Effects of dry and humid climates on exercise-induced asthma in children and preadolescents

Oded Bar-Or, M.D., lttai Neuman, M.D., and Raphael Dotan, M.Sc. Wingate Post Office, Israel

Among factors which possibly in@ence the responses of asthmatic children to exercise, climate has received little attention. This study was performed to determine whether the level of air humidity is a factor to be considered. Twenty asthmatic (extrinsic perennial) girls and boys, 6 to 14 yr of age. with unverified history of exercise-induced asthma (EIA) took part. They rested and exercised in a climatic chamber in dry (25% relative humidity) and humid (9070) sessions at 25” to 26” C. One to three weeks separated the sessions, the order of which was counterbalanced. No changes in pulmonary functions (FVC, FEV,,,, MMEF, MBC) were found ,following a sitting period of 60 min in either climate. Five and ten minutes following the treadmill run, however, bronchoconstriction was distinctly more pronounced in the dry than in the humid climate. Exercise heart rate and the subjective rating of effort were not affected by climate. It was concluded that, under the above experimental conditions, EIA is more likely in dry air than in humid air, possibly due to heat loss at the airway mucosa caused by evaporation. High humidity of inspired air could be the reason why EIA is less prevalent in swimming, as compared with other modes of exercise.

Exercise-induced Asthma (EIA) has been shown to exist in the majority of asthmatics, especially during childhood.1-3 Yet, this highly prevalent syndrome may occur inconsistently in a given child, who may experience EIA one day and have symptom-free exer- cise response on another. Such variability in response to exercise depends on various conditions and has been given attention by several investigators. Factors such as type, duration, and intensity of exercise have been implicated. 3-10 Others included type of asthma, severity of the disease, nature of medication, the time elapsed since the last medication, since the last meal, or since previous exercise testing.3, *, a* 11, l2 Occur- rence of EIA has also been shown to depend on sea- sonal variations.‘”

Although extrinsic asthma is, by definition, en-

From the Department of Research and Sports Medicine, Wingate Institute, and Department of Pediatric Allergy, Hasharon Hos- pital.

Supported in part by the Sports and Physical Education Authority, Ministry of Education and Culture, Israel.

Received for publication Feb. 14, 1977. Accepted for publication May 6, 1977. Reprint requests to: 0. Bar-Or, M.D., Department of Research and

Sports Medicine, Wingate Institute for Physical Education and Sport, Wingate Post Office, Israel 42902.

vironment-dependent, only little attention has been given so far to the possibility that climatic conditions may determine the variability in EIA, some climates being less favorable than others to the exercising asthmatic. Lebowitz and colleaguesi reported some decrease in forced vital capacity (FVC), forced ex- piratory volume in 1 second (FEV,.,), and in the max- imal midexpiratory flow (MMEF) of healthy adoles- cents who exercised under conditions of moderate oxidant or reducing type pollution, high ambient tem- perature, and low relative humidity (RH). The rela- tive role played by each of these ambient factors was not determined.

It has been a common clinical practice to advise asthmatics to change climate and move to a dry geo- graphic region such as Phoenix, Arizona in the United States or Arad and Jerusalem in Israel. Yet, no sys- tematic studies are available to show whether it is dryness per se or the paucity of allergens in these places that plays a beneficial role. The use of humid- ification for acute treatment of the asthmatic is debat- able. In a recent study Rodriguez, Branch, and Cot- ton15 exposed asthmatic children to mist produced in various ways and monitored changes in their resting pulmonary functions. Responses ranged from no ef- fect to either reduction or increase in bronchial resis-

Vol. 60, No. 3, pp. 163-168

164 Bar-Or, Neuman, and Dotan

TESTINQ PROTOCOL

J. ALLERGY CLIN. IMMUNOL. SEPTEMBER 1977

--dLii - IN CHAMBER

i

- REST4 z REST &U-TlNG) _ u Y d-REST--

1

.20 0 20 40 80 SO

TIME , Yin.

FIG. 1. Schema of a session protocol. Arrows denote time of pulmonary function testing.

TABLE I. Heart rate (HR) and rating of perceived exertion (RPE) in the final two workloads in both

climates (mean * 1 SD)

Climate

Pre-final load Final load

HR RPE HR RPE

Humid x 170.3 12.8 186.4 15.6 SD 15.5 3.5 14.7 2.6

DV x 169.6 12.0 184.3 14.5 SD 13.3 3.4 13.5 3.0

All differences between sessions are nonsignificant.

tance. Fontana, Fost, and Rappaportl‘j found no dif- ference in resting pulmonary functions of asthmatic children exposed to either high or normal humidity.

