Ventilatory patterns during steady state and progressive exercise

Summary. This study was conducted to differentiate the ventilatory and metabolic response to supine exercise at low levels (V?O₂, < 1000 ml/min) from the well-documented response to high level upright exercise. Further, the respiratory cycle during exercise is analysed in terms of inspiratory time, flow and expiratory time as well as tidal volume and frequency. Using a canopy system for non-invasive measurement of breathing patterns and gas exchange, nine male subjects were studied while performing steady state (SSE) and progressive exercise (PRE). Work loads were: SSE 1·5 Kgm/sec for 17 min; PRE 1·5, 2·5, 3·75 and 5·0 Kgm/sec with 2 min increments. Total work was the same (1548 Kg·m) in both types of exercise. With SSE tidal volume (VT) and respiratory rate (f) rose 70% and 30%, respectively. Minute ventilation (V?_E) rose 113%. With PRE, f rose during the first work level, then remained stable, while V_T and V_E rose with each incremental exercise level. In both cases a decrease in expiratory time accounted for the major component of the decrease in total cycle time. With the onset of exercise, the rate of increase of inspiratory time and respiratory frequency exceeded that of tidal volume and inspiratory flow. This would suggest that these two groups of parameters are controlled by separate mechanisms, possibly, timing being under neurogenic control and flow determined by humoral factors. The respiratory quotient decreased with both forms of exercise and remained low throughout the exercise period.     

Breathing pattern and additional work of breathing in spontaneously breathing patients with different ventilatory demands during inspiratory pressure support and automatic tube compensation

Objective: We designed a new ventilatory mode to support spontaneously breathing, intubated patients and to improve weaning from mechanical ventilation. This mode, named Automatic Tube Compensation (ATC), compensates for the flow-dependent pressure drop across the endotracheal tube (ETT) and controls tracheal pressure to a constant value. In this study, we compared ATC with conventional patient-triggered inspiratory pressure support (IPS). Design: A prospective, interventional study. Setting: A medical intensive care unit (ICU) and an ICU for heart and thoracic surgery in a university hospital. Patients: We investigated two groups of intubated, spontaneously breathing patients: ten postoperative patients without lung injury, who had a normal minute ventilation (V_E) of 7.6 ± 1.7 l/min, and six critically ill patients who showed increased ventilatory demand (V_E = 16.8 ± 3.0 l/min). Interventions: We measured the breathing pattern [V_E, tidal volume (V_T), and respiratory rate (RR)] and additional work of breathing (WOB_add) due to ETT resistance and demand valve resistance. Measurements were performed under IPS of 5, 10, and 15 mbar and under ATC. Results: The response of V_T, RR, and WOB_add to different ventilatory modes was different in both patient groups, whereas V_E remained unchanged. In postoperative patients, ATC, IPS of 10 mbar, and IPS of 15 mbar were sufficient to compensate for WOB_add. In contrast, WOB_add under IPS was greatly increased in patients with increased ventilatory demand, and only ATC was able to compensate for WOB_add. Conclusions: The breathing pattern response to IPS and ATC is different in patients with differing ventilatory demand. ATC, in contrast to IPS, is a suitable mode to compensate for WOB_add in patients with increased ventilatory demand. When WOB_add was avoided using ATC, the patients did not need additional pressure support. Received: 24 April 1996 Accepted: 17 February 1997     

Anticipating maximal or submaximal exercise: no differences in cardiopulmonary responses

