The stability of blood gases and CO-oximetry under slushed ice and room temperature conditions.

OBJECTIVES: Human blood gas stability data is limited to small sample sizes and questionable statistical techniques. We sought to determine the stability of blood gases under room temperature and slushed iced conditions in patients using survival analyses. METHODS: Whole blood samples from ∼200 patients were stored in plastic syringes and kept at room temperature (22-24 °C) or in slushed ice (0.1-0.2 °C) before analysis. Arterial and venous pO2 (15-150 mmHg), pCO2 (16-72 mmHg), pH (6.73-7.52), and the CO-oximetry panel [total hemoglobin (5.4-19.3 g/dL), percentages of oxyhemoglobin (O2Hb%, 20-99%), carboxyhemoglobin (COHb, 0.1-5.4%) and methemoglobin (MetHb, 0.2-4.6%)], were measured over 5-time points. The Royal College of Pathologists of Australasia's (RCPA's) criteria determined analyte instability. Survival analyses identified storage times at which 5% of the samples for various analytes became unstable. RESULTS: COHb and MetHb were stable up to 3 h in slushed ice and at room temperature; pCO2, pH was stable at room temperature for about 60 min and 3 h in slushed ice. Slushed ice shortened the storage time before pO2 became unstable (from 40 to 20 min), and the instability increased when baseline pO2 was ≥60 mmHg. The storage time for pO2, pCO2, pH, and CO-oximetry, when measured together, were limited by the pO2. CONCLUSIONS: When assessing pO2 in plastic syringes, samples kept in slushed ice harm their stability. For simplicity's sake, the data support storage times for blood gas and CO-oximetry panels of up to 40 min at room temperature if following RCPA guidelines.

Standardisation and application of the single-breath determination of nitric oxide uptake in the lung.

Diffusing capacity of the lung for nitric oxide (DLNO), otherwise known as the transfer factor, was first measured in 1983. This document standardises the technique and application of single-breath DLNO This panel agrees that 1) pulmonary function systems should allow for mixing and measurement of both nitric oxide (NO) and carbon monoxide (CO) gases directly from an inspiratory reservoir just before use, with expired concentrations measured from an alveolar "collection" or continuously sampled via rapid gas analysers; 2) breath-hold time should be 10 s with chemiluminescence NO analysers, or 4-6 s to accommodate the smaller detection range of the NO electrochemical cell; 3) inspired NO and oxygen concentrations should be 40-60 ppm and close to 21%, respectively; 4) the alveolar oxygen tension (PAO2 ) should be measured by sampling the expired gas; 5) a finite specific conductance in the blood for NO (θNO) should be assumed as 4.5 mL·min-1·mmHg-1·mL-1 of blood; 6) the equation for 1/θCO should be (0.0062·PAO2 +1.16)·(ideal haemoglobin/measured haemoglobin) based on breath-holding PAO2 and adjusted to an average haemoglobin concentration (male 14.6 g·dL-1, female 13.4 g·dL-1); 7) a membrane diffusing capacity ratio (DMNO/DMCO) should be 1.97, based on tissue diffusivity.

Team Logo Predicts Concussion Risk: Lessons in Protecting a Vulnerable Sports Community from Misconceived, but Highly Publicized Epidemiologic Research.

BACKGROUND: Observational research has linked altitude to concussion risk, but the physiologic and epidemiologic bases for this association remain questionable. METHODS: We performed a retrospective cohort study by analyzing four seasons of National Football League data from a widely used database (Concussion Watch) to determine if previous claims that altitude ≥196 m reduced concussion risk were replicable and whether an arbitrary predictor variable (animal vs. non-animal team logo) was related to concussion risk. Relative risk (RR) and 95% confidence intervals (95% CIs) were computed. RESULTS: The previous association with altitude was reproduced for earlier seasons, but not replicable for recent seasons (RR = 0.92 [95% CI = 0.70, 1.22]). Across four combined seasons, "higher altitude" (RR = 0.78 [0.64, 0.96]) and animal logo (RR = 0.75 [0.63, 0.89]) were similarly associated with reduced concussion risk. CONCLUSIONS: Inconsistent epidemiologic effects, combined with weak physiologic rationale, suggest links between altitude and concussion are coincidental. Interdisciplinary critique of concussion research is necessary to ensure that marketing claims and clinical recommendations are scientifically justified.See video abstract at, http://links.lww.com/EDE/B234.