Two recent preliminary reports refer to the effect of humidity on EIA. Weinstein and colleagues” found a beneficial effect of ultrasonically nebulized normal saline, delivered in an aerosol mask to running asth- matic adolescents and adults. Chen, Morton, and Souhrad’* report that a combination of warm and humid air prevented EIA, as compared to dry air at 23” C, both administered by the closed breathing method.

The purpose of the present study was to clarify the role played by very dry or highly humid air (at the same air temperature) on the free-breathing exercising asthmatic in an allergen-free environment.

MATERIAL AND METHODS

Twenty children, 7 girls and 13 boys, participated in this study. They were all diagnosed as having extrinsic peren- nial asthma. EIA was reported by the child or the parents but was not verified by a standardized exercise provocation prior to this study. Their age was 10.7 -+ 2.3 yr and they were within normal body height, weight, and adiposity. All children were kept symptom-free by maintenance of hypo- sensitization and all but one required either round-the- clock bronchodilators (theophyllines) or sodium cromogly-

cate (Intal). Twenty percent of the subjects were given beclomethasone dipropionate (Viarex) inhalations. Nine- teen children had positive history of family atopy. They all had combined clinical symptoms and laboratory findings consistent with extrinsic asthma and allergic rhinitis. Pul- monary function testing at the outpatient clinic indicated hyperreactive airways, based on reversibility of airway obstruction by use of salbutamol inhalation.

Testing within this study was performed during the winter months of 1976. This season was selected to reduce the chance that seasonal allergens may affect the results. The children were tested in the morning hours following discontinuation of all medication for 12 hr. Each child underwent two testing sessions in a climatic chamber. The protocols in the two sessions were identical, with one ex- ception: in one session RH in the chamber was set at 90% (“humid”) and in the other 25% (“dry”). Air temperature was kept constant in both sessions at 25” to 26” C. One to three weeks separated the two exposures, the order of which was randomly assigned for each child.

A schematic outline of the protocol is presented in Fig. 1. Following a rest period of 20 to 30 min in neutral environ- ment (25” to 26” C, 50% to 60% RH) baseline evaluation of pulmonary functions was performed using an Enraf Respotest 9-L spirograph. These included FVC, FEVl.o, MMEF, and maximal breathing capacity (MBC). The sub- ject then entered the climatic chamber and sat for 60 min. This was followed by pulmonary function determination, as above, to detect possible changes due to sitting in either humid or dry environment. The treadmill exercise was then performed in the chamber followed by a rest period. Retest- ing of pulmonary functions was performed 5 and IO min postexercise. In cases of marked EIA the child was ob- served for a further 10 min. The exercise consisted of treadmill (Quinton 18-60) running, or walking uphill at fast speeds. The grade, or speed, was increased every 2 min to a total walking time of 6 to 8 min. The workloads were planned so that the final load would yield a heart rate (HR) of 85% to 90% of the predicted maximal HR. The running or walking protocol for a given child was identical in both sessions. HR was determined at the last 15 set of each load from a bipolar (CM,) ECG lead, followed by the subject rating his perceived exertion (RPE) using the Borg scale.lY

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NUMBER 3 Exercise-induced asthma in children and preadolescents 165

TABLE II. Pulmonary functions in absolute terms as determined at each stage of the two sessions (mean +- 1 SD, p values (n = 20)

Variable

FVC (L,)

FEV1.o W

MMEF (L/min)

MBC (Llmin)

Time DW Humid P

Baseline 2.00 +- 0.54 2.04 k 0.51 NS Pre-ex 2.06 k 0.55 2.07 +- 0.52 NS 5 min post- 1.86 2 0.63 2.05 t 0.59 0.02 10 min post- 1.88 f 0.69 2.03 -+ 0.62 NS Baseline 1.60 + 0.46 1.57 i- 0.39 NS Pre-ex 1.59 i 0.46 I .63 -+ 0.44 NS 5 min post- 1.37 ? 0.48 1.59 +- 0.47 0.01 10 min post- 1.36 ? 0.55 1.57 k 0.47 0.02 Baseline 99.0 k 42.7 95.8 F 38.3 NS Pre-ex 99.1 -t 49.2 98.2 t 45.0 NS 5 min post- 73.2 -+ 43.6 91.7 zi 42.9 0.03 10 min post- 72.9 t 47.5 87.3 F 33.2 NS Baseline 72.6 k 23.9 70.0 k 23.3 NS Pre-ex 74.5 k 22.7 74.0 i 23.4 NS 5 min post- 72.4 t 29.0 76.3 -I 25.7 NS IO min post- 66.4 k 28.2 76.0 +- 23.1 0.01

