Craig A. Harms

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 (V̇O2,max) than age‐ and height‐matched men. 2 Twenty‐nine healthy young women with widely varying fitness levels (V̇O2,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 V̇O2,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 V̇O2,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 V̇O2,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 V̇O2,max, implies that lung structure/function subserving alveolar to arterial O2 transport is abnormally compromised in many of these habitually active subjects.

Does gender affect pulmonary function and exercise capacity

It is well established that women exhibit several anatomic and physiologic characteristics that distinguish their responses to exercise from those of men. These factors have been shown to influence the training response and contribute to lower maximal aerobic power in women. Additionally, the reproductive hormones, estrogen and progesterone, can influence ventilation, substrate metabolism, thermoregulation, and pulmonary function during exercise. Pulmonary structural and morphologic differences between genders include smaller vital capacity and maximal expiratory flow rates, reduced airway diameter, and a smaller diffusion surface than age- and height-matched men. These differences may have an effect on the integrated ventilatory response, respiratory muscle work, and in pulmonary gas exchange during exercise. Specifically, recent evidence suggests that during heavy exercise, women demonstrate greater expiratory flow limitation, an increased work of breathing, and perhaps greater exercise induced arterial hypoxemia compared to men. The consequence of these pulmonary effects has the potential to adversely affect aerobic capacity and exercise tolerance in women.

Effects of inspiratory muscle training on exercise responses in normoxia and hypoxia

The purpose of this study was to determine the effects of inspiratory muscle training (IMT) on exercise in hypoxia (H) and normoxia (N). A 4-week IMT program was implemented with 12 healthy subjects using an inspiratory muscle trainer set at either 15% (C; n=5) or 50% (IMT; n=7) maximal inspiratory mouth pressure (PImax). Two treadmill tests (85% VO2max) to exhaustion and measures of diaphragm thickness (Tdi) and function were completed before and after training in H and N. Significant increases of 8-12% and 24.5+/-3.1% in Tdi and PImax, respectively, were seen in the IMT group. Time to exhaustion remained unchanged in all conditions. Inspiratory muscle fatigue (downward arrowPImax) following exercise was reduced approximately 10% (P<0.05) in IMT after both N and H. During H, IMT reduced (P<0.05) VO2 by 8-12%, cardiac output by 14+/-2%, ventilation by 25+/-3%; and increased arterial oxygen saturation by 4+/-1% and lung diffusing capacity by 22+/-3%. Ratings of perceived exertion and dyspnea were also significantly reduced. These data suggest that IMT significantly improves structural and functional physiologic measures in hypoxic exercise.

Effect of exercise-induced arterial O2 desaturation on VO2max in women

PURPOSE We have recently reported that many healthy habitually active women experience exercise induced arterial hypoxemia (EIAH). We questioned whether EIAH affected VO2max in this population and whether the effect was similar to that reported in men. METHODS Twenty-five healthy young women with widely varying fitness levels (VO2max, 56.7 +/- 1.5 mL x kg(-1) x min(-1); range: 41-70 mL x kg(-1) x min(-1)) and normal resting lung function performed two randomized incremental treadmill tests to VO2max (FIO2: 0.21 or 0.26) during the follicular phase of their menstrual cycle. Arterial blood samples were taken at rest and near the end of each workload during the normoxic test. RESULTS During room air breathing at VO2max, SaO2 decreased to 91.8 +/- 0.4% (range 87-95%). With 0.26 FIO2, SaO2, at VO2max remained near resting levels and averaged 96.8 +/- 0.1% (range 96-98%). When arterial O2 desaturation was prevented via increased FIO2, VO2max increased in 22 of the 25 subjects and in proportion to the degree of arterial O2 desaturation experienced in normoxia (r = 0.88). The improvement in VO2max when systemic normoxia was maintained averaged 6.3 +/- 0.3% (range 0 to +15%) and the slope of the relationship was approximately 2% increase in VO2max for every 1% decrement in the arterial oxygen saturation below resting values. About 75% of the increase in VO2max resulted from an increase in VO2 at a fixed maximal work rate and exercise duration, and the remainder resulted from an increase in maximal work rate. CONCLUSIONS These data demonstrate that even small amounts of EIAH (i.e., >3% delta SaO2 below rest) have a significant detrimental effect on VO2max in habitually active women with a wide range of VO2max. In combination with our previous findings documenting EIAH in females, we propose that inadequate pulmonary structure/function in many habitually active women serves as a primary limiting factor in maximal O2 transport and utilization during maximal exercise.

Gender and pulmonary gas exchange during exercise.

HOPKINS, S. R., and C. A. HARMS. Gender and pulmonary gas exchange during exercise. Exerc. Sport Sci. Rev., Vol. 32, No. 2, pp. 50–56, 2004. Relative to body size, women have a lower diffusing capacity for carbon monoxide, smaller airway diameter, and smaller lung volumes than men. The effect that these differences have on gas exchange during exercise is incompletely understood. Women may have a larger alveolar-arterial PO2difference that may be compensated for, in part, by increased alveolar ventilation.

Clothing fabric does not affect thermoregulation during exercise in moderate heat.