Controlled Frequency Breathing Reduces Inspiratory Muscle Fatigue.

Burtch, AR, Ogle, BT, Sims, PA, Harms, CA, Symons, TB, Folz, RJ, and Zavorsky, GS. Controlled frequency breathing reduces inspiratory muscle fatigue. J Strength Cond Res 31(5): 1273-1281, 2017-Controlled frequency breathing (CFB) is a common swim training modality involving holding one's breath for approximately 7-10 strokes before taking another breath. We sought to examine the effects of CFB training on reducing respiratory muscle fatigue. Competitive college swimmers were randomly divided into either the CFB group that breathed every 7-10 strokes or a control group that breathed every 3-4 strokes. Twenty swimmers completed the study. The training intervention included 5-6 weeks (16 sessions) of 12 × 50-m repetitions with breathing 8-10 breaths per 50-m (control group) or 2-3 breaths per 50-m (CFB group). Inspiratory muscle fatigue was defined as the decrease in maximal inspiratory pressure (MIP) between rest and 46 seconds after a 200-yard freestyle swimming race (115 seconds [SD 7]). Aerobic capacity, pulmonary diffusing capacity, and running economy were also measured pre- and posttraining. Pooled results demonstrated a 12% decrease in MIP at 46 seconds post-race (-15 [SD 14] cm H2O, effect size = -0.48, p < 0.01). After 4 weeks of training, only the CFB group prevented a decline in MIP values before to 46 seconds after race (-2 [13] cm H2O, p > 0.05). However, swimming performance, aerobic capacity, pulmonary diffusing capacity, and running economy did not improve (p > 0.05) posttraining in either group. In conclusion, CFB training appears to prevent inspiratory muscle fatigue; yet, no difference was found in performance outcomes.

Hydration assessment among marathoners using urine specific gravity and bioelectrical impedance analysis.

The present study examined the relationship between urine specific gravity (Usg), body mass (BM) and bioelectrical impedance determined variables [total body water (TBW), per cent TBW and impedance values] before and after a marathon (n = 25 men; 10 women). A significant reduction in BM (pre: 71.2 ± 12.4 kg; post: 69.6 ± 12.0 kg; p < 0.001) and an increase in Usg (pre: 1.009 ± 0.007; post: 1.018 ± 0.009; p < 0.001) was observed post-race. TBW was not significantly decreased (pre: 42.7 ± 8.0 kg; post: 42.4 ± 7.7 kg) while per cent TBW significantly increased post-race (pre: 60.0 ± 3.9%; post: 60.8 ± 3.8%; p < 0.001). Impedance values were significantly greater post-race (pre: 3288 ± 482; post: 3416 ± 492 Ω; p < 0.001). There was no correlation between the change in Usg and the change in BM or any of the bioelectrical impedance determined variables. On average, BM, Usg and impedance values appear to express changes in hydration; however, the observed changes among these variables for a given individual appear to be inconsistent with one another.

Faces and fitness: attractive evolutionary relationship or ugly hypothesis?

In recent years, various studies have attempted to understand human evolution by examining relationships between athletic performance or physical fitness and facial attractiveness. Over a wide range of five homogeneous groups (n = 327), there is an approximate 3% shared variance between facial attractiveness and athletic performance or physical fitness (95% CI = 0.5-8%, p = 0.002). Further, studies relating human performance and attractiveness often have major methodological limitations that limit their generalizability. Thus, despite statistical significance, the association between facial attractiveness and human performance has questionable biological importance. Here, we present a critique of these studies and provide recommendations to improve the quality of future research in this realm.

The Effects of Pre-Exercise Ginger Supplementation on Muscle Damage and Delayed Onset Muscle Soreness.

Ginger possesses analgesic and pharmacological properties mimicking non-steroidal antiinflammatory drugs. We aimed to determine if ginger supplementation is efficacious for attenuating muscle damage and delayed onset muscle soreness (DOMS) following high-intensity resistance exercise. Following a 5-day supplementation period of placebo or 4 g ginger (randomized groups), 20 non-weight trained participants performed a high-intensity elbow flexor eccentric exercise protocol to induce muscle damage. Markers associated with muscle damage and DOMS were repeatedly measured before supplementation and for 4 days following the exercise protocol. Repeated measures analysis of variance revealed one repetition maximum lift decreased significantly 24 h post-exercise in both groups (p < 0.005), improved 48 h post-exercise only in the ginger group (p = 0.002), and improved at 72 (p = 0.021) and 96 h (p = 0.044) only in the placebo group. Blood creatine kinase significantly increased for both groups (p = 0.015) but continued to increase only in the ginger group 72 (p = 0.006) and 96 h (p = 0.027) post-exercise. Visual analog scale of pain was significantly elevated following eccentric exercise (p < 0.001) and was not influenced by ginger. In conclusion, 4 g of ginger supplementation may be used to accelerate recovery of muscle strength following intense exercise but does not influence indicators of muscle damage or DOMS.