TABLE III. Postexercise pulmonary functions in percentage of values at rest; comparison of two climates (mean 2 1 SD, p values (n = 20)

Measurement

FVC

FEV (vol)

MMEF

MBC

Time

5 min post- 10 min post- 5 min post-

10 min post- 5 min post-

10 min post- 5 min post-

10 min post-

Dry

84.4 AZ 17.4 84.0 t 27.1 87.5 2 15.9 89.2 of- 22.3 80.5 2 33.2 73.5 k 32.8 92.4 t 17.8 86.4 k 20.9

Humid

94.1 2 14.8 95.2 L 14.7 95.9 ? 16.5 97.2 k 17.3 96.4 k 28.9 94.9 it 28.0

100.6 k 15.8 103.8 -I- 10.1

P

0.04 0.02 0.02 0.04 0.03 0.01 0.04 0.001

The latter measurement was taken to compare the subjective strain incurred during exercise in the two climates.

The climatic chamber was spot-checked for foreign al- lergenic particles, such as molds, spores, and pollen, using a Hirst spore trap. It was found completely allergen-free.

Dependent t test was performed to calculate the interses- sion level of significance for each variable.

RESULTS

HR and RPE values, as obtained in the final two stages of the treadmill exercise, are summarized in Table I. It is evident that both cardiac and subjective strains were similar under the two climatic condi- tions. The target HR of 85% to 90% of the child’s predicted maximal HR was indeed reached as origi- nally planned. All children were exercising 2 to 4 min at this HR. It should be pointed out that in the Borg RPE scale 13 denotes “somewhat hard,” 15, “hard,” and 17, “very hard” exercise.

In Table II are summarized the absolute values for the four pulmonary functions as measured prior to

entering the chamber (‘ ‘baseline”), following the 60-min rest in the chamber (‘ ‘pre-ex”), and during the recovery period (“5 min post” and “10 min post”). Whereas no change is evident in any function following 60 min rest in either environment, the postexercise response in the dry condition indicates lower values as compared with those obtained at the corresponding stages of the humid session.

To evaluate the magnitude of postexercise bron- choconstriction in the two climates, a value of 100% was assigned to the “pre-ex” measurement, as dem- onstrated in Table III. All four functions are reduced by 15% to 20% at the postexercise stages in the dry weather but not during exposure to humidity. This interclimatic difference is significant for all variables. A greater decrease is noted at 10 min post, as com- pared with 5 min post.

To demonstrate how many children had signs of EIA, individual data are plotted in Fig. 2 for FEV,,o, comparing the IO-min “post-ex” response in both

166 Bar-Or, Neuman, and Dotan J. ALLERGY CLIN. IMMUNOL.

SEPTEMBER 1977

.

t

- l l

l *

100 l

/

l l

l t

FEV,,D DRY

FIG. 2. Individual data of FEV,,o at IO min postexercise expressed as percentage of pre-exercise values. Com- parison of the response in humid and in dry climates.

climates. Assuming a decrement of more than 10% as an indicator of “positive” EIA responses,20, 21 9 only out of the 20 children showed a definite bron- choconstriction in either climate. Plotting the corre- sponding data for FVC, MMEF, and MBC yielded similar results. Altogether, taking the 4 mea- surements combined, 10 children could be defined as “responders.”

If only the 10 responders are evaluated as to the relative effects of dryness and humidity (Fig. 3), one can note a difference which is much more marked than might be concluded from Table II, in which all subjects, nonresponders included, were evaluated. The mean decrements in the dry session were 26.3%, 36.8%, 51.5%, and 30.2% for FVC, FEV1.o, MMEF, and MBC respectively, compared with some 0% to 10% decrements in the humid sessions.

DISCUSSION

This study indicates that, under the preceding ex- perimental conditions, dryness proved less favor- able to the free-breathing exercising asthmatic child than did high-ambient humidity. Weinstein and CO-

workers17 reported a 29.5% decrease in FEV1.o fol- lowing exercise performed in dry environment as compared to a decrement of 13.5% when the children were inhaling nebulized saline via a mask. In Wein- stein’s study the humid air was systematically given 2 hr following the “dry” test, and one could argue that the benefit demonstrated in the “humid” test was

biased by interaction with the previous run, rather than representing a true humidity effect. In our study, the two environments were randomly assigned, tests were performed on separate days, and still the humid environment proved beneficial. One may conclude then that humidity did play a real protective role. Chen, Morton, and Souhrad,iE in a preliminary re- port, indicated that a combination of high humidity and warm air temperature (37” C) practically pre- vented EIA in 8 asthmatics. Both Weinstein and Chen used a closed-breathing method. The present study extends their findings to a free-breathing situation.