Background: Anticipation before the start of exercise may influence the cardiopulmonary responses during exercise. If anticipation influences the responses differently with maximal and submaximal exercises, normative values for submaximal responses will not be comparable unless exercise has been continued to the same end point. Methods: Twelve healthy subjects (five men) aged 18–27 years had a maximal exercise test and a submaximal exercise test on a cycle ergometer on different days and in random order. They were not aware of the specific purpose of the study and were informed 15 min before the tests whether it should be maximal or submaximal. Workload increased with 15 W min^?1 until exhaustion or to 80% of predicted maximal heart rate (HR). HR, oxygen uptake (VO₂), carbon dioxide production (VCO₂), minute ventilation (V_E) and tidal volume (V_T) were averaged over 20 s intervals. Linear regression of the HR–VO₂ relationship and quadratic regression of the V_T–V_E relationship were performed for each individual, and the regression coefficients for maximal and submaximal tests were compared. Results: The regression models described the V_T–V_E responses with a R² > 0·85 in 23 of 24 tests, and the HR‐VO₂ responses with a R² > 0·90 in all tests. The regression coefficients of the relationships were not significantly different with maximal and submaximal exercises. Conclusion: Anticipation appears not to influence the responses to progressive maximal and submaximal exercise tests with the same rate of increase in load. Normative values at submaximal exercise levels are not influenced by the targeted end point of exercise.     

Effect of Expiratory Muscle Fatigue on the Respiratory Response during Exercise

[Purpose] The aim of this study was to reveal the effect of expiratory muscle fatigue (EMF) on respiratory response under two different exercise conditions: exercise (EX) with EMF (EMF-EX) and control EX without EMF (CON-EX). [Methods] Nine healthy adult men performed cycle exercise with a ramp load, and a spirometer was used to measure forced vital capacity (FVC), forced expiratory volume in one second, percent of forced expiratory volume, maximal expiratory mouth pressure, and maximal inspiratory mouth pressure (PI_max) to evaluate respiratory functions immediately and at 15 and 30 min after exercise. To assess the respiratory response during exercise, an exhaled gas analyzer was used to measure minute ventilation (V_E), respiratory frequency (f), tidal volume (V_T), oxygen uptake, and carbon dioxide output. In addition, the Borg Scale was used to evaluate dyspnea, while electrocardiography was used to measure heart rate. [Results] The results showed that compared with the CON-EX condition, no change in V_E, an increase in f, or a decrease in V_T was observed under the medium-intensity EMF-EX condition, while high-intensity exercise reduced V_E and f without changing V_T. [Conclusion] These results suggest that during medium-intensity exercise, EMF modulates the respiratory response by inducing shallow and fast breathing to increase ventilation volume.Key words: Expiratory muscle fatigue, Maximal mouth pressure, Respiratory response     

Autonomic nervous function at rest in aerobically trained and untrained oldermen

Therelationship between aerobictraining, vagal influence on the heart and ageing was examined by assessing aerobic fitness andresting heart rate variability in trained and untrained older men. Subjects were 11 trained cyclistsand runners (mean age=6±61·6 years) and 11 untrained, age-matchedmen (mean age=66±1·2 years). Heart rate variability testing involvedsubjects lying supine for 25 min during which subjects’ breathing was paced andmonitored (7·5 breaths min^?1). Heart rate variability was assessedthrough time series analysis (HRV_ts) of the interbeat interval. Results indicated thattrained older men (3·55±0·21 l min^?1) hadsignificantly (P<0·05) greater VO _2maxthan that of control subjects (2·35±0·15 l min^?1).Also, trained older men (52±1·8 beats min^?1) hadsignificantly (P<0·05) lower supine resting heart rate than that of controlsubjects (65±4·2 beats min^?1). HRV_ts at highfrequencies was greater for trained men (5·98±0·22) than for untrainedmen (5·23±0·32). These data suggest that regular aerobic exercise inolder men is associated with greater levels of HRV_ts at rest.     

Potassium and ventilation during positive and negative work inpatients with chronic obstructive pulmonary disease