The effect of l-citrulline and watermelon juice supplementation on anaerobic and aerobic exercise performance.

Citrulline has been proposed as an ergogenic aid, leading to an interest in watermelon given its high citrulline concentration. The aim of this study was to determine the effects of a single, pre-exercise dose of l-citrulline, watermelon juice, or a placebo on the total maximum number of repetitions completed over 5 sets, time to exhaustion, maximal oxygen consumption (VO2max), anaerobic threshold, and flow-mediated vasodilation. A randomised double-blind within-participants study design was used to examine these effects among 22 participants (n = 11 males). Supplementation included either a 7.5% sucrose drink containing 6 g of l-citrulline, 710 mL of watermelon juice (~1.0 g citrulline), or a 7.5% sucrose placebo drink. Supplementation was administered 1 or 2 h before exercise testing to investigate a timing effect. There was no significant effect between the three supplements for the total number of repetitions, time to exhaustion, VO2max, anaerobic threshold, or flow-mediated vasodilation. There was also no interaction observed relative to gender or supplement timing (P > 0.05). A single dose of l-citrulline or watermelon juice as a pre-exercise supplement appears to be ineffective in improving exercise performance; however, greater doses of l-citrulline have been shown to be safe and are currently left unexamined.

The effect of increased physical activity on pulmonary diffusing capacity in unfit women.

The purpose of the study was to determine whether short-term high-intensity aerobic interval training improves resting pulmonary diffusing capacity for nitric oxide (DLNO) and carbon monoxide (DLCO). Twenty-eight sedentary women [mean (SD) age 32 (11) years, body mass index 24.3 (5.7) kg m(-2)] were randomly assigned to either a self-directed moderate-intensity physical activity (n = 14) group or a supervised high-intensity aerobic interval training group (n = 14). The moderate physical activity group and the aerobic interval training group increased weekly physical activity energy expenditure by 800 and 1600 kcal week(-1), respectively. After 6 weeks, aerobic capacity increased to a similar exent in both groups (mean improvement 8%, effect size 0.39). The DLNO, but not DLCO, increased to a similar extent in both groups, by 4% or 3.0 (5.7) [95% confidence interval 0.8, 5.2] ml min(-1) mmHg(-1) m(-2) from pre- to post-training (effect size 0.27). There was no correlation between the change in aerobic capacity and the change in DLNO (P > 0.05) or between the change in aerobic capacity and the change in total weekly physical activity energy expenditure (P > 0.05). Interval training does not provide additional improvements in DLNO or aerobic capacity compared with self-directed moderate-intensity physical activity (4-6 metabolic equivalent tasks, 800 kcal week(-1), for 6 weeks) in unfit women. Despite the slight improvement in both DLNO and aerobic capacity, true meaningful physiological changes in these parameters remain questionable.

Ramp-incremented and RPE-clamped test protocols elicit similar VO2max values in trained cyclists.

PURPOSE: The present study compared the efficacy of ramp incremented and ratings of perceived exertion (RPE)-clamped test protocols for eliciting maximal oxygen uptake (VO2max). METHODS: Sixteen trained cyclists (age 34 ± 7 years) performed a ramp-incremented protocol and an RPE-clamped protocol 1 week apart in a randomized, counterbalanced order. The RPE-clamped protocol consisted of five, 2-min stages where subjects self-selected work rate and pedal cadence to maintain the prescribed RPE. After completing both test protocols subjects were asked which they preferred. RESULTS: The mean ± SD test time of 568 ± 72 s in the ramp protocol was not significantly different to the 600 ± 0 s in the RPE-clamped protocol (mean difference = 32 s; p = 0.09), or was the VO2max of 3.86 ± 0.73 L min(-1) in the ramp protocol significantly different to the 3.87 ± 0.72 L min(-1) in the RPE-clamped protocol (mean difference = 0.002 L min(-1); p = 0.97). Furthermore, no significant differences were observed for peak power output (p = 0.21), maximal minute ventilation (p = 0.97), maximal respiratory exchange ratio (p = 0.09), maximal heart rate (p = 0.51), and post-test blood lactate concentration (p = 0.58). The VO2max attained in the preferred protocol was significantly higher than the non-preferred protocol (mean difference = 0.14 L min(-1); p = 0.03). CONCLUSION: The RPE-clamped test protocol was as effective as the ramp-incremented protocol for eliciting VO2max and could be considered as a valid alternative protocol, particularly where a fixed test duration is desirable.

