5a Sex Differences in Respiratory Responses during Exercise in Obesity

Study Notes on "Sex differences in the ventilatory responses to exercise in mild to moderate obesity"

Author Information

Dharini M. Bhammar
Bryce N. Balmain
Tony G. Babb
Vipa Bernhardt Institutions:
1. Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas and UT Southwestern Medical Center, Dallas, TX, USA
2. Center for Tobacco Research, Division of Medical Oncology, Department of Internal Medicine, The Ohio State University, Columbus, OH, USA
3. Department of Health & Human Performance, Texas A&M University - Commerce, Commerce, TX, USA
Correspondence: Dharini M. Bhammar, 3650 Olentangy River Road, Suite 420, Columbus OH, 43214, USA, Email: Dharini.Bhammar@osumc.edu
Funding Information: NIH, Grant/Award Number: R01 HL096782-01A2; King Charitable Foundation Trust; Cain Foundation; Texas Health Presbyterian Hospital Dallas

Abstract

Obesity affects ventilatory responses, possibly more in females due to sex-related morphological traits in the respiratory system.
Study aimed to examine sex differences in ventilatory responses during exercise in adults with obesity.
Participants: 73 adults with obesity, 48 females.
Key assessments:
- Pulmonary function testing
- Underwater weighing
- MRI
- Graded exercise test to exhaustion
- Two constant work rate exercise tests: one at a fixed work rate and another at relative intensity (50% of peak oxygen uptake, $V̇ O_2peak$ ).
Results showed females use less of their ventilatory capacity at peak exercise compared to males.
The study emphasizes customization of exercise prescriptions to improve respiratory comfort, especially in females.

Keywords

Breathing limitations
Dynamic hyperinflation
Dyspnoea
Expiratory flow limitation
Operating lung volumes

Introduction

Increasing evidence suggests significant sex differences in respiratory anatomy and physiology.
Findings:
- Females typically have smaller lungs for their age and stature, impacting airflow resistance.
- Differences in rib cage structure lead to varied muscle reliance during breathing (intercostal muscles vs. diaphragm).
Impact of Obesity on Respiration:
- Mechanical load restricts functional residual capacity (FRC) and alters breathing mechanics.
- Enhanced impact of obesity-related changes on females’ respiratory functions due to existing morphological differences.
Fat Distribution:
- Females usually display gynoid obesity (more subcutaneous fat), while males show android patterns (visceral fat).
Findings highlight the need for studies on sex impacts regarding obesity and ventilatory function.

Methods

Ethical Approval

UT Southwestern IRB approved the study.
Participants provided informed consent, aligning with the principles of the Declaration of Helsinki.

Participants

Aged between 20-45, non-smokers, BMI ranging from 30-50 kg/m².
Exclusion criteria: history of asthma or cardiovascular issues, significant physical activity in the last 6 months.
No restrictions on menstrual cycle phases as hormonal fluctuations do not significantly affect ventilation responses.

Study Design

Participants attended four laboratory sessions to collect various data:
1. Visit 1: Measurements for height, weight, body composition, and pulmonary function recording.
2. Visit 2: Constant work rate exercise test and graded exercise test to exhaustion.
3. Visit 3: 50% $V̇ O_2peak$ constant work rate exercise test.
4. Visit 4: MRI for fat distribution assessment.

Pulmonary Functions

All participants underwent spirometry, lung volumes, and diffusing capacity assessments using the body plethysmograph according to ATS/ERS guidelines.
Reference values were derived from established equations.
Bronchodilator responsiveness tested after administering 360 µg of albuterol sulfate.

Constant Work Rate Exercise Tests

Tests were conducted with participants on a cycle ergometer:
- Session included two 6-minute constant work rate tests:
- Test 1: Males: 105 W, Females: 60 W.
- Session focused on standardizing work for perceived breathlessness measurements.
- Moderate breathlessness ratings led to exclusion in the primary study.
Second test elicited a work rate targeting 50% $V̇ O_2peak$ .

Graded Peak Exercise Test

Intensity increased by fixed increments based on sex personality, leading to peak exhaustion.

Measurements During Exercise

Various metrics collected: heart rate, oxygen uptake ( $V̇ O<em>2$ ), carbon dioxide production ( $V̇ CO</em>2$ ), andminute ventilation ( $V̇ E$ ).
Flow metering via pneumotachographs during inhalation/exhalation.
End-expiratory lung volume (EELV) calculated as total lung capacity (TLC) minus inspiratory capacity (IC); end-inspiratory lung volume (EILV) as sum of EELV and tidal volume (VT).
Expiratory flow limitation (EFL) defined as a percentage of tidal volume where flow reaches its maximum capacity, and dynamic hyperinflation assessed via resting vs. exercise IC changes.

MRI Assessments

Multiple MRI scans through designated anatomical regions for fat distribution were performed.

Statistical Analysis

Data represented as means ± SD with sex differences analyzed via Student’s t-test or Wilcoxon rank-sum test.
Analyzed relationships among variables using Pearson or Spearman correlation, with a two-way ANOVA to compare differences by sex and EFL status.
Linear mixed models utilized to assess variability in responses matched by ventilation ranges.
Statistical significance established at p < 0.05.

Results

Participant Demographics

73 participants included in analysis; 48 females, 25 males.
Key Findings:
- Males exhibited lower body fat percentage compared to females.
- Significant pulmonary function differences noted (e.g., FEV1, FVC).
- Differences in fat distribution were evident between sexes.

Constant Work Rate Exercise Tests

Higher oxygen requirements in male participants at selected work rates reflecting physiological differences.
Females adopted a shallower breathing pattern during exercise.
Peak $V̇ E$ percentages indicated differences in ventilatory capacity usage.
Summary of findings:
- Higher EELV and differences in operational lung volumes between sexes.
- Males experienced greater EFL.

Peak Exercise Tests

Males’ absolute $V̇ O_2peak$ was higher while females had lower tidal volume.
No differences in perceived exertion between sexes at matched ventilation levels.
Females’ ventilatory response remained more significant throughout submaximal exercise levels.

Discussion

Findings indicate that females with obesity exhibit distinct ventilatory responses compared to males.
EELV was greater in females, correlating with a shallower breathing strategy contributing to lower $V̇ E$ effectiveness.
Contradicted initial hypotheses regarding EFL prevalence between sexes; males had more EFL multi-faceted highly correlated with fat mass.
Suggests potential weight loss strategies and exercise plans may vary by gender.
Dyspnoea perception nuances comparing daily activities indicate the importance of addressing discomfort in obesity management.

Limitations

Lack of control group without obesity limited comprehensive understanding.
Fixed work rates exceeded ventilatory threshold for 70-80% participants; however, overall conclusions remained valid due to consistent reported results in submaximal testing ranges.
Interaction of psychological and social variables relevant to dyspnoea perception requires further examination.
Younger participant demographics may not generalize to older groups.

Conclusion

Ventilatory constraints in obesity present differently across sexes.
Tailoring exercise programming to address specific dyspnoea experiences in obesity management is recommended.

Acknowledgments

Acknowledgment of funding sources and contributors involved during various stages of project development

References

American Thoracic Society Guidance for Lung Function Testings and Reference Values.
Numerous studies evaluating sex differences in respiratory function.