake, (.-)VO(2peak), 65.4 +/- 7.0 mL x kg x min] performed incremental treadmill exercise from rest to exhaustion with radial artery blood samples collected at the end of each 2-min workload for gas analysis. The thermogenic effect of exercise was monitored with rectal, arterial blood, and esophageal temperature probes, and the values obtained at all three sites, simultaneous with blood sampling, were used to correct the standard blood gas measurements made at 37 +/- C.

RESULTS

The mean increase in rectal temperature across exercise (1.4 +/- 0.4 +/- C) was approximately half that recorded in radial arterial blood (2.3 +/- 0.5+/- C) and the esophagus (2.4 +/- 0.5 degrees C). In consequence, the uncorrected fall in PaO2 across exercise of 15.4 +/- 8.2 mm Hg was reduced to 8.4 +/- 7.7 mm Hg when corrected for rectal temperature, and to 2.9 +/- 7.4 and 2.1 +/- 8.8 mm Hg when corrected for arterial blood and esophageal temperatures. Using a fall of > or = 10 mm Hg as the index of EIH, the proportion in the 10 subjects in the present study fell from 80% (uncorrected) through 50% (rectal correction) to 20% (arterial blood and esophageal corrections).

CONCLUSION

When correcting arterial blood gas values for the thermogenic effects of exercise, the proportion of athletes meeting the definition of EIH depends on the site of core temperature measurement.

Arterial desaturation during exercise in man: implication for O2 uptake and work capacity

Exercise-induced arterial hypoxaemia is defined as a reduction in the arterial O2 pressure (PaO2) by more than 1 kPa and/or a haemoglobin O2 saturation (SaO2) below 95%. With blood gas analyses ideally reported at the actual body temperature, desaturation is a consistent finding during maximal ergometer rowing. Arterial desaturation is most pronounced at the end of a maximal exercise bout, whereas the reduction in PaO2 is established from the onset of exercise. Exercise-induced arterial hypoxaemia is multifactorial. The ability to maintain a high alveolar O2 pressure (PAO2) is critical for blood oxygenation and this appears to be difficult in large individuals. A large lung capacity and, in turn, diffusion capacity seem to protect PaO2. A widening of the PAO2-PaO2 difference does indicate that a diffusion limitation, a ventilation-perfusion mismatch and/or a shunt influence the transport of O2 from alveoli to the pulmonary capillaries. An inspired O2 fraction of 0.30 reduces the widened PAO2-PaO2 difference by 75% and prevents a reduction of PaO2 and SaO2. With a marked increase in cardiac output, diffusion limitation combined with a fast transit time dominates the O2 transport problem. Furthermore, a postexercise reduction in pulmonary diffusion capacity suggests that the alveolo-capillary membrane is affected. An antioxidant attenuates oxidative burst by neutrophilic granulocytes, but it does not affect PaO2, SaO2 or O2 uptake (VO2), and the ventilatory response to maximal exercise also remains the same. It is proposed, though, that increased concentration of certain cytokines correlates to exercise-induced hypoxaemia as cytokines stimulate mast cells and basophilic granulocytes to degranulate histamine. The basophil count increases during maximal rowing. Equally, histamine release is associated with hypoxaemia and when the release of histamine is prevented, the reduction in PaO2 is attenuated. During maximal exercise, an extreme lactate spill-over to blood allows pH decrease to below 7.1 and according to the O2 dissociation curve this is critical for SaO2. When infusion of sodium bicarbonate maintains a stable blood buffer capacity, acidosis is attenuated and SaO2 increases from 89% to 95%. This enables exercise capacity to increase, an effect also seen when O2 supplementation to inspired air restores arterial oxygenation. In that case, exercise capacity increases less than can be explained by VO2 and CaO2. Furthermore, the change in muscle oxygenation during maximal exercise is not affected when hyperoxia and sodium bicarbonate attenuate desaturation. It is proposed that other organs benefit from enhanced O2 availability, and especially the brain appears to increase its oxygenation during maximal exercise with hyperoxia.