Two is better than one: the double diffusion technique in classifying heart failure.

Background: Heart failure (HF) is a chronic condition in which the heart does not pump enough blood to meet the body's demands. Diffusing capacity of the lung for nitric oxide (DLNO) and carbon monoxide (DLCO) may be used to classify patients with HF, as DLNO and DLCO are lung function measurements that reflect pulmonary gas exchange. Our objectives were to determine 1) if DLNO added to DLCO testing predicts HF better than DLCO alone and 2) whether the binary classification of HF is better when DLNO z-scores are combined with DLCO z-scores than using DLCO z-scores alone. Methods: This was a retrospective secondary data analysis in 140 New York Heart Association Class II HF patients (ejection fraction <40%) and 50 patients without HF. z-scores for DLNO, DLCO and DLNO+DLCO were created from reference equations from three articles. The model with the lowest Bayesian Information Criterion was the best predictive model. Binary HF classification was evaluated with the Matthews Correlation Coefficient (MCC). Results: The top two of 12 models were combined z-score models. The highest MCC (0.51) was from combined z-score models. At most, only 32% of the variance in the odds of having HF was explained by combined z-scores. Conclusions: Combined z-scores explained 32% of the variation in the likelihood of an individual having HF, which was higher than models using DLNO or DLCO z-scores alone. Combined z-score models had a moderate ability to classify patients with HF. We recommend using the NO-CO double diffusion technique to assess gas exchange impairment in those suspected of HF.

The Precision Between Transcutaneous Carbon Dioxide Versus PaCO2 in Infants Undergoing Therapeutic Hypothermia.

BACKGROUND: Infants with hypoxic-ischemic encephalopathy are often treated with therapeutic hypothermia and high-frequency ventilation. Fluctuations in PaCO2 during therapeutic hypothermia are associated with poor neurodevelopmental outcomes. Transcutaneous CO2 monitors offer a noninvasive estimate of PaCO2 represented by transcutaneously measured partial pressure of carbon dioxide (PtcCO2 ). We aimed to assess the precision between PtcCO2 and PaCO2 values in neonates undergoing therapeutic hypothermia. METHODS: This was a retrospective chart review of 10 neonates who underwent therapeutic hypothermia requiring respiratory support over 2 y. A range of 2-27 simultaneous PtcCO2 and PaCO2 pairs of measurements per neonate were analyzed via linear mixed models and a Bland-Altman plot for multiple observations per neonate. RESULTS: A linear mixed-effect model demonstrated that PtcCO2 and PaCO2 (controlling for sex) were similar. The 95% CI of the mean difference ranged from -2.3 to 5.7 mm Hg (P = .41). However, precision was poor as the PtcCO2 ranged from > 18 mm Hg to < 13 mm Hg than PaCO2 values for 95% of observations. CONCLUSIONS: The neonates' PtcCO2 was as much as 18 mm Hg higher to 13 mm Hg lower than the PaCO2 95% of the time. Transcutaneous CO2 monitoring may not be a good trending tool, nor is it appropriate for estimating PaCO2 in patients undergoing therapeutic hypothermia.

Perspectives of gynecologic oncology fellowship training and preparedness for practice.

