Sex differences in airway anatomy and fatigue of the diaphragm.
Effects of healthy ageing on the biology of exercise.
Respiratory influences on neurovascular control.
Other research projects that are of interest to trainees can often be developed in consultation with Dr. Sheel
The ideal applicant has a strong background in physiology. Successful students have the ability to work independently as well as with a larger group.
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Dissertations completed in 2010 or later are listed below. Please note that there is a 6-12 month delay to add the latest dissertations.
Purpose: The purpose of this thesis was to contribute to our understanding of the effects of ageing and sex on the skeletal muscle metaboreflex in the respiratory musculature (Chapter 2) as well as the limb during dynamic exercise (Chapters 3 and 4). Methods: Chapter 2 investigates the effects of age and sex on the cardiovascular response to the intense inspiratory muscle work in young males and females (18-35 years), relative to older males and females, post-menopause (55-75 years). Chapter 3 investigates the effect of sex on the cardiorespiratory response to the skeletal muscle metaboreflex evoked by dynamic exercise in young males and females (18-35 years). Chapter 4 investigates the effect of skeletal muscle mass on the cardiorespiratory response to the skeletal muscle metaboreflex evoked by intense, dynamic exercise in young males (18-35 years). Conclusions: In Chapter 2 we found the blood pressure response to the respiratory muscle metaboreflex is augmented with healthy ageing. The effect of sex observed in young females and males is absent in older adults when females are post-menopausal. In Chapter 3 we found that young females continue to have an attenuated blood pressure response to the skeletal muscle metaboreflex in the context of whole-body, dynamic exercise; however, there is no effect of sex in heart rate. The metaboreflex also has a greater influence on ventilatory control in young males compared to young females in dynamic exercise. Lastly, in Chapter 4 we found the mass of muscle stimulating the metaboreflex resulted in the dose-dependent arterial pressure and heart rate response following intense dynamic exercise. Additionally, we also found a ventilatory response to the metaboreflex can only be isolated with intense exercise and large muscle mass stimulus. Overall, our results suggest that circulating female sex hormones contribute to the attenuated arterial pressure response to the skeletal muscle metaboreflex when activated by the respiratory muscles and during dynamic exercise. Furthermore, the absolute mass activating the metaboreflex impacts the cardiorespiratory response to the metaboreflex even in the context of intense, dynamic exercise. Our findings point to age and sex differences in the control of blood flow during exercise.
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As a part of healthy aging, older individuals experience a decline in respiratory function making breathing more difficult, especially during exercise. Purpose: Here, I comprehensively examine the combined effects of healthy aging and biological sex on respiratory mechanics and the metabolic cost of breathing during exercise. Methods: In study #1 (Chapter-2), we validated a newer technology, optoelectronic plethysmography (OEP), which allows us to measure how different groups of respiratory muscles contribute to breathing and proposed a method for quantifying the mechanical work done by the ribcage and abdomen. In study #2 (Chapter-3) we used OEP with healthy adults to understand how differences in regions of the chest-wall contribute to breathing mechanics during exercise with respect to age and sex. In study #3 (Chapter-4) we used voluntary hyperpnea to estimate the metabolic cost of breathing and understand the physiological consequences of different respiratory mechanics across age and sex. Conclusion: Ventilation increases during exercise to meet the metabolic demands of the working muscles and is accompanied by an increased work to breathe. Older individuals and females have a higher work of breathing for a given ventilation and use different regional respiratory muscle to meet those demands relative to younger individuals and males, respectively. With exercise, there is an ample increase in the oxygen uptake by the respiratory muscles. Specifically, both younger and older females have a higher cost to breathe than their male counterparts during moderate and high-intensity exercise and older individuals incur a higher cost to breathe than younger individuals for a given ventilation. Our results suggest that both sex differences and normal age-related changes in respiratory structure and function, appear to have a significant effect on the ventilatory responses during exercise. Collectively, the results of this thesis suggest that sex differences in respiratory mechanics persist throughout healthy aging and contribute to the increased metabolic cost to breathe during exercise in healthy older females relative to males. Understanding the demands of the respiratory system during exercise of healthy older adults is especially important from a clinical perspective given that many diseases of the heart and lungs occur in older individuals.