Pulmonary disorders and exercise

The respiratory system rarely limits exercise in the normal subject. In patients with chronic pulmonary processes or in the elite athlete, however, the respiratory system may indeed be the limiting factor. Common respiratory disorders include chest pain syndromes, cough, exercise-induced asthma, and vocal cord dysfunction. Chronic lung diseases such as asthma, COPD, and interstitial lung disease impact exercise capacity and endurance. Exercise testing can be useful to distinguish acute and chronic pulmonary causes of dyspnea during exercise, as well as to differentiate between cardiac and pulmonary causes.

Early onset of pulmonary gas exchange disturbance during progressive exercise in healthy active men

Some recent studies of competitive athletes have shown exercise-induced hypoxemia to begin in submaximal exercise. We examined the role of ventilatory factors in the submaximal exercise gas exchange disturbance (GED) of healthy men involved in regular work-related exercise but not in competitive activities. From the 38 national mountain rescue workers evaluated (36 +/- 1 yr), 14 were classified as GED and were compared with 14 subjects matched for age, height, weight, and maximal oxygen uptake (VO2 max; 3.61 +/- 0.12 l/min) and showing a normal response (N). Mean arterial PO2 was already lower than N (P = 0.05) at 40% VO2 max and continued to fall until VO2 max (GED: 80.2 +/- 1.6 vs. N: 91.7 +/- 1.3 Torr). A parallel upward shift in the alveolar-arterial oxygen difference vs. %VO2 max relationship was observed in GED compared with N from the onset throughout the incremental protocol. At submaximal intensities, ideal alveolar PO2, tidal volume, respiratory frequency, and dead space-to-tidal volume ratio were identical between groups. As per the higher arterial PCO2 of GED at VO2 max, subjects with an exaggerated submaximal alveolar-arterial oxygen difference also showed a relative maximal hypoventilation. Results thus suggest the existence of a common denominator that contributes to the GED of submaximal exercise and affects the maximal ventilatory response.

Modelling human locomotion: applications to cycling

Mathematical models of performance in locomotor sports are reducible to functions of the sort y = f(x) where y is some performance variable, such as time, distance or speed, and x is a combination of predictor variables which may include expressions for power (or energy) supply and/or demand. The most valid and useful models are first-principles models that equate expressions for power supply and power demand. Power demand in cycling is the sum of the power required to overcome air resistance and rolling resistance, the power required to change the kinetic energy of the system, and the power required to ride up or down a grade. Power supply is drawn from aerobic and anaerobic sources, and modellers must consider not only the rate but also the kinetics and pattern of power supply. The relative contributions of air resistance to total demand, and of aerobic energy to total supply, increase curvilinearly with performance time, while the importance of other factors decreases. Factors such as crosswinds, aerodynamic accessories and drafting can modify the power demand in cycling, while body configuration/orientation and altitude will affect both power demand and power supply, often in opposite directions. Mathematical models have been used to solve specific problems in cycling, such as the chance of success of a breakaway, the optimal altitude for performance, creating a 'level playing field' to compare performances for selection purposes, and to quantify, in the common currency of minutes and seconds, the effects on performance of changes in physiological, environmental and equipment variables. The development of crank dynamometers and portable gas-analysis systems, combined with a modelling approach, will in the future provide valuable information on the effect of changes in equipment, configuration and environment on both supply and demand-side variables.