We aimed to examine the preparedness of recent gynecologic oncology fellowship graduates for independent practice.We conducted a web-based survey study using REDCap targeting Society of Gynecologic Oncology (SGO) members who graduated gynecologic oncology fellowship within the last six years. The survey included 52 items assessing fellowship training experiences, level of comfort in performing core gynecologic oncology surgical procedures and administering cancer-directed therapies. Questions also addressed factors driving participants' selection of fellowship programs, educational experience, research and preparedness for independent practice. A total of 296 participants were invited to complete the survey. Response rate was 42% with n = 124 completed surveys included for analysis. The highest ranked factor for fellowship selection was fit with program 36% (n = 45). Upon completing fellowship, most were uncomfortable performing ureteral conduit formation 84% (n = 103), ureteroneocystostomy 77% (n = 94), exenteration 68% (n = 83), splenectomy 67% (n = 83) and lower anterior resection 41% (n = 51). Most were comfortable managing intraoperative complications 85% (n = 104) and standard cancer staging procedures (range: 61%-99%). Majority were comfortable providing cancer directed therapies with chemotherapy 99% (n = 123), immunotherapy 84% (n = 104), and poly ADP-ribose polymerase (PARP) inhibitors 97% (n = 120). Upon completing fellowship, 77% (n = 95) report having mentorship that met their expectations during fellowship and 94% (n = 116) felt they were ready for independent practice. Majority of fellowship graduates were prepared for independent practice and felt comfortable performing routine surgical procedures and cancer directed treatment. However, most are not comfortable with ultra-radical gynecologic oncology procedures. Maximizing surgical opportunities during fellowship training and acquiring early career mentorship may help.

The influence of sexual activity on athletic performance: a systematic review and meta-analyses.

Several anecdotal reports suggest that sex before competition can affect performance. Our objective was to perform a systematic review and meta-analysis to determine whether athletic performance or some physical fitness measure is affected by prior sexual activity. Web of Science (all databases) and Google Scholar were used to identify studies from which adult healthy subjects were included. As all studies were crossover trials, an inverse variance statistical method with random effects was used to minimize the uncertainty of the pooled effect estimate. Bias was assessed via the revised Cochrane Risk of Bias tool (RoB 2) with a "per protocol" analysis. Nine crossover studies (133 subjects, 99% male) were used in this meta-analysis. All those studies did not examine athletic performance per se, but all studies assessed one or more physical fitness parameters. The RoB 2 suggested that overall, there were some concerns with bias. As there was moderate heterogeneity amongst the different outcomes (Tau2 = 0.02, Chi-square = 17.2, df = 8, p = 0.03, I2 = 54%), a random-effects model was used. The results neither favored abstinence nor sexual activity before a physical fitness test [standardized mean difference = 0.03 (- 0.10 to 0.16), Z = 0.47, p = 0.64, where a negative standardized mean difference favors abstinence, and a positive standardized mean difference favors sexual activity]. The results demonstrate that sexual activity within 30 min to 24 h before exercise does not appear to affect aerobic fitness, musculoskeletal endurance, or strength/power.

Stability of Whole Blood Electrolyte Specimens at Room Temperature vs. Slushed Ice Conditions.

BACKGROUND: Data on the stability of whole blood electrolytes is limited to small sample sizes. We sought to determine the stability of whole blood electrolytes under room temperature and slushed iced conditions in human patients at a major hospital center. METHODS: Whole blood samples were obtained from 203 patients hospitalized for various pathophysiological conditions. Electrolyte concentrations of sodium, potassium [K+], ionized calcium, and chloride were measured at 5 different timepoints spanning 3 h. Samples were stored at room temperature (22-24 °C) or under slushed ice conditions (0.1-0.2 °C) before analysis. RESULTS: Under both conditions, sodium, ionized calcium, and chloride did not show a measurable change up to 109 min compared to baseline; however, the mean increase in [K+] over 138 min of storage in slushed ice was 0.0032 (0.0021 [5th percentile] to 0.0047 [95th percentile]) mmol/L/min (adjusted R2 = 0.62, P < 0.001). Five percent of the specimens demonstrated a ≥0.3 mmol/L change in [K+] from baseline after 67 min of storage in slushed ice. In contrast, 1% of the specimens stored at room temperature showed the same change at the same timepoint. CONCLUSIONS: Whole blood sodium, [K+], ionized calcium, and chloride concentrations remain stable for at least 109 min at room temperature. However, whole blood specimens stored in slushed ice for not more than 67 min exhibit a 5% probability that the [K+] concentration will increase by at least 0.3 mmol/L compared to baseline. The other analytes do not destabilize for up to 178 min of slushed ice storage.

Stability of Whole Blood Lactate Specimens at Room Temperature Versus Slushed Ice Conditions.

