Oxygen cost of exercise hyperpnoea is greater in women compared with men

Abstract

Key pointsr The oxygen cost of breathing represents a significant fraction of total oxygen uptake during intense exercise.r At a given ventilation, women have a greater work of breathing compared with men, and because work is linearly related to oxygen uptake we hypothesized that their oxygen cost of breathing would also be greater.r For a given ventilation, women had a greater absolute oxygen cost of breathing, and this represented a greater fraction of total oxygen uptake.r Regardless of sex, those who developed expiratory flow limitation had a greater oxygen cost of breathing at maximal exercise.r The greater oxygen cost of breathing in women indicates that a greater fraction of total oxygen uptake (and possibly cardiac output) is directed to the respiratory muscles, which may influence blood flow distribution during exercise.Abstract We compared the oxygen cost of breathing (V O 2 RM ) in healthy men and women over a wide range of exercise ventilations (V E ). Eighteen subjects (nine women) completed 4 days of testing. First, a step-wise maximal cycle exercise test was completed for the assessment of spontaneous breathing patterns. Next, subjects were familiarized with the voluntary hyperpnoea protocol used to estimateV O 2 RM . During the final two visits, subjects mimicked multiple times (four to six) the breathing patterns associated with five or six different exercise stages. Each trial lasted 5 min, and on-line pressure-volume and flow-volume loops were superimposed on target loops obtained during exercise to replicate the work of breathing accurately. At ß55 l min −1 V E ,V O 2 RM was significantly greater in women. At maximal ventilation, the absoluteV O 2 RM was not different (P > 0.05) between the sexes, but represented a significantly greater fraction of whole-bodyV O 2 in women (13.8 ± 1.5 vs. 9.4 ± 1.1%V O 2 ). During heavy exercise at 92 and 100% V O 2 max , the unit cost ofV E was +0.7 and +1.1 ml O 2 l −1 greater in women (P < 0.05). AtV O 2 max , men and women who developed expiratory flow limitation had a significantly greaterV O 2 RM than those who did not (435 ± 44 vs. 331 ± 30 ml O 2 min −1 ). In conclusion, women have a greateṙ V O 2 RM for a givenV E , and this represents a greater fraction of whole-bodyV O 2 . The greaterV O 2 RM in women may have implications for the integrated physiological response to exercise. Abbreviations EFL, expiratory flow limitation; MEFV, maximal expiratory flow-volume;V E , expired minute ventilation;V Emax , maximal expired minute ventilation;V O2 , oxygen uptake;V O2 max , maximal oxygen uptake;V O2RM , oxygen uptake of the respiratory muscles; WOB, work of breathing.

Reducing the within-patient variability of breathing for radiotherapy delivery in conscious, unsedated cancer patients using a mechanical ventilator

“…Conscious and unsedated subjects can also be ventilated at their own spontaneous frequency and volume. 6 Mechanical ventilation, however, is inherently restful, not only because of the regular rhythm, but also because by taking over the work of the respiratory muscles (approximately 10% of metabolic rate 15,16 ), it removes the effort of voluntary breathing. 6 Thus, to satisfy ventilation now matching the 10% lower metabolic rate, patients would need to be mechanically ventilated only to achieve a minute ventilation of approximately 10% less (approximately 5.4 l min −1 ), using either a slightly smaller frequency and or volume.…”

Quantifying the shape of maximal expiratory flow-volume curves in healthy humans and asthmatic patients

“…All procedures in the original investigations received institutional ethical approval. To determine the relationship between the SR and EFL, eighty-four young healthy subjects were analyzed from published data (Dominelli et al, 2013, 2011, 2015b, 2014b). All subjects were non-smokers and had normal spirometry (Tan et al, 2011).…”

A proportional assist ventilator to unload respiratory muscles experimentally during exercise in humans

“…For example, if the WOB is reduced, and presumably the oxygen demand of the respiratory muscles is decreased, does this equate to measurable differences in whole-bodyV O 2 ? To verify this, we tested a subject whose oxygen cost of breathing we had previously determined (Dominelli et al 2015b) and had them exercise for a fixed duration and time with and without the PAV. The averageV E for the trial without the PAV was 140 l min −1 , which, based on the subject's measured WOB, corresponded to a respiratory muscle oxygen consumption (V O 2 RM ) of 262 ml min −1 .…”

“…The work of breathing (WOB) during eupnoea is minimal and represents a small fraction of whole-body energy expenditure (Otis, 1954). However, during dynamic exercise the WOB increases exponentially as minute ventilation (V E ) rises, and the respiratory muscle oxygen uptake can represent upwards of 15% of maximal O 2 uptake (V O 2 max ; Aaron et al 1992;Dominelli et al 2015b). In order to gain a better understanding of the complex interrelationships between ventilation, WOB and the bioenergetics of the respiratory musculature during exercise, a long-standing approach is to manipulate the WOB experimentally.…”