Effects of exhaustive endurance exercise on pulmonary gas exchange and airway function in women

Seventeen fit women ran to exhaustion (14 +/- 4 min) at a constant speed and grade, reaching 95 +/- 3% of maximal O(2) consumption. Pre- and postexercise lung function, including airway resistance [total respiratory resistance (Rrs)] across a range of oscillation frequencies, was measured, and, on a separate day, airway reactivity was assessed via methacholine challenge. Arterial O(2) saturation decreased from 97.6 +/- 0.5% at rest to 95.1 +/- 1.9% at 1 min and to 92.5 +/- 2.6% at exhaustion. Alveolar-arterial O(2) difference (A-aDO(2)) widened to 27 +/- 7 Torr after 1 min and was maintained at this level until exhaustion. Arterial PO(2) (Pa(O(2))) fell to 80 +/- 8 Torr at 1 min and then increased to 86 +/- 9 Torr at exhaustion. This increase in Pa(O(2)) over the exercise duration occurred due to a hyperventilation-induced increase in alveolar PO(2) in the presence of a constant A-aDO(2). Arterial O(2) saturation fell with time because of increasing temperature (+2.6 +/- 0.5 degrees C) and progressive metabolic acidosis (arterial pH: 7.39 +/- 0.04 at 1 min to 7.26 +/- 0.07 at exhaustion). Plasma histamine increased throughout exercise but was inversely correlated with the fall in Pa(O(2)) at end exercise. Neither pre- nor postexercise Rrs, frequency dependence of Rrs, nor diffusing capacity for CO correlated with the exercise A-aDO(2) or Pa(O(2)). Although several subjects had a positive or borderline hyperresponsiveness to methacholine, this reactivity did not correlate with exercise-induced changes in Rrs or exercise-induced arterial hypoxemia. In conclusion, regardless of the degree of exercise-induced arterial hypoxemia at the onset of high-intensity exercise, prolonging exercise to exhaustion had no further deleterious effects on A-aDO(2), and the degree of gas exchange impairment was not related to individual differences in small or large airway function or reactivity.

Influence of inhaled nitric oxide on gas exchange during normoxic and hypoxic exercise in highly trained cyclists

This study tested the effects of inhaled nitric oxide [NO; 20 parts per million (ppm)] during normoxic and hypoxic (fraction of inspired O(2) = 14%) exercise on gas exchange in athletes with exercise-induced hypoxemia. Trained male cyclists (n = 7) performed two cycle tests to exhaustion to determine maximal O(2) consumption (VO(2 max)) and arterial oxyhemoglobin saturation (Sa(O(2)), Ohmeda Biox ear oximeter) under normoxic (VO(2 max) = 4.88 +/- 0.43 l/min and Sa(O(2)) = 90.2 +/- 0.9, means +/- SD) and hypoxic (VO(2 max) = 4.24 +/- 0.49 l/min and Sa(O(2)) = 75.5 +/- 4.5) conditions. On a third occasion, subjects performed four 5-min cycle tests, each separated by 1 h at their respective VO(2 max), under randomly assigned conditions: normoxia (N), normoxia + NO (N/NO), hypoxia (H), and hypoxia + NO (H/NO). Gas exchange, heart rate, and metabolic parameters were determined during each condition. Arterial blood was drawn at rest and at each minute of the 5-min test. Arterial PO(2) (Pa(O(2))), arterial PCO(2), and Sa(O(2)) were determined, and the alveolar-arterial difference for PO(2) (A-aDO(2)) was calculated. Measurements of Pa(O(2)) and Sa(O(2)) were significantly lower and A-aDO(2) was widened during exercise compared with rest for all conditions (P < 0.05). No significant differences were detected between N and N/NO or between H and H/NO for Pa(O(2)), Sa(O(2)) and A-aDO(2) (P > 0.05). We conclude that inhalation of 20 ppm NO during normoxic and hypoxic exercise has no effect on gas exchange in highly trained cyclists.

