Impact Of Mild Dehydration On Pulmonary Function During Exercise
Faculty Advisor Name
Nick Luden
Department
Department of Kinesiology
Description
The pulmonary system historically has been believed to respond accordingly to increasing metabolic demands, even during severe exercise, through facilitating changes in ventilation, flow rates, operating lung volumes, and gas exchange. There recently has been a growing list of scenarios where this is not the case, like when mechanical constraints dictate the maximum attainable flow rate in a give expired breath which has been termed expiratory flow limitation. Dynamic hyperinflation, a result of increasing operating lung volumes, can result to help maintain ventilation and try to preserve performance. Dynamic compression of the airways from intrathoracic pressure compressing smaller airways during heavy breathing can lower expiratory flow limits and lead to expiratory flow limitation and contribute to dynamic hyperinflation by ending expiration prematurely. This may be exacerbated in a dehydrated state as it may compromise the stability of airways through reduced surface tension by altering airway surface liquid, which lines the airways, and pulmonary surfactant levels, a component of airway surface liquid. This has been thought to result in observed reductions in forced vital capacity and increases in residual volume and functional residual capacity with mild dehydration at rest with other studies finding reductions in expiratory flow in healthy individuals and small airway dysfunction in recreational athletes with asthma and following exercise in elite athletes, Therefore, the primary objective of this study is to test the hypothesis that mild dehydration will increase the presence and severity of expiratory flow limitation, and as a result will increase operating lung volumes, when compared to euhydration. Twelve healthy active adults, four female and eight male, with an average age of 20 years old, participated in the study. To be considered active, they had to have at least met American College of SPort's Medicine's Physical activity Guidelines and cycled about once a week for at least the past six weeks. Subjects with known pulmonary diseases or who experienced lasting symptoms from COVID-19 were excluded. Each subject completed three sessions, one preliminary, one hypohydrated, and one euhydrated trial in the James Madison University Human Performance Lab. A crossover design was implemented by which all subjects completed the euhydrated and hypohydrated trials in a randomly counterbalanced manner. All trials began in the morning at a time of day that did not deviate by more than two hours. During each trial, a VO2 peak test was performed that began with a 5-minute warmup at 50 watts while maintaining 50 rpms. Following the warm-up the test was conducted with 2-minute stages that increased by 25 watts for every workload and ended when the subject could no longer maintain 50 rpms or reached volitional cessation. Heart rate, rating of perceived exertion, and rating of perceived dyspnea were recorded in the last 10 seconds of each stage. Inspiratory capacity maneuvers were performed in the last 30 seconds of each stage. Maximum flow volume loops were performed before and after each VO2 peak test. A Multidimensional Dyspnea Profile questionnaire and selecting applicable dyspnea descriptors were also completed follow the post-exercise maximum flow volume loops. To ensure subjects arrived in a euhydrated state, subjects followed a similar food and beverage consumption to their 24-hour log from the preliminary trial and drank about 16 fluid ounces the night before and the morning of the trial. To ensure subjects arrived in a dehydrated state, subjects were asked to abstain from consuming any fluid and foods with greater than 30% water content fo 24-hours leading up to the trail. Hydration status before each trial was determined through nude body mass, urine color, urine specific gravity, hematocrit, and InBody Bio-electrical Impedance Analysis. Other standardized procedures consisted of abstaining from alcohol, caffeine, and exercise for 24 hours prior to each trial. Expiratory flow limitation will be assessed by super imposing the inspiratory capacity maneuvers within the largest maximum flow volume loop with its presence and severity determined on if there is overlap of the exercise-flow volume loop and the maximum flow volume loop. Dynamic changes in operating lung volumes will be recorded using the metabolic cart. Statistical analyses will be performed with IBM SPSS Statistics v 29.0.
Impact Of Mild Dehydration On Pulmonary Function During Exercise
The pulmonary system historically has been believed to respond accordingly to increasing metabolic demands, even during severe exercise, through facilitating changes in ventilation, flow rates, operating lung volumes, and gas exchange. There recently has been a growing list of scenarios where this is not the case, like when mechanical constraints dictate the maximum attainable flow rate in a give expired breath which has been termed expiratory flow limitation. Dynamic hyperinflation, a result of increasing operating lung volumes, can result to help maintain ventilation and try to preserve performance. Dynamic compression of the airways from intrathoracic pressure compressing smaller airways during heavy breathing can lower expiratory flow limits and lead to expiratory flow limitation and contribute to dynamic hyperinflation by ending expiration prematurely. This may be exacerbated in a dehydrated state as it may compromise the stability of airways through reduced surface tension by altering airway surface liquid, which lines the airways, and pulmonary surfactant levels, a component of airway surface liquid. This has been thought to result in observed reductions in forced vital capacity and increases in residual volume and functional residual capacity with mild dehydration at rest with other studies finding reductions in expiratory flow in healthy individuals and small airway dysfunction in recreational athletes with asthma and following exercise in elite athletes, Therefore, the primary objective of this study is to test the hypothesis that mild dehydration will increase the presence and severity of expiratory flow limitation, and as a result will increase operating lung volumes, when compared to euhydration. Twelve healthy active adults, four female and eight male, with an average age of 20 years old, participated in the study. To be considered active, they had to have at least met American College of SPort's Medicine's Physical activity Guidelines and cycled about once a week for at least the past six weeks. Subjects with known pulmonary diseases or who experienced lasting symptoms from COVID-19 were excluded. Each subject completed three sessions, one preliminary, one hypohydrated, and one euhydrated trial in the James Madison University Human Performance Lab. A crossover design was implemented by which all subjects completed the euhydrated and hypohydrated trials in a randomly counterbalanced manner. All trials began in the morning at a time of day that did not deviate by more than two hours. During each trial, a VO2 peak test was performed that began with a 5-minute warmup at 50 watts while maintaining 50 rpms. Following the warm-up the test was conducted with 2-minute stages that increased by 25 watts for every workload and ended when the subject could no longer maintain 50 rpms or reached volitional cessation. Heart rate, rating of perceived exertion, and rating of perceived dyspnea were recorded in the last 10 seconds of each stage. Inspiratory capacity maneuvers were performed in the last 30 seconds of each stage. Maximum flow volume loops were performed before and after each VO2 peak test. A Multidimensional Dyspnea Profile questionnaire and selecting applicable dyspnea descriptors were also completed follow the post-exercise maximum flow volume loops. To ensure subjects arrived in a euhydrated state, subjects followed a similar food and beverage consumption to their 24-hour log from the preliminary trial and drank about 16 fluid ounces the night before and the morning of the trial. To ensure subjects arrived in a dehydrated state, subjects were asked to abstain from consuming any fluid and foods with greater than 30% water content fo 24-hours leading up to the trail. Hydration status before each trial was determined through nude body mass, urine color, urine specific gravity, hematocrit, and InBody Bio-electrical Impedance Analysis. Other standardized procedures consisted of abstaining from alcohol, caffeine, and exercise for 24 hours prior to each trial. Expiratory flow limitation will be assessed by super imposing the inspiratory capacity maneuvers within the largest maximum flow volume loop with its presence and severity determined on if there is overlap of the exercise-flow volume loop and the maximum flow volume loop. Dynamic changes in operating lung volumes will be recorded using the metabolic cart. Statistical analyses will be performed with IBM SPSS Statistics v 29.0.