In patients with chronic obstructive pulmonary disease (COPD),reduced ventilatory reserves limit exercise tolerance. In these patients, the ventilatoryrequirements of eccentric exercise (negative work, W_neg) are lower thanthose of concentric exercise (positive work, W_pos) at similar workloads.In this study, we investigated the relationship between plasma potassium levels and ventilationduring W_pos and W_neg in these patients. Twelvepatients with stable COPD [mean (SD) FEV₁ 46% (16) of predicted]performed W_pos and W_neg on a cycle ergometer(6 min of exercise; interval ≥1 h) in a randomized order at a constant workload of50% of the individual maximum (positive) work capacity. Minute ventilation (V_E) and arterial plasma potassium concentration ([K⁺]_a) were measured at rest, and at 1-min intervals during exercise and during 3 min ofrecovery. V_E increased less during W_neg thanduring W_pos [6 (range 3–26) vs. 18 (range 8–28) l min^?1; P<0·01]. V_E during W_neg was reduced in proportion to VCO ₂.The increase in [K⁺]_a during W_pos and W_neg [0·45 (range 0·26–0·75) and0·34 (range 0·1–0·97) mM ] did not differsignificantly. V_E was closely correlated with VCO ₂ during both types of exercise. V_E was also closelycorrelated with [K⁺]_a, but the slope of the relationship between[K⁺]_a and V_E was steeper during W_pos than during W_neg [39·1 (range15·2–88·6) vs. 18·3 (range7·2–37·3) l min^?1 mM ^?1; P=0·012]. In contrast, the slope of the relationship betweenVCO ₂ and V_E was similar during bothtypes of exercise [27?8 (range 19·2–37·1) vs. 32·1 (range19·8–48·4)]. Thus, for a given increase in [K⁺]_a, the increase in V_E was significantly less during W_neg. In patients with COPD, potassium did not explain the difference inexercise ventilation between W_neg and W_pos, andmay not play a significant role in the control of breathing during low-intensity exercise.     

Proportional assist versus pressure support ventilation: effects on breathing pattern and respiratory work of patients with chronic obstructive pulmonary disease

Objective: To investigate the breathing pattern and the inspiratory work of breathing (WOB_I) in patients with chronic obstructive pulmonary disease (COPD) assisted with proportional assist ventilation (PAV) and conventional pressure support ventilation (PSV). Design: Prospective controlled study. Setting: Intensive care unit of a university hospital. Patients: Thirteen COPD patients being weaned from mechanical ventilation. Interventions: All patients were breathing PSV and two different levels of PAV. Measurements and main results: During PAV (EVITA 2 prototype, Dräger, Germany), the resistance of the endotracheal tube (R_et) was completely compensated while the patients' resistive and elastic loads were compensated for by approximately 80 % and 50 % (PAV₈₀ and PAV₅₀), respectively. PSV was adjusted to match the same mean inspiratory pressure (Pinsp_mean) as during PAV₈₀. Airway pressure, esophageal pressure and gas flow were measured over a period of 5 min during each mode. Neuromuscular drive (P_0.1) was determined by inspiratory occlusions. Mean tidal volume (V_T) was not significantly different between the modes. However, the coefficient of variation of V_T was 10 ± 4.%, 20 ± 13 % and 15 ± 8 % during PSV, PAV₈₀ and PAV₅₀, respectively. Respiratory rate (RR) and minute ventilation (V_E) were significantly lower during PAV₈₀ as compared with both other modes, but the differences did not exceed 10 %. PAV₈₀ and PSV had comparable effects on WOB_I and P_0.1, whereas WOB_I and P_0.1 increased during PAV₅₀ compared with both other modes. Conclusion: Mean values of breathing pattern did not differ by a large amount between the investigated modes. However, the higher variability of V_T during PAV indicates an increased ability of the patients to control V_T in response to alterations in respiratory demand. A reduction in assist during PAV₅₀ resulted in an increase in WOB and indices of patient effort.     

Entraînement en endurance à partir du membre inférieur sain chez des footballeurs amateurs opérés de ligamentoplastie de genou

Objective

To examine cardiorespiratory fitness changes in subjects having undergone knee surgery and to assess the benefits of one-leg cycling aerobic training program during the rehabilitation period.

Method

Two groups of 12 patients took part in this study. The control group profited from a five weeks conventional rehabilitation in day hospital without cardiorespiratory training. The second group profited in supplement from a one-leg cycling aerobic training program with the valid leg. The subjects were trained for 21 min, by alternating 3 min at 70% and 3 min at 85% of VO_2peak. They totaled 15 sessions spread over five weeks. The initial evaluation (T1) is carried out the first day of rehabilitation and the final evaluation (T2) at a distance within 35 days. The evaluation consisted in realizing a maximal graded tests starting from the valid leg.