It should be emphasised that the level of humidity affected the bronchial resistance only during exercise but not at rest. Some authors15* 22-24 found a harmful effect of humid air on the resting asthmatic. It should be stressed, though, that these authors used various sorts of mist inhalation with droplets of varying sizes. In the present study humidification was performed by mixing steam with dry air outside the climatic chamber. Thus the inhaled air was nonsaturated and the water was in true gas form rather than in droplets. In a study by Fontana, Fost, and Rappaport,” asth- matic and healthy children were exposed to 5-day periods of rest at 90% relative humidity in an en- vironment-control unit. The humidification system was, in principle, similar to that employed in the present study. No adverse effects were noted on the pulmonary functions of either group. It is possible, then, that the harmful effect of humidified air as de- scribed elsewhere is due to mechanical irritation by the droplets15 rather than by a high content of H20.

Six of the 10 “responders” in this study had a completely bronchoconstriction-free response while exercising in high humidity. It is suggested that this condition may be of some protective value to the exercising asthmatic child. The mechanisms for such protection are not clear, based on available literature. One possibility would be along the lines put forward by Chen, Morton, and Souhrad18 that the water and/or heat loss from the airway mucosa serves as one more nonspecific physical trigger to EIA. The hyperpnea or hyperventilation of exercise would en- hance such water and heat loss via evaporation when the inspired air is dry and less so when it is humid. Bronchoconstriction due to cooling has been previ- ously described by Wells, Walker, and Hickler.25

One should note that, even in the dry climate, only 50% of the children demonstrated a true EIA re- sponse,20* 21 while the others did not have a post- exercise decrement in function. A possible expla- nation is the rather conservative nature of exercise protocol employed in this study, namely, a progres- sive increment in load rather than a single high load,

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Exercise-induced asthma in children and preadolescents 167

FIG. 3. Changes in postexercise pulmonary functions of 10 “exercise responders” exposed to humidity (solid lines) and to dryness (broken lines). Data are presented in percentage of pre-exercise values (means 2 1 SEM).

previously shown to better elicit EIA.3, ‘* * Thus, instead of exercising at HR of 170 to 190 for 6 to 8 min, our children exerted at this level for 2 to 4 min only. This more conservative protocol was selected as a precaution to prevent untoward reactions in previ- ously little explored environmental conditions.

It might be argued that the favorable response to humidity represents a placebo effect. Although such an effect cannot completely be excluded in environ- mental conditions so noticeably different from one another, it is not very likely the case in this study: neither the subjects nor the parents knew which cli- mate was “supposed” to be more asthmogenic; the RPE scale, which was included to detect possible dif- ferences in subjective strain between the two climates, did not indicate that the children felt less comfortable in dryness.

The above data may help explain the well-docu- mented protection from EIA reached by swimming, as compared with other modes of exercise.j, ‘3 26 No valid explanation has so far been offered regard- ing this protection. 8* 27 It is possible that the high water content of the air inhaled by the swimmer makes the difference. This possibility is currently under experimental investigation in our laboratory.

It is of practical importance to determine whether an asthmatic child with history of EIA should be ad- vised to move to a humid geographic area. Such a recommendation is premature and cannot be made directly from this study, in which only short expo-

sures (80 min) to dry or humid climates were evalu- ated. In addition, long-standing humidity may induce the formation of spore aeroallergens2* and the combi- nation of heating and humidification-the growth of thermophilic actinomycetes,2ss 3o thereby enhancing hypersensitivity chest disease. Further studies in field conditions, in which chronic exposures to different levels of humidity can be analyzed, are indicated to further test the practical implications of this study. It is recommended, though, that during spells of dry weather, and possibly dry cool weather,‘* special precautions be taken regarding physical exertion in proved cases of EIA. The preceding findings also in- dicate the importance of monitoring and standardizing the climatic conditions in the laboratory whenever an exercise test is administered to an asthmatic child.

The authors wish to thank Dr. J. Ben Chaim, Mrs. Sara Erez, Mrs. Ruth Burstein, Miss Aya Tzur, and Mr. Amichai Jordan for their enthusiastic help during testing and Mr. Uri Goldbourt for his guidance on statistics.

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