What Is the Point of the Peak? Assessing Steady-State Respiratory Chemoreflex Drive in High Altitude Field Studies

Swallow-breathing coordination during incremental ascent to altitude

“…Additionally respiratory rate, heart rate, mean arterial pressure (MAP), truenormalV˙ I , SpO 2 , P ET CO 2 and steady-state chemoreflex drive (SS-CD) were measured. The SS-CD was computed by calculating a stimulus index (SI; P ET CO 2 /SpO 2 ), and then comparing minute ventilation against SI (Bruce CD, 2018; Pfoh et al, 2017). A repeated measures ANOVA was used to determine differences in swallow motor pattern and respiratory parameters across the three elevations with significance at p ≤ 0.05, and if significance was met the LSD post-hoc test was used.…”

“…Incremental ascent to high altitudes (>2,000m) produces hypoxia (low O 2 ) induced hyperventilation, resulting in hypocapnia (low CO 2 ) (Huang et al, 1984; Weil, 1986). As climbers acclimatize to high altitude they can reach a new “steady-state chemoreflex drive” in which balance is achieved between hypoxia and hypocapnia, while ventilation parameters can return to near baseline conditions (Bruce CD, 2018; Pfoh et al, 2017). Additionally, healthy individuals that are not acclimatized to high altitude conditions can have changes in pulmonary mechanics due to interstitial pulmonary edema, which can be accompanied with accumulation of fluid within and around the airway walls (Cremona et al, 2002; Pratali et al, 2010; Schoene et al, 1988).…”

Prior oxygenation, but not chemoreflex responsiveness, determines breath‐hold duration during voluntary apnea

“…The SS‐CD provides an indirect measurement of the ventilatory strategy employed from contributions of both peripheral and CCRs in the steady state, given the prevailing chemostimuli, including pressure of end‐tidal ( P ET )CO 2 (Torr) and peripheral oxygen saturation (SpO 2 ; %). Calculating the SS‐CD requires only steady‐state measures and minimal equipment, which could provide utility in fieldwork or clinical studies looking to assess chemosensitivity in the context of ventilatory acclimatization (e.g., Bruce et al., 2018). Voluntary breath‐hold duration (BHD) has also been explored as an alternative test for assessing peripheral chemoreceptor sensitivity (e.g., Feiner et al., 1995; Trembach & Zabolotskikh, 2017).…”

Coordination of airway protective behaviors and swallow: effects of afferent feedback and sex.

“…Additionally respiratory rate, heart rate, mean arterial pressure (MAP), V̇I, SpO2, PETCO2 and steady-state chemoreflex drive (SS-CD) were measured. The SS-CD was computed by calculating a stimulus index (SI; PETCO2/SpO2), and then comparing minute ventilation against SI (Bruce CD, 2018;Pfoh, Steinback, Berg, Bruce, & Day, 2017). A repeated measures ANOVA was used to determine differences in swallow motor pattern and respiratory parameters across the three elevations with significance at p ≤ 0.05, and if significance was met the LSD posthoc test was used.…”

“…Incremental ascent to high altitudes (>2,000m) produces hypoxia (low O2) induced hyperventilation, resulting in hypocapnia (low CO2) (Huang, Alexander, Grover, Maher, McCullough, McCullough, Moore, Sampson, Weil, & Reeves, 1984;Weil, 1986). As climbers acclimatize to high altitude they can reach a new "steady-state chemoreflex drive" in which balance is achieved between hypoxia and hypocapnia, while ventilation parameters can return to near baseline conditions (Bruce CD, 2018;Pfoh, Steinback, Berg, Bruce, & Day, 2017). Additionally, healthy individuals that are not acclimatized to high altitude conditions can have changes in pulmonary mechanics due to interstitial pulmonary edema, which can be accompanied with accumulation of fluid within and around the airway walls (Cremona, Asnaghi, Baderna, Brunetto, Brutsaert, Cavallaro, Clark, Cogo, Donis, & Lanfranchi, 2002;Pratali, Cavana, Sicari, & Picano, 2010;Schoene, Swenson, Pizzo, Hackett, Roach, Mills Jr, Henderson Jr, & Martin, 1988).…”