Correction of clothing insulation for movement and wind effects, a meta-analysis

A meta-analysis of the effect of body and air movement on the insulation provided by workwear and cold-weather clothing [1.22 clo (0.189 m ² °C W ^–1) <I _T<4.14 clo (0.642 m ² °C W ^–1)] using data from different sources was performed. For the effect of walking, datasets could be merged and a single prediction equation produced (r ²=0.91). For the effect of wind, and interaction of movement and wind, separate equations were required for regular workwear (r ²=0.93) and cold-weather clothing (r ²=0.97). Differences were mainly due to the different amounts of nude surface area. An interaction between wind and walking effects was present (the size of the combined effects is less than the sum of the separate effects), and for cold-weather clothing an effect of clothing air permeability (p) was present (high pbigger effect). The resulting prediction equations will be proposed for inclusion in European and ISO standards on protective clothing to assist the user in determining the real-life clothing insulation value.An erratum to this article can be found at     

Spatial differences in sensible and latent heat losses under a bicycle helmet

This research aims at quantifying spatial gradients in skin temperature and sweat production under a bicycle helmet. Distribution of sweat production, skin temperature and air temperature was measured at different positions under a bicycle helmet on five male and four female test persons. Effort level was 100 and 150 watt for men (low and high effort level) and 80 and 120 W for women (low and high effort level). Skin temperatures were found to be spatially different (P < 0.05): frontal and lateral region varied 4.6°C at low effort level and 5.3°C at high effort level. Sweat production was found to be not significantly different (P > 0.05). Finally, air temperature variations were found to be spatially different (P < 0.05). Average air temperature differed 2.3°C between lateral and frontal region at high effort level and 2.7°C at low effort level. The results of this research can be used to help designing helmets with better thermal comfort.     

头盔质量和质心对军机飞行员颈部肌力的影响

目的研究头盔质量和质心偏移对军机飞行员颈部肌肉活动特性的影响。方法基于AnyBody软件平台建立头颈部肌骨模型,包含C0、C1-7、T1和136组头颈部肌肉。采用集中载荷模拟头盔作用,对不同头盔质量、质心位置和加速度载荷下的7个主要肌群的肌力进行了仿真计算。结果当头盔质心与头部质心重合时,支配后伸的头半棘肌、肩胛提肌、头夹肌和颈夹肌处于收缩发力状态。当头盔质量增大,这些肌群肌力也随之线性增加,并且加速度载荷对肌力增大程度起放大作用。头盔质心后移,会降低后伸肌群的肌力,增大前屈肌群受力。头盔质心左右偏移引起的附加侧弯力矩则会激活支配侧弯功能的肌群的活动。结论头盔质量和质心位置对颈部肌群活动特性有明显影响,本文建立的头颈部肌骨模型可以计算不同状态下肌力的变化,头盔设计和使用过程可采用该技术进行定量分析。     

Independence of ventilation and blood lactate responses during graded exercise

The effect of power output increment, based on an increase in pedal rate, on blood lactate accumulation during graded exercise is unknown. Therefore, in the present study, we examined the effect of two different rates of power output increments employing two pedal rates on pulmonary ventilation and blood lactate responses during graded cycle ergometry in young men. Males (n=8) with an mean (SD) peak oxygen uptake of 4.2 (0.1) 1·min^–1 served as subjects. Each subject performed two graded cycle ergometer tests. The first test, conducted at 60 rev· min^–1, employed 4 min of unloaded pedaling followed by a standard power output step increment (SI) of 60 W every 3rd min. The second test, conducted at 90 rev·min^–1, employed 4 min of unloaded pedaling followed by a high power output step increment (HI) of 90 W every 3rd min. Venous blood was sampled from a forearm vein after 5 min of seated rest, 4 min of unloaded pedaling, and every 3rd min of graded exercise. Peak exercise values for heart rate, oxygen uptake ( O₂), and ventilation ( _E) were similar (P > 0.05) for SI and HI exercise, as was the relationship between _E and O₂, and between _E and carbon dioxide production ( CO₂). However, the relationship between blood lactate concentration and O₂ was dissimilar between SI and HI exercise with blood lactate accumulation beyond the lowest ventilatory equivalent of oxygen, and peak exercise blood lactate concentration values significantly higher (P < 0.05) for SI [12.8 (2.6) mmol·l^–1] compared to HI [8.0(1.9) mmol·l^–1] exercise. Our findings demonstrate that blood lactate accumulation and _E during graded exercise are dissociated. Blood lactate accumulation is influenced by the rate of external power output increment, while _E is related to O₂ and CO₂.     