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Purpose: Two optical coherence tomography (OCT) imaging studies were performed to examine how sex differences in airway anatomy affect respiratory mechanics during exercise and how airway anatomy may be altered due to swim training.Methods: Study #1 was designed as a proof-of-concept and is presented in Chapters 2 and 3. Chapter 2 presents respiratory mechanics during exercise, airway diameter, airway luminal area (Ai), index of airway size, and Weibel model area data measured from OCT images. Chapter 3 describes development of OCT software to measure Ai, wall area (WA), wall area percent (WA%), and wall thickness (WT). Reproducibility of OCT-derived airway measures are presented. In Study #2, males and females (19-30 years) performed exercise to exhaustion and OCT airway images were obtained. Of the 25 subjects, 7 (6 females, 1 male) were competitive swimmers. Chapter 4 investigated whether sex differences in Ai affect mechanical ventilatory constraint and resistive work of breathing (Wb) during exercise. Chapter 5 investigated whether swim training leads to airway remodeling detectable with OCT.Conclusions: Imaging the airways of healthy males and females with OCT provides measures of Ai across airway generations that are related to respiratory mechanics during exercise (Chapter 2). The software developed had a smaller coefficient of variation than other techniques and can detect smaller differences in OCT-derived airway measures between groups in future airway remodeling studies (Chapter 3). Females tend to have smaller 4th-6th generation Ai measures relative to males. When ventilation is high, resistance to inspired flow is larger in females and is associated with two measures of airway size: index of airway size and Weibel area. This study suggests that innate sex differences exist in Ai which result in a greater resistive Wb in females compared to males during exercise (Chapter 4). Lastly, OCT can be used to detect changes in airway wall structure in male and female swimmers (Chapter 5). Results of this thesis extend our understanding of how airway size is an important determinant of respiratory mechanics during exercise and provides evidence that OCT can be utilized to study airway anatomy in healthy humans and airway remodeling in swimmers.
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Purpose: Overweight children and adolescents have increased aortic stiffness conferring an increased risk of future cardiovascular events. This thesis evaluated exercise training as a means to modify aortic stiffness in obese youth. An institutional treadmill protocol (British Columbia Children’s Hospital, BCCH) for assessing metabolic gas exchange parameters (minute ventilation, tidal volume, breathing frequency, oxygen consumption, carbon dioxide production) was validated using a healthy cohort (study 1, Chapter 3). This protocol was used to test obese children and adolescents before and after an exercise intervention. Echocardiography was used to study changes to vascular properties pre- and post- training (study 2, Chapter 4). Pulmonary function tests were used to assess lung function pre- and post- training (study 3, Chapter 5).Study 1: A scaled institutional (BCCH) protocol was validated using 70 healthy boys and girls. This validated protocol was used in the subsequent training study to individually adjust intensity to V̇O2 capacity, in keeping with exercise intervention recommendations.Study 2: Ten to 18 year old children and adolescents (BMI ≥ 97th percentile for age) were recruited to undergo a 12-week exercise program in a randomized cross-over study. Standard echocardiographic dimensions and measures of systolic and diastolic cardiac function were recorded before and after both a 12-week exercise intervention and 12-week control phase. Biophysical properties of the aorta including pulsewave velocity were calculated using an echocardiographic-Doppler method. Treadmill exercise tests were also performed before and after each study phase.Study 3: The same participants that underwent the exercise training in study 2 were measured for resting pulmonary function and exercise spirometry as per the protocol described in the second study.Results: The institutional treadmill protocol produced similar peak exercises responses compared to the traditional protocol and was validated as an alternate for pediatric exercise testing. Ten participants completed the exercise intervention (age 14.3+3.2 yrs). Training showed a significant reduction in PWV (p=0.003), a modest reduction in body mass (p=0.0135), and exercise tolerance improved (METs, p=0.003; total exercise time, p=0.015).A reduction of aortic pulsewave velocity can be achieved with exercise training in obese children and adolescents and cardiovascular fitness can be modestly improved.
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Purpose: The purpose of the thesis was to: 1) establish the reliability of cervical magnetic stimulation and chest wall surface EMG in the assessment of the diaphragmatic compound muscle action potential (CMAP) in healthy men and women (Study #1, Chapter 3), and 2) explore sex-based differences in the mechanisms and consequences of diaphragmatic fatigue (DF), specifically, 2a) the cardiovascular response to inspiratory resistance (Study #2, Chapter 4), and 2b) the effect of DF on subsequent exercise performance (Study #3, Chapter 5).Methods: Diaphragmatic fatigue was assessed in healthy men and women by measuring transdiaphragmatic twitch pressure using cervical magnetic stimulation. Surface electrodes were placed on the left and right hemi-diaphragm. Inspiratory pressure-threshold loading (PTL) was used to induce DF at rest, whilst a host of cardiovascular variables were measured (including: heart rate [HR], mean arterial [MAP] and low-frequency systolic blood pressure variability [LFSBP]). A time-to-exhaustion cycle test was performed with and without the induction of DF.Results: All CMAP characteristics demonstrated high reproducibility within and between experimental sessions. At PTL task failure, the degree of DF was not different between sexes (~23%); however, time to task failure was longer in women than men (27 vs. 16 min). Furthermore, women exhibited less of an increase in HR (13 vs. 19 bpm) and MAP (10 vs. 14 mmHg), and significantly lower LFSBP (23 vs. 34 mmHg²) during PTL compared to men. Prior-induced DF negatively and equally affected subsequent exercise performance in men and women (~15%). Conclusions: Cervical magnetic stimulation is a reliable means to evaluate phrenic nerve conduction in healthy men and women. The female diaphragm is highly fatigue resistant, leading to an attenuation of the inspiratory muscle metaboreflex (i.e. cardiovascular consequences of DF). Yet, DF impairs exercise independent of sex.