Results

After five weeks of conventional rehabilitation, we record a reduction of peak power output (W_peak), peak oxygen uptake (VO_2peak) and peak minute ventilation (VE_peak), respectively of 11, 12 and 13% for the control group. On the other hand, in T2, the training group has on average identical maximum values and some of them increased (W_peak: +14%; VE_peak: +15%). The first and second ventilatory thresholds appear with higher intensities of exercises.

Conclusion

After knee surgery, conventional rehabilitation does not limit cardiorespiratory deconditioning. One leg cycling appears to be an adapted method to stop the effects of hypoactivity.     

Breathing exercises: influence on breathing patterns and thoracoabdominal motion in healthy subjects

BACKGROUND:

The mechanisms underlying breathing exercises have not been fully elucidated.

OBJECTIVES:

To evaluate the impact of four on breathing exercises (diaphragmatic breathing, inspiratory sighs, sustained maximal inspiration and intercostal exercise) the on breathing pattern and thoracoabdominal motion in healthy subjects.

METHOD:

Fifteen subjects of both sexes, aged 23±1.5 years old and with normal pulmonary function tests, participated in the study. The subjects were evaluated using the optoelectronic plethysmography system in a supine position with a trunk inclination of 45° during quiet breathing and the breathing exercises. The order of the breathing exercises was randomized. Statistical analysis was performed by the Friedman test and an ANOVA for repeated measures with one factor (breathing exercises), followed by preplanned contrasts and Bonferroni correction. A p<0.005 value was considered significant.

RESULTS:

All breathing exercises significantly increased the tidal volume of the chest wall (V_cw) and reduced the respiratory rate (RR) in comparison to quiet breathing. The diaphragmatic breathing exercise was responsible for the lowest V_cw, the lowest contribution of the rib cage, and the highest contribution of the abdomen. The sustained maximal inspiration exercise promoted greater reduction in RR compared to the diaphragmatic and intercostal exercises. Inspiratory sighs and intercostal exercises were responsible for the highest values of minute ventilation. Thoracoabdominal asynchrony variables increased significantly during diaphragmatic breathing.

CONCLUSIONS:

The results showed that the breathing exercises investigated in this study produced modifications in the breathing pattern (e.g., increase in tidal volume and decrease in RR) as well as in thoracoabdominal motion (e.g., increase in abdominal contribution during diaphragmatic breathing), among others.     

Leg uptake of calcitonin gene‐related peptide during exercise in spinal cord injured humans

Exercise‐induced increases in cardiac output (CO) and oxygen uptake (VO₂) are tightly coupled, as also in absence of central motor activity and neural feedback from skeletal muscle. Neuromodulators of vascular tone and cardiac function – such as calcitonin gene related peptide (CGRP) – may be of importance. Spinal cord injured individuals (six tetraplegic and four paraplegic) performed electrically induced cycling (FES) with their paralyzed lower limbs for 29 ± 2 min to fatigue. Voluntary cycling performed both at VO₂ similar to FES and at maximal exercise in six healthy subjects served as control. In healthy subjects, CGRP in plasma increased only during maximal exercise (33·8 ± 3·1 pmol l^?1 (rest) to 39·5 ± 4·3 (14%, P<0·05)) with a mean extraction over the working leg of 10% (P<0·05). Spinal cord injured individuals had more pronounced increase in plasma CGRP (33·2 ± 3·8 to 46·9 ± 3·6 pmol l^?1, P<0·05), and paraplegic and tetraplegic individuals increased in average by 23% and 52%, respectively, with a 10% leg extraction in both groups (P<0·05). The exercise induced increase in leg blood flow was 10–12 fold in both spinal cord injured and controls at similar VO₂ (P<0·05), whereas CO increased more in the controls than in spinal man. Heart rate (HR) increased more in paraplegic subjects (67 ± 7 to 132 ± 15 bpm) compared with controls and tetraplegics (P<0·05). Mean arterial pressure (MAP) was unchanged during submaximal exercise and increased during maximal exercise in healthy subjects, but decreased during the last 15 min of exercise in the tetraplegics. It is concluded that plasma CGRP increases during exercise, and that it is taken up by contracting skeletal muscle. The study did not allow for a demonstration of the origin of the CGRP, but its release does not require activation of motor centres. Finally, the more marked increase in plasma CGRP and the decrease in blood pressure during exercise in tetraplegic humans may indicate a role of CGRP in regulation of vascular tone during exercise.     

