Title: Ventilatory Mechanics in Endurance Athletes
Description: The lungs were once thought to be over-built for exercise. However, upon further research, endurance athletes have been found to reach their maximum ventilation, demonstrating an insufficiency of the lungs to accommodate the demands of highly demanding endurance sport. This knowledge has inspired researchers to look further into the exercise ventilatory responses and, in doing so, researchers discovered that the adaptations of the pulmonary system to endurance training are still not well understood. Potential reasons for this lack of knowledge may be methodological measurement limitations, as ventilatory mechanics have been measured classically either invasively or by breathing maneuvers. These measurements are difficult to perform during high intensity exercise and in large groups of athletes. However, recent innovations in motion analysis technology have allowed for ventilatory mechanics to be measured during high intensity exercise, potentially allowing for further insight into how high intensity endurance training impacts ventilatory mechanics.

The purpose of this study is to describe normal ventilatory mechanics during exercise in endurance trained and healthy untrained individuals, explore potential gender differences during exercise and investigate the impact of flow limitation during exercise on ventilatory mechanics, using a motion analysis system that allows researchers to obtain information on chest wall volume changes and chest wall compartmental interactions during high intensity exercise. This motion analysis system is called Optoelectronic Plethysmography (OEP). This dissertation is comprised of an introduction to the work and the 3 projects that comprise the dissertation along with an appendix, which includes a complete literature review. The three projects are as follows (1) an introduction to motion analysis as a tool in measuring ventilatory mechanics, (2) research determining the differences in the ventilatory mechanics in endurance athletes and healthy controls from rest to maximal exercise and (3) the differences in ventilatory mechanics between endurance trained women who demonstrate expiratory flow limitation during high intensity exercise versus endurance trained women who do not.

Project 1: Optoelectronic Plethysmography (OEP) is a motion analysis tool that can be used to define exercise ventilatory mechanics by analyzing chest wall movements and calculating volume changes. By analyzing breathing mechanics by motion analysis rather than traditional breathing maneuvers, individual components of the chest wall can be analyzed and changes in volume throughout the chest wall can be assessed without altering the individual's natural breathing pattern. This review presents the history and development of OEP technology, along with a summary of the methods used and a discussion of findings to date, giving insight into exercise ventilatory mechanics never investigated before. Project 2: Differences between the ventilatory mechanics of endurance athletes and non athletes using motion analysis have not yet been described. To determine how increased ventilatory demand impacts ventilatory kinematics, we compared the total chest wall volume variations (VCW) of 18 male and female endurance-trained athletes (ET) to 14 untrained individuals (UT) during exercise.

We hypothesized that training and gender would have an effect on VCW and kinematics at maximal exercise. Gender and training significantly influenced chest wall kinematics. Female ET did not change chest wall end-expiratory volume (VCW,ee) or pulmonary ribcage end-expiratory volume (VRCp,ee) with exercise, while female UT significantly decreased VCW,ee and VRCp,ee with exercise (p<0.05). Female ET significantly increased pulmonary ribcage end-inspiratory volume (VRCp,ei) with exercise (p<0.05), while female UT did not change VRCp,ei with exercise. Male ET significantly increased VRCp,ei with exercise (p<0.05); male UT did not. Men and women had significantly different VCW (p <0.05). Women demonstrated the greatest variation of VCW in the pulmonary ribcage compartment (VRCp). Men had similar volumes in the VRCp and the abdomen (VAb). In conclusion, gender and training had a significant association with ventilatory kinematics. Project 3: Research has found potential limitations of the airways to accommodate the large tidal volumes generated during high intensity exercise.

This airway limitation has been defined as expiratory flow limitation (EFL) observed during high intensity exercise in a large percentage of healthy women. Because of endurance athletes' ability to exercise at high intensities for prolonged periods of time and produce greater than average tidal volumes, female endurance athletes may be particularly susceptible to EFL and the impact EFL may have on performance. The purpose of this last chapter was to investigate the ventilatory mechanics and exercise capacity parameters of female endurance athletes with and without EFL. Female competitive cyclists participated in two days of testing; day one consisted of a maximal aerobic capacity test (V ̇o2max test) with spirometry and day two involved chest wall motion analysis testing during two steady state exercise tests. Baseline flow volume loops were performed prior to exercise and repeated post exercise. During exercise participants performed flow volume loops at minutes 4, 6, 8 and last 30 seconds of exercise.

EFL was considered present when the exercise flow volume loop surpassed the baseline flow volume loop. To quantify the degree of flow limitation when comparing the peak exercise flow volume loop to the baseline flow volume loop, we calculated the percent flow volume loop reserve (%FVL reserve). Two levels of submaximal constant-load exercise bouts (at 60% and 85% maximal watts) were employed to investigate if EEFL impacted ventilatory mechanics differently at different intensities. Optoelectronic plethysmography (OEP) was employed to measure VT from the pulmonary ribcage (VRCp), abdominal ribcage (VRCa) and the abdomen (VAb), as well as to measure end-expiratory volume chest wall volume (EEEV) to calculate potential dynamic hyperinflation. Comparison of participants with and without EFL was made using an ANOVA or Kruskal-Wallis test (p≤0.05). Predictors of %FVL reserve were explored with a multiple linear regression. Two participants were not included in the data analysis due to the presence of asthma (one at rest, one exercise induced) as determined by spirometry during day one testing.

Out of the other 28 participants, 6 participants had definite EFL (DEFL) demonstrated by overlapping of the peak exercise flow volume loop with the pre and post exercise flow volume loop, 5 had borderline EFL (BEFL) demonstrated by an overlapping of only the pre exercise flow volume loop and 17 had no EFL (NEFL) demonstrated by no overlapping of the pre or post flow volume loops. All participants had within normal limits of the percent predicted normal reference values in resting forced expiratory volume in 1 second (FEV1), forced mid expiratory flow rates (FEF25-75L/sec), forced vital capacity (FVC) and FEV1/FVC ratio. DEFL and BEFL participants' had a significantly lower FEV1/FVC ratio compared to NEFL (p=0.003), DEFL had significantly lower FEF25-75% predicted normal reference values before and after exercise compared to NEFL (p=0.004). There were no differences in the exercise capacity values between groups. During the day two steady state tests, there was a significant interaction effect between groups and exercise intensity in the %VRCa (p=0.045) and % VAb (p=0.049).

End-tidal carbon dioxide pressure, FEF25-75%, history of self reported excessive mucus with exercise and % VRCp during the 85% constant load test explained 71.6% of the variability in %FVL reserve in our regression model (p=0.002). Independent predictors of %FVL reserve were: end-tidal carbon dioxide pressure (p=0.033), FEF25-75% (p=0.010) and history of excessive mucus with exercise (0.014). In conclusion, female endurance athletes demonstrating EFL had normal but significantly different FeV1/FVC ratio and significantly different abdominal ribcage and abdomen percent contribution with increased exercise intensity, but similar exercise capacities compared to the female endurance athletes with no EFL. Also, independent predictors of %FVL reserve were found to be FEF25-75%, history of mucus production with exercise and end-tidal carbon dioxide level at peak exercise. This dissertation has provided further insight into the ventilatory mechanics of endurance athletes and how potential airway limitation can impact high intensity exercise.

Further research can seek to better understand if the differences in ventilatory mechanics between endurance athletes with EFL and no EFL allow for preservation of exercise capacity in the presence of airway limitation.