Effect of diet upon ventilation and effort perception during a physical stressor

The present research explored the effects of a high and low carbohydrate diet on ratings of perceived exertion (RPE) during a 10 minute bicycle ergometer test at high physical work capacity (70% of maximum aerobic capacity). Twelve female student volunteers participated and were randomly assigned the order of diet treatments in which they served as their own control and/or experimental group. Following each dietary regimen, subjects were instructed to pedal the bicycle ergometer for ten minutes at an intensity of 70% of their maximum capability. Throughout the cycling protocol, RPE scores were recorded at 2, 4, 6, 8, and 10 minutes; in addition expiratory gases were collected and analyzed by a computerized indirect calorimetry system. Results in the current investigation indicated that an increased carbohydrate intake resulted in an "ergogenic" or "work-producing" effect by attenuating the metabolic acidosis, possibly diminishing the sensations of the central cardiopulmonary effort, further attenuating the psychophysiological perceptions of effort. Conversely, ingestion of a low carbohydrate diet resulted in accentuation of the ventilatory drive eliciting higher signals of exertion during dynamic exercise.     

绵羊海水溺水血过氧化脂质、前列腺素、血气等改变及高频通气疗效探讨

本实验用健康成年绵羊16只,向气管内注入海水(6ml/kg)造成溺水模型。于溺水后10分钟,使用高频通气治疗。对照组不使用高频通气治疗。分别于溺水前及溺水后5、15、30、40、70、130min采取股动脉血测定指标:1.血清过氧化脂质(LPO),两组中均于溺水后短时间降低,后又迅速上升达溺水前10倍以上。2.TXB_2、6-keto-PGF_(1α)在两组中均增加。3.pH在对照组中明显降低,(7.133～7.219)。4.PaO_2在对照组中降低较为显著。5.PaCO_2在溺水后5、15min时轻度上升。6.血中K~+、Na~+、Cl~-两组中轻度升高,但高频通气组于溺水后60min即恢复正常。7.两组肺超微结构变化基本相似。作者认为高频通气治疗海水溺水虽有一定效果,但不满意。尚需采用其它新的治疗手段提高救治率。     

Relationship between plasma potassium and ventilation during successive periods of exercise in men

Summary During and after two successive incremental cycle ergometer tests (tests A and B), plasma potassium concentration ([K⁺]_p), plasma pH (pH_p), plasma partial pressure of carbon dioxide, blood lactate concentration ([Lac^–]_b) and ventilation (V_E) were measured. While there was a good correlation between the increase in [K⁺]_p and V_E or pH_p, respectively, in test A, in test B a close correlation was found only between the increase in V_E and [K⁺]_p (r>0.9 for nearly all single cases; r was 0.84 and 0.89 for all (pooled) cases in tests A and B, respectively; the correlation coefficients between changes in pH_p and V_E in tests A and B were r=0.74 and r=0.28, respectively, and r=0.89 and r=0.10 between the changes in [Lac^–]_b and V_E in tests A and B). The close relationship for individuals between V_E and [K⁺]_p in tests A and B supported the hypothesis that the extracellular increase in [K⁺] may contribute to the ventilatory drive during exercise. The comparison of the results of tests A and B further indicated that the relationship between pH_p and V_E was dependent on the experimental design, and that pH_p and V_E changes are unlikely to be cause and effect.The study was carried out in the Centre of Physiology, Department of Sports- and Exercise Physiology, Medical School, W-3000 Hannover, Federal Republic of Germany     

Factors which alter the relationship between ventilation and carbon dioxide production during exercise in normal subjects