Arterial hypoxaemia in endurance athletes is greater during running than cycling

The effect of both training discipline and exercise modality on exercise-induced hypoxaemia (EIH) was examined in seven runners and six cyclists during 5 min high intensity treadmill and cycle exercise. There were no significant interactions between training discipline, exercise modality and arterial P(O(2)) (Pa(O(2))) when subject groups were considered separately but when pooled there were significant differences between exercise modalities. After min 2 of exercise arterial hydrogen ion concentration, minute ventilation, alveolar P(O(2)) (PA(O(2))) and Pa(O(2)) were all lower with treadmill running with the largest differential for the latter occurring at min 5 (treadmill, 80.8+/-1.8; cycle, 90.2+/-2.5, mmHg, N=13, P< or = 0.05). At every min of exercise, the differences in Pa(O(2)) between the ergometers were strongly associated with similar differences in PA(O(2)) and alveolar to arterial P(O(2)) (PA(O(2))-Pa(O(2))). It is concluded that the greater EIH with treadmill running is a consequence of the combined effect of a reduced lactic acidosis-induced hyperventilation and greater ventilation-perfusion inequality with this exercise mode.

Expiratory flow limitation confounds ventilatory response during exercise in athletes

INTRODUCTION

A significant number of highly trained endurance runners have been observed to display an inadequate hyperventilatory response to intense exercise. Two potential mechanisms include low ventilatory responsiveness to hypoxia and ventilatory limitation as a result of maximum expiratory flow rates being achieved.

PURPOSE

To test the hypothesis that expiratory flow limitation can complicate determination of ventilatory responsiveness during exercise the following study was performed.

METHODS/MATERIALS

Sixteen elite male runners were categorized based on expiratory flow limitation observed in flow volume loops collected during the final minute of progressive exercise to exhaustion. Eight flow limited (FL) (VO2max, 75.9+/-2.4 mL x kg(-1) x min(-1); expiratory flow limitation, 47.3+/-20.4%) and eight non-flow limited subjects (NFL) (VO2max, 75.6+/-4.8 mL x kg(-1) x min(-1); expiratory flow limitation, 0.3+/-0.8%) were tested for hypoxic ventilatory responsiveness (HVR).

RESULTS

Independent groups ANOVA revealed no significant differences between FL and NFL for VO2max, VE max (136.2+/-16.0 vs 137.5+/-21.6 L x min(-1)), VE/VO2, (28.4+/-3.2 vs 27.6+/-2.9 L x lO2(-1)), VE/VCO2 (24.8+/-3.1 vs 24.4+/-2.0 L x lCO2(-1)), HVR (0.2+/-0.2 vs 0.3+/-0.1 L x %SaO2(-1)), or SaO2 at max (89.1+/-2.4 vs 86.6+/-4.1%). A significant relationship was observed between HVR and SaO2 (r = 0.92, P < or = 0.001) in NFL that was not present in FL. Conversely, a significant relationship between VE/VO2 and SaO2 (r = 0.79, P < or = 0.019) was observed in FL but not NFL. Regression analysis indicated that the HVR-SaO2 and SaO2-VE/VO2 relationships differed between groups.

DISCUSSION

When flow limitation is controlled for, HVR plays a more significant role in determining SaO2 in highly trained athletes than has been previously suggested.

Exercise-induced arterial hypoxaemia in athletes: a review

During exercise, healthy individuals are able to maintain arterial oxygenation, whereas highly-trained endurance athletes may exhibit an exercise-induced arterial hypoxaemia (EIAH) that seems to reflect a gas exchange abnormality. The effects of EIAH are currently debated, and different hypotheses have been proposed to explain its pathophysiology. For moderate exercise, it appears that a relative hypoventilation induced by endurance training is involved. For high-intensity exercise, ventilation/perfusion (V(A)/Q) mismatching and/or diffusion limitation are thought to occur. The causes of this diffusion limitation are still under debate, with hypotheses being capillary blood volume changes and interstitial pulmonary oedema. Moreover, histamine is released during exercise in individuals exhibiting EIAH, and questions persist as to its relationship with EIAH and its contribution to interstitial pulmonary oedema. Further investigations are needed to better understand the mechanisms involved and to determine the long term consequences of repetitive hypoxaemia in highly trained endurance athletes.