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Purpose: Three studies were performed in order to comprehensively examine the combined effects of healthy aging and biological sex on respiratory mechanics and the perception of dyspnea during exercise in healthy adults.Methods: Study #1 (Chapter 2) investigated the mechanical ventilatory and sensory responses to incremental exercise in a group of younger men and women (20-30 years old), and older men and women (60-80 years old). Study #2 (Chapter 3) examined inspiratory muscle recruitment patterns during incremental exercise in a group of younger men and women (20-30 years old), and older men and women (60-80 years old). Study #3 (Chapter 4) assessed whether experimentally manipulating the magnitude of mechanical ventilatory constraint during moderate-intensity exercise would alter the perception of dyspnea in a group of older men and women.Conclusions: Healthy aging and biological sex independently increase the magnitude of ventilatory constraint during exercise in healthy adults. Specifically, older individuals and women have a higher work of breathing for a given minute ventilation, and a higher propensity towards expiratory flow limitation during exercise than men and younger individuals, respectively. Additionally, older women have a higher perception of dyspnea during exercise than older men, which could be explained by the combined effects of age and sex on mechanical ventilatory constraint during exercise (Study #1). Healthy aging and biological sex also independently affect the pattern of inspiratory muscle recruitment during exercise, where older individuals and women rely on extra-diaphragmatic inspiratory muscles to a greater extent than older individuals and women, respectively (Study #2). Despite these differences in respiratory mechanics, acutely manipulating the magnitude of mechanical ventilatory constraint during moderate-intensity exercise did not have an effect of the perception of dyspnea (Study #3). Collectively, the results of this thesis suggest that sex-differences in respiratory mechanics during exercise persist throughout the healthy aging process, but do not contribute to the increased sensations of dyspnea observed in healthy older women relative to healthy older men.
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Purpose. The purpose of this thesis was to investigate sex differences in the integrated response to high respiratory muscle work during exercise. To accomplish this, I developed two novel methodologies (Chapters 2 & 4) in order to answer two subsequent research questions (Chapters 3 & 5).Methods. Chapter 2: Using computer software coupled with physiological measurements, I measured the oxygen cost of exercise hyperpnea in healthy subjects. Chapter 3: Healthy men and women performed voluntary hyperpnea while the oxygen cost of breathing was determined. The absolute and relative oxygen cost of breathing was compared between the sexes at different absolute and relative ventilation.Chapter 4: Using readily available components, I developed a proportional assist ventilator that could operate during all exercise intensities.Chapter 5: Healthy men and women completed three time-to-exhaustion (TTE) tests and quadriceps muscle fatigue was measured after each. The first TTE served as a control and during the 2nd and 3rd either a hyperoxic mixture was inspired or the work of breathing was lowered.Conclusion The oxygen cost of breathing can be consistently and reproducibly measured in healthy women when the work of breathing during exercise is precisely matched (Chapter 2). At ventilations above ~55 l min-¹, women have a greater oxygen cost of exercise hyperpnea. During intense exercise, the oxygen uptake of the respiratory muscles in women represents a greater fraction of total oxygen uptake (Chapter 3). A proportional assist ventilator can reduce the work of breathing to
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Purpose This thesis evaluated regional heterogeneity of pulmonary mechanical values within models of lung injury. To this end four separate studies were completed. I evaluated regional expiratory time constant (τE) heterogeneity and tissue strain (ε) in a lung model using functional respiratory imaging (FRI) (Study 1, Chapter 2), and developed an in vivo porcine model of lung injury (Study 2, Chapter 3). This model was used to assess changes in τE due to manipulations of respiratory gas density (Study 3, Chapter 4) and mechanical ventilation parameters (Study 4, Chapter 5). MethodsStudy 1: Using computerized tomography (CT) images we generated 3-dimensional lung models. These were used calculated global and regional values for resistance, elastance, ε and τE under three different airway pressure conditions. Study 2: Experimental lung injury was induced in 11female Yorkshire X pigs. Necropsy, light and electron microscopy of lung was performed.Study 3: I utilized a multi-compartment model to describe the effects of changes in tidal volume (VT) and positive end-expiratory pressure (PEEP) on lung emptying during passive deflation before and after experimental lung injury in 6 adult female Yorkshire X pigs. Expiratory time constants (τE) were determined by partitioning the expiratory flow-volume (V˙ V) curve into multiple discrete segments.Study 4: Tracheal pressure and flow were measured in 7 pigs before and after experimental lung injury. Gas density was altered by using helium-oxygen (He), sulfur hexafluoride-oxygen (SF6) and nitrogen-oxygen (N2) gas. ConclusionsFunctional respiratory imaging demonstrates regional variation in both ε and τE. These findings raise questions about the use of whole lung measures of ε and τE to guide clinical management of lung injury (Study 1). I developed a stable model of lung injury using SPA that replicates the light and electron microscopic findings seen in human ARDS (Study 2). A pragmatic strategy using changes in the pattern of expiration described by a multi-compartment model of τE reveals that alterations in and gas density (Study 3) as well as PEEP and VT (Study 4) change expiratory pulmonary mechanics. These observations lay the groundwork for future clinical studies in lung injured patients.