The slope of the linear relationship between ventilation and carbon dioxide production has been thought to indicate that is one of the major stimuli to . A group of 15 normal subjects undertook different incremental treadmill exercise protocols to explore the relationship between and . An incremental protocol using 1 instead of 3-min stages of exercise resulted in an increase in the to ratio [26.84 (SEM 1.23) vs 31.08 (SEM 1.36) (P < 0.008) for the first stage, 25.24 (SEM 0.86) vs 27.83 (SEM 0.91) (P < 0.005) for the second stage and 23.90 (SEM 0.86) vs 26.34 (SEM 0.81) (P = 0.001) for the third stage]. Voluntary hyperventilation to double the control level of during exercise resulted in an increase in the to slope [from 21.3 (SEM 0.71) for the control run to 35.1 (SEM 1.2) for the hyperventilation run (P < 0.001)]. Prolonged hyperventilation (5 min) during exercise at stage 2 of the Bruce protocol resulted in a continuted elevation of and the slope. A steady state of and metabolic gas exchange can only be said to have been present after at least 3 min of exercise. Voluntary hyperventilation increased the slope of the relationship between and . End-tidal carbon dioxide fell, but remained within the normal range. These results would suggest that a non-carbon dioxide factor may have been responsible for the increase we found in during exercise, and that factors other than increased dead space ventilation can cause an increased ventilation to slope, such as that seen in some pathophysiological conditions, such as chronic heart failure.     

Method for the analysis of the entrainment between heart rate and ventilation rate

Summary A digital computer program was developed which allows to continuously represent the relation between heart rate and ventilation rate. Using this program, experiments in anesthetized rabbits were performed. We found periods of synchronization, periods of transient entrainment and escape, and periods of complete desynchronization. By testing the respective roles for the entrainment mechanism of ventilation rate and heart rate it was found that spontaneous adjustments of the ventilation rate play a more pronounced role. Thus, as soon as spontaneous or induced variations of the heart rate and/or the ventilation rate shift both rhythms close to synchronization, variations of the ventilation pattern, which seem to be of reflex nature, tend to induce entrainment.This work was supported by the Austrian Research Fund     

Potassium kinetics and its relationship with ventilation during repeated bouts of exercise in women

The purpose of this study was to determine the electrolyte concentration changes in arterial plasma from high-intensity repeated bouts of cycling exercise in well-trained females and to determine the relationships between arterial plasma lactate, potassium (K⁺), bicarbonate (HCO₃⁻), and pH with minute ventilation. Fourteen female subjects (mean age = 27 ± 4 years; mean height = 170 ± 7 cm; mean weight = 62 ± 7 kg; maximal oxygen uptake = 50 ± 6 ml/kg/min) were recruited to perform 3 × 5 min bouts of exercise at 236 ± 27 W with 10 min recovery between each set. Minute ventilation, arterial plasma lactate, potassium, calcium, chloride, and sodium ion concentrations were measured a minute 0, 1, 2, 3, 4, 5 of each set and midway through recovery (21 sampling points total per subject). The results showed that the strongest relationship was between arterial plasma K⁺ concentration and minute ventilation (r ² = 0.91), and, that arterial plasma lactate mirrored both arterial plasma HCO₃⁻ and pH. In conclusion, this study demonstrates that women exhibit similar electrolyte responses as reported elsewhere in men, and support the idea that K⁺ may partly contribute to controlling ventilation during high-intensity exercise and recovery.     

Coincidental changes in ventilation and electromyographic activity during consecutive incremental exercise tests

These experiments examined the effect of metabolic acidosis, induced as a result of dynamic exercise, on ventilation, lactate concentration and electromyographic activity. Seven subjects performed two consecutive incremental exercise tests until volitional exhaustion was achieved. The two tests were identical and were separated by a 7-min period of light exercise. During the tests, ventilation, mixed expired oxygen and carbon dioxide, arterialized venous blood and electromyographic activity from the vastus lateralis was sampled. The results showed that the ventilation and electromyographic measurements followed a similar time course during both tests, although ventilation during the initial 6 min of the second test was significantly greater than the values recorded during the first test. In addition, throughout the first test lactate concentration increased with time, and pH, bicarbonate concentration and partial pressure of carbon dioxide decreased. In contrast, during the second test, lactate concentration decreased, and pH and bicarbonate concentration increased; during a period of time when ventilation and electromyographic activity were increasing. These findings have led us to conclude that changes in ventilation and electromyographic activity observed during incremental exercise are not related to changes in blood lactate concentration. It is suggested that such a conclusion supports the hypothesis that the changes in ventilation are mediated by an increase in neural activity originating from the subthalamic motor region or exercising limbs, induced in response to the need to progressively recruit fast twitch muscle fibres as exercise work rate is increased and as individual muscle fibres begin to fatigue.     