Evidence for an inadequate hyperventilation inducing arterial hypoxemia at submaximal exercise in all highly trained endurance athletes

PURPOSE

The majority of highly trained endurance athletes with a maximal oxygen uptake greater than 60 mL x min(-1) x kg(-1) develop exercise-induced hypoxemia (EIH). Yet some of them apparently do not. The pathophysiology of EIH seems to be multifactorial, and one explanatory hypothesis is a relative hypoventilation. Nevertheless, conflicting results have been reported concerning its contribution to EIH. The aim of this study was to compare the cardiorespiratory responses to maximal exercise of highly trained endurance athletes demonstrating the same aerobic capacity without EIH (N athletes) and with EIH (H athletes).

METHODS

Ten N athletes and twelve H athletes performed an incremental exercise test. Measurements of arterial blood gases and cardiorespiratory parameters were performed at rest and during exercise.

RESULTS

All athletes presented a significant decrease in PaO2 (P < 0.05) from rest up to 80% VO2max associated with an increase in PaCO2, both findings consistent with a relative hypoventilation. Then the H athletes, who had a greater training volume per week and a higher second ventilatory threshold than the N athletes (respectively, 17 +/- 1.1 vs 13.1 +/- 0.7 h x wk(-1); 91.8 +/- 1.7 vs 86.1 +/- 1.8% VO2max), presented a continuous PaO2 decrease up to VO2max. This was associated with a widening (Ai-a)DO2.

CONCLUSION

This study showed that a relative hypoventilation, probably induced by a high level of endurance training, induced hypoxemia in all athletes. However, a nonventilatory mechanism, perhaps related to the volume of training, seemed to affect gas exchanges beyond the second ventilatory threshold in the H athletes, thereby enhancing EIH.

Exercise-induced arterial hypoxemia

Exercise-induced arterial hypoxemia (EIAH) at or near sea level is now recognized to occur in a significant number of fit, healthy subjects of both genders and of varying ages. Our review aims to define EIAH and to critically analyze what we currently understand, and do not understand, about its underlying mechanisms and its consequences to exercise performance. Based on the effects on maximal O(2) uptake of preventing EIAH, we suggest that mild EIAH be defined as an arterial O(2) saturation of 93-95% (or 3-4% <rest), moderate EIAH as 88-93%, and severe EIAH as <88%. Both an excessive alveolar-to-arterial PO(2) difference (A-a DO(2)) (>25-30 Torr) and inadequate compensatory hyperventilation (arterial PCO(2) >35 Torr) commonly contribute to EIAH, as do acid- and temperature-induced shifts in O(2) dissociation at any given arterial PO(2). In turn, expiratory flow limitation presents a significant mechanical constraint to exercise hyperpnea, whereas ventilation-perfusion ratio maldistribution and diffusion limitation contribute about equally to the excessive A-a DO(2). Exactly how diffusion limitation is incurred or how ventilation-perfusion ratio becomes maldistributed with heavy exercise remains unknown and controversial. Hypotheses linked to extravascular lung water accumulation or inflammatory changes in the "silent" zone of the lung's peripheral airways are in the early stages of exploration. Indirect evidence suggests that an inadequate hyperventilatory response is attributable to feedback inhibition triggered by mechanical constraints and/or reduced sensitivity to existing stimuli; but these mechanisms cannot be verified without a sensitive measure of central neural respiratory motor output. Finally, EIAH has detrimental effects on maximal O(2) uptake, but we have not yet determined the cause or even precisely identified which organ system, involved directly or indirectly with O(2) transport to muscle, is responsible for this limitation.