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Humans have a remarkable ability to cope with and survive exposure to hypoxia. Some have suggested a benefit in certain physiological systems in response to such exposure. However, the physiological response to hypoxia is multifaceted and includes an orchestrated response from many autonomic mechanisms. Thus, the purpose of this thesis was to more fully understand the human autonomic response to hypoxia as an integrated unit. Furthermore, pathological models of hypoxia provide evidence that suggests hypoxia can result in an autonomic response that outlasts the hypoxic stimulus. However, the persistent effect of hypoxia is only evident in certain reflexes, although comorbidities that accompany a pathological model complicate interpretation. Therefore, employing a healthy human model with continued measurement of physiological measures in the post-hypoxia period provides a more complete understanding of the integrated human physiological response to hypoxia. This Doctoral thesis is comprised of four separate investigations, each focusing on autonomic control both during and following an acute hypoxic exposure. In the first study (Chapter 2), the microneurography technique was used to demonstrate that the chemoreflex plays an important role in persistent sympathoexcitation following acute isocapnic hypoxia. With the use of the spontaneous baroreflex analysis technique, the follow-up study (Chapter 3) implicated a resetting of the arterial baroreflex that works to permit the persistent sympathoexcitation. The focus of the third study (Chapter 4) was on cerebrovascular control during fluctuations in blood pressure via bolus injections of vasoactive drugs. There was an improvement in cerebral autoregulation to increases in blood pressure following acute isocapnic hypoxia. The final study (Chapter 5) considered the role of carbon dioxide on hypoxic cerebral autoregulation, and found an impairment in isocapnic hypoxia but no effect in poikilocapnic hypoxia. The findings from this series of studies demonstrate the acute and persistent effects of short-term hypoxia, and the integrated nature in which autonomic mechanisms orchestrate the human physiological response to hypoxia.
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No abstract available.
Theses completed in 2010 or later are listed below. Please note that there is a 6-12 month delay to add the latest theses.
Early mobilization (EM) has been an increasingly recognized tool in the intensive care unit (ICU) for critically ill patients. Advances in critical care medicine has led to the growth of the cohort of patients termed ‘chronically critically ill’. These patients successfully stabilize from acute critical illness, however due to deterioration of physical and/or cognitive function become dependent on full time hospital care. ICU acquired weakness (ICUAW) is a spectrum disease characterized by symmetrical physical and/or cognitive impairments developed while admitted to an ICU. The development of ICUAW is a contributing factor that leads to chronic critical illness. EM has been proposed as a tool that can be used to prevent or slow down the onset of ICUAW. PURPOSE: The purpose of this thesis was to describe and quantify the rehabilitation practices and the cardiopulmonary trends in critically ill sepsis patients in the Vancouver General Hospital’s ICU. METHODS: Patients (n = 21) who met the inclusion and exclusion criteria were observed during a four-week period, Monday to Friday. The chart notes were used for Saturdays and Sundays. Daily cardiopulmonary vitals (e.g. heart rate (HR), blood pressure (BP), respiratory rate, peripheral oxygen saturation etc.) were taken at three time points and the chart notes were used to record test results. Additionally, physiotherapy sessions were observed and described. RESULTS: Norepinephrine had a decreased median dose during EM compared to prophylactic management in the released to ward outcome group. Sequential Organ Failure Assessment (SOFA) score was significantly different between patients who achieved a mobility score of 0 compared to ≥ 3 (p = 0.014). Sitting on the edge of the bed (EOB) elicited a HR and BP response suggestive of exercise in some patients. Lastly, the cardiopulmonary trends were consistent with what was expected. CONCLUSION: Norepinephrine dose and SOFA score may independently be able to help predict the mobility score a patient is likely to achieve during physiotherapy. The HR and MAP response observed during EOB in some patients participating in EM, presented a trend suggestive of exercise and warrants further investigation.