Plasma endorphin species during dynamic exercise in humans

Summary. β-Endorphin is metabolized to γ- and α-endorphin. In order to evaluate endorphin metabolism during exercise, radioimmunoassay blood levels of α, β- and γ-endorphins were recorded during exercise for 2 h on a cycling ergometer in 12 endurance-trained and 11 untrained male subjects. In untrained subjects, mild exercise (49±4%VO_2max, mean±SD) did not show an increase in plasma β-endorphin, while the levels of its metabolites rose. No changes were noted in the endurance-trained subjects. More intensive exercise (66±6%VO₂max in untrained and 57±7%VO_2max in trained subjects) resulted in an increase in p-endorphin concentration in association with elevation of the a-endorphin level. While before and during exercise the β-endorphin levels did not differ significantly between athletes and untrained subjects, the levels of γ- and α-endorphins, as well as the molar ratios α/β and γ/β, were significantly higher in untrained subjects. In conclusion, blood levels of β-endorphin metabolites in the resting state and during exercise are dependent on previous training. In untrained subjects, mild exercise may result in accumulation of γ- and α-endorphins in blood without a concomitant change in β-endorphin level.     

Middle cerebral artery blood velocity during exercise in patients with atrial fibrillation

Atrial fibrillation limits the ability to increase cardiac output during exercise and may, in turn, affect the exercise-associated elevation in cerebral perfusion. In nine patients with atrial fibrillation (AF) and in five age-matched healthy subjects, middle cerebral artery blood velocity (MCA V_mean) was measured during incremental exercise using the transcranial Doppler. The AF patient group exhibited a lower aerobic capacity than the control group [peak work rate: 106 W (71–153 W; median and range) vs. 129 W (118–159 W) and maximal oxygen uptake: 1·4 l min^–1 (1·0–1·9 l min^–1) vs. 1·7 l min^–1 (1·4–2·2 l min^–1); P = 0·05]. At rest, MCA V_mean was not significantly different between the two groups [43 cm s^–1 (39–56 cm s^–1) vs. 52 cm s^–1 (40–68 cm s^–1)]. During intense cycling, the increase in MCA V_mean was to 51 cm s^–1 (40–78 cm s^–1) (9%) in the AF group and lower than in the healthy subjects [to 62 cm s^–1 (50–81 cm s^–1) 23%; P<0·05], which corresponded with the smaller than expected increase in cardiac output [156% (130–169%) vs. 180%]. Thus, there was a correlation between the increase in MCA V_mean and the ability to increase cardiac output (r² = 0·55, P<0·01). We suggest that, during exercise with a large muscle mass, atrial fibrillation affects the ability to elevate cerebral perfusion, and this results from an impaired ability to increase cardiac output.     

Comparison between ventilatory and mouth occlusion pressure responses to hypoxia and hypercapnia in healthy sleeping man