The effect of exercise modality on exercise-induced hypoxemia

To investigate the effect of exercise mode on arterial oxyhemoglobin saturation (SaO2), 13 healthy, actively training men who displayed exercise-induced hypoxemia (EIH) performed two incremental maximal exercise tests: uphill treadmill running and cycle ergometry. At maximum, treadmill running resulted in a lower SaO2 (88.6+/-2% versus 92.6+/-2.0%) a lower ventilatory equivalent for carbon dioxide (VE/VCO2; 28.8+/-0.6 versus 31.2+/-0.9), and a higher maximal oxygen consumption (VO2, MAX; 4.83+/-0.11 l x min(-1) versus 4.61+/-0.14 l x min(-1) when compared to cycle ergometry. When data were combined from maximal running and cycling. SaO2 was correlated to VE/VCO2 (r = 0.54). However, there was no relationship between the differences in SaO2 and ventilation between exercise modes. This suggests that ventilation is important in the maintenance of SaO2, but that the difference observed in SaO2 between treadmill running and cycle ergometry cannot be explained by differences in ventilation and must be due to differences in diffusion limitation or ventilation-perfusion inequality.

Effects of prior exercise on exercise-induced arterial hypoxemia in young women

Twenty-eight healthy women (ages 27.2 +/- 6.4 yr) with widely varying fitness levels [maximal O2 consumption (VO2 max), 31-70 ml . kg-1 . min-1] first completed a progressive incremental treadmill test to VO2 max (total duration, 13.3 +/- 1.4 min; 97 +/- 37 s at maximal workload), rested for 20 min, and then completed a constant-load treadmill test at maximal workload (total duration, 143 +/- 31 s). At the termination of the progressive test, 6 subjects had maintained arterial PO2 (PaO2) near resting levels, whereas 22 subjects showed a >10 Torr decrease in PaO2 [78.0 +/- 7.2 Torr, arterial O2 saturation (SaO2), 91.6 +/- 2.4%], and alveolar-arterial O2 difference (A-aDO2, 39.2 +/- 7.4 Torr). During the subsequent constant-load test, all subjects, regardless of their degree of exercise-induced arterial hypoxemia (EIAH) during the progressive test, showed a nearly identical effect of a narrowed A-aDO2 (-4.8 +/- 3.8 Torr) and an increase in PaO2 (+5.9 +/- 4.3 Torr) and SaO2 (+1.6 +/- 1.7%) compared with at the end point of the progressive test. Therefore, EIAH during maximal exercise was lessened, not enhanced, by prior exercise, consistent with the hypothesis that EIAH is not caused by a mechanism which persists after the initial exercise period and is aggravated by subsequent exercise, as might be expected of exercise-induced structural alterations at the alveolar-capillary interface. Rather, these findings in habitually active young women point to a functionally based mechanism for EIAH that is present only during the exercise period.

Exercise-induced arterial hypoxaemia in healthy young women

1. We questioned whether exercise-induced arterial hypoxaemia (EIAH) occurs in healthy active women, who have smaller lungs, reduced lung diffusion, and lower maximal O2 consumption rate (VO2,max) than age- and height-matched men. 2. Twenty-nine healthy young women with widely varying fitness levels (VO2,max, 57 +/- 6 ml kg-1 min-1; range, 35-70 ml kg-1 min-1; or 148 +/- 5%; range, 93-188% predicted) and normal resting lung function underwent an incremental treadmill test to VO2,max during the follicular phase of their menstrual cycle. Arterial blood samples were taken at rest and near the end of each workload. 3. Arterial PO2 (Pa,O2) decreased > 10 mmHg below rest in twenty-two of twenty-nine subjects at VO2,max (Pa,O2, 77.5 +/- 0.9 mmHg; range, 67-88 mmHg; arterial O2 saturation (Sa,O2), 92.3 +/- 0.2%; range, 87-94%). The remaining seven subjects maintained Pa,O2 within 10 mmHg of rest. Pa,O2 at VO2,max was inversely related to the alveolar to arterial O2 difference (A-aDO2) (r = -0.93; 35-52 mmHg) and to arterial PCO2 (Pa,CO2) (r = -0.62; 26-39 mmHg). 4. EIAH was inversely related to VO2,max (r = -0.49); however, there were many exceptions. Almost half of the women with significant EIAH had VO2,max within 15% of predicted normal values (VO2,max, 40-55 ml kg-1 min-1); among subjects with very high VO2,max (55-70 ml kg-1 min-1), the degree of excessive A-aDO2 and EIAH varied markedly (e.g. A-aDO2, 30-50 mmHg; Pa,O2, 68-91 mmHg). 5. In the women with EIAH at VO2,max, many began to experience an excessive widening of their A-aDO2 during moderate intensity exercise, which when combined with a weak ventilatory response, led to a progressive hypoxaemia. Inactive, less fit subjects had no EIAH and narrower A-aDO2 when compared with active, fitter subjects at the same VO2 (40-50 ml kg-1 min-1). 6. These data demonstrate that many active healthy young women experience significant EIAH, and at a VO2,max that is substantially less than those in their active male contemporaries. The onset of EIAH during submaximal exercise, and/or its occurrence at a relatively low VO2,max, implies that lung structure/function subserving alveolar to arterial O2 transport is abnormally compromised in many of these habitually active subjects.