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The pulmonary system can maintain arterial blood gas homeostasis during exercise in healthy, young adults. However, some endurance athletes demonstrate a significant reduction in arterial oxygenation during exercise, a phenomenon termed exercise-induced arterial hypoxemia (EIAH). EIAH has been previously observed in young adults, and male masters athletes but there are no reports of gas exchange impairment in female masters athletes. It was hypothesized the majority of female masters athletes will develop EIAH during submaximal, near maximal, and maximal treadmill exercise. Pulmonary function was assessed followed by an incremental exercise test to determine maximal O2 uptake (V̇O2max). Participants were instrumented with a radial arterial catheter, an oesophageal balloon-tipped catheter, and temperature probe. Arterial samples were drawn while participants exercised at 60-70, 75, 90-95, and 100% V̇O2max for 2-4 minutes. Participants (n=6, 48-57 years) had an average V̇O2max of 47±2 ml/kg/min (range 40-55 ml/kg/min, 135-186% predicted). During submaximal, near maximal, and maximal exercise the arterial partial pressure of O2 (PaO2) decreased from rest by 14±2 mmHg (range 6-21), 13±4 (range -6-24), and 11±7 mmHg (range -7-21), respectively. The arterial partial pressure of CO2 (PaCO2) decreased from rest by 1.8±1 mmHg (range -2-6), 4±1 mmHg (range 0.3- 8), and 5±2 mmHg (range 2-5) at submaximal, near maximal, and maximal exercise, respectively. There was a reduction in oxyhemoglobin saturation 2.5± 0.3% (range 1.9-3.4) and arterial O2 content 1.2± 0.2 mL O2/100 mL of blood (range 0.7-1.8) at all intensities. Participants with a minimal change to PaCO2 tended to have a greater reduction in PaO2 (r = -0.85, R2 = 0.73, p
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The muscle metaboreflex is a cardiovascular control mechanism that contributes to the reflex increase in mean arterial pressure (MAP) and blood flow redistribution during exercise, to meet metabolic demands. The MAP response to metaboreflex activation is attenuated in females compared to males, during both limb and respiratory muscle work. Whether this sex-based difference is similar in magnitude across muscle groups is currently not well-understood. PURPOSE: The purpose of this thesis was to compare sex-based differences in the pressure response to limb and inspiratory metaboreflex activation, during relative and absolute workloads. METHODS: Seventeen healthy participants (n=9 males, n=8 females) completed two experimental visits; the first visit included pulmonary function tests, forearm volume and circumference measurements, and two bouts of exercise. The second day mimicked the first, except with no pulmonary function measurements. The exercise performed on both days were acute bouts of intermittent handgrip exercise (IHE) and pressure threshold loading (PTL) to volitional exhaustion, performed in a randomized order, and separated by 30-min of rest. PTL is a resistive breathing task that requires participants to generate large inspiratory pressures to overcome a threshold load, and attain unimpeded breathing. Participants exercised at a predetermined relative (R) or absolute (A) workload, and cardiopulmonary measurements were recorded continuously throughout. RESULTS: A time-dependent rise in MAP was observed in all participants, regardless of sex, muscle, or workload (p
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INTRODUCTION: Pediatric solid organ transplant (SOT) recipients report lower physical activity levels, exercise capacity, muscular strength, and quality of life than their healthy peers. Opportunities for structured recreational activity are limited for this population. Virtual exercise programs may reduce barriers to exercise, allow better access to specialized care, and cost less than traditional exercise rehabilitation programs. The aim of this study was to implement an 8-week virtual exercise program for pediatric SOT recipients. METHODS: A circuit-based training program with a primary focus on strength was designed by a clinical exercise physiologist (AD). All participants completed a treadmill exercise stress test prior to starting the exercise program. Self-report surveys were used to assess quality of life (Pediatric Quality of Life Inventory, PedsQL), fatigue (Pediatric Quality of Life Multidimensional Fatigue Scale, PedsQL-Fatigue), and physical activity (Physical Activity Questionnaire for Children and Adolescents, PAQ) at baseline and at completion of the program. The strength subtest of the Bruininks-Oseretsky Test of Motor Proficiency (2nd Edition) was administered virtually pre- and post-intervention. Exercise classes were conducted via Zoom, thrice weekly for 30 minutes. Weekly engagement with the study team was provided through a web-based text messaging platform (WelTel Inc., Vancouver, BC). Participants who could not attend a class were sent a recorded link of the class via email. RESULTS: Prior to the intervention, the median z-score for strength was -1.00 (-1.65 - -0.60). After the exercise intervention, strength scores improved to a z-score of -0.20 (-1.30 - 0.40); p=0.007. There were no changes in z-scores for the PAQ (-0.53 (-1.60 - -0.01) vs. -0.28 (-1.78 – 0.21) p=0.959, PedsQL -0.83 (-1.79 - -0.02) vs. -0.81 (-1.80 - -0.20); p=0.441, or PedsQL Fatigue [-0.75 (-1.90 - -0.08) vs. -0.74 (-1.49 - -0.16), p=0.314].CONCLUSION: Results showed that the delivery of this program was successful amongst participants. Increases in strength were seen following the 8-week exercise program with no changes in total quality of life, daily physical activity levels, and fatigue. These results suggest that a virtual exercise program may be used in future studies involving pediatric SOT patients to promote exercise.