PURPOSE We investigated whether temperature regulation is improved during exercise in moderate heat by the use of clothing constructed from fabric that was purported to promote sweat evaporation compared with traditional fabrics. METHODS Eight well-trained, euhydrated males performed three exercise bouts wearing garments made from an evaporative polyester fabric (SYN), wearing garments made from traditional cotton fabric (COT), or dressed seminude (S-N) in random order. Bouts consisted of 15 min seated rest, 30 min running at 70% .VO(2max), 15 min walking at 40% .VO(2max), and 15 min seated rest, all at 30 +/- 1 degrees C and 35 +/- 5% relative humidity. COT and SYN clothing ensembles consisted of crew neck, short sleeve T-shirts, cycling shorts, and anklet socks made from their respective materials, and running shoes. The S-N condition consisted of a Lycra swim suit, polyester socks, and running shoes. RESULTS Mean skin temperature was lower for S-N during preexercise rest when compared with SYN and COT. No differences in mean body temperature, rectal temperature, or mean skin temperature were observed during or after exercise. No differences in VO2 or heart rate were observed. No differences in comfort sensations were observed. CONCLUSION In summary, before, during, or after exercise in a moderately warm environmental condition, neither the addition of a modest amount of clothing nor the fabric characteristics of this clothing alters physiological, thermoregulatory, or comfort sensation responses.

Mood, neuromuscular function, and performance during training in female swimmers.

The effect of seasonal changes in training load on mood, neuromuscular function, and measures of physical power were examined in 12 collegiate women swimmers. These subjects were studied at three training stages during a competitive swim season: baseline (5,000 m.d-1), peak training (8,300 m.d-1), and taper (2,300 m.d-1). Mood was evaluated with the Profile of Mood States. Neuromuscular function was measured via the soleus Hoffmann-reflex (H-reflex). Anaerobic swimming power was assessed with a 30-s tethered swim test, and maximal aerobic power was determined following a maximal 378-m swim. Repeated measures ANOVA revealed that at peak training H-reflex and peak anaerobic swimming power were reduced (P < 0.05) below baseline values by 8.6% and 9.4%, respectively, and total mood disturbance was elevated above baseline (P < 0.01). These variables returned to baseline values at the taper assessment. H-reflex values were correlated with peak (r = 0.52, P < 0.01) and mean (r = 0.39, P < 0.05) anaerobic swimming power. Total mood disturbance was correlated (r = -0.34, P < 0.05) with mean swimming power. The results suggest that neurological mechanisms play a role in the adaptations that result from periodized training.

Does Moderate Intensity Exercise Attenuate the Postprandial Lipemic and Airway Inflammatory Response to a High-Fat Meal?

We investigated whether an acute bout of moderate intensity exercise in the postprandial period attenuates the triglyceride and airway inflammatory response to a high-fat meal (HFM) compared to remaining inactive in the postprandial period. Seventeen (11 M/6 F) physically active (≥150 min/week of moderate-vigorous physical activity (MVPA)) subjects were randomly assigned to an exercise (EX; 60% VO2peak) or sedentary (CON) condition after a HFM (10 kcal/kg, 63% fat). Blood analytes and airway inflammation via exhaled nitric oxide (eNO) were measured at baseline, and 2 and 4 hours after HFM. Airway inflammation was assessed with induced sputum and cell differentials at baseline and 4 hours after HFM. Triglycerides doubled in the postprandial period (~113 ± 18%, P < 0.05), but the increase did not differ between EX and CON. Percentage of neutrophils was increased 4 hours after HFM (~17%), but the increase did not differ between EX and CON. Exhaled nitric oxide changed nonlinearly from baseline to 2 and 4 hours after HFM (P < 0.05,  η 2 = 0.36). Our findings suggest that, in active individuals, an acute bout of moderate intensity exercise does not attenuate the triglyceride or airway inflammatory response to a high-fat meal.

Respiratory muscle perfusion and energetics during exercise

The oxygen cost of breathing and blood flow requirements of the respiratory muscles during exercise are discussed along with the implications for limitation of locomotor muscle and exercise performance. Findings show that the oxygen cost of the hyperpnea achieved during very heavy exercise may approach 15% or more of VO2max under conditions that require extraordinary levels of ventilatory work. These conditions include those in the highly trained endurance athlete (at VE > 150 l.min-1), the older athlete at VE of 110-120 l.min-1), and athletic cursorial mammals at VO2max--all of whom experience significant expiratory flow limitation and sometimes even complete ventilatory limitation during heavy or maximum exercise. Rates of blood flow to the respiratory muscles under these peak exercise conditions may equal or exceed those to the limb locomotor muscles. The hypothesis is advanced that excessive requirements of ventilatory work (and therefore VO2 and blood flow) during heavy exercise may cause reflex vasoconstriction of locomotor muscles resulting in curtailment of endurance exercise performance.

Effects of N-acetylcysteine on respiratory muscle fatigue during heavy exercise.

Respiratory muscle fatigue (RMF) occurs during heavy exercise in humans. N-acetylcysteine (NAC) infusion has been shown to reduce RMF, suggesting that oxidative stress is a contributing factor. The purpose of the present study was to determine the effect of an acute oral dose of NAC on RMF during heavy exercise. Subjects (n=8) were given either placebo (PLA) or NAC (1,800 mg) 45 min prior to a 30 min constant load (85V(O)(2peak)), discontinuous exercise test. Maximum respiratory pressures (inspiratory, PI(max); expiratory, PE(max)) and venous blood samples were made prior to and following each 5 min of exercise. There was no difference (p>0.05) in PI(max) between NAC (127.9+/-34.1 cm H(2)O) or PLA (134.1+/-28.1cm H(2)O) at rest. During exercise, PI(max) was significantly lower with PLA ( approximately 14%) compared to NAC at 25 and 30 min suggesting less RMF with NAC. There were no differences (p>0.05) between groups in PE(max), V(O)(2), V(E), or heart rate at rest or throughout exercise. These results suggest that an acute dose of NAC reduces RMF during heavy exercise.