Reducing Turbulent Airflow Lowers Healthy Females Work Of Breathing During Exercise To A Level Similar To Males

Abstract

ObjectiveImaging studies have shown that healthy females have smaller conducting airways than height matched males. The smaller conducting airways would increase the propensity towards turbulent airflow and this is thought to be the underlying mechanism behind greater resistive and total work of breathing in females. Heliox (21% O2: balance He) is considerably less dense than room air and has a greater propensity towards laminar flow. As such, respiring heliox should produce a physiologically similar effect as increasing airway size and allows for experimental manipulation of work of breathing between the sexes. The objective of the study was to determine if turbulent flow is responsible for the greater work of breathing in healthy females.MethodsSix healthy men (Age=24±4 years) and five healthy women (Age=22±2 years) completed two step‐wise maximal exercise tests on separate days. On one day subjects respired compressed room air and on the other a compressed helium‐oxygen mixture (~21% O2: balance He). Room air and heliox were humidified and delivered in an identical manner. Esophageal pressure was measured with a balloon catheter and allowed for the determination of the work of breathing via integration of transpulmonary pressure‐volume loops. The work of breathing‐ventilation relationship was modelled using a previously described equation consisting of two constants that describe the mechanical work to overcome i) viscous resistance and laminar flow and ii) turbulent resistance.ResultsEnd‐exercise ventilation was significantly greater for females during the heliox trial (82±9 vs. 94±11 L min−1, P=0.02) but there was no difference in work of breathing (122±38 vs. 116±42 J min−1, P=0.45), for room air and heliox respectively. Using the modeled work of breathing data, compared to males, females had a significantly greater work of breathing at ~70 L min−1 during the room air trial and this was due to greater work to overcome turbulent resistance. When comparing the heliox trials between sexes, there was no difference in the work of breathing. Similarly, after ~60 L min−1 compared to the room air trial, the work of breathing among females had significantly lowered during the heliox trial and this was due to a lower contribution of turbulent resistance.ConclusionOur results suggest that increased turbulent flow, as a result of smaller conducting airways, is responsible for the greater work of breathing in healthy young females during exercise.Support or Funding InformationNatural Sciences and Engineering Research Council of Canada RGPIN‐2019‐04615 (PBD). Canada Foundation for Innovation #38432 (PBD).