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The mechanisms and sites that contribute to skeletal muscle fatigue vary depending on the specifications of the task, oxygen delivery, and fibre type composition. Due to anatomic and physiologic differences, men and women can have altered responses to a similar muscular fatiguing stimulus. The aerobic diaphragm muscle may exhibit neural protection under cases of potentially high fatigue, with a higher inhibition at the periphery. Hypoxia exacerbates key factors in diaphragm fatigue development, that may vary on the basis of sex. PURPOSE: The purpose of this thesis is to compare diaphragm fatigue between men and women under conditions of high-intensity exercise in normoxia and acute hypoxia. METHODS: Twenty healthy participants (n=10 men) came to the lab on three occasions, the first day included pulmonary characterization and a maximal graded exercise test. The final two trial days consisted of randomized exercise in a normoxic or a hypoxic condition (FIO₂ =0.21, 0.15, respectively). Exercise consisted of cycling at ~85% V̇O₂max until exhaustion; diaphragm force production was assessed via cervical magnetic stimulation pre- and post-exercise, and into recovery. RESULTS: There were no significant differences in the degree of diaphragm fatigue regardless of sex or FIO₂. Time-to-failure was significantly shorter in hypoxia for both groups (men: p = 0.016, women: p
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The diaphragm is the largest contributing muscle in a spontaneous breath. Classically, when failure in this muscle occurs, mechanical ventilation is implemented to reduce acute respiratory failure. The proportional assist ventilator (PAV) is a type of mechanical ventilator that can maintain gas homeostasis in dynamic exercise. However, PAV’s effect on the diaphragm, accessory respiratory muscles, and effectiveness during lower intensity exercise is still unclear. PURPOSE: To investigate the diaphragm electrical activity during low exercise intensity (10% below gas exchange threshold (GET)) while reducing the work of breathing via a PAV. METHODS: 8 participants (n = 4 male, n = 4 female; 26.8 ± 1 years) completed two days of testing. On day one, subjects performed a maximal VO2 exercise test on a cycle ergometer. On day 2, subjects cycled at 10% below GET while alternating breathing on the PAV and spontaneously. Electromyography of the diaphragm (EMGdi), scalenes (EMGSCA), and sternocleidomastoids (EMGSCM), work of breathing (WOB), pressure time product of the esophagus (PTPes), diaphragm (PTPdi) and gastric (PTPga) were measured throughout the experimental protocol. RESULTS: WOB was lower while breathing on the PAV during medium (p
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Competitive swimmers have high rates of exercise induced bronchoconstriction (EIB), which may be associated with repeated exposure to chlorinated pool water. The eucapnic voluntary hyperpnea (EVH) test is often used in a laboratory setting to provoke a reduction in lung function associated with EIB. Swimmers however, experience EIB symptoms in warm, humid and chlorinated environments. The relationship between EVH testing conditions and the development of EIB from swim exercise is unclear. PURPOSE: To compare the provoking effects of inspired air and high-intensity exercise in inducing EIB in swimmers to laboratory-based EVH method. METHODS: 15 collegiate swimmers (n=5 male, n=10 female; 21±2 years) completed three days of testing in random order. On day one, subjects performed an EVH test in a laboratory (EVH-L). On a separate day, swimmers performed a modified EVH test, while breathing chlorinated pool air (EVH-Cl). On a third day subjects completed a swimming challenge (Swim), performing consecutive 200 and 400 m freestyle efforts at 85% of their season’s best time (average achieved 200 and 400 m time; 2:18.52±7.79 and 4:55.22±20.38, respectively) and age-predicted heart rate maximum. Lung function was measured at baseline, as well as 3-, 5-, 10-, 15-, and 20-minutes following EVH testing and swim exercise. RESULTS: EVH-L elicited a -9.7±6.4 % fall compared to the EVH-Cl test, -6.6±9.2 % (p>0.05) and Swim, -3.0±7.5 % (p>0.05). A significant correlation in FEV1 fall index between EVH-L vs. EVH-Cl (r =0.78, p0.05) and EVH-CL vs. Swim (r =0.50, p>0.05). A greater reduction in forced expired flow between 25 and 75 % lung volume (FEF25-75) was induced by the EVH-L (-16.6±8.7 %) compared to the EVH-Cl (-8.2±14.9 %) (p>0.05) and Swim test (-1.3±15.6 %) (p
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Whether the large lungs of competitive swimmers result from intensive swim training or genetic endowment has been widely debated. Given that peak growth velocities for the lungs occur during puberty, this longitudinal study aimed to determine if competitive swimming during puberty affected lung development. Female swimmers (n=11) and healthy controls (n=10) aged 11-14 years old were assessed before and after one competitive swimming season. Pulmonary function testing included lung volumes, spirometry, diffusion capacity (DL,CO), and maximal inspiratory (PIMAX) and expiratory (PEMAX) pressures. Ventilatory constraints, including end-expiratory lung volume (EELV), expiratory flow limitation (EFL), and utilization of ventilatory capacity (V̇E/V̇ECAP), were assessed during an incremental cycling test. Despite being of similar age (p=0.10), maturational development (p=0.27), and height (p=0.38) as controls, swimmers had a larger total lung capacity (p0.05). Pubertal female swimmers already had larger lung capacities, higher flows, and greater indices of respiratory muscle strength, but similar ventilatory constraints while cycling. One competitive swimming season did not further accentuate this enhanced function or alter exercise ventilatory mechanics, suggesting that competitive swimming during puberty did not affect lung development.
