We sought to determine the impact of wearing cloth or surgical masks on the cardiopulmonary responses to moderate-intensity exercise. Twelve subjects (n=5 females) completed three, 8-min cycling trials while breathing through a: non-rebreathing valve (laboratory control), cloth, or surgical mask. Heart rate (HR), oxyhemoglobin saturation (SpO2), breathing frequency (Fb), mouth pressure, partial pressure of end-tidal carbon dioxide (PetCO2) and oxygen (PetO2), dyspnea, were measured throughout exercise. A subset of n=6 subjects completed an additional exercise bout without a mask (ecological control). There were no differences in Fb, HR or SpO2 across conditions (all p>0.05). Compared to the laboratory control (0.9±0.7cmH2O[mean±SD]), mouth pressure swings were greater with the surgical mask (4.7±0.9; p<0.0001), but similar with the cloth mask (3.6±4.8cmH2O; p=0.66). Wearing a cloth mask decreased PetO2 (-3.5±3.7mmHg) and increased PetCO2 (+2.0±1.3mmHg) relative to the ecological control (both p<0.05). There were no differences in end-tidal gases between mask conditions and laboratory control (both p>0.05). Dyspnea was similar between the control conditions and the surgical mask (p>0.05) but was greater with the cloth mask compared to laboratory (+0.9±1.2) and ecological (+1.5±1.3) control conditions (both p<0.05). Wearing a mask during short-term moderate-intensity exercise may increase dyspnea but has minimal impact on the cardiopulmonary response. Novelty bullets: • Wearing surgical or cloth masks during exercise has no impact on breathing frequency, tidal volume, oxygenation, heart rate • However, there are some changes in inspired and expired gas fractions that are physiologically irrelevant. • In young healthy individuals, wearing surgical or cloth masks during submaximal exercise has few physiological consequences.

Voluntary apnoea causes splenic contraction and reductions in heart rate (HR; bradycardia), and subsequent transient increases in haemoglobin concentration ([Hb]). Ascent to high altitude (HA) induces systemic hypoxia and reductions in oxygen saturation (S pO 2), which may cause tonic splenic contraction, which may contribute to haematological acclimatization associated with HA ascent. We measured resting cardiorespiratory variables (HR, S pO 2 , [Hb]) and resting splenic volume (via ultrasound) during incremental ascent from 1400 m (day 0) to 3440 m (day 3), 4240 m (day 7) and 5160 m (day 10) in non-acclimatized native lowlanders during assent to HA in the Nepal Himalaya. In addition, apnoea-induced responses in HR, S pO 2 and splenic volume were measured before and after two separate voluntary maximal apnoeas (A1

Maintenance of arterial blood gases is achieved through sophisticated regulation of ventilation, mediated by central and peripheral chemoreflexes. Respiratory chemoreflexes are important during exposure to high altitude owing to the competing influence of hypoxia and hypoxic hyperventilation-mediated hypocapnia on steadystate ventilatory drive. Inter-individual variability exists in ventilatory acclimatization to high altitude, potentially affecting the development of acute mountain sickness (AMS). We aimed to quantify ventilatory acclimatization to high altitude by comparing differential ascent and descent values (i.e. hysteresis) in steady-state cardiorespiratory variables. We hypothesized that: (i) the hysteresis area formed by cardiorespiratory variables during ascent and descent would quantify the magnitude of ventilatory acclimatization; and (ii) larger hysteresis areas would be associated with lower AMS symptom scores during ascent. In 25 healthy, acetazolamide-free trekkers ascending to and descending from 5160 m, cardiorespiratory hysteresis was measured in the partial pressure of end-tidal CO 2 , peripheral oxygen saturation, minute ventilation, chemoreceptor stimulus index (end-tidal CO 2 /peripheral oxygen saturation) and the calculated steady-state chemoreflex drive (SS-CD; minute ventilation/chemoreceptor stimulus index) using portable devices (capnograph, peripheral pulse oximeter and respirometer, respectively). Symptoms of AMS were assessed daily using the Lake Louise questionnaire. We found that: (i) ascent-descent hysteresis was present in all cardiorespiratory variables; (ii) SS-CD is a valid metric for tracking ventilatory acclimatization to high altitude; and (iii) the highest AMS scores during ascent exhibited a significant, moderate and inverse correlation with the magnitude of SS-CD hysteresis (r s = −0.408, P = 0.043). We propose that ascent-descent hysteresis is a

Smaller airways increase resistance and the propensity towards turbulent airflow, both of which are thought to be mechanisms behind greater resistive and total work of breathing (Wb) in females. Previous research examining the effect of airway size on the Wb between the sexes is limited by the inability to experimentally manipulate airway size. Heliox (21% oxygen, balance helium) is less dense than room air which reduces turbulent airflow and airway resistance. The purpose of our study was to utilize heliox inspiration in females to provide a physiologically similar stimulus as increasing airway size. We hypothesized that when breathing heliox, females would have a similar Wb to males breathing room air. Eighteen healthy young subjects (n=9 females) completed two maximal exercise tests on a cycle ergometer over two days. For one test subjects breathed room air and the other heliox. The Wb was assessed with an esophageal balloon catheter. During the room air trial, when ventilations were >65 l·min-1, females had a significantly greater Wb compared to males (p<0.05). The greater Wb in females was due to greater resistance to turbulent flow. For both sexes, breathing heliox resulted in increased expiratory flow (+132±18% of room air), an elimination of expiratory flow limitation, and a reduction in the Wb (69±12% of room air) (all p<0.05). When breathing heliox, the females Wb was not different than the males breathing room air. Our findings support the idea that the smaller conducting airways in females are responsible for a greater total and resistive Wb.

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