Summary. Ventilatory and mouth occlusion pressure (P_0·1) responses to progressive isocapnic-hypoxia and hyperoxic-hypercapnia were compared in eleven healthy sleeping men during the same night. Hypoxic and hypercapnic responses were determined during wakefulness, non-rapid and rapid-eye-movement sleep. The following parameters were measured: minute ventilation (V?E), tidal volume (V_T), ‘duty cycle’ (T_l/T_T), mean inspiratory flow rate (V_T/T_l) and P_0·1, an index of the neuromuscular inspiratory drive. To allow a direct comparison between the two types of chemostimuli, responses were characterized by the value of the different parameters at ‘equivalent’ levels of hypoxia and hypercapnia, i.e., at levels which produced the same P_0·1 during wakefulness: an oxyhaemoglobin saturation (Sao₂) of 94% during the isocapnic-hypoxic tests (P_ETco₂=42·5±1·2 mmHg) was found to be equivalent to a P_etco₂ of 47·4±3·7 mmHg during hypoxic-hypercapnic tests. For both tests, the arousal levels of the stimulus and of P_0·1 were similar in all sleep stages. Sleep did not significantly modify P_0·1 or breathing pattern responses to hypoxia (Sao₂=94%). In contrast, at the ‘equivalent’ level of hypercapnic stimulation, P_0·1 (P<0·05) and V?_E (P<0·01) responses were significantly impaired, particularly in REM sleep, with a decrease in V_T (P<0·01) and V_T/T_l (P<0·05) responses. The results suggest that CO₂ intracranial receptor mechanisms are more affected by sleep than the O₂ peripheral receptor activity.     

The non-invasive acetylene rebreathing method for estimation of cardiac output: influence of breath-by-breath variation

The inert gas rebreathing method enables non-invasive estimation of pulmonary capillary blood flow, lung tissue volume, transfer factor and functional residual capacity. In the present study, we have examined the influence of breathing pattern during the rebreathing manoeuvre on the precision of the rebreathing method, both theoretically and experimentally. We examined whether the precision of the method could be improved by the guidance and training of the subjects doing the rebreathing manoeuvre. The results of the theoretical study showed that the precision and accuracy of the rebreathing method are practically insensitive to random variation in the breathing pattern. Simulated breath-by-breath variations up to ±50% of the average 3·0 l V_T resulted in coefficients of variation of about 3% for Q_C and about 5% for V_TC. Simulated breath-by-breath variations indicate that with mean tidal volume or rebreathing bag volume lower than 1·0 l the precision will worsen, and with tidal volume lower than 1·5 l the accuracy will worsen. The experimental results showed no significant improvement in the precision of the rebreathing method by visual guiding and training of the subjects to optimize the breathing pattern during the rebreathing manoeuvre.     

Respiratory pattern during neurally adjusted ventilatory assist in acute respiratory failure patients

Purpose  

To investigate the effect of a wide range of assistance levels during neurally adjusted ventilatory assist (NAVA) and pressure support ventilation (PSV) on respiratory pattern, breathing variability, and incidence of tidal volumes (V _T) above 8 and 10 ml/kg in acute respiratory failure patients.     

Multiple breath nitrogen dead space

Summary. Ventilatory efficiency for eliminating CO₂ is expressed by the physiological dead space, V_Dphys = (1-PE CO₂/Pa CO₂) ×V_T, where PE is the mixed exhaled and Pa the arterial CO₂-tension and V_T the tidal volume. We used data from the multiple breath N₂-wash-out with oxygen for calculating a functional dead space for nitrogen. V_DFN₂= (1 -FEN₂/FEN₂/FidN₂) ×V_T. F_EN₂ is the mixed exhaled N₂-fraction and FidN₂ the calculated mean alveolar N₂-fraction during a wash-out with the same number of breaths to reach 2% N₂ in end tidal air, but having completely even distribution. FidN₂ is shown to be 0·20±0·01 for wash-outs using 20–150 breaths. The method was applied to wash-outs from 21 healthy volunteers, 18 patients with chronic obstructive lung disease and two subjects with acute bronchospasm. V_DF was well related to V_D phys CO₂ (r= 0·78) but higher than the latter. In subjects with lung disease V_DF was inversely related to the degree of obstruction expressed by forced expiratory volume in one second per cent of vital capacity (r= 0·85). The subjects with bronchospasm had very high V_D/V_TMF, in relation to their FEV%. If airway dead space predicted from height and sex is subtracted from V_DF, the resulting alveolar dead space will be a good expression for uneven gas distribution in the lungs. We also deduced a direct mathematical relation between lung clearance index and V_D/V_TF. The documented good reproducibility of LCI is thus also valid for V_D/V_TF, while the latter better expresses ventilatory efficiency.     