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Expiratory resistive loading (ERL) elicits inspiratory as well as expiratory muscle fatigue, suggesting parallel co-activation of the inspiratory muscles during expiration. It is unknown whether the expiratory muscles are similarly co-activated to the point of fatigue during inspiratory resistive loading (IRL). The purpose of this study was to determine whether IRL elicits expiratory as well as inspiratory muscle fatigue. Male subjects (n=10) underwent isocapnic IRL to task failure (60% maximal inspiratory pressure, 15 breaths/min, 0.7 inspiratory duty cycle). Abdominal and diaphragm contractile function was assessed at baseline and at 3, 15 and 30 min post-IRL by measuring gastric twitch pressure (Pga,tw) and transdiaphragmatic twitch pressure (Pdi,tw) in response to potentiated magnetic stimulation of the thoracic and phrenic nerves, respectively. Electromyographic activity of the diaphragm, rectus abdominis, and external oblique was monitored to ensure consistency of stimulation. Fatigue was defined as >15% reduction from baseline in Pga,tw or Pdi,tw. During IRL (mean ± SE; 11.9 ± 2.5 min), mean arterial pressure and heart rate increased in a time-dependent manner (13 mmHg and 50 beats/min for the final min, respectively). Pdi,tw was significantly lower than baseline (34.1 ± 3.2 cmH₂O) at 3 min (23.2 ± 1.9 cmH₂O, p
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Mechanical ventilatory constraints have been shown to develop in healthy endurance-trained (ET) men, and both ET and untrained women due to structural and functional sex-based differences with respect to the pulmonary system. The purpose of this study was to compare the effects of unloading the respiratory system using a heliox (He-O₂) inspirate on expiratory flow limitation (EFL), the work of breathing (WOB), operational lung volumes and sensory responses (leg and breathing discomfort) between men and women. It was hypothesized that He-O₂ would reduce EFL, operational lung volumes, the WOB and sensory responses while increasing airflow rates, minute ventilation (V’E) and exercise performance. The aforementioned changes would occur to a greater extent in women and those developing EFL breathing room air (RA). Endurance trained men (n = 11) and women (n = 11) competitive cyclists completed two 5 km time trials (TT), breathing either RA or He-O₂. The maximum expiratory flow-volume (MEFV) curve method was used to determine EFL. An esophageal balloon catheter was used to measure the WOB as determined by transpulmonary pressure (the difference between esophageal and mouth pressures). Sensory responses were recorded throughout the TTs. Both sexes had a small (albeit non-significant) 2.3% improvement in power output breathing He-O₂. During the RA TT, 60% of women and 36% of men developed EFL. Heliox significantly increased the MEFV curve for both sexes however 40% of women and 45% of men still developed EFL. The magnitude of EFL was variable throughout both TT’s for all subjects due to alterations in end expired lung volume and expiratory flow rates, as subjects utilized the He-O₂ induced enhanced ventilatory reserve. Despite significantly lower V’E, women had similar WOB and operational lung volumes as men. Sensory responses were not affected by sex, inspirate, or presence of EFL. Collectively these findings suggest that EFL occurs to various extents throughout endurance exercise in both sexes and may limit endurance performance. Sex-based differences in pulmonary structure and function predispose women to mechanical ventilatory constraints breathing RA and increase women’s relative cost of breathing compared to men.
