Table 1 Trials on vitamin C and EIB

Schachter & Schlesinger [56]

Selection:

12 subjects with asthma, selected from among employees of Yale University in the USA: “all 12 subjects gave a characteristic description of EIB.” All included participants had at least 20% reduction in FEF₆₀ or FEF_60(P) after exercise.

Sex, age:

5 Males, 7 Females; mean age 26 yr (SD 5 yr).

Exercise test:

All subjects performed the exercise studies on a cycloergometer. Cardiac frequency was measured with an electrocardiograph. Baseline heart rate was obtained and exercise was begun at a constant speed of 20 km/h against zero workload. At the end of each one min interval cardiac frequency was measured and the workload was increased by 150 kilopondmeters per min, keeping pedalling speed constant throughout the experiment. Exercise against progressively larger workloads was continued until either the heart rate reached 170 beats per min or the subject fatigued. Pulmonary function was assessed post-exercise at 0 and 5 min.

Cohen et al. [57]

Selection:

20 patients with asthma in Israel. All of them demonstrated EIB by having a “decline of at least 15%” in FEV₁ after a standard exercise test.

Sex, age:

13 Males, 7 Females; mean age 14 yr (range 7 to 28 yr).

Exercise test:

A 7-min exercise session using the treadmill. Each subject exercised to submaximal effort at a speed and slope to provide 80% of the motional oxygen consumption as adjudged by a pulse oximeter. Pulmonary function was assessed after an 8-min rest.

Tecklenburg et al. [51]

Selection:

8 subjects with asthma from a population of university students and the local community, Indiana USA. All subjects had “documented EIB as indicated by a drop of greater than 10%” in postexercise FEV₁. “All subjects had a history of chest tightness, shortness of breath and intermittent wheezing following exercise.”

Sex, age:

2 Males, 6 Females; mean age 24.5 yr (SD 5 yr).

Exercise test:

Each subject ran on a motorized treadmill which was elevated 1% per min until 85% of age predicted maximum heart rate and ventilation exceeding 40–60% of predicted maximal voluntary ventilation. Subjects maintained this exercise intensity for 6 min. Following the 6-min steady state exercise, the grade of the treadmill continued to increase at 1% per min until volitional exhaustion. Pulmonary function was assessed post-exercise at 1, 5, 10, 15, 20, and 30 min. The maximum percentage fall in FEV₁ from the baseline (pre-exercise) value was calculated and used as the outcome.