BACKGROUND: There are limited data on lactate stability in whole blood. The purpose of this study was to determine whole blood lactate stability at room temperature and in slushed ice conditions. METHODS: An equal number of arterial and venous samples were obtained from 202 subjects hospitalized for various pathophysiological conditions. Whole blood lactate concentration was measured over 5 different times spanning 80-90 min in a blood gas lab at a major hospital center. Samples were stored at room temperature (22-24°C) or in slushed ice conditions (0.1-0.2°C) before analysis. RESULTS: The mean increase in lactate concentration was 0.001 mmol/L/min in samples on slushed ice over 90 min. However, at room temperature conditions, the mean increase in lactate concentration was 0.008 mmol/L/min regardless of whether the sample was arterial or venous. An increase in whole blood lactate concentration of ≥ 0.4 mmol/L occured after 45 min at room temperature, with 5% of all whole blood specimens demonstrating a meaningful change at ≤ 20 min. The ≥ 0.4 mmol/L change in whole blood lactate is considered significant based on the College of American Pathologists instrument peer-group standards. CONCLUSIONS: Considering that a change in whole blood lactate concentration of ≥ 0.4 mmol/L is unacceptable instrument peer-group variation as defined by the College of American Pathologists, ice is no longer needed to stabilize whole blood lactate specimens when the draw time to analyze time is < 45 min. Samples remain stable even at 90 min when left on ice.

Week to week variability of pulmonary capillary blood volume and alveolar membrane diffusing capacity in patients with heart failure.

BACKGROUND: Alveolar-capillary membrane diffusing capacity for carbon monoxide (DMCO) and pulmonary capillary volume (Vcap) can be estimated by the multi-step Roughton and Foster (RF, original method from 1957) or the single-step NO-CO double diffusion technique (developed in the 1980s). The latter method implies inherent assumptions. We sought to determine which combination of the alveolar membrane diffusing capacity for nitric oxide (DMNO) to DMCO ratio, an specific conductance of the blood for NO (θNO) and CO (θCO) gave the lowest week-to-week variability in patients with heart failure. METHODS: 44 heart failure patients underwent DMCO and Vcap measurements on three occasions over a ten-week period using both RF and double dilution NO-CO techniques. RESULTS: When using the double diffusing method and applying θNO = infinity, the smallest week-to-week coefficient of variation for DMCO was 10 %. Conversely, the RF method derived DMCO had a much greater week-to-week variability (2x higher coefficient of variation) than the DMCO derived via the NO-CO double dilution technique. The DMCO derived from the double diffusion technique most closely matched the DMCO from the RF method when θNO = infinity and DMCO = DLNO/2.42. The Vcap measured week-to-week was unreliable regardless of the method or constants used. CONCLUSIONS: In heart failure patients, the week-to-week DMCO variability was lowest when using the single-step NO-CO technique. DMCO obtained from double diffusion most closely matched the RF DMCO when DMCO/2.42 and θNO = infinity. Vcap estimation was unreliable with either method.

Prior intense exercise reduces arterial carbon dioxide pressure in extreme obesity.

PURPOSE: Unlike normal weight individuals, individuals with extreme obesity do not show a decrease in arterial carbon dioxide pressure (PaCO2) from rest to peak exercise. This indicates that breathing is compromised. The objective of this study was to determine if prior high intensity exercise lowers PaCO2 in comparison with a first bout, normalized for the same metabolic rate. METHODS: Oxygen consumption during incremental, ramped exercise was matched to constant workload exercise (75% of peak power). Both protocols were to volitional exhaustion 39 ± 8 min apart. Eleven obese subjects (BMI = 47 ± 8 kg/m², aerobic capacity = 2.3 ± 0.6 L/min) were evaluated. Forty paired samples were obtained at the same metabolic rate between the two protocols. RESULTS: The mean absolute difference and 95% CI were large for arterial oxygen pressure (PaO2) = 9 (6, 11) mmHg and alveolar to arterial oxygen pressure difference (AaDO2) = 7 (5, 8) mmHg. The mean absolute difference for arterial oxyhemoglobin saturation (%SaO2) = 0.5 (0.4, 0.7) %; PaCO2 = 4 (3, 4) mmHg; physiological dead space to tidal volume ratio (VD/VT) = 0.04 (0.03, 0.05); and alveolar ventilation (VA) = 3 (2, 4) L/min. The recovery period after the first bout of exercise reduced the PaCO2 by 3 mmHg when matched for similar metabolic rates. Constant workload exercise predicted VA, %SaO2, V(D)/V(T), and PaCO2, but not PaO2 or AaDO2 during incremental exercise at similar metabolic rates. CONCLUSION: Given a sufficient chemical stimulus, obese subjects will attempt to breathe more, although this does not mean more VA, which removes CO2.