Secretion movement during manual lung inflation and mechanical ventilation

This project aimed to investigate the direction of artificial sputum movement during mechanical ventilation (MV) and bagging (MH) using a tube model. Three solutions of artificial sputum (ultrasonic gel, viscosity 100, 200 and 300 poise (P)) were prepared. About 1 ml of gel was placed in a glass tube connected to a test lung at one end and, via a pneumotachograph, to either a mechanical ventilator or a self-inflating bag, at the other. The position of the gel in the tube was recorded before and after 20 artificial breaths. Simultaneous breath-to-breath respiratory mechanics were measured. The procedure was repeated three times for each gel viscosity, with a fresh experimental set up for each measurement. Results showed that the distance travelled from the lung was significantly greater with MH compared with MV (P < 0.001). The lower the gel viscosity, the further the gel moved from the lung with both ventilatory modes (P < 0.001). MH was superior to MV for secretion mobilisation in a tube model.     

Effects of the ventilation pattern and pulmonary blood flow on lung heat transfer

To investigate the relative role of pulmonary perfusion compared to ventilation on lung heat exchange, we determined the effects of blood flow, tidal volume and frequency of ventilation on the rate of lung heat transfer. In anesthetized dogs and isolated, perfused lungs, we investigated the dependence of the overall lung heat transfer coefficient (HTC) and lung thermal capacitance upon ventilation and pulmonary blood flow. The relationship between the HTC and pulmonary blood flow was strongly dependent on ventilation parameters. A distributed model of non-steady-state heat exchange adequately described these observations and demonstrated that changes in pulmonary blood flow may be considered as changes in the effective conductivity of the bronchial walls as 0.4 (0.1) J s^–1m^–1 K^–1 per (l/min^–1) of pulmonary blood flow. Our model describes the complex relationship between HTC, ventilation pattern, and effective thermal conductivity of the bronchial walls, all of which present limitations for the use of lung heat transfer to determine pulmonary blood flow.     

Plasma potassium and ventilation during incremental exercise in humans: modulation by sodium bicarbonate and substrate availability

Summary It has recently been demonstrated that, compared to normal conditions, ventilation ( ) was increased during exercise after glycogen depletion, in spite of a marked increase in plasma pH (pH_P). It was further demonstrated that in patients with McArdle's syndrome was reduced when substrate availability was improved. In the present experiments, six endurance trained men performed two successive cyclo-ergometric incremental exercise tests (tests A, B) after normal nutrition (N) and after a fatty meal in conjunction with a sodium bicarbonate (NaHCO₃) solution (F_SB) or without NaHCO₃ (F), and the relationship between , plasma potassium concentration ([K⁺]P), and pHP was checked. Plasma free fatty acid concentration ([FFA]_P) was markedly increased in the F and FSB trials (P<0.001). In F_SB pH_P was significantly increased, compared to N and F (P<0.001). In all the B tests, pH_P increased during moderate and intense exercise and in F_SB, remained alkalotic even during maximal exercise intensity. In contrast, and [K⁺]_P changes were almost equal in all the trials and in tests A and B. It was found that exercise-induced changes of and [K⁺]_P in the present experiments were not markedly affected by [FFA]_P or pH_P values and that these changes also occurred independently of changes in pHP or plasma bicarbonate concentration. The often used glycogen depletion strategy may have slightly increased but apparently did not overcompensate for a possible decrease in due to increased pH_P. The close relationship between and [K⁺]_P was not affected by acid-base or substrate changes; this would further confirm the hypothesis that K⁺ may act as a stimulus for exercise .     

