Thesis Defence: Investigating Sex-Based Differences in Diaphragm Blood Flow and Fatigue in Humans
December 3 at 9:00 am - 1:00 pm
Megan Lance, supervised by Dr. Glen Foster, will defend their thesis titled “Investigating Sex-Based Differences in Diaphragm Blood Flow and Fatigue in Humans” in partial fulfillment of the requirements for the degree of Master of Science in Health and Exercise Sciences.
An abstract for Megan Lance’s thesis is included below.
Defences are open to all members of the campus community as well as the general public. Registration is not required for in-person defences.
ABSTRACT
The rhythmic contraction of the main inspiratory muscle, the diaphragm, is essential for maintaining ventilation. During exercise, the greater blood flow demands of the diaphragm are thought to be supported by an inspiratory muscle metaboreflex (IMM). However, how diaphragm blood flow (Q̇dia) is related to the IMM sensitivity and development of diaphragm fatigue is not well understood, as minimally invasive measures of Q̇dia have only recently become available. The IMM is attenuated in females compared with males during fatiguing pressure-matched diaphragmatic loading. This suggests that females develop less diaphragm ischaemia and metaboreceptor activation than males. We hypothesized that post-exercise hyperaemia of the diaphragm would be less in females than males during matched diaphragmatic work. Healthy males (n = 11, 28 ± 6 years, means ± sd) and females (n = 11, 26 ± 4 years) completed a 6-minute loading task targeting a transdiaphragmatic pressure (Pdi) of 80 cmH2O with a duty cycle of 0.7. Contrast-enhanced ultrasound was used to quantify Q̇dia during an end-expiratory apnoea at baseline, and 50% and 100% of the time to task completion. The change in mean arterial pressure (ΔMAP) during loading, and the pre- to post-task change in transdiaphragmatic twitch pressure (ΔPdi,tw; bilateral electrical stimulation of phrenic nerves), assessed metaboreflex activation and fatigue, respectively. Throughout loading, the accumulated pressure-time-product for Pdia (males: 14,351 ± 919 cmH2O, females 14,003 ± 1,947 cmH2O; P = 0.600) and percentage of maximal Pdia (%PDImax; males: 51 ± 8%, females: 51 ± 9%; P = 0.870) was not different between sexes.
Inspiratory loading resulted in IMM activation (ΔMAP, +21 [95% Confidence Interval: 18, 24] mmHg; P < 0.0001), diaphragm fatigue (ΔPdi,tw, -18.1 [-13.3, -7.6] %; P < 0.0001) and a post-exercise hyperaemia response (ΔQ̇dia, +15.8 [12.5, 19.1] AU/s; P < 0.0001) at 100% of task completion, but did not differ between sexes ( P > 352 ). There was a significant positive relationship between ΔQ̇DIA and %PDIMAX (r2 = 0.211; P = 0.032). There was no relationship between the ΔQ̇DIA and ΔMAP (r2 = 0.011; P = 0.638), ΔHR (r2 = 0.007; P = 0.706), or ΔPdi,tw (r2 = 0.001, P = 0.914). These data demonstrate that Q̇DIA relates to the degree of exercise intensity and that the metaboreflex response may depend more on inter-individual differences in MAP responses (i.e., genetics, fitness levels) or central command, as opposed to the post-exercise hyperaemic response.