Effects of wheelchair training on [Vdot]O2 kinetics in the participants with spinal-cord injury

Purpose.?We tested the hypothesis that, in eight participants (seven males, one female; 46.5 ± 8.3 years) with spinal-cord injury (complete lesions, T7-L1), the effects of exercise training on pulmonary O₂ uptake ([Vdot]O₂) on- and off- kinetics would appear early in this pilot study.

Methods.?The subjects underwent the wheelchair-training program (3 day/w, 30 min/day, and 50% HRreserve), and were evaluated before training (“time 0”, T0), and after 7 (T7), 15 (T15), 30 (T30), and 60 (T60) days of training. Breath-by-breath peak [Vdot]O₂ was determined during the incremental exercise until their exhaustion. At another day following the incremental exercise, the subjects performed three repetitions of a constant exercise at 50% peak [Vdot]O₂ workload so that [Vdot]O₂ could be determined for both on- and off-kinetics.

Results and conclusion.?Peak [Vdot]O₂ showed a tendency to increase with training; the increases became significant at T30. The time constants (τ₂) during “phase II” of the [Vdot]O₂ on-kinetics were 62.4 ± 13.0 (s) (T0), 51.2 ± 8.7 (T7), 46.1 ± 7.4 (T15), 45.0 ± 7.2 (T30), and 43.4 ± 6.4 (T60); a significant difference compared to T0 was observed from T7 onward. The same pattern of change as a function of training was described for the [Vdot]O₂ off-kinetics. It is concluded that in SCI participants, the acceleration of [Vdot]O₂ kinetics at the onset of exercise was observed over a short term.     

Trans‐sodium crocetinate does not affect oxygen uptake in rats during treadmill running

Trans‐sodium crocetinate (TSC), the isomer of the carotenoid compound crocetin, is found markedly to increase survival in hemorrhagic shock subsequent to 50–60% blood loss, mainly via restored resting oxygen consumption (VO₂), blood pressure and heart rate. The proposed mechanism is that TSC increases oxygen diffusivity, and thus availability, in plasma. If this were found to be a prominent feature in the oxygen transfer from blood to skeletal muscle fiber mitochondria, increased VO₂ during exercise would be expected because of reduced partial pressure of venous oxygen (increased utilization), which we aimed to elucidate in this study. Male Sprague‐Dawley rats were intravenously injected with 0.3?mL?kg^?1 TSC (40?µg?mL^?1) or placebo and immediately thereafter tested on a ramped treadmill test protocol. Rats were introduced to the experimental protocols beforehand. Administration of TSC had a neutral effect on submaximal and maximal VO₂ (VO_2max) as well as running performance measured as maximal running time and maximal aerobic running velocity. Thus, in this study we cannot report any effects of TSC on steady‐state submaximal VO₂ or VO_2max at exhaustive exercise.     

Heat and water respiratory exchanges: comparison between mouth and nose breathing in humans

Summary. The temperatures(T₁ T_E) of inspired and expired gas and the mass of expired water (M_EH₂O) have been measured in four subjects at rest during mouth and nose breathing of dry air at room temperature. T₁ and T_E were measured by copper-constantan thermocouples, M_EH₂O by freezing and ventilatory parameters by total body plethysmography. During mouth breathing, temperatures are significantly higher (T₁= 28·1°C, T_E= 31·5°C) and the amount of expired water larger (M_EH₂O = 27·8 mg dm^-3 BTPS) than during nose breathing (T₁, = 24·8°C; T_E= 29·6°C; M_EH₂O =26·6 mg dm^-3 BTPS). From these experimental data the appropriate computations show clearly that in humans, while either nose or mouth breathing, (1) the expired air is not water saturated; (2) the latent heat exchanges represent the larger part of the respiratory heat exchanges; (3) the counter current expiratory heat recovery is imperfect; (4) in terms of heat and water respiratory exchanges, no large difference exists between the oral and nasal routes. This last point is confirmed by the calculation of a difference less than 10% in the total respiratory heat losses between mouth and nose breathing.