Inhibition of histamine release by nedocromil sodium reduces exercise-induced hypoxemia in master athletes

During exercise in highly-trained older master athletes (MA), the impairment of pulmonary gas exchanges has been shown to be associated with a concomitant increase in histamine release (2). To determine the role of the histamine released (% H) during exercise-induced hypoxemia, seven MA (age 63.2 yr +/- 1.9), all of whom were known to develop exercise-induced hypoxemia, performed two maximal incremental exercise tests at a one-month interval after administration of nedocromil sodium (which inhibits histamine and other mediator release) or placebo in random double-blind order. During exercise testing, blood samples for arterial blood gas analysis and histamine assay were drawn at rest, exercise and recovery. Nedocromil sodium induced an inhibition in % H (0.57 +/- 0.03 at maximal load (Pmax) with placebo vs 0.24 +/- 0.02 with nedocromil sodium) linked with an improvement of pulmonary gas exchange (PaO2: 71.1 +/- 1.4 at Pmax with placebo vs 83.4 +/- 3 with nedocromil sodium; D(Ai-a)O2: 37.5 +/- 1.4 at Pmax vs 19.1 +/- 3.1, respectively). These results confirm the link established between the increase in histamine and exercise-induced hypoxemia in master athletes.

The relationship between test protocol and the development of exercise-induced hypoxemia (EIH) in highly trained athletes

Healthy male endurance-trained cyclists [n = 11, age = 27.3 (3.9) years; mass = 73.0 (9.3) kg; height = 180.5 (6.9) cm; maximal oxygen consumption (VO2max) = 71.1 (5.8) ml.kg-1.min-1, mean +/- (SD)] were recruited to assess the relationship between test protocol and the development of desaturation of arterial hemoglobin with oxygen, during incremental exercise tests to maximal aerobic capacity (VO2max). All subjects demonstrated resting pulmonary function within normal limits [forced vital capacity (FVC) = 6.0 (0.9); forced expiratory volume (FEV1.0) = 4.9 (0.6); FEV1.0/FVC = 0.8 (0.1)] and completed three ramped VO2max tests (Mijnhardt KEM-3 electronically braked cycle ergometer) beginning at 0 W with increments of either 20,30 or 40 W.min-1. All periods of testing were separated by a minimum of 72 h. VO2max, peak minute ventilation (VEpeak) (Medical Graphics, CPX-D), peak heart rate (fcpeak), peak power output (Wpeak), and minimum percentage arterial oxyhemoglobin saturation (% SaO2min) (Omeda Biox 3740 pulse oximeter) were determined. There were no significant differences (p > 0.05) in VEpeak [191.5 (26.2), 196.0 (24.4), 194.3 (23.9) l.min-1] fcpeak [191.4 (7.0), 190.3 (5.5), 187.8 (5.9) beats.min-1], VO2max [5.0 (0.5), 5.1 (0.4), 5.1 (0.5) l.min-1] or %SaO2min [89.5 (1.5), 89.6 (1.3), 90.0 (2.3)] between protocols. The 20-W protocol [417 (27) W] demonstrated significantly lower Wpeak (P < 0.05) than the 30-W [434 (36) W] and 40-W [453 (38) W] protocols, indicating that peripheral fatigue may play an important factor in response to these tests. The results of this study demonstrate that arterial desaturation occurs as a result of intense exercise in highly trained athletes independent of the rate of attainment of VO2max.