The ventilation,lactate and electromyographic thresholds during incremental exercise tests in normoxia,hypoxia and hyperoxia

These experiments examined the effect of hypoxia and hyperoxia on ventilation, lactate concentration and electromyographic activity during an incremental exercise test in order to determine if coincident chances in ventilation and electromyographic activity occur during an incremental exercise test, despite an enhancement or reduction of peripheral chemoreceptor activity. In addition, these experiments were completed to determine if electromyographic activity and ventilation are enhanced or reduced in response to the inspiration of oxygen-depleted and oxygen-enriched air, respectively. Seven subjects performed three incremental exercise tests, until volitional exhaustion was achieved, while inspiring air with a fractional concentration of oxygen of either 66%, 21% or 17%. In addition, another single subject completed two tests while inspiring air with a fractional concentration of either 17% or 21%. During the tests, ventilation, mixed expired oxygen and carbon dioxide, arterialized venous blood and the electromyographic activity from the vastus lateralis were sampled. From these values ventilation, electromyographic and lactate thresholds were detected during normoxia, hypoxia and hyperoxia. The results showed that although ventilation and lactate concentration were significantly less during hyperoxia as compared to normoxia or hypoxia, the carbon dioxide production values were not significantly different between the normoxic, hypoxic and hyperoxic conditions. For a particular condition, the time, carbon dioxide production and oxygen consumption values that corresponded to the ventilation and electromyographic thresholds were not significantly different, but the values corresponding to the lactate threshold were significantly less than those for the electromyographic and ventilation thresholds. Comparisons between the three conditions showed that the time, carbon dioxide production and oxyen consumption values corresponding to each of these thresholds were not significantly different. These findings have led us to conclude that the changes in lactate concentration observed during exercise may not be directly related to the fractional concentration of inspired oxygen, and that the peripheral chemoreceptors may not be the sole mediators of the first ventilatory threshold. It is suggested that this threshold may be mediated by an increase in neural activity originating from higher motor centers or the exercising limbs, induced in response to the need to progressively recruit fast twitch muscle fibers as exercise power output is increased and as individual muscle fibers begin to fatigue.     

Impaired ventilation and metabolism response to hypoxia in histamine H1 receptor-knockout mice

The role of central histamine in the hypoxic ventilatory response was examined in conscious wild-type (WT) and histamine type1 receptor-knockout (H1RKO) mice. Hypoxic gas (7% O(2) and 3% CO(2) in N(2)) exposure initially increased and then decreased ventilation, referred to as hypoxic ventilatory decline (HVD). The initial increase in ventilation did not differ between genotypes. However, H1RKO mice showed a blunted HVD, in which mean inspiratory flow was greater than that in WT mice. O(2) consumption (V(O2)) and CO(2) excretion were reduced 10min after hypoxic gas exposure in both genotypes, but (V(O2)) was greater in H1RKO mice than in WT mice. The ratio of minute ventilation to (V(O2)) during HVD did not differ between genotypes, indicating that ventilation is adequately controlled according to metabolic demand in both mice. Peripheral chemoreceptor sensitivity did not differ between genotypes. We conclude that central histamine contributes via the H1 receptor to changes in metabolic rate during hypoxia to increase HVD in conscious mice.     

The effects of pneumoperitoneum and controlled ventilation on peritoneal lymphatic bacterial clearance: experimental results in rats

OBJECTIVE:

To evaluate the effect of pneumoperitoneum, both alone and in combination with controlled ventilation, on peritoneal lymphatic bacterial clearance using a rat bacterial peritonitis model.

METHOD:

A total of 69 male Wistar rats were intraperitoneally inoculated with an Escherichia coli solution (10⁹ colony-forming units (cfu)/mL) and divided into three groups of 23 animals each: A (control group), B (pneumoperitoneum under 5 mmHg of constant pressure), and C (endotracheal intubation, controlled ventilation, and pneumoperitoneum as in Group B). The animals were sacrificed after 30 min under these conditions, and blood, mediastinal ganglia, lungs, peritoneum, liver, and spleen cultures were performed.

RESULTS:

Statistical analyses comparing the number of cfu/sample in each of the cultures showed that no differences existed between the three groups.

