The kinetics of the adjustment of pulmonary oxygen uptake (VO 2 )

Spencer MD, Murias JM, Grey TM, Paterson DH. Regulation of VO 2 kinetics by O2 delivery: insights from acute hypoxia and heavy-intensity priming exercise in young men. J Appl Physiol 112: 1023-1032, 2012. First published December 22, 2011 doi:10.1152/japplphysiol.01215.2011.-This study examined the separate and combined effects of acute hypoxia (Hypo) and heavy-intensity "priming" exercise (Hvy) on pulmonary O 2 uptake (V O2p) kinetics during moderate-intensity exercise (Mod). Breath-by-breath V O2p and near-infrared spectroscopy-derived muscle deoxygenation {deoxyhemoglobin concentration [HHb]} were monitored continuously in 10 men (23 Ϯ 4 yr) during repetitions of a Mod 1-Hvy-Mod 2 protocol, where each of the 6-min (Mod or Hvy) leg-cycling bouts was separated by 6 min at 20 W. Subjects were exposed to Hypo [fraction of inspired O 2 (FIO 2 ) ϭ 15%, Mod 2 ϩ Hypo] or "sham" (FI O 2 ϭ 20.9%, Mod 2-N) 2 min following Hvy in half of these repetitions; Mod was also performed in Hypo without Hvy (Mod 1 ϩ Hypo). On-transient V O2p and [HHb] responses were modeled as a monoexponential. Data were scaled to a relative percentage of the response (0 -100%), the signals were time-aligned, and the individual [HHb]-to-V O2 ratio was calculated. Compared with control (Mod 1), V O2p and the O2 deficit (26 Ϯ 7 s and 638 Ϯ 144 ml, respectively) were reduced (P Ͻ 0.05) in Mod 2-N (20 Ϯ 5 s and 529 Ϯ 196 ml) and increased (P Ͻ 0.05) in Mod 1 ϩ Hypo (34 Ϯ 14 s and 783 Ϯ 184 ml); in Mod 2 ϩ Hypo, V O2p was increased (30 Ϯ 8 s, P Ͻ 0.05), yet O 2 deficit was unaffected (643 Ϯ 193 ml, P Ͼ 0.05). The modest "overshoot" in the [HHb]-to-V O2 ratio (reflecting an O 2 delivery-to-utilization mismatch) in Mod 1 (1.06 Ϯ 0.04) was abolished in Mod 2-N (1.00 Ϯ 0.05), persisted in Mod 2 ϩ Hypo (1.09 Ϯ 0.07), and tended to increase in Mod 1 ϩ Hypo (1.10 Ϯ 0.09, P ϭ 0.13). The present data do not support an "O 2 delivery-independent" speeding of V O2p following Hvy (or Hvy ϩ Hypo); rather, this study suggests that local muscle O2 delivery likely governs the rate of adjustment of V O2 at V O2p greater than ϳ20 s. oxygen extraction; oxygen distribution; muscle blood flow; nearinfrared spectroscopy THE FUNDAMENTAL ADJUSTMENT of pulmonary O 2 uptake (V O 2p ) kinetics displays an exponential profile during the on-transient to moderate-intensity exercise (Mod). Whether the rate of this adjustment, given by the V O 2p time constant (V O 2p ), is limited by factors related to local muscle O 2 availability, intracellular factors related to metabolic substrate provision and enzyme activation, or a combination of both remains a topic of debate. Poole et al. (30) proposed that there is a "point" beyond which O 2 uptake (V O 2 ) kinetics are O 2 -dependent, such that the provision of O 2 becomes limiting and, thus, V O 2 is lengthened. While this proposal has received much attention within the literature, it has yet to be demonstrated that provision of "additional" O 2 resolves any potential O 2 delivery limitation.In contrast to this possibility, Grassi et...

Objective. Previous studies have demonstrated that various factors alter postural stability. Our aim was to examine the effect of plantar flexor fatigue on postural stability in quiet standing. Methods. Fifteen healthy male university students (age, 21.3 ± 1.7y; height, 1.83 ± 0.06m; weight, 81.6 ± 9.4kg) were instructed to stand on a force plate before and after calf fatiguing exercise. The sensory systems were controlled by blindfolding subjects and having them stand on a flat firm surface, without moving their head. Fatigue was achieved through repetitive weighted plantarflexor exercise. Standing balance was assessed by using a force plate to calculate Center of Pressure (CoP) displacement.

The adjustment of pulmonary oxygen uptake (VO2p), heart rate (HR), limb blood flow (LBF), and muscle deoxygenation [HHb] was examined during the transition to moderate-intensity, knee-extension exercise in six older adults (70 ± 4 years) under two conditions: normoxia (FIO₂ = 20.9 %) and hypoxia (FIO₂ = 15 %). The subjects performed repeated step transitions from an active baseline (3 W) to an absolute work rate (21 W) in both conditions. Phase 2 VO₂p, HR, LBF, and [HHb] data were fit with an exponential model. Under hypoxic conditions, no change was observed in HR kinetics, on the other hand, LBF kinetics was faster (normoxia 34 ± 3 s; hypoxia 28 ± 2), whereas the overall [HHb] adjustment (τ' = TD + τ) was slower (normoxia 28 ± 2; hypoxia 33 ± 4 s). Phase 2 VO₂p kinetics were unchanged (p < 0.05). The faster LBF kinetics and slower [HHb] kinetics reflect an improved matching between O₂ delivery and O₂ utilization at the microvascular level, preventing the phase 2 VO₂p kinetics from become slower in hypoxia. Moreover, the absolute blood flow values were higher in hypoxia (1.17 ± 0.2 L min(-1)) compared to normoxia (0.96 ± 0.2 L min(-1)) during the steady-state exercise at 21 W. These findings support the idea that, for older adults exercising at a low work rate, an increase of limb blood flow offsets the drop in arterial oxygen content (CaO₂) caused by breathing an hypoxic mixture.

Background: Lung cancer is one of the leading causes of cancer-related mortality worldwide. Its poor prognosis is associated with late detection and high recurrence rates. We aimed to determine if certain imaging characteristics of lung cancer recurrence were predictors of extra-pulmonary metastatic disease.Methods: We conducted a retrospective study of all patients at our institution with lung cancer recurrence detected on post-treatment imaging between January 2014-October 2019. Research ethics board approval was obtained. Included patients underwent pre-treatment imaging, surgical resection, and post-treatment imaging. Imaging characteristics and pathological findings of the pulmonary lesions were analyzed. Univariate logistic regression was performed to assess for potential predictors of extra-pulmonary metastatic disease. The variables evaluated were age, gender, original and recurrent lesion size and imaging characteristics, recurrence location, presence of chest wall or mediastinal invasion, lymphadenopathy, and malignancy subtype. Results: 76 patients were included (33 males; mean age 70.9, standard deviation [SD] 7.7). The primary lesions were adenocarcinoma (N=50), squamous cell carcinoma (N=21), and other (N=5). The mean time to recurrence was 24.3 months (SD=18.8) from date of surgical excision. The two significant predictors of extra-pulmonary metastatic disease were: having >1 recurrent lesion (odds ratio [OR], 8.1; p=0.004), and the presence of suspicious lymphadenopathy at the time of recurrence (OR, 14.1; p<0.001).Conclusion: In lung cancer recurrence, the presence of >1 recurrent lesion and suspicious lymphadenopathy at the time of recurrence were significant predictors of extra-pulmonary metastatic disease. These findings may help guide the risk stratification and management of patients with recurrent lung cancer.