Augmented hyperventilation via normoxic helium breathing does not prevent exercise-induced hypoxemia

The purpose of this study was to determine if augmented hyperventilation produced via normoxic helium breathing would reduce exercise-induced hypoxemia (EIH). Seven highly trained endurance athletes with a mean maximum oxygen uptake of 65 ml.kg-1.min-1, performed two cycle ergometer tests to volitional exhaustion. During one of the tests the subjects breathed ambient air, while during the other they breathed normoxic helium (21% O2, 79% He). Mean maximum expired ventilation significantly (p < .05) increased from 139 L.min-1 during the ambient trial to 168 L.min-1 while breathing normoxic helium. Mean arterial oxygen saturation obtained at maximum exercise, however, was not significantly different for the two trials (ambient = 90%, helium = 89%). These results suggest that significantly augmenting exercise hyperventilation by 21% essentially had no effect on EIH in endurance athletes. Thus, the data do not support the hypothesis that inadequate hyperventilation is an important mechanism for arterial oxygen desaturation during graded exercise to exhaustion in highly trained individuals.

[Hypoxemia and exhaustion time to maximal aerobic speed in long-distance runners]

A recent paper (Billat et al., 1994a) has shown the reproducibility but also the great variability between subelite long-distance runners in their time to exhaustion at the velocity which elicits VO2max, called the maximal aerobic speed (MAS). The present study delved further into the reasons for this large difference between runners having the same VO2max. The question addressed was whether the exercise-induced hypoxemia (EIH) was more important for athletes having the longest time to exhaustion at 90 (Tlim 90), 100 (Tlim 100), or 105% (Tlim 105) of MAS. The study was conducted on 16 elite male runners. EIH was observed, that is, arterial oxyhemoglobin saturation and arterial partial pressure of oxygen dropped significantly after all the Tlim tests. However, EIH was only correlated with Tlim 90 (r = -0.757; -0.531, respectively).

Exercise stimulus increases ventilation from maximal to supramaximal intensity

This study investigated the influence of an exercise stimulus on pulmonary ventilation (VE) during severe levels of exercise in a group of ten athletes. The altered ventilation was assessed in relation to its effect on blood gas status, in particular to the incidence and severity of exercise induced hypoxaemia. Direct measurements of arterial blood were made at rest and during the last 15 s of two intense periods of cycling; once at an intensity found to elicit maximal oxygen uptake (VO2max; MAX) and once at an intensity established to require 115% of VO2max (SMAX). Oxygen uptake (VO2) and ventilatory markers were continually recorded during the exercise and respiratory flow-volume loops were measured at rest and during the final 30 s of each minute for both exercise intensities. When compared to MAX exercise, the subjects had higher ventilation and partial pressure of arterial oxygen (PaO2) during the SMAX intensity. Regression analysis for both conditions indicated the levels of PaO2 and oxygen saturation of arterial blood (SaO2) were positively correlated with relative levels of ventilation during exercise. It was apparent that mechanical constraints to ventilate further were not present during the MAX test since the subjects were able to elevate VE during SMAX and attenuate the level of hypoxaemia. This was also confirmed by analysis of the flow volume recordings. These data support the conclusions firstly, that overwhelming mechanical constraints on VE were not present during the MAX exercise, secondly, the subjects exhibiting the most severe hypoxaemia had no consistent relationship with any measure of expiratory flow limitation, and thirdly, ventilatory patterns during intense exercise are strong predictors of blood gas status.