CONCLUSION:

Based on our results, we concluded that pneumoperitoneum, either alone or in association with mechanical ventilation, did not modify the bacterial clearance through the diaphragmatic lymphatic system of the peritoneal cavity.     

The effect of ventilation on spectral analysis of heart rate and blood pressure variability during exercise

Heart rate variability (HRV) and systolic blood pressure variability (BPV) during incremental exercise at 50, 75, and 100% of previously determined ventilatory threshold (VT) were compared to that of resting controlled breathing (CB) in 12 healthy subjects. CB was matched with exercise-associated respiratory rate, tidal volume, and end-tidal CO(2) for all stages of exercise. Power in the low frequency (LF, 0.04-0.15 Hz) and high frequency (HF, >0.15-0.4 Hz) for HRV and BPV were calculated, using time-frequency domain analysis, from beat-to-beat ECG and non-invasive radial artery blood pressure, respectively. During CB absolute and normalized power in the LF and HF of HRV and BPV were not significantly changed from baseline to maximal breathing. Conversely, during exercise HRV, LF and HF power significantly decreased from baseline to 100% VT while BPV, LF and HF power significantly increased for the same period. These findings suggest that the increases in ventilation associated with incremental exercise do not significantly affect spectral analysis of cardiovascular autonomic modulation in healthy subjects.     

The effects of exercise duration on dynamics of respiratory gas exchange,ventilation, and heart rate

This study investigated the effect of exercise duration on the response dynamics of oxygen consumptionVO₂, carbon dioxide outputVCO₂, ventilation V_E), and cardiac frequency (f _c) following stepped changes in exercise intensity, by manipulating the duration of the pretransition exercise period. A group of 11 healthy men performed a stepped exercise intensity cycling protocol on three separate occasions, each consisting of a stepped increase from 55% to 65% peak oxygen consumptionVO_2,peak of 6-min duration, followed by a stepped decrease to 55%VO_2,peak of 10-min duration. This stepped protocol was preceded by either 5, 15, or 60 min of cycling at 55%VO_2,peak. The response times for each variable were calculated at 10% increments between the prestep baselines and poststep plateaux. Following the stepped increase, the response times forVO₂ at the 50%, 60%, 70%, 80%, and 90% relative increments were significantly reduced in the 60-min condition compared to the 15-min condition (P< 0.05); however, the response times forVCO₂ andf _c were not significantly altered across the three conditions. No significant differences were found in the response times forVO₂,VCO₂ andf _c, across the three conditions following the stepped decrease in exercise intensity. It was concluded that the faster response time of aerobic metabolism to a stepped increase in exercise intensity was mediated by increases in active muscle temperature, leading to improved oxygen utilisation.     

Shortening ventilatory support with a protocol based on daily extubation screening and noninvasive ventilation in selected patients

BACKGROUND:

Prolonged invasive mechanical ventilation and reintubation are associated with adverse outcomes and increased mortality. Daily screening to identify patients able to breathe without support is recommended to reduce the length of mechanical ventilation. Noninvasive positive-pressure ventilation has been proposed as a technique to shorten the time that patients remain on invasive ventilation.

METHODS:

We conducted a before-and-after study to evaluate the efficacy of an intervention that combined daily screening with the use of noninvasive ventilation immediately after extubation in selected patients. The population consisted of patients who had been intubated for at least 2 days.

RESULTS:

The baseline characteristics were similar between the groups. The intervention group had a lower length of invasive ventilation (6 [4;9] vs. 7 [4;11.5] days, p = 0.04) and total (invasive plus noninvasive) ventilator support (7 [4;11] vs. 9 [6;8], p = 0.01). Similar reintubation rates within 72 hours were observed for both groups. In addition, a lower ICU mortality was found in the intervention group (10.8% vs. 24.3%, p = 0.03), with a higher cumulative survival probability at 60 days (p = 0.05). Multivariate analysis showed that the intervention was an independent factor associated with survival (RR: 2.77; CI 1.14-6.65; p = 0.03), whereas the opposite was found for reintubation at 72 hours (RR: 0.27; CI 0.11-0.65; p = 0.01).

CONCLUSION:

The intervention reduced the length of invasive ventilation and total ventilatory support without increasing the risk of reintubation and was identified as an independent factor associated with survival.