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Many young adult male athletes with a high maximal O₂ consumption (VO₂Max) show exercise-induced arterial hypoxemia (EIAH). In women, EIAH may occur at submaximal exercise intensities and at lower fitness levels, but this is controversial. Greater EIAH in women may be attributed to their increased mechanical constraints to ventilation owing to smaller airway diameters. Accordingly, the purpose of this study was to characterize EIAH, gas exchange and respiratory mechanics during exercise in young healthy women. Subjects (n=31, VO₂Max =48±1, range 28-62 mL/kg/min) completed a step-wise maximal test on a treadmill. A 3-stage constant load exercise test was also completed where the inspired gas was switched between room air and heliox (21% O₂: 79% He). Arterial blood gases (PaO₂, PaCO₂, pH), corrected for esophageal temperature, and oxyhemoglobin saturation (SaO₂) were measured at rest and during the last 30 s of each exercise stage. The work of breathing (WOB) was obtained using an esophageal balloon-tipped catheter. Expiratory flow limitation (EFL) was determined by superimposing tidal flow-volume loops on the maximum expiratory flow-volume curve. Twenty of the 31 women developed some degree of EIAH with a nadir PaO₂ and SaO₂ ranging from 58-103 mmHg and 87-98%; respectively. Subjects with EIAH were fitter (VO₂Max 51±1 vs. 42±2 mL/kg/min), had a greater VEMax (91±3 vs. 77±4 L/min) and had an increased resistive WOB (30±2 vs. 19±1 cmH₂O/breath); for the EIAH and non-EIAH groups respectively (P
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Yogic breathing exercises (YBE) are complex breathing patterns that can include hyperventilation, hypoventilation, and apnea. Some YBE can significantly alter blood gases and result in hypoxic hypercapnia. The consequence of consistent practice of these breathing exercises is unknown. Thus, the purpose of this Master’s thesis was to quantify the cardiovascular, respiratory, and cerebrovascular effects of two common YBE: bhastrika and chaturbhuj; and, to determine the effect of their consistent practice on chemosensitivity. The first study was cross-sectional and compared experienced yogic breathers (YB) with matched controls in the above categories. It determined three things. First, bhastrika and chaturbhuj result in significant hypoxic hypercapnia. Second, the increase in blood pressure during their practice was higher in experienced yogic breathers. Third, experienced YB had reduced chemosensitivity compared to controls. The second was a controlled, longitudinal training study where experimental subjects practiced yogic breathing exercises for 6 weeks. This study had three major findings. First, after 6 weeks of training, bhastrika and chaturbhuj produced hypercapnia and mild hypoxia. Second, chaturbhuj resulted in cyclic oscillation of cardiovascular variables including blood pressure, heart rate, stroke volume, and cerebral blood flow velocity with inspiration and expiration. Third, post intervention there was no change in chemosensitivity measures. The findings from these two studies demonstrate that YBE significantly alter end-tidal gases, resulting in complex oscillations of cardiovascular and cerebrovascular variables, and if practiced for the long term, may reduce chemosensitivity.
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It was hypothesized that intrapulmonary arteriovenous shunts would be recruited at lower exercise intensities in highly trained individuals, compared to untrained and moderately trained individuals. Twenty-four women with normal lung and cardiac function, completed a maximal exercise test on a semi-supine cycle ergometer, while agitated saline contrast echocardiography was performed. Subjects were considered either untrained (VO₂peak 45 ml/kg/min), as determined by their performance on the exercise test. One subject did not shunt, four subjects demonstrated shunt pre-exercise, and eleven subjects demonstrated shunt in stage one of exercise. Twenty subjects continued to shunt immediately post-exercise, and seventeen subjects continued to shunt three minutes post exercise. These findings contrast with other studies in the upright cycling position, indicating an effect of body position. Percent of VO₂peak at shunt onset was not different between the groups, indicating no influence of training status. Cardiac output was not different between groups, potentially due to the inability of subjects to reach their true maximum on the exercise test. Peripheral oxygen saturation did not drop significantly during exercise and there was no difference in the lowest value reached by each group, indicating no limitations to pulmonary gas exchange.
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Chronic obstructive pulmonary disease (COPD) is characterised by deteriorating lung and airway function. Altered peripheral skeletal muscle properties, favouring glycolytic metabolism, are also well-documented in this population. Skeletal muscle properties such as those found in COPD patients may have significant effects on the magnitude of the muscle metaboreflex. Hypotheses: It was hypothesized that the muscle metaboreflex would be magnified in people with COPD compared to healthy controls, and that disease severity and exercise capacity would be correlated with the magnitude of the muscle metaboreflex. Methods: Eleven people with mild-to-severe COPD (FEV₁.₀ = 56.3 ± 7.4% predicted) and 11 age- and gender- matched controls performed isometric handgrip exercise (IHG) for 2.5 minutes, at 35% MVC, followed by 2 minutes of post-exercise circulatory occlusion (PECO). Hemodynamic changes were measured throughout the protocol to assess the magnitude of the metaboreflex. Participants also performed a progressive cycle test to volitional exhaustion. Results: Heart rate, mean arterial pressure (MAP), leg blood flow and leg vascular resistance responses were similar between the COPD group and controls throughout IHG and PECO (% change from baseline) (p > 0.05). Heart rate was highest at minute 2.5 of IHG (COPD 18 ± 4%, control 18 ± 3%) and returned to baseline during PECO, while MAP peaked at minute 2.5 of IHG (COPD 29 ± 5%, control 30 ± 3%) and remained elevated throughout PECO (COPD 25 ± 3%, control 21 ± 2%). Total peripheral resistance rose more in the COPD group throughout the protocol and approached significance at minute 2 of PECO (COPD 39 ± 9, control 18 ± 4%, p = 0.09). Cardiac output remained significantly higher throughout IHG and PECO in the control group (IHG 2.5 min: COPD 0.08 ± 7, control 17 ± 4%, p = 0.01). There was no association between disease severity (r = -0.22, p = 0.32) or exercise capacity (r = -0.02, p=0.92) and the magnitude of the muscle metaboreflex. Conclusions: The muscle metaboreflex is preserved in people with COPD. The mechanisms responsible remain unclear, however, unchanged upper limb skeletal muscle properties and desensitization of peripheral afferents to metabolites are plausible explanations.
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